Survivorship and yield of a harvested population of Forsteronia glabrescens

Abstract

The exploitation of non-timber forest products may be an opportunity to reconcile the utilization of biological resources with biodiversity conservation. In Southern Brazil, the exploitation of liana stems for handicraft makes up an important part of the income of indigenous Kaingang people. In this study we evaluated the effects of stem harvesting on the survivorship of Forsteronia glabrescens Müll.Arg, the most exploited liana species in the region. We marked and monitored the survivorship, sprouting, changes in stem diameter and resource yield in control and harvested plots with two different resting times-six and twelve months. We associated variables of interest with individual attributes, harvesting regime and vegetation descriptors through linear mixed modelling. Survivorship and resource yield were lower in the harvested groups than in the control group, although the mean stem diameter was higher. Plants with larger stem diameter presented higher survival odds. Either six or twelve months of resting between harvests were not sufficient to recompose the yield and compensate mortality. Harvesting twice a year increases yield but reduces survivorship. Our results point that the sustainable exploitation of F. glabrescens require either large areas, low pressure or resting periods longer than the ones we tested.

Fig 1. Change in the population structure of Forsteronia glabrescens population one year after being submitted to stem harvesting.

Fig 2. Survivorship of Forsteronia glabrescens (mean ± standard error) in two harvesting periods of six-months each and after one year, comparing stems unharvested and submitted to harvesting once and twice a year.

Fig 3. Change in mean (± standard error) stem diameter of Forsteronia glabrescens surviving after six months and one year of harvesting and unharvested, control group.

Fig 4. Change in mean stem length of Forsteronia glabrescens (mean ± standard error) in six-months periods and accumulated after one year, comparing stems submitted to harvesting once and twice a year.