Heavy and frequent thinning promotes drought adaptation inPinus sylvestrisforests

Abstract

Droughts and their negative effects on forest ecosystems are projected to increase under climate change for many regions. It has been suggested that intensive thinning could reduce drought impacts on established forests in the short-term. Most previous studies on the effect of thinning on drought impacts, however, have been confined to single forest sites. It is therefore still unclear how general and persisting the benefits of thinning are. This study assesses the potential of thinning to increase drought tolerance of the wide spread Scots pine (Pinus sylvestris) in Central Europe. We hypothesized (1) that increasing thinning intensity benefits the maintenance of radial growth of crop trees during drought (resistance) and its recovery following drought, (2) that those benefits to growth decrease with time elapsed since the last thinning and with stand age, and (3) that they may depend on drought severity as well as water limitations in pre- and post-drought periods. To test these hypotheses, we assessed the effects of thinning regime, stand age, and drought severity on radial growth of 129 Scots pine trees during and after drought events in four long-term thinning experiments in Germany. We found that thinning improved the recovery of radial growth following drought and to a lesser extent the growth resistance during a drought event. Growth recovery following drought was highest after the first thinning intervention and in recently and heavily thinned stands. With time since the last thinning, however, this effect decreased and could even become negative when compared to unthinned stands. Further, thinning helped to avoid an age-related decline in growth resistance (and recovery) following drought. The recovery following drought, but not the resistance during drought, was related to water limitations in the drought period. This is the first study that analyzed drought-related radial growth in trees of one species across several stands of different age. The interaction between thinning intensity and time since the last thinning underline the importance to distinguish between short- and long-term effects of thinning. According to our analysis, only thinning regimes, with relatively heavy and frequent thinning interventions would increase drought tolerance in pine stands.

Last‐century forest productivity in a managed dry‐edge Scots pine population: the two sides of climate warming

“…Although Sohn et al. () suggest that only strong and frequent thinning interventions will yield substantial benefits, our results suggest that shelterwood as well is effective for reducing competition, presumably because this allows keeping the balance between the capacity of young trees to absorb the radiation and the protector effect given by adult trees.…”

“…, Sohn et al. ). Adaptation through managing the amount and distribution of individual trees in a stand is therefore a promising tool to maintain population stability (Keenan ) and to preserve future carbon reservoirs.…”

Potential of forest thinning to mitigate drought stress: A meta-analysis

“…For example, thinning intensity and frequency had an interactive effect on the growth response of Pinus sylvestris to drought (Sohn et al, 2016). However, this could not be tested in this study due to lack of information on the exact timing of follow-up thinning interventions in several studies.…”

“…After less intense thinning, stand transpiration can return within few years to the pre-thinning level (Breda et al, 1995;Lagergren et al, 2008) while canopy closure proceeds more slowly and stand water use remains low for longer time periods after more intense thinning (Bren et al, 2010). How long stand-level LAI and thus water interception remain lower in thinned compared to unthinned stands should depend not only on how much LAI was reduced (thinning intensity) but also on the species' potential to occupy newly available growing space and on the intervals between thinning interventions (Sohn et al, 2016). Additionally, benefits of thinning for the growth response of trees during and after drought have been found to decrease with stand age due to higher water demands of larger trees in open compared to closed stands (D'Amato et al, 2013).…”

Fine‐scale stand structure mediates drought‐induced tree mortality in pinyon–juniper woodlands

“…), P. sylvestris (Sohn et al. ) and ameliorated growth declines in mixed‐conifer forests (Vernon et al. ) and several community types across the United States (Gleason et al.…”