The predicted impacts show the necessity for smallholder farmers to adapt in order to counter the negative effects of climate change on their farming operation. In this context, several hundred studies have been evaluating various adaptation measures since the late 1990s \citep[see]{Kamukondiwa_1996}. This paper focuses on two recent studies performed by \citet{Deressa_2009} and \citet{Waha_2013} who identified the following coping mechanisms as the most promising measures adapt to climate change:
Planting trees
Soil conservation
Different crop varieties
Early and late planting
Irrigation
Multiple cropping systems
Many of these strategies can easily be implemented by a single adaptation measure called Agroforestry. Agroforestry is often used as a strategy that involves the combination of regular crop cultivation along with trees and shrubs to increase the resilience of the former. It commonly involves the following four aspects \citep{Nair_1993}:
At least two species of plants of which at least one is of woody perennial
Two or more outputs
A cycle exceeding one year
A system that is ecologically (structurally and functionally) more complex than a mono-cropping system, even for the most simplest system
Several methods for agroforestry are available, including: intercropping, alley cropping and hedgerow cropping or more complex systems that form a natural forest ecosystem \citep{Mbow_2014a}. The diversity and characteristics of agroforestry can be observed in figure \ref{diversity}. The main advantages of agroforestry over other measures is primarily found in its positive influence on farmers’ income security and through the provision of additional resources and its facilitating role in the growth of crops. Those both aspects add important security in a changing climate setting. Furthermore, agroforestry can even to some extent help mitigating climate change, thus allowing farmers to benefit in multiple ways with respect to food security \citep{Mbow_2014a}. A selection of feedback mechanisms under the application of agroforestry can be found in Figure \ref{feedback} and will be further discussed. By planting trees and shrubs, farmers can directly benefit through the harvest of additional yield such as fruits or firewood. These contribute to the farmers’ own food supply and possibly provide added income if they are able sell these fruits and firewood on local markets. Following the agroforestry typology, this is an example for a multiple cropping systems with the provision of at least two outputs. The cultivation of trees along with their use as firewood provides further benefits such as a decrease in time that is needed to search for firewood and the prevention of deforestation by reforestation \citep{Mbow_2014a}. However, the availability of additional cheap firewood can have a negative feedback in that it contributes to emission of greenhouse gasses and contributes to domestic air pollution since stoves in homes are often low efficiency \citep{Kiplagat_2011}.
It is particularly the indirect effects of agroforestry that are likely to help farmers adapt to a changing climate. For instance, nitrogen-fixing trees bind nitrogen in the ground, and thereby fertilizing it. Since nitrogen is often a limiting factor for plant growth, this extra nitrogen in the ground will help crops to grow without the need for synthetic fertilizers \citep{Fleischer_2013}. Studies already showed that using fertilizer tree species contributes to a larger maize yield than without the use of any fertilizer \citep{Lasco_2014}. Thus, agroforestry can be seen as a natural adaptation method to ensure soil conservation. Natural soil conservation by trees is also created through year-round surface cover. This stems from the fact that unlike most crops, trees will be on the land for multiple years. In comparison to conventional cultivation with large extents of surface litter and crop residue removal, resulting in soil erosion and increases in probability for water runoff, agroforestry ensures surface covering through trees and thus mitigating these effects \citep{Mbow_2014a}.
A second benefit provided by trees is the provision of shade for the surface below them that allows them to buffer against temperature extremes and therefore decreases evaporation \citep{Mbow_2014a}. This can contribute to a longer growing period for the crops, making them less likely to fail. Furthermore, shade will create a more comfortable working environment for the farmers with potentially positive socio-economic and health effects.
A third benefit comes as a result from water management by trees. If pruned correctly, the roots will grow to use water from deeper layers and therefore not compete over water with annual crops, which use water from the top soil. Since trees also contribute to soil conservation, the runoff from precipitation can be decreased, increasing the available water for crops. Furthermore, tree cover plays an important role in the water cycle. Analysis showed that trees have a direct influence on precipitation patterns \citep{Mbow_2014a}. Since a significant fraction of the precipitation originates from local evaporation, an increase in plant cover can increase the amount of local precipitation \citep{Bierkens2008}. This might eventually contribute to a positive feedback effect of increasing precipitation in local areas and reduce the need for a mechanical irrigation system. Therefore, planting of trees can be seen as a natural replacement for mechanical irrigation systems.
A fourth benefit from agroforestry refers to the reduction of pests without the use of pesticides. Trees can form a natural barrier and decrease the accessibility of the crops by limiting the movement of the pests. Furthermore, a diverse plant mix evaporates a mixture of odors that can potentially irritate insect pests and the provided free space can encourage the pests’ natural enemies to inhabit the area. Agroforestry can therefore increase yield by protecting it from pest impacts \citep{Rathore1995}.
Finally, agroforestry reduces CO2 concentration in the atmosphere. Since trees sequester carbon, the overall carbon concentration in the atmosphere will be reduced. Trees will use and store carbon for their entire lifetime, keeping it out of the atmospheric cycle longer than annual crops. If agroforestry is applied on a large scale, the sequestration of carbon can significantly contribute to GHG emission mitigation and thus lessen the severity of impacts due to human-induced climate change \citep{Mbow_2014a}.
In summing all these effects, agroforestry covers 4 out of the 6 aforementioned adaptation measures through a single measure of planting trees. Yet, other measures could still be incorporated, such as early and late planting by planting crops at the beginning of the seasonal rain period instead of at traditional dates \citep{Waha_2013}. Lastly, different crop varieties as a suggested adaptation measure might not be necessary with agroforestry as the latter harmonizes factors such as water availability and surface temperature, allowing traditional crops to prosper regardless of the increases in regional climate change.