Abstract
Assessing carbon (C) sequestration in forest ecosystems is fundamental to supply information to monitoring, reporting and verification (MRV) for reducing deforestation and forest degradation (REDD). The spatially-explicit version of Forest-DNDC (FDNDC) was evaluated using plot-based observations from Nez Perce-Clearwater National Forest (NPCNF) in Idaho of United States and used to assess C stocks in about 16,000 km2. The model evaluation indicated that the FDNDC can be used to assess C stocks with disturbances in this temperate forest with a proper model performance efficiency and small error between observations and simulations. Aboveground biomass in this forest was 85.1 Mg C ha-1 in 2010. The mean aboveground biomass in the forest increased by about 0.6 Mg C ha-1 yr-1 in the last 20 years from 1990 to 2010 with spatial mean stand age about 98 years old in 2010. Spatial differences in distributions of biomass, net primary production and net ecosystem product are substantial. The spatial divergence in C sequestration is mainly associated with the spatial disparities in stand age due to disturbances, secondly with ecological drivers and species. Climate variability and change can substantially impact C stocks in the forest based on the climatic variability of spatial climate data for a 33-year period from 1981 to 2013. Temperature rise can produce more biomass in NPCNF, but biomass cannot increase with an increase in precipitation in this forest. The simulation with disturbances using observations and estimates for the time period from 1991 to 2011 showed the effects of disturbances on C stocks in forests. The impacts of fires and insects on C stocks in this forest are highly dependent on the severity, the higher, the more C loss to atmosphere due to fires, and the more dead woods produced by fires and insects. The rates of biomass increase with an increase in stand age are different among the species. The changes in forest C stocks in the forest are almost species specific, non-linear and complex. The increase in aboveground biomass with an increase in stand age can be described by a high-order polynomial.
Highlights
Forests have been known an important terrestrial carbon (C) sink [1,2,3,4,5,6]
The four quantitative evaluation variables (Table 2) concluded consistently that FDNDC performed excellently to estimate C sequestration in this temperate forest in Idaho in USA with high performance efficiency; based on the model performance rating, FDNDC performance for assessing C stocks in stands over the temperate forest was within the range of “very good” (E ≥ 0.75; RRS ≤ 0.7; −25 ≤ PBIAS ≤ 25) [35, 36]
The results show that climate variability can substantially impact C stocks in the forest in Nez Perce-Clearwater National Forest (NPCNF) (Figure 7)
Summary
Forests have been known an important terrestrial carbon (C) sink [1,2,3,4,5,6]. Generally, C sequestration in forests can be expressed by using CO2 flux measurements. Recent applications of biogeochemical C models for assessing forests response to land use change and natural and human disturbances reflect their merits [2, 15,16,17,18,19,20,21]. Application of these effective tools is fundamental to evaluate the responses of forests to climate change and the role of forests in mitigating global warming, and to effectively assess C stocks and long-term dynamics for forest management and restoration
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