Vegetation growth models are used with remotely sensed and meteorological data to monitor terrestrial carbon dynamics at a range of spatial and temporal scales. Many of these models are based on a light-use efficiency equation and two-component model of whole-plant growth and maintenance respiration that have been parameterized for distinct vegetation types and biomes. This study was designed to assess the robustness of these parameters for predicting interannual plant growth and carbon exchange, and more specifically to address inconsistencies that may arise during forest disturbances and the loss of canopy foliage. A model based on the MODIS MOD17 algorithm was parameterized for a mature upland hardwood forest by inverting CO2 flux tower observations during years when the canopy was not disturbed. This model was used to make predictions during a year when the canopy was 37% defoliated by forest tent caterpillars. Predictions improved after algorithms were modified to scale for the effects of diffuse radiation and loss of leaf area. Photosynthesis and respiration model parameters were found to be robust at daily and annual time scales regardless of canopy disturbance, and differences between modeled net ecosystem production and tower net ecosystem exchange were only approximately 2 g C m-2 d-1 and less than 23 g C m-2 y -1. Canopy disturbance events such as insect defoliations are common in temperate forests of North America, and failure to account for cyclical outbreaks of forest tent caterpillars in this stand could add an uncertainty of approximately 4-13% in long-term predictions of carbon sequestration.
Bibliographical noteFunding Information:
This research was funded in part by the National Institute for Climatic Change Research (NICCR) and Terrestrial Carbon Processes (TCP) programs of the US Department of Energy (DoE). Any opinions, findings, and conclusions or recommendations herein are those of the authors and do not necessarily reflect the view of DoE. The authors wish to thank Dan Baumann and Aaron Berger, USDA Forest Service, North Central Research Station for their technical assistance and maintenance of the Willow Creek flux tower throughout this study. We extend our appreciation to Tom Steele, Gary Kellner, and Karla Ortman at the Kemp Natural Resources Station, University of Wisconsin, who provided technical support and accommodations throughout this project. Special thanks and appreciation goes to Wu Yang for her constant support and encouragement while writing this manuscript.
- Carbon utilization efficiency
- Ecosystem respiration
- Malacosoma disstria Hübner
- Primary production
- Quantum efficiency