火烧伤害对兴安落叶松树干径向生长的影响

在大兴安岭塔河林业局瓦拉干林场22支线截取3个兴安落叶松(Larix gmelinii)火疤圆盘,预处理和交叉定年后,测定垂直年轮(径向)和沿年轮(横向)方向2次火烧间的年轮宽度变化.通过生长趋势拟合、火烧后生长面积与正常(理论)生长面积比较,分析火烧伤害对兴安落叶松树干生长的影响.结果表明:火烧后横向年轮生长呈现出窄—宽—正常的趋势,这种趋势可以用3次曲线来拟合,即y=0.01x3-0.14x2+ 0.85x+ 0.56(DF=3,F=227.7,P＜0.0001,y为平均年轮宽度,x为偏离火烧点距离).在本文分析的3个圆盘中,火烧后的横向生长释放都出现在距火烧部位1/3范围内.火烧后径向上年轮宽度变化规律也较为明显,即在火灾后的几年时间内,年轮宽度值较火灾前都呈增加趋势.火烧后3个圆盘的径向生长释放持续时间分别为14、5a和11a.通过面积计算整体来看,火烧导致圆盘1较正常情况下损失了67.2％,圆盘2比正常情况下增加了6.6％,圆盘3增加了13.7％.上述分析表明,火烧导致的径向生长损失,可以较好地由横向和径向生长释放予以补偿,但是具体补偿多少因烧伤程度不同而有差异.火烧可直接改变树干径向生长变化,同时,这种变化也受其他因素影响,例如像树龄、树种特性、火灾间隔期等因素,这些因素的差异就可能导致补偿程度的不同.

Effects of fire damages on Larix gmelinii radial growth at Tahe in Daxing'an Mountains, China

Daxing'an Mountians was one of the most important forest areas in China, and also an area which was prone to suffering forest fires. Forest fires will damage tree trunks and lead to carbon losses. Fire damages, however, will also produce a stimulus in trees, which can compensate for the carbon losses caused by this injury. Well then, how many carbon losses could be compensated for by this stimulated callus due to fire damages? Three fire-scar discs of Larix gmelinii were collected at Walagan forest farm, Tahe Forest Bureau, Daxing'an Mountains, China. Discs were pretreated and the precise calendar dates were determined with cross-dating method. Variations of tree-ring widths along transverse and radial directions after firing were measured. Bole growths before and after firing were compared to discuss the effects of fire damages on bole growths of Larix gmelinii. Results showed that transverse tree-ring widths (along ring) after medium and low-intensity fires showed a narrow-wide-normal trend. This growth trend can be fitted by a cubic curve of y = 0.0069x³-0.1435x² + 0.8485x + 0.5586 (DF = 3, SS = 0.62, MS = 0.21, F = 227.7, P<0.0001), where y is mean tree-ring widths, and x is distances from fire wound points. The reasons causing this trend may be due to the following two points: (1) near the wound points, trees will be separated itself from the injured parts. Chemical protection zones will be produced near the wounds to limit the diffusion of rot organisms and form the anti-corrosion layer in cambiums to protect the new growth after fires. Meanwhile, the onset of cambial activities was late and weak; (2) the parts slightly away from the wound points, the nutrients originally supplied to the burned area gathered here. The losses of bole radial growth due to fire damages can be compensated for by abnormal increases of tree growth after fires, but the amounts of compensation varied in different trees and fire intensity. Among these three discs, transverse growth release stimulated by forest fires all were confined within the one third distances from fire points. Year-to-year variations of radial growth were also shown clearly. Tree-ring widths increased after fires. Times of radial growth releases in these three discs were 14, 5 and 11 years, respectively. By comparing the areas of actual burned and theoretical growth discs, the radial growth for disc 1 decreased 67.2% due to fire damages, while the growths for disc 2 and disc 3 increased 6.6% and 13.7%, respectively. In summary, the losses of tree bole radial growth caused by fires can be well compensated by transverse and radial growth release, but the amounts of compensation depended on burnt degrees of trees. Therefore, forest fires could possibly cause the variation of tree bole radial growth. Additionally, tree growths after fires were also influenced by many other factors, such as tree age, species trait, and fire characteristics. Differences in these factors will lead to different compensations.