Sustainable Management of Acacia auriculiformis Plantations for Wood Production over Four Successive Rotations in South Vietnam

Abstract

Vietnam’s forestry sector is facing rising demands for wood to support national and rural economies, and rural livelihoods. A feasible option to meet this demand is to improve productivity in the current plantation estates, especially in those owned by thousands of small growers. Growers have invested in short-rotation acacia plantations primarily for the woodchip market, but are being urged through government policies and pressured by certification bodies and some NGOs to shift to longer rotations, preferentially, for growing saw logs. In this context, we examined the productivity of an Acacia auriculiformis plantation in South Vietnam, over four successive rotations, spanning 25 years. We show that it is possible to increase and sustain wood production in the long term, by applying simple but integrated management practices, recognizing that the conservation of site resources is critical for sustainability. Practices which depleted site organic matter and nutrients lead to a hidden, but high, cumulative loss of production. Given the site and soil damaging practices prevalent in the country, it is likely that production foregone in those sites may be equivalent to the yield from one in every four or five rotations harvested. With sound management including the conservation of site resources, planting the best germplasm, appropriate stocking and judicious use of herbicide, total wood production and the proportion of saw logs (50–70% of the commercial wood at about 7 years of age) can be increased substantially. At the same time, these practices also can promote understory development and diversity in the stand. Such holistic benefits are possible without extending the rotation length and/or thinning, which are likely to raise the levels of risks for small growers, who are not covered by any insurance. Investments and support for small growers to enable higher productivity and value per unit area in their holdings, through sustainable management, would offer practical and low-risk options for the benefits of growers, processors and ecosystems.

Productivity of Eucalyptus pellita in Sumatra: Acacia mangium Legacy, Response to Phosphorus, and Site Variables for Guiding Management

“…As described in the results, the differences in the range of basal area (Figure 9) between P deficient and sufficient plots leads to the conclusion that adequate P nutrition reduced variations in productivity across the area, creating a more uniform stand which is an important management objective. A similar relationship between early basal area and final volumes were found in A. auriculiformis and Acacia hybrid in contrasting sites in South and Central Vietnam [13]. There may be opportunities for further developing these relationships (Figures 7-9) into predictive models for enabling site specific management decisions and appropriate interventions.…”

“…While we do not yet have a good understanding of the dynamics of soil P and its relationships with stand growth in our experimental ecosystem, it is important to recognize from a management perspective, that even when site organic matter was conserved, incorporation of fertilizer P in the planting hole and increasing the supply in the immediate vicinity of the roots improved wood volume at harvest. It is likely that at this site and in Vietnam [13], the response to P may not have occurred if the same amounts of P were broadcast over the slash-litter layer. In soils with low pH (typically pH 4.1-4.4, Table 1) and high P fixing properties, an increase in the nutrient flux density at the root-soil interface may have been a key process for promoting high uptake and growth.…”

“…The consistently higher concentration of extractable P in the surface soil under high organic matter retention (BL 3 ) compared to that under BL 0 treatment (Figure 4), suggests that there has been a transfer of P from surface organic matter to the soil, but we note that nutrients are also transferred in the soil through fine root turnover and decomposition. Extractable P has been found to be declining during a rotation of acacia [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Slash and litter retention in eucalypt plantations in Brazil affected the various pools of P in the soil [27].…”

“…In South Sumatra, even among the sites used in this research, soils varied considerably in critical properties (Table 1), for example, depth of A-horizon ranged from 3 to 15 cm, depth to plinthite (hence the rooting volume) from 34.2 to 109.9 cm, in addition to the large differences in soil textural components, nutrient status and tree growth rates (Figure 5). The critical importance of conserving site organic matter and nutrients is now well recognized as key for sustainable wood production and maintenance of ecosystem processes in short rotation forestry [12,13,30]. In Sumatra, retention of slash and litter and minimum tillage are by far the most common inter-rotation practice implemented by the forestry industry, as well as the application of P fertilizers at each planting cycle.…”

Synergistic Use of Sentinel-1 and Sentinel-2 to Map Natural Forest and Acacia Plantation and Stand Ages in North-Central Vietnam

“…In the tropics, acacia plantations are often managed on very short (less than 5 year) rotations. However, there has been a recent push by the Vietnamese government [24,25] and certification bodies to switch to longer-term rotations, in an attempt to convert acacia plantation from woodchip to sawlog markets. Plantation age has important impacts on carbon storage [26] and species richness [27].…”