Alternative conifer release treatments affect microclimate and soil nitrogen mineralization

In 1993, the Fallingsnow Ecosystem Project was initiated in northwestern On tario to assess the effects of alternative conifer release practices on eco system processes, wildlife populations, and spruce production. Conifer rele ase treatments: two herbicide (glyphosate and triclopyr), two cutting treat ments (brushsaw and Silvana selective mower), and controls were established on four 30-60 ha clearcut and planted (spruce) blocks. Unharvested control s adjacent to each block constituted a sixth treatment. Objectives of this study were: (1) to quantify soil nitrification rates for the control, glyph osate, brushsaw, and unharvested forest treatments and (2) to relate these rates to soil temperature and moisture. Weather stations and buried fibergl ass/resistance soil cells were established in 1994 to monitor soil temperat ures and moisture. During the second posttreatment growing season (1995), s oil samples were collected at 5, 15, and 30 cm depth and incubated in polye thylene bags at the same depth from which they were collected for 30 days p rior to exhumation. The above procedure was repeated for the months of June , July, August, and September. In the third posttreatment growing season (1 996), bags were buried (mid-June, mid-July mid-august) at 5 cm only and exh umed 30 days after burial. Higher levels of nitrate (NO3-) were observed fo r the glyphosate and brushsaw treatments in August 1995 compared with the c ontrol and unharvested forest treatments. Rates (mu g 100 g(-1) dry soil pe r day) of ammonium (NH4+) and nitrate production decreased with soil depth and exhibited a distinctive seasonal trend, decreasing as soil temperatures declined. Ammonium production was significantly correlated with soil tempe rature and moisture, increasing with increasing temperature, and decreasing at higher moisture levels. By the third (1996) posttreatment growing seaso n, no treatment-related differences were observed, and ammonium production was less correlated with soil temperature than during the second (1995) pos ttreatment growing season. These results affirm that application of glyphos ate is the best option evaluated for effective weed control and optimal-nut rient release. (C) 2000 Elsevier Science B.V. All rights reserved.