PARENT SESSION
Organized Oral Session 12: Multiple time scales of ecological processes: Results from the LTER Network
Organizer(s): JR Gosz and R Waide
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 510a, Level 5, Palais des congrès de Montréal
Analysis of two temporal behaviors in a forested landscape: Mechanism and consequence.
Harmon, Mark*,1, Johnson, Sherri2, Bond, Barbara1, Jones, Julia 3, Swanson, Frederick2, O'Connell, Kari1, 1 Department of Forest Science, Corvallis, OR, USA2 Pacific Northwest Research Station, Corvallis, OR, USA3 Department of Geosciences, Corvallis, OR, USA
ABSTRACT- Long-term observations and experiments have changed how ecosystems dynamics are analyzed and perceived. However, this raises a new challenge: understanding how the dynamics of different components of ecosystems and landscapes combine to influence overall response. The Andrews LTER program is examining these relationships under the rubric of temporal behaviors, determining both the mechanism controlling and the consequences of selected temporal behaviors. Hysteresis (i.e., variable lags between two state variables) is very common in ecological systems with examples ranging from daily transpiration to soil-drying wetting to long-term changes in carbon stores. A general mechanism involves the system capacitance and hysteresis is expressed when one system part cannot meet the demand of the other. While hysteresis does not necessarily propagate to longer time scales than initially observed, it may influence system response particularly for asymmetrical hysteresis loops. Spatial coherence (i.e., synchrony of response of one state variable in different places) has multiple causes but hypothetically decreases from abiotic to chemical to biotic state variables. While this general pattern is found in the Andrews system, abiotic variables (e.g., temperature) display lower spatial coherence than generally assumed. Biological variables (growth rates, population sizes, and carbon balance) show minimal spatial coherence due to the combined effect of different abiotic regimes, disturbance histories, and internal biological controls (e.g., age class structure). The low spatial coherence of many variables suggests responses to climatic variation may be more muted than previously projected. It also implies system-wide response rates may accelerate if climatic change exceeds a critical threshold.
Key words: spatial coherence, hysteresis, scaling