Effects of Forest Type and Stand Characteristics on Seasonal Abundance of Forest-Floor Invertebrates
- Johnston, Jason C.
University of Maine at Presque Isle
To improve our understanding of the effects of forest management on invertebrates as food for vertebrates, we sampled the differences in abundance of arthropod taxa at the habitat level within four stands in Maine commercial forests: even-age spruce plantation (30 years), even-age natural regeneration (30 years), mature spruce (>80 years since last harvest) and mature hemlock (>80 years since last harvest). During late April through early August, arthropod abundance was determined using pitfall traps and branch sampling. Since arthropod abundance does not equate to food availability, food use of ground foraging and foliage gleaning birds was determined through the use of crop and fecal sampling. There were significant differences in arthropod temporal and habitat abundance between forest stand types, with spiders highest in natural regeneration, ground beetles highest in spruce plantation and ants highest in mature spruce. We found a lower abundance of spiders within the spruce plantation. After a peak the third week of May, there was a significant seasonal decline in spiders overall. Small ground beetles (Carabids) were highest in diurnal samples while large ground beetles were highest in nocturnal samples. In bird crop and fecal samples, moth and butterfly larvae, beetles and spiders appear to be the most commonly used food items. Since invertebrates form the base of most forest vertebrate food webs, an understanding of how forest management practices may impact the abundance and availability of food can be used to implement strategies that mitigate the impacts of silviculture on habitat quality for terrestrial vertebrates. Facing possible changes in tree species composition in the Northern Forest due to both invasive species and climate change, this study provides a baseline of the arthropod-bird food web within four important northern forest habitat types. Furthermore, since each of these forest habitats either persisted through or were the result of the last spruce budworm outbreak, this community ecology study may inform best management practices for the impending budworm outbreak.
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