Abstract

Forest canopies buffer the macroclimate and thus play an important role in mitigating climate-warming impacts on forest ecosystems. Despite the importance of the tree layer for understory microclimate buffering, our knowledge about the effects of forest structure, composition and their interactions with macroclimate is limited, especially in mixtures of conifers and broadleaves. Here we studied five mixed forest stands along a 1800 km latitudinal gradient covering a 7 degrees C span in mean annual temperature. In each of these forests we established 40 plots (200 in total), in which air and soil temperatures were measured continuously for at least one year. The plots were located across gradients of forest density and broadleaved proportions (i.e. from open to closed canopies, and from 100% conifer to 100% broadleaved tree dominance). Air minimum, mean and maximum temperature offsets (i.e. difference between macroclimate and microclimate) and soil mean temperature offsets were calculated for the coldest and warmest months. Forest structure, and especially forest density, was the key determinant of understory temperatures. However, the absolute and relative importance of the proportion of broadleaves and forest density differed largely between response variables. Forest density ranged from being independent of, to interacting with, tree species composition. The effect of these two variables was independent of the macroclimate along our latitudinal gradient. Temperature, precipitation, snow depth and wind outside forests affected understory temperature buffering. Finally, we found that the scale at which the overstory affects soil microclimate approximated 6-7 m, whereas for air microclimate this was at least 10 m. These findings have implications for biodiversity conservation and forest management in a changing climate, as they facilitate the projection of understory temperatures in scenarios where both forest structure and macroclimate are dynamic. This is especially relevant given the global importance of ongoing forest conversion from conifers to broadleaves, and vice versa.

Keywords

Microclimate; Forest understory; Forest density; Broadleaves; Understory temperature; Latitudinal gradient

Published in

Agricultural and Forest Meteorology
2023, Volume: 341, article number: 109684
Publisher: ELSEVIER

SLU Authors

• Diaz Calafat, Joan

  • Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences
    

• Uria Diez, Jaime

  • Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences
    
  • Basque Research and Technology Alliance (BRTA)

• Brunet, Jörg

  • Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences
    

• Felton, Adam

  • Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences
    

• Öckinger, Erik

  • Department of Ecology, Swedish University of Agricultural Sciences
    

• Hedwall, Per-Ola

  • Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences
    

Associated SLU-program

SLU Forest Damage Center


Sustainable Development Goals

Take urgent action to combat climate change and its impacts
Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss


UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.1016/j.agrformet.2023.109684

Permanent link to this page (URI)

https://res.slu.se/id/publ/126785