Data from: Predicting the spread of an invasive tree pest: the pine wood nematode in Southern Europe

1. Invasive tree pests are increasingly threatening forest ecosystems. Understanding and controlling their spread presents a major challenge for managers, researchers, and policy makers. In 1999, the pine wood nematode Bursaphelenchus xylophilus, causal agent of pine wilt disease and native to North America, was first detected in Europe, more precisely in south western Portugal. Since then, it has spread to more than 30% of the country, producing large-scale damages in Portuguese forests.
2. We applied a new spatio-temporal network-based model to predict, at yearly intervals, the natural spread of the pine wood nematode on the Iberian Peninsula, as dispersed by the longhorn beetle Monochamus galloprovincialis, its only known vector in Europe. We compared the model predictions with independent observations of the natural spread of pine wilt disease in Portugal between 2005 and 2015. We simulated the effect of potential containment measures on the disease spread.
3. The model predicted the status (infected or non-infected) of forest areas with 93% accuracy, had 93% sensitivity and specificity, and AUC=0.96 (averages for 8 years with validation data).
4. Simulated clear-cut belts stopped the spread only if they were wider than 30 km, although thinner belts delayed invasion. Furthermore, clear-cuts were much more effective in slowing down the invasion when reinforced, in the adjacent areas, by the reduction of the vector beetle population through mass trapping and by the early detection and removal of infected trees.
5. Model projections identified areas through which the nematode is most likely to invade, by natural means, the phytosanitary buffer zone established along the Portuguese border, and Spain.
6. Synthesis and applications. In the absence of effective containment measures, the pine wood nematode may naturally spread into Spain in about 5 years. In less than 10 years, it may reach the major forest and climatic corridors that provide a gateway for subsequent expansion towards the rest of the Iberian Peninsula and, in the longer term, towards other European countries. Our model can considerably support management efforts by forecasting when areas are at highest risk of vector-mediated invasion as well as the effects of specific control measures on the disease spread.

1. 入侵性林木害虫正日益威胁森林生态系统。对其传播路径的解析与防控，是管理者、科研人员与政策制定者面临的重大挑战。1999年，原产于北美洲的松材线虫（pine wood nematode，Bursaphelenchus xylophilus）——松萎蔫病的致病菌——首次在欧洲被检出，具体地点位于葡萄牙西南部。自彼时起，该线虫已扩散至葡萄牙境内超30%的区域，对当地森林造成大规模破坏。
2. 本研究采用一种新型时空网络模型（spatio-temporal network-based model），以年为时间间隔，对伊比利亚半岛上松材线虫的自然传播路径进行预测——该线虫在欧洲的唯一已知传播媒介为松墨天牛（Monochamus galloprovincialis）。我们将模型预测结果与2005-2015年间葡萄牙境内松萎蔫病自然传播的独立观测数据进行比对，并模拟了潜在防控措施对病害传播的影响。
3. 该模型对森林区域的感染/未感染状态预测准确率达93%，灵敏度与特异度均为93%，受试者工作特征曲线下面积（Area Under the Curve，AUC）=0.96（基于8年验证数据集的平均值）。
4. 模拟结果显示，仅当皆伐带（clear-cut belts）宽度超过30km时，才能完全阻断病害传播，较窄的皆伐带仅能延缓入侵进程。此外，若在皆伐带相邻区域辅以诱捕灭杀（mass trapping）以压低媒介甲虫种群密度，并结合早期发现与移除感病林木的措施，则皆伐对延缓入侵的效果将显著提升。
5. 模型预测结果锁定了松材线虫最可能通过自然途径入侵葡萄牙边境沿线植物检疫缓冲区（phytosanitary buffer zone）以及西班牙的区域。
6. 研究总结与应用启示：若未采取有效防控措施，松材线虫将在约5年内自然扩散至西班牙；在不到10年的时间内，它将抵达主要森林与气候廊道，这些廊道将为其后续向伊比利亚半岛其余区域乃至更远的其他欧洲国家扩张提供通道。本模型可通过精准预测媒介介导的入侵高风险时段，以及特定防控措施对病害传播的影响，为病害管理工作提供有力支撑。