The take home, which no one wants to hear is that a forest is best
when it is a blend of multiple species. Humanity wants an orchard
but this is risky. We overcome that risk by short life spans and
ample attention. An orchard on its own soon collapses under the
assault of disease.
Tree husbandry is not something that can happen in nature and does
not. Stands are usually a blend of several species and unique
individuals within a species.
In time we will move to fully managed woodlots and full fiber
recovery even if it is wood chips for the trails. This allows a
mixed forest to be tightly managed and individual stems to be pulled
as justified.
In the meantime we continue to replant as forest mono-cultures and
harvest early to avoid the inevitable impact of uniform stands. It
is not great but it generally works.
Forest diversity
from Canada to the sub-tropics influenced by family proximity
by Staff Writers
Bloomington IN (SPX) May 28, 2012
Data from over 3 million trees in the eastern half of the US were aggregated into two-degree-latitude-by-longitude cells in order to study regional patterns of conspecific negative density dependence, a process where the mortality of a species rises in coincidence with its increasing abundance. Credit: Indiana University.
How species diversity is
maintained is a fundamental question in biology. In a new study, a
team of Indiana University biologists has shown for the first time
that diversity is influenced on a spatial scale of unparalleled
scope, in part, by how well tree seedlings survive under their own
parents.
Scientists have long
considered conspecific negative density dependence (CNDD), a
process where the mortality of a species rises in coincidence with
its increasing abundance, to be a key mechanism maintaining
diversity at the local scale. In new research to be published Friday
in the journal Science, the IU researchers show that this mechanism
is driving diversity from the borealforests to sub-tropical
forests.
The report,
"Conspecific negative density dependence and forest diversity,"
is authored by Daniel Johnson, a doctoral student in the IU
Bloomington College of Arts and Sciences' Department of Biology.
Co-authors are Wesley T. Beaulieu, also a doctoral student in the
Department of Biology, and biology professors James D. Bever and
Keith Clay, Johnson's major advisor.
Their work analyzed
data on forest composition from over 200,000 plots containing more
than 1.3 million trees and from paired plots containing over 1.7
million seedlings of 151 different tree species. The plots
were located from the Canadian border south to Florida and from the
Atlantic coast to the 100th meridian and covered over 1.5 million
square miles. The U.S. Forest Service spends about $62 million each
year to gather the publicly available forest inventory data used in
the IU study.
"We are now able
to provide robust evidence that CNDD is pervasive
inforest communities from boreal to sub-tropical regions
and that it can significantly affect the relative abundance and
richness of species with and between forests," Johnson said.
"And we now see
that the ability to which one tree species can sustain itself in the
same area has profound impacts on the diversity of species at a
spatial scale that has not been attainable previously. This is the
first time it's been shown to be happening not just at a local
spatial scale but over the entire eastern US."
The concept of CNDD is
based on the well-known Janzen-Connell hypothesis, which proposes
that the close proximity of adults reduces seedling survival of that
species through increased attack by host-specificpests and
pathogens.
Studies of CNDD in the
past have mostly focused on forest communities at single sites or of
a single species, with the most recent work showing that in tree
species, composition and abundance can be influenced by CNDD at the
scale of individual trees.
"Local
interactions have previously been considered to affect species
diversity at a local scale, but our findings indicate that local
interactions feed back to species richness and abundance over much
larger geographical scale, spanning most of eastern North America,"
Johnson said.
Evidence that local
interactions underlie regional species richness is in contrast to the
current understanding that patterns of forest diversity are primarily
driven by temperature, precipitation and other physical aspects of
the environment. This discovery has implications for how forest
modeling is conducted and conservation and management decisions are
made.
Related Links
Indiana University
Forestry News - Global and Local News, Science and Application
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