Remote sensing of tundra gross ecosystem productivity and light use efficiency under varying temperature and moisture conditions

• Published in: Remote sensing of environment Vol. 114; no. 3; pp. 481 - 489
• Main Authors: Huemmrich, K.F, Gamon, J.A., Tweedie, C.E., Oberbauer, S.F., Kinoshita, G., Houston, S., Kuchy, A., Hollister, R.D., Kwon, H., Mano, M., Harazono, Y., Webber, P.J., Oechel, W.C.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15.03.2010; Elsevier
• Subjects: Animal, plant and microbial ecology; Applied geophysics; Arctic tundra; Biological and medical sciences; CO 2 flux; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fraction of absorbed photosynthetically active radiation; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Gross ecosystem exchange; Internal geophysics; Leaf area index; Light use efficiency; Mosses; Normalized Difference Vegetation Index; Reflectance; Simulated environmental change; Teledetection and vegetation maps; Northern Alaska; United States; Alaska; USA, Alaska; Fraction of absorbed photosynthetically active radiation; Simulated environmental change; Light use efficiency; Gross ecosystem exchange; Arctic tundra; Mosses; CO 2 flux; Normalized Difference Vegetation Index; Leaf area index; Reflectance; experimental studies; Vegetation index; simulation; Greening; vegetation; North America; Modeling; Biological productivity; Fraction of absorbed photosynthetically; Radiation use efficiency; photosynthesis; temperature; humidity; flux; climate change; Ability; models; detection; Photosynthetically active radiation; Trend; Satellite observation; remote sensing; Increase; climate; CO; Response; tundra; Treatment; ecosystems; active radiation
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2009.10.003

Satellite observations have shown greening trends in tundra in response to climate change, suggesting increases in productivity. To better understand the ability of remote sensing to detect climate impacts on tundra vegetation productivity, we applied a photosynthetic light use efficiency model to simulated climate change treatments of tundra vegetation. We examined changes in the Normalized Difference Vegetation Index (NDVI) and photosynthetic light use efficiency ( ε) in experimental warming and moisture treatments designed to simulate climate change in northern Alaska. Plots were warmed either passively, using Open Top Chambers, or actively using electric heaters in the soil. In one set of plots water table depth was actively altered, while other plots were established in locations that were naturally wet or dry. Over two growing seasons, plot-level carbon flux and spectral reflectance measurements were collected, and the results were used to derive a light use efficiency model that could explore the effects of moisture and temperature treatments using remote sensing. Warming increased values of canopy greenness (NDVI) relative to control plots, this effect being more pronounced in wet plots than in dry plots. Light use efficiency (LUE), the relationship between absorbed photosynthetically active radiation (PAR) and gross ecosystem production (GEP), was consistent across warming treatments, growing season, subsequent years, and sites. However, LUE was affected by vegetation type, which varied with moisture; plots in naturally dry locations showed reduced light use efficiency relative to moist plots. Additionally moss exhibited reduced LUE relative to vascular plants. Understory moss production, not accounted for by the usual definition of the fraction of absorbed PAR ( f APAR), was found to be a significant part of total GEP, particularly in areas with low vascular plant cover. These results support the use of light use efficiency models driven by spectral reflectance for estimating GEP in tundra vegetation, provided effects of vegetation functional type (e.g. mosses versus vascular plants) and microtopography are considered.