Bernard Dell

Dalbergia tonkinensis (Yellow rosewood) is a rare timber species with high economic value in Vietnam and China. It was assessed as Vulnerable under criteria A1cd in IUCN Red List of Threatened Species and in the Vietnamese decree 84/2021/ND-CP to control illegal harvesting. The seed sources of this species are low in genetic diversity because few mature trees exist in natural populations. In the last decade, efforts have been made to study the market and use of the species, morphological characteristics, phenology, pests and diseases, and gene conservation in Vietnam. A study of morphological variation among provenances of D. tonkinensis in Vietnam revealed significant differences in traits such as total height, bark colour, stem form, fruit shells, and seed size. The species is propagated easily via seeds and cuttings. Seeds from plus trees have been safely stored in seed and field gene banks. Provenance/progeny tests in three field gene banks showed notable genetic variations in growth, form, and disease resistance. High individual heritability (0.33–0.49) and additive variation were observed for growth traits. Results highlight superior gene sources for early plantation growth and recommend conserving genetic diversity. Comprehensive information on D. tonkinensis has been reviewed in this chapter.

Soil water repellency (SWR) is a major problem across the globe and often occurs in sandy soils. SWR inhibits seed germination in crops and pastures, enhances surface runoff and erosion, and accelerates the movement of nutrients and pesticides into groundwater. SWR is caused by the accumulation of hydrophobic organic compounds released from plants and soil microbiota, and in some studies the severity of SWR has been related to soil organic carbon (OC) contents and the presence of particular organic compounds. In addition, factors such as root exudates, contributions from multiple plants, compounds produced during the decomposition of organic matter, and fungal bio-products influence SWR. SWR is also related to soil physical properties such as surface area and chemical properties such as pH. In general, SWR increases with increasing soil OC and decreases with increasing soil surface area; therefore sandy soils are more prone to SWR; however if a soil contains sufficient OC, it will be repellent. This review explores the linkage between SWR and physicochemical properties of soils and suggests research directions to uncover the interplay of the various contributing factors to SWR.

Deep soils are located in most continents of the world. Soil carbon measurements are invariably made from the surface horizons, whereas much larger carbon stores occur to depths of many meters, with plant roots providing the main source of carbon. This root biomass persists long after land is deforested for agricultural and other pursuits or forests are killed by pests and fires and may represent a considerable carbon store at the global scale. The impacts on these carbon stores of reforestation or climate change are mostly unknown as the estimation of root biomass and carbon dynamics is challenging in deep soils. This chapter explores deep soil carbon from the perspectives of its definition, source, and persistence; methodologies available to study deep soil carbon; and the effect of land-use change on this carbon store.

Beneficial soil-borne bacteria and fungi are central to the performance of most plants. Knowledge of beneficial microorganisms and the processes in topsoils that favour the association of beneficial organisms with plants allows us to better manage soils for higher productivity and environment sustainability. This review describes the main groups of symbiotic and free-living organisms and explores how they contribute to plant and soil health in managed and natural ecosystems. Many field studies have investigated the biodiversity, ecology and function of beneficial organisms in relation to root distribution in topsoils and land management practices. There is scant information however on whether beneficial bacteria and fungi can persist and enhance root function in subsoils. Opportunities for enhancing beneficial plant-microbe interactions in the subsoil deserve scrutiny particularly as crop productivity is becoming more dependent on subsoil moisture with declines in rainfall in many parts of the world.

Salinization of land is a form of desertification; salinization of rivers is a global threat to biodiversity and compromises the ecosystem goods and services of rivers, wetlands, and lakes. Salinization is caused by flooding or inundation with saline waters, breaching of dykes, storm surges, tsunamis, or the drying of large inland water bodies. Salinization can result where irrigation waters are compromised by salinity. Salinity intersects with major global concerns, including food security, desertification, and biodiversity protection. Soil salinity results from an excess of salts in the soil that reduces plant growth and crop productivity and affects soil biological activity. Salinized soils impose an osmotic stress on plants, reducing water uptake and concentrating toxic level of sodium and chloride. Different plant species exhibit different degrees of salinity tolerance. Salinization removes arable land from production, causing abandonment globally of 0.3–1.5 million hectare year−1. With adequate drainage, salts can be leached and the soil recovered but where the water table remains near the surface, the salinity problem will remain. It may be possible to reverse the effects of salinization. A crucial consideration is whether the desired end point is stabilizing the soils against further change, or reversing the process and restoring soils to another state. Approaches include prevention, stabilization, active management, or land retirement or abandonment. Successful restoration of salinity at the landscape-scale relies on broadscale land-use change. This is problematic where the most profitable land-use is agriculture, thus there has therefore been considerable investigation of land-use systems that at least replicate the profitability of the current agricultural system. Recent approaches have explored how to make the higher water using farming systems acceptable by making the replacement plants profitable in their own right.

Plantation forestry is making a significant positive contribution to the environment as well as to the livelihoods of millions of people in Asia. This chapter examines some of the major constraints facing commercial acacia and eucalypt plantations in South-east and East Asia and discusses adaptive actions in the face of climate change. Particular emphasis is placed on Vietnam and China but examples are also drawn from other parts of SE Asia where forest plantations are making a significant contribution to forest cover. The area of forest cover in Asia has declined greatly in the past 50 years due to an expanding population, and increasing demand for forest products and land for food and energy crops. For example, based on available documents, in 1943 Vietnam had 14.3 million ha of forests, with 43% forest cover; but by the year 1990 only 9.18 million ha remained, with a forest cover of 27.2%. During the period 1980 to 1990, the average forest lost was more than 100,000 ha each year. However, from 1990 to the present, the forest area has increased gradually, due to afforestation and rehabilitation of natural forest. Based on the official statement in Decision No. 1267/QD/BNN-KL-LN, dated 4 May 2009, as of 31 December 2009, the total national forest area was 13.2 million ha (forest cover of 39.1%), including 2.9 million ha of plantation forest. Recently, China too has also been able to reverse the decline in forest cover due to forest protection and afforestation. According to the 7th national forest resource inventory finished in 2008, there were 195.4 million ha (14.9 billion m3 of standing wood volume) of forest in China, an increase of 20.5 million ha (1.1 billion m3 standing wood volume) over the previous audit 5 years earlier. Of the increased forest area and volume, 3.9 million ha were from natural forests, and 8.4 million ha were from tree plantations. In the region, logging of natural forests is proceeding at alarming rates in some countries and is tightly controlled in others. In China, the “national natural forest protection program” was started in 2000, and any logging in natural forest is illegal, as is the case in Thailand. Following that the “national reforestation program” was initiated to established tree plantations in bare land for natural protection in north-west China and wood production in southern China. Forests are classified as ecological forests and natural forest reserves which the government will pay about 120 RMB per ha annually to the forest owners, or commercial forests for wood production. Likewise, the Government of Vietnam has given high priority to forest rehabilitation, as Program 327 and the 5 Million Hectare Rehabilitation Program (MHRP). Program 327, which lasted from 1993 until 1998, was effective in increasing afforestation and forest rehabilitation. The 5MHRP (1998 – 2010) had the objective of rehabilitating 5 million ha of forests and protecting existing forests, in order to increase forest cover to 43%. Unlike China and Thailand, Vietnam obtains more than 90% of its timber volume from natural forest.

Arbuscular mycorrhizal fungi (AMF) are keystone mutualists inhabiting roots of most plants including the majority of oil crops under cultivation. Therefore, sustainable yield of Jatropha (Jatropha curcas L.) in cultivation is likely to benefit from the inclusion of AMF in crop management cycles. Studies undertaken on acid and alkaline soils in a range of site conditions (productive cropping land, degraded land, mine spoil) indicate close association between Jatropha and AMF since roots were often heavily colonized by AMF in the field. Although a diverse range of AMF genera and species have been identified in the rhizosphere of Jatropha, not all are likely to be effective for sustainable production of Jatropha in plantations. For example, of 34 species of AMF in the rhizosphere of Jatropha in Thailand, only a few species were able to be trapped by Jatropha seedlings. Techniques for assessing the need for inoculation and approaches for inoculum production are discussed. The role of AMF in alleviating stresses is discussed in relation to (1) nutrient and water constraints that are likely to be the main factors limiting the production of Jatropha in many regions of the world and (2) the presence of heavy metals and salinity that will also be challenging for this crop.

Historical accounts of possible B roles in the protection of tree and horticulture species against frost damage were reported as early as 1950s, with more field observations and experimental evidence since then. Although the initial reports (Anon 1958: Beltram 1958) were no more than anecdotal evidence due to the lack of proper comparative control experiments, later field and glasshouse studies have provided more reliable evidence about the involvement of B in the protection against frost damage — decreased frost-induced shoot-tip dieback or increased flowering and fruit yield, for example: in subtropical eucalypts Eucalyptus grandis (Cooling 1967: Cooling and Jones 1970) and Eucalyptus grandis x Eucalyptus urophylla (Lu and Huang 2003): apple, pear and blueberry (Blevins et al. 1996: Hanson and Breen 1985; Milovankic et al. 1990) and in birch, Scots pine, and Norway spruce (Braekke 1983). Frost-induced “white top” (bleached young leaves) has been observed in low temperature-sensitive E. urophvila and E. grandis in south China (Xu Daping. pers. comm.) where B deficient soils arc common (Dell and Malajczuk 1994). Field observations have also suggested a link between low canopy temperature and enhanced leaf tissue damage (bleached patches) in oilseed rape grown in low B soil in south-east China (Ye et al. 1997).

Phytophthora cinnamomi has recently been recognized as a key threatening process to biodiversity in Australia. The impact of this introduced microscopic water mould on destruction of forests and heath land communities has been observed since 1921 in southwestern Australia. It took over 40 years for the causal agent to be identified in 1964. Over the next 40 years, State Government Departments formulated policy and implemented management measures to deal with the problem. These measures have changed greatly over time as new knowledge about the host range and extent of the epidemic have become available. Unfortunately, the pathogen had spread over large areas of estate prior to the identification of the causal agent and the development of a management response. The spread of P.cinnamomi into significant areas of the conservation estate, including biodiversity hotspots, highlights the urgency of ensuring that Phytophthora dieback and its management is adequately resourced and is underpinned by appropriate research and communication programs. This review describes the main historical events leading up to the formulation of the 2004 State Phytophthora Dieback Response Framework. These include: quarantining half a million hectares of State Forest in 1976/7 in order to map the extent of the disease and implement hygiene measures; developing policy and management practices for the conservation estate; the acceptance by the Hon. Minister for the Environment in 1996 of the 33 recommendations in the WA Dieback Review Panel Report; the establishment of community based Dieback Working Groups; the preparation of the National Threat Abatement Plan in 2001, and in 2004 the development of National Best Practices Management Guidelines and a risk assessment methodology suitable for national adoption. In spite of these actions, much remains to be done. Flora and fauna remain threatened by the continued expansion and impact of Phytophthora dieback. We have few tools available to reduce the extension, spread and impact of the pathogen and the diseases it causes. The community needs to be better informed of the direct and indirect impacts this disease has had on individual species and ecosystem function and health, and encouraged to take greater ownership of an environmental problem that encompasses all types of land tenure. Recent developments in policy development are encouraging but need to be underpinned by much further research and collaboration.