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Thi Tran Thanh Luu, Vietnam

Zuidema P.A.,University Utrecht | Jongejans E.,Radboud University Nijmegen | Chien P.D.,University Utrecht | Chien P.D.,Forest Science Institute of Vietnam | And 2 more authors.
Journal of Ecology | Year: 2010

Matrix models are popular tools for plant demographic studies, but their application to long-lived, slow-growing species is hampered by the fact that (i) model output is highly sensitive to category width and (ii) growth variation between individuals can only be partially accounted for. Integral Projection Models (IPMs) - an extension of matrix models - offer a solution to these problems. Here, we introduce a new method to parameterize IPMs for trees - the 'integration method'- which allows constructing IPMs for long-lived, slow-growing species. This approach is more suitable than the 'midpoint rule', which is customarily used. We built IPMs for six tree species from Vietnamese (sub)tropical forests. For four of these species, population growth rate (λ) was highly sensitive to the number of categories in the transition matrix. Population growth stabilized for IPMs with 100-1000 categories, corresponding to categories of 0.1-1 cm in trunk diameter. This preferred width is much narrower than the 10-cm-wide categories customarily used in tree models. The distribution of elasticity values over transition types (stasis, progression to next and further categories) is also highly sensitive to matrix dimension in IPMs. In addition, elasticity distribution is influenced by including or excluding growth variation. Age estimates obtained from IPMs were also highly sensitive to matrix dimension: an IPM with 1000 size categories yielded 2-4 times higher age estimates for large trees than one with 10 size categories. Observed ages obtained from tree ring analyses for four of the study species allowed validating these estimates. IPMs with 10 categories strongly underestimated age, while those with 1000 categories yielded slight age overestimates. Underestimating age in small matrices is caused by the occurrence of unrealistically fast pathways through the life cycle and is probably widespread among tree models with broad categories. Overestimating ages in IPMs with narrow categories may be due to temporally autocorrelated growth or errors in fitting growth curves. Synthesis. IPMs are highly suitable tools to analyse tree demography. We recommend that tree IPMs (and classical matrix models) apply narrow diameter categories (0.1-1 cm width) to obtain reliable model output. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.

Sang P.M.,Forest Science Institute of Vietnam | Lamb D.,University of Queensland | Bonner M.,University of Queensland | Schmidt S.,University of Queensland
Plant and Soil | Year: 2013

Purpose: Much tropical land requires rehabilitation but the capacity of reforestation with plantations or naturally regenerating secondary forests for overcoming soil degradation remains unclear. We hypothesised that desirable effects, including improved soil fertility and carbon sequestration, are achieved to a greater extent in Acacia mangium plantations and secondary forests than in Eucalyptus urophylla plantations. Methods: We tested our hypothesis across soil and climate gradients in Vietnam with linear mixed-effect models and other, comparing A. mangium and E. urophylla plantations, secondary forests and pasture. Results: A. mangium plantations and secondary forests showed a positive correlation between biomass production and desirable soils properties including increased soil carbon, nitrogen and phosphorus, and reduced bulk density. All plantations, but not secondary forests, caused increases in soil acidity. Eight-year old A. mangium plantations contained most carbon in biomass+soil, and secondary forests and pastures had similar or higher soil carbon. E. urophylla plantations had the lowest soil carbon status, raising doubt about their sequestration capacity in current 6-8 year rotations. Conclusions: The study demonstrates that appropriate reforestation enhances soil fertility and promotes carbon sequestration on degraded tropical lands and that unmanaged secondary forests are effective at improving soil fertility and sequestering carbon at low cost. © 2012 Springer Science+Business Media B.V.

Kien N.D.,Forest Science Institute of Vietnam | Harwood C.,International Center for Research in Agroforestry
Small-scale Forestry | Year: 2016

Households and wood processing businesses in the provinces of Son La, Dien Bien and Lai Chau in the Northwest of Vietnam were surveyed to determine patterns of local wood demand and supply, changes in species utilized over time, and whether timber from planted trees might substitute for species previously harvested from local natural forests. In each province, 5–6 sawmills and 4–6 villages representing 3 main ethnic groups were selected for investigation. Managers of selected sawmills and 3–4 randomly selected households in each village were interviewed using semi-structured questionnaires. There was high and uniform household demand for fuelwood in the surveyed villages, making fuelwood the dominant use, in terms of wood volume. Use of sawn timber for furniture, home repair and construction consumed less wood but required logs of acceptable species. Sawmills surveyed were small, with input capacity ranging from <15 to 500 m3 of logs per year, suggesting a total log requirement of about 30,000 m3/year for the 192 known wood processing businesses in the three provinces. Most sawmills still used wood from natural forests, sourced locally or imported from Laos. A trend of switching from prized timber species from natural forests, now effectively unavailable, to alternatives from natural and planted forests was reported by both sawmills and households. Some planted species grown on short-medium rotations appear able to substitute for local sawn timber requirements. © 2016 Steve Harrison, John Herbohn

Harbard J.L.,University of Tasmania | Griffin A.R.,University of Tasmania | Foster S.,University of Tasmania | Brooker C.,University of Tasmania | And 2 more authors.
Forestry | Year: 2012

Australian acacias are widely planted as exotics and in some cases as invasive. Impact may be reduced if sterile triploid planting stock can be developed. This article reports the first step in such a breeding programme, the production of a population of tetraploid lines for inter-breeding with diploids. Three methods of polyploid induction with colchicine were compared. A conversion rate of 8.9 per cent was obtained by applying 1.5 per cent colchicine to the shoot apical meristem of seedlings. A 7 per cent conversion rate was obtained by germination of scarified seed on filter paper saturated with 0.02 per cent colchicine for 16 h and this method is recommended on logistical and safety grounds. Poor results were obtained when scarified seed were submerged in aqueous solutions of colchicine. Flow cytometry is the preferred method for ploidy determination, sampling after vegetative phase change on a minimum of two opposing phyllodes per plant. Visual classification was inaccurate due to the confounding effects of growth-retarding properties of colchicine. Size and distribution of stomata can also be used but is more time consuming than flow cytometry. At 26 months, tetraploid plants had heavier, thicker, wider and more cupped shaped phyllodes than diploids and the bark: stem diameter ratio was greater.

Saintilan N.,Office of Environment and Heritage | Wilson N.C.,Forest Science Institute of Vietnam | Rogers K.,University of Wollongong | Rajkaran A.,Rhodes University | Krauss K.W.,U.S. Geological Survey
Global Change Biology | Year: 2014

Mangroves are species of halophytic intertidal trees and shrubs derived from tropical genera and are likely delimited in latitudinal range by varying sensitivity to cold. There is now sufficient evidence that mangrove species have proliferated at or near their poleward limits on at least five continents over the past half century, at the expense of salt marsh. Avicennia is the most cold-tolerant genus worldwide, and is the subject of most of the observed changes. Avicennia germinans has extended in range along the USA Atlantic coast and expanded into salt marsh as a consequence of lower frost frequency and intensity in the southern USA. The genus has also expanded into salt marsh at its southern limit in Peru, and on the Pacific coast of Mexico. Mangroves of several species have expanded in extent and replaced salt marsh where protected within mangrove reserves in Guangdong Province, China. In south-eastern Australia, the expansion of Avicennia marina into salt marshes is now well documented, and Rhizophora stylosa has extended its range southward, while showing strong population growth within estuaries along its southern limits in northern New South Wales. Avicennia marina has extended its range southwards in South Africa. The changes are consistent with the poleward extension of temperature thresholds coincident with sea-level rise, although the specific mechanism of range extension might be complicated by limitations on dispersal or other factors. The shift from salt marsh to mangrove dominance on subtropical and temperate shorelines has important implications for ecological structure, function, and global change adaptation. © 2013 John Wiley & Sons Ltd.

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