"Migration can lead to both agricultural intensification and disintensification, both of which can result in improved resilience," Priya Deshingkar told environmentalresearchweb. "For positive impacts to be sustained in the longer term, a conducive policy and market environment is needed."

Deshingkar analysed studies from three areas with a long history of migration – Western Mexico, the Central Plateau of Burkina Faso and Eastern India. Satellite images of all three regions indicate that vegetation has recently regenerated.

"The results of existing research on the impacts of migration and remittances on agriculture are mixed," said Deshingkar. "This work synthesizes evidence from three diverse locations to provide a comparative picture."

Migration can be viewed as a form of adaptation to environmental change. But what is its effect on agriculture? In some cases money sent home by migrant family members (remittances) can enable the family to invest in agriculture and boost production, overcoming the loss of labour caused by the departure of the family member. This is more likely where the migrant has moved internationally as larger remittances tend to result. For example, avocado cultivation on former forests in Michoacaán, Mexico, has grown rapidly over the last decade, enabled to a large extent by remittances from abroad.

In Mexico, intensification of agriculture was associated with households with ejido land (communal land granted to particular families in the 1930s), receiving substantial remittances, possessing business acumen, and that had already met their consumption needs.

Soil and water conservation in Mexico, on the other hand, has been little discussed. According to Deshingkar this suggests that there is not enough local knowledge, government support, or labour to invest in conservation measures because of migration.

In West Africa's semi-arid Burkina Faso agriculture is risky because of unreliable rainfall and poor-quality soil, and migration has been a traditional coping mechanism. Migration to other continents has been found to discourage labour-intensive activities but facilitate investment in livestock, which is easier to tend than crops.

Soil and water conservation techniques were adopted in Burkina Faso's Central Plateau in the early 1980s. One study found that migrant households had, on average, a significantly higher adoption rate of stone bunds to protect fields and boost yields. This may be because households with migrants were better educated and more able to access support for soil and water conservation under government and NGO schemes.

In the Eastern Indian state of Jharkhand, farming yields are so low that most farmers migrate on a seasonal basis to boost household income. Typically, only farmers with larger plots of land – more than five acres – invested remittances in agriculture, and migration appeared to be detrimental to soil and water conservation. Traditional techniques for soil and water conservation in Jharkhand, such as stone-cum-earthen bunding and brushwood weirs, seem to have become less prevalent because of a migration-induced shortage of labour. On the plus side, farmers who moved to work in agriculture in other areas were able to employ the skills they'd learnt upon return to their own farms.

"The three regions covered show that there is diversity in migration patterns and impacts even within a region," writes Deshingkar. "Broad categories such as international migrants are not homogeneous but are in fact composed of individuals with diverse characteristics and households with diverse endowments, which have implications for the way in which migration impacts on agriculture and resilience to environmental shocks and stresses."

According to Deshingkar, the case studies indicate that agricultural intensification through capital investments may improve the resilience of poor households to economic and environmental shocks, but this does not necessarily mean an improvement in the ecological resilience of the system.

Estimates of migration arising as a result of climate change are contentious – some researchers project that between 200 million and 1 billion people will be displaced by 2050, resulting in mass migration into Europe. Others foresee more mobility within developing regions rather than movement between continents.

As a result of the study, Deshingkar hopes that "the potential impacts of migration and remittances on agriculture and resilience will be taken more seriously by migration, agriculture and natural resource management researchers" and that "the importance of a conducive policy environment is highlighted for policymakers".

Deshingkar reported her analysis in the ERL Focus on Environmental Risks and Migration: Causes and Consequences.