"We found that there's a strong link between the species diversity of tree habitats and the population density of the spiders that live in them," said Karin Burghardt, senior author of the study and assistant professor of entomology at UMD. "Spiders really like complex habitats, so having a large variety of tree species with different structural features like height, canopy cover and foliage density will help increase spider abundance and also the natural pest regulation they provide."
"There have been some large-scale tree diversity experiments conducted in Europe and Asia, but our study is one of only a handful of experiments of its kind in temperate North America," Burghardt said.
On the plots, the researchers planted the same tree species or four or 12 different tree species.
After repeatedly sampling 540 trees in these plots by counting the number of spiders found in each tree, Burghardt and her team found that plots with higher tree species diversity also hosted greater spider populations.
By the end of the project in 2021, plots containing four or 12 different tree species supported approximately 23% to 50% more spiders than single species plots, due to their cooler, shadier conditions.
"Plots with more variation in tree species tend to have more canopy cover than plots with only a single tree species," Burghardt explained.
The researchers found the strongest relationship between tree diversity and spider populations during the late summer months when average temperatures were at their highest.