No abstract

Cunninghamia konishii Hayata is a rare and endangered plant species that plays a relevant role in ecological andcommercial systems of natural forests in Vietnam. In this research, we evaluated the potential geographic distribution ofC. konishii under current and future climatic conditions in Northern Vietnam using the ecological niche modelling approachbased on the largest available database of occurrence records for this species. C. konishii is mainly distributed inthe northern part of Vietnam at altitudes above 1000 m where the slopes range between 12 and 25 degrees, particularlyin special-use and protected forest. The optimal distribution area of C. konishii requires specific climatic conditions: anannual precipitation around 1200 mm, precipitation of the warmest quarter ranging from 600 to 800 mm, a precipitationseasonality of 90 to100 mm, an annual mean temperature ranging from 12°C to 19°C, and a temperature seasonalityranging from 300 to 350. Additionally, the species requires specific soil groups: humic acrisols, ferralic acrisols, andyellow-red humic soils. Considering these requirements, the results of our research show that the suitable regions for thegrowth of C. konishii are found in the provinces of Ha Giang, Son La, Thanh Hoa and Nghe An, covering a total area of1509.56 km2. However, analyzing the results under the Community Climate System Model version 4 (CCSM4) model, itis possible to observe that the area will decline to 504.39 km2 by 2090 according to RCP 2.6 scenario, to 406.25 km2 inthe RCP 4.5 scenario, and to 47.62 km2 in the RCP 8.5 scenario. The findings of this present research may be applied toseveral additional studies such as identifying current and future locations to establish conservation areas for C. konishii.

The suitability of land for C. konishii was evaluated using the analytic hierarchy process (AHP) method, which included multiple criteria, such as elevation, soil, climate, and vegetation characteristics. 120 different sites of C. konishii were studied and the model approximations were verified by a confusion matrix. The subsistence of C. konishii was mainly affected by topographic features (elevation, slope) and soil (soil texture) conditions. 15 variables were selected for the ecological analysis and construction of the land suitability map. They were combined into four main groups for weights approximation. The weights obtained by AHP were calculated as follows: topographic features (65%), soil (21.3%), climate conditions (7.4%), and vegetation type (6.3%). The total area with the highest suitability was estimated at 4, 6, 2 and 8% of the province area in Son La, Ha Giang, Thanh Hoa, Nghe An, respectively. The suitable areas for planting were located in Mai Son, Muong La, Moc Chau, Sop Cop districts of Son La province; Hoang Su Phi, Xin Man districts of Ha Giang province; Muong Lat district of Thanh Hoa province; Que Phong, Ky Son, Tuong Duong, Con Cuong districts of Nghe An province. Nghe An province has the largest suitable area for planting. The estimated AHP accuracy was 91.6%, which indicates that the approach is reliable for forestry management. The current study will provide a ground to the local population for the selection of suitable lands, ensuring the sustainability of natural resources, sustainable use and quality forest production.

Abstract. Bao TQ, Viet LH, Hai NH, Tuan NT, Cuong LV. 2021. Population dynamics and regeneration of Shorea roxburghii, a threatened timber species in Southern region, Viet Nam. Biodiversitas 22: 5649-5656. Despite its wide distribution in South and Southeast Asia, Shorea roxburghii G. Don is classified as Vulnerable in the IUCN Red List of Threatened Species due to over-exploitation for its valuable timber. This study aims to investigate the population dynamics and regeneration of S. roxburghii in southeastern Vietnam, serving for conservation and sustainable development plan. Six plots of 2,500 m2 each (50 m × 50 m) were established at two forest conditions: i) forest with standing volume > 200 m3/ha (SV>200), and ii) < 200 m3/ha (SV<200); to investigate stems with diameter at breast height (DBH) ? 5 cm and that < 5 cm. Moisture (%), pHH2O of the topsoil and the occurrence of regenerating S. roxburghii were collected from 125 points in the study site. The results indicated that mean stem height, DBH, basal area, and aboveground biomass were significantly higher at the forest stand with SV>200 than that at the forest stand with SV<200 for the pool of all species. Similar higher figures were found in SV>200 for the pool of S. roxburghii compared to that in SV<200, except mean DBH, which was larger in SV<200. There were missing stems with DBH < 5 cm in SV<200, while it was numerous in SV>200 (1,313 stems/ha). DBH/stem distributions in both forest types had an inverted-J shape with a peak at 10-15 cm DBH for the pool of all species, while there was no clear pattern for the pool of S. roxburghii in both forest types. Regression analysis indicated that higher total crown area of stems ? 23 tall leads to higher S. roxburghii stems, while the higher total crown area of stems < 23 tall leads to fewer S. roxburghii stems with DBH < 5 cm. It is concluded that the total crown area of forest stand plays an important role in the sustainable regeneration of S. roxburghii. Silvicultural treatment should be applied to reduce stand density and crown area of stems < 23 m tall to enhance sunlight reaching the forest floor for germination, growth, and survival of S. roxburghii. The moisture of the topsoil ranging from 60 - 80% and the pHH2O ranging from 3.8 - 4.6 are suitable conditions for natural regeneration of S. roxburghii.