Coarse Woody Debris in Monsoon Tropical Forests of Vietnam.

In tropical forests, especially in the Southeast Asia, there are only fragmentary estimates of coarse woody debris (CWD) pools and dynamics. Our study examines the volume and structural diversity of CWD in forests not affected by commercial felling in the territories of the Bidoup Núi Bà and Bù Gia M p National Parks of the Republic of Vietnam. In the lowland Dipterocarp forests of Bù Gia M p National Park, the average volume of CWD was almost two times lower than the average CWD stock in the mixed montane forests of Bidoup Núi Bà national park: 44 m³ ha^–1 versus 78 m³ ha^–1. The mass of CWD depended linearly on its volume and averaged 24 t ha^–1. The projective cover of CWD averaged 269 m² ha^–1. Snags prevailed among the substrate categories (position types), accounting for 42 and 31% in the Bidoup Núi Bà and Bù Gia M p forests, respectively. The proportion of large branches in the montane forests of Bidoup Núi Bà National Park was 8%, while in the lowland forests of Bù Gia M p it reached 33% of the CWD volume. Very high termite activity was noted in the Bù Gia M p National Park—in 73% of the studied CWD pieces. The percentage of thermite tunnels partially filled with soil was, on average, 32% of the CWD volume. The high projective cover of CWD with various types of mass loss: consumption by invertebrates, white- and brown-rot decay suggests a significant role of CWD in the soil-forming processes. The similarities were revealed in the volume and size of CWD in the studied monsoon tropical forests of South Vietnam and in the primeval European boreal Norway spruce forests with fine-scale gap dynamics. The predominance of snags among the CWD categories and the nearly bell-shaped distribution of the CWD volume by decay classes complement the similarity of the CWD pool in tropical lowland and montane mixed forests with that in uneven-aged spruce boreal forests. However, a high proportion of branches in the structure of CWD, especially in lowland deciduous mixed forests distinguishes the CWD in tropical forests from the CWD in boreal and temperate forests. [ABSTRACT FROM AUTHOR]