Invertebrate diversity: is the diversity of arthropod species affected by forest age and succession?

Abstract

The purpose of this study is to determine whether fire disturbance of burned forest plots on glacial otuwash soils causes changes in arthropod species diversity and composition. We hypothesize that as time since burning increases; the resulting older forest will have higher arthropod species richness. We suggest this because later successional forests create more diverse and suitable environments for a broader variety of arthropods. We also hypothesize that by knowing the succession patterns of a forest (i.e. tree species diversity, leaf litter, % soil organic matter etc.) we can predict the species of arthropod that will inhabit them in the future. We compared habitat structural characteristics and relative abundance and diversity of ground-dwelling arthropods among six different experimental burned forest patches and one control forest site located on UMBS property in Pellston, Michigan. All the forests, including our control, were experimentally clear-cut and burned in 1911. Slugs, land snails, grasshoppers, beetles, ants and other arthropods were methodically sampled and collected using alcohol filled pitfall traps. The collection lasted throughout a period of seven days during the month of July 2004. 30 by 30m plots were set up 30 meters in the forest (forest edge picked at random). Pitfall traps were dug in the center of the plot and toward the middle of each of the subplots, a total of five pitfall traps per plot (Figure 1). We collected soil samples to determine percent moisture and percent organic matter. We collected leaf litter in plots of 1m2 to analyze amount of leaf litter to observe how it correlates with arthropod abundance and diversity. We took counts of tree species composition present within our 30 by 30m plots and recorded ground cover plants for species composition within a 4 m2 plot centered in our plot. The data collected was analyzed using Systat 10.0. Several regression tests were run to find any signficant correlations or differences within our data. Results show that: Arthropods species richness is significantly different (p=0.001, r2=894, df=1) when compared to tree species richness. Araneida (spiders) species richness is also positively correlated to tree species richness (p-value = 0.005, r2=0.817, df=1). Diptera (flies) (p = 0.001, r2=.0664, df=1) and Hymenoptera (bees, wasps, and ants) are also positively and signficantly correlated to tree species richness (p-value = 0.033, r2=0.757, df=1). The role of fire is an important one because although it destroys an ecosystem its consequences are much more beneficial on the long run. Disturbances like fire help in maintaining the biodiversity of these ecosystems always in shape. This suggests that fire causes considerable changes in the abundance and species composition of soil living invertebrates. In conclusion, the results of this study are signficant because ecologically it implies that land management and natural or human induced disturbances do increase changes of arthropod and tree diversity, abundance and composition in disturbed habitats which in the end may affect the entire ecosystem health function.