By Lindsey Rudd (2020, M.E.S., University of Saskatchewan)
Shelterbelts are beneficial for protection against soil erosion, as well as for the promotion of biodiversity and wildlife habitat. Additionally, they play an integral role in carbon sequestration through growth in tree biomass and agricultural soil. The widespread adoption of shelterbelts was, in part, triggered by concerns about erosion of topsoil caused in the drought-prevalent years in the early to mid-20th century. In recent years, it has become more common to remove these shelterbelt trees to convert land to crop production or due to the increasing size of equipment imposing difficulty navigating around the shelterbelt during seeding, spraying, and harvest. In addition, soil erosion is no longer a risk due to wide spread conservation farming practices being employed. Life Cycle Assessment (LCA) is a tool that observes and analyzes the entire life of a phenomenon from ‘cradle to grave’. A Carbon-LCA of planted shelterbelts accounts for the processes by which carbon dioxide is sequestered through the function of photosynthesis by tree species and micro-organisms in agricultural soils as well as its emission produced during various life stages. The pan-Canadian framework outlined by federal government of Canada in 2018 has made a goal of a nation-wide carbon tax or cap and trade equivalent. There is likely potential for financial incentives to adopt management plans, which reduce one’s carbon footprint. There is a lack of information on the amount of carbon sequestered and emitted at each life cycle stage for the six common shelterbelt tree species (hybrid poplar, green ash, Manitoba maple, Scots pine, white spruce, and caragana) found in the Saskatchewan prairies. This study aims to estimate the net carbon sequestered by various tree species by various production stages. Net amount of carbon sequestered was a sum of that emitted as well as sequestered. Overall analysis was divided into two major parts with the first being the carbon dioxide (CO2) emissions for one year of seedling production, roughly 500,000 seedlings, was 1,100 tonnes (t), or 0.002 t per individual seedling. The second LCA stage, transportation a typical full shipment had CO2 emissions of 6.08 t for delivery to Regina, SK from Estevan, SK. For shipments of the same number of seedlings to Saskatoon, SK and Prince Albert, SK, the emissions were 14.10 t and 17.20 t CO2, respectively. Production of seedlings accounted for 95-98% of total emissions during this stage, depending on where the shipment was delivered. The highest emitters in the production phase included electricity at roughly 83% (or 914.71 t CO2) and heating at 11% (or 121.00 t CO2). The planting phase accounted for 1.90 t CO2/1000 seedlings. Maintenance accounted for 0.49 t CO2/1000 trees. These life stages added an insignificant amount of CO2 emissions comparatively to the amount that a shelterbelt can sequester over its life. All of these emissions are balanced by carbon sequestered by trees and the soil. Each shelterbelt species sequestered a different rate of carbon, with hybrid poplar sequestering the most carbon in all three soil zone clusters selected for the study. Hybrid poplar is a rapid growing tree and subsequently sequesters the most carbon of the six species in all soil zones, with a km stretch of shelterbelt sequestering upwards of 1460 t CO2 by age 60. Manitoba maple and white spruce are the next highest carbon sequesters. The final stage of the shelterbelts is its eventual disposal – assumed in this study to be their removal. This stage of removal boasted CO2 emissions for two reasons: the physical process of removing the trees as well as the carbon lost due to burning of removed biomass. The removal of a km long shrub shelterbelt released 0.82 t CO2. The removal of coniferous and deciduous trees in a shelterbelt equated 1.12 t CO2. Removal of a shelterbelt of large sized hybrid poplars produces 2.43 t CO2.
By Chuckwudi Amadi (2016, Ph.D., University of Saskatchewan)
For more than a century, over 600 million shelterbelt trees have been distributed to land owners in the Canadian Prairies mainly to protect farms from soil erosion and extreme wind events. In Saskatchewan, there exists over 60,000 km of planted shelterbelts; however, there is a lack of data quantifying the role of shelterbelts in mitigating greenhouse gas (GHG) emissions in agricultural landscapes. These limited estimates of carbon (C) sequestration and GHG mitigation potential for shelterbelts are needed for regional C budgets and GHG inventories. The objective of this research was to quantify the role of shelterbelts on the mitigation of CO2, CH4 and N2O in cultivated fields. Chamber-based GHG monitoring and modeling approaches were employed. Nitrous oxide emissions were lower in shelterbelts (0.65 kg N2O-N ha-1 yr-1) than in cultivated soils (2.5 kg N2O-N ha-1 yr-1), attributed to the capability of deep rooting trees to remove excess available N and soil water. Both shelterbelt and cultivated soils were small sinks for CH4, though the sink potential was 3.5-times greater for the shelterbelt soils. Soil-derived CO2 emissions were greater in the shelterbelts (4.1 Mg CO2-C ha-1 yr-1) than in the adjacent fields (2.1 Mg CO2-C ha-1 yr-1). Nevertheless, cumulative emissions of non-CO2 GHGs was reduced by 0.55 Mg CO2e ha-1 yr-1 in the shelterbelts and soil C storage (0–30 cm soil depth) was 27% greater, representing an increase of 28 Mg ha-1 in the shelterbelts than in the cropped fields, attributed to long-term inputs from tree litter. Holos model simulations of GHG fluxes in a cereal-pulse rotation indicated that a shelterbelt planting occupying 5% of the farmland resulted in total farm emissions being reduced by 8.2 – 23% during a 60-year period, depending on selected tree species. Between 90 – 95% of GHG mitigation by shelterbelts was through C sequestration in tree biomass and in stable SOC pools, while the reduction in N2O emissions and increased oxidation of soil CH4 totalled 5.1 – 9.8% of the overall GHG mitigation by shelterbelts. Faster growing trees (e.g. hybrid poplar) were more effective in accumulating C in tree biomass and soil and in mitigating soil GHG emissions. This study provides evidence that farm shelterbelts function as net biological sinks of CO2 and can play a role in mitigating soil-derived GHG emissions in agricultural landscapes.
By Gubhir Dhillon (2016, Ph.D., University of Saskatchewan)
The increase in atmospheric concentration of carbon dioxide (CO₂) is contributing to global climate change. Agroforestry systems, such as shelterbelts, can contribute to the mitigation of increasing CO₂ levels, through carbon (C) sequestration in plant biomass and soils. However, little information is available on the storage and dynamics of soil organic carbon (SOC) for shelterbelt systems. The objective of this research was to examine the effect of shelterbelt plantings on the storage, physical stabilization and chemical composition of SOC for major shelterbelt species across Saskatchewan compared to adjacent agricultural fields. Soil and litter samples were collected for six major shelterbelt species including green ash (Fraxinus pennsylvanica), hybrid poplar (Populus spp.), Manitoba maple (Acer negundo), white spruce (Picea glauca), Scots pine (Pinus sylvestris) and caragana (Caragana arborescens) and the adjacent agricultural fields at 59 sampling sites across the agricultural region of Saskatchewan. Measurement of SOC concentration for soil samples was preceded by fumigation with concentrated HCl (12N), which was determined to be the efficient method for SOC determination in carbonate-rich soils. Physical stabilization of SOC was characterized by using the density fraction technique to separate SOC into uncomplexed, plant-derived debris (i.e. light fraction) and mineral-associated organic matter (i.e. heavy fraction). Changes in SOC composition due to shelterbelt plantation were studied using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and synchrotron based carbon K-edge X-ray absorption near edge structure (XANES) spectroscopy. Concentration of SOC for shelterbelts was significantly higher compared to agricultural fields throughout the soil profile (0-50 cm). Sequestration of SOC for shelterbelts varied from 6-38 Mg C ha⁻¹ under different shelterbelt species, along with 3-8 Mg C ha⁻¹ stored in the litter layer. Shelterbelts led to an increase in SOC content for both the labile light fraction and the mineral-associated heavy fraction. The increase in the heavy fraction was higher in coniferous shelterbelt species including white spruce and Scots pine, while the increase in the light fraction C was higher in hybrid poplar, Manitoba maple, green ash and caragana. These trends were attributed to differences in quality and decomposition rate of litter among shelterbelt species. Maximum amount of SOC was sequestered at the 10-30 cm soil depth, and the majority (70%) of it was in the stable mineral-associated form. Light fraction C was predominant in the surface layer (0-10 cm), where it accounted for 92% of the total sequestered C. Younger shelterbelts tended to lose SOC in the early years of shelterbelt establishment, but eventually resulted in net addition of C after about 20 years of age. SOC sequestration potential of shelterbelts was positively related to shelterbelt characteristics including stand age, tree height, diameter and crown width and density of litter layer. These variables together explained 56-67% of the inter-site variability in the amount of SOC sequestered. Analysis of molecular composition of SOC revealed shelterbelts had higher abundance of processed forms of C such as aromatic and conjugated carboxyl groups for hybrid poplar and white spruce shelterbelts and aromatic and aliphatic C moieties for Manitoba maple shelterbelts. In contrast, agricultural field soils were enriched in easily degradable C forms such as polysaccharides. These results revealed a strong effect of initial litter quality and extent of decomposition on SOC composition. Together, these findings indicate that shelterbelt planting leads to sequestration of SOC, resulting in the decrease of atmospheric CO₂ concentration. Additionally, shelterbelts also influence organo-mineral association and molecular composition of SOC, which may affect stabilization and dynamics of sequestered SOC.
By Janell Rempel (2015, M.E.S., University of Saskatchewan)
The role of shelterbelts within prairie agriculture is changing. In the past, shelterbelts have been promoted and adopted for soil stabilization and their ability to protect farmsteads and livestock from harsh prairie climates. In today’s agricultural landscape advances in production technology, an increase in farm size, and changes to policy have changed the circumstances in which decisions related to shelterbelts are made. The objective of this research is to identify the costs, benefits and the barriers to adoption and retention of shelterbelts that influence agricultural producers and landowners’ management decisions related to shelterbelts in the Canadian Prairies. In the summer of 2013, surveys of producers and landowners from throughout the province of Saskatchewan (and several from Alberta) were conducted. Using the information collected in the surveys, the costs and benefits (both economic and non-economic), and potential barriers to adoption and retention of shelterbelts that influence producer’s management decisions were identified and analyzed. This research identified that overall shelterbelts removal is increasing and that there are many barriers to adoption and retention for agricultural producers related to the economic costs. In addition, it was found that many of the benefits of shelterbelts are non-economic and more difficult for producers and landowners to recognize within their operations. Going forward, shelterbelts have the potential to play a major role in climate change mitigation by sequestering significant amounts of atmospheric carbon dioxide (CO2) into the soil and as biomass carbon in aboveground and belowground parts of planted shelterbelt trees or shrubs within the agricultural landscape. In addition, shelterbelts provide many ecological goods and services to landowners and society. In conclusion, understanding the context in which producers are making decisions related to shelterbelts within their operations is important from an agricultural production, climate change, and policy perspective.
By Bryan Mood (2013, B.Sc., Mount Allison University)
Climate change has resulted in the northward migration of many tree species in Canada and is likely to continue as greenhouse gas emissions alter weather patterns. The northern range limit and expansion of trees has been frequently studied but there has been little research concerning the effects of climate change on the fluctuations that will occur at the southern range margins of some of the same species. White spruce (Picea glauca) shelterbelts, an agroforestry product in southern Saskatchewan, represent a unique opportunity that offers significant insight into the future physiological stresses on the boreal forest in central and northern Saskatchewan. A regional pattern of radial growth for white spruce in both shelterbelts and natural forests throughout Saskatchewan was constructed using dendrochronological techniques. Thirty chronologies were established ranging from 36 to 188 years old and it was found that mean sensitivity had a significant relationship with latitude and longitude (R2= 0.790; p< 0.0000). Using eigenvector analysis it was found that white spruce growth variance is associated with June temperature, spring precipitation, and changes in soil characteristics. Using mean sensitivity as a measure of physiological stress on white spruce, two implications can be interpreted. First, results of past growth taken in combination with future climate predictions of increasing surface temperature and changes in precipitation patterns suggest a physiological stress imposed on white spruce in southern Saskatchewan. And second, a future contraction of the optimum climate-envelope of white spruce in the southern boreal forest range margins will likely occur.
By Emma Davis (2012, B.Sc., Mount Allison University)
In the summer of 2012, students from the Mount Allison Dendrochronology Lab (MAD Lab) visited Saskatoon, Saskatchewan to complete fieldwork as a part of a four-year research program in association with the University of Saskatchewan and the Agricultural Greenhouse Gas Project. Shelterbelts, which include trees and shrubs planted around farmsteads and crops, were the subject of the research, and this thesis describes an effort to determine the carbon sequestration capacity of the nine of the most commonly planted shelterbelt species in the Canadian Prairies. The analysis and results contained within this thesis represent the data collected in May 2011. Chapter I, “Evaluating the suitability of nine shelterbelt species for dendrochronological purposes in the Canadian Prairies”, is a manuscript submitted for publication. This manuscript details the initial creation of nine master chronologies for the Saskatoon area, and strives to determine the usefulness of each of the species for dendrochronological purposes. Chapter II, “Radial-growth Forecasting: the projected status of nine shelterbelt species in 2100”, uses Canadian Global Circulation Model data to forecast the likely growth patterns of shelterbelt species under three different climate scenarios. The results of this analysis will serve as an indicator to farmers landowners, informing their decision of which trees to plant in the present based on their ability to grow successfully and sequester carbon in the future.