The demography of Oritrophium peruvianum (LAM.) Cuatr. and the impacts of harvesting on its populations in the Venezuelan Andes
Oritrophium peruvianum (Lam.) Cuatr. is a perennial species, endemic to the Páramos of the Cordillera of Los Andes. In Venezuela, where it is known as Frailejón morado, it is harvested for its widely acclaimed medicinal properties in treating asthma, bronchitis, and influenza. This study aimed to investigate the biology and ecology of O. peruvianum and the impacts of harvesting on its populations. Undisturbed populations of O. peruvianum were dominated by adult vegetative individuals, with middle-sized plants prevailing and with low densities of large adults, whilst densities of small plants were variable. The population structure changed slightly after one year and annual plant growth was shown to be extremely slow. Flowering started at the beginning of the rainfall period and overlapped with fruiting throughout the wet season (April to November), with only a few scattered individuals reproducing during the dry season. Seed production was very variable and germination under experimental conditions was successful (51 to 88%). The population dynamics of two populations were analyzed using a five stages time-invariant linear matrix model with field data collected over two years. The growth rate of the first population was higher (?1 =1.32) than that of the second population (?1 = 1.13). Sensitivity analysis showed that their growth rates were more sensitive to a change in the survival of individuals than to reproduction, due to the low survival rate of newly emerged seedlings. Plants were contributing more to the growth rate if they remained in the same stage class than if they grew to the following stage class. The most significant transition was the survival of stage class 3 (small adults) whilst stage class 5 (large adults) contributed little to the population growth rate. A uniform harvesting of the adult stages each year up to 21% and 43% respectively in each of the two populations could be applied without threatening their survivals. The harvesting of small adults would affect the growth rates of the populations most, whilst the complete removal of stage class 5 would have the least impact. The most sustainable practical policy, considering larger plants with higher economic value, allows harvesting of all plants from stage class 5 in both populations, each year. In the population with the higher proportion of plants in stage class 3, more than one half (63%) of this stage class could be also harvested, whilst in the second population 83% of the plants from stage class 4 (middle-sized plants) could be harvested instead.