Abstract
Early plant stages may be the most vulnerable within the life cycle of plants especially in arid ecosystems. Interference from exotic species may exacerbate this condition. We evaluated germination, seedling survival and growth in the endangered Caribbean cactus Harrisia portoricensis, as a function of sunlight exposure (i.e., growing under open and shaded areas), different shade providers (i.e., growing under two native shrubs and one exotic grass species), two levels of predation (i.e., exclusion and non-exclusion) and variable microenvironmental conditions (i.e., temperature, PAR, humidity). Field experiments demonstrated that suitable conditions for germination and establishment of H. portoricensis seedling are optimal in shaded areas beneath the canopy of established species, but experiments also demonstrated that the identity of the shade provider can have a significant influence on the outcome of these processes. Harrisia portoricensis seedlings had higher probabilities of survival and grew better (i.e., larger diameters) when they were transplanted beneath the canopy of native shrubs, than beneath the exotic grass species, where temperature and solar radiation values were on average much higher than those obtained under the canopies of native shrubs. We also detected that exclusion from potential predators did not increase seedling survival. Our combined results for H. portoricensis suggested that the modification of microenvironmental conditions by the exotic grass may lower the probability of recruitment and establishment of this endangered cactus species.
Highlights
Germination, seedling establishment, and survival of young plants appear to be the most critical phase in the life cycle of cacti (Bowers 1997, Pimienta & Del Castillo 2002, Valiente et al 2002, Godínez et al 2003, Valverde et al 2004)
In this study we evaluated whether or not germination and seedlings survival of H. portoricensis was influenced by micro-environmental variation and by extension whether or not these processes were influenced by the type of species under which they were occurring
We hypothesized that micro-environmental conditions would be most favorable for H. portoricensis seedlings beneath the canopies of native shrubs than beneath the leaf cover of the exotic grass, and as a result seedling survival and growth would be higher under native shrubs
Summary
Germination, seedling establishment, and survival of young plants appear to be the most critical phase in the life cycle of cacti (Bowers 1997, Pimienta & Del Castillo 2002, Valiente et al 2002, Godínez et al 2003, Valverde et al 2004). In this study we evaluated whether or not germination and seedlings survival of H. portoricensis was influenced by micro-environmental variation and by extension whether or not these processes were influenced by the type of species under which they were occurring (i.e., exotic grass: M. maximus or native shrubs: C. discolor and R. uncinata). We used this information to understand on how vulnerable are H. portoricensis populations to the potential effects of an exotic grass species, how important is the presence of shade providers for germination and establishment, and how susceptible are seedlings and young individuals to changes in micro-environmental factors. We hypothesized that micro-environmental conditions (i.e., temperature, PAR, humidity) would be most favorable for H. portoricensis seedlings beneath the canopies of native shrubs than beneath the leaf cover of the exotic grass, and as a result seedling survival and growth would be higher under native shrubs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
