甘肃南部林区4种天然林种群结构特征

Structural Characteristics of 4 Natural Populations in the Southern Forest Region of Gansu Province

【目的】分析甘肃南部白龙江、洮河林区的紫果云杉、岷江冷杉、油松和辽东栎4种天然林种群结构特征,揭示种群生存现状,预测种群发展趋势,以期为该林区的森林保护和可持续经营提供理论依据。【方法】通过样地调查和数据统计,绘制种群结构图,编制静态生命表,拟合并分析存活曲线,运用数量化分析法研究种群动态,并用时间序列模型预测种群发展趋势。【结果】紫果云杉与岷江冷杉幼苗数量充足,但死亡率高,幼龄期过后种群逐渐稳定,存活曲线均符合Deevey-Ⅲ型,为增长型种群;油松林也有较大的幼苗比例,在幼龄、中龄和中老龄期各出现了1次死亡高峰,存活曲线符合Deevey-Ⅱ型;辽东栎幼苗数量不足,幼龄和中龄期各出现了1次死亡高峰,存活曲线接近于Deevey-Ⅱ型;数量化动态分析表明,4个种群均为增长型,增长潜力表现为岷江冷杉>紫果云杉>油松>辽东栎种群;考虑外界环境干扰时,4个种群也表现为增长型,但辽东栎受干扰概率大,油松林次之,岷江冷杉和紫果云杉受随机干扰概率小;时间序列预测表明,4个种群在未来2、4、6、8个龄级后个体数量均有增长,增长比例与幼龄个体数量呈正相关。【结论】4个种群均为增长型,紫果云杉与岷江冷杉林种群自然更新好,结构稳定,增长潜力大;油松林幼苗优势不明显,增长潜力较小;辽东栎林自然更新较差,易受外界环境干扰,增长潜力最小。种群自然更新过程中,幼龄个体高死亡率现象普遍存在并成为其更新和发展的“瓶颈”,光照和空间限制而导致的竞争和自疏作用是造成幼苗、幼树存活率偏低的关键因素。近自然状态下的紫果云杉与岷江冷杉种群更新主要受自身生物学特性和环境因子影响,油松林还主要受病虫害和人为影响,辽东栎林则主要受到人为破坏。对岷江冷杉和紫果云杉需采取抚育间伐等措施,提高幼龄个体存活率,增加中、成年林木比例;对油松林还需加强病虫害防治,对辽东栎则需要重点加强保护,并采取人工辅助促进种群更新。

【Objective】Four natural populations of Picea purpurea,Abies faxoniana,Pinus tabulaeformis and Quercus liaotungensis in Bailongjiang and Taohe forest regions in southern Gansu Province were investigated to characterize population structure,to reveal the current status of population survival and to predict future trend of population development,so as to provide a theoretical basis for the protection and sustain able management of the forests of the regions.【Method】Based on field surveys and data analysis,population structure diagram were drawn,static life table were designed,survival curve were fitted and analysed.Quantification method was used to study the population dynamics,and population development trend were predicted by using time-sequence model.【Result】There were sufficient seedlings of P.purpurea and A.faxoniana but with a high mortality,and the populations gradually become stable after the young age,survival curves of both populations conformed to Deevey-Ⅲtype,indicating expansion of the populations.P.tabulaeformis had also a larger percentage of seedlings,there was a peak of death in young age,middle age and middle old age,survival curve conformed to Deevey-Ⅱtype.The number of young individuals in the population of Q.liaotungensis was insufficient,with a peak of death occurred at young age and middle age,survival curve conformed to Deevey-Ⅱtype.The quantitative dynamic analysis also showed that the 4 populations are all growth type,and growth potential is ranked in the order of A.faxoniana>P.purpurea>P.tabulaeformis>Q.liaotungensis.The 4 populations all showed growth type when considering interference of external environment,and Q.liaotungensis has a high probability of disturbance,followed by P.tabuliformis,A.faxoniana and P.purpurea have a low probability of random interference by external factors.Time series prediction indicated that the number of individuals in the 4 populations will all increase after 2,4,6,8 age classes in future,the proportion of population increase was positively correlated with the number of young individuals.【Conclusion】The 4 populations were all growth type.P.purpurea and A.faxoniana were well naturally regenerated,with a stable population structure and great growth potential;the advantages of P.tabulaeformis seedlings was not obvious with small growth potential;Q.liaotungensis was poorly naturally regenerated,and it was vulnerable to external environment with the least growth potential.High mortality rate of young individuals was a“bottle neck”for natural regenerationand development of the population.Competition and self-thinning caused by the limitation of light and space what was the key factors leading to low survival rate of seedlings and saplings in seedling stage.Population regeneration of A.faxoniana and P.purpurea in a close-to-nature state have been affected mainly by their biological characteristics and environmental factors.P.tabulaeformis has been affected mainly by pests and diseases and Q.liaotungensis has been damaged mainly by human.For this reason,artificial measures should be taken to improve the survival rate of young individuals in A.faxoniana and P.purpurea and increasing the proportion of adult trees in the forest.It was necessary to strengthen pest control for P.tabulaeformis forest,and Q.Liaotungensis needs to strengthen protection and take artificial assistance to promote regeneration.Moreover,policy support was also needed to conserve forest resources in the region.