Summary

Siamangs (Symphalangus syndactylus) and agile gibbons (Hylobates agilis) are present in Bala Forest.
In 2005 it was estimated that 19 groups of siamangs and 136 groups of agile gibbons occur in the site.
The population trends are unknown.
The site has a total size of 168 km².
Key threats to apes are forest fragmentation as a result of agricultural expansion and collection of non-timber products.
Conservation activities are not documented.
The site is part of the Hala-Bala Wildlife Sanctuary.

Site characteristics

The site is located in the southernmost part of Thailand, in the San Kara Kiri mountain range, bordering Belum Forest Reserve in Malaysia (BirdLife International 2021). The site is part of the Hala-Bala Wildlife Sanctuary, which comprises two non-adjacent sectors: the Bala sector in Narathiwat province, and the Hala sector in Yala province (BirdLife International 2021). Although both siamangs and agile gibbons occur in southern Thailand, the range of siamangs is very small and confined to the Bala Forest (Nongkaew et al. 2018). The Bala Forest is found in a mountain range with an altitudinal range of 100 to 953 m above sea level (Nongkaew et al. 2018). The forest resembles the Malayan mixed dipterocarp forests more than the more seasonal, semi-evergreen forests farther north (Nongkaew et al. 2018).

Table 1. Basic site information for Bala Forest

Area	168 km²
Coordinates	5.787548 N, 101.809392 E
Designation	Wildlife Sanctuary
Habitat types	Subtropical/tropical moist montane forest

IUCN habitat categories Site designations

Ape status

In a 2005 survey, siamangs occurred mostly in the southwestern part of Bala Forest, close to the Malaysian border, while agile gibbons were more evenly distributed throughout the site (Nongkaew et al. 2018).

Table 2. Ape population estimates in Bala Forest

Species	Year	Total number indiv. (95% CI)	Total number groups (95% CI)	Density [groups/km²] (95% CI)	Area	Method	Source	Comments	A.P.E.S. database ID
Symphalangus syndactylus	2005		19	0.32	Bala Forest	Fixed-point triangulation	Nongkaew et al. 2018	The density of siamangs ranged from 0 to 1.43 groups km–2 (average = 0.32, standard error (SE) = 0.08 groups km–2)
Hylobates agilis	2005		136	2.27	Bala Forest	Fixed-point triangulation	Nongkaew et al. 2018	Densities ranged from 1. 05 to 3.27 groups km–2. Mean density of agile gibbons in Bala Forest was 2.27 groups km–2 (SE = 0.18).

Threats

The expansion of agricultural areas along the border with Malaysia has resulted in loss of forest connectivity between Bala Forest and the forests in Kelantan, Malaysia. Although most of the forest appears to be old-growth, much of the forest was selectively logged before 1990 (Nongkaew et al. 2018). Local people were not found hunting gibbons during a survey of the area in 1995. However, local communities do collect non-timber products such as fruits of Baccaurea spp., Dialium spp., and Garcinia atroviridis species, which are also foods for the apes (Nongkaew et al. 2018). About 9% of people collect these fruits by cutting trees, thus reducing available food sources for the gibbons. It is therefore crucial to reduce the cutting of fruit trees to allow both species to survive in this small area (Nongkaew et al. 2018).

Table 3. Threats to apes in Bala Forest

Category	Specific threats	Threat level	Description	Year of threat
1. Residential & commercial development		Unknown
2. Agriculture & aquaculture	2.1 Annual & perennial non-timber crops	Unknown whether the threat category is present	Loss of forest connectivity to the forests across the border with Malaysia, due to expansion of agricultural areas along the border (Nongkaew et al. 2018).	Ongoing (2018)
3. Energy production & mining		Unknown
4. Transportation & service corridors		Unknown
5. Biological resource use	5.1 Hunting & collecting terrestrial animals	Absent	In a 2005 survey, local people were not found hunting gibbons (Nongkaew et al. 2018).	Ongoing (2018)
	5.2 Gathering terrestrial plants	High	People from neighbouring villages collect non-timber products, including fruits that are also food for siamang and agile gibbons (Nongkaew et al. 2018).	Ongoing (2018)
	5.3 Logging & wood harvesting	Low	Much of the forest was selectively logged before the 1990s (Nongkaew et al. 2018).	Ongoing (2018)
6. Human intrusion & disturbance		Unknown
7. Natural system modifications		Unknown
8. Invasive & other problematic species, genes, diseases		Unknown
9. Pollution		Unknown
10. Geological Events		Absent
11. Climate change & severe weather		Unknown
12. Other options		Absent

IUCN Threats list

Conservation activities

Table 4. Conservation activities in Bala Forest

Category	Specific activity	Description	Year of activity
1. Residential & commercial development	Not reported
2. Agriculture & aquaculture	Not reported
3. Energy production & mining	Not reported
4. Transportation & service corridors	Not reported
5. Biological resource use	Not reported
6. Human intrusion & disturbance	Not reported
7. Natural system modifications	Not reported
8. Invasive & other problematic species, genes, diseases	Not reported
9. Pollution	Not reported
10. Education & Awareness	Not reported
11. Habitat Protection	Not reported
12. Species Management	Not reported
13. Livelihood; Economic & Other Incentives	Not reported

Conservation activities list (Junker et al. 2017)

Challenges

Table 5. Challenges reported for Bala Forest

Challenge	Source
Not reported

Research activities

Documented behaviours

Table 6. Ape behaviors reported for Bala Forest

Behavior	Source
Not reported

External links

Relevant datasets

A.P.E.S Portal

References

BirdLife International (2021) Important Bird Areas factsheet: Hala Sector, Hala-Bala Wildlife Sanctuary and Bang Lang National Park. Downloaded from http://www.birdlife.org on 19/12/2021.
Nongkaew, S., Bumrungsri, S., Brockelman, W. Y., Savini, T., Pattanavibool, A., & Thong-Ari, S. (2018). PoPulation Density anD Habitat of siamang anD agile gibbon in bala forest, soutHern tHailanD. Natural History Bulletin of the Siam Society, 62(2).

Page completed by: A.P.E.S. Wiki team Date:29/12/2021

Bala Forest

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