The Darwinian theory on biodiversity which advocates the planting of more species of grass to achieve higher yields, has been upheld by a recent study conducted in the US. Indeed, the well being of the ecosystem hinges on the vicissitude displayed by its components
MORE than 100 years ago, Charles
Darwin had concluded his book The
Origin of Species by declaring that the
stability of an ecosystem 'was related to
the diversity of life forms present therein. According to him, a grassland would
yield a higher quantity of grass if more
varieties of grass rather than a single
species, were to be sown. Scientists from
the Universities of Minnesota
in the US and Toron1o in
Canada, under the leadership
of David Tilman, an ecologist
working with, the former,
now claim to have confirmed
Darwin's theory. The
researchers, having studied
experimental prairie grasslands, found that the greater
the number of species a plot
held, the more was the biomass produced and the better
was the retention of nitrogen
- an essential plant nutrient.
Though conservationists had
long believed in this theory,
there was very little scientific
data to support their stand.
The team working with
over 50 people burned,
plowed, planted and tended
147 plots at the Cedar Creek
Natural History area in
Minnesota. The 100-sq foot
plots were sown with upto 24
native prairie species each. A
year later, each plot as
examined to ascertain the '
growth, yield and nitrogen-
consumption pattern. It was found that
the plots planted with more species,
yielded greater amounts of biomass and
retained more nitrogen in the process of
growing. The grass in the plots with
fewer species showed-poor growth and
leached large amounts of nitrogen from
the top soil. As a result, the roots of the
plant suffered from nitrogen deficiency,
and on the whole, the plants lacked sustained growth. Tilman and colleagues
confirmed their findings by studying,
natural grasslands too.
As to the question of how exactly
biodiversity leads to greater productivity and sustainability, once again
Darwin's hypothesis has proved
correct. He had explained it by saying
hat competition between various
species is avoided because different
plants utilise resources in different
ways, resulting in greater quantities of
plant mass.
But the contentious issue that
remains to be solved is the number
of species which are actually required
to do the job. Precisely how much is
'many'? According to some, relatively
few would do. Tilman's study found
that there was a dramatic increase in
productivity till the different plants
numbered 10, but after that, the
addition of each new plant resulted in
lesser productivity. Even though this
trend supports the 'few-would-do'
theory, Tilman insists that there was an
increase with each, new addition even if
it was not very significant. There are
others like Peter Karieva of the
University of Washington in Seattle,
us, who, support the use of many species.
According to Katieva, an ecosystem
has to perform many functions and
more plants may prove helpful to
achieve the same.
Although studies conducted by
others in this field have not been as
conclusive as this one - either because
of doubts about the plot's size or the
levels of nitrogen retained - even this
latest experiment has not been very
enthusiastically received by some.'
Says ecologist, Peter Vitousek at the
Stanford University in Palo Alto,
California, us, "I think it is a building
block, but not the final answer.
The application of this theory in
practice is yet to take shape 4s the
researchers work out which hypothesis
would best help in the management of
multiple agricultural crops or forest
species."
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