| Being the key and link of harmonious development between human being and natural environment, forest has multiple ecological functions including regulating climate, conserving water, keeping soil and water, fixing carbon and protecting biodiversity. Therefore, it plays important roles on improving the living conditions.Zhejiang is one of the most developed provinces with higher economic growth.However, during the development process, forest has been damaged and consequential environmental problems should not be ignored. Public welfare forest has been constructed in Zhejiang province since the end of last century, but it still face the problems like poor quality and unreasonable structure. Therefore, speeding up the construction of public welfare forest will benefit the realization of 'beautiful Zhejiang'and enhance the sustainable economic and social development. In this study, biomass was selected as the public welfare forest indicator by combining the field investigation and remote sensing based modeling process to analyze the spatial and temporal characteristics of public welfare forest in Zhejiang province as well as in typical counties. The main contents and conclusions are as follows:The spatial and temporal characteristics of public welfare forest were systematically analyzed through large-scale field investigation in Zhejiang province.Among different forest species, the biomass of coniferous and broad-leaved mixed forest in public welfare forest was the highest, followed by fir forest, broad-leaved forest, pine forest and shrub forest. From the perspective of vertical gradient, the highest biomass was in the Chinese fir and the shrub forest was the lowest among the tree layer, while for the undergrowth broad-leaved forest was the highest and Chinese fir was lowest, but opposite for the herbaceous layer. There were no significant differences in biomass of shrub forest community under different altitudinal gradients.The spatial and temporal characteristics of biomass of community forest were systematically analyzed by using the ecological monitoring data of ecological public welfare forest in Zhejiang Province. The biomass of coniferous and broad - leaved mixed forest in public welfare forest was the highest, followed by fir forest, broad -leaved forest, pine forest and shrub forest. From the vertical gradient analysis, the biomass of the tree layer was the highest in the Chinese fir and the shrub forest was the lowest. The biomass of the lower layer was the highest in the broad-leaved forest and the lowest in the Chinese fir. The biomass of the herbaceous layer was the highest and the broad-leaved forest was the lowest. There were no significant differences in biomass of shrub forest community under different altitudinal gradients. The biomass of Pinus tabulaeformis and Cunninghamia lanceolata community increased with the elevation. Moreover, the biomass of coniferous and broad-leaved mixed forest and broad-leaved forest were highest in 0-200m and 1000-15000 meters.From 2001 to 2010, different species including pine forest, Chinese fir forest,broad-leaved forest, coniferous and broad-leaved mixed forest, bamboo and shrub were increased by 72.5%, 84.3%, 38.4%, 24.8%, 33.4% and 133.9% respectively. The average annual growth rate of biomass per unit was 5.69%. The biomass of Pinus koraiensis and broad-leaved forest increased relatively small in the middle and late period, but for coniferous and broad-leaved mixed forest and broad-leaved forest,biomass still increased largely even for the mature forest in term of tree-age.The biomass spatial distribution of different communities varies with different terrain conditions. The biomass of Pinus koraiensis, Cunninghamia lanceolata and broad-leaved forest from high to low was located in the middle mountains, low mountain and hilly, respectively. For coniferous and broad-leaved mixed forest, the order was low mountain, hilly and middle mountains, but for bamboo forest the order was low mountain, middle mountains and hills. Pine, fir and bamboo forest had the highest biomass in the middle slope position, and broad-leaved forest and the coniferous and broad-leaved mixed forest had the highest in whole slope. From the perspective of slope, pine, fir and bamboo forest got the highest biomass at steep slope, and all communities had lowest biomass in gentle slope. Moreover, the biomass of pine, fir and bamboo forest was highest in the northwest aspect, while for coniferous and broad-leaved mixed forest and shrub forest, the highest was located in the south, southwest and northeast aspect. In addition, highest biomass of Pinus tabulaeformis, Cunninghamia lanceolata, broad-leaved forest, coniferous and broad-leaved mixed forest and shrubbery were located in high thick soil, but bamboo located in soil with middle thickness. Thick soil is the highest. In the low mountain area, the annual increase of biomass was higher than that in hilly and mountainous areas. Therefore, pine, fir, broad-leaved forest, coniferous and broad-leaved mixed forest and bamboo forest located in low mountain had higher biomass than that in hilly. Furthermore, biomass was relatively low when the site was better available because of higher frequent human development.Grey Association Degree method was used to analyze the factors influenced the biomass. As a result, the most important factors were tree-age, slope, landforms. The factors that had the greatest impact on broad-leaved forest were consistent with the whole public welfare forest, while for coniferous and broad-leaved mixed forest,forest age, slope, aspect were the most significant, and for pine forest was forest age,slope, and elevation. But for fir forest age, topography and elevation were the key factors. Slope,elevation and topography determined bamboo biomass distribution and shrub forest biomass mainly depends on slope and soil thickness.Based on the biomass map with a spatial resolution of 250m and net primary productivity (NPP) map of different vegetation, characteristics of biomass in Zhejiang Province were analyzed. Among different administrative regions, biomass and NPP in the public welfare forest were quite different. The average biomass density of Hangzhou and Shaoxing was the highest, 86.46t/ha and 83.59 t/ha respectively, while the average NPP in Quzhou and Wenzhou was the highest, 10.966gC/m2 and 10.843gC/m2 respectively. The relationships between biomass, NPP, temperature and average rainfall were investigated. The results showed that the biomass density and the average annual temperature were negatively correlated, but NPP and temperature were weakly positively correlated. The average biomass and average NPP of public welfare forest in Zhejiang Province were higher when the temperature was among 16.51 ? to 17.58 ?, which indicated that temperature conditions greatly affected the growth of public welfare forest. Positive correlation between biomass density(NPP) and average annual rainfall in public welfare forest in Zhejiang Province was found, which means that annual rainfall affected the growth of ecological public welfare forest. Therefore, the increase of annual rainfall would promote the increase of biomass and net primary productivity.Dinghai District in Zhanzhou city, Wuyi County in Jinhua city and Xianju County in Taizhou city were taken as the representative of typical landforms including island, basin and mountain area in Zhejiang Province. Biomass quantization at the county level was realized through using the random forest modeling method and combining the ecological monitoring data based on field investigation and multi-period Landsat data were combined, and the temporal and spatial dynamics of biomass in public welfare forest were analyzed.Biomass increased apparently from 2010 to 2015 in the three regions. In the basin areas and islands where human activity was more frequent, biomass grew faster at low altitudes, while in mountainous areas, the highest growth of biomass tended to take place at high altitudes. The rate of biomass increase in the basin area increased with the slope, but the increase rate in the mountainous area decreased with the increase of the slope, and the increase rate in the island area increased first and then decreased with the increase of slope, which indicated that the rate of biomass with different slope condition in these three regions were quite diverse. From the perspective of aspect, biomass in the mountainous and basin area was relatively higher in the east, southeast and south slope, but in island area, higher biomass was located in the northwest, west and southwest slope. Furthermore, biomass increase rate of different aspect was uniform in the island area, which may due to the reason that the environment for vegetation was quite similar as the islands were surrounded by sea and were less affected.Combined with the traditional ground survey data and remote sensing technology,we propose to carry out comprehensive monitoring of the resources and ecological conditions of public welfare forest, and then make fast and accurate objective evaluation for the quality, dynamic changes and the ecosystem service functions for public welfare forest resources, so as to provide scientific guidance for construction,management and protection. |
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