Spring flowering trends in Alberta, Canada: response to climate change, urban heat island effects, and an evaluation of a citizen science network

Abstract

In documenting biological response to climate change, the Intergovernmental Panel on Climate Change used phenology studies from many parts of the world, but data from high latitudes of North America are scarce. This thesis reports climate trends and corresponding changes in sequential bloom times for seven plant species in the central parklands of Alberta, Canada (52–57° north latitude). The data span seven decades (1936–2006), drawing on historic Agriculture Canada data, observations by the Federation of Alberta Naturalists, and the Alberta PlantWatch program in both urban and rural areas of central Alberta. An analysis of historical weather station data revealed a substantial warming signal over the study period (1936–2006), which ranged from +5.3°C for mean monthly temperature in February to +1.5°C in May. The earliest blooming species (Populus tremuloides and Anemone patens) advanced their bloom dates by two weeks over seven decades, while the later species advanced their bloom dates between zero and six days. Early-blooming species advanced faster than predicted by thermal time models, which may be due to decreased diurnal temperature fluctuations. This unexpectedly sensitive response resulted in an increased exposure to late spring frosts. A criticism by climate change skeptics is that the observed warming signal is an artifact of the increasing heat island effect of growing cities. The current dataset offered the opportunity to test this claim due to the spatially and temporally extensive phenology database. The data indeed show an increasing heat island effect over the period 1931–2006 in both weather station data and plant phenology response. Across all seven plant species, the advance in phenology observed in Edmonton was 2.1 days (±0.9 SE) greater than in the surrounding rural areas over the last 70 years. This accounted for one third of the general warming signal, while the remaining advance of 3.7 days observed in rural settings was attributed to climate change. Finally, as guidance for those initiating new observer networks, an analysis of factors that determined the quality of the PlantWatch phenological data was carried out. The thesis concludes with recommendations for effective volunteer training, observer motivation, and program protocols.