David López-Carr

Population, poverty, environment, and climate dynamics in the developing world

This paper reviews extant evidence and offers a conceptual framework for the investigation of complex dynamics among human population growth, environmental degradation, poverty, and climate change. The paper introduces theories relating to population growth, environmental degradation, the impact on human well-being, and potential relations with climate change. Poverty is discussed in detail as both a contributing factor to and consequence of population growth and environmental change. The empirical literature on land cover change and environmental change in coastal and marine resources and potential relations with climate change are examined. Despite notable limitations to current knowledge on links among population growth, ecosystems, climate, and poverty, implications for further research and policy application are rich.

Opinion: Endogenizing culture in sustainability science research and policy

Integrating the analysis of natural and social systems to achieve sustainability has been an international scientific goal for years (1, 2). However, full integration has proven challenging, especially in regard to the role of culture (3), which is often missing from the complex sustainability equation. To enact policies and practices that can achieve sustainability, researchers and policymakers must do a better job of accounting for culture, difficult though this task may be.

The effects of migrant remittances on population–environment dynamics in migrant origin areas: international migration, fertility, and consumption in highland Guatemala

International migration impacts origin regions in many ways. As examples, remittances from distant migrants may alter consumption patterns within sending communities, while exposure to different cultural norms may alter other behaviors. This paper combines these insights to offer a unique lens on migration’s environmental impact. From an environmental perspective, we ask the following question: is the likely rise in consumption brought about by remittances counterbalanced by a reduction in fertility in migrant households following exposure to lower fertility cultures? Based on ethnographic case studies in two western highland Guatemalan communities, we argue that the near-term rise in consumption due to remittances is not counterbalanced by rapid decline in migrant household fertility. However, over time, the environmental cost of consumption may be mitigated at the community level through diffusion of contraception and family planning norms yielding lower family size.

Migration, remittances and smallholder decision-making: Implications for land use and livelihood change in Central America

We model Central American migrant-sending household agricultural practices given labor losses and the concomitant infusion of remittances. Under the new economics of labor migration (NELM) framework, it is hypothesized that smallholder farm households invest remittance income in their land either to increase crop production or to transition to cattle ranching. We test this hypothesis by developing a combination of multivariate logistic, Poisson and beta regression techniques using Latin American Migration Project data to determine how agricultural land use change compared among migrant and non-migrant households in Costa Rica, El Salvador, Guatemala, and Nicaragua. Results indicate that a rise in months spent abroad and remittances returned do not translate into a higher percentage of farm sales, intensification or transition to cattle ranching – counter to NELM. However, farmers are investing remittances to increase row crop and pasture land holdings. These findings suggest remittance investments in quantitative increase rather than qualitative change in land use practices. Given the expansive land demands supporting low intensity smallholder agriculture and cattle, and the land degradation cattle precipitate particularly, the trend does not augur well for the sustainability of rural landscapes increasingly transformed by international remittances. Appropriate policies to champion coupled human-land system sustainability in Central America might usefully consider viable land use alternatives to remittance investments dedicated to crop and pasture expansion.

Does External Funding Help Adaptation? Evidence from Community-Based Water Management in the Colombian Andes

Abstract Despite debate regarding whether, and in what form, communities need external support for adaptation to environmental change, few studies have examined how external funding impacts adaptation decisions in rural resource-dependent communities. In this article, we use quantitative and qualitative methods to assess how different funding sources influence the initiative to adapt to water scarcity in the Colombian Andes. We compare efforts to adapt to water scarcity in 111 rural Andean communities with varied dependence on external funding for water management activities. Findings suggest that despite efforts to use their own internal resources, communities often need external support to finance adaptation strategies. However, not all external financial support positively impacts a community’s abilities to adapt. Results show the importance of community-driven requests for external support. In cases where external support was unsolicited, the results show a decline, or “crowding-out,” in community efforts to adapt. In contrast, in cases where communities initiated the request for external support to fund their own projects, findings show that external intervention is more likely to enhance or “crowds-in” community-driven adaptation.

Deforestation Drivers: Population, Migration, and Tropical Land Use.

The tiny global minority residing in rural frontier areas--how long they remain there; the timing, magnitude, and characteristics of their consumption; and their demographic transitions--promises a vast impact on future tropical deforestation. It is here, not in cities and not in long settled rural areas, where fertility and native population growth is extremely high, rural migration is dynamic, and where land cover change remains extraordinarily expansive per capita. According to recent UN projections (United Nations 2011), the vast majority, indeed very likely all, the world’s net population growth over the next several decades will occur in the world’s poorest cities. Yet the direct imprint of this urbanization remains minute. Although urban food demand has a large and increasing impact on rural land change, less than 1% of the terrestrial surface is covered by urban settlements (Schneider et al. 2009). The highest population growth rates and old growth forest conversion will continue to occur in remote rural environments, with notable implications for land cover change research and policy (Turner et al 2007) specifically, and coupled human-environmental systems more broadly (An and Lopez-Carr 2012).

Agro-ecological drivers of rural out-migration to the Maya Biosphere Reserve, Guatemala

Migration necessarily precedes environmental change in the form of deforestation and soil degradation in tropical agricultural frontiers. But what environmental factors may contribute to these migration streams in the first place? Identifying environmental characteristics related to this process is crucial for understanding how environmental change and migration may form recurrent feedback loops. Further understanding this process could be useful for developing policies to reduce both environmentally induced migration from origin areas and also to palliate significant environmental change unleashed by settler deforestation in destination areas. Evidently, apprehending this holistic process cannot be approached only from the destination since this ignores environmental and other antecedents to rural out-migration. This paper presents data from surveys conducted in areas of high out-migration to the agricultural frontier in northern Guatemala. Results suggest that land scarcity and degradation in origin communities are linked to out-migration in general and to the forest frontier of northern Guatemala in particular.

Nearly 400 million people are at higher risk of schistosomiasis because dams block the migration of snail-eating river prawns

Dams have long been associated with elevated burdens of human schistosomiasis, but how dams increase disease is not always clear, in part because dams have many ecological and socio-economic effects. A recent hypothesis argues that dams block reproduction of the migratory river prawns that eat the snail hosts of schistosomiasis. In the Senegal River Basin, there is evidence that prawn populations declined and schistosomiasis increased after completion of the Diama Dam. Restoring prawns to a water-access site upstream of the dam reduced snail density and reinfection rates in people. However, whether a similar cascade of effects (from dams to prawns to snails to human schistosomiasis) occurs elsewhere is unknown. Here, we examine large dams worldwide and identify where their catchments intersect with endemic schistosomiasis and the historical habitat ranges of large, migratory Macrobrachium spp. prawns. River prawn habitats are widespread, and we estimate that 277–385 million people live within schistosomiasis-endemic regions where river prawns are or were present (out of the 800 million people who are at risk of schistosomiasis). Using a published repository of schistosomiasis studies in sub-Saharan Africa, we compared infection before and after the construction of 14 large dams for people living in: (i) upstream catchments within historical habitats of native prawns, (ii) comparable undammed watersheds, and (iii) dammed catchments beyond the historical reach of migratory prawns. Damming was followed by greater increases in schistosomiasis within prawn habitats than outside prawn habitats. We estimate that one third to one half of the global population-at-risk of schistosomiasis could benefit from restoration of native prawns. Because dams block prawn migrations, our results suggest that prawn extirpation contributes to the sharp increase of schistosomiasis after damming, and points to prawn restoration as an ecological solution for reducing human disease. This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications’.

Trophic cascades induced by lobster fishing are not ubiquitous in southern California kelp forests.

Fishing can trigger trophic cascades that alter community structure and dynamics and thus modify ecosystem attributes. We combined ecological data of sea urchin and macroalgal abundance with fishery data of spiny lobster (Panulirus interruptus) landings to evaluate whether: (1) patterns in the abundance and biomass among lobster (predator), sea urchins (grazer), and macroalgae (primary producer) in giant kelp forest communities indicated the presence of top-down control on urchins and macroalgae, and (2) lobster fishing triggers a trophic cascade leading to increased sea urchin densities and decreased macroalgal biomass. Eight years of data from eight rocky subtidal reefs known to support giant kelp forests near Santa Barbara, CA, USA, were analyzed in three-tiered least-squares regression models to evaluate the relationships between: (1) lobster abundance and sea urchin density, and (2) sea urchin density and macroalgal biomass. The models included reef physical structure and water depth. Results revealed a trend towards decreasing urchin density with increasing lobster abundance but little evidence that urchins control the biomass of macroalgae. Urchin density was highly correlated with habitat structure, although not water depth. To evaluate whether fishing triggered a trophic cascade we pooled data across all treatments to examine the extent to which sea urchin density and macroalgal biomass were related to the intensity of lobster fishing (as indicated by the density of traps pulled). We found that, with one exception, sea urchins remained more abundant at heavily fished sites, supporting the idea that fishing for lobsters releases top-down control on urchin grazers. Macroalgal biomass, however, was positively correlated with lobster fishing intensity, which contradicts the trophic cascade model. Collectively, our results suggest that factors other than urchin grazing play a major role in controlling macroalgal biomass in southern California kelp forests, and that lobster fishing does not always catalyze a top-down trophic cascade.

China’s Grain for Green policy and farm dynamics: simulating household land-use responses

Analyzing the interaction between environmental policies and farmers’ responses to them is an important dimension to understand regional agro-ecosystem sustainability. We examine land-use outcomes of perhaps the largest government-planned rural reforestation program in the history of humankind, China’s “Grain for Green” (GFG) policy from 1999 to 2006. Specifically, we simulate household responses to the GFG policy in Western China’s Shaanxi Province, a region experiencing acute climate and land change-related environmental degradation. We develop a “farmer group decision-making model” to simulate the probability of land-use change. Elevation, slope, and farm household characteristics emerge as key factors influencing farmers’ land-use decisions and subsequent land-use patterns. Land reversion and abandonment in the study area have been significantly affected by the GFG program. Policy recommendations suggest potential avenues to enhance the effectiveness of the GFG program and to improve the efficient use of under-used farmland. Results may help inform the Chinese government as it crafts policy guiding a coupled rural migration and reforestation program of unprecedented scale.