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Transcript
Biodiversity and changing land use systems Mária Abigél Gonda The United Nations declared 2010 to be the International Year of Biodiversity. We heard several definition of biodiversity from the very simple “Biodiversity is everything that is good” or “Biodiversity is life” to the more complex definition of the Wikipedia: “Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet.” From the talk of Professor Ilka Hanski we could learn that a large number of species live in fragmented habitats like the naturally fragmented tropical forests or the artificially (resulting from human activity) fragmented boreal forests of Finland. The rate of species extinction has changed during the last centuries and definitely shows a strong increasing trend. Fragmentation of habitats and habitat loss are very important factors in the extinction of species. Metapopulations that occupy fragmented habitats persist long if the fragments are big, well connected and close to each other. There is a critical value of the landscape, called extinction threshold under which the given metapopulation cannot exist. Fragmentation decreases the metapopoulation capacity, which refers to the landscape structure and quality, and hence decreased metapopulation capacity results in a decreased viability of the given (meta)population. Samples of several distinct taxa (like butterflies, fungi or birds) have shown that species response to habitat fragmentation and habitat loss in a non-linear way, i.e. they can go extinct before they lose all their habitats. In 1950 a study showed a surprising result; species richness was not related to the size of forest they occupied. But decades later the expected relation between habitat size and species number on the same study area was shown. There were no new fragmentations between the two studies on the studied land. It seems that species show a delay in their response to habitat fragmentation and loss which generates an extinction debt. Hence, even if the conditions of a habitat are maintained and do not go worse species can keep on going extinct. A study on beetles in Finnish forests showed that species went extinct in the south and in the south west of Finland more than in the north. Considering that there has been an intensive forestry in the southern areas for a long 1 time while intensive forestry started not so long ago in the northern areas and that species have a delay in their response to habitat loss and fragmentation it is expected that the number of species will also decrease in north of Finland as well in the future. Further, it has also been shown that communities that live close to their extinction threshold have bigger delay in their response to habitat loss than those who live further. Hence, communities that consist of a lot of species and live on landscape that have metapopulation capacity that is close to the threshold value have a big extinction debt. Even though, metapopulations can survive and persist long on fragmented areas if the fragments are large enough, their genetic viability decreases due to genetic drift and inbreeding. During management and conservation of fragmented areas it should be considered that a lot of uncommon or endangered species can go extinct even if the quality of their habitat does not decrease. Hence the quality of these habitats must increase to save these species. Newly developed models that take the viability of metapopulations into account are available for estimating areas that should be conserved. While Professor Ilka Hanski was talking about the species inhabiting different fragmented areas, Professor Tima Kuuluvainen based his talk on different habitat types, especially the forests and forestries in the Scandinavian area. There were a dramatic decrease in the amount of natural forest in Finland during the last centuries and this decrease was especially significant in the last two centuries. Although the proportion of the land covered by forest is still very high and remained almost the same as it used to be, the structure of these forests has changed a lot due to the management that is in use in Finland. The management model that is used nowadays in Finland applies old theories that date back to the 19th century using new modern techniques. Finnish landscape shows the so called fully regulated forest model. This means that there are continuous areas with trees of the same age. Due to this management strategy, there are no trees more than 100 year old. However, from 1990, to increase the conservation of biodiversity, new strategies (such as retention trees) have 2 been involved in the forest management. Beside the structure of the forests, the ecological conditions have also changed dramatically. The biodiversity of forests declines permanently, so the management tools and methods need to be reconsidered. Especially if we consider that a lot of endangered species lives in forest. For applying effective management techniques the history of the dynamics of natural forest must be understood. Forest fires have always had important role in the history of Finnish forest (especially in Pinedominated forests). The old forestry management was based on the idea of high severity fires that legitimated clears cuttings. But beside these processes there are other even more important events like the non pyrogenic senescence or low severity fires. The new classification of forests’ dynamics involves both low and intermediate severity disturbances and senescence beside the high severity forest fires. Professor Kuuluvainen emphasized that the importance of high severity forest fire is only a modern myth and is not applied as a basis of modern management anymore. There were two case studies showed about the dynamics of natural forests, focusing on Pinus sylvestris and Picea abies dominated forests. Pine-dominated forest in Finland consists of different age cohorts and characterized by old trees that survived forest fires while senescence is also a very important process in these forests. Modern forestry changed the cohort structure towards even aged forests, producing a drastic change in the structure of Pine-dominated forest. In nonpyrogenic Picea-dominated forests we can find different aged trees throughout the forest while cohorts are not typical. Old forests are still very dynamic and the modern management changed the structure of these forests as well. If the present management is going to be applied in the future the old forests will disappear. This will result in a loss of several threatened species and a dramatic decrease of biodiversity. To save the characteristics of old forest new approaches (like increasing protected areas, increased rotation length and adapted silviculture) are needed. Three are two models for ecological restoration in use, the ASIO (Aldrig Sällan Ibland Ofta) and the Multi-cohort model. 3 The Scandinavian ASIO model is based on natural fire dynamics considering that fires are not equally serious in all landscape. Fires are rarer and less serious on a humid land than on arid lands and silvicultural tools should take this dynamic into account. The Canadian multi cohort model is based on an observation that lands usually consist of cohorts with different dynamics and the forestry management should be based on it. In order to maintain or increase biodiversity the structure of natural habitats should be maintain. For that purpose the management techniques should be revised. From the talk of Anu Mikkonen I have learned that contrary to my expectations the most diverse habitat on Earth is the soil and not the coral reefs or the rain forests. 10g of soil may contain 20 times more different microbe species (107) than the estimated number of plant species on Earth. Microbes play a very important role in the life on Earth such as controlling several biochemical processes or having important role in climate change. The extreme diversity of microbes in soil is mainly due to the structure of the soil habitat. It contains gas, water and solid elements as well. Soil is very complex and spatially heterogeneous. In general we can say that soil is the most complicated biomaterial on Earth. Maintaining the biomass of microbes is not enough as the biomass of microbes are not equal with diversity of microbes. A less diverse microbe community is more vulnerable and as microbes are very important from several aspects we should protect the diversity of them in the soil. Microbial diversity can be protected by agricultural processes by maintaining neutral pH or by increasing plant diversity. Plants have a selective effect on microbes as the root of plants directly influences the soil near to the root. These root-influenced narrow regions of soil (rhiospheres) are less diverse than the rest of the soil (bulk soil). Heavy metals can also have a strong affect on the biodiversity of microbes and can reduce biodiversity with 99.9% without affecting the biomass. Even though the soil and the microbes that it contains are very important in life on Earth the ecology of the soil is hardly known and understood. 4 Petri Nummi talked about the “Effects of alien species on biodiversity” and showed that how dangerous alien species can be for the native fauna. Alien species are species that are found outside of their native distribution range as a result of human activity. They are responsible for a high per cent of extinction of native species. Isolation is a key factor in biodiversity. If some species eliminate native species of an isolated area the local diversity can increase but the global diversity can decrease. Alien species can be introduced several ways. They can be transported accidentally as stowaways by plane or by international transport such as garden plants. The effects of them can be diverse from predation and competition to spreading diseases. Alien predators for example can have stronger effect on native species than native predators. The introduction of the brown tree snake in the Guan Island resulted in the extinction of most of the native bird and lizard species. Invasive herbivores like rabbits can also be very dangerous, especially on island environments. Rabbits can cause distinction of native species through changing the vegetation, competing with endemic species or providing predators with an alternative prey resource that can increase the size of predator populations. Introducing the omnivore possum to New Zealand resulted in the decline of a plant species throughout a series of independent effects of these animals, like eating the plant itself and by eating the bird species that plays an important role in the reproduction of this plant. On the other hand, controlling the abundance of alien species can result in an increase of the abundance of native species. For example the removal of an introduced mink species in Finland resulted in the increase of its native prey species such as ducks or scoters. In general we can say that alien species can have very strong and very serious effects on native species by changing the native ecosystem dramatically 5