青藏高原东缘3种次生林优势种的种群结构与数量动态

Structure and quantity characteristics of three secondary forests on the eastern margin of the Qinghai-Tibet Plateau

【目的】以青藏高原东缘甘肃南部3种主要次生林为研究对象,探讨其优势种种群结构和数量动态。【方法】选择具有代表性的辽东栎、红桦和糙皮桦种群,各设置8块40 m×40 m的样地,对样地内所有树木进行每木检尺,以测定的胸径数据为基础,以径级代替龄级,将胸径<3 cm作为Ⅰ龄级,其后以4 cm为标准进行龄级划分,统计各龄级个体数量并进行相关整理后,分析各种群的龄级结构,编制包括死亡率(q_(x))、消失率(K_(x))和平均期望寿命值(e_(x))等参数在内的种群静态生命表,绘制存活曲线,计算考虑外部干扰时的种群数量变化动态指数(V_(pi))、不考虑外部干扰时的种群数量变化动态指数(V′_(pi))和对外界干扰所承担的风险概率指数极大值(P_(max)),最后对未来经过2,4,6,8个龄级后各种群的数量动态进行时间序列预测,以揭示青藏高原东缘甘肃南部3种次生林优势种的种群现状、种群结构及预测种群未来发展趋势。【结果】①辽东栎、红桦和糙皮桦3种次生林种群Ⅰ龄级幼苗数量不足,均以Ⅱ龄级幼苗数量最多,分别占种群个体总数的43.62%,30.07%和43.30%;其后随着龄级的增大,种群个体平稳下降,虽然群落为稳定型,但是林木径级较小,各龄级个体数分布不合理。②辽东栎、红桦、糙皮桦种群的q_(x)和K_(x)在Ⅰ龄级最大,q_(x)分别为78.0%,72.0%和76.2%,K_(x)依次为151.3%,127.3%和143.5%,且随着龄级的增加,q_(x)和K_(x)均逐渐减小;各种群e_(x)随着龄级增加先增大后减小,辽东栎和红桦均在Ⅵ龄级最大,糙皮桦在Ⅴ龄级最大;种群结构均呈增长型,且存活曲线趋近于Deevery-Ⅲ型。③3种次生林种群结构的V_(pi)大于V′_(pi)且均大于0,P_(max)也均大于0,说明3种次生林均属于对外界干扰敏感的增长型种群。④时间序列预测结果表明,未来经过2,4,6,8个龄级后,各种群个体发展呈增长趋势,但辽东栎和红桦种群在发展过程中存在波动性,表现出前期略减、后期稳定的特征。【结论】3种次生林种群结构和发展趋势均呈稳定增长型,但是Ⅰ龄级幼苗数量不足,应采取禁牧、禁采等措施,保护幼苗成活,保证种群的更新发展。

【Objective】The purpose of study was to explore the population structure and quantity dynamics of dominant tree species in three secondary forests(Quercus wutaishansea Mary,Betula albosinensis Burk and Betula utilis D.Don)in southern Gansu on the eastern edge of Qinghai Tibet Plateau.【Method】Eight sample plots with size of 40 m×40 m were set up in each secondary forests.Then,data of all trees including tree species,tree height,DBH,crown width were collected.DBH was used to classify ages with DBH<3 cm as theⅠage-class and each age-class covered 4 cm.After the number of individuals in each age-class was counted and sorted out,the age-class structure of various groups was analyzed,the population static life table including mortality(q_(x)),disappearance rate(K_(x))and average life expectancy(e_(x))was compiled,and the survival curve was constructed.Then,the indexes of population(V_(pi)),population by external interference(V′_(pi))and maximum of probability in random disturbance(P_(max))were calculated.Finally,the quantitative dynamics of various groups after 2,4,6 and 8 age-classes in future were predicted.【Result】(1)The number ofⅠage-class seedlings of the three secondary forests populations was insufficient,and the number ofⅡage-class seedlings was the largest with contributions of 43.62%,30.07%and 43.30%to total number of individuals in Q.wutaishansea,B.albosinensis and B.utilis,respectively.When the age-class was older thanⅡ,the individual population decreased steadily with the increase of age-class.The community was stable,but the tree size-class was small and number distribution was unreasonable.(2)Main secondary forests had the largest q_(x) and K_(x) in theⅠage-class with q_(x) values of 78.0%,72.0%and 76.2%and K_(x) values of 151.3%,127.3%and 143.5%for Q.wutaishansea,B.albosinensis and B.utilis,respectively.The q_(x) and K_(x) values decreased gradually with the increase of age-class,while e_(x) of each population first increased and then decreased with the increase of age-class.Q.wutaishansea and B.albosinensis had the largest e_(x) in theⅥage-class,while B.utilis had the largest in theⅤage-class.The population structure showed an increasing trend and the survival curve was close to the Deevery-Ⅲtype.(3)The V_(pi) of the three secondary forests was greater than V′_(pi) and greater than 0,and P_(max) was also greater than 0,indicating that the three secondary forests were sensitive to external interference.(4)After 2,4,6 and 8 age-classes,the individual development of various groups would show an increasing trend,but the populations of Q.wutaishansea and B.albosinensis would fluctuate in the development process,showing the characteristics of slight decrease in the early stage and stable in the later stage.【Conclusion】The population structure and development trend of the three secondary forests were in stable growing trend,but the number ofⅠage-class seedlings was insufficient.Measures such as grazing prohibition and mining prohibition should be taken to protect seedlings and ensure the renewal and development of populations.