Targeted reforestation could reverse declines in connectivity for understory birds in a tropical habitat corridor

Abstract

Re-establishing connectivity between protected areas isolated by habitat clearing is a key conservation goal in the humid tropics. In northeastern Costa Rica, payments for environmental services (PES) and a government ban on deforestation have subsidized forest protection and reforestation in the San Juan-La Selva Biological Corridor (SJLSBC), resulting in a decline in mature forest loss and the expansion of tree plantations. We use field studies and graph models to assess how conservation efforts have altered functional connectivity over the last 25 years for four species of insectivorous understory birds. Field playback studies assessed how reforestation habitat quality affected the willingness of Myrmeciza exsul, Henicorhina leucosticta, Thamnophilus atrinucha, and Glyphorynchus spirurus to travel outside forest habitat for territorial defense. Observed travel distances were greatest in nonnative and native tree plantations with high understory stem density, regardless of overstory composition. In contrast, tree plantations with low stem density had travel responses comparable to open pasture for three of the four bird species. We modeled landscape connectivity for each species using graph models based on varying possible travel distances in tree plantations, gallery forests, and pastures. From 1986 to 2011, connectivity for all species declined in the SJLSBC landscape (5825 km ) by 14% to 21% despite only a 4.9% net loss in forest area and the rapid expansion of tree plantations over 2% of the landscape. Plantation placement in the landscape limited their potential facilitation of connectivity because they were located either far from forest cover or within already contiguous forest areas. We mapped current connectivity bottlenecks and identified priority areas for future reforestation. We estimate that reforestation of priority areas could improve connectivity by 2% with only a 1% gain in forest cover, an impressive gain given the small area reforested. Results indicate key locations where spatial targeting of PES within the SJLSBC study region would protect existing forest connectivity and enhance the connectivity benefits of reforestation.

Protected areas and forest fragmentation: sustainability index for prioritizing fragments for landscape restoration

“…The mosaic comprised by agriculture, pasturelands, and planted forest allows restoration implementation, unlike in urban areas. According to Fagan, DeFries, Sesnie, Arroyo-Mora, and Chazdon (2016), the reforestation of priority areas in tropical agricultural landscapes can improve connectivity by 2% with only 1% gain in forest cover.…”

Incorporating natural regeneration in forest landscape restoration in tropical regions: synthesis and key research gaps

“…, Fagan et al . ). From a socioeconomic perspective, natural regeneration is best suited to areas with low opportunity costs for other land uses ( e.g., agriculture in steep slopes or areas with low fertility soils) or in remote areas where access to resources and technical support for active restoration may be lacking (Mukul et al .…”

A proposal for practical and effective biological corridors to connect protected areas in northwest Costa Rica

“…In addition, the majority of the areas where sub-corridors are proposed already have relatively high proportions of forest cover and would therefore require a small amount of restoration work, such as active native tree planting. Other small corridors in the process of being established in Costa Rica also share these characteristics (Fagan et al 2016). As has been seen across the country, simply allowing natural regeneration to occur would probably be sufficient to create a forested corridor within a relatively short period of time (e.g.…”

“…However, the corridors established by SINAC are typically quite large (Chacón Cascante et al 2012) and often include areas with large human populations (e.g. portions of the Paso de las Nubes have > 250 people/ km 2 , CIESIN 2016), extensive deforestation (greater than 50% in some corridors, Sánchez-Azofeifa et al 2003, Morse et al 2009, Fagan et al 2016 and extensive economic activity, in particular agriculture (Fagan et al 2013). These factors make true functional connectivity difficult or unlikely (i.e.…”