Elevational distribution and photosynthetic characteristics of the invasive tree Spathodea campanulata on the island of Tahiti (South Pacific Ocean)

Abstract

Successful invasion is often due to a combination of species characteristics (or invasiveness) and habitat suitability (or invasibility). Our objective was to identify preferred habitats and suitable environmental conditions for the African tulip tree Spathodea campanulata (Bignoniaceae), one of the most invasive alien trees on the tropical island of French Polynesia (South Pacific Ocean), in relation to its distribution and photosynthesis capacity. Spathodea abundance and leaf chlorophyll fluorescence Fo', ETRmax, and Y(II)effective were examined in relation to topography and micro-climate along elevational transects between 140 m and 1,300 m. Results showed that Spathodea is (1) present up to 1,240 m with lowest maximum July-October (cool season) temperature of 9.4 °C and an average July-October temperature of 14.6°C, (2) is able to colonize slope steepness of more than 45°, (3) is well represented in the elevational range of 140-540 m as well as in the native forests between 940 m and 1,040 m, suggesting a high threat for native and endemic plants species. Along one of the transects, in the elevation range of 541-940 m, Spathodea was under-represented, Chl fluorescence Fo' increased significantly while Y(II)effective decreased significantly supporting the hypothesis that this range is a non-preferred environment, probably due to micro-climate conditions characterized by punctual air dryness. Among Spathodea plants surveyed along a wetter transect, Y(II)effective and ETRmax were comparable from low elevation to mid-high elevation indicating that the potential photosynthesis rate of Spathodea may be similar from sea level until mid-high elevation. Major infestations on the island of Tahiti were reported on the leeward (drier and urbanized) west coast, but Spathodea has also been recently found on the slopes of the windward (wetter) east coast. Chlorophyll fluorescence measurements indicate a high photosynthetic capacity among Spathodea in wet environments suggesting that Spathodea will become invasive across most of the island of Tahiti.