Litterfall collection is a non-destructive direct method to estimate forest leaf area index (LAI) and validate indirect LAI products. However, the potential errors associated with the variation in specific leaf area (SLA) are rarely explored. Here, we measured the SLA of leaf litter for each tree species in a temperate deciduous forest using the litterfall collection method from 2012 to 2018, and assessed the spatial and temporal variation in SLA and its consequence on LAI estimates. The results showed that the spatial and temporal variation in SLA for the 10 major species across the seven years ranged from 0.8% to 24.3%, with the variation across the nine permanent plots (20 m × 30 m) being higher than that within plot (five 1-m² traps), and interannual higher than seasonal. Across the 63 plot-years, the 10 simplified SLA sampling protocols introduced the errors in LAI by −12.4% to 22.2% relative to the reference protocol (sampling leaves from each trap at each collection date for the major species). Applying the SLA obtained from one trap in each plot, one plot, at the leaf fall peak for each year, or for a single year induced the errors in LAI by –3.7% to 2.9%, −6.4% to 14.7%, −9.2% to 4.7%, and −8.1% to 8.6%, respectively. Considering the trade-off between inter-plot and interannual variation, we recommend sampling from one-trap for each plot at the leaf-fall peak for measuring SLA and quantifying the spatial pattern of LAI, and sampling each species in the typical plot for measuring SLA and monitoring the temporal fluctuation in LAI. The tight relationship between the MODIS and ground reference LAI across the seven years (R² = 0.77) validated the use of MODIS LAI to study the long-term change in forest LAI. These findings help to establish a standardized protocol for long-term accurately measuring forest LAI with the litterfall collection.

凋落物收集是一种非破坏性的直接方法，用于估算森林叶面积指数（LAI）和验证间接LAI产品。但是，很少探讨与特定叶面积（SLA）变化相关的潜在错误。在这里，我们使用2012年至2018年的凋落物收集方法，测量了温带落叶林中每种树种的凋落物的SLA，并评估了SLA的时空变化及其对LAI估计的影响。结果表明，在7年中10个主要物种的SLA时空变化范围从0.8％到24.3％，其中9个永久样地（20 m×30 m）的变化高于样地（五个1-m ²陷阱），并且每年高于季节。在63个样地年中，相对于参考方案（主要物种在每个采集日期从每个陷阱采集叶片），10个简化的SLA采样协议引入的LAI误差为-12.4％至22.2％。在每一年或一年的落叶高峰期应用从每个地块，一个地块的一个陷阱获得的SLA，导致LAI的误差为–3.7％至2.9％，− 6.4％至14.7％，−9.2 ％分别为4.7％和-8.1％至8.6％。考虑到地块间和年际变化之间的权衡，我们建议从每个陷阱的一个陷阱处取样，以测定叶落峰时的SLA和量化LAI的空间格局，并在典型地块中对每个物种进行抽样以进行测量SLA和监视LAI中的时间波动。R ²  = 0.77）验证了使用MODIS LAI研究森林LAI的长期变化。这些发现有助于建立标准化协议，以长期准确地利用凋落物收集量来测量森林LAI。