Key message

Simulated spruce budworm (SBW; Choristoneura fumiferana (Clem.)) defoliation generally becomes ubiquitous in 3 years after its initiation in agreement with historical observations despite varying environmental and stand conditions over large ranges. Current-year defoliation has almost no correlation with defoliation more than 1 year ago at the same location, which may be related to the role of SBW dispersal in sustaining defoliation across space and time. Mitigation practices like insecticide spraying may be more efficient if applied early to initial spots (epicenters) of defoliation, while management probably should focus on improving forests’ resilience to withstand repeated defoliation by altering species composition.

Context

SBW defoliation during its periodic and extensive outbreaks greatly affects forest productivity at large spatial and temporal scales. A generalized modeling framework that simultaneously accounts for both highly variable spatial and temporal dynamics of SBW outbreaks has not been developed.

Aims

To develop a flexible parametric spatiotemporal model to explicitly predict defoliation in continuous space and time in order to evaluate the dynamics of SBW outbreaks across a complex forested landscape.

Methods

A novel model was developed on extensive defoliation data covering approximately 50,000 km² and 10 years of the last SBW outbreak during the 1970s and 1980s in Maine, USA. Simulations of various outbreak scenarios were performed using this model.

Results

The developed model provided a sufficient fit of the data (R² of 0.63 and mean bias of +0.3%) and was relatively consistent with expectations. Simulations show that defoliation generally becomes ubiquitous in 3 years despite varying environmental and stand conditions. Current-year defoliation has almost no correlation with defoliation more than 1 year ago at the same location, which may be related to the role of SBW dispersal in sustaining defoliation across space and time.

Conclusion

Mitigation practices like insecticide spraying may be more efficient if applied early to initial spots (epicenters) of defoliation, while management probably should focus on improving forests’ resilience to withstand repeated defoliation by altering species composition. Our model provides quantitative information flexible in spatial and temporal scales yet directly usable in existing forest growth and yield modeling frameworks and management decision support systems. This generalized spatiotemporal model is readily extendable for evaluating spatial and temporal dynamics of other forms of defoliation across complex forest landscapes.

中文翻译：

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评估美国缅因州森林茂密景观中的云杉bud虫暴发的时空动态

关键信息

尽管环境和林分条件在很大范围内变化很大，但模拟云杉芽虫（SBW；Choristoneura fumiferana（Clem。））的脱叶一般在其萌发后的3年内与历史观察一致，普遍存在。当前一年的落叶与一年多以前在同一地点的落叶几乎没有关联，这可能与SBW分散在维持时空中的落叶中所起的作用有关。如果将杀虫剂喷洒等减缓措施提早应用到落叶的初始点（中心），则可能会更有效，而管理工作可能应着重于提高森林的适应力，以通过改变物种组成来抵御反复的落叶。

语境

SBW在其周期性和大范围爆发中的落叶在很大的时空范围内极大地影响了森林的生产力。尚未开发出能够同时说明SBW爆发的时空动态高度变化的通用建模框架。

目的

开发一个灵活的参数时空模型，以明确预测连续空间和时间中的落叶，以便评估整个复杂森林景观中SBW爆发的动态。

方法

根据广泛的落叶数据，开发了一种新颖的模型，该数据覆盖了大约50,000 km ²和1970年代和1980年代在美国缅因州的上一次SBW爆发的10年。使用此模型对各种爆发情况进行了模拟。

结果

开发的模型提供了足够的数据拟合度（R ²为0.63，平均偏差为+ 0.3％），并且与预期相对一致。模拟表明，尽管环境和林分条件各不相同，但脱叶一般在3年内变得普遍。当年的落叶与一年多以前在同一地点的落叶几乎没有关联，这可能与SBW分散在维持时空中的落叶中所起的作用有关。

结论

如果将杀虫剂喷洒等减缓措施提早应用到落叶的初始点（中心），则可能会更有效，而管理工作可能应着重于提高森林的适应力，以通过改变物种组成来抵御反复的落叶。我们的模型提供了在时空尺度上灵活的定量信息，但可直接用于现有的森林生长和产量建模框架以及管理决策支持系统。这种广义的时空模型很容易扩展，以评估复杂森林景观中其他形式的落叶的时空动态。