Strong influence of trees outside forest in regulating microclimate of intensively modified Afromontane landscapes

Abstract

Abstract. Climate change is expected to have detrimental consequences on fragile ecosystems, threatening biodiversity, as well as food security of millions of people. Trees are likely to play a central role in mitigating these impacts. The microclimatic conditions below tree canopies usually differ substantially from the ambient macroclimate as vegetation can buffer temperature changes and variability. Trees cool down their surroundings through several biophysical mechanisms, and the cooling benefits occur also with trees outside forest. The aim of this study was to examine the effect of canopy cover on microclimate in an intensively modified Afromontane landscape in Taita Taveta, Kenya. We studied temperatures recorded by 19 microclimate sensors under different canopy covers, as well as land surface temperature (LST) estimated by Landsat 8 thermal infrared sensor. We combined the temperature records with high-resolution airborne laser scanning data to untangle the combined effects of topography and canopy cover on microclimate. We developed four multivariate regression models to study the joint impacts of topography and canopy cover on LST. The results showed a negative linear relationship between canopy cover percentage and daytime mean (R2=0.65) and maximum (R2=0.75) temperatures. Any increase in canopy cover contributed to reducing temperatures. The average difference between 0 % and 100 % canopy cover sites was 5.2 ∘C in mean temperatures and 10.2 ∘C in maximum temperatures. Canopy cover (CC) reduced LST on average by 0.05 ∘C per percent CC. The influence of canopy cover on microclimate was shown to vary strongly with elevation and ambient temperatures. These results demonstrate that trees have a substantial effect on microclimate, but the effect is dependent on macroclimate, highlighting the importance of maintaining tree cover particularly in warmer conditions. Hence, we demonstrate that trees outside forests can increase climate change resilience in fragmented landscapes, having strong potential for regulating regional and local temperatures.

Synergistic Impact of Complex Topography and Climate Variability on the Loss of Microclimate Heterogeneity in Southeast Asia

“…Due to a lack of reliable distribution data for local species, most studies rely primarily on measurements of climatic exposure to track potential changes (Ashcroft et al., 2012; Garcia et al., 2014; Jiao et al., 2021; Yuan et al., 2019) and are often quantified by coarse‐grid climate data sets. However, these local macroclimate changes quantified by coarse‐grid data sets are often substantially different from microclimate changes quantified by fine‐scale data sets (Aalto, Maeda, et al., 2022; Aalto, Tyystjärvi, et al., 2022; De Frenne et al., 2021; Maclean & Early, 2023; Zu et al., 2023), leading to a failure to interpret the extraordinarily high biodiversity of tropical mountains. Therefore, research on microclimate change based on high‐resolution data sets is emerging as a local research focus.…”

“…At the local scale, microclimate variability is strongly influenced by biotic and abiotic characteristics, such as climatic, topographical, ecological, and land‐cover factors (Aalto, Maeda, et al., 2022; Aalto, Tyystjärvi, et al., 2022; Beck et al., 2018; De Frenne et al., 2021; Niittynen et al., 2020; Stein et al., 2014; Ye et al., 2022). These microclimate drivers commonly modify surface hydrothermal conditions through heat budget and water redistribution (Garcia et al., 2014).…”

“…For example, deforestation has been shown to produce cooling with increased albedo and warming with decreased evapotranspiration in tropical mountainous regions (Zeng et al., 2020). However, in tropical savanna bushlands in Kenya, clearance of bushlands to croplands has caused an increase in land surface temperature despite increased albedo and decreased evapotranspiration (Aalto, Maeda, et al., 2022; Aalto, Tyystjärvi, et al., 2022; Abera et al., 2020). Furthermore, temperature and precipitation fluctuations are viewed as direct drivers of microclimate (Aalto, Maeda, et al., 2022; Aalto, Tyystjärvi, et al., 2022).…”

“…However, in tropical savanna bushlands in Kenya, clearance of bushlands to croplands has caused an increase in land surface temperature despite increased albedo and decreased evapotranspiration (Aalto, Maeda, et al., 2022; Aalto, Tyystjärvi, et al., 2022; Abera et al., 2020). Furthermore, temperature and precipitation fluctuations are viewed as direct drivers of microclimate (Aalto, Maeda, et al., 2022; Aalto, Tyystjärvi, et al., 2022). Collectively, these biotic and abiotic drivers alter hydrothermal conditions and microclimate distribution.…”

“…changes quantified by fine-scale data sets (Aalto, Maeda, et al, 2022;Aalto, Tyystjärvi, et al, 2022;De Frenne et al, 2021;Maclean & Early, 2023;Zu et al, 2023), leading to a failure to interpret the extraordinarily high biodiversity of tropical mountains. Therefore, research on microclimate change based on high-resolution data sets is emerging as a local research focus.…”