Comparison of soil CO2 efflux between different surface covers on a clear-cut and forest stand in southern Sweden, Hyltemossa

University essay from Lunds universitet/Institutionen för naturgeografi och ekosystemvetenskap

Abstract: Large amounts of carbon in the terrestrial biosphere are stored in forest ecosystems and its soil. Once the forest ecosystem is disturbed the release of this carbon can drive positive feedback to global warming. Humans impact the forest ecosystem through clear-cutting for wood production and other commercial purposes. Clear-cutting is still a standard forestry management method, but its effect on the global carbon cycle and climate change is not yet fully understood. Soil respiration releases carbon from the soil in the form of carbon dioxide (CO2), and net ecosystem exchange (NEE) regulates the ecosystem carbon sink, therefore, making it an important component to global carbon balance. This thesis aims to analyze the impact of man-made disturbances, in the form of clear-cutting, on the carbon balance by comparing soil respiration between a forest stand and a clear-cut area on three types of forest surface covers (vegetation, bare soil, and mineral layer). Furthermore, the influence of soil temperature and soil moisture on soil respiration, as well as the influence of photosynthetically active radiation (PAR) on NEE has been analyzed for those forest surface covers. The results show no distinct difference in soil respiration between the clear-cut and the forest stand, but small differences between the surface covers of the clear-cut and the forest stand. The bare soil and mineral layers have higher (0.15 µmol m-2 s -1) soil respiration in the form of CO2 than the vegetation cover. Soil respiration is higher (about 0.2 µmol m-2 s -1) on the forest stand for all surface covers compared to the clear-cut. This is because of a difference in vegetation specimen leading to reduced microbial activities and root respiration on the clear-cut. The NEE is positive on the forest stand and the clear-cut with a higher net release on the forest stand, while the PAR is lower on the forest stand than on the clear-cut. This is explained by the difference in vegetation type of the forest stand thus affecting its gross primary production (GPP) and ecosystem respiration (Reco) along with factors such as canopy cover that could hinder radiation in the forest. The field measurement in the study was not taken over a longer period, which is why the correlation between the soil temperature, soil moisture, and PAR with soil respiration and NEE cannot be seen. In conclusion, the data on soil respiration and NEE was not enough to see distinct differences between the clear-cut and the forest stand, however there are differences between the surface covers. The full scale of human impact on the carbon cycle through soil disturbances cannot be analyzed with this dataset.

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