Ali Qasim, Bauch Chris T, Anand Madhur
Department of Applied Mathematics, Western University, London, Ontario, Canada.
Department of Mathematics and Statistics, University of Guelph, Guelph, Ontario, Canada; Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario, Canada.
PLoS One. 2015 Oct 2;10(10):e0139353. doi: 10.1371/journal.pone.0139353. eCollection 2015.
The transportation of camp firewood infested by non-native forest pests such as Asian long-horned beetle (ALB) and emerald ash borer (EAB) has severe impacts on North American forests. Once invasive forest pests are established, it can be difficult to eradicate them. Hence, preventing the long-distance transport of firewood by individuals is crucial.
Here we develop a stochastic simulation model that captures the interaction between forest pest infestations and human decisions regarding firewood transportation. The population of trees is distributed across 10 patches (parks) comprising a "low volume" partition of 5 patches that experience a low volume of park visitors, and a "high volume" partition of 5 patches experiencing a high visitor volume. The infestation spreads within a patch--and also between patches--according to the probability of between-patch firewood transportation. Individuals decide to transport firewood or buy it locally based on the costs of locally purchased versus transported firewood, social norms, social learning, and level of concern for observed infestations.
We find that the average time until a patch becomes infested depends nonlinearly on many model parameters. In particular, modest increases in the tree removal rate, modest increases in public concern for infestation, and modest decreases in the cost of locally purchased firewood, relative to baseline (current) values, cause very large increases in the average time until a patch becomes infested due to firewood transport from other patches, thereby better preventing long-distance spread. Patches that experience lower visitor volumes benefit more from firewood movement restrictions than patches that experience higher visitor volumes. Also, cross-patch infestations not only seed new infestations, they can also worsen existing infestations to a surprising extent: long-term infestations are more intense in the high volume patches than the low volume patches, even when infestation is already endemic everywhere.
The success of efforts to prevent long-distance spread of forest pests may depend sensitively on the interaction between outbreak dynamics and human social processes, with similar levels of effort producing very different outcomes depending on where the coupled human and natural system exists in parameter space. Further development of such modeling approaches through better empirical validation should yield more precise recommendations for ways to optimally prevent the long-distance spread of invasive forest pests.
运输受亚洲长角天牛（ALB）和翡翠灰螟（EAB）等非本地森林害虫侵染的营火木对北美森林有严重影响。一旦入侵性森林害虫定殖，就很难根除它们。因此，防止个人长途运输木柴至关重要。
在此，我们开发了一个随机模拟模型，该模型捕捉了森林害虫侵染与人类关于木柴运输决策之间的相互作用。树木种群分布在10个斑块（公园）中，包括一个由5个斑块组成的“低流量”分区，这些斑块的公园游客流量较低，以及一个由5个斑块组成的“高流量”分区，这些斑块的游客流量较高。侵染根据斑块间木柴运输的概率在一个斑块内——以及斑块之间——传播。个人根据本地购买与运输木柴的成本、社会规范、社会学习以及对观察到的侵染的关注程度来决定运输木柴还是在当地购买。
我们发现一个斑块被侵染前的平均时间非线性地取决于许多模型参数。特别是，相对于基线（当前）值，树木砍伐率适度增加、公众对侵染的关注度适度提高以及本地购买木柴成本适度降低，会导致一个斑块因从其他斑块运输木柴而被侵染前的平均时间大幅增加，从而更好地防止长途传播。游客流量较低的斑块比游客流量较高的斑块从木柴运输限制中受益更多。此外，斑块间的侵染不仅会引发新的侵染，还会在令人惊讶的程度上使现有侵染恶化：即使侵染在各地都已成为地方病，高流量斑块中的长期侵染也比低流量斑块更严重。
防止森林害虫长途传播的努力是否成功可能敏感地取决于爆发动态与人类社会过程之间的相互作用，根据耦合的人类和自然系统在参数空间中的位置，类似程度的努力可能会产生非常不同的结果。通过更好的实证验证进一步发展此类建模方法，应该会为最佳防止入侵性森林害虫长途传播的方法产生更精确的建议。
