Bark beetle outbreaks benefit wild bee populations, habitat

Date:
October 15, 2020
Source:
Colorado State University
Summary:
Researchers found significant increases in floral abundance and wild
bee diversity in outbreak-affected forests, compared to similar,
undisturbed forest.



FULL STORY ==========================================================================
When southern Rocky Mountain forests are viewed from a distance these
days, it may not look like much is left. Large swaths of dead, standing Engelmann spruce trees tell the tale of a severe regional spruce beetle epidemic in its waning stages. But among those dead trees, researchers
have found good news. Zoom-in to the ground cover of these forests and
there is life, even more abundant because of this disturbance.


==========================================================================
New research led by Colorado State University and published online
in Scientific Reports suggests that spruce beetle outbreaks may help
create habitat for pollinator communities in wilderness settings. The
research team found significant increases in floral abundance and wild bee diversity in outbreak-affected forests, compared to similar, undisturbed forest. Lead author Seth Davis said it may seem counterintuitive that landscape-level damage by one type of insect could still benefit another.

"Disturbances from bark beetles are typically regarded as undesirable for ecosystem function and human use," said Davis, an assistant professor
in the Forest and Rangeland Stewardship department. "But there is
conservation value in post-outbreak forests; they appear to be the areas supporting more robust bee populations." This is good news for wild bee communities, which have been declining in recent years. The different
bee species identified in this high-elevation study are made for harsh,
cold environments. The fact that a natural disturbance can boost their
presence is a boon to these rare, endemic creatures not found in warmer habitats. It's also a benefit for these forests, because wild bees
perform essential pollination services in ecosystems with very short
growing seasons.

A serendipitous observation Davis regularly works in high-elevation
forests. A few years ago, during another research project with department colleagues, he noticed a correlation between the number and diversity
of bees observed, and the structure of the forest. He has since opened
up this new thread of bee diversity research by combining it with his
training in bark beetles.



========================================================================== "Disturbance studies on bees have primarily focused on fire," said Davis.

"There hasn't been a lot of research looking at bee responses to beetle outbreaks." For this new study, his team developed a natural experiment, collecting parallel data in 28 beetle-affected and undisturbed alpine
sites in north- central Colorado. They collected bees for two years
at three different times across each growing season, and also recorded
standard tree measurements and understory, or ground cover, plant data
at the collection sites.

The team found that average floral abundance in spruce beetle-affected
stands was 67 percent higher than in non-affected stands. The average
number of bee species was also 37 percent greater in beetle-affected
stands, with more species present in June than later in the growing
season. Davis said the relationship between these insects and their
surrounding vegetation may be more complex.

"It appears there are different controls over bee abundance and
diversity," Davis said. "Bee abundance was correlated to the floral
species, while the diversity is more related to the forest structure, both
of which are affected by bark beetles." In other words, bark beetles
directly changed the forest structure which indirectly improved wild
bee populations by providing a more robust food source for the buzzing
insects on the ground.

Spruce beetle-affected forests offer a few advantages for understory
plants and wild bees. Tree mortality typically opens up the forest canopy, allowing more light to reach plants and flowers on the forest floor. Dead
trees also remain standing for up to 25 years after this disturbance. This offers more cavities for wild bees that nest in trees and dead wood.

Davis said he is interested in exploring this topic further to better understand these relationships over a longer time period and at a
larger scale.

As forests recover from outbreaks, he would like to see how long
this benefit lasts. There is also the size disparity between small
bee populations in one locale and the regional magnitude of these
disturbances. It will be important to understand how well one small spot predicts these results at the landscape level.


========================================================================== Story Source: Materials provided by Colorado_State_University. Original
written by Karina Puikkonen. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Thomas Seth Davis, Paul R. Rhoades, Andrew J. Mann, Terry
Griswold. Bark
beetle outbreak enhances biodiversity and foraging habitat
of native bees in alpine landscapes of the southern
Rocky Mountains. Scientific Reports, 2020; 10 (1) DOI:
10.1038/s41598-020-73273-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201015173124.htm

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