Conservation prospects for threatened Vietnamese tree species: results from a demographic study

Abstract

Given that changes in population size are slow, information on future prospects of long‐lived tree species is necessarily obtained from demographic models. We studied six threatened tree species in four Vietnamese protected areas: the broad‐leaved Annamocarya sinensis, Manglietia fordiana and Parashorea chinensis, and the coniferous Calocedrus macrolepis, Dacrydium elatum and Pinus kwangtungensis. With data from a 2‐year field study on recruitment, growth and survival, we constructed matrix models for each species. All species showed continuous regeneration, as indicated by annual seedling recruitment and inverse J‐shaped population structures. To evaluate the future prospects of our study species, we calculated three parameters: (1) asymptotic growth rates (λ) from matrix models indicated significant population declines of 2–3%/year for two species; (2) population trajectories for 50–100 years showed slight population declines (0–3%/year) for five species; and (3) the reproductive period required for an adult tree to replace itself was excessive for three of the six species, suggesting that these species presently have insufficient recruitment. Overall agreement of the three parameters was low, showing that reliance on just one parameter is risky. Combining the three parameters we concluded that prospects are good for Dacrydium and Parashorea, worrisome for Annamocarya, Manglietia and Pinus, and intermediate for Calocedrus. We argue that conservation should involve strict protection of (pre‐)adult trees, as their survival is crucial for population maintenance in all species (high elasticity). For species with poor demographic prospects, active intervention is required to improve seedling and tree growth, enrich populations with seedlings from controlled germination, and restore habitat. Finally, our study suggests that these conservation measures apply to long‐lived trees in general, given that their demography is highly similar. Such measures should be taken before populations decline below critical levels, as long‐lived species will respond slowly to management.

Ages and long-term growth patterns of four threatened Vietnamese tree species

“…Three species (Calocedrus, Dacrydium and Pinus) are conifers, while Annamocarya is a broad-leaved deciduous species. The coniferous species grow in subtropical forests in high mountains, while the broad-leaved Annamocarya occurs in lowland tropical Age at reaching reproductive size is based on the diameter at breast height (DBH) at which 50% of the individuals are reproductive (Chien et al 2008). Maximum height and DBH are based on Chien (2006), and age at maximum DBH is estimated based on Fig.…”

“…The following measurements were taken for all individuals [1 diameter at breast height (DBH), total height and signs of reproduction (flowers, fruits). These measurements were repeated in 2004 and 2005 (Chien et al 2008). The relation between reproductive status and DBH was analyzed using logistic regression; this yielded the probability of reproduction for each DBH (results presented in Chien et al 2008).…”

“…A third analysis involved the comparison of diameter growth obtained from tree ring data with those from permanent plots (Chien et al 2008). We only used tree ring data from trees [30-cm diameter, as these are mostly wellestablished adult trees.…”

“…In this study, we investigated the ages and long-term growth patterns of four threatened tree species in Vietnam (Chien et al 2008). As a result of large-scale deforestation and unsustainable forest exploitation, over 300 tree species in Vietnam are threatened (Chien 2006).…”

“…Furthermore, we reconstructed individual growth trajectories and analyzed to what extent growth rates were autocorrelated over time, meaning that fast growers remained fast growers and slow growers remained slow growers. Next, we checked for gradual changes in diameter growth over time, and compared diameter growth rates obtained from ring analysis with values from permanent sample plots (Chien et al 2008). To our knowledge, this is one of the first dendro-ecological studies for tropical Asian species (Baker et al 2005;Buckley et al 2007) and the first of its kind on threatened tree species.…”