Than-Dahat dry grassy forests have an open tree canopy dominated by two species, Terminalia oliveri (Combretaceae) and Tectona hamiltoniana (Lamiaceae). They may also include species found in drier areas, such as Acacia catechu (Fabaceae) and patches of bamboo (Dendrocalamus strictus, Poaceae). Other tree species include Dalbergia paniculata, Bauhinia racemosa (Fabaceae), Diospyros burmanica (Ebenaceae), Grewia tilifolia (Malvaceae), Limonia acidissima (Rutaceae) and Shorea siamensis (Davis, 1960; Oo and Koike, 2015). The vines Hiptage benghalensis (Malpighiaceae) and Cissampelos pareira (Menispermaceae) grow into the tree canopies and C4 grasses such as Aristida depressa (Poaceae) dominate the understorey with scattered shrubs of Waltheria indica (Malvaceae). This ecosystem is important habitat for endemic and near-endemic birds including Burmese Collared-dove Streptopelia xanthocycla, Jerdon's Minivet Pericrocotus albifrons (NT), Hooded Treepie Crypsirina cucullate (NT) Burmese Bushlark Mirafra microptera, Burmese Prinia Prinia cooki, Ayeyarwady Bulbul Pycnonotus blanfordi and White-throated Babbler Chatarrhaea gularis. It also supports remnant populations of the Endangered Eld’s Deer Rucervus eldii (EN); (Thu et al., 2019) and Burmese Star Tortoise Geochelone platynotan (CR).
Central Ayeyarwady Than-Dahat grassy forest
ဧရာဝတီအလယ်ပိုင်း သန်း၊ဒဟတ် မြက်ခင်းတော
Extinction Risk
Climate and ecology
RealmTerrestrial
BiomeSavannas And Grasslands
Functional GroupPyric tussock savannas
Description
This ecosystem is a grassy open woodland dominated by Tectona hamiltoniana (dahat) and Terminalia oliveri (than) that occurs throughout the rolling hills of the dry zone, corresponding to community types 1-7 of Oo and Koike (2015). The presence of dry clay soils is thought to be the key driver of its distribution (Davis, 1960). Trees in Than-Dahat grassy forests are rarely greater than 10 metres tall, and have a fairly sparse, open, distribution, as is characteristic of a savanna. A thick ground cover of grasses is present, and bamboo may occur (Oo and Koike, 2015). Mostly deciduous with C4 grassy groundcover (Ratnam et al., 2016). Two other isolated Than-Dahat ecosystems fringe the central dry zone in Myanmar.
Restricted to the central dry zone of Myanmar, primarily on low rolling hills where soil type and monsoonal patterns of rainfall patterns are sufficient to support a savanna ecosystem. Note that there remains uncertainty in the distribution of this ecosystem, and our map may overpredict Central Ayeyarwady Than-Dahat grassy forest in hillier terrain.
Native biota
Abiotic environment
Mean temperature
No data
Soil
Peguan Clay and dry soils
Precipitation
800 - 1,000 mm per annum
Elevation
No data
Mean annual rainfall of between about 800 mm and 1,000 mm (Stamp, 1924b; Khaine et al., 2017). A seasonally dry period occurs from October to late May. Temperatures are hot with little seasonal variation. Generally, occurs on clays (such as Peguan Clay) and dry soils, mostly on low rolling rises and foothills.
Key processes and interactions
The interaction of rainfall, soil type and the presence of fire are important in maintaining this ecosystem. The amount and very strong seasonality of monsoonal rains determine annual flushes of productivity in vegetation punctuated by prolonged water deficit over the dry season (Khaine et al., 2017). Most of the trees are equipped with thick bark enabling survival through recurring surface fires that consume the grassy groundcover when it cures in the dry season. The native vegetation is well adapted to fire, quickly resprouting while other woody species fail to establish.
Major threat
The ecosystem has been extensively fragmented by conversion to agriculture and the remnants are harvested for firewood and other human uses (Davis, 1960). Most fragments are highly degraded
Instruction: The visualization shows threats that are present within each ecosystem. According to IUCN, direct threats are the proximate human activities or processes that have impacted, are impacting, or may impact the the status of the taxon being assessed. Click of the highlighted icons to see details each threat category.
Assessment Summary
This ecosystem has a restricted range, and ongoing threats suggest that it is undergoing a continuing decline. The ecosystem is assessed as Vulnerable under Criterion B1. Further work is recommended to fill key knowledge gaps in biotic and abiotic degradation, as well as refining the distribution map for this ecosystem type.
Instruction: Click on the chart to view the detailed assessment result for each RLE risk criteria. Risk is defined as the probability of an adverse outcome over a specified time-frame. Here, the adverse outcome is the endpoint of ecosystem decline, which the RLE terms ecosystem collapse.
Ecosystem collapse definition
Central Ayeyarwady Than-Dahat Grassy Forest scrub is regarded as collapsed when its area has declined to zero or when cover of either grass or woody plant decline below 2% per hectare.
Date Assessed
2019-12-05
Year published
2019
Assessed by
Nicholas Murray,David Keith
Reviewed by
Hedley Grantham
Contributed by
references
Resources
ecosytems-MM view.csv
Myanmar Translation
