Invasion Success in a Marginal Habitat: An Experimental Test of Competitive Ability and Drought Tolerance in Chromolaena odorata

Abstract

Climatic niche models based on native-range climatic data accurately predict invasive-range distributions in the majority of species. However, these models often do not account for ecological and evolutionary processes, which limit the ability to predict future range expansion. This might be particularly problematic in the case of invaders that occupy environments that would be considered marginal relative to the climatic niche in the native range of the species. Here, we assess the potential for future range expansion in the shrub Chromolaena odorata that is currently invading mesic savannas (>650 mm MAP) in South Africa that are colder and drier than most habitats in its native range. In a greenhouse experiment we tested whether its current distribution in South Africa can be explained by increased competitive ability and/or differentiation in drought tolerance relative to the native population. We compared aboveground biomass, biomass allocation, water use efficiency and relative yields of native and invasive C. odorata and the resident grass Panicum maximum in wet and dry conditions. Surprisingly, we found little differentiation between ranges. Invasive C. odorata showed no increased competitive ability or superior drought tolerance compared to native C. odorata. Moreover we found that P. maximum was a better competitor than either native or invasive C. odorata. These results imply that C. odorata is unlikely to expand its future range towards more extreme, drier, habitats beyond the limits of its current climatic niche and that the species’ invasiveness most likely depends on superior light interception when temporarily released from competition by disturbance. Our study highlights the fact that species can successfully invade habitats that are at the extreme end of their ranges and thereby contributes towards a better understanding of range expansion during species invasions.

Native‐range habitats of invasive plants: are they similar to invaded‐range habitats and do they differ according to the geographical direction of invasion?

“…In contrast, relatively few invasive species appear to have recruited from dryland, saline and aquatic habitats. In general, stress factors such as drought, extreme temperatures, high salinity or low nutrient levels are considered to lower the invasibility of habitats (Alpert et al, 2000), which may be at least partly related to the fact that few invaders are adapted to stressful environments in their native ranges (Te Beest et al, 2013). On the other hand, the relatively small area of some specific habitat types, such as saline habitats, is also a likely cause of small numbers of invasive aliens recruited from such habitats.…”

Minimizing Risks of Invasive Alien Plant Species in Tropical Production Forest Management

“…Enemy release has been shown to facilitate the invasion of Hawaiian forests by Clidemia hirta [65] and hybridization appears to have been involved in the origin of the highly invasive form of Rubus alceifolius on Réunion Island [66]. Among the invasive species listed in Tables 1 and 3, Chromolaena odorata has high specific leaf area, relative growth rate and relative investment in stems, and is a prolific source of wind-dispersed seeds [67][68][69], Piper aduncum is fast growing, freely flowering and fruiting, and well-dispersed by both birds and bats [21,[70][71][72], invasive Pinus spp. produce frequent massive crops of well-dispersed seeds from a young age [42,73,74], and Maesopsis eminii is a fast growing, massively fruiting and well-dispersed [60,61,75,76].…”

Mapping the occurrence of Chromolaena odorata (L.) in subtropical forest gaps using environmental and remote sensing data

“…This challenge is further exacerbated by the plasticity of species to new ecosystems that were previously thought to be unsuitable for invasion (Beest et al 2013). Controlling the infestation of protected areas by alien C. odorata requires integrated efforts that will overcome processes leading to species establishment and proliferation (Jarošik et al 2011).…”

“…For example, Gils et al (2004Gils et al ( , 2006 observed that the abundance of C. odorata was highest in the partially open forest and lower in open and closed canopy forests of KwaZulu-Natal province. However, more recently, Beest et al (2013) observed that C. odorata is highly effective in intercepting light, which indicates that the species might be a good competitor for light in open habitats at similar ecological region. Granted, modelling the occurrence of invasive C. odorata in their forest habitats is imperative for management and control of indigenous subtropical forests (Maitre 2002;Underwood et al 2003).…”

“…Previous studies by Gils et al (2004Gils et al ( , 2006 have documented that C. odorata abundance was high in the indigenous forest compared to other land management regimes. This study aimed at integrating remote sensed data with environmental data for modeling the probability of occurrence of C. odorata in forest gaps, which were found to be habitable to this alien species due to its light requirement (Beest et al 2013) and seed dispersal mechanisms (Gils et al 2006). …”