21 Oct 2021
21 Oct 2021
Status: a revised version of this preprint is currently under review for the journal BG.

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

Iris Johanna Aalto1, Eduardo Eiji Maeda1, Janne Heiskanen1,2, Eljas Kullervo Aalto3, and Petri Kauko Emil Pellikka1 Iris Johanna Aalto et al.
  • 1Department of Geosciences and Geography, University of Helsinki, P.O. Box 64, FI-00014, Helsinki, Finland
  • 2Institute for Atmospheric and Earth System Research, Faculty of Science, University of Helsinki, Finland
  • 3Department of Economics, Turku School of Economics, 20014 University of Turku, Finland

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.

Iris Johanna Aalto et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-261', Anonymous Referee #1, 16 Nov 2021
    • AC1: 'Reply on RC1', Iris Aalto, 01 Feb 2022
  • RC2: 'Comment on bg-2021-261', Anonymous Referee #2, 12 May 2022
    • AC2: 'Reply on RC2', Iris Aalto, 30 May 2022

Iris Johanna Aalto et al.

Iris Johanna Aalto et al.


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Short summary
Tree canopies are strong moderators of understory climatic conditions. In tropical areas, trees cool down the microclimates. We show using remote sensing and field measurements how even intermediate canopy cover and agroforestry trees contributed to buffering the hottest temperatures in Kenya. The cooling effect was the greatest during hot days and in lowland areas, where the ambient temperatures were high. Adopting agroforestry practices in the area could assist in mitigating climate change.