Light intensity is a limiting factor to the inland expansion of Cape ivy (Delairea odorata)

Abstract

Cape ivy (Delairea odorata) is a highly invasive climbing perennial vine that is primarily distributed in coastal communities of California and Oregon, with patchy infestations in some inland riparian areas. In this study, we evaluated light as a potential environmental limitation to the spread of Cape ivy into inland regions of the western United States. Cape ivy was collected from four locations representing the north to south range. Plants were grown for 9 to 11 weeks in full sunlight and under two shade regimes (20 and 6% of full sunlight). The experiment was conducted twice at two temperature regimes. Results show some within-and among-population variability, with the southernmost San Diego County population having the highest biomass under the warmer growing conditions and the three northern populations responding most favorably in the cooler growing conditions. Despite the minor differences within and between populations, Cape ivy grew very poorly in full sunlight in both experiments. Although plants growing under 6% light grew better than those in full sunlight, they were far less robust compared to plants growing at 20% light. Our results indicate that while Cape ivy will not persist in areas with prolonged high intensity sunlight, characterized by much of the interior regions of California and Oregon, it is expected to invade and spread in areas with reduced light, including coastal regions frequently exposed to fog or cloudy conditions, or sub-canopy layers of riparian forests or woodlands. These communities should be the target areas for early detection and rapid response programs to prevent further Cape ivy invasion.

<p><strong><em>Delairea aparadensis</em> (Asteraceae, Senecioneae), the first native species of the genus in the Americas</strong></p>

“…One of those smaller genera, Delairea Lemaire (1844: 379), has been considered monospecific (Nordenstam 2007). Its only species, D. odorata Lemaire (1844: 380), is native to South Africa but has been introduced to most continents, having become naturalised and even a noxious invasive species in Australia, New Zealand and many countries in Asia, Europe and the Americas (Balciunas & Smith 2006, Robison & DiTomaso 2010, Robison et al 2011, Prabu et al 2012, Mehelis et al 2015.…”