Effects of alternative conifer release treatments on terrestrial gastropods in northwestern Ontario

Abstract

Changes in terrestrial gastropod species richness and density in regenerating spruce plantations following application of four conifer release treatments including two chemical herbicides (Vision® [a.i. glyphosate] and Release® [a.i. triclopyr]), cutting by mechanical means (Silvana Selective/Ford Versatile), and motor-manual cutting with brush saws are discussed. Mean gastropod density increased to a maximum of 21 m−2 over the summer of 1993 (pre-treatment) when a total of 27,396 gastropods were collected but remained fairly stable at about 10 m−2 throughout the summer of 1994 (post-treatment) when only 20,199 were collected. This difference between years was not related to the conifer release treatments, since gastropod densities on both treated and control areas were lower in 1994. The decline in 1994 was probably due to decreased population size and detectability because of less rainfall. The lack of difference following treatments was attributed to rapid re-establishment of the herbaceous layer which probably continued to provide favourable conditions for snails and slugs.Gastropod density was higher in a nine-year-old regenerating spruce plantation (15.5 ± 1.3 m−2) than in a 70-year-old mixedwood forest (9.4 ± 0.6 m−2) and species richness was also slightly greater (20 spp. vs. 18 spp.) in the plantation. These differences were attributed to the more abundant near-ground vegetation and the greater amount of deciduous litter characterizing the regenerating plantation. Key words: clearcutting, terrestrial gastropods, snails, slugs, conifer release, Fallingsnow Ecosystem Project, herbicides, spruce plantations, vegetation