The effects of climatic warming on the phenology of Arctic plants and their principal herbivore

Abstract

There is mounting evidence that many plants and animals may be unable to adjust the timing of their various life cycle events rapidly enough to adjust to predicted rates of climate change. For example, the close synchronisation between bud-burst and herbivore emergence may be disrupted by increased temperatures. However, many experimental studies demonstrating these effects have only used short term temperature manipulations, despite the possibility that strong selection pressure could lead to rapid adaptation to a changing climate over several years. This study therefore investigated whether phenological synchrony between plants and their herbivores was disrupted after five years of simulated climate change. A series of warming chambers was set up across the forest-tundra ecotone in Arctic Sweden. The chambers increased temperatures relative to control plots in line with average predictions from climate change models. The warming chambers did not affect the timing of snow melt, suggesting that hydrological conditions were broadly similar in warming chambers and control plots. Plants growing in areas with a late-melting snow pack showed accelerated development and growth in comparison with plants in early-melting areas, so that plants in all areas completed development at about the same time. However, invertebrate herbivores were more closely synchronised to their host plants in areas where immature foliage was only available for a short period of time. Experimental warming advanced the onset of leaf development and also increased the area of leaf tissue available to herbivores. However, phenological synchrony between invertebrate herbivores and their host plants was not affected by warming, as the lag between leaf emergence and the onset of herbivory was similar in warming chambers and control plots. This suggests that herbivores may be able to respond relatively rapidly to changes in host plant phenology. However, elevated temperatures were associated with an increase in defoliation, with potentially severe consequences for the birch forests of northern Fennoscandia.