暖温带地区3种森林群落叶面积指数和林冠开阔度的季节动态

 以辽东栎(Quercus liaotungensis)为主的落叶阔叶林、华北落叶松(Larix principis-rupprechtii)林和油松(Pinus tabulaeformis)林是暖温带林区具有代表性的森林群落类型。该研究应用国内外流行的半球图方法，通过对这3种森林群落叶面积指数和林冠开阔度的测定和综合比较，分析了叶面积指数和林冠开阔度的季节动态，揭示了暖温带地区不同类型森林群落叶面积指数和林冠开阔度的特征。研究结果表明，落叶阔叶林(优势种为辽东栎、棘皮桦(Betula dahurica)和五角枫(Acer mono))和华北落叶松林两种落叶森林群落的叶面积指数值均随生长季的到来而呈现增长的趋势，最大值出现在8月；林冠开阔度值随着生长季的到来而下降，最大值出现在11月。落叶阔叶林的叶面积指数和林冠开阔度的季节动态较之华北落叶松林明显。油松是常绿树种，其群落叶面积指数和林冠开阔度的变化程度均不明显，但林冠开阔度的变化趋势也是与叶面积指数的变化趋势相反。通过计算得出叶面积指数和林冠开阔度相关显著，并且呈现指数回归的关系。此研究结果为以遥感途径获取暖温带地区叶面积指数提供了地面校正依据，为研究该地区植被林冠的异质性及其造成的影响，以及进一步对该地区林分、景观和区域尺度上碳、水分和通量等方面的模拟提供了基础数据。

DYNAMICS OF LEAF AREA INDEX AND CANOPY OPENNESS FOR THREE FOREST COMMUNITIES IN THE WARM TEMPERATE ZONE OF CHINA

Aims Leaf area index (LAI) and canopy openness are two important biophysical parameters of canopy structure related to water and carbon fluxes and light interception. They are not only key variables in ecological and climate models, but also important indicators of forest ecosystem productivity. Accurate estimates of LAI and canopy openness are required in studies of ecophysiology, atmosphere-ecosystem interactions, and global change. Many researches have been done in Dongling Mountain in the warm temperate zone; however, fewer studies have focused on LAI and canopy openness. The objective of this study is to measure and analyze the dynamics of LAI and canopy openness of three typical forest communities in this area. Results will be useful in testing and validating LAI estimations based on remote sensing, providing reference for study of canopy heterogeneity and its effects and modeling carbon, water and energy fluxes from stand to landscape levels. Methods We used hemispherical photographs taken from the ground through a fisheye lens for indirectly assessing LAI and canopy openness. Photos were taken in May, August, September and November 2005 in deciduous broad-leaved forest (DBF), Larix principis-rupprechtii forest (LF) andPinus tabulaeformis forest (PF). Important findings The LAI of DBF and LF increased gradually with plant growth and development to August. The lowest value of canopy openness appeared in November. DBF maintained a higher LAI in August and was more open in November compared to LF. For PF, we observed few changes of LAI and canopy openness, which we attribute to leaf retention of this evergreen species. In all forests, canopy openness varied inversely with LAI. The correlation was exponential and significant; therefore, canopy openness is a good indicator of LAI in these forests .