The consequences for amphibians of the conversion of natural, mixed-species forests to conifer plantations in southern New Brunswick

Abstract

We examined amphibian abundance and species richness in stands of natural, mixed-species forest and in a chronosequence of Black Spruce (Picea mariana) plantations up to 16-years old in southern New Brunswick, Canada, during 1993 and 1994. We studied seven species of amphibians in 64 terrestrial sites of 10+ ha, and at 16 ephemeral ponds. Eggs, larvae, and adult numbers were estimated using a variety of sampling methods (visual pond surveys, night calling, pit-fall traps, and searches of coarse-woody debris). The low abundance of woody angiosperm vegetation in conifer plantations, particularly those with incomplete canopy closure, resulted in less leaf litter and drier coarse-woody debris than in natural forest. Amphibians were more abundant in natural forest than in plantations of any age. The most common terrestrial amphibian in natural forest was the Redback Salamander (Plethodon cinereus; average density 4/100 m2), but it occurred in only one of 33 plantations examined. Amphibians bred in all study ponds, including those in plantations, but only small numbers of American Toad (Bufo americanus), Yellow-spotted Salamander (Arabystoma maculatum), and Red-spotted Newt (Notophthalmus viridescens) were observed in terrestrial habitats of plantations outside of the breeding season. The densities of A. maculatum and Wood Frog (Rana sylvatica) breeding in ponds within plantations were most strongly related to the distance to the nearest natural forest. For Spring Peeper (Pseudacris crucifer) and A. maculatum, the high exposure and short hydroperiod of plantation ponds resulted in poor recruitment in both study years. Our study suggests that the conversion of natural, mixed-species forest into conifer plantations is most detrimental to A. maculatum, P. cinereus, P. crucifer, and R. sylvatica, and less-so for B. americanus.