Litter fall collection method and a quantitative model of leaf fall were used to study the leaf-fall phenology of Betula platyphylla and Populus davidiana. Results indicated that the leaf fall of B. Platyphylla was obviously earlier than that of P. Davidiana. The initiation time and peak of leaf fall for B. Platyphylla were 41 days and 20 days earlier than those of P. Davidiana, respectively, but the two species completed their leaf fall on nearly the same day. Therefore, the duration of leaf fall of B. Platyphylla was 42 days longer than that of P. Davidiana. In addition, the concentration degree of leaf shedding of B. Platyphylla was much higher than that of P. Davidiana, and the peak production of leaf litter was only about one fifth of that of P. Davidiana. The higher nitrogen concentration and lower C : N ratio in the leaves of B. Platyphylla resulted in faster decomposition rate of leaves compared with P. Davidiana. It is concluded that although growing in the same environmental conditions, the two pioneer tree species might have very different ecological strategies in light interception and use efficiency as well as nutrient cycling.%用凋落物收集法和凋落物候模型研究了白桦(Betula platyphylla)和山杨(Populus davidiana)的叶凋落物候.结果表明:白桦叶凋落显著早于山杨,凋落开始时间和凋落高峰分别比山杨早41和20d,但它们的叶凋落结束时间基本相同,这导致白桦的凋落期比山杨长42 d.此外,白桦叶凋落集中程度也明显小于山杨,凋落峰值仅是山杨的五分之一.白桦的叶N质量分数较高,碳氮比较低,导致了白桦叶分解较山杨叶快.这体现了处于相同的环境条件,白桦和山杨在能量利用和养分循环方面可能具有不同的生态策略.
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