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Climate Change Mitigation: A Low-Hanging Fruit of Agroforestry P. K. R. NAIR Distinguished Professor University of Florida, Gainesville, FL, USACBSAF, Belém, PA, Brazil: 21 – 25 Nov 2011
Objective and ScopeSeparate the chaff from the grain: Evaluate the current state of scientific knowledge on the role of AFS in climate- change mitigation (and adaptation) meditated through C sequestration Identify the management factors that influence C seq in land-use systems and the extent of their relevance to AFS
SPECIAL SUBMISSIONS: AGROFORESTRY SYSTEMS AND ENVIRONMENTAL QUALITYJournal of Environmental Quality Volume 40 (3), May–June 2011, pages 784–866.
Climate Change Global warming refers to increase in temperature of the earth’s near-surface • Increased by an average 0.6°C since 1970 • IPCC (Intergov. Panel on Climate Change) projects an average rise of 1.1 – 6.4°C during this century • Believed to be caused by the increase in atmospheric concentration of greenhouse gases (GHGs) GHGs include: • CO2 , carbon monoxide (CO), methane (CH4), nitrous oxide (N2O) • CO2 is the major GHG.
Mitigation (of) & Adaptation (to) Climate ChangeMitigation Avoiding emissions and sequestering GHGs: [Technological change and substitution that reduce emissions]Adaptation Reducing the vulnerability of natural systems against actual or expected climate change effects
Climate Change MitigationGoal: Reduce net emissions and enhance sink capacity1. Avoiding or Reducing the Emissions • Increasing input-use efficiency (Management interventions) • Decreasing losses (Soil and water conservation)2. Sequestering CO2 in Terrestrial Biosphere • Forest/woody biomass (Aboveground, belowground) • Soil C sequestration (Aggregation, physical protection, recalcitrant C)
Climate Change AdaptationGoal: Develop strategies to reduce negative impacts1. Enhancing Soil Resilience • Increasing SOC pool • Restoring degraded lands2. Adopting efficient land-use systems/practices • Conservation agriculture • Agroforestry • INM, IPM, …3. Improving NPP • New and improved germplasm • GM crops, etc.
Carbon SequestrationThe process of capture and secure storage of C from the atmosphereIt entails the transfer of atmospheric C, especially CO2, and its secure storage in long-lived pools.(UNFCCC = UN Framework Convention on Climate Change)
C Sequestration in Land-Use Systems Aboveground (Vegetation) Belowground (Soils)• Soils play a major role even in the terrestrial C cycle.• The soil C pool, to 1 m depth, consists of: Soil organic C (SOC) estimated at 1550 Pg Soil inorganic C about 750 Pg (1 petagram = 1015 g = 1 billion ton)Total soil C pool (2300 Pg) is 3X the atmosph pool.
Agroforestry and Carbon Sequestration The UNFCCC allows use of C seq. through afforestation and reforestation (A & R) as GHG offset activities. Agroforestry is recognized as an A & R activity. AFS have a higher potential to sequester C because of their perceived ability for greater capture and utilization of growth resources (light, nutrients, and water) than in single-species crop- or pasture systems.
21 3 Silvopasture Dehesa, Northern Spain Homegardens Florida, USA Kerala, India 2 1 4 3 46 5 6 Silvopasture Shaded cacao Parklands MG, Brazil Bahia, Brazil Ségou, Mali Univ. Florida, Cent for Subtropical Agroforestry: Carbon Sequestration Studies, 2005 -
Locations of CSTAF (Univ of FL) Soil Carbon Sequestration Studies Sites Location Climate (m.a.p; mean Soil Agroforestry Systems Coordinates temp. range)Florida, USA Humid subtropical; 1330 Ultisols Silvopasture: slash pine (Pinus elliottii) o28°to 29° N; 81° to 83° mm; -3 to 28 C + bahiagrass (Paspalum notatum); 5–W 20 yrNorthern/ Central Humid Atlantic/ subhumid Alfisols Dehesa oak silvopasture (QuercusSpain Mediterranean; 1200/ 600 suber); >50 yr40 to 43o N; 6 to 7o W mm; 6-18°C/ 8-26°CKerala, India Humid tropical; Inceptisols Homegardens: Intensive multispecies mixtures of trees, shrubs, and herbs in10o32’ N; 76o14’E 2700 mm; 27 to 32oC small (< 0.5 ha) holdings; > 35 yrSégou, Mali Semiarid tropical; Alfisols Parklands: Intercropping under 500 to 700 mm; 29 to 36oC scattered trees, > 30 yr old; and live13o 20’ N; 6o 10’ W fences and fodder banks, ~ 9 yr.Bahia, Brazil Humid tropical; Reddish- Cacao (Theobroma cacao) under yellow thinned natural forest (cabruca) or14o 0’ S; 39o 2’ W 1500 mm; 25 to 32oC Oxisols planted shade trees; 30-yr old.Minas Gerais, Brazil Cerrado: Subhumid Oxisols Silvopasture: Eucalyptus spp. with tropical; 1350 mm; 22oC understory of Brachiaria spp (fodder17o 36’ S; 46o 42’ W grass) or rice (Oryza sativa).
General Objectives Quantify SOC accumulation and sequestration in different types of agroforestry systems in a variety of ecological and geographical conditions. Determine C storage in different soil fractions up to at least 1 m depth. Quantify, wherever possible, C contribution by C3 and C4 plants (~ trees and herbaceous plants) using natural C isotopic differences between the two groups.
Carbon Sequestration and Stable Aggregates Hierarchical organization of aggregates: Silt+clay – microaggregates – macroaggregates Macroaggregates Microaggregates Silt+clay aggregatesSize, µm 250 – 2000 53 – 250 < 53Mean residence 1-10 10 – 100 100-1000time (MRT) of CyearsC:N; Enzyme High Medium LowactivityBinding agents Fungal hyphae, Micr. polymers, Organomineral fine roots, plant/ root exudates, complexes microbial residues polyvalent cationsMgmnt effects High Medium Low Parton et al. (1987); Christensen (2001).
100 262.5 Agroforestry vs. 80 Agricultural System Near Tree vs. Far from Tree Agroforestry vs. Forest 60 40 ∆AF (%) 20 0 -20 -40 -60 -80 1 2 3 4 5 6 7 8 Land-use Types 0 − 50 cm 50 − 100 cm ∆AF (%) = [(AF-Non AF) / Non AF] *100 # Systems; age (# years since AF system installation) Location Soil Order 1 Pine + pasture vs. treeless pasture; 30 yr Florida, USA Ultisols 2 Pasture under birch trees vs. treeless pasture; Northern Spain Inceptisols 3 Home garden vs. rice paddy; >50 y Kerala, India Inceptisols 4 Under tree vs. away from trees (Dehesa); 80 y Northern Spain Alfisols 5 Under trees vs. away from trees; Parkland system; >50 y Ségou, Mali Alfisols 6 Homegardesn vs. forest: >50 y Kerala, India Inceptisols 7 Cacao under shade vs. forest; > 30 y Bahia, Brazil Oxisols 8 Brachiaria + Eucalyptus vs. Treeless forage stand; 30 y Minas Gerais, Brazil OxisolsChanges in soil C stock under different AF vs. non-AF systems (Nair et al., 2010).
Summary of Results Tree-based systems, compared to treeless under similar conditions, store more C in deeper soil. High tree density → high SOC content, esp. in the upper 50 cm soil and <53 µm soil fraction. SOC stock under longer term AF systems with high tree-density (e.g., homegardens, shaded perennials) comparable to that of natural forests. In sparse tree-density AFS, soil stores more C near than away from the tree. C3 plants (trees) contribute to more C in the silt- + clay-sized (<53 µm) fractions than C4 plants in deeper soil profile. Traditional systems with large C stock seem to have limited potential for sequestering additional C.
Some Recent PublicationsBook: Kumar BM, and Nair PKR 2011 C Seq in AF Systems. Springer, Netherlands
Some Recent Publications …Journal Articles:Nair PKR. C seq studies in AF systems: A reality check Agroforest Syst (in press)Nair PKR. Introduction to Sp Collection of papers 2011 J Env Quality 40: 784–790Howlett D, Mosquera-Losada M-R, Nair P KR, Nair, VD. 2011 J Env Quality 40: 825–832Tonucci RG, Nair PKR, Nair VD, Garcia R 2011 J Env Qual 40: 825 – 832Nair PKR, Nair VD, Kumar BM, Showalter JM 2010. Adv Agron 108: 237–307.Haile SG, Nair VD, Nair PKR. 2010. Global Change Biology 16: 427–438.Gama-Rodrigues EF, Nair PKR, Nair VD, et al. 2010. Environ Manage 45: 274–283.Saha SK, Nair PKR, Nair VD, Kumar BM. 2010. Plant and Soil 328: 433–446.Nair PKR, Kumar BM, Nair VD. 2009. J. Soil Sci. Pl Nutrition 172: 10–23.Nair PKR, Nair VD, Kumar BM, Haile SG. 2009. Environ Sci Policy 12: 1099–1111.Saha SK, Nair PKR, Nair VD, Kumar, B. M. 2009. Agrofor Syst 76: 53–65.Haile SG, Nair PKR, Nair VD. 2008. J. Environ. Qual. 37: 1789–1797.Takimoto A, Nair PKR, Nair VD. 2008. Agri Ecosyst Env 125:159–166.Takimoto A, Nair PKR, Alavalapati JRR. 2008. Mitig Adapt Strategy 13: 745–761.Takimoto A, Nair VD, Nair PKR. 2008. Agrofor Syst 76: 11–25.
Methodological Challenges• Ambiguous Concepts• Allometric Equations• Soil Sampling: Depth, Sampling Plan• Soil Analytical Issues• Fixed Effect Models: Pseudo-replication Repeated measures• Inadequate/Inaccurate Reporting: Soil BD, extrapolation of site specific values
Estimates of Carbon Sequestration Potential of AF systemsAF System sub-group Distribution (major regions) Approx. Estimated C stock Potential CSP in new including potential area, mill range (kg ha-1 yr-1) area (kg ha-1 yr-1) ha Above Below Above Below (including ground ground ground ground potential)Alley cropping and other tree Humid and subhumid tropics 650 Up to 15 Very low 2–5 5 – 75intercropping systems to 150 Temperate (N. America, Europe) 50 Up to 10 Up to 200 2- 6 30 – 100Multistrata systems (Shaded Mostly tropical humid and 100 2 to 18 Up to 300 2 – 10 50 – 150perennials, homegardens) subhumid lands, predominantly lowlands, but up to 2000 m altitudeProtective systems (Windbreak, Arid and semiarid lands of the 300 2 to 10 Up to 100 1–8 10 – 30riparian buffer, shelterbelts, etc.) world, primarily sub-Saharan Africa, China and N. and S. America,Silvopasture Grazing systems: mostly semiarid 450 2 to 15 Up to 250 3 – 10 20 – 90 and sub humid lands in Africa, India, and the AmericasWoodlots (firewood, fodder, land Firweood and fodder-tree lots are 50 1 to 12 Up to 140 1–5 20 – 70reclamation, etc.) mostly in tropics; Land reclamation plantings in special problem areas. (Nair, 2012)
Influence of Management Factors on Climate Change M & AMgt Factors Premises CriticismsTillage Aids in incorporation of plant Tillage only helps move the C(Reduced/ materials and gaseous down. Benefits of reducedMinimum exchange bet. soil and tillage based on surface-soilTillage) atmosphere. sampling may be misleading.Residue Mgt, More plant materials added Overall, a good practice.Nutrient Cycling to the soil means more C Extent of benefits depends on added to the soil litter quality and local factors.Plant diversity Continuous plant cover; Evidence on long term benefitand admixture niche-complementarity of biodiversity on soil C seq is hypothesis anedotal at present.Soil erosion Keeps soil in place; No adverse criticismcontrol enhances productivityManure/Fert. Promotes crop growth and All C additions to soil may notapplication soil-aggregate formation enhance microaggr. formation. (Nair, 2012)
Possible Management Factors Related to Climate Change M & A under AFSAFS Sub-Groups Location/ Possible Mgt Ecological Factors regionAlley Cropping and Tree Humid tropics, RM (NC), PD/PSM,Intercropping Temperate EC, RTMultistrata (Shaded Humid and PD/PSM, RM (NC),Perennials, Homegardens, …) subhumid tropics ECProtective Systems Temperate, EC, NC, RM(Windbreak, Rip. Buffer, …) semiarid tropicsSilvopasture Semiarid tropics, PSM, RT, EC, NC(Grazing, Browsing, …) Temperate EC = Erosion control; NC = Nutrient cycling; PD = Plant diversity; PSM = Plant-species mixture RM = Residue management; RT = Reduced (minimum/zero) tillage (Nair, 2012)
Strengths Opportunities High above ground biomass Enhanced above-ground C storage production Increased SOM content Deep root systems of trees More stable C in deeper soil layers High litter-fall and ground cover More ground cover and litter fall Efficient nutrient cycling facilitating better nutrient cycling More stable C in deeper soil layers and control of soil erosion More plant diversity leading to Plant diversity and biodiversity “safety net” of nutrients and Species admixture reduced NPSP Control of wind and water erosion Overall, better ecosystem Amelioration of non-point source sustainability pollutants Increasing global interest in Biodiversity conservation environmental ethics Weaknesses (Internal) Threats (External) Lack of rigorous and long-term Lack of adequate recognition of quantitative data on potential AFS and trees on farms in int’l benefits policy initiatives and mechanisms Site specific nature of systems such as REDD+ making large-scale extrapolation Insufficient valuation methods for difficult assessing ecosystem service Paucity of standardized methods benefits and procedures for sampling and Excessive importance to economic estimation of C seq in AFS over environmental benefits in Multiplicity of factors and complex adoption incentives nature of interactions Inadequate institutional niche for Difficulty in estimating area under agroforestry at national and different AFS international levels Figure 1. A SWOT analysis of the role of agroforestry systems in climate change M & A. (Nair, 2012)
Carbon Sequestration – Biodiversity Relationship Functional relationship between biodiversity and C seq. based on the “niche-complementarity” hypothesis: • a larger array of species in a system leads to a broader spectrum of resource utilization making the system more productive. Biodiversity cannot be expressed quantitatively unless its attributes can be expressed in quantitative terms. Evidence on whether the carry-over effect of higher biodiversity will translate into long-term C storage in soils is anecdotal at present.
Concluding Remarks Climate-Change M & A is a “low-hanging fruit” of agroforestry. Given that AFS are estimated to be practiced in ~ 1.6 billion ha globally, the potential benefits are credible, but are seldom recognized. Lack of rigorous scientific data on the perceived benefits is the main reason for the lack of realization and even recognition of this potential. The way forward: Break away from rhetoric and focus on development of management practices based on integrated scientific data on biophysical and socioeconomic parameters.