Top-Down Effects of Wildlife and Bottom-up Drivers of Soils and Productivity in Intensively Managed Forest Plantations.

Intensive forest management (IFM) reduces vegetation to decrease competition for resources for planted conifer seedlings. This may alter the quality and quantity of organic inputs to the forest floor, which may affect soil and conifer productivity. IFM may also alter songbird and arthropod abundance, as well as cervid foraging, each of which may have direct or indirect effects on decomposition and mineralization processes. This study aims to determine how interactions between IFM and wildlife affect litter layer accumulation, decomposition, mineralization processes, and ultimately soil and Douglas-fir (Pseudotsuga menziessii) productivity.

Four herbicide treatment plots representing a gradient of IFM intensities were established in units harvested across seven replicated blocks in the Northern Oregon Coast Range. Open-herbivory and paired songbird/cervid exclosures were constructed within each plot. Five years after harvest, O-horizons, mineral soils, and Douglas-fir needles were collected from all exclosures.

Preliminary results indicate a trend of decreasing O-horizon depth and increasing bulk density with increasing vegetation control intensity, with significant differences between controls and intensive herbicide treatments. However, despite increasing impacts to litter layer accumulation with increasing vegetation control intensity, no differences between treatments in foliar or mineral soil carbon contents, nitrogen contents, or C:N ratios were detected. Additionally, no effects of wildlife exclusion on mineral soil and foliar C, N, and C:N were observed.

Future work will seek to determine if the high degree of heterogeneity observed in terms of vegetative and detritivore communities among herbicide treatment plots and wildlife exclosures in different site locations can be linked to litter layer C, N, C:N, and stable isotopic signatures. This information may allow us to elucidate linkages between aboveground biotic heterogeneity to variability in mineral soil C, N, and C:N.