Structure and Regeneration Dynamics of Abies densa Forests in Central Bhutan

Wien

2002

S. 279-288

6 Tab., 23 Lit. Ang.

Unselbständiges Werk

200097817

The uppermost forest belt of the temperate conifer forests in Bhutan is formed by monospecific stands of Abies densa. In order to study their structure and dynamics, multivariate analysis of regeneration classes, recorded in a forest inventory, was performed in order to extract main factors influencing natural regeneration for further analysis. In a next step, regeneration ecology was studied on 32 permanent sample plots. Presence of the understory species Rhododendron hodgsonii and the bamboo Yushania microphylla as well as the number of canopy layers significantly differentiated the regeneration classes and explained 90 % of their variance. Abies densa has different regeneration modes on sites with the different understory species and on sites without understory of rhododendron or bamboo: On the latter sites, frequent fine scale disturbances caused by snow breakage of branches and parts of crowns provide enough input of radiation for continuous regeneration without the need for formation of treefall gaps. Abies densa showed microsite preferences on exposed mineral soil and moss in terms of growth and survival. On sites with the two understory species, regeneration is highly gap driven. R. hodgsonii shows strong height growth in the understory. On these sites, fir maintains a seedling bank, which provides a large head start for the slower growing fir when gaps form. Regeneration on sites with bamboo understory is also highly gap dependent but needs either destroying of the bamboo through fallen trees or parts of trees or the die-back of the understory species after flowering. Nurse logs were shown to play an important role as safe sites since light climate on these elevated surfaces allows fir to survive and grow. No seedling bank can develop under dense bamboo understory. The results of the study show the pronounced influence of understory species on dynamics of the studied forest ecosystems. Codes of practice for selection of cable lines, groups within cable lines as well as trees within groups were developed and implemented in the field.