Complex terrain influences ecosystem carbon responses to temperature and precipitation. Issue 8 (26th August 2017)

• Record Type: Journal Article
• Authors: Reyes, W. M.; Epstein, H. E.; Li, X.; McGlynn, B. L.; Riveros‐Iregui, D. A.; Emanuel, R. E.
• Is Part Of: Global biogeochemical cycles. Volume 31:Issue 8(2017:Aug.)
• Page Start: 1306
• Page End: 1317
• Publication Date: 2017-08-26
• Subjects: ecosystem responses to climate -- carbon cycle -- complex terrain -- land‐atmosphere interactions -- climate change -- landscape ecology; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2017GB005658
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: Terrestrial ecosystem responses to temperature and precipitation have major implications for the global carbon cycle. Case studies demonstrate that complex terrain, which accounts for more than 50% of Earth's land surface, can affect ecological processes associated with land‐atmosphere carbon fluxes. However, no studies have addressed the role of complex terrain in mediating ecophysiological responses of land‐atmosphere carbon fluxes to climate variables. We synthesized data from AmeriFlux towers and found that for sites in complex terrain, responses of ecosystem CO2 fluxes to temperature and precipitation are organized according to terrain slope and drainage area, variables associated with water and energy availability. Specifically, we found that for tower sites in complex terrain, mean topographic slope and drainage area surrounding the tower explained between 51% and 78% of site‐to‐site variation in the response of CO2 fluxes to temperature and precipitation depending on the time scale. We found no such organization among sites in flat terrain, even though their flux responses exhibited similar ranges. These results challenge prevailing conceptual framework in terrestrial ecosystem modeling that assumes that CO2 fluxes derive from vertical soil‐plant‐climate interactions. We conclude that the terrain in which ecosystems are situated can also have important influences on CO2 responses to temperature and precipitation. This work has implications for about 14% of the total land area of the conterminous U.S. This area is considered topographically complex and contributes to approximately 15% of gross ecosystem carbon production in the conterminous U.S. Key Points: AmeriFlux data reveal that terrain complexity influences the response of ecosystem CO2 fluxes to temperature and precipitation In complex terrain, CO2 responses to climate variables are organized by topographic variables associated with water and energy availability Complex terrain gives rise to emergent ecosystem behaviors that may not be captured by current land surface modeling approaches Plain Language Summary: Land‐based ecosystems remove carbon dioxide from Earth's atmosphere, filling a critical role in the global carbon balance. Approximately half of Earth's land area occupies hilly or mountainous terrain (i.e., complex terrain), but relatively little research has examined how complex terrain influences the ability of ecosystems to remove carbon dioxide from the atmosphere. We analyzed data from 30 research towers around the United States used to measure carbon dioxide movement between ecosystems and the atmosphere. Some towers were located in complex terrain, and others were located in relatively simple, flat terrain. For each site, we examined patterns of carbon dioxide exchange (photosynthesis, respiration, and the net exchange) in response to changes in temperature and precipitation. For towers located in complex terrain, we found that the average slope angle surrounding a site predicted daily responses of carbon dioxide exchange to temperature and the average drainage area surrounding a site predicted annual responses of carbon dioxide exchange to precipitation. Towers in simple terrain showed no such relationships. The results show that in complex terrain, slope and drainage area affect ecosystem carbon cycles in predictable ways. The patterns and behavior that we observed apply to approximately 14% of the conterminous United States.