Climate Change in the Northeast

Climate Change in the Northeast
		by *Ray T. Oglesby* Cornell University *Charles R. Smith* Cornell University
Climate is a principal determinant of biological distributions and of patterns that characterize the seasonal physiology and behavior of many organisms (Gates 1993). Consequently, a changing climate should elicit responses in these biological properties. Detecting and characterizing such changes are logical early steps in assessing the significance of climate change to species and ecosystems (Schwartz 1990). Most published work on this subject involves species and ecosystem modeling based on known physiological and behavioral traits of selected species. This article presents evidence from an array of phenological data suggesting that climate change is occurring and that its biological effects may already be of considerable magnitude. (Phenological data are those associated with the relationship between climate and periodic phenomena like bird migration and flowering.)
Most research intended to explore possible effects of climate change on vegetation has understandably focused on agricultural and forest plants. Our approach, however, focuses on examining historical trends at the regional level and identifying species of potential value as climate change indicators. With the assumption, based on climate models, that unidirectional warming is already occurring and will probably accelerate over the next few decades, we began to search for evidence of biological responses among very different groups of organisms. Specifically, dates of the first return of spring-migrating birds and of the first bloom of spring wildflowers in the Northeast were sought in long-term (50 or more years), continuous, reliable records.

Fig. 1. New York locations from which phenological data were obtained. 1Allegheny Plateau (birds); 2Cayuga Lake basin, Ithaca (birds); and 3Hudson Highlands (flowering plants and birds).

We computerized and analyzed two major and several minor long-term data sets from handwritten records from three New York State locations (Fig. 1). An especially rich source was records from the Cayuga Bird Club at Ithaca. Highly reliable observers recorded first spring sightings of migratory birds from 1903 to the present in the Cayuga Lake basin of central New York as delineated by Wiegand and Eames (1925). A second source of extensive, high-quality information was records for dates of first spring arrival for migrating birds and dates of first bloom for spring wildflowers at the Mohonk Preserve, an upland site in the mid-Hudson Highlands region of southeastern New York; these records extend from the late 1920's onward. Both sites are expected to continue generating comparable data sets. A third data set includes dates of first spring arrival for Louisiana waterthrush (Seiurus motacilla) and solitary vireo (Vireo solitarius) in western New York (1952 to present) on the Allegheny Plateau.

Fig. 2. Trend for hepatica (Hepatica acutiloba) from the Hudson Highlands (Mohonk Preserve) of southeastern New York, showing tendency for earlier spring blooming. The negative slope of the trend is significant at P < 0.05.
Our general approach to data analysis has been in the form of species plots with date of first arrival or first bloom as the vertical axis and sequence of years as the horizontal axis (Figs. 2-4).

Status and Trends
Flowering Plants

Fig. 3. Trend for purple martin (Progne subis) from the Cayuga Lake basin of central New York showing a clear tendency for earlier spring arrival. The negative slope of the trend is significant at P < 0.005.

Phenological data were examined for 15 species of spring wildflowers on time of first blooming at the Hudson Highlands site (Fig. 2). Six species of wildflowers all exhibited significantly earlier (P ¾ 0.05) rather than later blooming (averaging -19.8 days/50 yr; R² = 0.26). The remaining nine species showed no significant patterns of change. We only can speculate why six species exhibited such a pronounced change and nine others did not. Clues may be obtained when existing data for other plant species at this site are examined. For example, the set of species showing earlier blooming appears to include plants typically found in more open locations where soil temperature would show the earliest and most rapid response to warming. One woody shrub, common witch-hazel (Hamamelis virginiana), which blooms in early fall, also showed a significant trend toward earlier bloom.

Migratory Landbirds

Fig. 4. Trend for blackpoll warbler (Dendroica striata) from the Cayuga Lake basin of central New York, showing no tendency for earlier spring arrival. The slope of the trend is not significantly different from zero.

Records of first sightings of spring migrants from the Cayuga Lake basin of central New York are from 1903 to the present and represent 130 species. More than 5,000 first arrival dates were examined for 76 species of migratory landbirds, excluding waterfowl, hawks, and shorebirds. Thirty-nine species (51%) showed 90-year trends of significantly earlier (P ¾ 0.05) arrival, with an average shift of about 5.5 days/50 yr (for example, see Fig. 3). Thirty-five species (46%) showed no significant change (P ¾ 0.05) in dates of first spring arrival (Fig. 4). Louisiana waterthrush and mourning warbler (Oporornis philadelphia) were the only species showing significant trends (P ¾ 0.05) toward later spring arrival dates.

Of those species showing significantly earlier arrival dates, 85% are long-distance Neotropical migrants, which normally overwinter in Central and South America. For the Mohonk Preserve data, 6 of 10 migratory bird species examined showed significant trends toward earlier arrival. For the western Allegheny Plateau, first-arrival data, covering a 40-year period beginning in 1952, were available for two species of birds, Louisiana waterthrush and solitary vireo. Both species tended to earlier arrival.
Conclusions
The trends reported here toward earlier arrival dates for migratory birds and earlier blooming dates for spring wildflowers are concurrent with patterns of climatic warming and consistent with what might be expected in the context of global warming. At the same time, local changes in land cover, with the forested area of the region increasing by more than 30% since 1900, may provide greater amounts of suitable habitat for attracting and holding migrating landbirds, thereby contributing to observed patterns of change in migratory behavior.
It is noteworthy that only two bird species examined, and no plant species, showed trends to either later spring arrival or later blooming. If explanations of trends for only one of these two major groups were sought, alternative explanations could be advanced, such as expansion of bird ranges due to changes in land use (see Root and Weckstein, this section). In addition, a recent examination of dates of fall departure for migrating birds in Germany (Gatter 1992) shows later fall departures. Such fall trends would be expected in the context of climatic warming and agree with the spring trends we report.
Given the patterns reported here, climate change is the one variable affecting diverse groups of organisms that offers a rational and parsimonious explanation for the observed changes in timing of migration in birds and blooming in plants we and others have observed. Research either planned or in progress includes analyzing additional data sets as well as more sophisticated statistical analysis; determining the species most appropriate for monitoring climate change; finding and analyzing data sets that describe the phenology of other taxa; and possibly extending the study to other locations.
		For further information: Ray T. Oglesby Cornell University Department of Natural Resources New York Cooperative Fish and Wildlife Research Unit Ithaca, NY 14853

References
Gates, D.M. 1993. Climate change and its biological consequences. Sinauer Associates, New York. 280 pp. Gatter, W. 1992. Zugzeiten und zugmuster im herbst: einfluss des treibhauseffekts auf den vogelzug. Journal für Ornithologie 133:427-436.	Schwartz, M.D. 1990. Detecting the onset of spring: a possible application of phenological models. Climate Res. 1:23-29. Wiegand, K.M., and A.J. Eames. 1925. The flora of the Cayuga Lake basin, New York. Cornell University Agricultural Experiment Station Memoir 92. 491 pp.

Climate Change in the Northeast

Status and Trends

Conclusions