Abstract: Microclimate variation at small spatial scales has the potential to affect plant phenology, which is a key indicator of the biological effects of climate change. Most studies of phenology, however, ignore the influence of microclimates.
We investigated the effects of microclimate over four years on flowering phenology for 35 populations of Canada mayflower (Maianthemum canadense) occupying a range of sites varying in microclimate characteristics in a mixed deciduous forest in Newton, Massachusetts (USA).
Flowering dates varied by around 6 days. Soil temperatures varied by about 5°C across sites before and during the flowering season. Temperatures differences among sites were consistent across years. Among 21 populations, plants flowered earliest at sites with the warmest microclimates—one day earlier for each 1°C warmer temperature. Differences among sites were consistent over the four years of the study. In most other published phenology studies, spring wildflowers flower 2-5 days earlier for each 1°C of warming of air temperatures. Fourteen additional populations, selected because they flowered extremely early or late, showed greater phenological responses to temperature. Field and lab experiments demonstrated that differences among populations in flowering phenology were mainly due to phenotypic responses to temperature.
This study demonstrates that microclimates, specifically fine-scale variation in temperature, can influence flowering phenology and are important to consider when assessing phenological responses to macroclimate change based on weather stations. These microclimate effects may also affect the ability of species to persist in the face of climate change and influence pollinator behavior. Other species and habitats should be investigated to determine the relative strength of these microclimate effects.
