Effects of the Interplay Between Wildlife, Plant Communities, Decomposition and Soils on 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 menziesii) 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 IFM intensity in open-access plots and cervid exclosures, with significant differences between controls and intensive herbicide treatments. No significant differences between herbicide treatments for bulk densities or depths were observed in songbird exclosures. However, 0-15cm mineral soils contained significantly more C in intensively treated songbird exclosures compared to the other herbicide treatments, as well as non-significantly higher C:N ratios. The increased C in mineral soils in intensively treated songbird exclosures is likely the result of increased root decomposition, dissolved organic matter leaching, or translocation of particulate organic matter. The latter two possibilities may have been amplified if the relative proportion of litter fragmented by arthropods was greater in the intensive treatment. Future analysis of arthropod abundance and stable isotope analyses will aid in elucidating these effects.