高山林线作为树木分布的高度上限，是全球范围最重要的植被过渡带之一，是目前全球变化重点监测的区域之一。林线树木生长对环境变化十分敏感，限制性因子微弱的改变会立刻影响到树木的生长。本文在华北芦芽山荷叶坪北坡高山林线， 2011年1月1日到2011年12月31日对林线树种华北落叶松和白杄径向变化和相关环境因子进行了动态监测，研究了林线树木径向生长对环境因子的响应关系，通过分析得到了以下主要结论： 1）在生长季晴天条件下，林线树种华北落叶松和白杄的茎干日变化规律相同，即茎干日变化划分为3个阶段：1）收缩阶段；2）膨胀阶段；3）增长阶段。在雨天，受降雨的影响树木茎干日变化动态有所变化，会出现持续的茎干膨胀，之后为不断的收缩变化。2）在生长季（5-9月）中，华北落叶松和白杄的月均径向日变化规律基本一致。茎干径向最大值基本出现在早晨时分，最小值出现在午后傍晚时分。在不同的月份间，日变化的幅度和时间节点存在一定差异。3）华北落叶松和白杄的茎干径向日变化量（ΔR）在冬季（12-2月）相对较小，此间出现较明显的茎干波动变化，主要是气温急剧变化导致茎干出现冻融作用而导致的。在生长季，茎干径向日变化量（ΔR）受降水的影响较大。4）华北落叶松和白杄茎干年径向累积变化曲线都基本呈现出“S”型。1-4月，茎干径向变化相对稳定，变化幅度相对较小。5月份，为树木茎干的水分恢复时期，茎干因水分恢复而表现出大幅度的膨胀。6-7月为茎干生长的快速时段，径向生长速率较大。8-9月，进入生长季末期，茎干变化进入一个相对稳定的平台期。9月份之后，树木茎干表现出不断的收缩，之后逐渐进入冬季的休眠期。5）通过Gompertz模型对生长季林线树木径向生长的拟合发现，整个生长季树木径向生长呈现出典型的“S”型曲线。树木茎干生长速率表现为单峰型曲线，最大生长速率出现在第171天（6月20日），即出现在一年中白天最长的夏至日（6月22日）左右。生长季中，华北落叶松茎干径向生长最大速率和生长量都要略高于白杄。6）在生长季的不同阶段，影响华北落叶和白杄茎干径向累积变化的环境因子略有差异。通过分析发现，在生长季中土壤温度和土壤含水量是影响林线树木径向生长的主导环境因子。

Treeline, defined as the upper limit of altitudinal tree distribution, is one of the most conspicuous vegetation boundaries in the world, which has become an important field of global change research. Tree growth of treeline is very sensitive to environmental changes, and it may be immediately influenced by weak changes of the limiting factors. In this paper, stem radial growths of Larix principis-rupprechtii and Picea meyeri were measured by using dendrometer from 1-Jan 2011 to 31-Dec 2011, and the environmental factors of treeline of Luya Mts were also dynamically monitored. The main conclusions were as follows:1. In the clear days during the growing season, the diurnal stem variation patterns of Picea meyeri and Larix principis-rupprechtii at the treeline were resolved into three phases: (1) contraction, (2) expansion, (3) radius increment. In rainy days, stem radial variations were affected by precipitation. Stem showed a continuous expansion when precipitation occurred, and then a continuos contraction. 2. The monthly average daily stem radial variations of Picea meyeri and Larix principis-rupprechtii in the growing season were similar. The maximum stem radius appeared early in the morning, and the minimum value in the late afternoon. There were some differences between the diurnal variation amplitude and time node in different months of the growing season.3. The daily stem radial variations (ΔR) of Picea meyeri and Larix principis-rupprechtii were relatively small in winter（Dec.-Feb.）, and the obvious changes in the stem were related to daily stem freeze-thaw cycles due to rapid air temperature changes. Stem radial variations of trees at treeline were manily affected by precipitation in the growing season（May.-Sep.）.4. Seasonal changes of cumulative radial variation of Picea meyeri and Larix principis-rupprechtii showed an “S” shape curve within a year. The stem radius was relatively stable with less change in the months of January to April. Due to stem water rehydration in May, the stem radius showed a large swelling amplitude. The radial growth rates of Picea meyeri and Larix principis-rupprechtii were larger from June to July. The stem variation of tree at the treeline entered a relatively stable period from Augest to September. The stem of trees at the treeline showed a continous contraction, and then entered the dormant period in winter.5. The results of curver fitting based on Gompertz model showed that tree radial growth showed a typical “S” curve during the growing season, and the rate of tree growth appeared a single peak curve. The maximum growth rates of Picea meyeri and Larix principis-rupprechtii occurred at 20-Jun, around the time of maximum day length (summer solstice). The growth amount and the maximum growth rate of Larix principis-rupprechtii were larger than Picea meyeri.6. The dominant factors controlling the radial variation were inconsistent in different periods of the growing season. Soil temperature and soil water content were the most important environmental factors affecting radial growth in the growing season.