|DOLD, CHRISTIAN - Orise Fellow|
|THOMAS, ANDREW - University Of Missouri|
|PHILIPP, D - University Of Arkansas|
|Sauer, Thomas - Tom|
Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2019
Publication Date: 4/4/2019
Citation: Dold, C., Thomas, A.L., Ashworth, A.J., Philipp, D., Brauer, D.K., Sauer, T.J. 2019. Carbon sequestration and nitrogen uptake in a temperate silvopasture system. Nutrient Cycling in Agroecosystems. 114(1):85-98. https://doi.org/10.1007%2Fs10705-019-09987-y.
Interpretive Summary: Agroforestry systems have been recognized for their potential to store carbon in woody above ground biomass. This study aims to determine the rate of carbon uptake and growth of trees in a 17-year-old northern red oak- pecan agroforestry planting in Fayetteville, AR, USA. Tree diameter was measured, and the annual increase in tree diameter was calculated. In addition, seven oak and pecan trees were felled in 2016, and biomass and carbon content of trunk, stems, and branches were estimated. The average carbon concentration of the trunk, stems, and branches was 47.9% and 47.3% for oak and pecan. Biomass and carbon content of all trees were 7.1 and 3.4 metric tons per hectare for pecan and 29.8 and 14.3 metric tons per hectare for oak, which corresponds to a linear annual increase in carbon uptake of 0.84 and 0.20 metric tons for the 17-year-period, respectively. However, the annual increase of tree diameter followed a non-linear model, and reached its maximum of 1.70 and 1.79 cm per year for oak and pecan 11 years after planting. Assuming similar behavior of carbon uptake suggests an oversimplification of classic annual carbon uptake estimations. This research is important to scientists and policy analysts interested in more accurate estimates of carbon sequestration by woody biomass
Technical Abstract: Agroforestry systems (AFS) have been recognized for their potential to foster long-term carbon sequestration in woody perennials. This study aims to determine the carbon sequestration rate and growth of above-ground woody biomass in a 17-year-old northern red oak (Quercus rubra) - pecan (Carya illinoinensis) silvopastoral planting (141 and 47 trees/ ha) in Fayetteville, AR, USA. Diameter at breast height (DBH; 137 cm above ground) was measured annually, and a three-parameter logistic non-linear mixed effect model was used to estimate absolute (AGR) and relative (RGR) growth rates. In addition, seven oak and pecan trees were felled in 2016, and woody above-ground biomass (DWw) and carbon content (Cw) were estimated using AFS-specific allometric equations. The carbon concentration in ligneous material was 47.9% and 47.3% for oak and pecan, respectively. Total DWw and Cw were 7.1 and 3.4 Mg ha-1 for pecan and 29.8 and 14.3 Mg ha-1 for oak, which corresponds to a carbon sequestration rate of 0.84 and 0.20 Mg C ha-1 yr-1 for the 17-year-period, respectively. The mixed effect model having individual-tree-level random effects for all parameters provided the best representation of DBH growth of oak and pecan, likely due to the high heterogeneity of site characteristics. The AGR of DBH explained the non-linear behavior of plant growth, and reached its maximum of 1.70 and 1.79 cm yr-1 for oak and pecan 11 years after planting. Assuming similar behavior of carbon uptake suggests an oversimplification of classic carbon sequestration rate estimations.