Lombardero María J, Vázquez-Mejuto Patricia, Ayres Matthew P
Departamento de Producción Vegetal, Universidad de Santiago, 27002 Lugo, Spain.
Ecol Appl. 2008 Jul;18(5):1171-81. doi: 10.1890/07-1048.1.
Plantations of rapidly growing trees are becoming increasingly common because the high productivity can enhance local economies, support improvements in educational systems, and generally improve the quality of life in rural communities. Landowners frequently choose to plant nonindigenous species; one rationalization has been that silvicultural productivity is enhanced when trees are separated from their native herbivores and pathogens. The expectation of enemy reduction in nonindigenous species has theoretical and empirical support from studies of the enemy release hypothesis (ERH) in the context of invasion ecology, but its relevance to forestry has not been evaluated. We evaluated ERH in the productive forests of Galicia, Spain, where there has been a profusion of pine plantations, some with the indigenous Pinus pinaster, but increasingly with the nonindigenous P. radiata. Here, one of the most important pests of pines is the indigenous bark beetle, Tomicus piniperda. In support of ERH, attacks by T. piniperda were more than twice as great in stands of P. pinaster compared to P. radiata. This differential held across a range of tree ages and beetle abundance. However, this extension of ERH to forestry failed in the broader sense because beetle attacks, although fewer on P. radiata, reduced productivity of P. radiata more than that of P. pinaster (probably because more photosynthetic tissue is lost per beetle attack in P. radiata). Productivity of the nonindigenous pine was further reduced by the pathogen, Sphaeropsis sapinea, which infected up to 28% of P. radiata but was absent in P. pinaster. This was consistent with the forestry axiom (antithetical to ERH) that trees planted "off-site" are more susceptible to pathogens. Fungal infections were positively correlated with beetle attacks; apparently T. piniperda facilitates S. sapinea infections by creating wounds and by carrying fungal propagules. A globally important component in the diminution of indigenous flora has been the deliberate large-scale propagation of nonnative trees for silviculture. At least for Pinus forestry in Spain, reduced losses to pests did not rationalize the planting of nonindigenous trees. There would be value in further exploration of relations between invasion ecology and the forestry of nonindigenous trees.
速生人工林越来越普遍，因为其高生产力能够促进地方经济发展，支持教育系统改善，并总体提升农村社区的生活质量。土地所有者常常选择种植非本土树种；一种理由是，当树木与其本土食草动物和病原体隔离开时，造林生产力会提高。在入侵生态学背景下，非本土物种中减少天敌的预期得到了天敌释放假说（ERH）研究的理论和实证支持，但其与林业的相关性尚未得到评估。我们在西班牙加利西亚的高产森林中评估了ERH，那里有大量的松树人工林，一些种植的是本土的海岸松，但越来越多地种植非本土的辐射松。在这里，松树最重要的害虫之一是本土的树皮甲虫，即松墨天牛。为支持ERH，与辐射松相比，松墨天牛对海岸松林分的攻击次数多出两倍多。这种差异在一系列树龄和甲虫数量范围内都存在。然而，从更广泛的意义上说，ERH在林业中的这种延伸并不成立，因为甲虫攻击虽然对辐射松的次数较少，但对辐射松生产力的降低幅度比对海岸松更大（可能是因为每次甲虫攻击在辐射松中损失的光合组织更多）。非本土松树的生产力还因病原菌——松球壳孢菌而进一步降低，该病原菌感染了高达28%的辐射松，但在海岸松中不存在。这与林业公理（与ERH相反）一致，即“异地”种植的树木更容易受到病原菌的侵害。真菌感染与甲虫攻击呈正相关；显然，松墨天牛通过造成伤口和携带真菌繁殖体促进了松球壳孢菌的感染。本土植物群减少的一个全球重要因素是为造林而故意大规模繁殖非本土树木。至少对于西班牙的松树造林来说，害虫损失的减少并不能成为种植非本土树木的合理理由。进一步探索入侵生态学与非本土树木林业之间的关系将会有价值。
