Effects Of Tending On Chinese Arborvitae And Chinese Pine Recreational Forests In Xishan Mountain Of Beijing

Xishan Mountain of Beijing is an important recreational area for the local residents. Forests in this area are defined as scenic and recreational forests and managed for aesthetic and recreational needs of the general public. With the great efforts of the local forest managers, these forests have played important roles in water and soil conservation, environment improvement and biodiversity conservation etc since establishment. However, the presence of large amount of deadwoods and messy shrub vegetations make the stand quality a relatively low level at present. Therefore, aesthetic and recreational as well as other functions were not much achieved. Exploration of scientific and feasible tending measures for these forests is a key issue to be resolved in the local silvicultural practices.To determine the optimal tending regime and corresponding tending interval for the Chinese arborvitae and Chinese pine recreational forests, based on previous research on stand aesthetic quality assessment, different tending regimes were applied to typical stands of these two forests on shady and sunny slope in Xishan Mountain of Beijing in summer2007. The applied tending regimes in Chinese arborvitae forests were six pre-optimized combinations (Al、A2and A3; B1、B2and B3) of two pruning height (2-3m and3-4m) and four remained shrub cover(10%、20%、25%and50%). While in Chinese pine forest, they were four pre-optimized combinations (C1and C2; D1and D2) of two pruning height (4～5m and5～6m) and three remained shrub cover (10%、20%and30%). The dynamics of stand structure, aesthetic quality, understory plant diversity and natural regeneration in34permanent plots were monitored and investigated for five successive years before and after treatment. Stand spatial structure was analyzed based on the Voronoi method, and then the influence of different tending regimes on the characteristics of stand canopy and understory vegetation was explored. Based on Scenic Beauty Estimation Method, scenic effects of applied tending regimes were analyzed. At last, the effects of different tending regimes on understory plant diversity and natural regeneration were analyzed. The major conclusions were as follows:(1) The stand spatial structure in both Chinese arborvitae and Chinese pine stands were reasonable approximately, therefore different tending regimes were feasible from the perspective of non-spatial structure. There were6to7units of stand spatial structure in these stands, and the unit was mostly formed by one reference tree and five neighbors. The aggregation index of most plots in these stands was significantly larger than one, which indicated that the distribution pattern of tree individuals was uniform. The mingling degree of stands was between0.4and0.6, which indicated that the extent of segregation among tree species was in a middle level. The stand was in a middle level of competition with neighborhood comparison in DBH and height around0.5. Moreover, the stand was relatively open with open degree of above0.3.(2) Different tending regimes were able to increase the species numbers of understory vegetation within four years after tending, and the newly occurred species were mainly shade-intolerant herbs. The effect of A1and A3regimes in shady slope stand of Chinese arborvitae forest was optimal, under which the average increased number of species was17and15respectively. While in sunny slope stand of Chinese arborvitae, the effect of B1and B2regimes was better with increased number of species of about8and6respectively. In shady slope stand of Chinese pine, the effect of C2regime was better, and the newly occurred species was11in average. However, in sunny slope stand of Chinese pine, both D1and D2regimes had equal effect, under which there was3and4newly occurred species.(3) The species number, composition and dominance of understory dominant populations were not significantly influenced by tending regimes, thus the structure of understory vegetation remained relatively stable after tending. The dominant species were Vitex negundo var. heterophylla and Grewia biloba var. parviflora in shrub vegetation and Oplismenus undulatifolius in herb vegetation during the investigation periods.(4) Assessment of stand aesthetic quality based on SBE method indicated that different tending regimes could largely increase the preference degree of stands in a short term after tending, and thus its aesthetic quality was significantly improved. The aesthetic effects was equal for A1、A2and A3regimes in shady slope stand of Chinese arborvitae forest. Under these three tending regimes, the preference degree increased by70.0、64.7and73.9respectively. While in sunny slope stand, B1regimes was better for the increased preference degree of79.0. Different tending regimes in Chinese pine forest had the same excellent effect. C1and C2regimens in shady slope stand increased the preference degree by78.2and58.3respectively. While in sunny slope stand, preference degree of D1and D2regimens increased by53.4and42.4respectively.(5) Different tending regimes can maintain or improve understory plant diversity in both Chinese arborvitae and Chinese pine forest. In Chinese arborvitae forest, the effect of A3regime was better in shady slope stand and H’ index of shrub and herb vegetation under this regime was increased by54.7%-73.7%and1.6-2.5times respectively. In sunny slope stand, all three tending regimes were able to maintain plant diversity in shrub and herb vegetation. In Chinese pine forest, the effect of C2regime was better in shady slope stand and H’index of shrub and herb vegetation under this regime was increased by54.9%-59.3%and0.93～1.25times respectively. In sunny slope stand, D1and D2were able to maintain plant diversity in shrub and herb vegetation.(6) Different tending regimes can facilitate the increment of species number and density for regenerated broadleaf trees. However, this effect was not found for the coniferous trees in both Chinese arborvitae and Chinese pine forest. In shady slope stand of Chinese arborvitae forest, the effect of A2and A3regimes were better and regeneration density increased by4424stem/hm2and4456stem/hm2respectively. While in sunny slope stand, the effect of B2regime was better with regeneration density increased by6433stem/hm2. In shady slope stand of Chinese pine forest, the effect of C1regime was better and its regeneration density increased by5900stem/hm2. While in sunny slope stand, the effect of D2regime was better with regeneration density increased by4000stem/hm2.From the perspective of forest aesthetics and ecology, the optimal tending regime and interval for the recreational forests of Chinese arborvitae and Chinese pine were proposed. In Chinese arborvitae forest, A3regime (pruning height of2-3m plus remained shrub cover of about20%plus ground clearance) was better for the shady slope stand, and corresponding tending interval should be2years; while in sunny slope stand, B1regime (pruning height of2-3m plus remained shrub cover of about25%plus ground clearance) was more appropriate and its tending interval should be at least4years. In Chinese pine forest, C2regime (pruning height of5-6m plus remained shrub cover of about20%plus ground clearance) was better for shady slope stand, and corresponding tending interval should be1year; while in sunny slope stand, D2regime (pruning height of4-5m plus remained shrub cover of about20% plus ground clearance) was more appropriate and its tending interval should be2years.