Disentangling the environmental heterogeneity, floristic distinctiveness and current threats of tropical dry forests in Colombia

Roy González-M,Hernando García,Álvaro Idárraga-Piedrahíta,Karen Pérez,Camila Pizano,Paola Isaacs,Hermes Cuadros,Rubén Jurado,Francisco Mijares,Hernando Vergara,Alejandro Castaño-Naranjo,Nelly Rodríguez,René López-Camacho,Alicia Rojas

doi:10.1088/1748-9326/aaad74

Abstract

Tropical dry forests (TDFs) have been defined as a single biome occurring mostly in the lowlands where there is a marked period of drought during the year. In the Neotropics, dry forests occur across contrasting biogeographical regions that contain high beta diversity and endemism, but also strong anthropogenic pressures that threaten their biodiversity and ecological integrity. In Colombia, TDFs occur across six regions with contrasting soils, climate, and anthropogenic pressures, therefore being ideal for studying how these variables relate to dry forest species composition, successional stage and conservation status. Here, we explore the variation in climate and soil conditions, floristic composition, forest fragment size and shape, successional stage and anthropogenic pressures in 571 dry forest fragments across Colombia. We found that TDFs should not be classified solely on rainfall seasonality, as high variation in precipitation and temperature were correlated with soil characteristics. In fact, based on environmental factors and floristic composition, the dry forests of Colombia are clustered in three distinctive groups, with high species turnover across and within regions, as reported for other TDF regions of the Neotropics. Widely distributed TDF species were found to be generalists favored by forest disturbance and the early successional stages of dry forests. On the other hand, TDF fragments were not only small in size, but highly irregular in shape in all regions, and comprising mostly early and intermediate successional stages, with very little mature forest left at the national level. At all sites, we detected at least seven anthropogenic disturbances with agriculture, cattle ranching and human infrastructure being the most pressing disturbances throughout the country. Thus, although environmental factors and floristic composition of dry forests vary across regions at the national level, dry forests are equally threatened by deforestation, degradation and anthropogenic pressures all over the country, making TDFs a top priority for conservation in Colombia.

Highlights

Tropical dry forests (TDFs) occur in America, Asia and Africa, where mean annual temperature is greater than 17 ◦C, annual rainfall ranges from 250–2000 mm and potential evapotranspiration is higher than precipitation (Holdridge 1967, Murphy and Lugo 1986, Kalacska et al 2004, Dirzo et al 2011)
In terms of floristic composition, TDFs strongly differ between South America, Africa and Asia (Dexter et al 2015), and have a high plant species turnover across the Neotropics, where species of different floristic groups are commonly restricted to a single region (DRYFLOR et al 2016)
Matching the variation in environmental conditions, we found that 73.3% of TDF plant species were only found in one region, and that the floristic composition of dry forests in Colombia is clustered in the same three groups: the Caribbean and the interAndean valleys (Patia, Cauca and Magdalena Valleys and North Andean), as suggested by (DRYFLOR et al 2016), and the Orinoquia (p < 0.001), a region where TDFs have been poorly studied, but has been suggested as a separate floristic entity by Espinal and Montenegro (1977) and Pizano et al (2014a) (figures 2(b)–(c))

Summary

Introduction

Tropical dry forests (TDFs) occur in America, Asia and Africa, where mean annual temperature is greater than 17 ◦C, annual rainfall ranges from 250–2000 mm and potential evapotranspiration is higher than precipitation (Holdridge 1967, Murphy and Lugo 1986, Kalacska et al 2004, Dirzo et al 2011). TDFs are used to represent 42% of all the worlds’ tropical forests (Brown and Lugo 1982), only 1000 000 km are left worldwide (Miles et al 2006, Portillo-Quintero and Sanchez-Azofeifa 2010, Powers et al 2011), with more than 50% left in South America (Miles et al 2006). These forests have been recognized as highly endangered ecosystems (Murphy and Lugo 1986, Janzen 1988). Recent studies showed high floristic turnover among different regions in the Neotropics (DRYFLOR et al 2016), but little is known on how differences in species composition may be related to climate and soil factors

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