Forests buffer temperature extremes through processes such as canopy shading, wind speed reduction, and evapotranspiration. As a result, microclimates are formed within forests whose climatic conditions are distinctly different from the surrounding macroclimate. This allows many species to thrive in the understory due to its reduced variation in temperature. However, the buffering capacity of these microclimates may be under threat as global temperatures keep rising and extreme events such as droughts are becoming more widespread. Prolonged exposure to droughts can lower the soil moisture, which, in turn, weakens the buffering by reducing the water available for evaporative cooling. Earlier research has shown that forest buffering is mainly dependent on the canopy cover, the local water balance, and the geographical location. At higher latitudes, the general consensus is that the temperature buffering depends mainly on the canopy cover as the solar radiation is not strong enough to initiate sufficient evaporative cooling. Yet, with ongoing climate change and the increasing frequency of heat waves, this might have changed. To that end, we locally investigate the influence of soil moisture and canopy openness on the temperature buffering at various forest stands within a Swedish coniferous forest during the summer months of 2021 and 2022. Our results showed that, in both years, the soil moisture had no significant impact on the forest temperature, while the canopy openness had a very strong influence on buffering both the maximum and minimum temperatures. More specifically, in both years, the forest lost its ability to buffer the maximum and minimum temperatures when the canopy openness exceeded roughly 22% and 15%, respectively. On average, the measured forest stands were not buffered as the summer average maximum and minimum temperature offsets in both years amounted to ⟨∆Tmax,tot⟩ = 0.21 ◦C and ⟨∆Tmin,tot⟩ = −0.28 ◦C in 2021 and ⟨∆Tmax,tot⟩ = 0.10 ◦C and ⟨∆Tmin,tot⟩ = −0.31 ◦C in 2022. However, the summers of 2021 and 2022 were climatically quite average, which could have influenced the correlation between the soil moisture and the air temperature. Overall, the results suggest that maintaining a canopy openness ≲ 22% is needed for microclimate buffering to occur in this Swedish coniferous forest during a climatically average summer
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-219129 |
| Date | January 2023 |
| Creators | Van der Keijl, Mark |
| Publisher | Stockholms universitet, Institutionen för naturgeografi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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