Effects of alternative conifer release treatments on terrestrial gastropods of regenerating spruce plantation

Abstract

This study examined changes in terrestrial gastropod densities and species richness associated with alternative methods of managing competing vegetation on regenerating spruce plantations. Data were collected monthly from June to September in 1995 and 1996, the second and third years following use of four conifer release treatments (herbicides. Vision® and Release®; manual clearing, brushsaw and mechanical clearing, Silvana Selective/Ford Versatile) on each of four replicate blocks. A total of 15,083 terrestrial gastropods, comprising 21 species, was collected from litter surface sampling sites (beneath cardboard sheets) over the two years. In 1995, recorded gastropod densities were low (4.2 ± 0.2m-2)(Mean ± S.E.) during an unusually dry summer and were similar among all treated and control areas. With wetter conditions in 1996, these numbers increased on all areas (6.9 ± 0.3 m-2, but were significantly lower on areas treated with herbicides (see document). This may be attributable to variability in near ground temperature and relativity humidity. As well, the decreased accumulation of broadleaf litter in these sites may have provided inadequate habitat conditions during dry periods. Despite this difference in surface active gastropods suggested by cardboard sheet collections, no difference in numbers was apparent in a limited number of soil core samples taken from untreated and Vision® treated sites (258 ± 145 and 377 ±221 m-2, respectively). Overall gastropod densities were highest where soil moisture, pH and calcium concentration were highest. Gastropod densities measured by surface sampling cardboard sheets were greater on a regenerating plantation than on an unharvested forest and on a complete removal plot (CRV), where vegetation was removed annually using Vision® (9.4 ± 0.5,6.7 ± 0.4 and 6.4 ± 0.5 m-2, respectively). These differences may be attributable to the more abundant near ground vegetation and larger broadleaf component of the litter layer in the regenerating plantation. Species richness was similar among these sites, but several species were not collected on all CRV plots.