The Effects of Timbering on Plethodon hubrichti: Short Term Effects

Effects of two types of timbering on populations of the Peaks of Otter salamander (Plethodon hubrichti) were determined using average numbers found during multiple night collections. Sampling was done prior to, and for two years after, timbering on four sites in each of three treatments (clearcut, shelterwood cuts, and reference). The average numbers of P. hubrichti at the reference and shelterwood cut sites were stable over time while those at the clearcut sites showed a significant decrease post-timbering. Two years after timbering, 30% of the pre-timbering populations remained at the clearcut sites. Jolly-Seber population estimates on one clearcut site decreased from 43 to eight animals after cutting. In contrast, one reference site had a population estimate that oscillated around a mean of 71. Of the animals marked before timbering, significantly fewer were recaptured after timbering at the clearcut site (17.5%) relative to the reference site (39.0%). Juveniles appeared to be the size class affected to the greatest degree. Adults and juveniles on clearcuts most likely emigrated and/or died after treatment. While most investigators believe that timbering is harmful to salamanders, it is difficult to document the effects. Most studies use population censuses in timbered areas and compare these numbers to adjacent untimbered areas. Salamander populations in timbered areas are usually lower, and sometimes absent, when compared to untimbered areas (Blymer and McGinnes, 1977; Bury, 1983; Enge and Marion, 1986; Pough et al., 1987; Ash, 1988; Bury and Corn, 1988; Stiven and Bruce, 1988; Welsh, 1990; Raymond and Hardy, 1991; Petranka et al., 1993; Dupuis et al., 1995). It is thought that opening the forest canopy increases exposure of the forest floor to sun and wind. This dessicates the habitat, thus reducing habitat quality for salamanders. Plethodontid salamanders may be particularly sensitive to habitat changes due to timbering since they are lungless, requiring moist skin for gas exchange, and are fully terrestrial, requiring moist microhabitats for egg development (Pough et al., 1987). Salamander populations are not the only part of the forest ecosystem affected by timbering. Duffy and Meier (1992) reported that the herbaceous community may not recover to the same pre-timbering species diversity in 40-150 year logging cycles. Forest floor organic matter decreased exponentially to about 50% of the initial levels within 15 yr following timbering, then recovered over the next 50 yr to within 5% of pre-timbering levels (Covington, 1981). Seastedlt and Crossley (1981) reported that microarthropod decomposers were significantly less abundant two years after timbering. Many changes can occur with loss of the forest canopy, some of which would directly affect food availability to salamanders (Mitchell et al., 1996). There are drawbacks to most earlier assessments of the effects of timbering on salamander populations. Foremost is most earlier studies assume that the pre-timbering population levels in the treatment and reference (control) sites were similar. Since salamander populations may have clumped dispersion patterns (Kramer et al., 1993) this assumption may not be justified. In this study both pre and post-timbering population levels were assessed for an endemic species, Plethodon hubrichti. METHODS AND MATERIALS Initially 18 sites were searched at night for P. hubrichti. Only salamanders that were surface active were counted. No logs, rocks, or other debris were disturbed in order to minimize damage to the salamander's habitat. All sites were located within the range of P. hubrichti in the Glenwood district of the Jefferson Nation Forest off the Blue Ridge Parkway in Bedford and Botetourt counties, Virginia. From these 18 sites, 12 were selected based upon (1) having adequate numbers of P. hubrichti and (2) logistical constraints associated with timbering such as having harvestable timber or being sufficiently distant from a waterway to permit timbering. These 12 sites were randomly assigned to three treatments (four sites per treatment): reference (no timbering), shelterwood cut (partial removal of canopy), and clearcut (total removal of canopy). At these sites P. hubrichti were monitored one year prior to and two years after timbering. At one site from each treatment, salamanders were individually marked (toe clip) and measured (snout-vent length, SVL) for a mark/recapture study which provided a more detailed picture of how the populations of P. hubrichti were being affected by timbering. At each of the 12 sites, one 5 × 5 m plot was established. Plots at timbered sites were located at least 20 m from the edge of the timbered area which ranged from 0.6 to 1.2 ha. The size of the plot ensured that all sites could be surveyed during a single night, thus avoiding temporal variation (Kramer et al., 1993). In 1993 baseline population levels were established for all 12 sites during 10 night surveys. The four shelterwood cut and clearcut sites were timbered in May 1994. Following timbering, eight surveys were conducted in 1994 and eight in 1995. Average numbers of P. hubrichti were calculated per site for each year. A repeated measures ANOVA with Huynh-Feldt adjustments to the probability levels (SYSTAT, 1996) was used to assess impacts since the averages were repeated, non-independent, measurements taken over time on each site. The reference sites were compared pairwise with the shelterwood cut and clearcut sites. The interaction of treatment and time was the key model parameter considered since this would indicate whether the populations at the reference sites were changing differently from those at the timbered sites. If the interaction parameter was significant (P < 0.05) then the sums of the squares was decomposed into linear and quadratic polynomials. The polynomials were used to determine whether the shape of the population changes over time was primarily linear or quadratic. For the mark/recapture sites, the 5 × 5 m plots had 5 m buffer zones. The entire plot was laid out in a grid of 1 m[sup2] units. These 1 m[sup2] units were marked with a flag in the lower lefthand corner. The 1 m[sup2] units were further visually divided into quadrants with each quadrant being assigned a lower case letter (a, b, c, and d) in a clockwise fashion starting with the top left quadrant. All the animals collected at these sites, except for unmarked animals from the buffer zone, were placed in zip lock bags and left at the capture location. Unmarked animals from the buffer zone were not marked before being released at the capture location. Following examination of the entire study plot and buffer area, animals collected were marked and measured (SVL), and released in the same location they were collected. The marking technique consisted of digital amputation using finger nail clippers. Large salamanders received a unique mark corresponding to a numerical value. Any animal not large enough to be marked uniquely was given a non-specific digital amputation mark (one to several digits removed from the front left foot). At the mark/recapture sites, several population parameters were estimated including population size, size class structure, losses of salamanders, growth rates, and movement rates. The Jolly-Seber method for open populations (Krebs, 1989) was used to estimate populations. Collection days were lumped into three groups per year in order to assure that recaptures were available for each group. Size class structure was analyzed using contingency tables to test for homogeneity between sites for adults (>40 mm) and juveniles ([less or equal]40 mm). Losses of salamanders due to mortality/emigration or reduced surface activity was analyzed using contingency tables to test for homogeneity between sites for animals marked before timbering and seen again after timbering versus the number of animals marked before timbering and never seen again. Growth rates (mm/day) were measured within a calender year by change in SVL divided by the time between recaptures. A two-way ANOVA with variables of treatment and year were used to analyze the data. The growth rates were not significantly correlated with size and therefore no distinction for size classes was made in the ANOVA. Movement rates (cm/day) were calculated by dividing the distance between recaptures by the time between recaptures within a calender year. When an animal was recaptured multiple times in a calendar year an average was calculated. The analysis was then similar to that for growth rates.