Is the introduction of novel exotic forest tree species a rational response to rapid environmental change? - A British perspective

Both plantation forests and native woodlands are currently facing challenges in the form of rapid climatic change and unprecedented increases in damage by exotic pests and diseases. To combat these problems it has been proposed that a range of novel exotic tree species (non-native species that have not yet undergone thorough operational testing or previously been grown at a forestry scale) should be grown as part of an adaptive management strategy, and that non-native (including novel) species should be introduced into native woodland. Justifications for this policy are that novel exotic species are required to maintain forest productivity under climate change, to create a more diverse, and by implication more resilient forest, and to substitute for native species threatened by introduced pests and pathogens. Here we examine these arguments in the context of British forestry, where there is a long history of utilising non-native species. On the basis of this documented experience we conclude that in the commercial sector of British forestry, where production is the main objective, there are strong arguments for undertaking a programme of rigorous testing and domestication of a very limited number of the most promising novel exotics which, in addition to good timber and growth, also have attributes that will allow the development of more naturalistic silvicultural systems and a move away from current clear-fell regimes. However this must be undertaken within a comprehensive risk assessment framework, where candidate species are rigorously screened both for any biosecurity threats, and their potential for causing ecological damage if they become invasive outside their initial planting sites. Widespread planting of candidate species should only be recommended after the completion of full species and provenance trials, and when reliable sources of appropriately adapted seed have been established. Conversely where conservation of biodiversity is an objective we find no support for introduction of any non-native species. This is based on the greater ecological and economic risk they pose compared to the use of native species. Use of non-natives is likely to lead to an increase rather than a decrease in pest and disease problems, and to hinder rather than support the retention of threatened native tree species and their associated biodiversity.

人工林和原生林地目前都面临着快速气候变化以及外来病虫害损害空前加剧等形式的挑战。为应对这些问题，有人提议将一系列新的外来树种（尚未经过全面的实际操作测试或之前未在林业规模上种植过的非本地树种）作为适应性管理策略的一部分进行种植，并将非本地（包括新的）树种引入原生林地。这一政策的理由是，需要新的外来树种在气候变化下维持森林生产力，创建一个更多样化且意味着更具复原力的森林，并替代受到外来害虫和病原体威胁的本地树种。在此，我们结合英国林业的情况审视这些论点，英国利用非本地树种有着悠久的历史。基于这些有记录的经验，我们得出结论：在英国林业的商业领域，生产是主要目标，有充分的理由对数量非常有限的最有前景的新外来树种开展严格的测试和驯化计划，这些树种除了木材质量好和生长良好外，还具有能够发展更自然的营林系统以及摆脱当前皆伐制度的特性。然而，这必须在一个全面的风险评估框架内进行，对候选树种要严格筛选，既要考虑任何生物安全威胁，也要考虑如果它们在最初种植地点之外变得具有入侵性可能造成的生态破坏。只有在完成全面的树种和种源试验，并建立了经过适当改良的可靠种子来源之后，才应建议广泛种植候选树种。相反，在生物多样性保护是目标的情况下，我们不支持引入任何非本地树种。这是基于与使用本地树种相比，它们带来更大的生态和经济风险。使用非本地树种可能会导致病虫害问题增加而非减少，并阻碍而非有助于保护受威胁的本地树种及其相关生物多样性。