Human activity threatens gene pool of key timber species in China
Protected groups of Madhuca hainanensis have higher genetic diversity than unprotected groups. This is according to a study by Dai et al in Biochemical Systematics and Ecology, which also states that genetic differentiation among regions is caused by human activity over the past century in Hainan Island. Strict in-situ conservation efforts are recommended to prevent further deforestation and loss of this endemic top-priority canopy species that is already in high risk of extinction.
Hainan Island has the most extensive and best-preserved tropical forests in China. However, in the last century, nearly 96% of the natural tropical forests there have regenerated into secondary natural forests because of excessive timber exploitation and other human disturbances. Hainan’s natural forests still suffer deforestation and degradation, which makes conservation of the remaining natural forests urgent, especially the remaining fragments with endemic populations.
Madhuca hainanensis is one of the most important commercial hardwoods in Hainan. Due to its high economic value, the tree has been overexploited over time, leading to a sharp decline in numbers. Currently, it is found in limited separated populations, and only in mixed forests, in the western and the southern mountainous regions of the island. Although it is known that logging, even selective logging, results in loss of alleles and genotypes in this species, the genetic diversity of the tree is generally poorly understood. M. hainanensis is known for its longevity, so the existing genetic make-up of its remnant wild populations could well reflect the impacts that human activities have had on its genetic variation over the past century.
To study the impacts of human activity on M. hainanensis on Hainan Island, a number of researchers, including World Agroforestry Centre’s Deli Zhai, studied the genetic variability and differentiation of 112 trees from six natural wild populations in various areas on the island. They were looking to ascertain the genetic diversity in this high-value species; the genetic diversity distributed within and among populations; the influence of human disturbance on genetic diversity; and, thereafter, to come up with scientific guidelines for effective conservation. Management and conservation of forest and tree resources, which involves research on threats to and conservation of high-value tree species is a key focus of the CGIAR’s Collaborative Research Programme on Forests, Trees and Agroforestry of which the centre is a key partner.
Although the natural distribution of M. hainanensis on Hainan Island is limited to a series of separated populations, higher genetic diversity is seen at species level with lower genetic diversity within populations. High genetic differentiation was detected among populations, with protected groups (with less human disturbance) having higher genetic diversity. These higher levels are clearly determined by the level of human activity, not geographic isolation, which demonstrates the impacts of human activities (especially logging) on the genetic diversity of the species.
What does this imply for conservation efforts? Owing to its short-lived seed, subhumid ecological zone and distribution of genetic variation within populations, ex-situ conservation might be not suitable for M. hainanensis. The authors recommend that strict in-situ conservation efforts be urgently implemented for all six investigated populations.
- populations in the western region, which have the highest genetic diversity, should be earmarked as key protection units.
- where populations have been severely affected by human disturbance and show extremely low diversity, the local government should enforce laws that prevent deforestation and degradation. Protection measures and supervision can then come into play.
- genetic sources for population enlargement should be selected from multiple populations within the western region to conserve the gene pool of this commercially and ecologically valuable species.
Dai Z-C, Si C-C, Zhai D-L, Huang P, Qi S-S, Zhong Q-X, Hu X, Li H-M, Du D-L. 2013. Human impacts on genetic diversity and differentiation in six natural populations of Madhuca hainanensis, an endemic and endangered timber species in China. Biochemical Systematics and Ecology 50: 212-219