| In the area of Picea asperata and Abies nephrolepis forest in Xiao Xing’an Mountains, due to the forest gaps formed by treefall, the pit and mound microsites formed by uprooted trees, increased the complexity of the forest, improved the light, temperature, the soil moisture and the other environmental conditions of the forest, and then had an effect on the trees and the grasses’regeneration in the community. So the forest gaps formed by treefall, and the pit and mound micro-topography formed by uprooted trees play an very important role in maintaining the species diversity and the forest landscape pattern of the forest.This paper main took the microclimate of the forest gaps formed by treefall and the pit and mound microsites, the soil properties on the pit and mound microsites as preliminary research object. A 1.5 hm2 permanent plot was set in the windthrow area of Picea asperata and Abies nephrolepis forest in Xiao Xing’an Mountains. (1) Selected three representative gaps (they are large, medium, and small forest gaps respectively.) which contains pit and mound were formed by the fallen trees in July,2013. the clearing and closed forest were set up as controls. Multi channel HOBO automatic weather stations were installed in the center of each gap, which were used to measure total radiation, PAR, air temperature and relative humidity in the gap center, mound top and pit bottom of different size gaps. The microclimatic difference and its dynamics change during the growing season in the center of different sizes of gap, as well as the mound top and pit bottom within the gaps were compared. The daily range of temperature under the typical weather conditions were analyzed too. In each month 6-10 typical sunny day were selected to measure the microclimatic factors of photosynthetic photo flux density(PPFD), relative air humidity(RH), the soil temperature of surface(Tso), the depth of 5 cm (TS5) and 10 cm (TS10), soil water content at the depth of 0-7.6 cm(SWC1),0-12 cm(SWC2) and 0-20 cm(SWC3) on 35 pairs of pit and mound microsites (mound top, mound face, pit bottom, pit wall). The intact forest floor (undisturbed by uprooting) was set up as the controls. Monthly variations in the microclimatic factors in 5 different microsites and the impacts of PPFD, RH, and SWC on Ts were compared. (3) Meanwhile the type and amount of herbaceous plants in each pair of pit and mound as well as controls were investigated, their richness and individual density were calculated, and then the effect of the microclimatic factors were analyzed. The surface soil sample on 0-10cm were collected in all of the pit and mound microsites on the sample plot. Analyzed their organic matter, total nitrogen and communicate their C/N.The results showed that:(1) total radiation, PAR and air temperature were in the order of large gap, medium gap and small gap. In the same gap, mean monthly air temperature and PAR were ranked in the decreasing order of July, August, and September, but mean daily range of air temperature was ranked in the decreasing order of July, August, and September, and followed the decreasing order of large gap, middle gap, and small gap. Mean relative humidity in all gaps decreased in the order of August, September, and July, increased in the order of clearing, large gap, medium gap, small gap, and the closed stand. In the same gap, PAR and air temperature on the mound top were higher than those in the pit bottom, but air relative humidity was opposite. (2) Mean monthly PPFD and Tso in pit and mound microstes(mound top, mound face, pit bottom and pit wall) were ranked in the decreasing order of July> August > September, but mean monthly RH, Ts5 and Ts10 were decreased in the order of August> July > September, mean monthly SWC was highest on August; In July, PPFD at mound top was the highest (736.1 μmol-m-2·s-1) and the lowest in intact forest floor (25.46 μmol-m-2·s-1), Ts at mound top was highest (26.29℃) and lowest in pit bottom (5.13℃); SWC in shallow soil layer is larger than in deep soil layer, SWC was the highest in pit bottom (51.58%) on August. (3) The pit and mound micro-topography created by uprooted trees changed the soil of carbon, nitrogen and organic matter. Compared the surface soil of carbon and nitrogen on the pit and mound, we found out the content of the nitrogen and organic matter on mound were higher than in pit. The organic matter content on the mound of Picea asperata was highest. Neither on the mound or in the pit, total nitrogen was in the order of. Picea asperata> Abies nephrolepis> Betula platyphylla Suk.This study took the valley of Picea asperata and Abies nephrolepis forest in Xiao Xing’an Mountains as a research object, measured the microclimate of the forest gaps formed by treefall and the pit and mound microsites, analyzed the organic matter, total nitrogen and communicate their C/N on the pit and mound. It aims to provide basis data and practical references for a period time of plant regeneration, the degraded ecosystem restoration and the sustainable management. |
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