Woodland - Summer 2019 - 14

Seedlings
Continued

HOW TREE DIVERSITY REGULATES INVADING FOREST PESTS
SOURCE: NORTH CAROLINA STATE UNIVERSITY

A national-scale study of U.S. forests
found strong relationships between the
diversity of native tree species and the
number of nonnative pests that pose
economic and ecological threats to the
nation's forests.
"Every few years we get a new
exotic insect or disease that comes
in and is able to do a number on our
native forests," said Kevin Potter,
a North Carolina State University
research associate professor in
the Department of Forestry and
Environmental Resources and coauthor of an article about the research
in Proceedings of the National
Academy of Sciences.
"Emerald ash borer is clobbering a
number of ash species in the Midwest
and increasingly in the South. The
chestnut, a magnificent tree that had

immense ecosystem value as well
as economic value in the South and
North, is pretty much gone because
of a pathogen. And hemlocks are
under attack by the hemlock woolly
adelgid from the Northeast along
the Appalachian Mountains into the
South."
To better understand how
nonnative insects and diseases invade
U.S. forests, researchers tested
conflicting ideas about biodiversity.
The first is that having more tree
species can facilitate the diversity
of pests by providing more places
for them to gain a toehold. Another
possibility is that tree biodiversity can
have protective effects for forests,
such as by diluting the pool of host
trees and making it harder for pests to
become established.  

"We found that both
facilitation and dilution seem
to be happening at the same
time," Potter said. "What
we found is that native tree
biodiversity really is important,
but it's important in different
ways at different times."
Combining two national countylevel data sets, researchers found that
relationships between tree diversity
and pest diversity follow a humpshaped curve.
"As you have an increasing
number of tree species, you have an
increasing number of pest species,
up to an inflection point where that
relationship changes," Potter said.
"Then you have a decreasing number
of pest species as the number of host
tree species increases."
Overall, counties where forests have
30 to 40 different host tree species
tend to have the most nonnative pests.
But the effects depend on whether the
invader is a specialist that can infest
only a single tree species or whether
it's a generalist, like the gypsy moth,
which can spread to more than 60
different hosts.
"What we see is that forests in the
Midwest and up into New England are
at the middle part of that hump-shaped
curve in terms of the number of host
tree species, and those are places
where there have been a lot of insect
and disease problems," Potter said.
"Out West we have fewer insect
and disease pests, but in some cases
they still do a lot of damage because
A combination of two nonnative pests, laurel wilt disease
and redbay ambrosia beetle, has killed hundreds of millions
of redbay trees in coastal areas of the Southeast, including
Evans County, Georgia.
PHOTO BY KEVIN M. POTTER, NC STATE UNIVERSITY

14 WOODLAND * Summer 2019



Woodland - Summer 2019

Table of Contents for the Digital Edition of Woodland - Summer 2019

Overstory
Foresets and Families
Forest Interactions
The Family Forest Carbon Program
2019 Regional Outstanding Tree Farmer of the Year Finalists Announced
Tree Farmers Visit Washington to Advocate for Family Forest Interests
Tools and Resources
Woodland - Summer 2019 - Intro
Woodland - Summer 2019 - cover1
Woodland - Summer 2019 - cover2
Woodland - Summer 2019 - 3
Woodland - Summer 2019 - Overstory
Woodland - Summer 2019 - 5
Woodland - Summer 2019 - Foresets and Families
Woodland - Summer 2019 - 7
Woodland - Summer 2019 - Forest Interactions
Woodland - Summer 2019 - 9
Woodland - Summer 2019 - 10
Woodland - Summer 2019 - 11
Woodland - Summer 2019 - 12
Woodland - Summer 2019 - 13
Woodland - Summer 2019 - 14
Woodland - Summer 2019 - 15
Woodland - Summer 2019 - 16
Woodland - Summer 2019 - 17
Woodland - Summer 2019 - 18
Woodland - Summer 2019 - 19
Woodland - Summer 2019 - 20
Woodland - Summer 2019 - 21
Woodland - Summer 2019 - The Family Forest Carbon Program
Woodland - Summer 2019 - 23
Woodland - Summer 2019 - 24
Woodland - Summer 2019 - 25
Woodland - Summer 2019 - 26
Woodland - Summer 2019 - 27
Woodland - Summer 2019 - 2019 Regional Outstanding Tree Farmer of the Year Finalists Announced
Woodland - Summer 2019 - 29
Woodland - Summer 2019 - 30
Woodland - Summer 2019 - 31
Woodland - Summer 2019 - 32
Woodland - Summer 2019 - 33
Woodland - Summer 2019 - Tree Farmers Visit Washington to Advocate for Family Forest Interests
Woodland - Summer 2019 - 35
Woodland - Summer 2019 - 36
Woodland - Summer 2019 - 37
Woodland - Summer 2019 - 38
Woodland - Summer 2019 - 39
Woodland - Summer 2019 - 40
Woodland - Summer 2019 - Tools and Resources
Woodland - Summer 2019 - 42
Woodland - Summer 2019 - cover3
Woodland - Summer 2019 - cover4
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