Plant community attributes 12 to 14 years following precommercial thinning in a young lodgepole pine forest

Abstract

We investigated plant community responses (abundance, species diversity, and structural diversity) to a range of precommercial thinning densities in young lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands 12 to 14 years after thinning, with both unthinned and old-growth stands for comparison. Abundance of understory plants, especially herbs, appeared to increase dramatically in the thinned stands. The moss layer was significantly more abundant in old-growth stands than in the young pine stands. Of a total of 108 species sampled, only three were introduced species, all of which occurred more frequently in the low-density stands than in any of the other stands. Thinning treatments appeared to increase the abundance of late-seral species. Our results suggest that by disrupting canopy closure, thinning decreased the dominance of tall trees and increased the abundance of herbs, shrubs, and trees in the understory height classes. As a result, thinning to low densities significantly increased the structural richness of the tree layer and caused an increase in total structural diversity, which, although only marginally significant (p = 0.06), was likely biologically important. Our results suggest that thinning will enhance the abundance, species diversity, and structural diversity of the plant community 12 to 14 years postthinning.

Effects of stand density on ecosystem properties of subalpine forests in the southern Rocky Mountains, USA

“…Because light is often limiting to the growth of understory plant communities in dense, subalpine forests (Lajzerowicz et al, 2004), a decrease in canopy cover due to harvest often stimulates production in the seedling bank, shrubs, and herbaceous species (Lindgren et al, 2006). Furthermore, increased light availability at the soil surface may increase temperatures in the short term, stimulating heterotrophic microbial communities responsible for decomposition and increasing N availability for understory plants during the time when competition is limited (Titus et al, 2006).…”

Long-term outcome of precommercial thinning on floristic diversity in north western New Brunswick, Canada

“…The results are contradictory, ranging from no differences (Moola & Vasseur 2004, Kern et al 2006, He & Barclay 2000, Berger & Puettmann 2000, Thomas et al 2001, to di versity going significantly higher (Lindgren et al 2006, Decocq et al 2004, Bailey et al 1998, Thysell & Carey 2000, Battles et al 2001, or lower (Thomas et al 1999, Jobidon et al 2004, Hansen et al 1991, Elliott et al 1997) following canopy thinning. Jobidon et al (2004) investigated the influence of thin ning and found that large increases in hard wood productivity occurred at the expense of species richness and diversity of the under story stratum, which could not be explained by variability in canopy light.…”

“…Some researchers predict that thinning of the forest overstory may result in increased light penetration into the understory, which will favor the development of forest floor ve getation (Bailey et al 1998, Thomas et al 1999, He & Barclay 2000, Lindgren et al 2006. However, there appears to be a para dox in the results of several thinning re search trials that suggest the dynamic nature of forest plant communities may override the influence of a particular limiting resource such as light.…”

“…In general, responses of species diversity to forest management are often assumed to be negative (Gilliam & Roberts 1995). Specific responses to PCT treatments are inconsistent, and range from increased diversity (Lindgren et al 2006, Thysell & Carey 2000 to decreased di versity (Thomas et al 1999, Jobidon et al 2004, Hansen et al 1991, Elliott et al 1997, to similar levels of diversity (Moola & Vas seur 2004, Kern et al 2006, He & Barclay 2000, Berger & Puettmann 2000, Thomas et al 2001), compared with unmanaged stands. Many of these studies are based on relatively short-term observations (e.g., < 20 years after thinning), or larger than typically ap plied spacings (Newmaster et al 2006).…”

“…Many of these studies are based on relatively short-term observations (e.g., < 20 years after thinning), or larger than typically ap plied spacings (Newmaster et al 2006). It is not clear whether these effects would still be evident in the longer term (e.g., after treated stands enter the stem exclusion stage -He & Barclay 2000, Lindgren et al 2006), or if op erational spacings (1.8 to 2.4 m) had been used. Further research is needed to clarify the numerous conflicting claims in the liter ature.…”