The Biodiversity of Bac Huong Hoa Nature Reserve - Birdlife ...

2.8.2 Medium quality forest
Just over half of BHH NR is covered in medium quality forest. Lowland evergreen forest and
mid-montane evergreen forest habitats in BHH NR have been strongly and negatively affected by
people. Lowland evergreen forest has been extensively logged for high value timber and because
it occupies the most productive agricultural land, it has also been cleared for shifting cultivation.
Mid-montane evergreen forest has also experienced some selective logging and in common with
lowland forest, it was affected by aerial spraying of chemical defoliants during the American
War. Faunal and floral diversity of medium quality forest is considerably lower than that of high
quality forest types.
Secondary forest following shifting cultivation
This is the dominant forest type on land below 600 m. In Bac Huong Hoa, short stature secondary
forest develops 8-10 years after shifting cultivation. The plant composition, structure and
appearance of this forest type, are completely different from primary forest. There are very few
lianas in secondary forest, fern diversity is low and orchids and arboreal ferns are typically
absent. It is generally very dense and chaotic in structure, with no defined layers; however, the
following four layers can sometimes be defined.
Upper canopy layer: This layer is characterised by light-demanding tree species which have
grown up from stumps or from the seed bank, following a cessation of farming activities. These
trees typically have a height of 8-10 m and a diameter of between 10 and 15 cm. Typically,
species from the families Litsea, Machilus, Lindera, Lauraceae, Euphorbiaceae, Rutaceae,
Ulmaceae, Fabaceae, Moraceae, Sapindaceae, Anacardiaceae and the genera Macaranga,
Mallotus, Sapium, Bridelia, Canarium, and Ficus are found; as well as the species Endospermum
sinensis, Euodia melifolia, Acronychia pedunculata, Gironniera subaequalis, Trema orientalis
and Centis sinensis.
Lower canopy layer: This layer is characterised by smaller trees, often similar to those in the
upper canopy layer, and shrubs with a height of 5-7 metres. The families most often recorded in
this layer are Rubiaceae, (especially Camellia spp. and Eugenia spp), Theaceae (especially
Grewia spp.) and Tilliaceae.
Mid-story: This layer consists of small trees and shrubs. Typically, species from this layer
include representatives from the families Melastomataceae, Rubiaceae, Verbenaceae and
Arecaceae and in particular, Rapis excelsa.
Understory: This layer is usually composed of ferns and grasses from the families Zingiberaceae
and Araceae. In areas where light penetrates to the ground, members of the family Poaceae are
often found and members of the Rubiaceae, Hydeotis and Acanthaceae families occur in humid
places.
2.8.3 Low quality forest and non-forest habitats
Bamboo forest
At elevations of 700-1200 m, degraded land is colonised by the large bamboo species
Arundiunria peteloti. It reaches 3-5 metres in height and grows in dense stands. Interspersed with
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