大兴安岭主要森林类型林分空间结构优化模拟

Spatial structure optimization simulation of main forest types in Great Xing’an Mountains, Northeast China

以大兴安岭地区4种主要林型[天然落叶松纯林(LF)、天然白桦纯林(BF)、针阔混交林(CBMF)和针叶混交林(CMF)]的1 hm^2固定样地调查数据为基础,选择常用林分空间[混交度(M)、大小比数(U)、角尺度(W)、竞争指数(CI)]和非空间结构参数[林分生长活力(DC)、林木稳定性(DH)],并结合熵值-AHP赋权法,构建单木综合抚育采伐指数(T),运用Excel VBA编制模拟抚育采伐过程;系统比较各林型不同抚育采伐强度(分别为10%、20%和30%)下T值,并确定各林型的最优抚育采伐强度.结果表明:初始状态下,各林型平均W均为0.57,属于典型聚集分布;各林分平均U在0.50~0.51,林木整体生长的优势程度处于典型的中庸状态;各林分平均M整体较低,其中,混交林明显大于纯林;林分内平均CI大于2.0,林木生长竞争压力较大;LF整体稳定性、活力均显著高于其他林分;整体来说,BF的经营迫切性程度显著高于其他林分.从同一林型内相邻抚育采伐强度间的T值增长率来看,LF的最佳抚育采伐强度为30%,其余3种林型的最佳抚育采伐强度均为10%,T值增长率分别为9.7%、7.9%、6.6%和3.9%;而从不同林型下T值大小和郁闭度来看,BF的最佳抚育采伐强度为20%,其余林型的最优抚育采伐强度均为30%,此时T值分别提高了28.9%、16.4%、17.5%和9.2%.抚育采伐后林分整体结构得到不同程度的改善,其中,林分M显著增大,林木水平空间分布格局趋向随机分布,优势树种优势程度增加,样地内林木竞争压力明显减小,DC略有降低,DH得到提升.

Based on the data from four 1 hm^2 permanent plots in main forest types[namely natural Larix gmelinii forest(LF),natural Betula platyphylla forest(BF),coniferous-broadleaved mixed forest(CBMF)and coniferous mixed forest(CMF)]in Great Xing’an Mountains,a comprehensive cutting index of individual tree(T),based on the commonly used spatial structure parameters[i.e.,mingling(M),neighborhood comparison(U),uniform angle index(W),and competition index(CI)]and non-spatial structure parameters[tree vigor index(DC),tree stability index(DH)],was constructed using combined AHP and entropy evaluation method.The cutting process was simulated by Excel VBA to determine the best tending intensity on the basis of systematic comparison of comprehensive T-value under different tending intensities(10%,20%,and 30%)of different forest types.The results showed that,in the initial state,the mean values of W were all 0.57,indicating a typical cluster distribution.The mean values of U ranged from 0.50 to 0.51 and the dominant degree of overall growth of trees was in a typical mean state.The mixed degree of four main forest types was generally low,with the mixed forest being obviously higher than the pure forest.The mean competition index within the stand was above 2.0,indicating higher competition pressure.The stability and growth vigor index of LF were significantly higher than those of other stands.Overall,the management urgency of BF was significantly higher than that of other stands.With regard to T-value growth rate between adjacent tending intensities,the optimal cutting intensity was 30%for LF forest and 10%for other types.The relative growth rates were 9.7%,7.9%,6.6%and 3.9%respectively.However,from the perspective of T-value and canopy density with different tending intensities,the optimal cutting intensity of BF was 20%,and the others were all 30%,in which the T-values were increased by 28.9%,16.4%,17.5%and 9.2%respectively.After simulated harvesting,stand structure was improved in various degrees and the mixed degree of tree species was increased.The horizontal distribution pattern of stand tended to random distribution.The dominance degree of dominant tree species was increased.The competition pressure of trees was decreased.DC of trees was slightly lower and the DH of trees was improved.