Estimation of carbon sequestration using large-scale forest inventory data has become important due to the link between possible climate change and the accumulation of greenhouse gases in the atmosphere [1
]. In 1992, 150 countries including the U.S. signed the United Nations Framework Convention on Climate Change that resulted in the development of annual reports of greenhouse gas inventories including carbon in forests. Forest carbon pools are often delineated as standing live trees, standing dead trees, down and dead woody materials, forest floor, understory, and soils. The down and dead woody materials pool (detritus) essentially consists of coarse woody debris, fine woody debris, and stumps. Coarse woody debris is defined by the Forest Inventory and Analysis (FIA) program of the USDA Forest Service as down and dead woody material at least 7.62 cm in diameter [3
]. Fine woody debris is defined by FIA as dead and down woody material with a diameter between 0.01 and 7.61 cm [3
]. In the U.S., it has been estimated that 35 % of the total forest carbon pool is in live vegetation, 52 % is in the soil, and 14 % is in dead organic material [4
]. Therefore, estimating coarse and fine woody debris carbon stocks across the United States is crucial to national carbon reporting and monitoring.
Forest terrestrial carbon sinks represent a fine balance between the influx of CO2
into photosynthesis and the efflux of CO2
through woody decay processes [1
]. The decay rate of any individual piece of forest dead wood is determined by substrate quality, microbial activity, air temperature, and available moisture [5
]. Similarly, the productive capacity of any given forest is partially governed by climatic variables such as temperature [6
]. Some studies have suggested that forest detritus production and decay may be in balance [7
], whereas others have suggested increased detritus decomposition rates may ultimately cause forest detritus carbon pools to become net CO2
]. Quantifying the dynamics of forest detritus carbon accumulation and turnover within a scenario of global climate warming is critical to predicting the future inventory of United States carbon stocks. Indeed, some studies have already indicated the effects that changing climate can have on the terrestrial carbon cycle [10
] and highlighted the possibility of increasing emission of CO2 from non-live forest carbon pools such as soils [11
]. Emerging suggestions to bury coarse woody debris as a cost effective carbon sequestration technique [12
] would be impacted if coarse woody decay rates are increased by changing climate. To date, initial investigations of coarse and fine woody debris carbon stocks across classes of latitude have indicated that these carbon stocks may be related to climatic variables [13
]. Therefore, correlating coarse and fine woody debris carbon stocks with climatic regions and variables across the United States is highly warranted.
The goal of this study is to relate forest coarse and fine woody debris carbon stocks to climatic regions and variables across the United States with specific objectives including: 1) to estimate mean coarse woody debris, fine woody debris, and total woody detritus carbon stocks (coarse + fine woody debris) by Köppen climatic regions, 2) to correlate/model coarse woody debris, fine woody debris, and total woody detritus carbon stocks with individual climatic variables (average annual precipitation (PRECIP), mean annual maximum temperature (TMAX), mean annual minimum temperature (TMIN), moisture index (MOIST), variability cause (VAR), and potential evapotranspiration (EVAP)), and 3) to interpret the results of this study in the context of possible climate change.