Plant reproductive fitness and phenology responses to climate warming: Results from native populations, communities, and ecosystems

Influences of climate on plant reproductive yields and phenology are likely among the first natural history observations made by early humans and continued in prominence through the agricultural revolution until today. Many natural populations are adapted to local abiotic and biotic environmental conditions they have experienced during their evolutionary histories. Currently, human actions are altering climatic and nonclimatic selection agents, which can lead to discrepancies between average phenotype and the phenotype associated with the greatest fitness under new environmental conditions. Climate change may impose strong novel selection, shifting fitness landscapes and reducing survival and fecundity in natural populations. Indeed, altered seasonal dynamics of plants and animals are one of the strongest biotic signals of contemporary climate change. In addition to depressing fitness, shifts in selection mediated by climate change could result in widespread patterns and increased risk of local—or even regional—extinction. Here we synthesize field studies using warming manipulations to investigate impacts on fitness components in wild plants (quantities of flowers, fruits, and seeds, seed viabilities, and seedling establishment success) and reproductive phenology (seasonal and interannual timing of reproductive events). We use a comprehensive approach in that we include reproduction and establishment events from initial flowering to survivorship and growth responses of resulting F1 seedlings with continued warming. In contrast to reproductive investigations of increased atmospheric CO2, we did not find many references addressing pollen responses to warming under field conditions, so we begin here with flowering, fruiting, and seed responses to soil warming. We include new data exploring warming impacts on plant reproduction from a temperate deciduous forest and a Low Arctic tundra and conclude with a reproductive case study covering desert and dryland ecosystems.