Do soil fauna increase rates of litter breakdown and nitrogen release in forests of British Columbia, Canada?

The objective of this study was to improve our understanding of the role of soil invertebrates in the breakdown of litter, cycling of nitrogen, and growth of seedlings in forests of British Columbia by comparing two experimental approaches. First, in the laboratory, breakdown of birch leaves was slightly higher in the presence of millipedes in the microcosms of forest floor collected from two coastal forests. Presence of smaller animals (mesofauna) and contaminant Diptera larvae did not hasten litter breakdown in microcosms made from forest floor from either a sub-boreal or a coastal forest. In general, inorganic nitrogen release was higher in the presence of fauna, but results were highly variable. Growth of seedlings was slightly greater in the coastal microcosms that included millipedes. In the second approach, a field experiment was conducted using intact forest floor cores enclosed with one of three mesh sizes (54 µm, 1 mm, and 5 mm) and defaunated with liquid nitrogen. Comminution of birch leaves, and to some extent, greater inorganic nitrogen release occurred in sacs that allowed access to larger animals compared with sacs with fine mesh that excluded them. Although differences among treatments were small, the results from both approaches agree and indicate that soil invertebrates increase rate of breakdown of forest litter and cycling of nutrients in coastal forests.