地形和森林植被因子对落叶松毛虫越冬代发生及数量的影响

目的 探讨地形和森林植被对落叶松毛虫越冬代发生的影响,并明确这两类因素与落叶松毛虫发生数量的关系,为该类虫害的防治提供科学参考。 方法 在大兴安岭落叶松毛虫主要分布区域的不同林型中设立142块20 m × 20 m的样地,调查地形、森林植被等因子,以及落叶松毛虫幼虫数量。运用二元Logistic回归和数量化理论Ⅰ分别建立落叶松毛虫发生概率模型和发生数量化模型,并进行模型评估。 结果 发生概率模型的判别精度较高 (AUC=0.826),坡向和草本盖度为影响落叶松毛虫发生的关键因子,阴坡发生概率最低,而阳坡最高。随着草本盖度的增加,落叶松毛虫发生概率增加。坡向、坡度等级、坡位、海拔、草本盖度和林分密度不同的林分的落叶松毛虫发生数量存在显著差异(P<0.05)。用坡向、坡度等级、坡位、郁闭度和林分密度5个因子建立的数量化模型与全因子模型拟合度差异小,决定系数 (R2)分别为0.635和0.685,均方根误差 (RMSE)分别为0.964和0.936。数量化模型显示,落叶松毛虫发生数量阴坡最少、阳坡最多。而随坡度等级增加,发生数量随之减少,山脊的落叶松毛虫发生数量最多。同样,森林郁闭度增加或林分密度降低,落叶松毛虫发生数量随之增多。 结论 研究揭示落叶松毛虫在阳坡、平坡和山脊的林分易发生,应作为防治重点,而配合补植、疏伐和定期除草等森林经营措施,有助于压低种群。

Effects of Topography and Forest Vegetation Factors on Occurrence and Population Size of Overwintering Dendrolimus superans

Objective The objective is to explore the influences of topography and forest vegetation on the occurrence probability of overwintering Dendrolimus superans and clarify the relationship between these factors and the occurrence quantity of Dendrolimus superans, which will provide scientific reference for the prevention and control of the infestations of this pest. Method Factors such as topography, forest vegetation, and the number of larvae of Dendrolimus superans were investigated in 142 plots (20 m × 20 m) of different forest types established in the main distribution area of Dendrolimus superans in the Great Xing’an Mountains. The binary logistic regression and the theory of quantificationⅠ were used to establish the models of the occurrence probability and quantity of Dendrolimus superans, respectively, and the performance of these models was evaluated. Result The discriminant accuracy of the probability model was relatively high (AUC=0.826), the slope aspect and herb cover were the key factors affecting the occurrence probability of Dendrolimus superans, the occurrence probability of which was the lowest on shady slopes and was the highest on sunny slopes. The occurrence probability increased with the increase of herb cover. There were significant differences in the number of Dendrolimus superans in the stands with different slope aspects, levels of slope gradients, slope positions, altitudes, herb coverage, and stand density (P<0.05). The model of quantification established by the five factors of slope aspect, levels of slope gradient, slope position, canopy cover, and stand density had little difference in fitting degree from the model established by the full factors. The coefficient of determination (R2) of them was 0.635 and 0.685, respectively, and their root mean square error (RMSE) was 0.964 and 0.936, respectively. The model of quantification showed that the occurrence quantity of Dendrolimus superans was the least on the shady slope and the most on the sunny slope. As the levels of slope gradient increased, its occurrence quantity would decrease. The occurrence quantity of Dendrolimus superans was the most on the ridges. Similarly, with the increase of canopy cover, or the decrease of stand density, the occurrence quantity of Dendrolimus superans would increase accordingly. Conclusion The study revealed that Dendrolimus superans were prone to occur on sunny slopes, flat slopes, and ridges, which should be the focus of prevention and control, which forest management practices such as replanting, thinning and regular weeding could help restrain the population growth.