Northern Triangle temperate forests

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The Northern Triangle Temperate Forests [IM0402] ecoregion lies in the extreme northern area of the Golden Triangle of Myanmar. The region is scientifically unexplored, and the biological information, especially of its flora, is still based on the early, pioneering exploration done by Kingdon-Ward (1921, 1930, 1952). There have been no detailed scientific surveys in this area since then, and current assessments of its biodiversity probably are underestimated. In all probability this ecoregion harbors many more species than are now attributed to it. Satellite imagery indicates that the ecoregion is still largely clothed in intact forests and presents a rare opportunity to conserve large landscapes that will support the ecological processes and the biodiversity within this eastern Himalayan ecosystem.

  • Scientific Code
  • Ecoregion Category
  • Size
    4,100 square miles
  • Status
    Relatively Stable/Intact
  • Habitats

Location and General Description
The mountains originated more than 40 million years ago, when the collision between the drifting Deccan Plateau and the northern Laurasian mainland created the Himalayan Mountains, including these mountains in the Golden Triangle. Therefore, the mountains are young and unweathered; the terrain is rugged and dissected, with north-south-oriented ranges that reach south, toward the central plains of Myanmar. The peaks along this range rise steeply to attain heights of more than 3,000 m. The Chindwin, Mali Hka, and N'mai Hka rivers originate in these mountains and flow south to converge in the lower reaches to form the Irrawaddy River.

Biogeographically, the mountains are an ecotone of the Assam-Indian, Eastern Himalayan, Indo-Malayan, and Chinese floras. Gondwana-era relicts that rafted north on the Deccan Plateau have also taken refuge here. Therefore, floristically, the ecoregion is extremely diverse. And the complex topography and moist conditions produced by the southwestern monsoon funneled in from the Bay of Bengal have provided the localized climatic variations that promote endemism.

Floristically, the ecoregion is very similar to the middle mountain forests of the Eastern Himalaya. The temperate forests lie between 1,830 and 2,700 m. At lower elevations the forest transitions into the subtropical forests and, in the upper elevations, into the sub-alpine conifer forests. The temperate forests are characterized by Alnus nepalensis, Betula cylindrostachya, Castanopsis spp., Schima spp., Callophylus spp., Michelia spp., and Bucklandia populnea (WWF and IUCN 1995; Lwin 1995). Rich epiphytic rhododendron shrub vegetation is common. At higher elevations rhododendrons, especially Rhododendron decorum, R. magnificum, R. bullatum, R. crinitum, and R. neriiflorum become a dominant component in the vegetation.

At elevations above 2,100 m, the broadleaf forests transition into a mixed forest, where species of Quercus, Magnolia, Acer, Prunus, Ilex, and Rhododendron are mixed with Picea brachytyla, Tsuga dumosa, Larix griffithiana, and Taiwania flousiana. The rich, diverse shrub flora persists here but is characterized by species of Acer, Berberis, Clethra, Enkianthus, Euonymus, Hydrangea, Photinia, Rhododendron, Rubus, Betula, and Sorbus (WWF and IUCN 1995; Blower n.d.).

Biodiversity Features
Ninety-one mammal species are known from this ecoregion, but additional surveys may well reveal the presence of additional species. But for now the only ecoregional endemic mammal attributed to the Northern Triangle Temperate Forests [IM0402] is the Gongshan muntjac (Muntiacus gongshanensis) (table 1). However, there are several other threatened species in the ecoregion's assemblage that deserve conservation attention, namely the tiger (Panthera tigris), takin (Budorcas taxicolor), clouded leopard (Pardofelis nebulosa), red panda (Ailurus fulgens), wild dog (Cuon alpinus), Asiatic black bear (Ursus thibetanus), stump-tailed macaque (Macaca arctoides), capped leaf monkey (Semnopithecus pileatus), red goral (Naemorhedus baileyi), great Indian civet (Viverra zibetha), back-striped weasel (Mustela strigidorsa), Irrawaddy squirrel (Callosciurus pygerythrus), and particolored squirrel (Hylopetes alboniger).

Table 1. Endemic and Near-Endemic Mammal Species.

  Family Species
Cervidae Muntiacus gongshanensis

An asterisk signifies that the species' range is limited to this ecoregion.

Of the 365 birds known from this ecoregion, the rusty-bellied shortwing (Brachypteryx hyperythra) is the only ecoregional endemic (table 2). But there are several species that need mature habitats, have low tolerances for disturbances that are indicators of habitat integrity, and deserve conservation attention. These species include the Oriental pied-hornbill (Anthracoceros albirostris), wreathed hornbill (Aceros undulatus), Blyth's tragopan (Tragopan blythii), Himalayan flameback (Dinopium shorii), and Sclater's monal (Lophophorus sclateri). The ecoregion also overlaps with the Eastern Himalayas EBA (130), which contains seven restricted-range species (Stattersfield et al. 1998).

Table 2. Endemic and Near-Endemic Bird Species.

  Family Common Name Species
Turdidae Rusty-bellied shortwing Brachypteryx hyperythra

An asterisk signifies that the species' range is limited to this ecoregion.

But the conservation priority of this ecoregion goes beyond the species lists. A critical component of the Himalayan ecosystems is the dependence of ecological processes-from seasonal bird and mammal migrations to watershed protection-on altitudinal connectivity and the intactness of ecosystems that are stratified by elevation. Loss of habitat or even large-scale degradation can have far-reaching consequences. Birds that migrate up and down the steep slopes will lose staging and feeding habitat, thus disrupting their migrations. Loss of ground cover in the high elevations can result in erosion on steep slopes, with the consequences being manifested as floods and silting far away, in lowland plains and mangroves in the river deltas.

Current Status
Because of the remoteness and inaccessibility of this high-elevation ecoregion that sits on steep, rugged mountains, most of the habitat in this ecoregion is still intact. However, it receives no formal protection.

Types and Severity of Threats
Throughout Myanmar, the hill tribes who still practice shifting cultivation are being pushed further and further into marginal, steeper lands for a variety of reasons, including logging in the lower elevations that were the traditional agricultural areas. The consequent clearing of new forests for shifting cultivation and poppy cultivation will result in severe erosion and loss of habitat and biological diversity.

Justification of Ecoregion Delineation
In a previous analysis of conservation units across the Indo-Malayan region, MacKinnon (1997) identified a subunit (09b) that includes the tropical and subtropical moist broadleaf forests in the Kachin and upper Chindwin areas of northern Myanmar. In keeping with our rules for defining ecoregions, we represented the temperate broadleaf forests in this subunit with the Northern Triangle Temperate Forests [IM0402].

References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List

Prepared by: Eric Wikramanayake
Reviewed by: