Warming experiments underpredict plant phenological responses to climate change.

Warming experiments are increasingly relied on to estimate plant responses to global climate change. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.

Climate extremes: observations, modeling, and impacts.

One of the major concerns with a potential change in climate is that an increase in extreme events will occur. Results of observational studies suggest that in many areas that have been analyzed, changes in total precipitation are amplified at the tails, and changes in some temperature extremes have been observed. Model output has been analyzed that shows changes in extreme events for future climates, such as increases in extreme high temperatures, decreases in extreme low temperatures, and increases in intense precipitation events. In addition, the societal infrastructure is becoming more sensitive to weather and climate extremes, which would be exacerbated by climate change. In wild plants and animals, climate-induced extinctions, distributional and phenological changes, and species' range shifts are being documented at an increasing rate. Several apparently gradual biological changes are linked to responses to extreme weather and climate events.

INCORPORATION OF A EUROPEAN WEED INTO THE DIET OF A NORTH AMERICAN HERBIVORE.

Populations of the butterfly Euphydryas editha living within a 30 times 100-km region on the eastern slope of the Sierra Nevada range were compared for oviposition preference and ability of larvae to grow and survive on two host plants, Collinsia parviflora and Plantago lanceolata. Since its introduction approximately 100 years ago, P. lanceolata has been incorporated in the diet of E. editha in one of the study populations. The populations differed in oviposition preference; only the population that uses P. lanceolata contains some individuals that prefer P. lanceolata. Larvae from two populations, one using both P. lanceolata and C. parviflora, the other using only C. parviflora, were not found to differ in relative abilities to grow or survive on P. lanceolata. The potential for E. editha to use P. lanceolata appears in populations that have had no prior exposure to this plant, while oviposition preference for this plant has evolved in the population in which the plant now grows.