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Natural forest cover in Sabah has been decreasing across all forest types for more than two decades since the 1990s, being replaced mostly by man-made forests. This contributes to the overall degradation of the forest ecosystem, which changes soil nutrient content and subsequently modifies forest species composition, as well as vegetation structure. This study investigated the association between soil nutrients and tree species in unlogged and logged tropical lowland forests in Sabah, Borneo, Malaysia. A total of eight and 27 sampling plots were established in randomly placed locations at the Danum Valley Conservation Area representing the unlogged site, as well as the Sapat Kalisun area of the Ulu Segama Forest Complex representing the logged site. Soil samples at two depths (0-5 cm; 5-10 cm) were collected from each plot and analyzed for soil nutrients: total N, available P, inorganic N (NO3- and NH4+), exchangeable cations (K+, Ca2+, Mg2+, and Na+), exchangeable Al3+, and exchangeable acidity. Results showed that certain exchangeable cations and soil nutrient concentrations were greater in the unlogged forest compared to the logged forest except for K+, Na+, and inorganic N. Greater inorganic N concentrations were observed in the logged forest, hence suggesting a dominant shift toward inorganic N in the soil. PCA results indicated that exchangeable acidity and exchangeable Al3+ were correlated to logged forests, whereas Ca2+ and Mg2+ were associated with unlogged forests. CCA ordination showed the existence of association between specific tree species with K+, Ca2+, Mg2+, and Na+ in the unlogged forest only. Logging, to some extent, influenced the status of certain soil nutrients but their association with tree species was complex. This could be attributed to the heterogeneous habitat resulting from past logging disturbances. [ABSTRACT FROM AUTHOR]

A high-resolution climate archive was reconstructed based on carbon isotope analysis and radiocarbon dating of the Chapman baobab in northeastern Botswana. The Chapman baobab, which exhibited an open ring-shaped structure composed of six stems, collapsed in January 2016 during an intense El Niño event. Two samples belonging to the oldest stems were investigated in order to obtain a proxy rainfall record, which provides insight into the precipitation regime over the last millennium, evincing centennial and decadal scale variability. The results indicate that the Medieval Warm Period was marked by relatively stable precipitation, whereas rainfall variability and drought frequency increased during the Little Ice Age. The investigated area has experienced both wetter and drier conditions in the past. The wettest conditions of the last millennium were registered before 1450 while the driest period occurred in 1835. For southern Africa, inter-annual rainfall variability is mainly associated with sea surface temperatures in the Agulhas Current core region, which determine the east–west displacement of tropical temperate troughs. Previous studies suggested that positive sea surface temperature anomalies in the Mozambique Channel led to an eastward movement of the troughs but the Chapman record demonstrates a westward displacement in the past, causing drought in northeastern South Africa and wetter conditions in the central part of southern Africa. The positive rainfall correlation with SST anomalies reversed after 1900, causing a gradual decrease in precipitation and confirming the current aridity trend for Botswana. The results contribute to a better understanding of the past climate of southern Africa for which paleoclimate reconstructions remain scarce. [ABSTRACT FROM AUTHOR]

Southern Africa is dominated by fire-prone arid and semi-arid landscapes that are expected to experience increased maximum temperatures, rainfall variation and frequency of extreme rainfall events in the future. These conditions will affect fire and vegetation dynamics, but feedback and interactions among fire, rainfall and woody cover limit our ability to predict future ecosystem changes. Moreover, human activities can also drive changes in these components and their interactions. There are few long-term datasets available to monitor these changes over ecologically relevant time-scales. Here the combined analysis of a rainfall proxy, developed from a baobab tree core (Adansonia digitata) and fire proxy, from a sediment core, in the savanna-woodland transition zone in South Central Africa elucidates the history of two major drivers of savanna structure for the past 600 years. They show a system that oscillates between wooded and grassy vegetation states over time, as well as a change in the spatial scale of fires, which could be linked to human activities and recent fire management legislation. [ABSTRACT FROM AUTHOR]

Key message: Increasing water-use efficiency, due to rising atmospheric CO2, did not stimulate radial growth in tropical trees, probably because negative impacts of changing climate on tree growth have overridden the small positive influence of rising atmospheric CO2. Global environmental changes affect tree growth and physiological behavior across the major biomes around the world. However, it is not yet clear how tree growth and physiology of tropical trees responded to global environmental changes in a long term, yet such information is critical to get insight into how tropical trees will respond to future global changes. The main objective of this review article is to explore the long-term trends in tree growth, carbon isotope discrimination (Δ13C), intercellular CO2 concentration (Ci), and intrinsic water-use efficiency (iWUE) across the tropics and subtropics. We distinguished between data generated on plot levels or on species or tree individual levels. Stand-level growth trends were not consistent across the studies and plots, although recent studies indicated a declining growth trend. Ci and iWUE consistently increased during the past decades, while Δ13C remained nearly constant. Increased iWUE either caused by higher photosynthetic capacity or reduced stomatal conductance did not translate into tree- and species-level radial growth, probably because assimilated carbon was allocated more to the root development to facilitate water absorption from moisture-limited soils rather than to basal area growth or xylem cell differentiation and maturation processess were impared by cavitation induced hydraulic limitations. Thus, higher temperature or drought-induced soil moisture deficit might have strongly impaired radial growth which has probably overridden the small positive effect of atmospheric CO2. Yet, disentangling the role of multiple drivers in explaining stem radial growth variation and their interactive effects on tropical trees under natural field conditions are not adequately studied and hence future research should focus on this aspect. Tree hydraulics should be taken into account in future research when predicting radial growth variability in tropical trees. [ABSTRACT FROM AUTHOR]

Background: Dipterocarpaceae is a pantropical tree family that plays an important role in our understanding of the ecology of Asian tropical rain forests. However, genome sizes for members of the Dipterocarpaceae are still poorly known. Aims: To report the genome size of 115 dipterocarp species and examine the variation and evolution of genome size in this family. Methods: Genome size was estimated using flow cytometry. Both therpoBandtrnL intron were sequenced to uncover the evolution of genome size within a phylogenetic framework. Results: The 1Cgenome size varied between 0.267 and 0.705 pg inShorea hemsleyanaandShorea ovalis, respectively, a 2.64-fold variation across the family. Most dipterocarps are characterised by very small genomes with a mean 1Cvalue of 0.416 pg (sd = 0.075) and five polyploids are recorded. The ancestral genome size for dipterocarps was reconstructed as 1Cx = 0.481 pg (95% CI = 0.433–0.534). Conclusions: Genome size variation in dipterocarps was characterised by very small values with a narrow range. Overall, genome size reduction from the ancestral state is a general trend in Dipterocarpaceae. [ABSTRACT FROM PUBLISHER]

Carbon isotope analysis of four baobab (Adansonia digitata L.) trees from the Pafuri region of South Africa yielded a 1000-year proxy rainfall record. The Pafuri record age model was based on 17 radiocarbon dates, cross correlation of the climate record, and ring structures that were presumed to be annual for two of the trees. Here we present the analysis of five additional baobabs from the Mapungubwe region, approximately 200km west of Pafuri. The Mapungubwe chronology demonstrates that ring structures are not necessarily annually formed, and accordingly the Pafuri chronology is revised. Changes in intrinsic water-use efficiency indicate an active response by the trees to elevated atmospheric CO2, but this has little effect on the environmental signal. The revised Pafuri record, and the new Mapungubwe record correlate significantly with local rainfall. Both records confirm that the Medieval Warm Period was substantially wetter than present, and the Little Ice Age was the driest period in the last 1000 years. Although Mapungubwe is generally drier than Pafuri, both regions experience elevated rainfall peaking between AD 1570 and AD 1620 after which dry conditions persist in the Mapungubwe area until about AD 1840. Differences between the two records correlate with Agulhas Current sea-surface temperature variations suggesting east/west displacement of the temperate tropical trough system as an underlying mechanism. The Pafuri and Mapungubwe records are combined to provide a regional climate proxy record for the northern summer rainfall area of southern Africa. [ABSTRACT FROM AUTHOR]

Species diversity is the most important component of biodiversity and plays an important role in maintaining forest ecosystem processes and stability. The assessment of the forest conservation value of species diversity is commonly carried out based on the Shannon-Wiener index. However, endangered and endemic species were always ignored in previous studies aimed at assessing the conservation value of forest species diversity. In this study, the conservation value of forest species diversity was assessed in two representative provinces of southern and northern China (Yunnan and Jilin provinces, respectively). The conservation values of species diversity for different forest types was calculated based on the standard Shannon-Wiener index, and on two different indexes derived from it by including: (i) an endangered species index (Ei] ) based on the China Species Red List; (ii) an endemic species index (Bx) based on the geographic distribution of the species considered. The results showed that the inclusion of the endangered and endemic species indexes dramatically increased the forest conservation values in these two provinces. The total conservation value in the Yunnan province was 268.65 billion yuan yr-1 based on the Shannon-Wiener index, 269.78 billion yuan yr-1 after including Ei in the assessment, and 324.44 billion yuan yr-1 after the inclusion of both Ei and Bx. In Jilin province, the total conservation value was 123.94 billion yuan yr-1 based on the standard Shannon-Wiener index, 124.60 billion yuan yr-1 after including Ei, and 125.74 billion yuan yr-1 after including both Ei and Bx in the assessment. Therefore, the inclusion of endangered and endemic species in the assessment of forest conservation values, as well as other aspects related to biodiversity like the presence of ancient trees, can contribute to the protection of endangered and endemic species in these two provinces of China. [ABSTRACT FROM AUTHOR]

This study dealt with a restoration project conducted at South-East New Territories Landfill in Hong Kong, in order to screen suitable tree and shrub species (both native and pioneer species) for revegetation. For engineered landfills, landfill gas migration and leachate contamination to the topsoil are rarely problematic, but the lack of nutrients and moisture and poor physical soil conditions may jeopardize potential woodland establishment. The growth performance of 25 woody plant species subjected to 12 different soil amelioration and seedlings planting methods was compared. The results showed that the general performance (mortality rate, apical height, crown diameter and basal diameter) of pioneer species (notably Acacia species) was much better than that of native species in all blocks of woodland mix and scrub mix. The notch planting method was effective in helping seedling roots to have better contact with soil for water uptake, which subsequently increased the survival rates of seedlings, leading to a better tree coverage. Soil ameliorations (horticultural soil with fertilizer and horse and pig manure) generally increased the seedling survival rate and improved plant growth. Tree coverage on all the plant trial blocks was mainly established by the three Acacia species. A planting distance of 1 m was recommended for woodland establishment, and such dense seedlings planting would achieve a better tree coverage under a shorter period of time (than the distance of 3 m). Difficulties in woodland establishment were discussed, and the strategies for achieving a better tree growth were recommended. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone. [ABSTRACT FROM AUTHOR]