The influence of natural fire and cultural practices on island ecosystems: insights from a 4800 year record from Gran Canaria, Canary Islands

Aim: Long-term ecological data provide a stepped frame of island ecosystems transformation after successive waves of human colonizations, important to determine the baselines for restoration, eradication, and monitoring. Here we focus on timing and ecological impact of human settlement on the Canary Islands. We report analyses from a 4800-year sedimentary sequence from Gran Canaria, disentangling forest responses to natural fire from early human pressure. Location: La Calderilla, a volcanic maar caldera at 1770 m a.s.l. on Gran Canaria. Taxon: plants and fungi. Methods: A core from the caldera infill was analysed for sediment properties, pollen, micro- and macrocharcoal, with radiocarbon and biochronology dating. Fossil data were statistically zoned and interpreted with the help of cross-correlation and ordination analyses. Surface samples and a pollen-vegetation training set were used as modern analogues for vegetation reconstruction. Results: Before human settlement (4800-2000 cal. yr BP), pine (Pinus canariensis) pollen dominated. Extensive dry pine forests characterised the highlands, although with temporary declining phases, followed by prompt (sub-centennial scale) recovery. Towards 2280 cal. yr BP there was a shift to open vegetation, marked by an increase in coprophilous spores. Coincidental with independent evidence of human settlement in the pine zone (2000-470 cal. yr BP) there was a decline of pine and a peak in charcoal. Following historic settlement (470-0 cal. yr BP), pollen producers from anthropogenic habitats, secondary vegetation and coprophilous fungi increased in abundance, reflecting higher pressure of animal husbandry and farming. Modern moss polsters reflect extensive reforestation since 1950 CE (Common Era). Main conclusions: From 4800 cal. yr BP, the pristine vegetation covering the Gran Canaria highlands was a mosaic of dry pine forests and open vegetation. The pine forests sustained intense fires, which may well have promoted habitat diversity. Human interference was initiated around 2280 cal. yr BP probably by recurrent cultural firing and animal husbandry, triggering a steady trend of forest withdrawal and expansion of grasses and scrubs, until the final disappearance of the pine forest locally in the 20th century. Grasslands were found to be of ancient cultural origin in the summit areas of Gran Canaria, although they underwent an expansion after the Castilian Conquest.