桥山林区麻栎种群不同发育阶段空间格局及关联性

为探究麻栎种群不同发育阶段的空间分布特征及关联性,以黄土高原南部桥山林区麻栎天然次生林为研究对象,用L(r)函数对麻栎种群不同发育阶段空间分布特征及关联性进行分析。结果表明:(1)样地内麻栎种群各发育阶段数量结构均为不规则倒"J"型,种群结构稳定,能实现持续更新。(2)麻栎种群总体的空间分布特征受生境异质性影响较大,纯林样地中,种群在0—10 m尺度上表现为高强度聚集分布,5—35 m尺度表现为低强度聚集;混交林样地中,0—5 m尺度上表现为高强度聚集分布,5—35 m尺度上则表现为低强度聚集分布。(3)随着种群的发育及尺度的增大,麻栎种群空间聚集强度减弱,纯林样地内,麻栎幼苗在0—6 m的小尺度表现为聚集分布,6—12 m尺度上表现为随机分布;幼树在各尺度上均表现为聚集分布;中龄树与成龄树在各尺度上均表现为随机分布。混交林样地中,仅幼苗在0—6 m尺度上表现为聚集分布,其余各阶段在各尺度下均趋于随机分布。(4)种群不同发育阶段不同尺度空间关联性不同,纯林样地中,幼苗与幼树在1—2 m小尺度上呈负相关,幼树与中龄树在8 m尺度呈正相关,其余各生长阶段之间在任意尺度上均无关联性;混交林样地中,幼树与中龄树在2—12 m尺度上表现为正相关,其余各生长阶段之间在各尺度上均无关联。在未来的森林经营中,应对不同发育阶段、不同生境的种群进行不同抚育措施,促进种群良性发育。

Spatial pattern and spatial association of Quercus acutissima at different developmental stages in the Qiaoshan Mountains

Spatial pattern and spatial association analysis are important in the study of population characteristics and interspecies relationships. To investigate the spatial distribution pattern and association in different developmental stages in a Quercus acutissima population, the natural secondary Q. acutissima forest of the Qiaoshan Mountains in the southern area of the Loess Plateau was used as our study area. One forest plot (50 m×50 m) was established in each Q. acutissima natural secondary pure forest (plot A) and Q. acutissima-Pinus tabuliformis natural secondary mixed forest (plot B). The coordinate of each Q. acutissima was mapped, the diameter at breast height and height of each individual were measured by plot to investigate means. We divided the individuals into four growth stages using the method of diameter class. The spatial distribution pattern and associations were analyzed using Ripley''s L(r) Function. The results showed the followings: (1)The quantity structure of each developmental stage of the Q. acutissima population in the Qiaoshan Mountains exhibited an irregular inverted "J" type, indicating a stable population structure with persistent regeneration capability. (2) The spatial distribution of the two populations was greatly influenced by habitat heterogeneity. Spatial distribution exhibited high aggregation at the scale of 0-10 m in plot A, whereas it showed low aggregation at the scale of 5-35 m. In plot B, the degree of aggregation changed quickly in response to habitat heterogeneity. It exhibited high aggregation at the 0-5 m scale and low aggregation at the 5-35 m scale. (3) With the development of populations and increase in scale, the spatial aggregation of the Q. acutissima population was reduced. In plot A, the seedling stage showed an aggregated distribution at the small scale of 0-6 m and a random distribution at the larger scale of 6-12 m. The sapling stage showed an aggregated distribution at all scales. The mid-mature stage and mature stage showed a random distribution at all scales. In plot B, all stages showed a random distribution at all the scales, except for the aggregated distribution of the seedling stage at the small scale of 0-6 m. (4) The spatial correlation between different growth stages and scales was discriminating in the two plots. In plot A, we found a negative correlation between the seedling and sapling stage at the 1-2 m scale. Positive correlation was found between the sapling and mid-mature stage at the 8 m scale. However, the relationship among other stages was not significant at any scale. In plot B, there was a significant positive correlation between the sapling and mid-mature stage at the 2-12 m scale. There was almost no correlation among other stages at any scales. Population distribution patterns were influenced by developmental stages, biological characteristics, and ecological factors. In future forest management, different managerial measures need to be taken to promote the regeneration of the population according to the different developmental stages and different habitats of the population.