Invasive Species, Climate Change and Forest Health

Abstract

Species have been invading new territories ever since life appeared on Earth, as invasion is part of the struggle for life. From the times of supercontinents Rodinia and then Pangea to the current distribution of the world’s continents, ­species have moved within and between land masses in search of opportunities for survival and growth. Species have always taken advantage of every opportunity to move that was within their behavioral and physiological capabilities. Homo sapiens is arguably one of the most successful invasive species on the planet, and his activities have greatly increased the range of opportunities for movement of other species. The ancient invasions of Europe and Asia, Australia, the Americas and New Zealand, and the more recent colonization of much of the world by Europeans, have spread a large number of human-associated species: crops, ornamentals, domesticated animals, pets, pests and diseases. International commerce (globalization) has ratcheted this process to new heights. While some of the species spread by humans are beneficial, at least to man himself, many have negative impacts on the ecosystems they invade. These negative impacts can be particularly profound in widespread, long-lived ecosystems such as forests, although undisturbed ecosystems tend to be resilient to invasion. We face an increasing prevalence and impact of invasive species on forest ecosystems as a result of increasing human transportation and commerce, our influence on Earth’s climate, and the increasing prevalence of disturbed ecosystems. In this paper, I discuss the issues of mitigation and adaptation in the context of land use changes and climate change. The focus is on the most fundamental aspects of biology that determine the potential range of invasive species in their new environments: development and survival during periods of extreme climatic conditions with specific examples using North American forest insects, the indigenous mountain pine beetle and the alien gypsy moth.