Download HENVI SEMINAR: BIODIVERSITY AND CHANGING LAND USE

Sara Nevalainen
HENVI SEMINAR:
BIODIVERSITY AND CHANGING LAND USE SYSTEMS
Biodiversity in fragmented landscapes (Professor Ilkka Hanski)
Professor Hanski’s presentation was about the fragmentation and its impacts at the population level
and the ongoing global wave of extinctions. Some ecosystems are naturally fragmented such as the
rainforest canopies with hundreds of tree species scattered around in a varying mosaic. However,
during the last couple of centuries human-induced fragmentation has posed an ever-growing threat
to habitats and species around the world.
The rate of extinctions has increased considerably. In the past the rate has been 0.001% of species
going extinct every 100 years. For the past 100 years, the rate has been 1%, and it is expected to
increase to 10-30% during this century if nothing changes in the way we use natural resources. The
extinction rates are based on studies done on vertebrate animals. The IUCN has studied and
evaluated 50% of the currently known vertebrate species and found that 30% of them are threatened
by extinction during the current century.
The response of the species to the changing environmental conditions is non-linear. There’s a
critical value known as the extinction threshold which describes the response of the species to the
environmental factors. For example, the amount of deadwood needed by rare polypore species is
around 30 m3/ha, and when the amount of deadwood goes below this threshold value, there’s a
drastic drop in the number of species. The typical amount of dead wood in the commercial forests in
Finland is around 1-3 m3/ha and rare polypore species are completely lacking in them.
Extinction debt means the delayed response habitat destruction and fragmentation. Professor Hanski
showed an example from Wisconsin, US, where forest cover has been rapidly destroyed since
1700s. The forest cover has remained quite stable during the latter part of 1900s without
considerable further losses. It was discovered in a study made in 1950 that there’s no relationship
between the percentage of forest (nearer than 5kms) and the number of vascular plant species.
However, the same study was conducted in 2005 and a clear positive correlation was found. With
the comparison of these two studies, the extinction debt of the year 1950 was estimated at 50%,
meaning that half of the species were doomed to extinction (which had then been realized during
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the next five decades). There are two ways to pay the debt: either let the species go extinct or pay
the debt through improving the environment. Another example was from Finland. The current
amount of old forests is similar throughout southern and middle parts of Finland. However, the
number of forest beetle species is notably smaller in the southern part of Finland. The reason for
this is the longer history of forest use in the southern parts of Finland. It is expected that the amount
of forest beetle species will be reduced to the same level in other parts of Finland too in the next
decades unless improvement in the environment happens.
Professor Hanski and his research group have also studied the impacts of fragmentation on the
genetic viability of the species. There’s a small island called Pieni Tytärsaari in the Baltic Sea south
from the Finnish coast, where an isolated population of Glanville fritillary butterfly has been
discovered. The species exists in much larger numbers in the Åland archipelago. In a study the egg
production rates of the butterfly were compared on Pieni Tytärsaari and Åland. A distinction was
made between sib-mating and non-sib mating. It was discovered that the egg production rate was
much lower in Pieni Tytärsaari and there was no considerable difference between sib and non-sib
mating (as compared to Åland where sib mating produced considerably smaller amounts of eggs
than non-sib mating). The small population of Pieni Tytärsaari and the consequential inbreeding had
led to heavy genetic load that threatened the survival of the species. This result shows that
fragmentation results in negative effects on the genetic viability and if a species goes through a
genetic bottleneck phase due to habitat destruction, its chances for survival may still continue to be
low even if the habitat would be recovered.
As a conclusion, the fragmentation needs to be addressed through preserving natural ecosystems
and creating more habitats for species. Otherwise the extinction debt will continue to grow and a
large proportion of species will go extinct during the ongoing century.
Forest management and biodiversity conservation based on natural ecosystem
dynamics in Northern Europe (Professor Timo Kuuluvainen)
The current management of Finnish forests is done with modern technology and old ideas. The
management is based on German forestry in the 1800s with even-aged stands and clear-cuttings.
The model has stayed largely the same, except that following the increased environmental
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awareness aroused by the Rio Earth Summit held in 1992, new components such as the retention
trees and the protection of key habitats have been incorporated in the management guidelines.
The current management model is based on the belief that the forests burn naturally every one
hundred years by stand replacing fires. There’s also the ideal of fully regulated forests, meaning that
there’s the same percentage of every age class (between 0-100 years) in the landscape, thus
providing continuous timber flow for the industries. However, the stand replacing fires are largely a
myth. More important disturbance patterns in most of the boreal forests are smaller scale dynamics
caused by wind disturbance, pathogens and senescence. Even after the fires, many of the trees
survive, thus leading to very diverse forest stands.
Apart from this fire-based even-aged dynamics, there is also smaller scale gap dynamics produced
by senescence, fungi and insects killing individual trees. Between these there’s also a third class of
dynamics, cohort dynamics that is created by fire and wind disturbance. In natural forests all of
these three scales of dynamics work together, though the even-aged dynamics is only found in
forests with relatively high fire recurrence and intensity.
In a research conducted in pine-dominated natural forests in Vienansalo it was discovered that only
3% of the fires are stand replacing, and there was high variability in the intensity of the fire damage.
Some of the largest pine trees survive the fire which results in a complex stand structure. The
current 80-100 year rotation cycles result in monotonous forest structures totally lacking trees from
the age classes above 100 years, thus removing the majority of the variation occurring in the natural
forests where most trees are above 100 years.
In the boreal forests, the decaying logs and wood debris are an important habitat for many deadwood associated species. Natural forests have a lot of dead wood and old trees reaching hundreds of
years of age. All this diversity has been removed in the current forest management, leading to lack
of habitats for many species depending on dead wood or old (especially deciduous) trees.
There are three approaches to preserving biodiversity in boreal forests: conservation forests, longer
rotation length and adapted silviculture. There are two recent models for management for ecological
restoration. The ASIO from Sweden takes different moisture gradients and the natural fire
frequency as a starting point for forest management. The stands with higher moisture would be
managed with selective cuttings. The drier stands in the landscape would be managed with clear-
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cuttings combined with prescribed burning, thus creating habitats for species dependant on burned
wood. The Canadian multi-cohort management system takes a more landscape level orientated
approach.
In conclusion, the myth of clear-cutting as natural dynamics should be thrown away and a more
comprehensive approach combining both forest conservation and more sustainable forest
management is needed to ensure the preservation of biodiversity in the boreal forests.
The most diverse habitat on Earth (MSc Anu Mikkonen)
Coral reefs? Rainforests? No, the most species-rich habitat on Earth is the soil. There are millions of
species of microbes in just 10 grams of soil. The researcher Anu Mikkonen’s presentation dealt with
the largely unknown and mysterious underground diversity of microbes and its peculiarities and
how land use and pollution affect the microbial species diversity. What is surprising is that there
isn’t a reduction in the species richness when moving away from the equator and the arctic soils are
just as abundant with microbes as the soils in the tropics.
Soil is important in the biogeochemical cycles of elements. The microbes are also able to degrade
many harmful pollutants in the soil. The microbes create a chain with microbes of different species
performing different functions in the degradation of substances and breaking them down into
elements, consequently if one link is lacking, the whole chain might stop functioning. The microbial
biodiversity may also play an important role in the resilience of the soil.
The diversity is largely caused by two facts. Firstly, the evolution happens at a quick pace in the
microbial life. Secondly, the soil is an incredibly varying habitat. The soil has three phases: liquid,
solid and gaseous. The combinations of these three phases create a mosaic of different surfaces and
microclimatic conditions. The surface area in the soil is large because of the small soil particles.
Microbial diversity is lower in the soils with plant cover. The plants provide resources such as root
exudates, which causes selection pressure among the microbes and the weakest ones are eventually
outcompeted. Sustainable agricultural practices such as reduced tillage and crop residue retention
increase the number of microbial species. Also the impacts of pollution on soil microbiology have
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been studied. Heavy metals reduced the species richness by 99%, however the total biomass
remained the same. In soil polluted by oil, there even occurred a slight increase in the biomass of
the microbes when more oil was added.
Currently the microbial functions of the soil remain a black box. What is well known are the fluxes
(CO2, CH4, N etc.) in and out of the box, but the inner life remains yet largely unknown. There’s a
need for more research on the microbial biodiversity and its importance for environment and
ecosystems.
Biodiversity in Agricultural landscapes (Dr. Iryna Herzon)
Agroecologist Iryna Herzon’s presentation dealt with biodiversity in the farmland and the effects of
agriculture on biodiversity and also ways to increase biodiversity through sustainable farming.
Many semi-open ecosystems occur naturally, so many species (including the wild ancestors of the
current livestock animals) were already adapted to agricultural landscapes when the humans started
growing crop plants at larger scales. High biodiversity is possible even under continuous extensive
management. For example meadows and agroforestry systems might have biodiversity comparable
to natural ecosystems. Some of the agricultural ecosystems provide important habitats for many
species of birds and butterflies. However, the current mode of industrialized agriculture is
threatening the existence of these habitats that used to be common in the more traditional methods
of farming. Currently EU requires the member states to assess these High Nature Value farmlands
(HNV) and to create national baseline indicators, monitoring and sustenance.
The current population growth results in a greater demand for food. There are two different
approaches to the constantly growing need of food while preserving the natural areas that are still
left. The first one is land sparing, which means increasing production per area unit on the current
agricultural land and freeing land for other uses. However, this approach is problematic due to
negative externalities, such as increased pollution and water use. And it is by no means guaranteed
that the freed land would be used to preserve biodiversity. Also, this approach doesn’t answer to the
needs of the species dependant on agricultural lands.
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Another approach is land sharing through wildlife-friendly farming. It would mean improving the
biodiversity of farmland (for example through systems such as agroforestry), and improving the
connectedness of natural ecosystems through more ecological agricultural practices and better
planned land use.
Something that should also be kept in mind is the current amount of food going to waste as an onfarm waste, during storage or just being thrown away by the consumers. This waste alone makes for
a considerable part of the growing demand for food. It was also pointed out that we should start
eating lower on the food chain, thus saving natural resources that are wasted by growing food for
livestock.
The agriculture can be seen both as an opportunity and a threat for biodiversity. Through choosing
more sustainable farming methods, we can increase the agricultural biodiversity and also preserve
biodiversity present in the surrounding natural habitats such as forests.