Tran Van Do

An estimate of the number of tropical tree species

Significance People are fascinated by the amazing diversity of tropical forests and will be surprised to learn that robust estimates of the number of tropical tree species are lacking. We show that there are at least 40,000, but possibly more than 53,000, tree species in the tropics, in contrast to only 124 across temperate Europe. Almost all tropical tree species are restricted to their respective continents, and the Indo-Pacific region appears to be as species-rich as tropical America, with each of these two regions being almost five times as rich in tree species as African tropical forests. Our study shows that most tree species are extremely rare, meaning that they may be under serious risk of extinction at current deforestation rates. The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher’s alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼40,000 and ∼53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼19,000–25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼4,500–6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

Estimation of fine-root production using rates of diameter-dependent root mortality, decomposition and thickening in forests

Current studies indicate that fine roots of different diameter classes show different rates of decomposition. This study developed a new method to estimate fine-root production by considering the difference in the production of fine roots of two size classes, fine roots thinner than 1 mm and those between 1 and 2 mm, and their corresponding rates of decomposition. A litter bag experiment was used to estimate the decomposition rates, while the sequential soil core technique was used to identify mass values of live roots and dead roots at a given period of observation. The continuous inflow method was applied to estimate the amount of root decomposition, mortality and production with a framework of two diameter classes of fine roots and for quantification of the amount of mass transfer from the thicker fine-root class to the coarser root category (>2 mm). The results indicated that the estimate of fine-root production was greater when two size classes of fine roots were distinguished. Using a framework of two size classes developed in this study resulted in 21.3% higher fine-root production than a method that did not recognize fine-root size classes or mass transfer to the category of coarse roots. In addition, using shorter collection intervals led to higher production estimates than longer intervals. The production estimate with a 1-month interval was 21.4% higher than that with a 6-month interval. We consider that the use of the sequential soil core technique with continuous inflow estimate method by differentiating size classes of fine roots is likely to minimize the underestimation of the parameters of fine-root dynamics by accounting for decomposition and mortality of fine roots more appropriately.

Carbon stocks in tropical evergreen broadleaf forests in Central Highland, Vietnam

SUMMARY This is the first study on carbon stock estimation in the tropical evergreen broadleaf forests in Central Highland, Vietnam. As result of selective logging and shifting cultivation, remaining forests are silviculturally classified to five categories by governmental standard basing on standing volume (V), including very poor forest (V ≤ 10 m3/ha), poor forest (10 < V ≤ 100 m3/ha), medium forest (100 < V ≤ 200 m3/ha), rich (200 < V ≤ 300 m3/ha), and very rich forest (V > 300 m3/ha). Carbon stock of four pools including big trees (diameter at breast height/dbh ≥ 5 cm), short vegetation layer (dbh < 5 cm), necromass, and soil was measured by using 150 plots of 50 m × 50 m each. Soil carbon stock was assessed from soil samples taken to 30 cm depth. The results indicated total carbon stock increased from 75 tons C/ha in very poor forest to 199 tons C/ha in medium forest, and to 255 tons C/ha in very rich forest. Carbon stock in necromass was significant different (ANOVA; F(4,145) = 61.70, p < 0.001) among forest categories (from 4 to 8 tons C/ha). Meanwhile, there were no differences of carbon stock in soil and short vegetation layer among forest categories, which ranged 59–64 tons C/ha and 3–4 tons C/ha, respectively. There was a linear positive relationship between carbon in big trees and that in necromass (R(149) = 0.61, p < 0.01). It is concluded that the degree of human disturbance had significant impacts on carbon sink in the present study forests.

Aboveground biomass increment and stand dynamics in tropical evergreen broadleaved forest

ABSTRACT Forest ecosystems can modify the atmospheric CO2 through biomass accumulation mostly in tree stems with diameter at breast height (DBH) ≥ 10 cm. Aboveground biomass increment (ΔAGB), and changes in stand AGB, no. stems and basal area (BA) were calculated from mortality, recruitment, and growth data of tree stems in tropical evergreen broadleaved forest, Central Highland Vietnam. Data were derived from ten 1-ha permanent plots established in 2004, where all stems with DBH ≥ 10 cm were tagged, identified to species, and measured for DBH in 2004 and 2012. In an 8-year duration, the increment was 53 ± 10 stems ha–1, 7.8 ± 0.3 m2 ha–1 for BA and 86.0 ± 4.6 Mg ha–1 for AGB. The stem mortality rate was 0.9% year–1 and the stem recruitment rate was 2.2% year–1. Annual ΔAGB was 10.8 Mg ha–1 year–1, equaling to 5.4 Mg C ha–1 year–1. Of which, tree stems of 35–80 cm DBH classes accounted for 65%. The results indicated that the forest is in stage of carbon sequestration. Any disturbances causing death of 35–80 cm DBH tree stems will much reduce carbon sequestration capacity and it will take a long time for AGB to return to pre-disturbance stage.

Cost - Benefit Analysis for Agroforestry Systems in Vietnam

Agroforestry has been practiced for a long time in Vietnam. In this study, the cost - benefit was analyzed in four agroforestry systems, which have been widely established in north mountainous provinces with Star Anise ( Illicium verum ) + t ea (IT), bead tree ( Melia azedarach ) + cassava (MC), Acacia hybrid + cassava (AC) and Acacia mangium + maize (AM). A questionnaire was used to obtain information on (1) Inputs , which included costs for seeds/seedlings, fertil izers, pesticides, and labor costs, and (2) Incomes , which included benefits from selling fruits, leaves, corns, and timbers. The results indicated that IT had the highest economic benefit (6,527 US

Altitudinal Changes in Species Diversity and Stand Structure of Tropical Forest , Vietnam

ha - 1 y - 1 ), followed by MC (2,905 US

Toward Carbon Certificate in Vietnam: Net Ecosystem Production and Basic Income for the Local Community

ha - 1 y - 1 ), AC (1,043 US

Large trees drive forest aboveground biomass variation in moist lowland forests across the tropics

ha - 1 y - 1 ), and AM (870 US

Recovery process of a mountain forest after shifting cultivation in Northwestern Vietnam

ha - 1 y - 1 ), respectively. However, even with such economic benefits, these agroforestry models could not be established across all mountainous regions because of site specific ecological requirements of tree species and crops. In addition, unstable market and fluctuating price of agroforestry product s is a big concern leading to un sustainability of these agroforestry systems. It is recommended that

Relationship between aboveground biomass and measures of structure and species diversity in tropical forests of Vietnam

Ba Vi National Park (BNP) is known as one of the first parks established in Vietnam and has been well pre served against human disturbances. A study was conducted to understand altitudinal changes and aspect differences of species diversity and stand structure in evergreen broadleaf forest in BNP. Twenty plots (40 m x 50 m), distributing between 130 and 1,195 m above sea level were used for stem census, which were equally established in both eastern and western aspects. All stems with diameter at breast height (DBH) ≥ 10 cm were identified to species and measured for DBH. Results indicated significant linear relationships between elevation and basal area (G), top canopy height, species density, Shannon diversity index, and E venness. Elevation zone of > 1,000 m above sea level had highest species density, Shannon diversity index, Evenness, stem density, G, and top canopy height, which were significant higher than that in 500 - 1,000 m and < 500 m elevational zones. Species compo sition in BNP was different between eastern aspect and western aspect, and both aspects shared 86 species in total 219 species found. While, stand structure and species diversity were not significant different between two aspects.