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Biodiversity
The influence of biodiversity on ecosystem processes
Why study biodiversity?
Earth’s biodiversity—or biological diversity—is
one of our planet’s most striking features. The
variety of life, long a source of wonderment and
scientific curiosity, has recently become a source
of concern as human influence reduces the
diversity of species in many habitats worldwide.
“But what good is a snake, or a mosquito, or a
sand spur?” one might ask. “If they were extinct,
it wouldn’t bother me one bit.” Or would it? One
of today’s big questions is to what extent this
loss of diversity matters. In other words, does
biodiversity affect the way an ecosystem operates
- does biodiversity influence the stability,
productivity and sustainability of an ecosystem?
An ecosystem such as...Earth.
Aerial view of the experimental plots
Biodiversity Research
Charles Darwin was one of the first scientists to
hypothesize the impact of biodiversity on
ecosystem processes. After a lapse of more than
a century, research on the topic began in earnest
in the 1990s. Here at Cedar Creek Ecosystem
Science Reserve, two major experiments began in
1994. Dubbed Biodiversity I and Biodiversity II,
they were designed to use prairie ecosystems to
study the effects of plant diversity on:
Primary productivity (measure of biomass;
how much a plant grows in a year)
Levels of carbon and nitrogen in the soil
Overall stability of the ecosystem
Resistance to invasion by unwanted species
(“weedy” plants)
Research Results
After over 15 years of study, several trends have
emerged from the Biodiversity experiments.
Plant productivity significantly increases as diversity
increases.
Simply stated, plants in diverse plantings tend to
produce more biomass, or growth above and below
ground, than plants in less diverse situations.
Graph showing the diversity-productivity relationship
Plants have to compete for water, sun and soil nutrients.
Compared to a monoculture such as corn or switchgrass,
plants in a diverse planting comprise a variety of
species, each using the resources in a different way.
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Because there is such a range of plants,
resources are used efficiently and productivity,
or biomass, increases. It’s the same idea behind
a city full of various occupations and one filled
with only, say, lawyers. Which would be more
productive?
Plant productivity increases as functional
diversity increases.
An extension of the first trend, this means
productivity increases not only with an increase
in species diversity, but when those species are
members of four groups, each with a distinct
function in prairie ecosystems. They are:
C3 grasses (cool weather grasses)
C4 grasses (warm weather grasses)
Forbs (broad-leafed, flowering plants)
Legumes (forbs that “fix” nitrogen)
Graph showing the diversity-nitrogen relationship
These four groups work together to maximize
resource use resulting in increased biomass
production.
Legumes, via symbiotic bacteria in their roots, take
nitrogen from the air and “fix” it into a form they can
use. Excess nitrogenous compounds not used by the
legume leach out into the soil for use by other plants.
Carbon dioxide uptake increases as biodiversity
increases.
Plants use carbon dioxide, CO2, to
photosynthesize and produce new biomass.
The more plants grow, the more CO2 is used, or
sequestered. If a more diverse planting
produces more biomass (both above and under
the ground—remember the roots!) then a more
diverse planting will also sequester more CO2
than a monoculture.
Diverse plantings contain more legumes, meaning more
nitrogen in the soil for the other plants. A variety of
plants will each use nitrogen in a particular way with
overall increased efficiency than a monoculture. Hence,
the graph shows a decrease in overall available soil
nitrogen.
Graph showing the diversity-carbon storage
relationship
Invasion of weedy plant species decreases as plant
biodiversity increases.
A more diverse planting of prairie species tends to keep
its same species composition while preventing
establishment of weedy species. The low soil nitrogen
levels found with increased plant biodiversity seems to
be the key—weedy plants compete better in areas with
high soil nitrogen.
Soil nitrogen levels decrease as biodiversity
increases.
The element nitrogen is essential for plant
growth. While nitrogen composes 78% of
Earth’s atmosphere, most plants are unable to
use nitrogen in this gaseous form.
The overall stability of an area increases as plant
biodiversity increases.
An area with a variety of species is more resistant to
adverse conditions than a monoculture. For example, in
a drought, plants susceptible to low water amounts may
decrease in productivity, but those that are droughtresistant will survive and may increase their productivity
due to decreased competition from the droughtsusceptible species. The entire grassland will weather
the drought whereas a monoculture that is dependent
on water may have limited success and will generally
show a decrease in biomass.
The Biodiversity research project is funded by the Long
Term Ecological Research program, a branch of the
National Science Foundation.
August 2008