Abstract
Information on carbon (C) sequestration potential of agroforestry practices (AP) is needed to develop economically beneficial and ecologically and environmentally sustainable agriculture management plans. The synthesis will provide a review of C sequestration opportunities for AP in temperate North America and the estimated C sequestration potential in the US. We estimated carbon sequestration potential for silvopasture, alley cropping, and windbreaks in the US as 464, 52.4, and 8.6 Tg C yr¯¹, respectively. Riparian buffers could sequester an additional 4.7 Tg C yr-1 while protecting water quality. Thus, we estimate the potential for C sequestration under various AP in the US to be 530 Tg yr ¯¹. The C sequestered by AP could help offset current US emission rate of 1,600 Tg C yr¯¹ from burning fossil fuel (coal, oil, and gas) by 33 %. Several assumptions about the area under different AP in the US were used to estimate C sequestration potential: 76 million ha under silvopasture (25 million ha or 10% of pasture land and 51 million ha of grazed forests), 15.4 million ha (10% of total cropland) under alley cropping, and 1.69 million ha under riparian buffers. Despite data limitation and uncertainty of land area, these estimates indicate the important role agroforestry could play as a promising CO2 mitigation strategy in the US and temperate North America. The analysis also emphasizes the need for long-term regional C sequestration research for all AP, standardized protocols for C quantification and monitoring, inventory of AP, models to understand long-term C sequestration, and site-specific agroforestry design criteria to optimize C sequestration.
Generated Summary
This research article reviews carbon (C) sequestration opportunities within agroforestry practices (AP) in temperate North America and estimates the C sequestration potential in the US. The study uses a literature review and analysis to assess the potential of silvopasture, alley cropping, windbreaks, and riparian buffers for C sequestration. The analysis included the evaluation of data on C sequestration influenced by factors such as management practices, soil type, precipitation, and hydrology. The primary objective is to provide a comprehensive overview of C sequestration under different AP in temperate North America and to estimate their potential within the US. The research also emphasizes the need for long-term regional C sequestration research for all AP, standardized protocols for C quantification and monitoring, inventory of AP, and models to understand long-term C sequestration, and site-specific agroforestry design criteria to optimize C sequestration.
Key Findings & Statistics
- The study estimates carbon sequestration potential for silvopasture, alley cropping, and windbreaks in the US as 464, 52.4, and 8.6 Tg C yr⁻¹, respectively.
- Riparian buffers could sequester an additional 4.7 Tg C yr⁻¹.
- The potential for C sequestration under various AP in the US to be 530 Tg yr⁻¹.
- The C sequestered by AP could help offset current US emission rate of 1,600 Tg C yr⁻¹ from burning fossil fuel by 33%.
- Current atmospheric CO2 concentration is 36% greater than the pre-industrial period concentration of 280 ppm.
- The projected doubling of atmospheric CO2 by the latter half of the twenty-first century raises concerns for everyone.
- In the US, pasture and grazed forests are 248 and 51 million ha, respectively.
- Using a sequestration potential of 6.1 Mg C ha⁻¹ yr⁻¹ on 10% marginal pasture land (25 million ha) and grazed forests (51 million ha), the total C sequestration potential for silvopastoral lands in the US could be as high as 464 Tg C yr⁻¹.
- The C input from trees pruned at 1-m height in year two were 1.42 and 1.08 Mg ha⁻¹ yr⁻¹ from leaves and twigs, respectively.
- Contribution from tree mulch was 2.5 Mg C ha⁻¹.
- The SOC content in OP were 450 and 62 Mg ha⁻¹ for 0–50 and 50–125 cm depths, respectively, compared to corresponding values of 491 and 101 Mg ha⁻¹, respectively, in the silvopasture.
- Compared to forestry that often has a large aerial footprint, many AP sequester substantial amounts of C on a relatively small land base, leaving a large portion of the landscape still available for agriculture.
- Converting 10% of crop land with a sequestration value of 3.4 Mg C ha⁻¹ yr⁻¹ to potentially sequester 52.4 Tg C yr⁻¹ through alley cropping.
- In a 6-year-old hybrid poplar site (111 trees ha⁻¹) in Canada, Thevathasan and Gordon (Thevathasan and Gordon 1997) reported 1.07 Mg C ha⁻¹ was contributed by litterfall.
- In a 6-year-old hybrid poplar site (111 trees ha⁻¹) in Canada, Thevathasan and Gordon (Thevathasan and Gordon 1997) reported 1.07 Mg C ha⁻¹ was contributed by litterfall. In the same study, hybrid poplar leaves and branches had C stocks of 1.3 and 5.5 Mg C ha⁻¹ when trees were 13-year-old (Peichl et al. 2006).
- After 13 years trees (branches, stem, and leaves) added 14 Mg C ha⁻¹ in addition to the 25 Mg C ha⁻¹ added by litter and fine roots (Thevathasan and Gordon 2004).
- Based on 2007 statistics, cropland in the US is between 144 and 165 million ha.
- If 80 million ha of cropland, as estimated by Nair and Nair (2003), is put under alley cropping, it would significantly increase the C sequestration potential to 272 Tg C yr⁻¹.
- State and national levels agencies recommend buffer widths between 15 and 100 m for protection of water bodies, water quality improvements, stream-bank stabilization, and to reduce sediment and nutrient losses.
- A 30-m wide riparian buffer along both sides of 5% of total river length that would occupy 1.69 million ha, the potential C sequestration by riparian buffers along rivers in the US could be as high as 4.7 Tg C yr⁻¹.
- The estimated average aboveground C sequestration potential is 2.46 Mg C ha⁻¹ yr⁻¹.
- The C sequestration potential of silvopasture varies from a low of 1.8 to a high of 3.3 Mg C yr⁻¹.
- A total potential of 260 Tg yr⁻¹ for managed forests, cropland, and pasture was estimated by Heath et al.
- The amount of C stored (biomass and soil) was 5.8 and 8.2 Mg C ha¯¹ greater in silvopasture than pasture or Douglas fir plantation.
- Soil organic carbon (SOC) and root mass were significantly greater in soils under a cottonwood silvopasture in the 1-m soil profile compared to maize rotation.
- SOC derived from trees was significantly greater throughout the 1.25-m soil profile and clay + silt fractions in a slash pine and bahiagrass silvopasture compared to open pastures (OP).
Other Important Findings
- Agroforestry practices (AP), which integrate woody plants into agricultural systems, are identified as crucial for developing economically beneficial and environmentally sustainable agricultural management plans.
- The analysis indicates the important role agroforestry could play as a promising CO2 mitigation strategy in the US and temperate North America.
- The enhanced C sequestration concept in agroforestry is based on efficient use of resources by the structurally and functionally more diverse and complex plant communities compared to sole crop or grass systems.
- Adoption of AP has a greater potential to increase C sequestration of predominantly agriculture dominated landscapes than traditional agriculture without changing the land use to forestry.
- The amount of C stored on a site is a balance between long-term fluxes, the net C gain depends on the C content of the previous system that the AP replaces.
- The spatial distribution of C, both above and belowground is determined by the silvopastural design and its management.
- The amount of C sequestered per unit area is substantially higher in agroforestry compared to conventional row-crop agriculture.
- Windbreaks have been used throughout history to protect homes, structures, livestock, and crops, control wind erosion and blowing snow, provide habitat for wildlife, improve landscape, reduce evaporation loss of water from soil and leaf surfaces, and for odor mitigation.
- In general, potential C sequestration and storage are greater in riparian buffer systems compared to row crops or upland forests.
- The results of the study show that perennial vegetation in the buffer areas, either trees or grasses, had significantly greater respiration rates compared to the annual crops.
Limitations Noted in the Document
- There are several limitations in the data sets used for this analysis, especially due to a lack of accurate estimates of C sequestration for all regions and systems.
- The study emphasizes the need for long-term regional C sequestration research for all AP, standardized protocols for C quantification and monitoring, and models to understand long-term C sequestration.
- Lack of accurate estimates of C sequestration for all regions and systems, and land area under each AP can introduce errors in the calculations.
- The literature lacks such information for integrated AP, which can affect the accuracy of C sequestration estimates.
- Since harvest cycles vary from 10 to 80 years for tree species, research focus should be changed to understand long-term benefits of multi-species and multi-year systems.
Conclusion
The study emphasizes the potential of agroforestry as a key strategy for carbon sequestration in temperate North America. It highlights the importance of AP in developing economically beneficial and ecologically sustainable agricultural management plans. Key to this is the enhanced C sequestration concept in agroforestry, which is based on the efficient use of resources by diverse plant communities compared to simple crop systems. The analysis underlines that adoption of AP offers a greater potential for increasing C sequestration in agricultural landscapes without changing land use to forestry. The research stresses the need for long-term, region-specific C sequestration research for all AP, along with standardized protocols for C quantification and monitoring. Further, models are needed to understand the long-term effects of C sequestration and site-specific agroforestry design to optimize C sequestration. The study concludes by emphasizing that agroforestry is a promising practice to sequester carbon. The research highlights the numerous environmental, economic, and social benefits of AP. Further research is needed to develop accurate estimates and to formulate policies and guidelines that align with landowner expectations. The article also recommends a standardized protocol for sampling, analyzing, and handling data so that C data can be used in models to examine long-term effects, scaling up for larger landscapes.