12 Jul2009

Overstory #220 - Adapting to climate change

Written by K.P.C. Rao, Louis V. Verchot, and Jan Laarman.

Agroforestry systems have potential to mitigate effects of climate change, while strengthening communities.

Introduction

Over the past two decades climate change has evolved from a debate about whether the planet is really warming to an increased focus on how to mitigate and adapt to its impacts, due mainly from the growing acceptance among scientists, policy makers, and even the general public that climate change is real and happening. This acceptance is based on the overwhelming evidence presented by the scientific community through intensive monitoring of global climatic systems, extensive observations on changes in terrestrial and aquatic systems, and predictive modeling (IPCC, 2007; Stern, 2007; Hansen et al., 2007).

The main objective of this article is to review briefly the potential risks and probable opportunities that are associated with the expected changes in global and regional climates and present ideas about how agroforestry systems could be used to adapt to, or mitigate, the predicted impacts of climate change on smallholder agriculture. It deals with the widely accepted knowledge of the impacts of climate change; that warmer temperatures will lead to a northward shift in the thermal regimes and domains of various crops, increase water and heat stresses, increase evapotranspiration, and generally reduce average rainfall amounts accompanied by an increase in inter-annual variability. The focus is on tropical agricultural systems in general and on sub-Saharan Africa in particular where many of the world's poorest countries are located.

Adaptation challenges

While communities in the past have shown resilience and capacity to adapt to changes in climate through keen observation, experimentation and practice, adaptation to the rapid changes that are taking place in global climate and other sectors are beyond that of a natural self-correcting process. As communities are exposed to unexpected or unforeseen changes in weather patterns and increased risk, more robust adaptation plans are required to manage the additional risk. Some of the adaptation challenges include:

1. Managing the heat stress both on crops and animals which requires use of crop varieties and management systems that do well under a broad range of soil and climatic conditions

2. Reversing land degradation through adoption of practices that reduce erosion and loss of organic carbon

3. Effective management of climate related risks through promotion of innovative and sustainable diversification of farm activities and supporting informed decision making on climate information

4. Efficient capture, storage and utilization of rainfall through adoption of appropriate soil and water conservation practices, provision of irrigation and use of systems and practices with high use efficiency

5. Maintaining soil fertility and productivity by arresting nutrient mining and building or sustaining soil fertility

6. Limiting greenhouse gas emissions and encouraging carbon sequestration by promoting management options that reduce tillage and use of fuels

7. Guarding against pest and disease pressure

8. Enhancing the resilience of communities by better targeting investments and improving their use efficiency

9. Ensuring maintenance of food and nutritional security

10. Protection of women and other disadvantaged groups from the adverse impacts of climate change

Role of agroforestry in adapting to climate change

Agroforestry, the integration of trees and shrubs with annual crops production, is an age old management system practiced by farmers to provide shade, a steady supply of food and/or income throughout the year, arrest degradation and maintain soil fertility, diversify income sources, increase and stabilize income, enhance use efficiency of soil nutrients, water and radiation, and provide regular employment.

--> Agroforestry systems play a critical role in moderating the microclimate

The full genetic potential of many crops and varieties can only be realised when environmental conditions are close to optimum. Any change in these conditions, especially during the reproductive stage, will have a direct impact on the production and economic viability of certain crops. While removing the extra energy accumulated and trapped by atmosphere is not feasible, agroforestry systems with appropriate shade trees offer a promising option to moderate the effects of heat stress locally. Trees on farm bring about favourable changes in the microclimatic conditions by influencing radiation flux, air temperature, wind speed, saturation deficit of understorey crops all of which will have a significant impact on modifying the rate and duration of photosynthesis and subsequent plant growth, transpiration, and soil water use (Monteith et al., 1991). Some examples where the beneficial aspects of microclimatic changes are extensively used are shade trees to protect heat sensitive crops like coffee, cacao, ginger and cardamom from high temperatures, wind breaks and shelter belts to slow down the wind speed to reduce evaporation and physical damage to crops, mulches to reduce soil temperature and various crop tree mixes to reduce erosion and maximize resource use efficiency.

In general, shade will create microclimates with lower seasonal means in ambient temperature and solar radiation as well as smaller fluctuations. Beer et al. (1998) while reviewing the literature on shade management in coffee and cacao plantations have observed that shade trees buffer high and low temperature extremes by as much as 5°C. According to Steffan-Dewenter et al. (2007) the removal of shade trees increased soil surface temperature by about 4 0C and reduced relative air humidity at 2 m above ground by about 12%. Soil temperature under the baobab and Acacia tortilis trees in the semi-arid regions of Kenya at 5-10 cm depth were found to be 6°C lower than those recorded in open areas (Belsky et al., 1993). In the Sahel, where soil temperatures often go beyond 50° to 60°C, a major constraint to establish a good crop, Faidherbia trees lowered soil temperature at 2-cm depth by 5° to 10°C depending on the movement of shade (Vandenbeldt and Williams, 1992). Shelterbelts, parallel rows of trees over the landscape, is another widely used option to improve microclimates, more specifically to reduce the velocity of the wind by increasing the surface roughness and control wind erosion and evapotranspiration. The effects of properly designed shelterbelts extend from about 10 to 25 times the height of the belt downwind with the greatest effect close to the leeward side.

--> Agroforestry systems are highly effective in soil and water conservation through provision of permanent cover.

With nearly two thirds of the continent occupied by deserts and drylands, Africa faces the biggest threat of desertification and degradation. Since climate exerts a strong influence over various soil processes that contribute to degradation, the expected changes in climate will have the potential to alter these processes and thereby soil conditions. A recent assessment by IIASA predicted that the arid and semi-arid areas in Africa will increase by 5-8% by 2080 (Fischer et al., 2005). There are several ways by which climate change manifests soil degradation. Higher temperatures and drier conditions lead to lower organic matter accumulation in the soil resulting in poor soil structure, reduction in infiltration of rain water and increase in runoff and erosion (Rao et al., 1998) while the expected increase in the occurrence of extreme rainfall events will adversely impact on the severity, frequency, and extent of erosion (WMO, 2005). These changes will further exacerbate an already serious problem the continent is facing.

Arresting degradation and restoring the productive potential of soil calls for improvement in the physical, chemical and biological conditions. The advantage with agroforestry systems is in their ability to bring favourable changes in all the three conditions. Agroforestry systems like improved fallows, contour hedgerows and other systems involving permanent cover play an important role in arresting and reversing land degradation via their ability to provide permanent cover, improve organic carbon content improve soil structure, increase infiltration, enhance fertility, and biological activity.

--> Agroforestry systems offer a major pathway for sustainable diversification of agricultural systems and incomes

Diversification of agricultural enterprises is one of the oldest practices adopted by the farmers to reduce/spread the risks and capitalise on the opportunities associated with variable climate through better exploitation of potential synergies and complementarities among different farm enterprises. Diversification is an adjustment of the farm enterprise pattern in order to increase farm income or reduce income variability by reducing risk, exploiting new market opportunities and existing market niches, diversifying not only production, but also on-farm processing and other farm-based, income-generating activities (Dixon et al., 2001). At the farm level it is the adoption of multiple production activities that are complementary in economic and/or ecological dimensions involving crops, trees, livestock and post harvest processing. Integrated agroforestry systems are a suitable pathway for sustainable diversification of agricultural systems. Examples of such systems are abound. The fast growing poplar has become a major tree component on many farms in South Asia. Across Africa, home gardens with a diverse range of vegetable and fruit yielding trees are quite popular (Mendez et al., 2001; Vogl et al., 2002; Wezel and Bender, 2003) and contribute significantly to food security by providing products year round. A global review on the contribution of home gardens to food and nutrition of households found that up to 44% of calorie and 32% of protein uptake are met by the products from home gardens (Torquebiau, 1992). Besides meeting the subsistence needs of households, the role of home gardens in generating additional cash income cannot also be overlooked (Christanty, 1990; Torquebiau, 1992; Dury et al., 1996; Mendez et al., 2001).

It is now being recognized that expanding market opportunities for smallholders particularly in niche markets and high value products is critical to the success of agroforestry innovations (Russell and Franzel, 2004). The major constraints to the growth of the small holder tree product sector in Africa are forest policies, physical and social barriers to smallholder participation in markets, the overall lack of information at all levels on markets for agroforestry products, and the challenges to outgrowing schemes and contract farming. Notwithstanding these constraints, there are promising developments including contract fuelwood schemes, small-scale nursery enterprises, charcoal policy reform, novel market information systems, facilitating and capacity building of farmer and farm forest associations, and collaboration between the private sector, research and extension (Russell and Franzel, 2004). The possibilities for integrating farms with traditional and non-traditional trees that provide fruits, nuts and other food products, medicinal plants (Rao et al., 2004), short rotation woody crops (Rockwood et al., 2004), and biomass energy plantations (Hall and House, 1993) are plenty, if suitable market structures are put in place.

--> Agroforestry systems have the capacity to enhance the use efficiency of rain water

Water is already a scarce resource and climate change is expected to make the situation worse. Climate change has both direct and indirect impacts on water availability. The direct impacts include changes in precipitation patterns while the indirect ones are increases in losses through runoff and evapotranspiration. Based on the results from extensive studies conducted under the Comprehensive Assessment of Water Management in Agriculture, CA warns that today's food production and environmental trends, if continued, will lead to crises in many parts of the world (CA, 2007). Hence with or without climate change, improving agricultural productivity of water is extremely important in managing the acute water shortages that the humankind is expected to face over the next 50-100 years.

There are several mechanisms whereby agroforestry may use available water more effectively than the annual crops. Firstly, unlike in annual systems where the land lies bare for extended periods, agroforestry systems with a perennial tree component can make use of the water remaining in the soil after harvest and the rainfall received outside the crop season. Secondly, agroforests increase the productivity of rain water by capturing a larger proportion of the annual rainfall by reducing the runoff and by using the water stored in deep layers. Thirdly, the changes in microclimate (lower air temperature, windspeed and saturation deficit of crops) reduce the evaporative demand and make more water available for transpiration.

--> Agroforestry systems provide economically viable and environmentally friendly means to improve soil fertility

Nutrient mining from continuous cropping without adequately fertilizing or fallowing the land is often cited as the main constraint to increase in productivity in most countries across Africa. It is estimated that on average African soils have been depleted by about 22 kg nitrogen, 2.5 kg phosphorus, and 15 kg potassium per hectare of cultivated land over the past 30 years in 37 African countries - an annual loss equivalent to $4 billion worth of fertilizers (Sanchez, 2002). While fertilisers offer an easy way to replenish the soil fertility, at the current prices it is very unlikely that there will be any change in the investments made by African farmers in fertilisers. In this context, Agroforestry systems have attracted considerable attention as an attractive and sustainable pathway to improve soil fertility. World Agroforestry Center made substantial progress in the identification and promoting of agroforestry systems aimed at improving soil fertility.

--> Agroforestry systems have the potential to limit carbon emissions and sequester carbon

The greatest role of agroforestry in relation to climate change is perhaps in mitigating the emissions of CO2 by productively sequestering carbon from the atmosphere. The tree component of the agroforestry systems can be a significant sink for carbon in lands devoted to agriculture. The three major paths through which tree can help reduce atmospheric carbon are: conservation of existing carbon pools through practices such as avoided deforestation and alternatives to slash and burn; sequestration through improved fallows and integration with trees, and substitution through biofuel and bioenergy plantations to replace fossil fuel use (Montagnini and Nair, 2004).

A number of studies have estimated the potential of agroforestry systems to act as effective carbon sinks (IPCC, 2000; Albrecht and Kandji, 2003; Montagnini and Nair, 2004, Palm et al., 2005). Assuming mean carbon content of above ground biomass of 50%, average carbon storage by agroforestry practices has been estimated to be 9, 21, 50, and 63 Mg C ha-1 in semiarid, subhumid, humid, and temperate regions respectively (Schroeder, 1994). The quantitative importance of agroforestry as carbon sink derives from its wide applicability in existing agricultural systems. Worldwide it is estimated that 630 x 106 hectares are suitable for agroforestry.

Conclusions

The growing and compelling evidence about global warming and its impact on global climatic systems has firmly established that climate change is real and that its consequences will be serious especially for Africa more than any other continent. The agricultural impacts of climate change are of the greatest concern to most developing countries, particularly in the tropics, because of higher dependence on agriculture, subsistence level of operations, low adaptive capacity and limited institutional support.

Agroforestry systems offer a win-win opportunity by acting as sinks for atmospheric carbon while helping to attain food security, increase farm income, improve soil health and discourage deforestation. While agroforestry systems clearly offer economic and ecological advantages, the management of these systems is complicated by the tradeoffs between subsistence requirements, acceptable risks, and costs involved. A critical and scientific assessment of these trade offs requires quantitative data and tools to make a realistic assessment of the complex interactions involved in natural resource use and economic and environmental benefits. Because of the long lead time required to study agroforestry systems thorough complete rotations and high research costs associated with such studies, much of the current assessment is based on incomplete data. Well calibrated and validated system simulation models have the potential to contribute significantly to the understanding and quantify the benefits. Though not much progress has been made in simulating agroforestry systems, the progress made in simulating the annual crop production suggests that it can be done.

In addition to an in depth understanding of the benefits from the systems and farmer requirements, mainstreaming of agroforestry requires better market linkages for the goods and services produced. An analysis of consumer needs, local and regional markets including the opportunities for linking carbon sequestration benefits to the CDM, and promotion of market intelligence systems and farmer associations are some of the areas where interventions are required to link smallholder farmers with markets.

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Original Source

This article has been excerpted with kind permission of the publisher from:

Rao, K.P.C., L.V. Verchot, and Jan Laarman. 2007. Adaptation to Climate Change through Sustainable Management and Development of Agroforestry Systems. SAT eJournal 4:1. http://ejournal.icrisat.org