| Phenology, the timing of biological events, is a common metric used to measure the effect of climate change on ecosystems. Leaf out timing is a particularly important indicator because it is highly sensitive to temperature, represents a critical transition point of annual seasonality, and is an important driver of ecosystem processes. The mechanisms behind this have recently gained attention, and I wrote a literature review on the topic that surveyed what is known and identified topics that require further investigation (Chapter 1). In the next chapter, I focused on specific aspects of leaf out phenology using observation and experimentation. To examine the effects of climate change on leafing, I utilized historical records (1852-1860) and made observations (2009-2012) of leaf out in Concord, Massachusetts (Chapter 2). Leafing is now an average of 19 days earlier than in the past. Recently published studies suggest that the continued advance of leaf out is uncertain; with continued warming, unmet chilling requirements may lead to delays in leafing. To address this, I experimentally investigated chilling requirements of local species (Chapter 2). I compared the sensitivity of leaf out to spring temperature as measured by field observations, remotely sensed data, and experimental warming to determine differences resulting from these methods (Chapter 3). Earlier leaf out with warmer temperatures was found with all methods; however, leafing was more than twice as sensitive to temperature in the field study as under experimental warming, with remote sensing intermediate.;To better understand the effects of climate change on ecosystems, we must obtain reliable information about multiple trophic levels. I examined the effects of temperature on the flight dates of ten species of Massachusetts butterflies (1895-2009) using both museum specimen records and citizen science data: the response of these species is similar to that of flowering and bee flight times and significantly greater than changes in bird arrival (Chapter 4). As long as investigators are aware of the limitations of each data source, historical data, remote sensing, experiments, and citizen science data are all effective tools for studying the effect of climate change on phenology. |
