作 者 ：郭志华,向洪波,刘世荣*,李春燕,赵占轻
期 刊 ：生态学报 2010年 30卷 5期 页码：1200~1209
Keywords:leaf area index, leaf litter collection, sampling strategy, deciduous broadleaf forest,
摘 要 ：叶面积指数(LAI)是植被冠层结构的一个重要参数，它不仅是许多生态和气候模型的重要输入变量，而且是生态系统动态变化监测的一个重要指标。LAI可通过各种间接和直接的手段来观测，而间接观测的LAI值常常需要直接的观测数据来校验。落叶收集法是一种广泛使用的直接观测LAI的方法，过去的研究还未发现有涉及落叶收集的取样技术及其观测精度的内容。对长白山和北京地区落叶阔叶林的落叶进行了3a的观测，每年一次性收集落叶样品分析，研究结果表明：①不同层次落叶的含水量差异巨大，且落叶含水量的日变化明显。上下层落叶的含水量绝对值差异高达10%以上，日变化绝对值差异高达20%以上。因此，在野外收集落叶样本时，为减小落叶含水量变化所导致的LAI观测误差，应从上到下直到地面进行取样，且尽可能多地收集落叶样本。②在落叶阔叶人工林和天然林里，无论样地的大小(1hm2或30m×30m样地)，无论取样单元的大小(1m2或25m2分辨率)，林内的LAI分布很不均匀，LAI介于0-15.5(1m2分辨率的1hm2样地)或者2.6-9.1(25m2分辨率的30m×30m样地)。③要准确测定落叶林的LAI，收集落叶的样地面积越大越好，且尽量选择地势平坦的样地。对于1hm2或者30m×30m大小的样地，可随机布设一个10m×10m的小样地来观测，精度分别可达85%、80%。④10m×10m小样地的LAI观测，可将其分为4个相邻的5m×5m小样进行取样。对每个5m×5m小样，快速的取样方法是：Ⅰ. 随机布设6个1m2取样，这样取样可以保证在99%概率水平上，100m2、30m×30m和1hm2样地的LAI观测精度分别为90%、75%、70%左右。Ⅱ. 随机布设11个1m2取样。可以保证在99%概率水平上，100m2、30m×30m和1hm2样地的LAI观测精度分别为94%、80%、75%左右。
Abstract:Leaf area index (LAI), an important biophysical parameter of canopy structure, is not only a variable of significance to ecological and climatic models, but also a indicator for monitoring ecosystem dynamic. LAI can be estimated using various indirect and direct methods. The leaf litter collection method is widely used as a direct method to measure LAI in deciduous forests. Indirect measurements using radiation transmittance and gap fraction theory are often compared and calibrated by direct litter fall measurement, which is considered as a reference method. However, few studies have addressed the question of sampling strategy and the precision of LAI estimation by leaf litter collection so far. This study examined the above methodology with disposable leaf litter collection in the deciduous forests in Changbai Mountain and Beijing region after defoliation. The main results were showed as follows: (1) The difference of moisture content between the upper and lower layer of the leaf litter was significant with the absolute variation of 10.0% and the diurnal variation of the leaf litter moisture content was also significant with the absolute variation of 20%. Therefore, litter samples must be directly collected as much as possible from top to bottom layer in order to reduce the error of LAI measurement caused by leaf litter moisture content variability. (2)The distribution of LAI measured either in plantation or natural forests was uneven, regardless of sampling size (1 m2 or 25 m2) and the size of sampling units at resolution of 1 hm2 plot or 30 m×30 m plot. The variation ranged from 0 to 15.5 (at 1m2 resolution) or from 2.6 to 9.1 (at 25m2 resolution). (3) The larger area of the litter sampling, the higher accuracy of LAI estimation in deciduous forests, and the sampling should be conducted in a flat land surface, For a plot of 30 m×30 m or 1 hm2, a 100 m2(10m×10m) subplot should be randomly sampled, and this led to the precision of LAI estimation up to 85% and 80%, respectively. (4) For the subplot (10m×10m), the four adjacent 5 m × 5m sub-plots could be further divided and sampled. The rapid measurement for each 5 m × 5m sub-plot was conducted in the following: Ⅰ Six sampling units of each 1m2 in size were randomly set up and the precision of LAI estimation in 100 m2 plot, 30 m×30 m plot and 1hm2 plot were 90%, 75% and 70% respectively (at the level of 99% probability). Ⅱ Eleven sample units of each 1m2 in size were randomly set up and the precision of LAI estimating in 100 m2 plot,30 m×30 m plot and 1hm2 plot were about 94%, 80%, and 75% respectively (at the level of 99% probability).
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