Photo 1: Peltophorum dasyrrhachis in the paddy field

Photo 2: Young trees of Peltophorum dasyrrhachis in the shifting cultivation field

(2) Hilly plains spread in midland Laos and northeast Thailand. Dry dipterocarp forest, mixed deciduous forest, evergreen forest and their substitutive communities can be found on the undulating terrain consist of Mesozoic era red sandstone. The objective of this study is to estimate the secondary succession pattern of the vegetation and to examine the current conditions of the local land-use system and forest management.

(3) The latest field survey was conducted at Nakhou village and Bak village, Champhone District in Savannakhet Province, Laos, from 16 March to 3 April, 2003. Both villages are located on a continuous slope, with paddy fields spreading over the lowland from Nakhou village to the center of Bak village, and shifting cultivation being performed on the higher land. Some water sources were found around Bak village, which is on the boundary between the paddy field zone and the shifting cultivation zone. A vegetation survey inside and around the cultivated land and an interview survey regarding the former vegetation and useful plants were conducted at both villages.
          First, at Nakhou village, all (2,000) trees standing in the paddy fields along both sides of the village road (3 km long and 100 m wide) were measured, and the species name, DBH, height and location were recorded. Among them, 89 species were growing naturally, 20 species had been planted by villagers, and five of the planted species were considered to be able to regenerate naturally after planting. In the interview survey, villagers mentioned that the trees in the paddy fields (Photo 1) promoted the growth of rice plants, offered shade to both livestock and humans, and provided important fuel for the village, which has only little wooded land. It is also said that there has once been large numbers of large trees such as Dipterocarpus alatus and Pterocarpus macrocarpus, but that they had all been logged.
          Next, at Bak village, we selected study plots that had been slashed and burned one year ago, four years ago, nine years ago, and more than 20 years ago, as well as the conservation area. It is said that large trees of Dipterocarpus alatus, Pterocarpus macrocarpus and other valuable species had been logged around this area in the 1970s, the era of revolution. The plot survey showed that many seedlings of Peltophorum dasyrrhachis sprouted after burning and grew among the crops such as pineapple, banana, etc. (Photo 2). In one plot, more than 20 years after burning, the seedlings of climax species such as Dipterocarpus alatus, Dalbergia sp., etc., were growing under a canopy of Peltophorum dasyrrhachis and Dialium cochinchinense. This secondary forest produces many types of NTFPs, such as cardamon, shoots and fruits of rattan, etc. On the other hand, in the conservation area where valuab trees had been formerly logged, but where burning was not performed, we could not find any Peltophorum dasyrrhachis.
          These findings suggest the following secondary succession of vegetation around the research site. Formerly, evergreen forest and mixed deciduous forest abundant in Dipterocarpus alatus and Pterocarpus macrocarpus were widespread. After people settled, paddy fields were established in the lowland, whereas shifting cultivation was performed in the higher land. The tree species in paddy fields have changed from the pre-existing species from the primary forest to species growing preferably in villages. In the forest on the higher land, Peltophorum dasyrrhachis and Dialium cochinchinense formed a wide canopy layer, owing to the previous logging and shifting cultivation. One notable point is the existence of Peltophorum dasyrrhachis, which is a pioneer species often found in paddy fields or shifting cultivation areas. Though its wood has little commercial value, it is often used as timber or fuel wood in the villages. This study showed that the primary forest disappeared due to reclamation, logging and shifting cultivation, but that the secondary growth plants are of great use in both villages.