Neobalanocarpus heimii is a monotypic genus that belongs to the family Dipterocarpaceae and is better known as chengal in Malay. Penak is another common name used in some parts of Selangor, Negeri Sembilan and western Pahang (Symington, 2004).
Chengal is an important Malaysian commercial wood species because it is durable and hard. It has anti-termitic properties, so that there is no need to treat it chemically (Kadir et al., 2014). Also, its natural extractives makes the wood resistant to fungal decay (Yamamoto & Tnah, 1988). Hence, it is suitable for bridges, boats, buildings, power-line poles and heavy construction as well as wood carving. In addition, chengal is the source of damar penak which is one of the finest natural dammars that is traditionally used for torches and caulking boats as well as in the manufacture of certain classes of varnish (Symington, 2004).
In terms of wood anatomy, N. heimii is quite similar to timber in the Hopea section Hopea. However, unlike Hopea, there are ripple marks on the tangential surface of N. heimii sapwood. The leaves are alternate and simple, leathery and elliptical-lanceolate. Neobalanocarpus heimii is bisexual bearing flowers with both male and female reproductive structures. The anthers are linear-oblong and the appendage to connective is short, while the ovary is glabrous and stigma minute. The five petals of each flower are creamy white or greenish-yellow. In contrast with other dipterocarps, the seed of N. heimii is heavy and wingless, and is acorn-like (Symington, 2004). Also, unlike most dipterocarps, this species does not show masting behaviour, instead it flowers and fruits annually (Orwa et al., 2009).
Neobalanocarpus heimii can only be found in Peninsular Malaysia and southern Thailand. In Peninsular Malaysia, it is widespread and can be found in many forest reserves except in those of Perlis and Melaka. This species is found on low-lying flat land and on hills of up to 900 m elevation (Symington, 2004). Chengal is listed as Vulnerable under the IUCN Red List (Chua, 1998) and Malaysia Plant Red List (Chua et al., 2010) because there is a decline in its area of distribution and extent of occurrence, and increase in actual or potential level of exploitation. The high market demand and soaring price are the major causes of illegal logging. To combat illegal logging, forensic studies have been conducted by FRIM to track down illegally logged timber (Tnah et al., 2012a). If not protected, this tree species may become endangered in the near future.
Based on molecular data and due to the high proportion of unique haplotypes, the distribution of Malayan Chengal is segregated into three groups, i.e., northern Peninsular Malaysia (PM), central PM and southern PM (Tnah et al., 2012b). These three separate groups need to be given priority in long-term forest management in order to ensure the population viability is maintained or enhanced. Conservation of mature trees and increasing the population size by in-situ and ex-situ conservation methods must be carried out in order to protect this species. In-situ conservation can be carried out by keeping a minimum population size of 5000 trees in an area of no less than 100 ha for each haplotype (Lawrence and Marshall, 1997). For ex-situ conservation, the authorities can collect the seeds and plant them in botanical gardens and arboreta, thereby preserving the genetic resources (Lee et al., 2006).
