Forestry trial data can be used to evaluate climate-based species distribution models in predicting tree invasions

Abstract

Climate is frequently used to predict the outcome of species introductions based on the results from species distribution models (SDMs). However, despite the widespread use of SDMs for pre-and post-border risk assessments, data that can be used to validate predictions is often not available until after an invasion has occurred. Here we explore the potential for using historical forestry trials to assess the performance of climate-based SDMs. SDMs were parameterized based on the native range distribution of 36 Australian acacias, and predictions were compared against both the results of 150 years of government forestry trials, and current invasive distribution in southern Africa using true skill statistic, sensitivity and specificity. Classification tree analysis was used to evaluate why some Australian acacias failed in trials while others were successful. Predicted suitability was significantly related to the invaded range (sensitivity = 0.87) and success in forestry trials (sensitivity = 0.80), but forestry trial failures were under-predicted (specificity = 0.35). Notably, for forestry trials, the success in trials was greater for species invasive somewhere in the world. SDM predictions also indicate a considerable invasion potential of eight species that are currently naturalized but not yet widespread. Forestry trial data clearly provides a useful additional source of data to validate and refine SDMs in the context of risk assessment. Our study identified the climatic factors required for successful invasion of acacias, and accentuates the importance of integration of status elsewhere for risk assessment.

Even well-studied groups of alien species might be poorly inventoried: Australian Acacia species in South Africa as a case study

“…During the field visits in the cities of Bloemfontein and Johannesburg, people that had A. cultriformis in their gardens reported that this species was present in many gardens in neighbouring areas. As this species has been widely planted, it is likely that the extensive seed bank and high climatic suitability (Motloung et al 2014) could make it a high invasion risk (Wilson et al 2011). Of the naturalised species that were detected in this study, A. cultriformis is the only one for which nation-wide eradication is likely to be not feasible (given the problems with locating all horticultural plantings).…”

Invasion debt – quantifying future biological invasions

“…For each species, we calculated the additional area of natural habitats that a species could potentially invade (based on 2009 land cover; source: South African National Biodiversity Institute). We subtracted the area known to be occupied (obtained from SAPIA, GBIF and forestry trials (Motloung et al ., )) from the area predicted to be suitable by the habitat suitability model (we only considered natural habitats). This represents the total area the species could occupy (based on 15‐min cells) without considering its density.…”

Australian acacias as invasive species: lessons to be learnt from regions with long planting histories

“…Alternative explanations are that foresters actively select areas where invasions are most likely to occur, i.e. by selecting environmental conditions very similar to those in the native ranges of the species (Donaldson et al 2014;Motloung et al 2014), or that invasions are simply driven by their introduction effort (propagule pressure), i.e. more plantings over a longer period provide more chances to spread.…”