Thinning reduces late-spring frost impact on stem radial growth in a beech forest stand

Abstract

Resistance and resilience to multiple stresses depend on competition among trees, thus they can be improved by means of silvicultural practices reducing stand density. However, we often ignore whether thinning is an appropriate practice to increase the resistance and resilience to late-spring frosts. These climatic events can damage tree species, especially when leaf emergence is advanced by warmer springs. Here, we compared the effect of a late-spring frost on crown damage and stem radial growth in beech trees (Fagus sylvatica) from areas thinned and not thinned. The study area is a mixed forest of F. sylvatica, Quercus petraea and Q. pyrenaica, and is located in central Spain, near the southern limit of beech distribution. The proportion of trees damaged by frost was not significantly different in thinned vs non-thinned areas. However, severely damaged trees in non-thinned areas showed higher growth reductions and a longer legacy effect than severely damaged trees in thinned plots. Severely damaged trees were those with earlier leaf and stem growth phenology in the frost year. These trees, compared to slightly damaged trees, delayed growth cessation and had a longer growth period in the frost year, and the year afterwards in non-thinned areas. Growth recovery was size-dependent in non-thinned areas, in which bigger trees recovered growth faster. The positive effect of thinning in attenuating frost impact on growth and accelerating growth recovery adds up to other beneficial effects of thinning for stress tolerance. Similar results could occur in other deciduous species highly sensitive to spring temperatures, which are likely to increase with global warming.