The effects of forest management on terrestrial salamanders

Maintaining a balance of timber production and conservation in forest management requires an understanding of how timber harvest techniques affect wildlife species. Terrestrial salamanders are useful indicators of mature forest ecosystem health due to their importance to ecosystem processes and their sensitivity to environmental change. The topic of timber harvests and their effect on terrestrial salamanders has received much attention in the literature but disagreements and uncertainty about the severity and duration of these effects persist. I employed artificial cover objects (ACOs) to monitor salamander relative abundance in six forest management treatments both before and after harvests. Prior to harvests, I assessed the efficacy of two cover-object materials in sampling forest herpetofauna. In a side-by-side comparison of 930 pairs of ACOs, salamanders were found more under wood objects than plastic objects (p \u3c 0.001), a result likely due to a greater capacity of wood objects to retain moisture and buffer temperature fluctuations. Pre-harvest data showed little variation in mean salamander counts across treatment types, but counts were greater in spring than fall. Counts varied by slope aspect in the fall but not the spring. Mean encounters of Eastern Red-backed (Plethodon cinereus) and Northern Slimy Salamanders (P. glutinosus) declined from pre- to post-harvest in group selection cuts (p \u3c 0.001); however, mean encounters of red-backed salamanders also declined in uncut control sites (p = 0.025). The effect of sample period was statistically significant for all species tested (p \u3c 0.001), suggesting high temporal variation in salamander abundance. Average daily air temperature was negatively correlated with counts of red-backed and Northern Zigzag Salamanders (P. dorsalis ; rs ≈ -0.43, p \u3c 0.001). In general, harvests which removed the forest canopy had a negative effect on salamander relative abundance during the years immediately following harvest. Salamander declines were not as severe as those seen in most previous research, a fact which may be explained in part by the relatively small size (≤ 4 ha) of the harvests examined here. I found no effect of controls, shelterwoods, and forested sites adjacent to harvests. Much of the variation in salamander counts is likely driven by seasonal patterns in precipitation and temperature. Longer-term monitoring will be necessary to understand the full impacts of forest management on terrestrial salamanders

Salamander encounters by distance to edge and by slope aspect.

<p>Mean encounters per sampling occasion of (A) eastern red-backed salamanders (<i>Plethodon cinereus</i>) at edge effect grids from March 2010 to March 2011 were significantly greater at 20, 40, and 60 m than at −40 m on southwest slopes (SW, n = 3). Mean encounters of (B) zigzag salamanders (<i>P. dorsalis</i>) were significantly greater at −40 m than at 40 m on northeast slopes (NE, n = 3). Encounters of both species generally increased from the clearcut interior to the forest interior on southwest slopes. Counts of (C) slimy salamanders (<i>P. glutinosus</i>) are presented graphically but were low and could not be normalized for analysis. Error bars represent ± standard error. Results were considered significant at <i>α</i> = 0.05.</p

Salamander encounters by treatment type and treatment period.

<p>Mean encounters per sampling occasion decreased significantly from pre- (fall 2007 and spring 2008) to post-harvest (spring and fall 2009, 2010, and spring 2011) in group cuts and clearcuts for (A) eastern red-backed salamanders (<i>Plethodon cinereus</i>), and (C) slimy salamanders (<i>P. glutinosus</i>). Mean encounters of red-backed salamanders also decreased significantly in control sites, while mean encounters of (B) northern zigzag salamanders (<i>P. dorsalis</i>) increased significantly in clearcut adjacent sites. One sampling occasion consists of a single visit to a single cover-board grid. Error bars represent ± standard error. Results were considered significant at <i>α</i> = 0.05. Ctrl = control; Group = group selection; CC = clearcut; CC adj = clearcut adjacent; Sh = shelterwood; Sh adj = shelterwood adjacent.</p

Type III fixed effects for analysis of variance of salamander counts at edge effect grids.

<p>Models were run for eastern red-backed (<i>Plethodon cinereus</i>) and northern zigzag (<i>P. dorsalis</i>) salamanders.</p><p>*Significant effect at <i>α</i> = 0.05.</p>a<p>Interaction terms are indicated by an ‘×’ between two or more factors.</p>b<p>Dist = distance to edge.</p>c<p>A = slope aspect (northeast or southwest).</p>d<p>fall or spring in a given year.</p><p>Type III fixed effects for analysis of variance of salamander counts at edge effect grids.</p

Spearman rank correlation tests for associations between salamander encounters and environmental variables at edge effect grids.

<p>Tests were conducted for counts of eastern red-backed (<i>Plethodon cinereus</i>), northern zigzag (<i>P. dorsalis</i>), and northern slimy (<i>P. glutinosus</i>) salamanders.</p><p>*Significant effect at <i>α</i> = 0.05.</p>a<p>Precipitation 48 hours prior to sampling vs. mean salamanders per grid per sampling day.</p>b<p>Air temperature as recorded by data loggers on stakes at ACO grids vs. salamander count per sampling occasion.</p>c<p>Temperature as recorded by data loggers under ACOs vs. salamander count per sampling occasion.</p>d<p>Average percent soil moisture vs. salamander count per sampling occasion.</p>e<p>Average percent canopy cover vs. mean salamanders per grid per sample period.</p>f<p>Average depth of leaf litter vs. mean salamanders per grid per sample period.</p>g<p>Volume of downed woody debris (all decay classes) vs. mean salamanders per grid per sample period.</p>h<p>DWD by decay class (1 = little decayed; 5 = well decayed <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114683#pone.0114683-Maser1" target="_blank">[44]</a>).</p><p>Spearman rank correlation tests for associations between salamander encounters and environmental variables at edge effect grids.</p

AIC values for N-mixture models for edge effect grids.

<p>Models were run in program PRESENCE to estimate abundance <i>λ</i> and detection probability <i>p</i> for repeated count data from edge effect grids for eastern red-backed (<i>Plethodon cinereus</i>), northern zigzag (<i>P. dorsalis</i>), and northern slimy (<i>P. glutinosus</i>) salamanders. The lowest AIC values are shown in bold and indicate the best supported model for a given species.</p><p>AIC values for N-mixture models for edge effect grids.</p

Habitat characteristics (mean ± 1SE) across the edge gradient.

<p>Canopy cover, leaf litter depth, and soil moisture were measured at five points within each grid of each edge transect (n = 6 grids×6 transects = 36). (A) Percent canopy cover and (B) litter depth increased with distance away from the edge into the forest, while percent soil moisture was fairly constant across distance intervals but varied greatly by season, being much greater during (C) spring 2010 and (E) spring 2011 than during (D) fall 2010.</p

Diagram of edge transect.

<p>Edge transects contained six grids of artificial cover objects (ACOs) laid out at 20-m intervals with 3-m spacing between objects. ACOs were solid wood boards, 30×30×5 cm, represented here by open and shaded boxes. Shaded boxes also represent the location of canopy, leaf litter, and soil sampling within the grid.</p

Spearman rank correlation tests for associations between salamander encounters and environmental variables at harvest effect grids.

<p>Tests were conducted for counts of eastern red-backed (<i>Plethodon cinereus</i>), northern zigzag (<i>P. dorsalis</i>), and northern slimy (<i>P. glutinosus</i>) salamanders.</p><p>*Significant effect at <i>α</i> = 0.05.</p>a<p>Precipitation 48 hours prior to sampling vs. mean salamanders per grid per sampling day (treatment types and sample periods pooled).</p>b<p>Average daily air temperature vs. mean salamanders per sampling occasion during the pre-harvest period (treatment types pooled).</p>c<p>Average daily air temperature vs. mean salamanders per sampling occasion during the post-harvest period where canopy was retained (control, clearcut adjacent, shelterwood, and shelterwood adjacent).</p>d<p>Average daily air temperature vs. mean salamanders per sampling occasion during the post-harvest period where canopy was removed (clearcuts and group cuts).</p>e<p>Volume of downed woody debris (all decay classes) at each grid vs. mean salamanders per grid per sample period (treatment types pooled).</p>f<p>DWD by decay class (1 = little decayed; 5 = well decayed <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114683#pone.0114683-Maser1" target="_blank">[44]</a>); data from 2010 and 2011 only.</p><p>Spearman rank correlation tests for associations between salamander encounters and environmental variables at harvest effect grids.</p