Discipline: Ecology Environmental and Earth Sciences
Yuliana Rowe - Humboldt State University
Co-Author(s): Dave Karowe, Western Michigan University, MI Brian Scholtens, College of Charleston, SC
We examined the effects of forest disturbance on spider diversity in the Forest Accelerated Succession Experiment (FASET) in northern Michigan. The FASET was initiated by the University of Michigan to study how the Great Lake region’s future forest would respond to climate-induced disturbances. In 2008, over 35% of the basal area making up FASET was removed by selective girdling of mature Aspen (Populus) and Paper birch (Betula). The fraction of basal area girdled varies throughout the 21 plots that make up FASET, and thus, each plot has a unique disturbance severity. Our study aimed to use FASET to mimic a scenario of co-dominant tree mortalities as a result of an insect outbreak. We hypothesized that the diversity indices of forestfloor spider assemblages would be negatively influenced by higher disturbance severities. We collected spiders using pitfall traps and measured the following variables known to affect spider assemblages: abundance of non-spider arthropods (insects), the downed woody volume (DWV), length (DWL) and area (DWA) as well as canopy cover, number of trees, and number of dead trees. In total, 245 spiders representing over 13 families and over 3,000 insects were captured.
Our results supported our main hypothesis, as we found that the total abundance, diversity and richness of spiders were lower in more disturbed plots. The abundance of insects was the most strongly correlating variable explaining spider abundance. Interestingly enough, the diversity and richness of spiders were significantly less in plots with higher DWA (p < 0.05). However, family-level analyses revealed different patterns. Despite the commonly occurring positive relationship of downed wood and spider diversity, our results did not always support this. Spiders are very selective of microhabitat characteristics and these characteristics rely on a variety of variables that are susceptible to change in lieu of forest disturbance. The diversity of all forestfloor arthropods, leaf litter composition and biomass, vegetative structural complexity, leaf area index (LAI), and temperature measurements, should be taken into consideration in future studies. The interaction between spiders and their prey, as well as the impact that climate change may have on these interactions, are important to study in order to better predict the implications of future forest pest outbreaks in northern temperate forests.
Funder Acknowledgement(s): I thank J. Douglas and Z. Fogel for help in the field. The faculty at the University of Michigan Biological Station provided equipment and help. Funding was provided by a NSF grant to Dave Karowe, Director of the University of Michigan Biological Station’s REU program.
Faculty Advisor: David Karowe,