Waiving the extinction debt: Can shade from coffee prevent extinctions of epiphytic plants from isolated trees?

Abstract

Aim Local extinction after habitat modifications is often delayed, leading to an extinction debt. Our first aim was to develop a conceptual model for natural and human‐mediated habitat improvements after a disturbance that may waive part of the predicted extinction debt. Second, we wanted to test this model on the distribution of epiphytic plants on trees that had been isolated in the agricultural matrix after forest clearing, around which coffee subsequently had been planted with a possible improvement of the microclimate. Location Bonga, Southern Nations, Nationalities and Peoples Region (SNNPR), Ethiopia. Methods We studied 50 trees that had been isolated for periods ranging from a few years to half a century after clearing. The trees were now located in the agricultural landscape at different distances from intact Afromontane forests. Fourteen trees in the forests were used as references. Each tree was inventoried for all vascular epiphytic plants, mosses and liverworts. Results Time since clearance had a direct negative effect on number of forest specialist species via delayed extinctions and the detected large extinction debt of both bryophytes and vascular plants continued to be paid over several decades. However, time since clearance had an indirect positive effect on number of forest indicator species via the reappearance of shade from coffee planted surrounding the trees, even if the waiving effect on the extinction debt was rather small. Additionally, trees at further distances from the forest edge had fewer forest‐associated species. Main conclusions Our results show that the ability of agroecological landscapes to foster forest biodiversity may be overestimated if meta‐community processes over time and space are not taken into account. However, the possibility of initiating counteracting processes that modify the level of expected local extinctions should be evaluated more often to find ways of improving conditions for biodiversity in human‐modified landscapes.

The effect of habitat transformation on a twig epiphytic orchid: Evidence from population dynamics

“…Previous studies of tropical epiphytic communities have shown that species diversity and abundance decrease over gradients of increasing human impact (Larrea and Werner, 2010;Hylander and Nemomissa, 2017). However, in the present study, the populations of R. granadensis colonizing isolated fruit or shade trees within a transformed pasture matrix had a higher density of plants per phorophyte compared with the forest sub-sites (Supplement Table 1).…”

Land‐use history determines ecosystem services and conservation value in tropical agroforestry

“…Extinction debts suggest a continuing loss of biodiversity as populations that are not viable under new conditions go extinct (Jackson & Sax, 2010). Evidence for extinction debts comes from forest‐derived agroforests in Ethiopia, where epiphytes are less likely to occur in long‐converted agroforests further away from the historic forest edge (Hylander & Nemomissa, 2017). Conversely, open‐land‐derived agroforests may enjoy an immigration credit (Jackson & Sax, 2010; Shumi et al., 2018), implying that species have not yet immigrated into newly established agroforests, despite suitable habitat.…”

Smallholder vanilla agroforestry in Madagascar: biodiversity, ecosystem services and yields in a land-use context

“…However, the long-term stability of tropical mosaic landscapes has been questioned because inherent intensification incentives may drive land-use change and land-use intensification (Tscharntke et al, 2012). Additionally, questions of extinction debts (Kuussaari et al, 2009) in 'young' tropical landscapes remain largely unresolved (but see Hylander & Nemomissa (2017) for an exception), further questioning whether current day patterns of biodiversity are stable in the long run. A combination of the two factors may drive the long-term decline of biodiversity in tropical agricultural landscapes (Şekercioğlu et al, 2019;Socolar et al, 2019).…”

“…Evidence for extinction debts comes from forest-derived agroforests in Ethiopia, where epiphytes are less likely to occur in long-converted agroforests further away from the historic forest edge (Hylander & Nemomissa, 2017). Conversely, open-land-derived agroforests may enjoy an immigration credit (Jackson & Sax, 2010;Shumi et al, 2018), implying that species have not yet immigrated into newly established agroforests, despite suitable habitat.…”