A recent study from Leipzig University, the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, and the Max Planck Institute for Biogeochemistry has found that gaps in the canopy of a mixed floodplain forest influence soil temperature and moisture levels significantly, while having a limited effect on soil biological activity. These findings were published in Science of the Total Environment.
Canopy gaps in the forest, whether created by human actions like logging or the natural death of large trees, significantly affect the microclimate and the biological activities in the soil. With the looming impacts of climate change, understanding how these gaps influence temperature and soil health is crucial. The researchers examined how various sizes and structures of forest gaps impacted the microclimate and decomposition processes within the soil of a mixed floodplain forest in Leipzig, Germany, during the notably dry year of 2022.
Study lead Annalena Lenk from the Institute of Biology at Leipzig University reports, “As we anticipated, there was an increase in soil temperature in areas with gaps compared to denser parts of the forest, and the temperature variations were more pronounced.” Specifically, during summer, average soil temperatures in gap areas could be as much as 2.05 °C higher than in closed forest areas. Interestingly, the soil moisture in these gaps was also higher—sometimes significantly so—likely due to reduced transpiration from fewer large trees and less rainfall being captured by the reduced canopy.
Moreover, the study revealed that the density of shrubs and smaller trees often had a stronger influence on soil temperatures than the larger trees overhead. “In areas with a thicker understorey, temperatures and their fluctuations tended to be more moderate compared to regions where the understorey had been artificially reduced,” Lenk notes.
To assess how these changing microclimatic conditions affected vital ecosystem functions, Lenk and her team monitored soil organism activity. They conducted experiments to observe the decay rates of various organic materials (such as green tea, rooibos tea, and wooden spatulas) and the feeding behavior of soil-dwelling fauna using bait strips. “Contrary to our expectations, we did not observe significant differences in soil biological activity between the gaps and closed forest areas,” says Lenk. However, she notes that higher soil temperatures over the season corresponded with increased feeding activity among soil organisms, despite a drop in soil moisture. “Even amid the severe drought, decomposition rates remained consistent with our expectations, indicating that the microclimate differences between gap and closed forest were not substantial enough to greatly influence soil activity.” This is a hopeful finding, as both increases and decreases in decomposition rates could negatively affect the ecosystem.
Lenk emphasizes that these outcomes underscore the intricate relationships among forest structure, microclimate, and soil processes. “This research marks a significant advancement in our understanding of how forests adapt to structural changes amid climate change,” she explains. The results may also hold importance for conservation practices that advocate for partial canopy removal to enhance biodiversity. To develop effective forest management strategies that account for changing macroclimatic conditions, further investigations into these relationships across various forest types and the inclusion of microclimatic data in forest monitoring programs are needed.
