Increased clonal growth in heavily harvested ecosystems failed to rescue ayahuasca lianas from decline in the Peruvian Amazon rainforest.
Abstract
Increasing harvest and overexploitation of wild plants for non-timber forest products can significantly affect population dynamics of harvested populations. While the most common approach to assess the effect of harvest and perturbation of vital rates is focused on the long-term population growth rate, most management strategies are planned and implemented over the short-term. We developed an integral projection model to investigate the effects of harvest on the demography and the short- and long-term population dynamics of Banisteriopsis caapi in the Peruvian Amazon rainforest. Harvest had no significant effect on the size-dependent growth of lianas, but survival rates increased with size. Harvest had a significant negative effect on size-dependent survival where larger lianas experienced greater mortality rates under high harvest pressure than smaller lianas. In the populations under high harvest pressure, survival of smaller lianas was greater than that of populations with low harvest pressure. Harvest had no significant effect on clonal or sexual reproduction, but fertility was size-dependent. The long-term population growth rates of B. caapi populations under high harvest pressure were projected to decline at a rate of 1.3% whereas populations with low harvest pressure are expected to increase at 3.2%. However, before reaching equilibrium, over the short-term, all B. caapi populations were in decline by 26% (high harvested population) and (low harvested population) 20.4% per year. Elasticity patterns were dominated by survival of larger lianas irrespective of harvest treatments. Life table response experiment analyses indicated that high harvest caused the 6% reduction in population growth rates by significantly reducing the survival of large lianas and increasing the survival-growth of smaller lianas including vegetative reproductive individuals. Synthesis and applications. This study emphasizes how important it is for management strategies for B. caapi lianas experiencing anthropogenic harvest to prioritize the survival of larger size lianas and vegetative reproducing individuals, particularly in increased harvested systems often prone to multiple stressors. From an applied conservation perspective, our findings illustrate the importance of both prospective and retrospective perturbation analyses in population growth rates in understanding the population dynamics of lianas in general in response to human-induced disturbance.