Demographic response of an invasive hybrid, Kalanchoe xhoughtonii (Crassulaceae) to different control methods in central Mexico
Invasive plants are a current threat to biodiversity and can dramatically modify ecosystems. Demographic modeling has proven useful to identify strategies for reducing population growth rate of invasive plants, yet few studies have addressed the demography of these organisms. In this study we address the invasive hybrid Kalanchoe xhoughtonii (Crassulaceae), native to Madagascar but currently widespread in different ecosystems around the globe. In Mexico, its presence has increased in the last decades and threatens native plants in arid ecosystems. In the semi-arid region of Metztitlán it has even become dominant in some areas. We are conducting a demographic analysis of K. xhoughtonii, subject to different management methods to identify the best strategy to reduce its dominance at the area. The management methods are mechanical extraction, herbicide application and the simultaneous application of both. Also, we are using two different application seasons: rainy (August) and dry (February) season. The treatments were applied to four 50 x 50 cm plots per treatment x season. Population projection matrices were built for each treatment to identify which of them had a greater impact on finite population growth rate. Also the establishment and growth of vegetatively produced plantlets were monitored to asses the clonal propagation potential of the hybrid.
Population size of K. xhoughtonii is increasing in the control plots while it is decreasing in the managed plots, particularly in those where both treatments were applied. Kalanchoe xhoughtonii has a great propagation potential as it produces clonal offspring (plantlets) profusely from the meristems on the leaf margins, the inflorescence stalk and cyme ramifications. Plantlet size at the time of detachment has an effect on establishment probability, with largest plantlets having a significantly higher survival rate (0.97) compared to the smallest plantlets (0.56). Also, plantlet size has an effect on relative growth rate (RGR), with the smallest plantlets showing the highest RGR (0.38 cm/cm/mo). Individuals start producing plantlets when they are ca. 1 cm tall, and in natural conditions plantlet production is highest in the late dry season (May), thus increasing their establishment probability with the onset of the rainy season.