白龙江沙滩林场次生林群落优势种群结构与生态位特征

Dominant population structure and niche of secondary forest community in the Shatan forest farm in Bailongjiang River forest region

【目的】了解甘肃白龙江林区沙滩林场次生林群落的生存现状,预测群落发展趋势,为次生林的科学经营提供理论依据。【方法】以云杉人工林退化形成的次生林群落为对象,设置50 m×50 m的标准样地6块,测量样地内胸径(D)≥3 cm的全部乔木的胸径、树高、冠幅,并记录林木生长状况;对胸径(D)<3 cm的乔木幼苗、幼树,测量并记录其地径、高度、冠幅和林木生长状况;并在每个样地设置3个10 m×10 m的灌木样方,调查灌木物种组成、数量等。基于以上调查数据,以径级代替龄级分析优势种群的年龄结构,运用数量化方法研究优势种群的数量化动态,并以物种重要值作为生态位的计测指标,计算优势种群生态位宽度,分析种间总体联结性。【结果】次生林群落为岷江冷杉桦木林群落,乔木层共有树种13种,云杉已大量死亡。现存群落中,岷江冷杉种群结构完整,幼龄个体比例大,存活率高,为增长型种群;桦木(红桦和糙皮桦)幼龄个体比例低,存活率不高,已呈现出衰退趋势;槭树、花楸等小规模种群结构多不完整。种群数量化分析表明,各种群生存状态不稳定,易受随机干扰,受随机干扰时岷江冷杉种群最稳定,红桦种群次之,槭树、花楸等种群结构均不稳定。岷江冷杉种群在乔木层和灌木层均有最大的生态位宽度;桦木在乔木层的生态位宽度仅次于岷江冷杉,优势明显,但其更新不良,在灌木层不具优势。乔木层、灌木层物种间总体均表现为不显著正关联。【结论】研究区次生林群落为正向演替,种群优势度与生态位随环境变化而改变,各种群结构与功能处于相互适应的变化阶段,群落结构尚不稳定。桦木种群在乔木层优势尚存,但在灌木层更新受到限制,不具备发展成优势种群的条件;云杉人工林则必被淘汰;岷江冷杉在乔、灌木层均有较大优势和生态位宽度,表现出进一步扩散的可能。因此本研究区次生林的经营应以培养冷杉林为主,为冷杉林的生长创造有利条件。

【Objective】This study clarified the survival situation of secondary forest community in the Shatan forest farm of Bailongjiang River forest region in Gansu and predicted the development trend to provide basis for scientific management of secondary forests.【Method】The secondary community formed by the degradation of artificial spruce forest was taken as the object,and 6 sample plots of 50 m×50 m were set up.The DBH,height and crown width of trees with DBH≥3 cm in sample plots were measured and the growth status was recorded.The ground diameter,height,crown width and growth status of trees with DBH<3 cm were measured and recorded one by one.Three shrub plots of 10 m×10 m were set up in each sample plot to investigate species composition and quantity.Based on these survey data,the dominant population age structure was analyzed,the population dynamics were studied by quantitative method,and the species important value was used as the niche measurement index to calculate the Levins niche breadth and analyze the overall interspecific association.【Result】Abies faxoniana and Betula forest communities were the major community of the secondary forests.There were 13 kinds of trees in arborous layers.Artificial Picea asperata forest had dead trees in large numbers.A.faxoniana forest was an increasing population because of its integral population structure,high percentage of seedlings and survival rates.Betula forest showed lower percentage of seedlings and survival rates,and appeared a recession trend already.Among the existing communities,others small-scale populations were incomplete of structure.Population quantitative analysis indicated that all populations had unstable living conditions and were vulnerable to random interferences.A.faxoniana forest populations had the most stable structure,followed by Betula albo-sinensis forest.A.faxoniana forest population owned biggest niche breadth in arborous and shrub layers,while Betula had great advantages in arborous layers but was disadvantaged in shrub layers because of poor regeneration ability.Overall,there was insignificant positive correlation among species in arborous and shrub layers.【Conclusion】The secondary forest communities had positive succession,population dominance and ecological niche changed with environment,and population structures and functions were still at mutual adaptation and changing stage with unstable community structure.The Betula forest population was still dominant in the arbor layer,but limited in the shrub layer without possibility to develop into dominant population.The artificial P.asperata forest would be eliminated.A.faxoniana had large advantage and niche width in both arborous and shrub layers with the possibility of further expansion.The management of secondary forests in the study area should focus on cultivating A.faxoniana forest and creating favorable conditions.