Dynamics of Fallow Vegetation in Shifting Cultivation in Northern Laos: A Case Study in Houay Phee Village, La District, Udomxay Province
HIROTA Isao*, NAKANISHI Asami**, VILAYSAK Vanhna*** and Eiji NAWATA*

* Graduate School of Agriculture, Kyoto University, Japan
** Field Science Education and Research Center, Kyoto University, Japan
*** Faculty of Forestry, National University of Laos


Dynamics of fallow vegetation in shifting cultivation was studied in Houay Phee Village, La District, Udomxay Province, Lao P. D. R. by comparing various characteristics of fallow and conservation forests, which were able to be regarded as long fallow forest. DBH (diameter at breast height) and height of all woody plants in 20x20 m quadrats were investigated in a conservation forest, a secondary forest after the fallow period of more than 20 years and fallow forests with various fallow periods from 1 to 8 years. In each quadrat, 5 species were ranked according to the abundance and Shanon-Weaver index was calculated. Canopy openness was measured by photographs of the canopy. The biomass of woody plants increased gradually in the first 2 years, and rapidly in the 3rd year, and the increase of the biomass continued up to 8th year. The increase of biomass at early stages of the fallow period was mainly accounted for that of bamboo. The biomass of the other woody species increased as fallow periods prolonged. The biomass of bamboo was less than 5% of the whole biomass in the conservation forest. Among tree species, Euphorbiaceous plants were dominant in all quadrats except the conservation forest. Fagaceous and Juglandaceous plants, known as climax species in this area, appeared in later stages of fallow period. These species were especially abundant in the conservation forest. Bamboo was dominant species in all quadrats except the conservation forest. As it is unnatural that the biomass of bamboo have been decreased sharply in the fallow forests in about ten years and bamboo grows much faster than the other woody species at early growth stages, bamboo may have flourished more remarkably in recent years.

Meanwhile, according to the interviews with the villagers, the main non-timber forest products (NTFPs), like cardamom, paper mulberry, peuak meuak (Boehmeria malabarica), or tiger grass, were begun gathering about from 5 to 10 years ago. At this time, forest utilization of the villagers abruptly changed, while NTFPs is mainly gathered in the fallow forests. As a result, there have been two impacts, which are the shortening of fallow periods and the gathering of NTFPs, on the fallow forests in these about ten years, and that causes recent vegetation change in this area.