The role of species interactions for forest resilience to drought

Abstract

Increasing durations and frequencies of droughts under climate change endanger the sustainable functioning of forests worldwide. The admixture of species with complementary resource use may increase the resilience of forests towards drought; however, little is known about modifications of species interactions (i.e. facilitation and competition) by increasing drought severity in mixed forests. In particular, knowledge on the regulation of central ecohydrological processes, such as tree water fluxes, is lacking. Therefore, we conducted a literature review to assess the impact of species interactions on tree resilience (resistance + recovery) under increasing drought severity. The classification of studies into three drought classes suggested that beneficial species interactions, i.e. through improved water relations, were prevalent under mild droughts. However, with increasing drought, negative effects, such as interspecific competition, occurred. These negative interactions were prominent under extreme droughts, where even trees with complementary resource‐use strategies competed for water resources. Fewer data are available on recovery of water fluxes. The limited evidence supported the patterns observed for drought resistance, with facilitation and complementarity of species in mixtures enhancing tree recovery after moderate droughts. However, after extreme droughts, competition effects and reduced recovery for some species were observed, which can strongly compromise tree resilience. While we acknowledge the importance of mixed forests for biodiversity, ecosystem services or pest resistance, we caution that beneficial species interactions may shift under extreme droughts. Thus, there is an urgent need to investigate species interaction effects on resilience in more depth to adapt forest trees to increasing drought stress.

Neighbourhood species richness and drought-tolerance traits modulate tree growth and δ13C responses to drought

“…1A; Jansen et al, 2021), we did not detect an overall decrease in δ 13 C with NSR and thus no general enhancement of water availability in more diverse tree neighbourhoods. Similarly to our finding, other studies found mixed results and no universal decrease in δ 13 C in mixtures compared to monocultures (Grossiord, 2020; Haberstroh & Werner, 2022). Jansen et al (2021) found the strongest relationship between NSR and δ 13 C for trees with high a high degree of crown competition from neighbours and only marginal effects for trees with low crown competition.…”

Central European 2018 hot drought shifts scots pine forest to its tipping point

“…After 2018, P. sylvestris mortality most likely induced a competition release for understorey trees, which can lead to a higher understorey productivity in the growing period (Cavin et al . 2013; Ogaya & Peñuelas 2021; Haberstroh & Werner 2022). Thus, the growth of the understorey explained the recovery of NDVI in 2019 and 2020, as well as the partial recovery of summertime NEE and GPP in 2020.…”

Plant invasion modifies isohydricity in Mediterranean tree species

“…Grossiord et al (2015) reported negative impacts of plant–plant interactions on water fluxes for Pinus sylvestris , but positive effects for Quercus faginea and Pinus nigra . Thus, plant–plant interactions can buffer or amplify drought stress for co‐existing plants (Grossiord, 2020; Haberstroh & Werner, 2022). Therefore, it is likely that plant competition or facilitation trigger modifications of the plants' hydraulic strategy in comparable ways to abiotic factors.…”