Trees are out of equilibrium with climate

Date:
December 14, 2020
Source:
University of Maine
Summary:
A research team studied the current ranges of hundreds of
North American trees and shrubs to assess the degree to which
species are growing in all of the places that are climatically
suitable. Researchers found evidence of widespread 'underfilling'
of these potential climatic habitats -- only 50% on average --
which could mean that trees already have disadvantage as the world
continues to warm.



FULL STORY ========================================================================== Forecasts predicting where plants and animals will inhabit over time
rely primarily on information about their current climate associations,
but that only plays a partial role.


========================================================================== Under climate change, there's a growing interest in assessing whether
trees and other species can keep pace with changing temperatures and
rainfall, shifting where they are found, also known as their ranges, to
track their suitable climates. To test this, a University of Maine-led
research team studied the current ranges of hundreds of North American
trees and shrubs, assessing the degree to which species are growing in all
of the places that are climatically suitable. Researchers found evidence
of widespread "underfilling" of these potential climatic habitats -- only
50% on average -- which could mean that trees already have disadvantage
as the world continues to warm.

Benjamin Seliger, a then UMaine Ph.D. student with the Climate
Change Institute, spearheaded the study with his doctoral adviser,
Jacquelyn Gill, a UMaine associate professor of paleoecology and plant
ecology. Brain McGill, a UMaine professor of biological sciences, and Jens-Christian Svenning, a macroecologist and biogeographer from Aarhus University in Denmark also contributed.

The team used species distribution models to assess the degree to which
447 North American trees' and shrubs' "fill" their potential climatic
ranges by comparing regions that are climatically suitable, known as
potential ranges, against where trees are actually found, or their
realized ranges.

The Journal of Biogeography published the team's research paper for
the study.

Seliger, now a postdoctoral researcher at the Center of Geospatial
Analytics at North Carolina State University, and co-authors discovered a significant difference between where the trees they studied could grow,
and where they actually grow, also known as range filling. The average
range filling value across all 447 species equalled 48.6%, indicating
that on average, trees are not found in about half of the areas that
are climatically suitable for them, according to researchers.



==========================================================================
"We found tree ranges are more limited by non-climatic factors than
expected, suggesting trees may not simply track warming climates." Seliger says.

Species distribution models (SDMs) are a common tool to predict how
climate change will affect biodiversity and the future ranges of plants
and animals.

Various studies, including the one from the UMaine-led group, however,
caution that because this tool assumes that species live in all areas that
are climatically suitable, known as experiencing climatic equilibrium,
it may not provide an accurate prediction of where species will be found
in the future.

An SDM relies on what has been considered a foundational principle, "that geographic ranges generally appear to be in equilibrium with contemporary climate," according to researchers. Growing evidence suggests otherwise
for many species, which experience climatic disequilibrium.

Seliger and his team found that North American trees and shrubs with large ranges tended to show much stronger evidence of climatic equilibrium,
meaning they had high range filling. Small-ranged species, however,
had much lower range filling overall, performing worse than predicted
by a null model.

According to researchers, that means small-ranged tree species, including
many rare trees and species the International Union for the Conservation
of Nature (IUCN) lists as vulnerable, will face additional challenges
as they try to track their climates into the future.

The group also found that small-rage species may be more limited by
nonclimatic influences, such as soils or pathogens. Conservation efforts
for these plants and animals, therefore, should "account for a complex interplay of factors in addition to climate when preparing for the next
century of global change," according to researchers.

Their findings support a growing body of evidence that for a climatic disequilibrium among various flora. As to what causes the disequilibrium
could be due to two factors, according to researchers: dispersal lags
that date back to the time when glaciers covered large portions of North American 21,000 years ago, or by non-climatic factors that may influence
ranges more than previously appreciated, such as soil, competition with
other plants, or symbiosis.

"It's been thought that if you zoom out to the scale of North America,
climate was the most important factor in determining where species would
be found. This study reveals some striking gaps in our knowledge; even
at the scale of an entire continent, soils or other plants and animals
may be playing an important role too. We used to think those were more important at the more local scale - - think of how the trees might change across two areas of your favorite park," Gill says. "All of this means
that when it comes to plants, our predictive tools need to get a lot
more sophisticated, if they're going to be useful for conservation."

========================================================================== Story Source: Materials provided by University_of_Maine. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Benjamin J. Seliger, Brian J. McGill, Jens‐Christian Svenning,
Jacquelyn L. Gill. Widespread underfilling of the potential
ranges of North American trees. Journal of Biogeography, 2020;
DOI: 10.1111/ jbi.14001 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/12/201214192406.htm

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