Casuarina: biogeography and ecology of an important tree genus in a changing world

Abstract

Important insights on the invasion ecology of woody plants are emerging from the study of model groups, but it is important to test how widely such results can be generalised. We examined whether drivers of introduction and invasion in the genus Casuarina are similar to those identified for other groups. We reviewed the literature, mapped current global distributions, and modelled the potential global distribution of the genus. We assessed the rationale behind introductions, impacts of invasions, and the evolution of management approaches. Casuarinas have been introduced to about 150 countries. Ten of the 14 species in the genus have been introduced outside their native ranges, but only three species are recorded as naturalized or invasive (C. equisetifolia, C. cunninghamiana and C. glauca). Species with large native ranges are more likely to be introduced, and the three invasive species have the largest native ranges and the most records of introduction. There were no clear relationships between life-history traits (e.g. seed mass, plant height, or resprouting ability) and the extent of invasion. About 8 % of the Earth's land surface is potentially suitable for casuarinas and largescale plantings in some climatically suitable areas have not yet resulted in large-scale invasions; there is a substantial global Casuarina invasion debt. Experiences in Florida and the Mascarene Islands highlight that casuarinas have the potential to transform ecosystems with significant control costs. The challenge is to develop management approaches that minimise the impacts of invasions while preserving economic, environmental and cultural values of species in their introduced ranges.

Casuarina Invasion Alters Primary Succession on Lava Flows on La Réunion Island

“…It typically grows to a height of 20–30 m and has been widely planted in many parts of the world for agroforestry, erosion control, intercropping, shelter, and windbreaks, and has become invasive on four continents (Potgieter et al . ). It is also invasive on many islands, including Ascension, Bermuda, Canary Islands, Cayman Islands, Dominican Republic, Hawaii, Jamaica, Ogasawara, Puerto Rico, Seychelles (Kueffer et al .…”

“…The species has a range of traits that enhance its invasive capacity and ability to cause impacts on invaded ecosystems, including rapid growth; tolerance of high salinity, cold temperatures, low soil fertility and arid conditions; the capacity to establish and propagate easily and the ability to coppice (Potgieter et al . ). Symbiotic associations with N‐fixing actinobacteria from the genus Frankia as well as ecto‐, endo‐, and arbuscular mycorrhizal fungi allow C. equisetifolia to grow on extremely nutrient‐poor substrates (Zhong et al .…”

Critical issues and new challenges for research and management of invasive plants in the Pacific Islands

“…For instance, the ironwood Casuarina equisetifolia, which is considered a Polynesian introduction in eastern Polynesia (Whistler 1991), may be native on Rapa Nui where fossil pollen grains have been found (Prebble 2008). This species, known to be invasive in other tropical islands and countries (Potgieter et al 2014), has spread in several atolls in the Tuamotu (French Polynesia), where it is a recent (1960s) modern introduction (J.-Y. Meyer, unpublished data).…”

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

“…Most insights in this regard have come from pines (Box 1), but similar patterns are emerging for other tree species (e.g. the genus Casuarina; Potgieter et al 2014). We address these issues here, focusing on the recent and considerable plantings of Australian acacias (wattles) in South-east Asia and the example posed by over a century of dealing with wattle invasions in South Africa.…”