Assessing coexisting plant extinction debt and colonization credit in a grassland–forest change gradient

Abstract

Changes in species richness along the ecological succession gradient may be strongly determined by coexisting extinction debts of species from the original habitats and colonization credits of those from the replacing habitats. The magnitude of these processes and their causes remain largely unknown. We explored the extinction debt and colonization credit for grassland and forest specialist plants, respectively, and the local and landscape factors associated to the richness of these species groups in a 50-year process of forest encroachment into semi-natural Mediterranean grasslands. A set of sampling plots of persistent grasslands and forests and their transitional habitat (wooded grasslands) was selected within fixed-area sites distributed across the landscape. Our results confirm the extinction debt and suggest colonization credit (according to observed trends and model predictions) in wooded grasslands when compared to persistent forests, despite wooded grasslands and persistent forests having similar tree cover. Grassland connectivity and solar radiation had opposing effects on the richness of both grassland and forest specialists, and it is possible that the availability of seed sources from old forests may have accelerate the payment of colonization credit in the wooded grasslands. These results suggest that extinction debt and colonization credit have driven species turnover during the 50 years of forest encroachment, but at different rates, and that local and landscape factors have opposing effects on these two phenomena. They also highlight the importance of documenting biodiversity time lags following habitat change when they are still in progress in order to timely and adequately manage habitats of high conservation value such as the grasslands studied here.

Zero‐sum landscape effects on acorn predation associated with shifts in granivore insect community in new holm oak (Quercus ilex) forests

“…Conversely, only few authors have explored the effects of habitat recovery on the assembly of plant-animal interactions (de la Peña et al, 2016). Recent formation and high isolation of habitat patches may result in time lags (namely, colonization credits) for some species, especially those with poor dispersal ability (Bagaria, Helm, Rodà, & Pino, 2015;Heiniger et al, 2014). Recent formation and high isolation of habitat patches may result in time lags (namely, colonization credits) for some species, especially those with poor dispersal ability (Bagaria, Helm, Rodà, & Pino, 2015;Heiniger et al, 2014).…”

Plant community assembly in suburban vacant lots depends on earthmoving legacy, habitat connectivity, and current mowing frequency

“…Species richness and nestedness (although marginally) were affected by present connectivity, but not by past connectivity (Figure d,e), indicating that current immigration from surrounding habitats maintains high species richness and grassland specialist plants. In contrast to this result, time‐delayed responses to landscape change (Jackson & Sax, ) have been reported for species richness (Bagaria, Helm, Roda, & Pino, ; Helm et al, ; Koyanagi, Kusumoto, Yamamoto, Okubo, et al, ; Lindborg & Eriksson, ; Otsu, Iijima, Nagaike, Takuo, & Hoshino, ) and nested components (Koyanagi, Furukawa, & Osawa, ) of grassland plant communities. Cousins () found that time‐delayed response is detected in regions where contemporary landscapes retain >10% of traditional habitats.…”

Projected regional forest plant community dynamics evidence centuries‐long effects of habitat turnover

“…Projected generalist plant dynamics indicate that the order of magnitude of relaxation times ranges from several centuries to near a millennium (Figure a). Previous studies about immigration credit reported smaller time lags, mainly decades or several centuries (Bagaria, Helm, Rodà, & Pino, ; Naaf & Kolk, ; Hautekèete et al., ). First, these differences could be explained by the extinction debt that slows down the use of the immigration credit in our study area in comparison to that of Naaf and Kolk () who concluded that the extinction debt was already paid.…”

“…; Bagaria et al. ; Hautekèete et al., ) without regard to the time needed to reach a novel equilibrium (i.e. the relaxation time).…”