Elmore, Andrew: UMCES Appalachian Laboratory (Project Lead)
Project Funding:
2012 - 2015
NRA: 2011 NASA: Terrestrial Ecology
Funded by NASA
Abstract:
A trend towards a longer growing season, here defined by the number of days between the spring onset and autumn offset of greenness, has been observed in regional- to global- scale remote sensing time-series spanning the past 30 years. This phenological change is thought to be occurring in response to human-induced changes in climate and atmospheric chemistry. Although observed phenology trends contain uncertainties and depend, in part, on algorithm selection, such shifts are likely to have large impacts on water and carbon cycling, as well as energy balance, in temperate forests. For example, satellite data and atmospheric CO2 concentration ([CO2]) data suggest that a longer growing season has led to increased plant growth in the northern hemisphere. Increased tree productivity might create a negative feedback to increasing atmospheric [CO2] and climate change, although uncertainty surrounds this hypothesis due to complexity between phenological timing and ecosystem responses. Thus there are strong scientific imperatives for developing a mechanistic understanding of the relationship between phenological changes and carbon uptake by forest ecosystems. Remote sensing scientists have long been interested in relating temporal trends in phenology to field observations of the carbon cycle. However, such work requires a 30-year record of ecosystem processes that is easily, and relatively inexpensively, scaled from trees to forest stands, thus enabling assessment of ecosystem responses to variations in phenology over broad spatial extents. We propose that dendroecological analysis provides the ideal opportunity to meet this challenge and to comprehensively investigate the influence of changes in phenology on the productivity of forest trees in the eastern US.
The proposed research will be conducted in two regions of the deciduous-forest biome that exhibited contrasting trends in the onset of spring greenness over the past 30 years. If annual variation and long-term trends in growing season length are influencing forest productivity, we hypothesize that this influence will be a function of phenological variability occurring at local scales. The project would specifically investigate the importance of growing-season stability in canopy greenness on the response of tree productivity to a change in growing season length. Conceptually, the stability of summer greenness (i.e., the degree to which canopies 'greendown' throughout the growing season) is directly related to the capability of forests to utilize a longer growing season for carbon assimilation. We will test this concept using measurements of multi-species tree productivity and indicators of plant stress and nitrogen availability (carbon and nitrogen isotopes in tree rings) at sites spanning gradients of spring onset and greendown. The specific objectives of the project are: (1) assess the influence of environmental factors on medium-resolution spatial patterns in the spring onset, growing-season stability, and autumn offset of greenness; and (2) determine how change in the timing of spring onset, recorded by coarse-resolution sensors, has influenced forest productivity across gradients in medium-resolution phenology and growing-season greenness stability. The project would meet these objectives through synergistically use of phenology observations at coarse- and medium-resolution, LiDAR observations of canopy complexity, and tree ring records of carbon and nitrogen isotopes to understand the influence of growing season length on tree productivity, measured as tree basal area increment. Overall, the proposed research provides an unparalleled opportunity to understand cross-scale linkages between spatial and temporal phenology patterns and how these patterns influence tree productivity.
Publications:
McLauchlan, K. K., Gerhart, L. M., Battles, J. J., Craine, J. M., Elmore, A. J., Higuera, P. E., Mack, M. C., McNeil, B. E., Nelson, D. M., Pederson, N., Perakis, S. S. 2017. Centennial-scale reductions in nitrogen availability in temperate forests of the United States. Scientific Reports. 7(1). DOI: 10.1038/s41598-017-08170-z
Reaves, V. C., Elmore, A. J., Nelson, D. M., McNeil, B. E. 2018. Drivers of spatial variability in greendown within an oak-hickory forest landscape. Remote Sensing of Environment. 210, 422-433. DOI: 10.1016/j.rse.2018.03.027
Elmore, A. J., Nelson, D. M., Craine, J. M. 2016. Earlier springs are causing reduced nitrogen availability in North American eastern deciduous forests. Nature Plants. 2(10). DOI: 10.1038/NPLANTS.2016.133
2013 NASA Terrestrial Ecology Science Team Meeting Poster(s)
- Assessing the influence of local phenology on the response of forest productivity to changes in growing season length
-- (Andrew Elmore, David Nelson)
[abstract]
[poster]
More details may be found in the following project profile(s):
