Download Biodiversity and changing land use systems

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