毛竹林老竹水平和经营措施对新竹发育质量的影响

毛竹林是我国重要的森林资源类型,在森林固碳和林业应对气候变化中具有不可替代的重要作用。由于毛竹林的持续采伐与自我更新特性,在竹林经营过程中,新竹的发育数量和质量成为评价竹林固碳功能变化的决定性因子。利用两因素随机区组设计,排除地形因子等影响,选取施肥和采伐留养方式这两个因素,研究老竹水平和经营措施对2010年和2013年毛竹林新竹发育质量的影响。结果表明:无论2010年还是2013年,新竹平均胸径、株数和碳储量与3年生和5年生老竹的相关性均高于2年生和4年生老竹。新竹碳储量与3年生和5年生老竹碳储量呈线性相关,建立线性回归模型y=0.675x-2.2491,R~2=0.8561,而新竹碳储量与2年生和4年生老竹碳储量相关性较低,线性回归模型为y=-0.1109x+6.7287,R~2=0.0061。不同经营措施实施后,新老竹之间关系发生了很大的改变,新竹平均胸径与老竹的相关性大幅下降,新竹株数和碳储量与老竹几乎没有相关性,新竹碳储量与3年生和5年生老竹碳储量的线性回归模型为y=0.1036x+3.7539,R~2=0.0981,新竹碳储量与2年生和4年生老竹碳储量的线性回归模型为y=-0.0408x+5.9069,R~2=0.0151。不同经营措施的实施对新竹的平均胸径、株数和地上碳储量产生了很大的影响。处理A_1B_2(大量施肥中度采伐中密度留养)、A_2B_2(中等施肥中度采伐中密度留养)和A_3B_2(不施肥中度采伐中密度留养)新竹平均胸径、新竹株数和新竹碳储量都有所增加,新竹平均胸径增幅为:处理A_2B_2(8.78%)A_1B_2(2.43%)A_3B_2(2.06%),新竹株数增幅为:处理A_1B_2(81.0%)A3B2(35.4%)A2B2(15.2%),新竹地上碳储量增幅为:处理A_1B_2(90.8%)A_3B_2(35.7%)A_2B_2(49.7%),而其余处理基本都会减少,说明适度采伐留养最有利于提高毛竹林新竹的发育质量。仅仅从固碳最大化的角度出发,大量施肥中度采伐中密度留养最有利于新竹碳储量的增加,而从培养大径竹材的角度考虑,中等施肥中度采伐中密度留养能收到更好的效果。

Effects of old bamboo forests and relevant management measures on growth of new bamboo forests

Moso bamboo forest, an important forest resource in China, plays an irreplaceable and important role in forest carbon sequestration and in adaptation of the forestry to climate change. Because of the special characteristics of Moso bamboo forests in continuous cutting and self-renewal, the quantity and quality of new bamboo''s development become a decisive factor in evaluating functional changes of Moso bamboo forest carbon sequestration in the process of bamboo forest management. This research examined the effect of old bamboo forest and relevant management measures on growth of new bamboo forest based on the 2010 and 2013 Moso bamboo forests. A two-factor randomized block design was employed, which fertilization amount and cutting/leaving ways were selected based on the removal of topographical impacts. Results showed that the correlation coefficients of average diameter at breast height (DBH), number of culms and carbon storage between new bamboo forest and old bamboo forest of 3 and 5 years have higher values than those between new bamboo forest and old bamboo forest of 2 and 4 years either in the year of 2010 or 2013. The carbon storage between new bamboo forests and old bamboo forests of 3 and 5 years has linear relationships (e.g, y=0.675x-2.2491, R²=0.8561); in contrast, there is no correlations between new bamboo and old bamboo of 2 and 4 years (e.g., y=-0.1109x+6.7287, R²=0.0061). After different management measures were implemented, the relationships between new and old bamboo forests changed considerably, that is, the correlation of average DBH between new and old bamboo forests decreased dramatically; no correlation in number of culms and carbon storage between new and old bamboo forests existed. The linear regression model of carbon storage between new bamboo and old bamboo forests of 3 and 5 years was y=0.1036x+3.7539, R²=0.0981, and between new and old bamboo forest of 2 and 4 years was y=-0.0408x+5.9069, R²=0.0151. These results implied that the implementation of different management measures had a great effect on average DBH, number of culms and aboveground carbon storage of new bamboo forest. These attributes increased with treatments A₁B₂ (high fertilization with moderate-intensity cutting and leaving), A₂B₂ (intermediate fertilization with moderate-intensity cutting and leaving) and A₃B₂ (no fertilization with moderate-intensity cutting and leaving). The order of average DBH increase rate of new bamboo forest is A₂B₂ (8.78%) > A₁B₂ (2.43%) > A₃B₂ (2.06%), and the increase rates of number of culms and aboveground carbon storage are A₁B₂ (81.0%) > A₃B₂ (35.4%) > A₂B₂ (15.2%) and A₁B₂ (90.8%) > A₃B₂ (35.7%) > A₂B₂ (49.7%). The rest of treatments result in decrease of these attributes. These situations imply that moderate-intensity cutting and leaving method was useful in improving the quality of new bamboo forest. In terms of carbon sequestration maximization, high fertilization combining with moderate-intensity cutting and leaving was useful in increasing carbon storage of new bamboo forests. On the other hand, considering cultivating large-diameter bamboo forests, intermediate fertilization combining with moderate-intensity cutting and leaving was preferable.