Monitoring vegetation phenology along an elevation gradient to delineate regional vegetation-climate trends

Background/Question/Methods

There is ample evidence that climate change has notable effects on the phenology of vegetation; effects that are variable at different elevations and among species. This long-term study was established to evaluate climate change impacts on the phenology of plants along an elevation gradient to clarify altitudinal range and response variation across species. This research, in combination with other regional efforts, will help identify climate change impacts on temperate forest ecosystems.  By expanding the network of long-term datasets utilizing both land-surface phenology and digital imagery we can narrow the gap between on-the-ground and remotely-sensed observations that are examining large scale seasonal phenomena, such as growing season length.  Additionally, the ongoing nature of this study will yield valuable information to resource managers who need to understand the ecological impacts of climate on the northeastern forest.

Six herbaceous plots and twenty-five trees were marked along an elevation transect on 1,220m Mount Tecumseh in New Hampshire.  Ground-based vegetation data such as the timing of leaf color change and senescence were combined with daily mean temperatures for regional-scale modeling.   Microclimate indicators were continuously obtained throughout the collection season via dataloggers measuring ambient air and soil temperature at regular intervals. Phenology and microclimate data will be incorporated into a larger meteorological dataset obtained from the Lorenz Weather Station on Mount Tecumseh’s summit.

Results/Conclusions

Preliminary data demonstrated vegetation leaf color change and senescence that correlates with an elevation gradient.  Mid-upper elevation deciduous tree species experienced initial leaf color change up to ten days earlier than lower elevation trees and initial leaf senescence up to five days earlier.  The data was used to establish a baseline for monitoring climate change impacts on phenophase starts and seasonal phase progressions.  Phenophase measurements were gathered using the USA National Phenology Network’s observation protocols ensuring data collected can be incorporated into regional and national datasets for broader application.  Soil and air temperature measurements demonstrated readings that correlate with an elevation gradient with average seasonal temperatures progressively decreasing by 6°F in air and 5°F in soil over 369 meters in elevation change.  Evaluating the vegetation and temperature data will allow for predictions on the growth and senescence threshold temperature indices responsible for seasonal on and off “switching” of phenologic stages.  Initial predictive modeling will rely upon the aggregation of basic thermal unit calculations, such as daily mean temperature, then monitoring for correlating fluctuations in temperature and phenologic response.