Consequences of Changing Winter Climate for Carbon Balance in a Temperate Forest
Abstract
Winter conditions influence biogeochemical cycling in temperate forests through multiple processes. Temperatures below freezing induce dormancy in above-ground vegetation, but insulation by deep snow pack can keep soils thawed, maintain microbial, and prevent root damage. Climate warming may have unexpected consequences depending on whether precipitation comes as rain or snow. Net carbon flux, as a tracer of overall metabolism, tracks the balance between respiration and photosynthesis. We postulate that carbon balances in the summer growing season are affected by conditions during the antecedent winter that have influenced nutrient cycling, root health, and moisture availability. We have measured hourly carbon fluxes at the Harvard Forest Environmental Measurements Site (HFEMS) tower since 1992, along with meteorological variables, snowcover, and soil properties. Over the measurement period Harvard Forest has experienced a wide range of winter conditions. Temperature, as quantified by February mean air temperature has ranged from -10°C to near 0°C. The snowpack has varied from over 1 m deep and persisting through March to bare soils and ice patches throughout the winter. The multi-decade record of flux and meteorological observations defines an average state that we use to compute anomalies. Anomalies in the fluxes or their functional relationship to driving variables and other ecosystem state variables can be compared to variations in winter conditions to assess how winter variability is affecting ecosystem metabolism. Carbon uptake in the spring and fall shoulder seasons increases when temperatures above 0°C arrive earlier or persist longer. Varied environmental conditions during spring and summer can obscure the winter legacy. We focus on average physiological properties rather than cumulative fluxes. For example peak photosynthetic rates during the summer are positively related to canopy leaf area (LAI). For years that had warmer soil temperatures in winter the peak photosynthetic rates during the summer were enhanced by ~15 μmole m-2s-1 compared to the rate expected for the observed LAI. Canopy-scale photosynthetic capacity is sensitive to the presence/absence of soil freezing during the preceding winter.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B41E..02M
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCES;
- 0716 Cryobiology;
- CRYOSPHERE