Invasive shrubs in Northeast US forests grow leaves earlier and keep
them longer
Citizen scientists confirm that invasives seem to have advantage over
native shrubs, contributing to their proliferation, impacts

Date:
August 19, 2020
Source:
Penn State
Summary:
The rapid pace that invasive shrubs infiltrate forests in the
northeastern United States makes scientists suspect they have a
consistent advantage over native shrubs, and the first region-wide
study of leaf timing supports those suspicions.



FULL STORY ==========================================================================
The rapid pace that invasive shrubs infiltrate forests in the northeastern United States makes scientists suspect they have a consistent advantage
over native shrubs, and the first region-wide study of leaf timing,
conducted by Penn State researchers, supports those suspicions.


==========================================================================
With the help of citizen scientists spread over more than 150 sites in
more than 20 states, researchers collected thousands of observations
over four years of exactly when both invasive and native shrubs leaf
out in the spring and lose their leaves in the fall. The study area was expansive, stretching from southern Maine to central Minnesota south to southern Missouri, to North Carolina.

"Eastern North America is the recipient of more invasive shrub species
into natural areas than any other geographic region of the world,"
said lead researcher Erynn Maynard-Bean, postdoctoral researcher in
the College of Agricultural Sciences, working under the guidance of
Margot Kaye, associate professor of forest ecology. "Invasive shrubs are growing in both abundance and in the number of species established at
the expense of many types of native species." The researchers reported
in Biological Invasions that invasive shrubs can maintain leaves 77 days
longer than native shrubs within a growing season at the southern end
of the area studied. The difference decreases to about 30 days at the
northern end of the study area. At the southern end of the study area,
the time when invasive shrubs have leaves and native shrubs do not is
equally distributed between spring and fall; in the northern reaches of
the study area, two-thirds of the difference between native and invasive growing seasons occur in fall.

The longer period with leaves gives invasive plants an advantage in
acquiring more energy from sunlight and their leaves create shade in
early spring and late fall that may limit growth of native species,
such as forest ephemeral wildflowers, Maynard-Bean explained. "This
helps explain their negative impact on native tree regeneration, plant diversity and abundance," she said. "But invasive shrubs also have a
negative impact on communities of animal species sensitive to light and temperature, such as bees, butterflies and amphibians." Small, local
studies in Northeast forests have shown that invasive shrubs have leaves
longer than native shrubs. However, because the phenomenon -- known as
extended leaf phenology -- varies geographically, the degree to which
it benefits invasive shrubs across the region had previously been unknown.

The difference between native plants and invasive plants having leaves
is not consistent, Maynard-Bean noted. It varies, depending on latitude, species studied and weather for the study period.

"But with the help of citizen scientists with USA National Phenology
Network watching plants with us from around the eastern U.S., we found
a pattern of greater extended leaf phenology as you move south," she
said. "This provides a unified framework for connecting local-scale
research results from different parts of the eastern U.S. that had
previously not agreed with one another." With the goal of understanding on-the-ground implications for eastern deciduous forest ecosystems, the researchers chose common, widespread species that co- occur in forest understories. Native shrubs followed in the study included alternate-leaf dogwood, flowering dogwood, gray dogwood, spicebush, mapleleaf viburnum, southern arrowwood, hobble-bush and black haw. Invasive shrubs native to
Europe or Asia followed in the study included Japanese barberry, burning
bush, multiflora rose and several species of honeysuckles and privet.

About 800 citizen scientists collected more than 8,000 observations
of leaf timing for 804 shrubs at 384 sites, from 2015 through 2018. In addition, Maynard-Bean made observations at three sites in Pennsylvania.

The patterns of extended leaf phenology for invasive shrubs compared
to native shrubs found in this study have important implications for
policy and management, according to Kaye, whose research group has
been evaluating invasive shrubs in Northeast forests for more than a
decade. She pointed out that invasives included in this study are still commonly used for horticultural purposes in some states but are banned
in others.

"The presence of this phenomenon may serve as a predictive trait for
the invasion potential of new horticultural specimens," Maynard-Bean
said. "From a management perspective, extended leaf phenology makes
invasive shrubs an easier 'green target' in the spring and fall for
detection, removal and treatment, which can protect dormant, non-target
native species."

========================================================================== Story Source: Materials provided by Penn_State. Original written by Jeff Mulhollem. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Erynn Maynard-Bean, Margot Kaye, Tyler Wagner, Eric
P. Burkhart. Citizen
scientists record novel leaf phenology of invasive shrubs in
eastern U.S.

forests. Biological Invasions, 2020; DOI: 10.1007/s10530-020-02326-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200819150904.htm

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