Bouchard Mathieu, Kneeshaw Daniel, Bergeron Yves
Groupe de Recherche en Ecologie Forestière Interuniversitaire (GREFi), Université du Quebec a Montréal, C.P. 8888, Succursale Centre-Ville, Montréal, QC H3C 3P8 Canada.
Ecology. 2006 Sep;87(9):2319-29. doi: 10.1890/0012-9658(2006)87[2319:fdassb]2.0.co;2.
In order to assess the long-term spatiotemporal influence of the spruce budworm in sub-boreal mixedwood forests, we studied the effect of three successive outbreaks in a region of western Quebec, Canada. We used dendrochronology to detect past outbreaks in three areas (111-185 ha), based on the recruitment age of balsam fir (Abies balsamea) and on growth patterns of white spruce (Picea glauca), the two main host species of this defoliating insect. We also used a series of aerial photographs taken between 1935 and 2003 to evaluate overstory mortality and post-outbreak succession patterns in these same areas. Individual outbreaks had a spatially homogenous impact on host species throughout the region, but successive outbreaks differed in intensity: the two outbreaks around 1910 and 1980 caused widespread mortality in the overstory, but an outbreak around 1945 had little impact, probably because the forest mosaic had not yet recuperated from the 1910 outbreak. No clear outbreak was detected in the later part of the 19th century. In portions of the study areas where the 1910 outbreak had a major impact, between 36% and 50% of the stands were reoccupied by balsam fir stands in the period up to the 1980 outbreak (cyclic succession), the rest being at least partly replaced by nonhost species such as Betula spp. Changes in forest composition after the 1910 outbreak were mostly associated with upper-slope positions in all study areas. The 1980 outbreak also had a higher impact than earlier outbreaks in lower-slope positions dominated by black spruce (Picea mariana)-balsam fir mixtures. These results suggest that, at the regional scale, the abundance of mature or over-mature balsam fir stands does not determine the outbreak cycle. When an outbreak occurs, however, its impact will be strongly constrained by forest characteristics such as stand composition and structure, which are themselves influenced by previous disturbances and slope position.
为了评估云杉芽虫对亚寒带混交林的长期时空影响，我们研究了加拿大魁北克西部一个地区连续三次爆发的影响。我们利用树木年代学，根据香脂冷杉（Abies balsamea）的招募年龄和白云杉（Picea glauca）的生长模式，检测了三个区域（111 - 185公顷）过去的爆发情况，这两种树是这种食叶昆虫的主要寄主物种。我们还使用了1935年至2003年期间拍摄的一系列航空照片，来评估这些相同区域的上层林冠死亡率和爆发后的演替模式。个别爆发对整个区域的寄主物种具有空间上的均匀影响，但连续爆发的强度有所不同：1910年左右和1980年左右的两次爆发导致上层林冠普遍死亡，但1945年左右的一次爆发影响很小，可能是因为森林镶嵌体尚未从1910年的爆发中恢复过来。在19世纪后期未检测到明显的爆发。在1910年爆发产生重大影响的部分研究区域，到1980年爆发时，36%至50%的林分被香脂冷杉林分重新占据（周期性演替），其余部分至少部分被桦树属等非寄主物种取代。1910年爆发后森林组成的变化在所有研究区域大多与上坡位置相关。1980年的爆发在以黑云杉（Picea mariana） - 香脂冷杉混交林为主的下坡位置也比早期爆发产生了更大的影响。这些结果表明，在区域尺度上，成熟或过成熟香脂冷杉林分的丰度并不能决定爆发周期。然而，当爆发发生时，其影响将受到森林特征（如林分组成和结构）的强烈限制，而这些特征本身又受到先前干扰和坡位的影响。
