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.

Thursday, 10 May 2012

Farming Fungus

In autumn the leaves of the bigleaf maple (Acer macrophyllum) turn yellow, and fall from the trees. This is our coastal maple tree with the great big leaves. If you look closely at some of those leaves, however, you will see that a few of them have big green spots, and in the big green spots are little black spots. Both the green and the black are due to a very unusual fungus, and its remarkable life cycle. It is green because the maple tar spot fungus (Rhytisma punctatum) is keeping pieces of the fallen leaf alive! The black spots are the fungus itself, or rather the reproductive parts of the fungus. The actual fungus is microscopic and lives in the green zones.

Maple tar spot fungus (Rhytisma punctatum) on Bigleaf maple (Acer macrophyllum
All photos by Kelly Sekhon

The tar spot fungus is only visible in the autumn, when it starts to reproduce. It is actually  there right through spring and summer, but shows no evidence of its presence. The leaves of summer show no sign of disease, and are completely healthy. This is a very successful parasite, in balance with its host. It is only when the leaves start to die that the fungus takes over. When those leaves die the chlorophyll disappears, and they turn yellow. Actually the leaves do not really turn yellow, the yellow was there all along, but was hidden by the green chlorophyll. When the chlorophyll breaks down the yellow becomes visible. It is a compound called xanthophyll. Xanthophyll also captures sunlight for the tree, but in a different frequency range than chlorophyll does. In addition it protects the chlorophyll from energy overload. Too much light is too much of a good thing, like too much ice cream. It can destroy chlorophyll. The yellow pigment dissipates some of this extra energy.

Newly fallen yellow maple leaves make a beautiful carpet around the bases of their parent trees, and the large green patches stand out vividly against the yellow background. Chlorophyll is contained within tiny spherical structures called chloroplasts, and the chloroplasts are densely packed within leaf cells, where they intercept incoming sunlight. Just before leaf fall a corky layer forms at the leaf base, cutting off the leaf from incoming water and nutrients. The chloroplasts then die. The xanthophylls are more stable and last a little longer. The tar spot fungus, however, produces a hormone which stimulates the chlorophyll, keeping the chloroplasts alive for a while, even after the rest of the leaf has died. These green zones continue to produce glucose, which feeds the developing fungus spores. The fungus is farming small areas on leaves that are no longer attached to the trees which originally produced them.

The next generation of spores, however, do not mature until the spring. The old leaves with their little black spore cases lie on the ground right through the winter. The new spores infect the immature leaves as they emerge. If a spore lands on the underside of a maple leaf it produces a microscopic fungus thread called a hypha. The hypha grows across the surface of the leaf until it finds a breathing pore - a stomate. Stomata are also microscopic and the undersides  of most leaves are covered by thousands of these little holes. Carbon dioxide and oxygen enter plants through the holes. The fungus grows through the stomate and establishes itself within the leaf, where it remains in an almost dormant state until the autumn. 

How do the spores get from rotten leaves on the ground to the tops of tall trees? They obviously do so successfully every spring, as tar spots are very common on fallen maple leaves. The spores are shot into the air from the spore cases, but only for a distance of about a millimetre. Possibly they are then captured by eddy currents, and drift upwards. Possibly they are splashed from the ground by raindrops and are carried in aerosol particles. Possibly they are carried by birds or flying insects. Possibly all of these modes of transport occur. There are so many possibly’s because we are unable to observe what actually occurs. These are microscopic processes beyond our level of vision. Most of the other processes that run the living world also lie beyond the level of our senses. To study them we need to use technologies that expand our senses - technologies such as microscopes, DNA sequencing, and biochemistry.

When the maple leaves turn golden next autumn, look for the green patches with their  little black dots. Next spring some of their offspring will be back in the treetops.    

Monday, 7 May 2012

Hands In The Forest - Dwarf Mistletoe

Sometimes when walking through a hemlock forest you will see peculiar clusters of  branches. On a dark winter day they conjure up visions of the Mirkwood in Lord of the Rings. These branches are short, thick and bunched close together. Old ones that have lost their needles look like hands projecting from the tree trunk. Usually if one tree has these clusters its neighbors will also have them. They look very different from the normal long tapering branches. What you have seen is abnormal growth caused by a small parasitic plant, hemlock dwarf mistletoe (Arceuthobium tsugense). A hemlock that is not infected does not produce these clumpy branches.

Dwarf mistletoe is a parasitic plant that lives only on coniferous trees. It belongs to the same family as the Christmas-time mistletoe. The coastal form is found almost exclusively on hemlocks. You seldom see the actual plant, just the swollen tree branches. The living plant is only seen on branches that are high up on the tree. After a winter storm, however, look around on the ground for any hand-like clusters which still possess needles. The mistletoe grows on these clusters. It is about 7 cm. tall, of an olive-green color, and has no leaves, just the little olivey shoots. Unlike tree branchlets they are soft, and break off easily.

What is the mistletoe doing? It is growing within the living wood of the tree and taking  food made by the tree for the tree, to build its own tissues. It is a flowering plant but its roots do not grow in soil they grow in wood. The little shoots have some chlorophyll, but most of its nutrition comes from the host. If the shoots get broken off it does not hinder the plant. Its roots just continue to grow within the host. These aerial branches are only needed for reproduction. They produce nondescript little green flowers which mature into sticky berries. These berries, however, are not eaten by birds as most other berries are. They are held tightly inside their skins, and the pressure builds up to such an extent that when mature they are shot into the air with a great deal of force. In fact, they are reported to move at 50 kilometres per hour! If they strike the bark of another hemlock tree they will cement themselves to it,  germinate and send a root into the tree. If they land on the needles the sticky surface can slide down until it contacts the bark. 

Are these peculiar plants just strange oddities, or do they have important ecological and economic effects on the forest? The answer is yes, to the second part of the question. Let’s look at their ecological role first. There are no simple answers to most questions, and if we look at mistletoe in a general way, and ask is it good or bad, we get two conflicting answers. It is a parasite, and is bad for the tree it infects, but it is good for the ecology of a hemlock forest. This parasite steals water and nutrients from the tree and weakens it. It also causes it to grow in a contorted manner, reducing its ability to gather sunlight or transport water and food. The swellings also develop cracks and crevices where disease causing fungi can invade. If the mistletoe becomes established on the trunk of the tree this trunk becomes swollen and weakened, adversely affecting not just individual branches but the whole tree. In a windstorm the weakened trunk is more susceptible to breaking.

Considering the above paragraph, how can mistletoe be healthy for the forest? That revolves around the nature of hemlock trees. Western hemlock has developed ways to maximize its success in competition with other trees and plants. It poisons and shades out its competitors. Noon on a rainy winter day under a hemlock canopy is more like twilight. Densely packed, dark green needles capture most of the light, with very little reaching the forest floor. Only the most shade tolerant plants can survive in such places. Dead hemlock needles are very acidic and low in nutrients. When they fall to the ground they form a duff layer which is also inimical to plant growth. This is where the mistletoe comes in. When trees weakened by mistletoe and fungal infection die, or blow over, gaps are created in the otherwise continuous forest. Sunlight now reaches the forest floor where shrubs such as salmonberry and elderberry can grow, along with a number of wildflowers. These in turn attract various songbirds and insects, thus increasing biodiversity. Mistletoe and hemlock have developed together over thousands of year to such an extent that mistletoe is an integral part of the western hemlock ecosystem. 

Although mistletoe is so important ecologically, economically it creates a considerable problem for British Columbia’s forest industry, weakening and distorting the wood on many hemlock trunks. Hemlock is now an important timber tree, and mistletoe causes more financial losses for hemlock products than any other single cause. A century ago this was not an issue, as hemlock was considered a weed tree. The industry was only interested in Douglas fir at that time. If something removed hemlock forests that was considered a good thing. One of the things that removes hemlocks is fire. Mistletoe infected branches break easily and dry branches on the forest floor increase the probability of fire. Fire acts as a limiting factor for mistletoe because it destroys the host tree. Fire, however, favors Douglas fir which needs sunlight and bare soil to germinate. Ironically fire suppression has probably increased the frequency of mistletoe infection. Western hemlock has gone from weed to forest product. Other forest inhabitants, such as salal and chanterelle mushrooms, have become forest products in recent years. As we do not know what other forest components will become valuable in future years there is an economic incentive for preserving as much biodiversity as possible. 

A small parasitic plant that most hikers never see, which is common in our forests, and controls the structure of the entire forest ecosystem. Is this not another secret of the coastal rainforest? Although you will probably not find the plant itself, you can readily see evidence of mistletoe’s presence. The hemlock forest would not be the same without it.  

Wednesday, 2 May 2012

The Fertilizer Tree - Red Alder

Did you know there is a tree in our local forests that adds fertilizer to the soil? It is the red alder (Alnus rubra), and it does the same thing for the forest as alfalfa does for the farm. It makes   nitrate fertilizer. To be more accurate the microscopic partners living in the alder roots make the fertilizer. Alder roots have clusters of little round nodules on them, and in these nodules there is a special kind of bacteria. It is called Frankia alni, an actinomycete. The actinomycete bacteria are medicinally very important, as this group of organisms produce two thirds of our antibiotics. Legumes such as alfalfa and peas have similar bacteria-containing nodules, although they contain a different group of bacteria. The bacteria take nitrogen out of the air and combine it with oxygen to make nitrate. The nitrate is then taken by the tree to build its proteins. In return the alder roots provide a home for the Frankia. When alder leaves fall in the autumn their rich stores of nitrogen go into the soil as fertilizer. Over the years this rich humus accumulates and transfers its nutrients to other plants.

Have you also noticed that alder leaves are still green when they fall in the autumn. Other deciduous leaves turn yellow, red, or purple as the summer draws to a close but not those of alder. There is a good reason for this. Other trees take some of the old nutrients from the dying leaves and store them in the outer part of the trunk and branches, or in next year’s buds. This provides an extra spurt of nutrition to prime the first growth early in the spring, before photosynthesis gets under way. The dying leaves stay on the trees for a while until this food source is re-claimed. Alder leaves drop from the branches while there is still lots of chlorophyll in them. They may turn yellow, but only after they have been shed. Alders do not need to store their valuables. The microscopic allies supply them with all the fertilizer they require. 

Alder prepares the way for the coniferous trees which come later. It’s seedlings are the first to germinate after a fire, logging, or on a bare river bank. It grows rapidly, and is short-lived for a tree, about 70 or 80 years. An abandoned logging road can be home for thousands of young alders. In order to germinate they require sunlight and bare gravely or sandy soil. They do not grow in shade or in humus. If you walk through an alder woodland you will not see baby alder trees, because they cannot grow in the shade or in the rich soil that the mature alders have created. Instead the seed, which possesses a small wing, must be transported by the wind to another bare disturbed area. The young trees growing within the alder forest are conifers such as redcedar and western hemlock. These trees live up to ten times as long as the alders which preceded them. In an old hemlock or cedar forest there is no evidence remaining of the alder forest which came first, but it was the nutrients from alders that nurtured the big conifers when they were babies. 

Take a close look at the bark of an old alder. You will see two obvious things, one of which belongs to the alder, and another that many people think belongs to the alder but doesn’t. Alder bark is essentially smooth, except for tiny, pale colored bumps on its surface. These bumps, called lenticels, are softer than the bark itself, and are the breathing holes of the tree. Bark is impervious and one of its functions is to prevent disease from entering the tree. This is why it is not a good idea to chop pieces out of trees. The air is a whole ecosystem of fungus spores looking for a wounded tree where they can build a new home. Bark is also impervious to air and water, and many trees and shrubs produce lenticels which are porous spots where oxygen can diffuse into the tissues below. Lenticels are most easily seen on birch and cherry trees. The horizontal lines on the trunks of these trees are big lenticels, where the trunks breathe.

The features which look like part of the bark, but are not, are the pale splotches which many of the alders sport. These are separate living organisms that use the bark as a surface on which to grow. They are primitive lichens, and there are several different kinds growing on alder trunks. If you look closely at the splotches you will often see small details on them, and the details often differ from one lichen to another. The small markings on them are the reproductive bodies of the lichens, and if they look different from one splotch to another splotch it is because the splotches are different kinds of lichens. If there are no markings on the crusts, the different kinds look essentially the same.

If there are black squiggles, like cuneiform writing, on the surface you have a script lichen (Graphis scripta). Both the scientific and common names refer to the fact that the black markings look like writing. The lichen reproduces by producing spores in the dark lines. Rather, half the lichen reproduces by producing spores. A lichen is a composite organism - two in one. Most of it is composed of fungus. Imbedded deep inside the fungus coating are single cells of a microscopic plant. Like all plants this one uses photosynthesis to make sugar, and the fungus makes its living and builds its structure by stealing sugar from the plant. The spores float away on the wind, with an almost non-existent possibility they will land on the right plant cells to regenerate a lichen. All this, of course, occurs on a microscopic level, and nobody has ever seen the process taking place. Our knowledge of what takes place is based on circumstantial evidence.

Script lichen (Graphis scripta) on Red Alder
Photo by Kelly Sekhon

Other common lichens which form these bark patches are the rim-lichens (Lecanora spp.), that have tiny disc-shaped reproductive structures on the surface, and the bitter wart lichen (Pertusaria amara) with tiny, dusty warts. 

During the winter when food supplies are hard to come by, and cold dark days are the norm the alder produces another kind of sustenance. It is on the bare branches of the alders where the songbirds congregate. The little cones are densely packed with tiny seeds, which supply the birds with food over this time of famine. Cracks in the bark also conceal small insects, providing the birds with a little extra protein.

As the winter draws to a close an alder forest announces its presence in a subtle, but colorful way. Alder buds are a pinkish color, as are the young male catkins. These are elongated clusters of densely packed flowers, but look different from what we generally consider flowers because they are wind pollinated. Therefore, they do not have showy petals to attract bees or other insects. As spring approaches the catkins grow in the crowns of the trees. At this time there are no leaves on these trees, and the branches are readily visible. Alders usually grow in pure stands, and the masses of young catkins, combined with young buds give a pink glow to the slopes of many a hillside, announcing the approach of spring.

At one time alders were considered weed trees, as the wood is not as valuable as that of some of the coniferous trees. Foresters now have a better understanding of alder’s role in the forest, and forest practices have also changed with changes in knowledge and economics. Therefore, alder trees are viewed in a more favorable light than in previous decades. Next you go hiking in a deciduous woodland take a closer look at this tree which is doing so much for the health of a future forest which we will never see.

Vascular Plants Seen On Galiano Island

 Native Plant Society trip to Galiano Island
April 21, 2012
Photo by Murat Gungoraydinoglu

Following is a list of species I remember seeing at Bluffs Park, Matthews Point, Bellhouse Park and along the roads:

Abies grandis
Acer glabrum var. douglasii
Acer macrophyllum
Achlys triphylla
Adenocaulon bicolor
Aira praecox
Alnus rubra
Amelanchier alnifolia
Anthoxanthum odoratum
Aphanes arvensis
Arbutus menziesii
Artemisia suksdorfii
Bellis perennis
Brodiaea coronaria?
Calypso bulbosa var. occidentalis
Cardamine hirsuta
Carex obnupta
Cerastium arvense
Cerastium fontanum ssp. triviale
Cerastium glomeratum
Circaea alpina
Claytonia perfoliata
Claytonia sibirica
Collinsia grandiflora
Collinsia parviflora
Corallorhiza sp.
Cynosurus echinatus
Cytisus scoparius
Daphne laureola
Daucus pusillus
Digitalis purpurea
Draba verna
Equisetum telmateia var. braunii
Eriophyllum lanatum
Erodium cicutarium
Erythronium oregonum
Fragaria vesca
Fumaria officinalis
Galium aparine
Galium triflorum
Gaultheria shallon
Geranium molle
Goodyera oblongifolia
Hedera helix
Heuchera micrantha
Holodiscus discolor
Hyacinthoides hispanica
Hypericum perforatum
Juncus effusus
Lamium purpureum
Lathyrus nevadensis var. pilosellus
Linnaea borealis ssp. longiflora
Lomatium utriculatum
Lonicera hispidula
Lotus corniculatus
Lunaria annua
Lupinus bicolor
Luzula fastigiata
Luzula subsessilis
Lychnis coronaria
Lysichiton americanus
Madia madioides
Mahonia aquifolium
Mahonia nervosa
Melissa officinalis
Mimulus alsinoides
Moehringia macrophylla
Montia fontana
Montia linearis
Myosotis discolor
Narcissus pseudo-narcissus
Nemophila parviflora
Oenanthe sarmentosa
Osmorhiza berteroi
Physocarpus capitatus
Piperia sp.
Plantago lanceolata
Plantago major
Plectritis congesta
Pseudotsuga menziesii
Pteridium aqulinum
Quercus garryana
Ranunculus acris
Ranunculus occidentalis
Rosa nutkana
Rubus discolor
Rubus spectabilis
Rubus ursinus ssp. macropetalus
Rumex acetosella
Rumex obtusifolius
Salix sp.
Sanicula crassicaulis
Satureja douglasii
Saxifraga integrifolia
Scirpus microcarpus
Sedum reflexum
Selaginella wallacei
Senecio jacobaea
Stachys chamissonis var. cooleyae
Symphoricarpos albus
Symphytum x uplandicum
Taraxacum officinale
Taxus brevifolia
Trifolium subterraneum
Triphysaria pusilla
Ulex europaeus
Urtica dioica ssp. gracilis
Vaccinium ovatum
Vaccinium parvifolium
Verbascum sp.
Veronica arvensis
Vinca major
Vinca minor