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, and 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 5.7 °C in mean temperatures and 10.2 °C in maximum temperatures. Canopy cover reduced LST on average by 0.05 °C/%CC. The influence of canopy cover on microclimate was shown to vary strongly with elevation and ambient temperatures. These results demonstrate that trees have substantial effect on microclimate, but the effect is dependent on macroclimatic conditions, 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.
Highlights
Climate change poses an imminent threat to the rich biodiversity and frequently found fragile socio–economic conditions that characterize Afromontane ecosystems and their surroundings
The influence of canopy cover on microclimate was shown to vary strongly with elevation and ambient temperatures. These results demonstrate that trees have substantial effect on microclimate, but the effect is dependent on macroclimatic conditions, highlighting the importance of maintaining tree cover in warmer conditions
The effect of Canopy cover (CC) was evident at all three measurement heights: mean temperatures were lower in high CC sites than in open areas, yet some low CC sites exhibited relatively low temperatures
Summary
Climate change poses an imminent threat to the rich biodiversity and frequently found fragile socio–economic conditions that characterize Afromontane ecosystems and their surroundings. Forests and TOF provide vital ecosystem services including water regulation, air purification, carbon sequestration, and climate regulation. They are a source of goods for humans (Martínez Pastur et al, 2018). Climatic conditions below forest canopies can differ substantially from the ambient macroclimate They can vary spatially within the forest (Chen et al, 1999). The temperature buffering provided by tree cover may protect ecosystems from climate change consequences (Zomer et al, 2016; Ellison et al, 2017; De Frenne et al, 2019; Wanderley et al, 2019), but the magnitude of the buffering is affected by the forest area (Ewers and Banks-Leite, 2013). Forest microclimates will likely warm like the macroclimate around them, and fragmentation may accelerate this process (Ewers and Banks-Leite, 2013; Li et al, 2016)
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