Browsing by Author "Ghasemi Falk, Homa"

Greenhouse gases are essential in controlling the surface temperature of the Earth. Methane is one of the most abundant greenhouse gases in the atmosphere. it has an important role in the atmospheric chemical processes, and its atmospheric concentration has increased dramatically from pre-industrial time. In 2006, studies revealed that terrestrial plants are capable of emitting methane under aerobic conditions which led to the conclusion that the contribution of forests to the global methane budget needs to be considered. In my thesis the aim was to assess the capacity of boreal tree stems to transport methane, to quantify the radial diffusivity of methane in the stem of different tree species and evaluate the effects of various factors on regulating stem gas transport. Gas transport of Scots pines (Pinus sylvestris) and Birches (Betula pubescens) tree stems were examined in the laboratory under controlled conditions. The results highlighted that birch stem samples have a higher methane stem fluxes compared to pine samples. The result also indicated that birches accumulated less methane inside the stem compare with pine samples. One of the most significant findings from this study is that birch stem samples have the higher average methane and carbon dioxide diffusivity compared to pine samples. This finding also explains the smaller accumulated methane gas inside the birch stems compared to pine stems. Also, the differences in the diffusivity may result from differences in the anatomical composition of these tree species, including heartwood, sapwood, bark tissue and lenticel densities.