Abstract
Estimating underlying mechanisms and dynamics from observed tree patterns can provide guidance for plantation management. Robinia pseudoacacia can reproduce via clonally produced ramets, leading to a complex distribution of stems. Three second generation plots and three third generation plots (each plot 50 m × 50 m) were established across a wide age range after clear-cutting in a Robinia pseudoacacia plantation in central China. We measured spatial coordinates, diameter at breast height (DBH) or diameter at basal stem, and heights of all recruits, as well as the coordinates and base diameter of all stumps, in six plots. The spatial pattern in different plots and the spatial relation between stumps and regenerations after clear-cutting were analyzed. To estimate the underlying processes of the observed patterns, we fitted Matérn and Variance-Gamma cluster processes to the observed dataset. The results revealed that the percentage of ramets from stumps decreasing with age in the two types of stands (from 40.4% to 30.1%, from 57.6% to 35.7%), and trees exhibited an aggregated distribution in all plots, but the degree of aggregation exhibited a decreasing trend with age, and aggregation occurred at different scale. Furthermore, a large proportion of ramets had their nearest neighbor at a short distance (<1 m) based on analysis of the nearest neighbour function. The bivariate analysis revealed that the spatial relation between stumps and ramets changed with age, and a repulsion trend was found between them in all the six plots. The Variance-Gamma process with covariate of Cartesian coordinates fitted the observed patterns better than others. The observed pattern was likely driven by root dispersal limitation, seed dispersal limitation, human disturbance, and intraspecific competition. Spatial patterns are important characteristics in forest stand structure, and understanding the pattern change and its underlying mechanisms could allow for better timing of artificial disturbances to optimize stand structure and promote stand growth.
Highlights
Regeneration plays a vital role during forest ecosystem restoration and sustainable management.It is essential to understand natural regeneration processes for economic and ecological reasons [1].Logging of natural forests over the last century has led to large areas of artificial forests and semi-natural forests
The number of R. pseudoacacia recruits varied from 1300 to 5171, and the mean diameter varied from 1.34 cm (±0.61 SD, plot III-1, diameter at basal stem) to 5.32 cm
Our findings indicated that there are differences in growth and spatial patterns among intergenerational stages and age stages of black locust stands in central-China, as well as the spatial correlation between stumps and SR
Summary
Regeneration plays a vital role during forest ecosystem restoration and sustainable management.It is essential to understand natural regeneration processes for economic and ecological reasons [1].Logging of natural forests over the last century has led to large areas of artificial forests and semi-natural forests. Forests 2019, 10, 1066 example, retaining tree when clear-cutting could increase the structural diversity [2], and natural regeneration could be improved by commercial thinning [3]. The shelterwood system can help prevent high losses of soil nitrogen during the start of regeneration [4], and appropriate regeneration can be ensured after combining seed-tree harvesting with the shelterwood and scarification in black spruce stands [5]. These studies have focused on regeneration growth, but there is a lack of understanding about spatial patterns and regeneration processes after anthropogenic disturbances such as clear-cutting and tending-felling
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