Life of trees and forest ecosystems
Biology Books environment

Life of trees and forest ecosystems

Have you ever wondered why trees are the way they are? Why do they form forests? Could they grow on their own, or do they prefer company? In the (below) named book we find almost all the answers and what’s more, they are delivered in a very interesting and humorous style.

All the facts are collected from the book Hidden life of trees by Peter Wohlleben.

Trees form networks below and above ground in different types of forests. There are rules in the forests in order to help individuals survive the challenging weather and climate conditions. For that to be possible, trees have to be capable of sensing the world around them and also communicate to inform each other about more or less sudden changes in the environment. The actions of nutrient exchange and neighbouring emergency aid are a rule in forests and have helped to establish the fact that forests are a superorganism. A similar structure as we know it, for example, in the anthill. That’s why most single-growing trees have it difficult to bear the environmental challenges. On the other hand, some, called pioneer species, prefer to germinate on their own – with no shadow from other plants to block their growth.

Quick information exchange is mostly provided by fungi. Thin hyphae are very densely intertwined. One fungus can spread out its hyphae several kilometers wide in the centuries of its existence and thus network the whole forest. Research on how much and what data travel through these networks is still ongoing.

forest ecosystems
Fagus sylvatica

Forest ecosystems

Forests create an ideal habitat for themselves. Due to reduced wind power humidity increases which changes the microclimate. So the forest-based soils do not dry because they are in the shade and protected with leaves.

– Due to different forms of trunks, growth of branches and crown shapes, leafy forests take advantage of 15 % more water than coniferous forests. Spruce are adapted to colder climates, where there is little water evaporation and lots of snow, so their branches grow downwards, as they have to. Whereas beeches store water in their roots, trunks and branches. Furthermore their branches grow upwards so water drops flow down the branches, trunks and towards the roots where it can be absorbed. We can notice this difference a mild rainfall, as the soil under spruce remains dry.

– Coniferous forests on northern hemisphere have a way to regulate its climate and water supply. They release terpenes, which are of primary importance in the defense against diseases and parasites. Once these molecules evaporate, small water drops in the air bond with them and condense. This way in the sky above coniferous forests clouds form, which have twice the density as clouds that form in the skies above lands with little or no forests. Likelihood of precipitation increases and about 5 % more sunlight is reflected than with less clouds. Consequently, local climate cools down and becomes more humid.

– How does water get on land? The answer is as you could expect – forests. In the summer trees consume 2500 m3 of water per km2, which they emit to the air as they breathe. Because of this vapour clouds are formed which move further inland where they release water in form of rain. The process is repetitive, so even more remote areas are provided with water. The only condition for this process to be enabled is that there is a forest between the sea and the vast land area. If the first factor is missing – coastal forest – the system collapses. Research has proven, whether it be a rain forest or a taiga, trees are always the ones that bring water inland.

– Forest floor acts as a large pantry where all the rainfall is collected. When the floor is soaked and trees’ reservoirs full, residual moisture flows into deeper layers of soil for many years. Fluctuations between drought periods and strong falls are thus cleared, stable conditions remain with permanent springs and streams.

– Streams in forests have better chances of existence than waters in open spaces. Because of deep soils, springs have constant temperatures of about 8°C, so do not heat up in summer and almost never freeze during winter. In summer the leaves provide enough shade and in winter bare branches descend to the ground to release more heat to the floor.

 

Health of a single tree = health of a forest and vice versa

Forest ecosystems protect all individuals, which enables them to live longer as they are less exposed to the environmental challenges. So each tree is vital for the community and is good that it lives as long as possible. It is not good for the forest to lose its weakest links because this way holes are formed which break the microclimate. That’s why trees help each other, help the weakened to get better. When a tree weakens, its defensive power drops as well as the ability to communicate.

– Example: acacia trees in savannahs. When giraffes start eating acacia leaves, toxins build up in the leaves in a matter of minutes and they start emitting ethylene which informs all the neighbour trees to build up toxins as well. The giraffes then leave the whole area and move on. So the message is transmitted by air flow in the form of odor.

– When caterpillars nibble on the leaves of beeches, pines and oaks, trees detect the attack. Around the wounds plant tissue changes and the tree emits electrical signals along its body. These impulses travel with the speed of 1 cm/min. So it takes another hour to for all the leaves to build up defense material.  Information also reaches the neighbours via roots, consequently, all the nearby trees activate by supplying leaves from bark with bitter poisonous tannins, which kill or at least discourage the attackers.

– In crop plants, the ability to communicate under and over ground is significantly reduced due to planned production. Basically they are deaf and mute, which makes them easy pray for insects. This is the reason for the enormous amounts of pesticides used. We should follow the forests example and let the crops have more self-sufficiency and, consequently, eloquence.

– In the unspoiled beech forests, we notice a specialty in photosynthesis; each tree grows in its own place and conditions over a few m2 can vary considerably. Scientists have discovered that trees mutually compensate advantages and disadvantages. Consequently both thin and thick, younger and older trees produce similar amounts of sugar per leaf. The process is aligned through the roots and various fungi are involved in this process. For this reason it is good for the beeches to grow densely. The treetops are consequently small and foresters are confident that this is not good for the forest and so interfere with harvesting of the alleged excess trees. Here enters science which showed that densely scattered beech forests are indeed more fertile. If one tree gets removed, bonds are broken, leading to great differences in productivity. One single tree can never be more productive than the forest which surrounds it. Tree prosperity depends on the whole community, not the survival of the fittest. If the weaker specimens die or get removed, every tree is left for worse. Forest is no longer closed, so hot sunlight and strong winds reach the ground thus changing humidity and temperature. Even the fittest trees get ill in their long lives and at those times depend on the support of the neighbour trees. But if these no longer exist, a minor insect attack is sufficient to knock them down. Also in this way more exposed trees become easy prey for insects and fungi.

– Conifers seed every year, whereas deciduous trees don’t. It would be better for the forest trees to all seed in the same time frame for the gene pool to cross well. But there is a negative factor – boars and deer. These animals have an endless appetite for beechnuts and acorns with which they increase their fat layer for the winter. No other nuts contain a better fat-starch ratio (50:50). For that reason the trees don’t bloom, seed and fruit every year – to restrain the animals with their offspring. When every few years the trees do bloom, there is not enough animals to eat all the seeds and fruits. Thus leaving sufficient seeds for germination. This flowering at multiannual intervals has consequences for all insects, specially bees. Their numbers decrease significantly during the breaks. It’s a natural cycle.

– Slow growth of young trees is a prerequisite for achieving a high age. Cells in the center of tree trunks are small due to slow growth and contain little air, therefore are flexible and resistant to breakage. Even more important is the fact that this way they are more resistant to fungi which cannot spread through tough trunks. »Waiting« to grow higher is not hard for the young trees as their parent trees provide them with all the necessary nutrients they cannot acquire themselves yet.

 

Roots and fungi connections

Links in between trees and between trees and fungi are moderated through the mycelium that envelops the root endings and helps them to exchange nutrients. In some cases the tree roots are fused directly. The roots of an individual tree spread very far, more than twice as far as the treetop. The roots intertwine with those of the adjacent trees, this way communication is enabled. This communication does not depend on the weather (whereas scents from leaves spread through air where they can be disabled by winds and rainfall). Messages spread chemically and electrically with a speed of 1 cm/min. There are various types of connections underground: tree-tree (roots of the same species), tree-tree (different species), fungi-fungi, of same and different species and, most importantly, tree-fungi.

– When a tree and fungus connect, they also cooperate. The hyphae cling to the roots and spread across the nearby forest floor. Thus exceeding the range of tree roots and extending to other trees where it connects with other partner fungus and neighbour tree roots. Not only trees benefit from these connections, fungi draw sugar and other carbohydrates from its partner, up to one-third of total tree production.

– Along with its tree fungi can live up to 100 years, unless the environmental conditions change. In such case even a stable and efficient system can quickly die off. Changes can lead also to only fungus dying off, in such case, the tree can connect with another fungus, most likely other species, that thrives at the foot. Fungi are more sensitive, they are mostly specialized for one type of host, while trees can be linked to different types of fungi. There are some exceptions, for example chanterelle can link to several types of trees: oak, beech and spruce.

– An example of cooperation between white pine (Pinus strobus) and fungus Laccaria bicolor: in case of nitrogen deficiency the fungus excretes a deadly poison to the soil which causes all the small animals to die (Collembola, etc.) and the nitrogen bound in their bodies is released and free for the tree to take it in.

– Mycelium of suitable species of fungi for each tree can increase the effective root surface several times so that the tree can drain significantly more water and minerals. Plants that cooperate with fungi, store twice as much of essential nitrogen and phosphorus as in plants that draw nutrients only with their own roots. In this exchange fungi also filter out heavy metals. Excreted harmful substances are then concentrated in the above ground growths – mushrooms, which are collected also by people. For example: radioactive cesium, which is still present in the soils across Europe because of the nuclear accident in Chernobyl, is most often found in mushrooms, which is a carpophore – the fruiting body of fungi.

– If a forest is cut out for the purpose of cultivating surfaces and then replanted, the new forest at first glance after a few years seems like a regular forest. But the fact is, forest floor needs a lot more time to recover. It was assumed that in some 10 years the original composition of fungi and bacteria is resettled. But it was discovered that even after a hundred years the base composition of living matter does not return to its original state. So the circulation of matter doesn’t function properly and as effectively as before. In addition, there is still excess nitrogen from fertilization in such soils. So 100 years is not enough. What then? The only solution is to leave a part of the original forest and when the purpose of reforestation occurs, the original part greatly contributes to forest restoration. Because roots are more important than treetops. Why? For one, if a tree dies off, roots can survive and grow a new tree. Hence the underground part is the most durable. It is also the part where all the survival information is stored. We know that because the new tree is proven more, or at least as resistant, as the previous was.

– Not all fungi live in harmony with trees; a large predator of young trees is the honey mushroom whose carpophores appear on the stumps in the autumn. There are 7 species which with their mycelium penetrate the roots of spruce, beech, oaks and other tree species. They grow upwards under the bark and form fan-shaped white formations. Sugar and nutrients from the cambium are depleted by thick funiculus (a specialty in the world of fungi). Later on they stretch into timber, causing the tree to start to rot and die.

 

Interesting facts

– In Switzerland, a species of tin was found, which spread to almost half a kilometer and reached the age of about 1000 years.

– In Oregon a fungus has grown over 9 km2 and weighs 600 t, its age estimated at 240 years.

– One beech produces 1.8 million fruits in its 400-year existence, whereas poplars produce 26 million seeds. But statistically, each tree submits one offspring which takes its place somewhere close or quite far.

– Where does the chlorophyll go when trees restore it from the leaves before dropping them? Most of the trees do restore it (some don’t, they just drop still green leaves (e.g. alder)), others keep the leaves even through the winter (conifers). Chlorophyll is stored in the trunk of live trees to be reused next spring.

– An adult beech can run more than 500 l of water through its branches and leaves. Stocks are filled in winter.

– Trees can be spoiled too. Specimens of the same species are variously wasteful with water. This becomes clear when draught hits. Its effects are stronger on trees that otherwise grow on water rich grounds. Which is proof trees learn as they grow. Those that grow in more arid conditions, supply themselves with enough water, while trees of the same species on more humid soils are more wasteful.

– The other clear learning process is trees’ own strength. When trees have an opportunity to lean on their neighbours, they eagerly do so and consequently don’t form thick, sturdy trunks. When a stronger tree falls or is cut, hollow spaces are formed and many leisurely beech or spruce remain without support. It takes 3 to 10 years for the trees to recover after such a change. Even though they receive more light in such case, it takes several years before they can fully exploit new conditions.

– In time every tree stops growing in height because the roots and water transport systems cannot draw it so high, so it continues to only grow thick.

– Alder drop still green leaves. They mostly grow on wet and rich soils so they can afford to build new chlorophyll every year. All the other trees recover and store chlorophyll from their leaves before dropping them. In case of alder elemental substances for chlorophyll are recycled from old leaves at the foot of trees by fungi and bacteria, so the roots can regain it. Alder can also lay off returning of nitrogen, since they live in coexistence with tuberous bacteria, which are constantly providing it to them in sufficient quantities. A km2 of alder woods can absorb up to 30 t of nitrogen per year from the air.

– Conifers have an energy reserve for defense against harmful organisms. They can draw these reserves at any time. Depending on the species, there are a number of effective defense materials in these substances. One of them are phytoncides. In 1956, a phenomenon was described: when a drop of water, containing protozoa, was added one drop of shredded pine needles, living organisms died in less than a second. Air in pine forests due to phytoncides migrating from needles is almost pathogen-free.

– The reason for the white color of birch is the active substance betulin, which forms the bulk of the bark. White bark reflects sunlight and so protects the bark from burning heat. In addition, it prevents overheating in the warm light of the winter sun, sometimes causing unprotected trees to burst. Betulin also works antiviral and antibacterial, which is used in medicine, this substance is also added to skin care products.

– Birch as a pioneer species often grow alone in a spacious area where they have no neighbors that would cast a shadow on them.

– In the national forest of Fishlake in Utah, one aspen has spread over 400.000 m2 in thousands of years, creating more than 40.000 stems. This creature looks like a great forest, called Pando (from latin pandere = to expand).

– A marine chemist from the University of Hokkaido discovered that acids from depleted leaves along streams and rivers flow into the sea, where they stimulate the growth of plankton, which is, as we know, the primary and most important part of the food chain. The trees along the coastline, as proven, contribute to this.

 

Conclusion

All the plants, all the trees, all the forests and all the ecosystems are, of course, vital to this planet. Forests are not a timber factory and a warehouse of raw materials, as is obviously a belief of modern management. They are complex living spaces for thousands of species. Whenever plants have the smallest chance of developing properly functioning systems, their function is distinctly well-performed, no flaws.

We have destroyed many ecosystems, but we can help the existing ones not only to continue existing, but to thrive. Some by making sure at least they are not polluted, others by just leaving them in peace, quietly observing them with respect. We are so lucky to be able to do that, never take that for granted.

 

More on this topic: http://www.nytimes.com/2012/04/12/opinion/why-trees-matter.html

 

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