Seasonal drivers of understorey temperature buffering in temperate deciduous forests across Europe

Abstract

AimForest understorey microclimates are often buffered against extreme heat or cold, with important implications for the organisms living in these environments. We quantified seasonal effects of understorey microclimate predictors describing canopy structure, canopy composition and topography (i.e., local factors) and the forest patch size and distance to the coast (i.e., landscape factors).LocationTemperate forests in Europe.Time period2017–2018.Major taxa studiedWoody plants.MethodsWe combined data from a microclimate sensor network with weather‐station records to calculate the difference, or offset, between temperatures measured inside and outside forests. We used regression analysis to study the effects of local and landscape factors on the seasonal offset of minimum, mean and maximum temperatures.ResultsThe maximum temperature during the summer was on average cooler by 2.1 °C inside than outside forests, and the minimum temperatures during the winter and spring were 0.4 and 0.9 °C warmer. The local canopy cover was a strong nonlinear driver of the maximum temperature offset during summer, and we found increased cooling beneath tree species that cast the deepest shade. Seasonal offsets of minimum temperature were mainly regulated by landscape and topographic features, such as the distance to the coast and topographic position.Main conclusionsForest organisms experience less severe temperature extremes than suggested by currently available macroclimate data; therefore, climate–species relationships and the responses of species to anthropogenic global warming cannot be modelled accurately in forests using macroclimate data alone. Changes in canopy cover and composition will strongly modulate the warming of maximum temperatures in forest understories, with important implications for understanding the responses of forest biodiversity and functioning to the combined threats of land‐use change and climate change. Our predictive models are generally applicable across lowland temperate deciduous forests, providing ecologically important microclimate data for forest understories.

Unfolding the effects of different forestry treatments on microclimate in oak forests: results of a 4‐yr experiment

“…Effect sizes induced by the applied silvicultural treatments presumably depend on the macroclimate (especially temperature and precipitation), topography, site conditions (e.g., soil moisture) and stand type (mainly tree species composition and structural heterogeneity; Aussenac 2000; von Arx et al 2013, Ashcroft and Gollan 2013, De Frenne et al 2019. Nevertheless, in the case of air temperature, we found similar order of magnitude of temperature offset in various European forest stands reported by Zellweger et al (2019).…”

Plant functional trait response to environmental drivers across European temperate forest understorey communities

“…Future studies should consider microclimatic buffering effects on below‐canopy temperatures by including measured temperatures at the forest floor, since this buffering effect ( i.e. likely reduced temperature ranges) may confound the temperature–trait relationships found here (Zellweger et al, ). That is, our plots comprised closed canopy forests that have not had much disturbance in the recent past, and where canopy cover has increased over time.…”

Hedging against biodiversity loss: Forest herbs’ performance in hedgerows across temperate Europe

“…Temperature offset values were calculated for each summary statistic as microclimate temperatures minus macroclimate temperatures. In this study, we mainly focused on the effect of maximum summer temperature offsets, because this summary statistic has been shown to differ most between forests and hedgerows (Zellweger et al ., 2019; Vanneste et al ., 2020b). Finally, it should be noted that sub‐canopy temperature measurements were available for all sampled sites, except for the four forest–hedgerow combinations in Poland.…”