Paradise burnt: How colonizing humans transform landscapes with fire

摘要

A striking feature of Southern Hemisphere landscapes is the occurrence of grasslands in regions that are climatically suitable for forests (Fig. 1). Ecologists and biogeographers working in these southern lands have developed a range of theories to account for the biogeographic anomaly of grassland-forest mosaics (1-7). Broadly speaking, these theories divide into those that privilege the importance of an ensemble of environmental factors, including fire, or those that stress the legacy of human landscape burning. The report by McWethy et al. in PNAS (8) provides incontrovertible evidence that anthropogenic burning transformed temperate forested landscapes on the South Island of New Zealand. They show that Polynesian (Maori) firing commenced shortly after colonization around A.D. 1280 and transformed 40% of the original forest cover of the island to grassland and fern-shrubland. There is little room for doubting their findings given the elegant integration of a range of paleoecological methodologies, very precise dating, and a high level of replication across the island. This report will spark renewed interest in the relative importance of fire, humans, and climate in shaping forest-grassland landscape mosaics worldwide (9).