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Mass conversion of native vegetation to agricultural land-use triggered secondary salinity, a hydrological imbalance, which has damaged more than 1.75 million ha of farmland in south-western Australia. Various types of reforestation have been proposed and tested to restore the hydrological balance, however the economic returns from these cannot compete with existing farm practice and land-holders thus have a reluctance to adopt. An alternative approach has been to reforest abandoned saline areas with salinity and/or water-logging tolerant trees to avoid displacement of farming activities and to minimize opportunity costs. We propose an improved evaluation methodology for saline site reforestation and in this paper test its feasibility. Three eucalypts species (Eucalyptus salubris, E. camaldulensis and E. sargentii) were planted adjacent to a salt scald in Wickepin, Western Australia, and their survival and growth were monitored under increasing soil salinity ranging from moderate (ECe: 400-800 mS m-1), high (800-1,600 mS m-1) or extreme (>1,600 mS m-1) with shallow (< 1 m depth) saline ground water (EC: 2,000-3,000 mS m-1). Survival and growth of E. sargentii and E. salubris in the saline discharge areas were comparable to those in the arable area, and reforestation by these species can thus avoid land competition and opportunity costs.

Large-scale afforestation is a key measure to mitigate global warming, however, implementation may result in land-use competition with agriculture. To avoid such competition, carbon mitigation methods using arid and semi-arid areas have been proposed, but to our knowledge there is no report of rates of sequestration based on long-term observations from actual experimentation. In this study (1999–2015), in an arid area near Leonora, Western Australia (annual rainfall: 220 mm year−1; pan evaporation: 3400 mm year−1), carbon sequestration was assessed in above and below ground biomass in Eucalyptus camaldulensis under ambient conditions and with active site amelioration (combination of water harvesting with large mounds and hardpan blasting). The carbon sequestration rate was estimated at 7.92 Mg-CO2-e ha−1 year−1 for a total carbon sink of 230 Mg-CO2-e ha−1. Carbon mitigation may thus be a viable option in arid regions, not only in Western Australia but globally, and can be enhanced with active site engineering.

Drought-induced tree death has become a serious problem in global forest ecosystems. Two nonexclusive hypotheses, hydraulic failure and carbon starvation, have been proposed to explain tree die-offs. To clarify the mechanisms, we investigated the physiological processes of drought-induced tree death in saplings with contrasting Huber values (sapwood area/total leaf area). First, hydraulic failure and reduced respiration were found in the initial process of tree decline, and in the last stage carbon starvation led to tree death. The carbohydrate reserves at the stem bases, low in healthy trees, accumulated at the beginning of the declining process due to phloem transport failure, and then decreased just before dying. The concentrations of non-structural carbohydrates at the stem bases are a good indicator of tree damage. The physiological processes and carbon sink-source dynamics that occur during lethal drought provide important insights into the adaptive measures underlying forest die-offs under global warming conditions., 乾燥を受けた樹木が枯死に至る生理過程を解明 --地球温暖化の森林への影響を高精度に予測する道を開く成果--. 京都大学プレスリリース. 2019-01-28.

Drought-induced tree death has become a serious problem in global forest ecosystems. Two nonexclusive hypotheses, hydraulic failure and carbon starvation, have been proposed to explain tree die-offs. To clarify the mechanisms, we investigated the physiological processes of drought-induced tree death in saplings with contrasting Huber values (sapwood area/total leaf area). First, hydraulic failure and reduced respiration were found in the initial process of tree decline, and in the last stage carbon starvation led to tree death. The carbohydrate reserves at the stem bases, low in healthy trees, accumulated at the beginning of the declining process due to phloem transport failure, and then decreased just before dying. The concentrations of non-structural carbohydrates at the stem bases are a good indicator of tree damage. The physiological processes and carbon sink-source dynamics that occur during lethal drought provide important insights into the adaptive measures underlying forest die-offs under global warming conditions., Yuri Kono et al. show that drought-induced tree death is caused by initial hydraulic failure followed by carbon starvation. They find that the loss of the carbon sink-source balance in stem bases due to phloem transport failure is the key factor governing wilting, providing insight to developing adaptive measures to prevent forest die-offs under global warming conditions.

The frequency of extreme weather has been rising in recent years. A 3-year study of street trees was undertaken in Tokyo to determine whether: (i) street trees suffer from severe water stress in unusually hot summer; (ii) species respond differently to such climatic fluctuations; and (iii) street trees are also affected by nitrogen (N) deficiency, photoinhibition and aerosol pollution. During the study period (2010-12), midsummers of 2010 and 2012 were unusually hot (2.4-2.8 °C higher maximum temperature than the long-term mean) and dry (6-56% precipitation of the mean). In all species, street trees exhibited substantially decreased photosynthetic rate in the extremely hot summer in 2012 compared with the average summer in 2011. However, because of a more conservative stomatal regulation (stomatal closure at higher leaf water potential) in the hot summer, apparent symptoms of hydraulic failure were not observed in street trees even in 2012. Compared with Prunus × yedoensis and Zelkova serrata, Ginkgo biloba, a gymnosperm, was high in stomatal conductance and midday leaf water potential even under street conditions in the unusually hot summer, suggesting that the species had higher drought resistance than the other species and was less susceptible to urban street conditions. This lower susceptibility might be ascribed to the combination of higher soil-to-leaf hydraulic conductance and more conservative water use. Aside from meteorological conditions, N deficiency affected street trees significantly, whereas photoinhibition and aerosol pollution had little effect. The internal CO2 and δ(13)C suggested that both water and N limited the net photosynthetic rate of street trees simultaneously, but water was more limiting. From these results, we concluded that the potential risk of hydraulic failure caused by climatic extremes could be low in urban street trees in temperate regions. However, the size of the safety margin might be different between species.

We clarified the relationship between environmental factors and the growth of seven Eucalyptus species and Casuarina obesa planted at an afforestation site in southern Western Australia's wheatbelt. The site consisted of abandoned fields damaged by secondary salinity associated with waterlogging. Afforestation is expected to progressively rehabilitate the land, which has a slight slope generating a large environmental gradient. During the rainy season, waterlogging (soil becoming saturated with water) occurred at the lower part of the site, but not at the higher part. The level of salt in the soil (EC1:5) increased gradually from higher to lower ground (0.34—2.7 dS m-1). Tree size and growth rate were negatively related to waterlogging intensity and showed small values at the lower part of the site, with only a slight effect on tree size and growth rate. Moreover, interspecific differences in size and growth rate were observed. Eucalyptus sargentii and E. occidentalis had larger sizes and faster growth rates than E. camaldulensis. Trees planted under waterlogging conditions at the lower part of the site are likely to fail due to poor growth; therefore, afforestation should begin on higher ground where trees would experience normal growth, and in doing so, reduce the soil water content to rehabilitate the land. Improvement of water balance through afforestation would confirm the benefits of appropriate agroforestry management.

Afforestation of arid land is a promising countermeasure against global warming. We had previously found, through modeling and mass balance analyses of an arid land afforestation experimental project in Western Australia, that a significant amount of litter could have been physically removed from the floors of natural forests. In order to analyze litter carbon dynamics in depth, we investigated the actual mobility of litter in several natural forests in Sturt Meadows in an arid region of Western Australia, and estimated the difference between the removal rate of leaf and woody (twigs and branches) litter on the forest floor. Then we redeveloped a litter carbon dynamics model by incorporating physical removal of litter to show the different mobilities of leaf and woody litters. We also analyzed carbon balances and the effect of differential litter mobility on litter carbon dynamics. Except for twigs in one plot in a high density forest, 29–100% of leaf litter and 10–100% of woody litter was removed annually, demonstrating the physical removal of litter in these natural forests. The main cause of litter removal was wind, not flooding. Decreases in leaf and woody litters could be approximated as first order decay functions in most plots; first order decay or disappearance rate constants were then determined. Estimated disappearance rate constants of leaf and woody litter ranged from 0.19 to 11 and 0.11–12 year −1 , respectively; most of the constants ranged from 0.19 to 2.0 and 0.11–0.74 year −1 , respectively. Based on the disappearance rate constant, the mobility of woody litter was estimated to be roughly 20% that of leaf litter, confirming that climatic factors move leaves more easily than twigs. The improved model, which took into account the different mobilities of leaf and woody litters, showed that annual physical removal of litter reached 70–82% of the annual litter fall in Acacia aneura forests, and that roughly 40–60% of the existing litter was removed annually from all sites. Incorporating into the model the difference in mobilities of leaf and woody litters showed that the ratio of annual litter removal to annual litter fall increased about 10% points compared with the assumption of that both litter types had equal mobility.

Old-growth forests consist of various types of small patches that reflect their own gap-forming process, which includes changes in environmental conditions occurring over several decades. We reconstructed the gap-forming processes that had occurred during a 40-year period for eight representative patches of an old-growth evergreen broad-leaved forest in Japan, and examined the current community structure. The selected patches were based on (1) changes in canopy heights estimated from aerial photographs taken in four different years, (2) long-term ecological research (LTER) monitoring records, and (3) a recent field survey, so that they sufficiently covered characteristic gap-forming processes such as a new gap, an old gap and consistently closed canopy. Height and diameter at breast height (DBH) were measured on all living trees taller than 1.3 m. In their height distributions, currently almost closed patches that were open in 1966 show a rotated sigmoid, whereas their DBH distributions are an inverse J-shape. In contrast, patches that have been consistently under a closed canopy exhibit gentle inverse J-shapes for both distributions. For species composition, there are no clear contrasts associated with the past gap-forming processes except for the existence of fast-growing deciduous species in large currently open patches. Our results suggested that the variation in several decades of gap-forming processes played a central role in the high patch diversity and the complex patch mosaic of the forest. Diverse gap-forming processes created micro-environmental heterogeneity both vertically and horizontally, and contributed to the maintenance of the species-rich, warm-temperate old-growth forest.

Matrix models have been widely used to investigate the population dynamics of plant species. To make use of this method, we first divide individuals into groups and estimate transition probabilities per pair of groups. When a continuous variable, such as plant size, is used for grouping, there is often a trade-off: if the class intervals are narrow each group will only include a small number of samples, but if the intervals are wider, this may obscure some changes. This paper introduces a new matrix model in which we no longer have to divide individuals into arbitrarily defined size classes. The methodology is based on the Bayesian non-parametric binary regression. We first divide the data into ‘very fine’ intervals. For estimating transition probabilities in a ‘large’ matrix, we do not use the observed transition rate per class directly, but we smooth neighboring observed rates and select the most appropriate degree of smoothing using an information criterion called the Akaike Bayesian Information Criterion (ABIC). Our approach is illustrated using long-term forest monitoring data from an old-growth, warm-temperate evergreen forest, in which we examined the population dynamics of four evergreen subcanopy tree species. Transition probabilities allowed us to represent d.b.h.-related growth and mortality patterns graphically, and matrix analysis provided stable size distributions, reproductive values and elasticity that vary smoothly for trees of different sizes. The quantitative approach makes it possible to determine characteristic patterns of population dynamics for qualitatively similar species.

Developmental processes and biomass allocation of a multi-stemmed shrub, Stephanandra incisa, were measured to reveal the advantages of a multi-stemmed growth form on matter production. Stephanandra incisa is a low shrub species that mainly grows in the forest understory. The current-year shoots become shorter by yearly branching that effectively increases the allocation ratio to photosynthetic organs. The frequency distribution of relative current-year shoot length (the ratio of current-year shoot length to stem length) in each ramet (a stem and its crown) of a clump (genet) were skewed to larger length classes in younger ramets and gradually skewed to shorter length classes in older ramets. The biomass allocation ratio of non-photosynthetic organs to photosynthetic organs in ramets changed from a declining trend to a rising trend as the age of the ramets increased. The biomass allocation ratios of ramets and clumps increased with their size, but the ratio of clumps showed lower values than that of ramets of the same size. The age and size structures of ramets in clumps contributed to the narrow variability of the biomass allocation ratio. Stephanandra incisa showed a high biomass allocation ratio to leaves and maintained the ratio with a multi-stemmed growth form.

Various MFI-type zeolites were synthesized and the catalytic activities of them were compared for conversion of hexane, which is one of the main components of light naphtha. The reaction of propane was also studied toobserve the selectivity of cracking and dehydrogenation reaction.In Fig.1, product distributions of hexane conversion reaction are shown for MFI-type zeolites with Si02/Al203 molar ratios varying from 29 to 1490. Selectivity of aromatic hydrocarbon increased with decreasing Si02/Al203 ratios. The highest selectivity of aromatic hydrocarbons, 55.3 wt% in carbon base, was obtained by the zeolites with the lowest Si02/Al203 ratio of 29. Fig.1 also shows that methane formation increased with lower SiO2fA l203ratios. Zn or Ga loaded MFI-type zeolite gave the higher selectivity for the production of aromatic hydrocarbons. (Figs.2 and 3)The reaction of propane is summariz ed in Table 1. The conversion of propane by the zeolite with Si02/Al203 of 29 is higher than that by the zeolite with SiO2/Al203 of 66. However, the selectivity of cracking and dehydrogenation are of similar values. Selectivity of the dehydrogenation by Zn or Ga loaded zeolites is much higher than that of cracking. The selectivity of dehydrogenation in the propane conversion reaction is considered to be an important step for the enhancement of aromatic hydrocarbon yield.