The flowering response of Greater Philadelphia native piedmont plants to long term climate change

Abstract

There is growing evidence that many plant species are flowering earlier in recent years and that climate change is a contributing factor. These studies have predominantly used field observations as their data source while an increasing number of reports are utilising herbarium specimens. The current research uniquely combined different data sources in the form of herbarium specimens, field observations and dated photographic images to study plant species response to rising temperatures. An analysis of 28 Greater Philadelphia species, native to Pennsylvania and Delaware Piedmont, and 2539 flowering records from 1840 to 2010 indicated that plants are responding to rising minimum monthly temperatures. On average, these species are flowering 16 days earlier over this 170 year period and 2.7 days earlier per °C rise in monthly minimum temperature. Monthly minimum temperatures one or two months prior to flowering correlate with flowering time most significantly. Short flowering plants and woody plants are better indicators of climate change. Phenological studies across areas of at least 80 km in radius produce significant results. Individuals, public gardens and institutions holding historic botanical data can play an important role in topical research such as climate change.