Friday, 7 December 2012

A Moss Mystery

If you observe nature closely enough and long enough, you begin to notice changes and anomalies. I am probably more interested in mosses than any other organisms, and as a result observed something I had never seen previously. Whether any other naturalists noticed it, I do not know, but for a bryologist it stood out loud and clear.

In the spring of 2011, while walking along the Cleveland Trail in Pacific Spirit Park I saw that one of the mosses, Ulota obtusiuscula, had died. This is a common moss that grows on alder trunks, where it forms compact dark green clumps. When dry its leaves are very shriveled, much more so than other mosses. It often has spore cases, and the cap which covers these cases has many little projecting hairs. If you are interested in finding Ulota, these are the three features to look for. 

On this particular day not only were the Ulota shriveled but every clump on every alder trunk along the trail edge was brown and dead! There are several other mosses on these trees, and none of them showed the least sign of being unhealthy. First conclusion was that something had occurred along this trail, and poisoned the Ulota, but that no other species was as sensitive as this one. 

Ulota obtusiuscula
Photo by Terry Taylor

It has been claimed that there is a psychological principle which states something to the effect that if you notice something unusual or it is pointed out to you, you will have difficulty not seeing it on future occasions. I could not help but be aware of Ulota everywhere I went, and it soon became apparent that this dieback was not a local thing. It was all across the Lower Mainland. As of autumn 2012 the little dead moss clumps are still clinging to the trees, and I also saw some on alders on the lower slopes of Mt. Fromme

How does Ulota differ from other mosses? For one thing it is adapted to grow on the driest, most exposed parts of the tree. Mosses with this growth form are those of extreme environments. Mosses which creep across the substrate require humid conditions. That is why they are the dominant growth form in shady forests. Look at a big leaf maple trunk. you will see that creeping mosses occupy the lower levels, but the branches are covered by mosses in clumps.

The other mosses on these tree trunks are clustered on the lower, humid zones of trunks, or in cracks, and other sites where conditions are less extreme. The Ulota is found on the smooth bark where the other species do not grow. Maybe Ulota occupies a niche too dry for its competitors, close to the edge of survival. If conditions remain stable there is no problem. Something like running out of food in the refrigerator. No problem as long as the grocery store is open. I do not know if there was an extreme weather event at that time, but have never experienced a Ulota catastrophe in previous years. 

There may be many processes taking place in nature that few notice, or that nobody notices. Others that I have seen over the years involve slugs and ants. The common slug in the forest is the banana slug (Ariolimax columbianus). The common one in urban areas is the black European one (Arion sp.). The black slug did not live in the forest, but now it is fairly common in the surrounding second growth conifer stands. Does it compete with the banana slug or do they eat different things? Probably nobody knows, but there may be a problem here. 

During the 1950’s and 1960’s an ant that belongs to the Formica fusca group was extremely common in Vancouver. When I was a child I used to call them sidewalk ants, because they could be seen running rapidly across sidewalks all over town. Now these ants are very rare within the city limits, although they are still common on mountain tops, and are found in surrounding areas. 

If you look closely for long enough you will notice changes taking place in our local ecology. Some of these are rapid like the moss dieback. Others are slower like the ant and slug ones. They all, however, indicate some sort of environmental change, although the nature of this change may be hidden from us.

Saturday, 24 November 2012

The Autumn Colours. What are They?

One of the wonders of autumn, along with the flowering of the mushrooms, is the spectacle of the autumn colours. You do not need to be a naturalist to appreciate this. Unlike many natural processes there is nothing subtle about this change. Virtually everybody notices these brilliant colours, even though few know anything about their causes and chemistry. In eastern North America there is a tourist industry based on this phenomenon. Rooms in the eastern deciduous forest may be booked up a year in advance.

Why do leaves show these striking reds, oranges, and yellows before they fall? Like may other natural processes, the basics are known, but many of the details have yet to be discovered. 

The shedding of leaves by deciduous trees and shrubs is  a complicated procedure. Deciduous species are not able to grow and photosynthesize under winter conditions. The conifers, in contrast, are the trees of cold areas. They have turned their leaves into narrow needles with minimum surface area, and protected them with a thick waxy surface. One of the problems for plants in winter is desiccation. When the ground is frozen, water is not able to enter the roots. If too much evaporation takes place such a situation can prove fatal. Conifer needles are an adaptation to this. They still photosynthesize through the winter, but decrease the surface area where water loss can take place. Larches (Larix spp.) are an exception to this rule. They are deciduous conifers that shed their needles in the fall. It is believed that this is an adaptation to extreme winter cold, as many larches grow in the high north or at high altitude, where the ground is completely frozen for much of the year.

Broad leaved trees are able to survive in colder climates, by growing in the summer, and going into dormancy in the winter. Before going into this dormancy they take some of the nutrients from the old leaves, and store them over the winter. These are then used next spring to supply a short spurt of food to the newly developing buds. The base of the leaf also forms a weak corky layer of cells, called the abscission layer. This is weaker than the original leaf base. The old leaf is now supported by the vein of woody tissue which at one time brought water into the leaf, and transported glucose from the leaf to the rest of the plant. The weakened vein eventually breaks, and the old leaf falls to the ground.

The predominant colours in autumn leaves are yellows and reds, and the pigments that make these colours are produced in quite different ways. The yellows are most often due to pigments called xanthophylls. They are present in the leaf right through the growing season, but you cannot see them because they have been hidden by the green of the chlorophyll. Chlorophyll continually breaks down and is replaced by new chlorophyll. When the old leaf is cut off from the tree’s nutrient supply, no new chlorophyll is made. Xanthophylls are more stable than chlorophyll and take longer to break down. They are  light gathering compounds and collect light in frequencies where chlorophyll is less efficient. They also protect chlorophyll from excess light. Chlorophyll can be degraded if the light intensity is above that which is needed for photosynthesis. Xanthophylls absorb some of this excess. One place you probably see xanthophylls is at the breakfast table every morning. They give the yellow color to egg yolks, and this originates in the leaves eaten by the chicken.

The reds are quite different from the yellows. Autumn reds are not there during the growing season. They are usually due to anthocyanins, the same compounds that make blueberries blue. As some leaves begin to die, sugars accumulate. Normally these would be exported to the rest of the tree. Sunlight reacting with these sugars produces the anthocyanins. One tree that illustrates this relation to sunlight is the vine maple (Acer circinatum). In shady forests its leaves turn yellow, but in sunny sites they become a bright red. Young emerging leaves in the spring may also have a red tinge. This is also due to anthocyanins. They protect the newly developing leaves from damaging ultraviolet light. There is also evidence that they may also serve a protective role in senescing leaves. 

Our most common deciduous tree, red alder (Alnus rubra) does not change color at all. It just dumps its leaves when they are still green! Alders have nitrogen fixing bacteria (Frankia alni) in their roots. These take nitrogen from the air to produce ammonium compounds as fertilizer for their host tree. The alder does not need to hold on to its leaves until they deliver some of their contents back to the tree. For most trees availability of nitrogen is a limiting factor for growth. It is like money for most people. Alders have all the currency they need to do whatever they want. When its leaves fall this currency is delivered to all of its neighbors.

In eastern North America there is a tourist industry based on the autumn leaves. This is the area of the eastern deciduous forest. Not only are there more deciduous trees to create this spectacle, but the cooler temperatures, and bright sunny days favor the development of bright red leaves. In Vancouver most of our fall colouration is produced by street trees, some of which are native to the eastern forest. Two frequently planted ones which give a good show are the red maple (Acer rubrum) and the sweet gum (Liquidambar styraciflua).



                                                               Red Maple Leaves
                                                          Photo by Rosemary Taylor

There are, however, places to go to see local native species with beautiful fall displays. Although our forests are coniferous, our shrubs are deciduous. In the mountains where shrubs of the heather family dominate the subalpine slopes and ridges, there can be magnificent panoramas of yellows, oranges, and reds. The closest of these displays for Vancouverites are the ski slopes of Hollyburn Ridge, along the trail to Hollyburn Peak. During an October with sunny days these slopes can be stunning.

The most striking colours are from the blueberries. Since these are the dominant shrubs of many subalpine slopes, these slopes can be a painted a brilliant red, visible from kilometres away. The most common species at Hollyburn is the Alaska blueberry (Vaccinium alaskaense). It tints the ski runs a purple red. Mixed with it is the black huckleberry (Vaccinium membranaceum). Ordinarily you need to look at them up close to distinguish one from the other. But at this time of year that is not the case. Its leaves turn a brilliant red and the two species can be identified from a distance. Scattered among these reds are splashes of yellow from copperbush (Cladothamnus pyroliflorus), and white rhododendron (Rhododendron albiflorum). The white rhododendron has a way of changing color that is unlike that of any others of our native shrubs. The leaves do not turn completely yellow. They develop a yellow spot on a completely green leaf. This spot gradually increases in size until the entire leaf yellows. 


                                                                          
                                                                    Hollyburn Colours
                                                             Photo by Rosemary Taylor

Scattered among the major players of this display are some lesser ones that fill in the gaps. Fireweed (Epilobium angustifolium) patches present their red withering leaves. Devil’s club (Oplopanax horridus) is yellow. The occasional Sitka mountain-ash (Sorbus sitchensis), even though it is in low numbers, stands out because its leaves often turn orange. 

A trip up to Cypress Provincial Park on a sunny October day is well worth the effort, and if you are looking for some exercise you can continue past the little lakes, and up to the peak for its panoramic view across Burrard Inlet to Vancouver.

Autumn displays with all their beauty are still shrouded to a great extent with mystery. Although the basic processes are now understood, the details have yet to be unravelled. Modern tools of molecular biology and biochemistry, however, are rapidly filling these details.   


Tuesday, 4 September 2012

The Kitsilano Natural Foreshore

Between Jericho Beach on the west, and Trafalgar Street on the east, lies the only section of undeveloped beach within the city of Vancouver. Contrary to what some people believe, this whole stretch of foreshore is public land, and is relatively easily reached from a number of access points. These points are located at Jericho Beach, Dunbar Street, Waterloo Street, Balaclava Street, Bayswater Street, Volunteer Park, and Trafalgar Street.

Other shoreline areas in the city such as Stanley Park, English Bay, Kitsilano Beach and False Creek are also public land, but all of them differ significantly from a natural foreshore. They are dedicated to active recreation, and the natural environment has been significantly altered. Between Jericho and Trafalgar, although the land has been converted to residential properties, the beach itself remains little altered from what it would have been like several centuries ago. There are many features and organisms here to entice the curious naturalist. It also remains an area for passive recreation, an oasis different from the frenetic pace of the other beaches. Such places are now difficult to find within the city.

There is, however, pressure to change this situation. A proposal has been made to build a seawall along the beach. Such development would seriously impact this last remaining piece of natural foreshore habitat. Contrary to some claims there are natural features here worthy of preservation.

In this article, we will take a walk along the beach from west to east, and look at these features. Before starting, however, there are a few safety precautions. This is a natural beach. For most of its length it lies at the base of a cliff. At high tide the sea comes up to the cliff. Before you take your walk check the tide tables on the Internet to make sure you can safely proceed. Also take note of the access stairs which are located approximately every two blocks. These will take you up to Point Grey Road, so you can explore the whole beach or just a portion of it. Where there is no sand the rocks are covered by a biofilm of diatoms. We will get back to the importance of diatoms later. Of immediate concern is the fact that this biofilm is very slippery and you can take a bad fall. So be careful walking across it.

The information here is gleaned from both my own knowledge of the beach, that I have acquired over the years, and also from other members of Nature Vancouver with whom I have visited the foreshore recently.

So let us begin with an overview of what is here. When the tide is out and you look to the north, you see a flat area stretching out to the water’s edge. Geologists call it a wave cut platform. The present site of Vancouver was below sea level during glacial periods, being pushed down by an ice sheet several kilometres thick. When the ice retreated, 11,000 years ago the land rebounded, and the cliffs which now lie at the back of the beach were out at the edge of the platform. The action of millennia of storms have cut away at them and left the platform which is now exposed at low tide. At the base of the cliffs you can see an undercut zone, where the sea is cutting into the present cliff. 

Although the platform is flat, you will notice that some of the rock strata on it, especially close to the beach are inclined. They are steep on the north side, and slope gently on the south side. The sea has not yet had time to completely level them. They are tilted because of the North Shore Mountains. The sediments were originally laid down flat, but that was long before the North Shore peaks existed. The original hills were worn away and their components deposited in places like this. Continental drift is pushing the Pacific Plate against North America, and part of this process has produced the local mountains. As the peaks have risen the rocks here at the beach have been tilted, so that they slope slightly to the south.



The tilted platform
Photo by Terry Taylor

Along the platform is the biofilm of diatoms. This is the brownish slippery coating over the sediment and rock surface. At a lower level than the sandy beach there is a coating of clay and silt. This has been deposited both as silt brought from the Interior and the Rockies by the Fraser River, and by the action of the sea upon shale within the cliffs. The upper beach is sand because the scour of the tides is stronger here and removes the finer materials. It is upon the silt and exposed rock platform where the diatoms and other micro-organisms can find a safe haven, and can establish themselves. Diatoms are single celled algae, or short chains of such cells. They are distantly related to brown seaweeds. Under the microscope they are very beautiful, and are reminiscent of bivalve mollusks. They cover themselves with two shells, but these shells are not calcium carbonate. They are made of silica, and are transparent, like two halves of a petri dish. Diatoms may not seem very important, but they, and other micro-organisms, are the beginning of the food chain. They feed juvenile fish, or the crustacea that are eaten by larger fish. Although, we are usually aware of the big organisms only, biologists have estimated that half the weight of the biosphere is composed of the microscopic ones.

Also very noticeable along the edges of the beach are rafts of seaweeds. The tides have torn them from the rocks and brought them ashore. As they decay they are eaten by crustaceans. The ones that jump about are often called sand fleas, although they have little in common with fleas, except that they are very good jumpers. They do not bite. If you lift up some seaweed you may see hundreds of them. They are food for the smaller fish, which in turn feed the larger fish such as salmon. There are two main species of seaweeds here. Most common is the rockweed (Fucus gardneri). This is the brown one which covers intertidal rocks. It has the floats which dry out and go pop when you walk on them. The other is sea lettuce (Ulva lactuca). These are the green sheets that look like thin lettuce. It is a green alga, related to the ancestors of land plants.

The beach too, has a tale to tell. Many of the pebbles here have been brought down by the Pleistocene ice sheet from the North Shore Mountains and beyond. They were dumped in the ocean by the advancing glaciers. The Point Grey Peninsula rose above sea level after the ice left, as the glacier was no longer pushing it below sea level. The sea cut away at the cliffs over the centuries, and the pebbles ended up on the beach. The smaller pebbles are also significant for another reason. During the summer, when the tide is in, smelt lay their eggs on them. The eggs hatch in a couple of weeks and the larval fish swim out to sea, feeding on micro-organisms as they migrate. Smelt are now a threatened species. They need all the help they can get to re-build their population levels. Overhanging shrubs and trees along the upper beach are also important for smelt spawning, as their shade cools the beach when the tide is out. These spawning gravels along the beach may be protected by fisheries legislation. During August, when I was in elementary school, and the tide was full in the evening, I often came to the beach with my smelting net.

Take a look at the cliffs when you have a chance and you will see that they are composed of two different types of rocks - sandstone and shale. These deposits are remnants of the ancient history of the British Columbia coast. They originated 40 million years ago, during the Eocene Epoch, and were laid down as sediments along the channels of rivers that have long ceased to exist. These rivers flowed westwards from a range of low mountains that fronted the coast millions of years before our North Shore mountains were uplifted. The sandstone was formed where the currents were flowing strongly, and the shales from fine clay in gently moving backwaters. If you go down to the Fraser delta and look at the estuarine plants along the edge you will see evidence of a similar process. These plants are covered by a gray coating. This is fine silt carried by the river from the interior of the province. 

In some spots there are sandstone layers that actually show how the river was flowing, possibly on individual days, so many millions of years ago. Within the layers of sand are occasional thin black deposits of organic material. These stand out from the lighter colored sand layers. You will see that some of them are tilted slightly from others, indicating how the currents were changing their course.

As we walk eastward from Jericho we will stop at various features of interest. The first of these is along the sand near the Royal Vancouver Yacht Club. At this site you will see what a natural, undisturbed deep sand beach looks like. There are two robust grassy plants here. On the right, shoreward side is the dune grass (Leymus mollis). This is a very large grass that can grow up to two metres tall. Notice how thick and tough the wide blades are. This is an adaptation to the harsh conditions posed by growing in sand. These blades resist the abrasion of wind blown sand and also retard water loss. Upper layers of sand can be very dry, plus the fact that the water which does occur at lower levels is often salty, and not easily absorbed by plants. The dune grass also has a gray coating to retard water loss. It has deep roots which penetrate down to the water table, and stabilize the plant in this shifting unstable environment.

To the left, the seaward direction is a plant with shiny grass-like leaves. This is a grass relative, but not actually a grass. It is a sedge, the big-headed sedge (Carex macrocephala). The leaves are smaller than the dune grass and are a bright green color. It grows close to the sand in little tufts. These tufts are sometimes in straight lines as they are often not single plants but shoots attached at intervals along long, horizontal, underground stems. The most noticeable feature of big-headed sedge are the compact clusters of dark brown seed heads. The seeds themselves are contained within seed cases that possess two sharp points. This sedge is now reported as a rare plant in Washington State.

The next point of interest is just down the beach, where the sandstone cliff begins. Projecting from the cliff as well as upon the beach are large rounded sandstone boulders. This is the only site along the entire foreshore where these strange boulders are found. They are called concretions, and they consist of sandstone which has been cemented together by calcium carbonate, deposited within them by water. They stand out because they are harder than the surrounding rock, and are, therefore, more resistant to weathering. How this lime material was deposited, why it is here and not in other parts of the cliffs, and how old it is, are all unknown. One of the geological mysteries of the Kitsilano foreshore, and one which is worthy of protection. 



One of the mysterious concretions at Jericho Beach
Photo by Terry Taylor

The next feature is just east of the Dunbar Street access steps. It is right at the base of the cliff, where the force of the waves is cutting into the rock. It is at the cliff base where the energy of storms is at its greatest. Basically what they are doing is gradually extending the wave cut platform landwards. At this particular undercut there is a layer of shale with black coatings on it. If you look closely you will see the impressions of leaves. These are fossils of leaves from deciduous trees which once grew along the river banks 40 million years ago. When you look at one of these leaves you are looking at something that happened one autumn of one year, so many eons ago. These were deciduous trees. They shed their leaves during the fall the same as our trees do. The leaves fell into the river, were carried down stream until they became waterlogged, fell to the riverbed and were covered by silt which accumulated above them for century after century, metre upon metre.



One of the fossils from the cliff near Dunbar Street
Photo by Rosemary Taylor

About a block east of the Waterloo Street stairs is a strange looking rock formation projecting northwards from the shore. Most people just see it as an impediment that must be climbed over and makes them wait until the tide is low enough for them to proceed. This, however, is another structure worthy of protection. Notice that the central part of it is darker and harder rock that that on either side. It is a volcanic dyke. It is the only one along the entire beach. A similar dyke in Stanley Park has been dated at 32 million years, so this is likely to be of a comparable age. The dark central part is basalt or a related volcanic rock and it was pushed upwards from a magma chamber below it. These structures are the roots of volcanoes or lava flows. So, 30 million years ago there may have been a Kitsilano volcano, or a lava flow like the Columbia Plateau. Note that sandstone occurs on either side of the dyke. When the lava erupted it roasted the sandstone through which it was extruded. The sediments on either side are, therefore, harder and more resistant to erosion than the surrounding rock and we now have this long three layered stone sandwich. 

When you reach Bayswater Street, if it is a low tide, look out along the exposed flats. You will see there is a smooth area without rocks. This is a piece of local history. Over a century ago the rocks were cleared away and the English Bay Cannery was built here. Although this salmon cannery is long gone, the smooth surface bears witness to its existence. 

As Trafalgar Street is approached, look carefully at the cliff face. At one spot there are a couple of coal exposures. Again, these are the remains of the ancient trees that once grew here. 

The above features are some of the highlights along the Kitsilano foreshore. They contribute to making this beach unique within the city of Vancouver. Construction of a seawall would destroy this uniqueness and eliminate the last un-impacted beach within the city.    

Saturday, 11 August 2012

Timberline

As you hike up the mountain the trees gradually get smaller and farther apart. There are more sunny openings with wildflowers and views. Eventually, if you climb high enough the trees disappear altogether, and the ridges are occupied by low-growing shrubs. This transition occurs at about the 1800 metre level, and has been called the timberline. It is the zone where the snow stays so long into the summer that the growing season is too short for trees to survive. Only shrubs and herbaceous plants are able to live there. The snows do not melt until July and they come again in October. The plants that live here must leaf out, flower, and produce seeds in a period of three months, as they are snow-covered for three quarters of the year. This is the high country of alpine meadows and heather-covered summits. The bare rocks contrast sharply with the brilliant colors of the wildflowers. This is the country that enchants both the naturalist and the hiker. It is an environment which is rugged and delicate at the same time.



The lake in this photo is at 1900 metre elevation.
Photo by Kelly Sekhon

The low elevation forest along the coast is often referred to as the rainforest, because of the high rainfall levels. The higher elevation forest has been called the snow forest, as snow has more influence here than rain. Although snow cover lasts into the summer or late spring, the growing season is still long enough for trees to develop. As you hike through this upper forest, however, there are signs and indications that you are approaching the high country. Some of these indicators are the changes in the species of trees themselves. Even if you do not know the names of these trees, you will still see that they are different from the familiar trees near sea level. Those familiar trees are gradually replaced by others which are more adapted to the long winters and harsher conditions. Redcedar (Thuja plicata) is replaced by yellow cedar (Chamaecyparis nootkatensis). Western hemlock (Tsuga heterophylla) gives way to mountain hemlock (Tsuga mertensiana), and Douglas fir (Pseudotsuga menziesii), which is not actually a true fir, is superseded by amabilis fir (Abies amabilis). The low elevation forest, because its most common tree is the western hemlock, is called the Western Hemlock Zone, and the high forest which is dominated by mountain hemlock is called the Mountain Hemlock Zone. 

There are a number of features about the Mountain Hemlock Zone which tell you that you have reached the high elevation forest even before the trees begin to thin out. The thick snow  cover lasts well into the summer, at which time it becomes very hard and treacherous, especially on steep slopes. At such times it is advisable to have an ice axe and know how to do a self arrest. Another hazard on these slopes are deep tree wells. The snow melts away from the sides of the tree trunks. The trunks are dark and absorb heat, and there is also a small amount of heat released by the trunks themselves. In early summer the larger trees are surrounded by these deep vertical shafts. Another reason for carrying an ice axe. Once the snow has melted another characteristic of the trunks becomes visible. The tree itself may be vertical, but the base usually curves downhill. This twist was produced when the tree was young and small. For the large trees that was centuries ago. The weight of the snow bends small trees. It is only when they are older that they can become tall and straight, but the evidence of the long ago formative years remains. 

As the growing season becomes less and less, the trees get smaller and smaller, and farther apart. This means that sunlight can reach the ground, and is not blocked by the needles on the trees. If there is enough moisture herbaceous plants are able to grow, and they do so in great profusion. These are the subalpine meadows, and in July they present a panorama of colors. They  have little time to flower and set seed, and so they do so rapidly, and with a blaze of glory. With so many flowers it would seem that there must be an equally large number of seedlings. But like so many other things in life, this is an illusion. There are many seeds, but very few seedlings. Unlike the plants at lower elevations, the harsh conditions of the high country allow only a miniscule number of these seeds to be successful. As you hike through the meadows, look and see how many seedlings you can see. Usually there are none at all! 

The meadows bloom in two waves. First there are the plants that are the most cold resistant. These flower close to the melting snow. As the soil warms the second wave comes into bloom. By this time the early ones are already in seed. Some of the first shoots actually push their way through the melting snow, although usually there is a brown zone of dead vegetation immediately adjacent to the snowbanks, and outside this is the green zone of emerging shoots. The first flowers to appear are the yellow snowlilies (Erythronium grandiflorum), the little white spring beauties (Claytonia lanceolata), and the white flowered western anemone (Anemone occidentalis). The later stage is dominated by flowers such as the blue flowered lupins (Lupinus arcticus), and the orange flowered paintbrushes (Castilleja miniata).

The meadowlands grow where there is rich soil, and abundant seepage. If you leave the meadows and hike onto the rocky, dry ridges you find a much more hostile environment. Rain or snow melt runs rapidly off these sites, carrying nutrients with it. This moisture and dissolved minerals runs down slope to the lush herbaceous plants below. There is a striking difference between the dominant vegetation of the rocky sites and the moist, deep soil slopes below. The ridges belong to small shrubs with tiny needle-like leaves. These are the heathers (Ericaceae). Heathers are adapted to live in such extreme environments. Their roots contain efficient microscopic fungi that help them gather water and nutrients in such sites. Their leaves are like tiny coniferous tree needles. They are small, evergreen, and narrow, and have thick surfaces which resist water loss. The shrubs themselves are short and close to the ground, so that they are covered by a blanket of protective snow in the winter. Because they grow close together they are able to lessen the effects of desiccating winds. There are two common heather species on these ridges, the pink mountain heather (Phyllodoce empetriformis), and the white heather (Cassiope mertensiana). The pink flowered species tends to grow at lower elevations than the white one. Its leaves look like the needles on many conifer trees. The white one is adapted to more extreme sites where the snow lingers longer. Its leaves are shorter and pressed close to the stem, like scale leaves on cedars. This is an adaptation to the more rigorous conditions at these higher altitude ridges. 

Where the trees give way to the meadows or ridges, you may notice that they present some unusual growth forms. In the meadows there may be a few tree islands. These are spots where the snow leaves a little earlier, and the growing season is just long enough for tree seedlings to get started. They usually occupy little hillocks where the sun can heat the ground a little more. Once one tree gets started it produces some protection against the wind, and also lessens the accumulation of snow, and so other trees can get started. In this way a small grove develops after several centuries. On the ridges trees are often dwarfed, and grow densely packed together. This growth form is called krummholz, meaning crooked wood. During the winter these sites are bitterly cold and windy. Any buds or needles projecting above the snow surface are killed, but those protected by the covering of snow are able to survive. Therefore, the trees cannot grow upwards, but they can grow sideways. Hiking along such ridges is difficult because of the impenetrable shrubby barrier.  

One feature you cannot fail to notice on the alpine rocks are the lichens. Even if you are not consciously aware of them, they still form part of the subconscious impression of what a high mountain ridge looks like. The dry surfaces of such rocks are very inhospitable for living things, but many lichens are specially adapted for living is such places, especially the ones that form thin crusts. The splotches on the rocks are usually lichens, not mineral coatings. Although they may not appear so on casual observation, they are alive, growing and reproducing. Their growth rate, however, is very, very slow. Most of the year they are covered by snow, and most of the time when they are not covered by snow, they are dried out by the sun. It is only during or shortly after rainy periods that they can actually grow. These splotches can come in a number of different shades and colors, and are more complex than they seem. They are simple ecosystems composed of two different organisms. Most of the lichen is composed of fungus threads, and among these threads are microscopic green plant cells - algae. The plant cells gather sunlight the way all plants do. They use this energy to combine water and carbon dioxide into sugars. The fungus part then uses some of the sugar to build its own cells. 



Some of the lichen species seen on rocks above the timberline.
Photo by Kelly Sekhon

Monday, 25 June 2012

Secrets Beneath the Ground

Of all the mysteries in the natural world, probably the most mysterious and least understood are the ecosystems which lie hidden beneath the ground. Not only are these ecosystems hidden under a layer of leaves and twigs, they are also hidden from us because their size is far below our level of sensory perception. There are billions of individual fungi, protozoa and bacteria in every handful of soil. By far the greatest number are the bacteria. Microbiologists have estimated that there are more than 10,000 different species of these tiny organisms in that little pile of soil! Most of them are so small that a line of 1000 of them, end to end, will only stretch for a distance of a millimetre.

Just as the forest has many different habitats such as streambanks, logs, tree trunks, sunny openings, etc., so does the soil have many different habitats. Soil habitats, however, are microscopic ones. Particles which have come from the breakdown of leaves, wood, bark, insects, minerals and many other sources are all different, and support their own unique populations of bacteria. Each one forms its own special ecosystem, an ecosystem with a diameter about one-tenth of a millimetre. Most of these bacteria have not only never been named, they have never been seen. So how do scientists know there is this much diversity under the ground? The people who study genes and molecular biology have extracted DNA from soil samples and analyzed it. Some of this analysis involves observing how long it takes for pieces of DNA to recombine with other pieces of DNA. The longer it takes, the more kinds of different DNA are in the sample. After the mathematicians have made their calculations, the conclusion is that there are more than 10,000 strains in a sample of good rich soil. This is more than three times the number of higher plant species in all of British Columbia! It is also twice as many species of bacteria than are described in Bergey’s Manual.

Bergey’s Manual is a multi-volume set of books that contains information on all the named species of bacteria. There are about 5000 of these. How can a few grams of soil contain more bacterial species than this? One of the most significant reasons involves how we study and grow bacteria. Most kinds of bacteria that are known, are known because they have been cultured on a Petri dish, a clear plastic dish containing agar, which is a nutrient-rich jelly substance. The nutrients can be varied, depending upon what kind of food the particular bacteria like to eat. If the bacteria like the food they are given they will form great big colonies on top of the agar. The average bacterium is only a thousandth of a millimetre long, so there are millions of individuals in such a colony. With this large a number, the bacteria in question can be studied in detail. To study bacteria in this way, bacteriologists must be able to grow them. They must be able to give them the food they like, and they must also be able to grow them in a monoculture, without other competing organisms. The species that can be cultured in this way are usually species that like lots of nutrients. Most of the pathogenic ones fall within this category.

Most bacteria, however, do not cause disease, and they do not live in habitats with lots of food. The bacteria we have names for are the ones we can grow. Scientists now believe that over 99% of species cannot be cultivated. In other words almost all the bacteria in nature are unknown. About 20 years ago biologists were first able to study the DNA from soil organisms, and these studies revealed that not only were there many times more strains of bacteria than had been surmised, but that the vast majority of these are not closely related to the known ones.  Many of those in the soil occur in very small numbers, in many different micro-ecosystems. Particles from such differing origins as insect skeletons, tree resin, leaves, wood, animal droppings, or different kinds of mineral grains will all have their own special types of bacteria, and there are innumerable kinds of micro-particles. Some bacteria appear to be dormant almost all the time, waiting in the ground until they receive the nutrients they require. When the food is exhausted they go back into dormancy again.

We cannot see the bacteria within their own environment. Some of them can be cultured in Petri dishes, but this is micro-agriculture, not nature. To study soil ecosystems themselves they need to be manipulated and disturbed, as these are worlds beyond our level of perception. To find individual organisms in this realm is more difficult than looking for a needle in a haystack, because we can see the needle when we find it. It is more comparable to clearing a piece of land with a bulldozer, and looking through the rocks to see what kind of mosses were growing there.

There is also evidence that bacteria have complex social relations with other bacteria. The majority of soil species may require contact with other soil bacteria. These requirements cannot be supplied in a laboratory environment. Bacterial cells talk to each other through a chemical language called quorum sensing. They produce substances which diffuse into their surroundings. When a critical level is reached they cause the individual cells to change their behaviour. They may tell them it is time to reproduce, or in the case of some disease-causing strains, there is a message that they have a high enough population to transform from a harmless state into an invasive, pathogenic one. Some of the most virulent disease organisms are completely harmless until they reach their critical density. Future medical treatments may involve neutralizing this communication system.

The majority of our antibiotics are produced by soil bacteria, and most of these come from a group of bacteria called Streptomyces. There are myriads of these compounds, and bacteriologists have discovered that in nature they do not act as antibiotics. They are used for chemical communication. The bacteria usually make them when they are ready to produce spores for reproduction. They, however, produce them in very small quantities, quantities which are below the minimum inhibitory concentration. This refers to the minimum amount of substance that is required to inhibit bacterial growth. The Streptomyces are grown artificially in pure cultures, which never occurs in nature where they occur with thousands of other micro-organisms. In large amounts, antibiotics disrupt the growth processes of other bacteria. That is the reason they can be used to kill disease organisms. Some researchers have expressed concerns about releasing these naturally occurring substances in unnaturally large amounts into the environment, which is what takes place in some agricultural settings.

As you walk through the woods, even if you can name every plant, animal or mushroom you see, you are only naming a small percentage of the diversity that surrounds you. Almost all of it is un-named and unknown, and will remain so for many decades to come. Scientists are only beginning to fathom the invisible ecosystems which are common here, and upon which all the larger living things depend. It is the soil and the secret realities within it that support all the ecology we see around us.

Thursday, 31 May 2012

The Spots on the Rocks

Have you ever seen speckled rocks? Rocks with gray or colored patches thinly covering the surface, patches that are not actually parts of the rock itself. Such spots are usually lichens. They are not just stains on the rock, but actual living organisms adapted to living in hostile, extreme environments that cannot be occupied by other living things, at least other living things that we can see. They are most frequent on rocks in open sunny locales, such as those on the seashore or on exposed mountain crests. In such places only organisms adapted to extremes such  as heat, cold, desiccation, or salt spray can survive, and these kinds of lichens are masters of the extreme. Such thin lichens are known as crust lichens. Rock surfaces in shaded forested sites are moister, and less severe, and usually covered by mosses.

Look closely at some of these patches and you will see that there are different kinds of patches, and that they often have little spots and structures upon them. The different kinds of patches are different species, and the little spots are reproductive bodies, where spores are produced. On a surface that has been undisturbed for a long period of time the lichens grow outwards until they make contact, and no actual rock surface is visible. What you are seeing is a living skin which follows the shape of its stony substrate. It has, however, taken many years for this thin covering to reach that stage, as these coatings are very slow growing. One of them, the map lichen (Rhizocarpon geographicum) grows at such a steady rate that geologists use it to date such events as landslides and retreat of glaciers. A map lichen increases its diameter at less than a millimetre a year. The species is called map lichen because it looks like a map. It covers large areas of surface, is bright green in color and has little black fruiting bodies. This lichen of granite-type rockfaces is very common and due to its bright color is easily identified.



 Map Lichen (Rhizocarpon geographicum)
Photo by Kelly Sekhon

The crust lichens are the most common lichen group, but because of their simple structure are very difficult to identify. Their more complex relatives which have shrub and leaf-like growth patterns are much more easily distinguished from each other. To really be able to identify crust lichens you need to be an expert on crust lichens, not just an expert on lichens, and there are very few scientists with such expertise. Many of these organisms are so nondescript that  they cannot be told from each other without microscopic study, and special chemical tests. No wonder we know so little about them. Over the years a number of European crust lichen specialists have come to British Columbia and discovered species not previously known from the province, and even species that are completely new to science. 

So, what are these living crusts and how did they reach their stony homes? All lichens are  strange composite organisms - part fungus and part plant. They are able to grow in such places because the single-celled microscopic plants, algae, that live inside them contain chlorophyll, and that chlorophyll does the same as the chlorophyll in higher plants. It makes sugar. Most of the lichen, however, is composed of mold-like fungus threads. The mold uses the majority of the sugars to built its own tissues, and in return gives the alga a secure and safe home. It farms the microscopic plant in a way that is similar to the way we farm things. Most of the milk produced by cows feeds people not calves. We protect our cows and the fungus protects its alga.

Most of these crustose lichens are gray, roughly circular stains on their stony substrates, and they are very difficult to tell from each other. The most common of them is probably Porpidia. Although it is basically rather nondescript, it possesses three features which stand out. You have probably never seen these features, but once you do see them you will probably not be able to un-notice them when you next see them. It is a curious thing that many common things go un-noticed unless our attention is drawn to them. In many cases these phenomena, which we unconsciously experienced many times, cannot fail to be seen once the requisite pathways have been activated in the brain. Porpidia usually has many round, raised black spots all over its surface. These are the fruiting bodies, apothecia, where the spores are produced. They are especially noticeable when they grow in concentric circular patterns. The second feature appears when two Porpidias touch one another. A black line forms between them. Several different  fungi and lichens make such lines. It is not known why this is so, but the most commonly accepted theory is territoriality. This is a fence between two different individuals. Something like Robert Frost’s poem that “good fences make good neighbors”. The third feature can only be seen after the lichen is damaged or dies, and the underlying rock becomes visible. Rock lichens produce acids that dissolve and react with minerals in the rock. In this case there is a reaction with iron compounds, and rusty patches are made. And you thought that gray, nondescript lichens are boring!

Probably the most striking of the crust lichens are the firedots (Caloplaca sp.). Most of these are bright orange in color, and are most common at two extremes of elevation - at the seashore and on high alpine mountains. At both these extremes there is bright sunlight, but there is something else the firedots like, and that is lots of fertilizer. Most lichens live under low nutrient conditions, but these orange lichens are exceptions. They like to grow where the birds like to perch. It has been suggested that the high nitrogen or calcium levels in bird droppings are the critical factors. Whatever the reason next time you are at the  beach look at the boulders where the seagulls sit and see if there are any orange splotches. 



Lichens growing on rocks above the timberline.
Photo by Kelly Sekhon

Bare, exposed rock surfaces are some of the most extreme environments on the planet. Yet, even here life thrives. On casual inspection it may not look alive, but these organisms are growing, photosynthesizing, reproducing and making chemicals that only living things can make. It has even been suggested that some of these rock lichens could thrive on Mars! They are that adapted to harsh conditions. In fact some of them cannot survive in more benign situations. They are the pioneers. As the minerals are dissolved by the lichens the rock is pitted, and a thin layer of soil is produced. The rough surface is then able to support more complex organisms, such as mosses and larger lichens. Next time you pass some bare rocks take at look at the simple ecosystem that lives here. These are the pioneers.   

Monday, 28 May 2012

The Mushroom Season

When the rains come in October they signal the beginning of the mushroom season. The season when the fungi, hidden beneath the ground, produce their flowers. For mycophiles, people who love mushrooms, this is the best season of the year. There is something about mushrooms, and the way they seem to arise spontaneously, that elicits a sense of wonder. Many cities have mushroom clubs that put on an annual mushroom show. Year after year people come out to these shows by the hundreds. Why is this so? What is it about mushrooms? Birds, trees, insects, geology, none of them can generate this level of sustained interest. As a channel into the mysteries of nature, mushrooms outdo them all. 

Why do mushrooms come out in October in greater profusion than at any other time of the year? To understand that we need to know what mushrooms are, and what they are doing. Mushrooms present a transient glimpse into an invisible, mostly microscopic world hidden beneath the soil. They do for fungi what flowers do for plants, reproduce the organisms producing them. Whereas flowers are smaller than the plants producing them, mushrooms are larger than the fungi that give rise to them. Flowers result in large seeds that are easily seen, but mushrooms produce spores, that function like seeds, but which can only be seen with a microscope.

Some mushrooms fruit in the spring, but most of them choose the autumn to do so. There is ample moisture for the mycelium - the underground, mold-like part of the organism, which gathers nutrients from organic matter or tree roots. There is also ample moisture for the germinating spores. Those spores produce fungal threads which over-winter, and then are really ready to grow once the spring rains arrive. Different mushroom mycelia have different life styles.  There are basically two of those life styles. They either tear down or build up. Some species are recyclers. They rot down organic matter such as wood, old leaves, or manure and send their byproducts back into the soil to be used by succeeding generations of plants or trees. The cultivated kinds of mushrooms belong to this group. The button mushroom lives on manure. Oyster mushrooms, enokis, and shiitakes are grown on logs or wood chips.

The other life style is the mycorrhizal one. Mycorrhiza means fungus root. The mushroom mycelium is attached to the roots of a tree, and both the mushrooms and the tree are dependent on each other for their survival. The microscopic fungal threads grow outward into the surrounding soil, gathering moisture and minerals such as phosphorus, and delivering them to the tree roots. In return the fungus takes some of the sugars made by the tree’s leaves to build its own tissues. The thin threads of the fungus travel far beyond the tree roots themselves, and although they are very small, in total, they have more surface area than the roots themselves, and therefore are very efficient at scavenging water and nutrients. Many trees could not survive the summer drought without their mushroom helpers. Many of the mushrooms growing on the forest floor are produced by mycorrhizal fungi, including some of the most sought after ones, such as chanterelles (Cantharellus formosus), pine mushrooms (Tricholoma magnivelare), and king boletes (Boletus edulis).  

Rough-stem Bolete (Leccinum scabrum) is a mycorrhizal partner of birches.
Photo by Terry Taylor

How many different mushrooms are there in British Columbia? Nobody knows for sure, but the number of species is in the thousands, not hundreds. The most detailed study ever done in  the province is at Observatory Hill near Victoria. As of 2009 it had been going on for five years. Although this is just a small hill, less than 100 hectares in area, 800 different kinds of mushrooms have been identified, and more are likely to be discovered. This gives an inkling of the complexity and diversity of the mushroom world. There are many more mushrooms out there than we imagined. If you cannot identify your shroom after carefully looking in a mushroom book, do not feel discouraged. Even the experts cannot identify a large number of them, because there are many that have yet to be named. Of those which are named, a large percentage require microscopic study before they can be distinguished from their close relatives. 

There are, however, a fair number which can be easily identified. Chanterelles, shaggy manes, oyster mushrooms, king boletes, and pine mushrooms are among this group. These are some of the prizes to be collected by the mushroom hunter when the rains come. By September fungal enthusiasts can hardly wait for the summer to be over. This does not mean, however, that you should buy a book, rush out into the woods, and greedily devour what you think you can eat. There are a number of poisonous look-alikes. Every year poison control centres have to deal with those who have made a mistake. Most of the time these people come away with merely a few unpleasant experiences, but that is not always the case. The old saying in mushroom clubs that “there are lots of old mushroom collectors, and lots of bold mushroom collectors, but no old bold mushroom collectors” is something to keep in mind. Start your new adventure by going out with an experienced mushroomer, or on a mushroom club field excursion. Identifying your finds by a picture in a book isn’t good enough. 

Sunday, 27 May 2012

A Hike Up the Mountain

On a bright summer day I like to start in a low elevation forest and hike up to the summits. Starting a hike at low altitude adds several components to the trip. You need to start earlier in the day in order to reach your destination and return. Consequently you get more exercise, more of a workout because of the greater elevation gain, and spend more time in the outdoors. There are also components other than those associated with the exercise. There are the changes to be seen between the base of the mountain and the peak.

In coastal British Columbia there is a considerable difference in the vegetation at sea level and that on the mountain crests. Even if you do not know their names, when you look at the trees you will see that those growing on the peaks are different. The low altitude forests are mostly western hemlock (Tsuga heterophylla). They grow close together, and their thickly clustered needles stop most of the sunlight from reaching the ground. It is a shady, cool walk to start the day. Associating with the western hemlock are Douglas fir (Pseudotsuga menziesii), and western redcedar (Thuja plicata). Because of the dominance of western hemlock, these forests are called the Western Hemlock Zone.

As you ascend the slopes you will see that the lower elevation kinds of trees are gradually replaced by different types of trees. This transition begins around the 1000 metre level. By the time you reach 1200 metres almost all the trees are different species from those down below. This is called the Mountain Hemlock Zone because mountain hemlock (T. mertensiana) is the dominant tree, replacing the lower elevation western hemlock. Red cedar is replaced by yellow cedar (Chamaecyparis nootkatensis), and Douglas fir gives way to amabilis fir (Abies amabilis).

When you proceed further not only are the trees different, they are also farther apart, with little seepage areas covered by grass-like sedges. Some of the ponds are rimmed with cotton-grass (Eriophorum angustifolium), which is actually a sedge, not a grass. Sedges are related to grasses, but belong to a different family. Most of the grasses in marshes are actually sedges. Cotton-grass has fluffy seed heads, like balls of cotton. The white edges of these ponds can be spotted from a long distance away. Higher up are the open rocky summits with little soil and few trees. From such vantage points you can look down on the route your journey has taken earlier in the day. Above 1500 metres are extensive meadow slopes clothed in wildflowers. These are the subalpine meadows. Scattered here and there are small clumps of little trees. Higher still the trees give out all together. The slopes and flat areas are covered with alpine flowers, whereas the rocky ridge crests are covered by heathers, with small, needle-like leaves. They look more like little conifers than flowering plants. The reason they have needle-type leaves is the same reason that conifers have them - to conserve moisture.

The lower forest is the rainforest, or at least on the outer coast it is a rainforest. In the Lower Mainland area it does not get quite enough moisture to be a true rainforest, but the plants are essentially the same in both areas. The most noticeable difference is the mosses. They are more luxurious in the true rainforest. The most striking is the cat-tail moss (Isothecium myosuroides). In humid places it hangs from the trees in long, thin streamers.  The sea level forest is wet and snow free for most of the winter. Except for the driest part of the summer, the evergreen trees and mosses continue to grow right through the year. The upper areas are the snow forest. The snow comes to the summits in October and does not completely leave until July. This means that even after the warm spring sun shines on the tree tops, and brings re-growth to the mosses and lichens growing there, the ground remains in winter right into the early summer. The plants found here have only four months to grow, flower, and set seed. Most of our familiar plants cannot survive under such extreme conditions. This is the land of the heathers, and alpine meadows. It is a land quite different from our familiar woodlands, a land where we are just casual visitors. We spend the day struggling upwards, stop a few fleeting minutes on the peak, and then return to our homes in the lowland.

Even though you may not know their names, if you look at the mosses of the forest floor you will see that they too change as you ascend the slopes. The most common moss on the ground at low elevations is the Oregon beaked moss (Kindbergia oregana). It is shaped like a little green feather, and forms dense carpets. Also common is a pale green species - wavy leaved cotton moss (Plagiothecium undulatum). It is closely appressed to the surface and looks superficially similar to a delicate cedar twig. Also forming thick carpets is the step moss (Hylocomium splendens). It is called step moss because it forms a new step-like shoot each year, and you can count each previous year’s growth, something like counting tree rings. When you get to about the thousand metre level the ground between the blueberry bushes is often densely clothed with a completely different moss, one with shaggy, wrinkled leaves. Because of this appearance it is called pipecleaner moss (Rhytidiopsis robusta). The appearance of pipecleaner moss tells us we are approaching the summits.

With the coming of spring, memories of summer hikes return, and anticipation of seeing the mountain plants re-awakens. Even if it is a peak that has been visited many times, there are still new experiences to be had, and new things to be seen. As the snow melts back the high altitude plants, which are cold resistant, push through its edges. To see these emerging shoots is to see the emergence of summer. They say in their own way that for a few months life has again returned to the high country.

Friday, 18 May 2012

Liverworts - The Unknown Plants

There is a common group of plants of which many knowledgeable naturalists are completely ignorant.  They are distantly related to mosses, and are referred to as liverworts, or in more technical jargon, hepatics. There is indeed a superficial resemblance to mosses, and both are classified together in a larger grouping called the bryophytes. This resemblance, however, is deceiving. Identifying small organisms such as these, is somewhat comparable to naming trees on the opposite side of a valley. With a telescope the task becomes considerably easier. In our case the task becomes considerably easier by using a hand lens, which is also considerably easier to transport through the bush.

According to the latest research findings, the liverworts have a very special geological history. Both genetics and the fossil record indicate that they are the oldest land plants. Their ancestors, 400 million years ago were the first little plants to colonize the land, and the liverworts have been here ever since.

Careful scrutiny with a hand lens or magnifying glass will show some of the differences between mosses and liverworts. In fact the differences are so great that the two groups are probably no more closely related to each other than grasses are to pine trees. 

There are two groups of hepatics - the marchantioids, and jungermannioids. The first group is named for Marchantia polymorpha, the classic liverwort, so called because its surface looks like that of the liver and according to the Medieval Doctrine of Signatures was a cure for conditions believed to be liver diseases. Unfortunately there does not appear to be any evidence to support this belief. The marchantioids form flat, fairly tough, green plates, usually on soil, and usually about 3 to 5 cm. long. Marchantia polymorpha is common on shaded soil in gardens and greenhouses. The larger, but similar Conocephalum conicum, the Great Scented Liverwort, is frequently seen on seepage sites in the coastal forest. When scratched it produces a perfume-like odor, hence the common name. Both these plants have a snakeskin-like upper surface of small polygons. 

The jungermannioids are often called the leafy liverworts because most of them have small leaves, and look very much like mosses. In fact the differences between the two groups are not readily apparent without a little experience. Although the distinctions are subtle, mosses and liverworts can soon be distinguished from each other, even when the actual species identifications cannot be ascertained.  Leafy liverworts tend to have a softer, more translucent, flatter appearance. The leaves are usually lobed, and this can sometimes be discerned with a lens. Except for a few rare exceptions, moss leaves are unlobed. But the most obvious dissimilarity from mosses involves the capsules - the cases in which the spores are produced, and the stems on which they are borne. Moss capsules are tough and remain on the plants for many months. They look like little jars with an opening at the top, an opening which is usually covered by a row of teeth. These teeth open and close with changes in humidity, thereby controlling spore release. The capsule is green and photosynthetic when young, but brown when old. The stem, or seta, below the capsule is strong and wiry. When young it is also green. Leafy liverwort capsules are entirely different, and look like small fungi. They are usually spherical, black and shiny, and when mature open out into four petal-like valves. The seta is a translucent white, and very evanescent. For this reason spore cases are only observable for a few weeks, and for most species this period occurs in the spring. Moss capsules last for many months.

Liverworts are more dependent on humid or moist environments than many of the mosses - sites such as stream banks or tree trunks in shaded coastal forests. Although mosses grow luxuriantly in such habitats, some moss species also flourish in dry areas where liverworts are almost always absent. 

Probably the primary reason these little plants are almost unknown revolves around their lack of economic importance. Liverworts do not destroy timber or compete with crops, and at the present time they do not produce commercial products. They may, however, offer the potential for future medicines. Within hepatic cells are small structures known as oil bodies. Dissolved within these structures are a number of complex chemicals that may deter parasites or predators. Such compounds could conceivably offer potential for new antibiotics.

Monday, 14 May 2012

Dust In The Forest

Have you ever seen pale whitish-green dusty patches on the undersides of stumps and boulders - the places that stay dry even on a rainy day? These dusty patches are very common in every forest. They are the dust lichens (Lepraria sp.), and form a whole unique ecosystem in places that are too extreme for anything else. The sites where they grow are micro-deserts within the rainforest. These are the spots that are so dry that mosses and other lichens cannot live here. Such micro-sites are on the lower sides of branches, boulders and stumps, as well as areas on tree trunks that are sheltered from rain or flowing water.

To live in very hostile environments requires special adaptations and the dust lichen has a very special way of dealing with this difficulty. Actually there are a number of different kinds of dust lichens, but many of them cannot be told from each other without complex chemical tests, so it is easier to think of them as one type of organism, unless you have access to a chemistry laboratory. The dust lichen has simplified its structure and life style about as much as it is possible to simplify a structure or life style. All parts of the dust lichen are the same - dust. Rub your finger across the surface of one and it will be covered by a fine layer of dusty particles. All the particles are exactly the same, and are called soredia. An individual soredium is so small we cannot see it without a magnifying lens. What we see as dust are thousands of these particles. Each one is a ball of fungus threads and in the centre of the ball are a few single-celled microscopic plants - green algae. The deep green coatings often seen on rocks and tree trunks are colonies of green algae that are closely related to those in the dust lichen. The little balls bud off other little balls and the whole lichen is entirely made of little balls. This is the way dust lichens live and reproduce. They have no form of sexual reproduction. There are millions of these little particles, each one a simple ecosystem of two organisms - a fungus and a plant. When we walk through the woods we disturb myriads of them, and carry them with us to other sites. Birds, insects, and breezes do the same. Most of the soredia do not find a favorable place to grow, but occasionally a few of them do find a newly created bare surface, and start a new dust lichen. This process of initiation, however, is well below our level of awareness and has never been directly observed in a natural environment.

How do dust lichens live in dark, dry places? They grow very slowly, and do not need much light. Because other organisms cannot grow in these dry spots the dust lichen does not need to worry about competition, and can take its time, depending on how much light it has available. The answer to the second question is very strange indeed. The dust lichen does not need liquid water. Unlike its neighbors it uses water vapor. In the forest during most of the year the air is very humid and this lichen can use the little bit of moisture that is delivered to it in the air. In fact dust lichens repel liquid water. Vapor can enter them but liquid cannot. You can see this quite easily. Pour a little water on a dust lichen and it rapidly runs off. What little remains on the surface pools in small droplets, and does not soak in. Whatever substance is responsible seems to be more effective than many rain-clothes. When viewed under a microscope the dust lichen fungus threads look quite different from the threads of other fungi. Other fungi are transparent and you can see right through them. The dust lichen is opaque. The algae inside its small particles cannot be seen unless the particle is broken open.

Wherever you walk in the woods you will encounter this unassuming little organism with its secret life style. The little lichen that makes its own simple ecosystem, one that is as simple as an ecosystem can be.