Paper Summary:
Hocking, D.J., K.J. Babbitt, and M. Yamasaki. 2013. Comparison of Silvicultural and Natural Disturbance Effects on Terrestrial Salamanders in Northern Hardwood Forests. Biological Conservation 167:194-202. doi: http://dx.doi.org/10.1016/j.biocon.2013.08.006
Unfortunately, this paper is behind a paywall. Please email me if you would like a copy for educational purposes.
We were interested in how red-backed salamanders respond to various logging practices compared with natural disturbance. Specifically, we compared abundance of salamanders in the two years following a major ice-storm with clearcuts, patch cuts, group cuts, single-tree selection harvests, and undisturbed forest patches in the White Mountains of New Hampshire (Northern Appalachian Mountains). The 100-year ice storm caused ~65% percent canopy loss in the effected areas. We know that clearcutting has detrimental effects on populations of woodland salamanders but the impacts of less intense harvesting and natural disturbances is less well understood.
We used transects of coverboards from 80m inside each forest patch extending to 80m outside each patch into the surround, undisturbed forest. Repeated counts of salamanders under these coverboards allowed us to employ a Dail-Madsen open population model to estimate abundance in each treatment, while accounting for imperfect detection. The results were quite clear as demonstrated in this figure:
There were slightly fewer salamanders in the ice-storm damaged sites compared with undisturbed reference sites. The single-tree selection sites were most similar to the ice-storm damage sites. The group cut, patch cut, and clearcut didn’t differ from each other and all had ~88% fewer salamanders compared with reference sites.
In addition to comparing natural and anthropogenic disturbances, we were interested in examining how salamanders respond along the edge of even-aged harvests. Wind, solar exposure, and similar factors are altered in the forest edge adjacent to harvested areas. This can result in salamander abundance being reduced in forest edges around clearcuts. Previous researchers have used nonparametric estimates of edge effects. A limitation of this methods is that effects cannot be projected well across the landscape. These methods are also unable to account for imperfect detection. We developed a method to model edge effects as a logistic function while accounting for imperfect detection. As with the treatment effects, the results are quite clear with very few salamanders in the center of the even-aged harvests, a gradual increase in abundance near the forest edge, increasingly more salamanders in the forest moving away from the edge, and eventually leveling off at carrying capacity. In this case, red-backed salamander abundance reached 95% of carrying capacity 34 m into the surrounding forest. As the model is parametric, predictions can be projected across landscapes. The equation can be used in GIS and land managers can predict the total number of salamanders that would be lost from a landscape given a variety of alternative timber harvest plans.
Hopefully other researchers find this method useful and apply it for a variety of taxa. It could also be incorporated into ArcGIS or QGIS toolboxes/plugins as a tool for land managers. You can read our paper for more details if you’re interested. In addition to methodological details there is more information on environmental factors that affect detection and abundance of salamanders in this landscape.
Daniel J. Hocking 