Plant and bird phenology and plant occurrence from 1851 to 2020 (non-continuous) in Thoreau's Concord, Massachusetts.

Concord, Massachusetts, USA has served as an active location for phenological observations since philosopher and naturalist Henry David Thoreau began recording plant and animal occurrence and phenology in 1851. Since that time, numerous naturalists, scientists, and researchers have continued this tradition, creating an invaluable time series of 758 species in a single location. In total, 13,441 phenological records, spanning 118 years, now exist, with observations of many species ongoing. Relative abundance data for an additional 200 plant species is also provided. Thoreau's published journals and records in Special Collections libraries at the Concord Free Public Library, Harvard University, Peabody Essex Museum, and Morgan Library and Museum provide insight into his methods of routinely walking around Walden Pond, through natural areas, and within the town of Concord, seeking the first leaf or flower on plants, seasonal observations of migratory birds, and fruit maturation times. Several amateur naturalists, and most recently the present research group, have followed this method of regularly searching Concord for the earliest signs of seasonal events, visiting many of the same locations including Walden Pond, the site made famous by Thoreau. While Thoreau's observations were initially made out of a curious desire to document the natural world, these data have led to dozens to contemporary studies, addressing timely issues such as climate change, conservation, ecology, and invasive species. This time series of data, initiated by Thoreau and continued by others, has resulted in dozens of peer-reviewed publications, a popular science book, and numerous educational and outreach opportunities. These data grow increasingly valuable with time and as new and creative studies are undertaken with Thoreau's historic records. No copyright restrictions apply to the use of this data set other than citing this publication.

Cranberry flowering times and climate change in southern Massachusetts.

Plants in wild and agricultural settings are being affected by the warmer temperatures associated with climate change. Here we examine the degree to which the iconic New England cranberry, Vaccinium macrocarpon, is exhibiting signs of altered flowering phenology. Using contemporary records from commercial cranberry bogs in southeastern Massachusetts in the United States, we found that cranberry plants are responsive to temperature. Flowering is approximately 2 days earlier for each 1 °C increase in May temperature. We also investigated the relationship between cranberry flowering and flight dates of the bog copper, Lycaena epixanthe-a butterfly dependent upon cranberry plants in its larval stage. Cranberry flowering and bog copper emergence were found to be changing disproportionately over time, suggesting a potential ecological mismatch. The pattern of advanced cranberry flowering over time coupled with increased temperature has implications not only for the relationship between cranberry plants and their insect associates but also for agricultural crops in general and for the commercial cranberry industry.

Tree leaf out response to temperature: comparing field observations, remote sensing, and a warming experiment.

Leaf out time is a widely used indicator of climate change and represents a critical transition point of annual seasonality in most temperate ecosystems. We compared three sources of data to determine the effect of spring temperature on tree leaf out: field observations, remotely sensed satellite data, and experimental warming. All three methods recorded earlier leaf out with warmer spring temperatures. However, leaf out timing was more than twice as sensitive to temperature in the field study (advancing at a rate of 6.1 days/°C), as under experimental warming (2.1 days/°C), with remote sensing intermediate (3.7 days/°C). Researchers need to be aware of the currently unexplained differences among methodologies when using phenological data to parameterize or benchmark models that represent ecosystem processes. The mechanisms behind these discrepancies must be better understood if we are to confidently predict responses of leaf out timing to future climates.

Drivers of leaf-out phenology and their implications for species invasions: insights from Thoreau's Concord.

To elucidate climate-driven changes in leaf-out phenology and their implications for species invasions, we observed and experimentally manipulated leaf out of invasive and native woody plants in Concord, MA, USA. Using observations collected by Henry David Thoreau (1852-1860) and our own observations (2009-2013), we analyzed changes in leaf-out timing and sensitivity to temperature for 43 woody plant species. We experimentally tested winter chilling requirements of 50 species by exposing cut branches to warm indoor temperatures (22°C) during the winter and spring of 2013. Woody species are now leafing out an average of 18 d earlier than they did in the 1850s, and are advancing at a rate of 5 ± 1 d °C(-1) . Functional groups differ significantly in the duration of chilling they require to leaf out: invasive shrubs generally have weaker chilling requirements than native shrubs and leaf out faster in the laboratory and earlier in the field; native trees have the strongest chilling requirements. Our results suggest that invasive shrub species will continue to have a competitive advantage as the climate warms, because native plants are slower to respond to warming spring temperatures and, in the future, may not meet their chilling requirements.

Leaf-out phenology of temperate woody plants: from trees to ecosystems.

Leafing-out of woody plants begins the growing season in temperate forests and is one of the most important drivers of ecosystem processes. There is substantial variation in the timing of leaf-out, both within and among species, but the leaf development of almost all temperate tree and shrub species is highly sensitive to temperature. As a result, leaf-out times of temperate forests are valuable for observing the effects of climate change. Analysis of phenology data from around the world indicates that leaf-out is generally earlier in warmer years than in cooler years and that the onset of leaf-out has advanced in many locations. Changes in the timing of leaf-out will affect carbon sequestration, plant-animal interactions, and other essential ecosystem processes. The development of remote sensing methods has expanded the scope of leaf-out monitoring from the level of an individual plant or forest to an entire region. Meanwhile, historical data have informed modeling and experimental studies addressing questions about leaf-out timing. For most species, onset of leaf-out will continue to advance, although advancement may be slowed for some species because of unmet chilling requirements. More information is needed to reduce the uncertainty in predicting the timing of future spring onset.