Decadal effects of thinning on understory light environments and plant community structure in a subtropical forest

Abstract

2018. Decadal effects of thinning on understory light environments and plant community structure in a subtropical forest. Ecosphere 9(10):Abstract. Canopy-opening disturbance such as thinning has immediate and substantive effects on understory microclimate and therefore the establishment and growth of understory plants. A large number of studies have reported the effects of thinning on tree growth, but few studies have examined long-term effects of thinning on understory light environments and species and functional diversity of understory plants. Even less is known whether the change in understory plant community structure observed following canopy disturbance is short-lived and would diminish as the canopy closes or a long lasting due to legacy effects. We examined the effects of an experimental removal of 25% and 50% of the woody vegetation on understory light availability and variability on understory plant community structure in a subtropical Cryptomeria japonica plantation nine years after the treatment. Differences in availability of understory light among treatments diminished nine years after the experimental vegetation removal (thinning), but variability of understory light was still two times higher in the thinned treatments than the un-thinned control. Species diversity of dominant and common understory plants was lower in the control than in the two thinning treatments, which were not different from each other. Community species and functional composition were also different between the un-thinned control and the two thinning treatments. The thinned plots had proportionally more individuals of grasses and forbs and fewer individuals of ferns. Our results indicate that the effects of thinning on understory light variability last longer than on light availability representing an important and long-lasting alteration of resource heterogeneity. At both species and functional group levels, greater diversity and unique composition in the thinned treatments compared to undisturbed control suggest a link between resource heterogeneity and biodiversity in the forest understory or legacy effects associated with the thinning-induced changes in understory plant community.

Forest operations, tree species composition and decline in rainfall explain runoff changes in the Nacimiento experimental catchments, south central Chile

“…Most studies report that runoff increases after thinning (Andréassian, 2004; Brown et al, 2005; Buttle et al, 2019; Douglass, 1983; Grant et al, 2013; Hawthorne et al, 2013; Lane & Mackay, 2001; Sun et al, 2015), although the increases may last only a few years (Perry & Jones, 2017). However, forest thinning also reduces competition for resources (McLaughlin et al, 2013), and increased light, water, and nutrients may increase transpiration (Bladon et al, 2006; Boggs et al, 2015; Hernandez‐Santana et al, 2012) and release understory shrubs and trees (Ares et al, 2010; Tsai et al, 2018), potentially explaining the initial reduction in runoff. The reduction in runoff after thinning in N02 is consistent with reported reductions in streamflow after drought and insect outbreak‐induced tree mortality in arid and semi‐arid areas (Goeking & Tarboton, 2020; Guardiola‐Claramonte et al, 2011).…”

Forest Understorey Vegetation: Colonization and the Availability and Heterogeneity of Resources

“…Furthermore, several studies have reported that high diversity in the overstorey canopy has beneficial effects for understorey abundance and diversity [60], as a consequence of the light variability in the understorey layer that is created through the complementarity and overlapping of overstorey crowns [63][64][65]. As such, the abundance and diversity of understorey vegetation are positively affected by light heterogeneity [47,55,66], as predicted by the resource heterogeneity hypothesis.…”

“…In contrast to stand-replacing wildfire that eradicates both overstorey and understorey vegetation, and releases soil nutrients through the combustion of coarse woody debris [15,69,118,120], clearcutting, which also removes overstorey vegetation, has a lesser impact on understorey vegetation [14,33,123]. Partial harvesting is divided into uniform harvesting and patch harvesting, both of which increase light availability and heterogeneity in the understorey, particularly with patch harvesting, and decrease the availability of soil moisture [66,119,[128][129][130].…”

Temporal Effects of Thinning on the Leaf C:N:P Stoichiometry of Regenerated Broadleaved Trees in Larch Plantations

“…The light availability could decrease rapidly form short term to long term after thinning and return to the initial levels before thinning quickly [30,31]. In our study, the low thinning intensity (15% of the stock volume) led to a quick reclosure of the canopy three years after thinning.…”

“…Much more attention has been paid to the effects of thinning intensity in previous studies [22,26,27]. However, the light availability (canopy openness) may obviously decrease over time after thinning due to the rapid growth of residual and regenerated trees or shrubs [28][29][30]. Most studies have reported the changes of light availability in the short term (1-3 years) after thinning [31], but the variations in the medium-and long-term after thinning remain unknown [32,33].…”