The neotropical reforestation hotspots: A biophysical and socioeconomic typology of contemporary forest expansion

Highlights

• Tropical reforestation is a significant component of global environmental change, yet it is far less understood than tropical deforestation.

• We delineated regional hotspots of significant net reforestation across Latin America and the Caribbean, and define a typology of these hotspots.

• Reforestation hotspots cover 11% of Latin America and the Caribbean, and include 167,667.7 km² of reforestation occurring between 2001 and 2014.

• We identified a typology of five reforestation clusters based on their topography, climate, population trends, and urbanization degree for Latin America and the Caribbean.

Abstract

Tropical reforestation is a significant component of global environmental change that is far less understood than tropical deforestation, despite having apparently increased widely in scale during recent decades. The regional contexts defining such reforestation have not been well described. They are likely to differ significantly from the geographical profiles outlined by site-specific observations that predominate in the literature. In response, this article determines the distribution, extent, and defining contexts of apparently spontaneous reforestation. It delineates regional ‘hotspots’ of significant net reforestation across Latin America and the Caribbean and defines a typology of these hotspots with reference to the biophysical and socioeconomic characteristics that unite and distinguish amongst them. Fifteen regional hotspots were identified on the basis of spatial criteria pertaining to the area, distribution, and rate of reforestation 2001–2014, observed using a custom continental MODIS satellite land-cover classification. Collectively, these hotspots cover 11% of Latin America and the Caribbean and they include 167,667.7 km² of new forests. Comparisons with other remotely sensed estimates of reforestation indicate that these hotspots contain a significant amount of tropical reforestation, continentally and pantropically. The extent of reforestation as a proportion of its hotspot was relatively invariable (3–14%) given large disparities in hotspot areas and contexts. An ordination analysis defined a typology of five clusters, distinguished largely by their topographical roughness and related aspects of agro-ecological marginality, climate, population trends, and degree of urbanization: ‘Urban lowlands’, ‘Mountainous populated areas’, ‘Rural highlands’, ‘Rural humid lands’ and ‘Rural dry lands’. The typology highlights that a range of distinct, even oppositional regional biophysical, demographic, and agricultural contexts have equally given rise to significant, regional net reforestation, urging a concomitant diversification of forest transition science.

Introduction

Changes in tropical forest cover are primary features of global environmental change. Most studies addressing tropical forest cover change have focused on deforestation and its drivers (Gibbs et al., 2010; Hansen et al., 2013; Graesser et al., 2015; Curtis et al., 2018), identifying the loss of ∼150 million hectares of tropical forest between 1990 and 2015 (Keenan et al., 2015). Tropical reforestation is, however, also a significant component of global environmental change (Meyfroidt and Lambin, 2008; Aide et al., 2013; Chazdon et al., 2016) that is far less understood and reportedly increased in extent during recent decades (Aide and Grau, 2004; Hecht and Saatchi, 2007). Reforestation would have major implications for global bio-geoclimatic and ecological dynamics, such as carbon sequestration (Chazdon et al., 2016), environmental services (Wilson et al., 2017), and biodiversity conservation (Catterall et al., 2008). Early research on spontaneous tropical reforestation was framed on the “forest transition” model (Mather, 1992), which is based on patterns and processes of the 19th and 20th centuries. Given the acceleration of socioeconomic changes over recent decades, patterns and processes of 21st century forest expansion are likely to differ. To further understanding of reforestation as an emergent regional land- change phenomenon, we delineate and characterize the reforestation hotspots of Latin America.

The forest transition narrative is based largely on early European precedents, and anticipates that reforestation arises from an “agriculture land-use adjustment” whereby agricultural modernization over fertile lands coincides with the abandonment of marginal agricultural land use (Mather and Needle, 1998). Localized case studies of recent tropical reforestation similarly purport that reforestation concentrated in agro-economically ‘marginal’ regions (Helmer, 2000, 2004; Sloan et al., 2016). In Latin America, emerging forests were observed predominantly in topographically steep uplands (Asner et al., 2009; Redo et al., 2012; Aide et al., 2013; Nanni and Grau, 2014), peri-urban zones offering non-farm livelihood alternatives (Grau et al., 2003; Baptista, 2008; Grau et al., 2008a,b; Gutiérrez-Angonese and Grau, 2014), and in areas of land abandonment following major socioeconomic shifts, such as loss of subsides for sugar production in Cuba (Álvarez-Berríos et al., 2013), or outmigration from Oaxaca, Mexico (Bonilla-Moheno et al., 2012). The land-use adjustment was considered to be induced or otherwise enhanced by urban-economic growth, rural emigration, and the globalization of land-use systems (Aide and Grau, 2004; Hecht and Saatchi, 2007) broadly aligned with modernistic notions of ‘development’ (Perz, 2007a,b; Redo et al., 2012).

However, the direct application of the forest-transition narrative to contemporary tropical reforestation risks its undue corroboration at the expense of alternative or complementary processes (Sloan, 2015). This has arguably occurred where studies have focused exclusively on generalized ‘drivers’ nominated by theory (e.g., ‘urbanization’) (DeFries and Pandey, 2010; DeFries et al., 2010) or on reforesting regions where the nominated drivers are known to have had a positive effect (Rudel et al., 2005). Comprehensive assessments of reforestation encompassing all possible host contexts would alleviate this bias to some degree. Such assessments across the Neotropics have observed higher rates of reforestation in marginal, high-elevation areas, as well as high rates of deforestation in the lowland moist forest biome (Aide et al., 2013; Hansen et al., 2013; Rudel et al., 2016), suggesting that reforestation and deforestation may arise differentially amongst biomes due to their respective land-use constraints (Redo et al., 2012; Aide et al., 2013).

Although reforestation is increasingly recognized as an emergent regional phenomenon, only recently has it been observed at such scales (Redo et al., 2012; Aide et al., 2013; Hansen et al., 2013; Rudel et al., 2016). The regional contexts influencing reforestation, which have not been described well, likely differ from the geographical profiles prominent in the literature (Perz, 2007a,b; Sloan, 2015; Sloan et al., 2016). Case studies provide a tenuous, potentially biased means of articulating overarching regional contexts or dynamics of reforestation (Sloan, 2015), particularly as many conflate small-scale reforestation and localized dynamics with a broader, long-term forest transition (Helmer, 2000). Meta-analyses of case studies similarly extrapolated local observations to regional scales (Rudel et al., 2005) and relied on theoretical suppositions to fill empirical gaps (Meyfroidt and Lambin, 2011). Large-scale surveys of reforestation (e.g. Aide et al., 2013; Hansen et al., 2013) have given scant attention to the contexts of regional net reforestation, instead tending to quantify aggregate gross tree cover gains without differentiating planted from natural forests or ephemeral from sustained trends. Narratives regarding the role of ‘development’ and ‘marginality’ and their variation amongst contexts, or indeed other drivers of tropical reforestation, thus remain somewhat unrefined.

A definitive characterization of the regional contexts of reforestation across Latin America is critical for three reasons. First, it would provide missing information about the biophysical and socioeconomic conditions under which reforestation occurs. In effect, a comprehensive regional geography of Neotropical reforestation would provide an authoritative complement to the continued reliance on case studies (Sloan, 2015) and narratives based on northern hemisphere land-change processes (Perz, 2007a,b). Improved contextual resolution is also essential for supporting reforestation and conservation initiatives that are increasingly assuming ambitious scales (Chazdon and Guariguata, 2016). Amongst these are various continental forest-landscape restoration schemes, such as the 20 × 20 Initiative (World Resources Institute, 2015) and the Bonn Challenge (The Bonn Challenge, 2015), as well as programs for Reducing Emissions from Deforestation and forest Degradation (REDD+; Sloan, 2015), which are rapidly improvising national-scale schemes (Sloan et al., 2018).

Second, identifying regions of persistentreforestation would help identify the long-term benefits and beneficiaries of new forests (e.g. rural population livelihoods, biodiversity conservation, ecosystem services provision; Rey Benayas et al., 2009; Chazdon and Uriarte, 2016). Their identification would also distinguish them from widespread areas of sporadic or ephemeral reforestation readily visible in satellite classifications (e.g., Hansen et al., 2013). Indeed, the persistence of new forests (Reid et al., 2017) t and the scale of forest transitions are major but largely unexplored uncertainties that regional delineations of contiguous, persistent reforestation would help address.

Third, a regional account of Neotropical reforestation would provide a necessary ontological correction to perspectives on the human dimensions of forest-cover change, which remain steeped in the rampant deforestation that characterized the latter half of the 20th century. Significant regional net reforestation is, by definition, the culmination of a longer-term forest transition (Mather, 1992). Thus, the identification of the regional contexts of reforestation would shed light on the generality and diversity of conditions hosting forest transitions.

To improve understanding of reforestation as an emergent regional phenomenon, this article presents the first continental depiction of significant Neotropical regional reforestation during the 21st century. It offers two novel insights into Neotropical reforestation to address the uncertainties of its geography and contexts. Drawing upon comprehensive satellite-imagery analysis, it delineates ‘hotspots’ of extensive, significant, and potentially persistent net reforestation across Latin America and the Caribbean between 2001 and 2014. Subsequently, it defines a typology of these hotspots with reference to the biophysical and socioeconomic characteristics that unite and distinguish amongst them. Finally, hotspots types are discussed with reference to case studies elaborating the biophysical and socioeconomic forces shaping regional conditions. In this way, we provide an empirical framework for further exploration of the conditions and processes of contemporary Neotropical reforestation.