Guangdong Ocean University, College of Agriculture,
以粤北车八岭2008年受冰灾破坏的山地常绿阔叶林为研究对象,设置2 hm2固定样地开展连续3a(2008-2010年)的群落调查,并采用半球面影像技术(Hemispherical photography)获取冠层结构和林下光照指标,分析灾后森林演替过程中冠层结构和林下光照的动态。研究发现:1)灾后森林恢复过程中,样地林下光照(直射光、散射光和总光照)均随林冠开度的减少、叶面积指数的增加而减少; 2)从2008到2010年,各年度冠层结构和林下光照的差异均极显著(P<0.0001),但年间差异程度有逐年减少的趋势;3)灾后森林恢复前3a,林下直射光对林下总光照的贡献大于散射光,其时空波动性也大于散射光;4)林冠开度对冠层结构的反映程度比叶面积指数高,冠层结构对林下散射光的影响比对直射光大。灾后林木先是迅速生长然后生长速度缓慢下来并逐渐稳定,随森林逐渐郁闭林下光照也随之减少,其中林冠开度用于评价冠层结构动态的效果更佳, 林下直射光比散射光的时空变化更复杂。
Natural disturbance is an important factor causing dynamic changes in forest canopies. An ice storm in southern China in 2008 was responsible for extensive damage to the forest ecosystem. The considerable distribution of canopy gaps created by the ice storm caused dynamic changes in the forest canopy. Therefore, studies to reveal the effects of the ice storm on forest regeneration and to monitor the restoration of damaged forest ecosystems will have significant implications for forestry research. Following the ice storm of 2008, a montane evergreen broad-leaved forest in Chebaling National Nature Reserve in northern Guangdong was investigated and a successive 3-year (2008-2010) community study of the 2 hm2 permanent plot was launched. We analyzed the changes in canopy structure (Canopy Openness and Leaf Area Index) and understory light (Transmitted Direct Solar Radiation, Transmitted Diffuse Solar Radiation and Transmitted Total Solar Radiation) in the forest following the ice storm using hemispherical photography to acquire canopy structure and understory light indexes. A quantitative study on the temporal and spatial variations in canopy structure and understory light as well as on environmental heterogeneity in the forest canopy is of considerable importance. Hemispherical photography is an example of optical remote sensing technology used to measure the parameters of canopy structure and understory light, and has now been widely recommended in the field of ecological research. The Kruskal-Wallis test (a non-parametric alternative to one-way ANOVA) and canonical correlation analysis were employed to analyze the changes in canopy structure and understory light. The main conclusions of this study are described in the following: 1) As the canopy openness shrank and the leaf area index increased, the understory light decreased in the forest during the recovery process following the ice storm; 2) A highly significant difference (P<0.0001) was detected in canopy structure and understory light during the 3 years, but between-year differences showed a tendency to decrease as the forest recovered from 2008 to 2010; 3) In the first three years of forest recovery, transmitted direct solar radiation demonstrated a greater spatial-temporal fluctuation and provided a greater contribution to total solar radiation than did transmitted diffuse solar radiation; 4) Canopy openness was more sensitive than leaf area index as an indicator of canopy structure change, while canopy structure had a greater influence on transmitted diffuse solar radiation than transmitted direct solar radiation. Initially, the trees in the ice storm damaged forest grew rapidly during the recovery period following the storm, but the growth slowed down gradually and stabilized. There was a gradual reduction in the understory light as the forest closed due to tree growth. Canopy openness is better for the evaluation of the dynamic effects of canopy structure. The spatial and temporal variations of transmitted direct solar radiation were more complex than transmitted diffuse solar radiation. Therefore, research to study the effects of an ice storm on canopy structure of a subtropical forest to reveal dynamics of canopy structure and understory light, and to monitor the restoration of a damaged forest ecosystem, will have significant implications for both theoretical and applied forest restoration efforts.