Science in the attic: Long-term spring phenology of trees, wildflowers and birds in Northern Maine building on a forgotten journal

Background/Question/Methods

Scientists documenting the effects of climate change on ecological communities have been well-served by phenological records.  Spring phenology, in particular, provides a clear signal of warming. Advancing phenology has implications for trophic interactions, biogeochemical cycles, and ecosystem services across many scales, from global to species.  However, the long-term monitoring records necessary for determining local shifts in phenology are scattered across a few well-studied sites.  Creative interdisciplinary approaches are needed to rapidly expand this dataset of long-term place-based phenology studies.  While networks like USANPN strive to compile contemporary citizen science observations of phenological events, ecologists interested in long-term trends today must uncover and utilize relevant historical records, such as diaries, herbaria specimens, and field notes.  Northern Maine, which has already experienced 0.2°C/decade warming since 1970, provides a unique case study for compiling and analyzing spring phenology records dating back to the mid-20^th century.  Eighteen years of historical flowering and leaf out data were discovered in the journal of an Oxbow hunting guide named Leonard Quackenbush.  These natural history observations from Oxbow, Maine, combined with weather records, may illuminate local phenology trends in an area of the country that has been traditionally underrepresented in climate change research.

Results/Conclusions

The Quackenbush journals include observations of leaf out for fourteen tree species and first flower for eleven plant species over eighteen years from 1940-1957.  Monthly mean temperatures were compiled from a weather station in Preque Isle, ME. We used linear regressions for each species to determine the relationship between date of leaf out and first flower and mean spring temperatures.  Every species exhibited a trend between warmer temperatures and earlier phenophases.  For seven of Quackenbush’s plants — Trillium erectum, Amelanchier, Apple, Cornus canadensis, Dandelion, White violet, and Wild strawberry — date of first flower was significantly (p < 0.05) correlated with warmer spring temperatures (R-square values in the range of 0.45-0.65).  For four other species — Acer sacchrum, Betula, Ostrya, and Populus tremuloides — date of leaf out was significantly (p < 0.05) correlated with warmer spring temperatures (R-square values in the range of 0.43-0.63).  Quackenbush also recorded observations of migratory bird arrivals, though over fewer years.  The Quackenbush observations add context to observations collected by citizen scientists in Northern Maine in recent years.  In addition, the Quackenbush dataset has inspired renewed interest in natural history monitoring in Aroostook county, Maine, where we hope to establish long term records of spring phenology.