Contributions of secondary forest and nitrogen dynamics to terrestrial carbon uptake

Abstract

Abstract.We use a terrestrial carbon-nitrogen cycle component of the Integrated Science Assessment Model (ISAM) to investigate the impacts of nitrogen dynamics on regrowing secondary forests over the 20th century. We further examine what the impacts of nitrogen deposition and land use change history are on terrestrial carbon uptake since preindustrial time. Our results suggest that global total net land use emissions for the 1990s associated with changes in cropland, pastureland, and wood harvest are 1.22 GtC/yr. Without considering the secondary forest regrowth, the estimated net global total land use emissions are 1.58 GtC/yr or about 0.36 GtC/yr higher than if secondary forest regrowth is considered. Results also show that without considering the nitrogen dynamics and deposition, the estimated global total secondary forest sink for the 1990s is 0.90 GtC/yr or about 0.54 GtC/yr higher than estimates that include the impacts of nitrogen dynamics and deposition. Nitrogen deposition alone is responsible for about 0.13 GtC/yr of the total secondary forest sink. While nitrogen is not a limiting nutrient in the intact primary forests in tropical regions, our study suggests that nitrogen becomes a limiting nutrient for regrowing secondary forests of the tropical regions, in particular Latin America and Tropical Africa. This is because land use change activities, especially wood harvest, removes large amounts of nitrogen from the system when slash is burnt or wood is removed for harvest. However, our model results show that carbon uptake is enhanced in the tropical secondary forests of the Indian region. We argue that this may be due to enhanced nitrogen mineralization and increased nitrogen availability following land use change in the Indian tropical forest ecosystems. Results also demonstrate that there is a significant amount of carbon accumulating in the Northern Hemisphere where most land use changes and forest regrowth has Correspondence to: A. K. Jain (jain1@uiuc.edu) occurred in recent decades. This study indicates the significance of secondary forests to terrestrial carbon sinks, the importance of nitrogen dynamics to the magnitude of secondary forests carbon uptake, and therefore the need to include both primary and secondary forests and nitrogen dynamics in terrestrial ecosystem models.

Above- and belowground ecosystem biomass, carbon and nitrogen allocation in recently afforested grassland and adjacent intensively managed grassland

“…Furthermore, N allocation, availability and turnover are linked to plant growth and thus ecosystem C dynamics (e.g. Booth et al 2005;Yang et al 2010). With land-use type being a major factor predetermining ecosystem C and N pools, any land-use change activity (e.g.…”

Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years

“…Before 1980, a negatively autocorrelated error component was added to dC/dt simulations. To assess the uncertainty in SF, we combined three independent inventories of F F emissions [14][15][16] with three independent inventories of F L emissions [17][18][19] . To each emission inventory, we added positively autocorrelated random errors to account for temporally persistent accounting errors 20 .…”

Representing anthropogenic gross land use change, wood harvest, and forest age dynamics in a global vegetation model ORCHIDEE-MICT v8.4.2

“…Stocker et al (2014) included secondary land in LPX-Bern 1.0 but only one tile of secondary land is available. Yang et al (2010) examined the contribution of secondary forests to terrestrial carbon uptake using the ISAM model by explicitly including secondary forest PFTs, but they did not include the dynamic clearing of secondary forests nor shifting cultivation in LUC. Therefore, none of these studies have included a dynamic decision rule regarding the ages of cohorts to be targeted in different LUC processes or the possibility of targeting different cohort ages in different geographical regions.…”