Spatial targeting of woodland creation can reduce the colonisation credit of woodland plants

Abstract

Colonisation credit refers to the temporal lag between positive conservation actions and species' responses and may be one of the reasons we fail to meet short‐term conservation targets. This is particularly evident in woodlands which take decades to develop and harbour slow colonising species. Given global objectives to increase woodland cover, it is important to know the timeframe within which colonisation credit will be fulfilled. The colonisation of woodland plants was examined in recent woodlands, created between 15 and 80 years ago, and located adjacent or isolated from existing ancient woodlands. Colonisation credit was calculated as the proportion of understory woodland plant species in the nearest ancient woodland which had not colonised recent woodlands. Looking at individual species traits also allowed us to tease apart their impact on the species colonisation and establishment ability. Spatial adjacency between created and ancient woodland reduced colonisation credit by an average of 28%, and more mature created woodlands (50–80 years old) had fulfilled 24% more of their colonisation credit on average than younger created woodlands (15–21 years old). However, mature woodlands created adjacent to ancient woodlands had still only been colonised by an average of 72% of the available species pool. Plants which had reached adjacent created woodlands were dispersed by a range of mechanisms, where those that had reached more isolated sites were largely dispersed by birds or mammals. Low community weighted mean shade tolerance, high community weighted nutrient affiliation, and the dominance of Hedera helix suggest that competition from dominant natives may be preventing certain species establishing in new woodlands. This research demonstrates the need to account for appropriate time‐lags when setting biodiversity targets, with most sites still displaying colonisation credit decades after they were created. The results also indicate that spatially targeting woodland creation adjacent to species‐rich mature woodlands should be prioritised. Still, poor local habitat conditions may lead to the dominance of specific competitors which prevent a range of other species from establishing. Local management interventions such as translocations and tree thinning may ameliorate this but further research is needed.

Larger and structurally complex woodland creation sites provide greater benefits for woodland plants

“…Unexpectedly, we found no influence of the surrounding landscape on species richness (specialists and generalists) or on the presence of the 10 most common specialists. This is contrary to previous studies linking plant richness (or occurrence) and distance to nearest woodland (Brunet et al, 2021;Hughes et al, 2023;Naaf & Kolk, 2015) or amount of woodland in the surrounding landscape (Jamoneau et al, 2011;Liira et al, 2012;Peña et al, 2011;Petit et al, 2004).…”

“…Those studies found that proximity to existing mature woodland is an important driver of plant colonisation and suggested that being more than 100 m away from nearest woodland may still incur a significant colonisation credit (i.e. lower richness than nearby old growth woodlands) after considerable time (~100 years; Brunet et al, 2021;Hughes et al, 2023). In comparison, woodland creation sites in this study were relatively isolated with a median distance of 153 m to the nearest broadleaf woodland (mean 218 m; range 7-1573 m), and 66% of woodlands over 100 m from the nearest woodland.…”

“…These temporal lags, or colonisation credits, have been observed in a wide range of species and ecosystems and found to operate over a broad range of spatial and temporal scales (Lira et al, 2019). Woodland plants are exceptionally slow colonisers as they struggle to reach new isolated patches, with colonisation credits existing for more than a century (Brunet et al, 2021;Honnay et al, 2002;Hughes et al, 2023;Naaf & Kolk, 2015;Vellend et al, 2006). However, attributes of the local site and surrounding landscape may also directly influence plant colonisation and establishment within newly created woodlands.…”

“…Whilst woodland creation sites located close to older or ancient woodlands have higher plant species richness (Brunet et al, 2021;Hughes et al, 2023;Naaf & Kolk, 2015), it is unclear at what spatial scales this relationship occurs as spatial proximity is rarely considered beyond a simple categorisation of contiguous or isolated (Brunet et al, 2021;Hughes et al, 2023). Furthermore, the spatial composition and configuration of the wider landscape, including the amount of other woodlands and smaller woody features (e.g.…”