安達曼常綠巨木林之樹種多樣性與森林構造

Tree Diversity and Structure of Andaman Giant Evergreen Forests, India

Andaman及Nicobar島位於世界上重要的生物多樣性熱點上-印緬熱點之上。我們調查了位於Andaman及Nicobar島上之常綠巨木林的樹種多樣性。在中安達曼的Kalapahad（KP）及Macarthy Valley（MV）地區，我們分別建立了一公頃的樣區，並調查區內所有胸高圓周徑（gbh）大於（含） 30公分的植株。兩區取樣共得105種，分屬63屬及49科。MV樣區種樹高出KP區約10%，然而兩區之間的樹種多樣性相差並不大。兩區共有1311棵植株（KP：579 ha-1；MV：732 ha-1）；樹木總斷面積值相近（KP：45.59 m2 ha-1；MV：47.93m2 ha-1）。調查所得之植株中有13種為安達曼之固有種（佔12.38%）；此外，有10個樹種為稀有植物。兩調查區的優勢科各有不同：KP以龍腦香科為優勢而MV區則為肉荳蔻科。樣區內大部分物種為印緬大陸中南部之常見物種。樹木徑級結構呈現典型的反J型，但MV地區的小徑級樹木量為KP地區的兩倍。巨大的龍腦香科樹木對地面總生物量貢獻頗巨。本研究認為這些多樣性高、固有種繁多的脆弱島嶼森林的保育優先度應被重視。

We investigated tree diversity in ‘giant evergreen forest’ of Andaman and Nicobar Islands, which falls within the Indo-Burma hot spot of biodiversity in the world. A one hectare square plot was established in sites Kalapahad (KP) and Macarthy Valley (MV) of Middle Andamans, in which all trees ≥ 30 cm girth at breast height (gbh) were enumerated. Tree diversity totaled 105 species that belonged to 63 genera and 49 families. Site MV harboured ~10% greater species richness than KP. Species diversity indices did not vary much between the two sites. In the two sites, there were 1311 individuals of trees (579 ha-1 in KP and 732 in MV). The stand basal area was nearly equal in both the sites (KP- 45.59 m2 ha-1; MV- 47.93 m2 ha-1). Thirteen tree species (12.38%) were strict endemics to Andamans. Ten species recorded are rare to the flora of these islands. The two sites are distinctly dominated by two different plant families; Dipterocarpaceae in KP and Myristicaceae in MV. Most of the species were common to central and lower region of Myanmar and Indian mainland. The forest stand structure exhibited a typical reverse-J shape, but site MV had double the density of stems in the lower tree size class than that of KP. The voluminous dipterocarps contributed more to the total above-ground live biomass. The need to preserve these species- and endemics- rich, fragile island forests, prioritized for biodiversity conservation, is emphasized.