Action: Harvest groups of trees instead of clearcutting
Key messagesRead our guidance on Key messages before continuing
- Three studies (including two randomized, replicated, controlled, before-and-after studies) in the USA found that compared to clearcutting, harvesting trees in small groups did not result in higher amphibian or salamander abundance. A meta-analysis of 24 studies in North America found that partial harvest, which included harvesting groups or individual trees, thinning and shelterwood harvesting, resulted in smaller reductions in salamander populations than clearcutting
- Two studies (including one randomized, replicated, controlled, before-and-after study) in the USA found that compared to no harvesting, harvesting trees in small groups significantly decreased salamander abundance and changed species composition.
- One randomized, replicated, controlled, before-and-after study in the USA found that compared to unharvested plots, the proportion of female salamanders carrying eggs were similar and proportion of eggs per female and juveniles similar or lower in harvested plots that included harvest of groups of trees.
Forests naturally undergo disturbances such as storms and lightning that can create open patches. Similarly, harvesting groups of trees rather than clearcutting forest creates a mix of different habitats, allowing a greater range of species to survive in a forest.
Supporting evidence from individual studies
A controlled, before-and-after study in 1994–1997 in a hardwood forest in Virginia, USA (Harpole & Haas 1999) found that harvesting trees in small groups decreased the relative abundance of salamanders, similar to clearcutting. Captures decreased significantly after group harvesting (before: 14; one year after: 11; three years: 2/search) and clearcutting (before: 10; one year after: 7; three years: 1/search). Abundance did not differ significantly within the unharvested plot (before: 10; one year after: 10; three years: 8). Treatments on 2 ha plots were: group harvesting (three groups of 0.5 ha), clearcutting (up to 12 wildlife and dead trees retained) and unharvested. Salamanders were monitored along 2 x 15 m transects with artificial cover objects (50/plot).
A randomized, replicated, controlled, before-and-after study in 1993–1999 of five harvested hardwood forests in Virginia, USA (Knapp et al. 2003) found that harvesting trees in groups did not result in higher salamander abundances than clearcutting. Abundance was similar between treatments (groups: 3; clearcut: 1/30 m2 respectively; see also Homyack & Haas 2009). Abundance was significantly lower compared to unharvested plots (6/30 m2). Species composition differed before and three years after harvest. There were five sites with 2 ha plots with each treatment: group harvesting (2–3 small area group harvests with selective harvesting between), clearcutting and an unharvested control. Salamanders were monitored on 9–15 transects (2 x 15 m)/plot at night in April–October. One or two years of pre-harvest and 1–4 years of post-harvest data were collected.
A randomized, replicated, controlled, before-and-after study in 1992–2000 of oak-pine and oak-hickory forest in Missouri, USA (Renken et al. 2004) found that there was no significant difference in amphibian abundance between sites with small group or single tree selection harvesting and those with clearcutting. Abundance of species declined after harvest but also declined on unharvested sites. Nine sites (312–514 ha) were randomly assigned to treatments: small group or single tree selection harvesting (5% area; uneven-aged management), clearcutting in 3–13 ha blocks (10–15% total area) with forest thinning (even-aged), or unharvested controls. Harvesting was in May 1996 and 1997. Twelve drift-fence arrays with pitfall and funnel traps were established/plot. Traps were checked every 3–5 days in spring and autumn 1992–1995 and 1997–2000.
In a continuation of a previous study (Knapp et al. 2003), a randomized, replicated, controlled study in 1994–2007 of six hardwood forests in Virginia, USA (Homyack & Haas 2009), found that harvesting groups of trees did not result in higher salamander abundance compared to clearcutting up to 13 years after harvest. Abundance was similar between treatments (groups: 4; clearcutting: 2/transect) and significantly lower than unharvested plots (7/transect). Proportions of juveniles and eggs/female were significantly lower in harvested (group harvesting, shelterwoods, leave-tree harvesting and clearcut with wildlife trees or snags left) compared to unharvested treatments for mountain dusky salamander Desmognathus ochrophaeus and juveniles for red-backed salamander Plethodon cinereus. Proportions of females carrying eggs were similar in harvested and unharvested plots for slimy salamander Plethodon glutinosus and southern ravine salamanders Plethodon richmondii. There were six sites with 2 ha plots randomly assigned to treatments: group harvesting (2–3 small area group harvests with selective harvesting between), clearcutting, other harvested treatments and an unharvested control. Treatments were in 1994–1998 and salamanders were monitored at night along nine 2 x 15 m transects/plot.
A meta-analysis of the effects of different harvest practices on terrestrial salamanders in North America (Tilghman, Ramee & Marsh 2012) found that partial harvest, which included harvesting groups or individual trees, thinning and shelterwood harvesting, resulted in smaller reductions in salamander populations than clearcutting. Overall, partial harvest produced declines 24% smaller than clearcutting. Average reductions in populations were lower following partial harvest (all studies: 31–48%; < 5 years monitoring: 51%; > 10 years monitoring: 29%) compared to clearcutting (all: 54–58%; < 5 years: 62%; > 10 years: 50%). There was no significant effect of the proportion of canopy removed in partial harvests. Sampling methodology influenced perceived effects of harvest. Salamander numbers almost always declined following timber removal, but populations were never lost and tended to increase as forests regenerated. Twenty-four site comparison and before-and-after studies that compared salamander abundance in harvested (partial or clearcut) and unharvested areas were analysed. Abundance measures included counts, population indices and density estimates.
- Harpole D.N. & Haas C.A. (1999) Effects of seven silvicultural treatments on terrestrial salamanders. Forest Ecology and Management, 114, 349-356
- Knapp S.M., Haas C.A., Harpole D.N. & Kirkpatrick R.L. (2003) Initial effects of clearcutting and alternative silvicultural practices on terrestrial salamander abundance. Conservation Biology, 17, 752-762
- Renken R.B., Gram W.K., Fantz D.K., Richter S.C., Miller T.J., Ricke K.B., Russell B. & Wang X. (2004) Effects of forest management on amphibians and reptiles in Missouri Ozark forests. Conservation Biology, 18, 174-188
- Homyack J.A. & Haas C.A. (2009) Long-term effects of experimental forest harvesting on abundance and reproductive demography of terrestrial salamanders. Biological Conservation, 142, 110-121
- Tilghman J.M., Ramee S.W. & Marsh D.M. (2012) Meta-analysis of the effects of canopy removal on terrestrial salamander populations in North America. Biological Conservation, 152, 1-9