Betula platyphylla is a pioneer tree species after fire disturbance in forest communities in the Daxing'an Mountains of China. Bark, as an external structure of vascular cambium, plays an important role in protection and transport. To understand the survival strategy of B. platyphylla under fire disturbance, we analyzed the functional traits of inner and outer bark of B. platyphylla at different heights (0.3, 0.8 and 1.3 m) in natural secondary forest of the Daxing'an Mountains. We further quantified the explanation of three environmental factors (stand, topography and soil) and identified the key factors driving the changes in those traits. The results showed that the relative inner bark thickness of B. platyphylla in burned plot followed an order of 0.3 m (4.7%) > 0.8 m (3.8%) > 1.3 m (3.3%), which was 28.6%, 14.4% and 3.1% higher than that in the unburned plot (30-35 years without fire disturbance), respectively. The relative outer bark thickness and the relative total bark thickness showed similar pattern with tree height. Fire had different effects on other bark functional traits of B. platyphylla. The inner bark density of B. platyphylla in burned plot was significantly decreased by 3.8%-5.6% and water content was significantly increased by 11.0%-12.2%, compared with that in unburned plot across the three heights. However, the contents of carbon, nitrogen, and phosphorus in inner (or outer) bark were not significantly affected by fire. Further, the mean inner bark nitrogen content at 0.3 m in burned plot (5.24 g·kg-1) was significantly higher than that at the other two heights (4.56-4.76 g·kg-1). Environmental factors explained 49.6% and 28.1% of the total variation in inner and outer bark functional traits, respectively, with the highest single explanation (18.9% or 9.9%) of soil factors. Diameter at breast height was the most important factor affecting the growth of inner and outer barks. In summary, fire affected survival strategies of B. platyphylla (e.g., increased the resource allocation to the base bark) via changing the environment factors, which would help improve their defense ability under fire disturbance.
白桦是我国大兴安岭地区森林群落中火干扰后的先锋树种,树皮作为其维管形成层的外部结构,具有重要的保护和运输作用。本研究以大兴安岭天然次生林中的白桦为对象,分析火干扰下白桦树干不同高度(0.3、0.8和1.3 m)处内、外树皮的功能性状,量化林分、地形和土壤3类环境因素的解释度并明确驱动其变化的关键因子,揭示易火环境下白桦的生存策略。结果表明: 火干扰后白桦的相对内皮厚度表现为0.3 m处(4.7%)> 0.8 m处(3.8%)> 1.3 m处(3.3%),与对照(30～35年未发生火干扰)相比分别增加28.6%、14.4%、3.1%;相对外皮厚度及总树皮厚度随树干高度呈现相似的规律。火干扰对白桦其他树皮功能性状具有不同程度的影响。其中,火干扰后白桦3个高度内皮密度与对照相比显著降低了3.8%～5.6%,含水率则显著升高了11.0%～12.2%,而火干扰对内(外)皮碳、氮、磷含量的影响不显著,但火干扰后白桦0.3 m处内皮氮含量(5.24 g·kg-1)显著高于另2个高度(4.56～4.76 g·kg-1)。环境因子分别解释了内、外皮功能性状变化的49.6%和28.1%,其中土壤因子的单独解释最高,分别为18.9%、9.9%。胸径是影响内外皮生长的最关键因子。综上,火干扰通过改变环境影响白桦的生存策略,增加其对树皮基部的资源分配,提高白桦在火干扰环境下的防御能力。.
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