[Impacts of thinning on canopy structure and understory light in secondary poplar-birch forests]
- PMID: 31257768
- DOI: 10.13287/j.1001-9332.201906.002
[Impacts of thinning on canopy structure and understory light in secondary poplar-birch forests]
Abstract
The variation of forest canopy structure and understory light caused by natural or human disturbances might account for environmental heterogeneity and species diversity in the understory. These factors play an important role in driving the structure, process and pattern in forest ecosystem. We set up two 0.25 hm2 permanent plots in secondary Betula platyphylla-Populus davidiana forests on the Taoshan Forest Farm, one of which was thinned in 2012 and the other one remained natural. The canopy images of two plots were collected by hemispherical photography technology from 2012 to 2016 and 2018. Analysis of variance and Markov matrix were applied to examine the dynamics of canopy structure, understory light, and canopy closing process after thinning. The results showed that thinning was effective in adjusting canopy structure and understory light availability. Such process lasted for a long time and the adjusting effect decreased over time. After thinning, the change rate of canopy structure and understory light decreased over time. The tree canopy quickly closed during the first three years and then reached a stable state. Understory light availability was positively correlated with canopy openness and negatively correlated with leaf area index. The correlation between understory scattered radiation and canopy structural parameters was the strongest. The correlation between canopy structure and understory light in the thinning plot was stronger than that of the control plot. After thinning, the recovery rate of canopy structure was related to the canopy openness, with larger canopy openness being accompanied with higher recovery rate. Thus, less time was required for the transfer to smaller canopy openness. The Markov matrix model could simulate changes in distributions of canopy structure and could be used to predict the dynamics of the canopy structure.
自然或人为干扰产生的森林冠层结构和林下光照差异是造成林下环境异质性、物种多样性的主要原因,对森林生态系统的结构、过程与格局具有重要作用.以桃山林场2块50 m×50 m的杨桦次生林固定样地为研究对象,分别作为间伐和对照样地,于2012—2016年、2018年获取样地冠层影像,通过方差分析、马尔科夫模型等方法分析其冠层结构、林下光照动态及间伐后林冠的恢复规律.结果表明: 间伐措施能显著调整冠层结构和林下光照,并能持续较长的作用时间,但调整效果随时间逐渐降低;间伐后冠层结构及林下光照的变化速度随时间推移而降低,间伐后前3年林冠恢复速度较快,3年后恢复速度降低并趋于平缓;林下光照与林冠开度呈显著正相关,与叶面积指数呈显著负相关,其中林下散射辐射与冠层结构参数的相关性最大,且间伐样地冠层结构与林下光照的相关性大于对照样地;间伐后冠层的恢复速度与林冠开度大小有关,林冠开度越大,林冠恢复越快,向更小林冠开度转移的时间越早.马尔科夫模型能够模拟冠层结构分布的变化,可用来预测冠层结构动态.
Keywords: Leaf area index; Markov matrix; canopy openness; hemispherical photograph; thinning.
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