Extreme drought alters competitive dominance within and between tree species in a mixed forest stand

Abstract

Summary1. The effect of extreme climate events on ecosystems is an important driver of biotic responses to climate change. For forests, extreme drought has been linked to negative effects such as large-scale mortality and reduced primary production. However, the response of plant communities to extreme drought events remains poorly understood. 2. We used mortality data from a long-term monitoring programme in the core of the focal species' ranges, in combination with annual growth data from tree-rings, to study the effect of, and recovery from, an extreme drought event. We examined both the intraspecific and interspecific drought response and explored how differential responses affect competitive dominance between the dominant species Fagus sylvatica and Quercus petraea. 3. Mortality for the most drought-susceptible species, F. sylvatica, occurred alongside a temporary reduction in competition-induced mortality of Q. petraea, resulting in the long-term alteration of the relative abundance of the two species. 4. Significant intraspecific variation occurred in post-drought recovery in surviving F. sylvatica, with two distinct cohorts identified. A prolonged recovery period was coupled with the failure to regain pre-drought growth levels in this species, whereas for Q. petraea, no severe drought impacts were observed. This species instead experienced competitive release of growth. 5. Our results demonstrate that ecosystem responses to extreme drought can involve rapid, nonlinear threshold processes during the recovery phase as well as the initial drought impact. These sudden changes can lead to the reordering of dominance between species within communities, which may persist if extreme events become more frequent.

Diverse responses of forest growth to drought time‐scales in theNorthernHemisphere

“…On the contrary, the forests located in drier environments respond to long-term droughts, which means that they may cope with short-term water deficits but longer and more severe water deficit episodes must occur to affect their radial growth. This suggests that tree species require different time periods to recover (resilience) after water conditions return to average values in dry environments (Granda et al, 2013) and even in humid temperate forests (Cavin et al, 2013). Therefore, the findings of this study not only support the different growth responses to drought in forests located under contrasting environmental conditions, but they stress the importance of considering different drought time-scales for better understanding how forests respond to drought under different climatic and environmental conditions.…”

Integrating plant ecological responses to climate extremes from individual to ecosystem levels

“…Such differential acquisition strategies can partially reduce competition for soil moisture and stabilize carbon uptake [105]. Differential drought sensitivity of codominant trees may also relax competitive interactions between species, allowing compensatory growth of the lesssensitive species to occur that offsets growth reductions of the other species, as was observed within mixed stands of deciduous forest [76].…”

“…Such changes to age structure or the successional state of vegetation may then impact the sensitivity of the ecosystem to future extremes [75]. Changes to dominance hierarchies due to differential sensitivities may further impact ecosystem productivity via competitive releases of a co-dominant [76], and may generate longer term impacts to the composition of the community [9]. Owing to the long temporal scales of forest ecosystem dynamics and tree life histories, climatically induced mortality events and loss of dominant trees may permanently alter the structure, distribution and function of the ecosystem.…”

Assessing future suitability of tree species under climate change by multiple methods: a case study in southern Germany

“…Zang et al 2011, Mette et al 2015, which are expected to further increase in frequency and severity over the course of the 21 st century (Trenberth 2010, Comou & Rahmstorf 2012, Seneviratne et al 2012, Bahn et al 2015. These analyses of climate-growth relationships based on tree rings allows a long-term evaluation of tree growth under various climatic conditions (Fritts 1976, Cook 1987, Cook & Peters 1997 and hence a relative ranking of species according to drought tolerance (Friedrichs et al 2009, Zang et al, 2011, Michelot et al 2012, Cavin et al 2013. As there are only few dendroecological studies addressing less common tree species (Gillner et al 2014, Zimmermann et al 2015, Cedro & Cedro 2015, Klemmt et al 2015, Cedro, 2016, a multiple methods approach seems to be promising to assess the future suitability for those species (Piedallu et al 2013, Fensham et al 2014.…”