Tree diversity increases forest temperature buffering

Abstract

Summary paragraphGlobal warming is increasing the frequency and intensity of climate extremes1. Forests may buffer such extreme events by creating their own microclimate below their canopy via cooling hot and insulating against cold macroclimate air temperatures2,3. This buffering capacity of forests may be increased by tree diversity4,5and may itself maintain forest functioning and biodiversity6,7. However, despite its relevance for many ecosystem processes, the effect of tree diversity on temperature buffering is largely unexplored. Here, we show that tree species richness consistently increases forest temperature buffering across daily, monthly, and annual scales over six years. This finding is based on data from a large-scale tree diversity experiment covering a species richness gradient of 1 to 24 tree species. We found that species richness strengthened both components of forest temperature buffering2,6: the attenuation of hot and of cold macroclimate air temperatures, with the cooling effect being more pronounced. The buffering effect of tree species richness was mediated by canopy density and structural diversity, assessed as leaf area index and stand structural complexity index5, respectively. Safeguarding and planting diverse forests8may thus mitigate negative effects of global warming and climate extremes on ecosystem functions and communities below the tree canopy.

Microclimate modulation: An overlooked mechanism influencing the impact of plant diversity on ecosystem functioning

“…Plant diversity was found to foster canopy thickness and complexity (Peng et al, 2017;Perles-Garcia et al, 2021;Williams et al, 2017), potentially also enhancing the buffering capacity of vegetation cover on microclimatic processes in the understorey. Results from experiments manipulating plant diversity in the field (BEF experiments) indicate that microclimatic conditions are even more stable with increasing plant species richness (Huang et al, 2023;Schnabel et al, 2023;Zhang, 2022) and that microclimate interacts with stand complexity in promoting forest productivity (Ray et al, 2023). Similar effects by more diverse plant communities on microclimatic conditions via thicker canopies were also observed in grasslands (Huang et al, 2023), yet empirical evidence in grassland ecosystems remains limited, particularly F I G U R E 2 Climate dependencies of various processes across different levels of organization, here using temperature dependency as an example: (1) Net ecosystem CO 2 exchange (NEE, Niu et al, 2012), (2) soil respiration (Jones et al, 2006), (3) tree seedlings survival (Dingman et al, 2013), (4) insect activity (Colinet et al, 2015) and (5) Rubisco activity (Galmés et al, 2019).…”

“…However, the effects of plant diversity on microclimate dynamics depend on seasons (Huang et al, 2023;Schnabel et al, 2023;Zhang, 2022), owing to structural mediation in winter (e.g. branch structure in forests) and leaf mediation in summer (Schnabel et al, 2023). Consequently, the impact of plant diversity on climate-dependent ecosystem functions is anticipated to be dynamic over time.…”

“…Microclimate is an ecologically important environmental parameter that regulates ecosystem functioning to an important degree (e.g. Gottschall et al., 2019; Joly et al., 2017; Kemppinen et al., 2023), which can be co‐determined by plant diversity and canopy structure (Huang et al., 2023; Schnabel et al., 2023; Zhang, 2022). Thus, integrating microclimate into the BEF relationship seems critically important and promises an enhanced understanding of the mechanisms underlying BEF relationships, particularly given the multitude of climate‐dependent processes at different organizational levels ultimately determining ecosystem functions.…”

“…Consequently, manipulating the species composition and canopy structure of a given ecosystem offers a promising strategy to modulate microclimate, and thus, the overall functioning of the focal ecosystem. Indeed, recent research highlighted the potential of plant diversity, and thus ecosystem structure, to influence microclimatic fluctuations (Huang et al, 2023;Ray et al, 2023;Schnabel et al, 2023;Zhang, 2022). This included the further reduction in temperature extremes experienced underneath a vegetation canopy that is composed of more species (Huang et al, 2023;Schnabel et al, 2023), and changes in sensible heat flux and evapotranspiration resulting in higher ecosystem CO 2 uptake (Milcu et al, 2016).…”

“…Indeed, recent research highlighted the potential of plant diversity, and thus ecosystem structure, to influence microclimatic fluctuations (Huang et al., 2023; Ray et al., 2023; Schnabel et al., 2023; Zhang, 2022). This included the further reduction in temperature extremes experienced underneath a vegetation canopy that is composed of more species (Huang et al., 2023; Schnabel et al., 2023), and changes in sensible heat flux and evapotranspiration resulting in higher ecosystem CO 2 uptake (Milcu et al., 2016). Higher plant diversity also promotes ecosystem functioning and stability by increasing and securing essential functions such as productivity and carbon storage (Beugnon et al., 2023; Huang et al., 2018; Liang et al., 2016, 2022; Schnabel et al., 2019).…”