Long-term climate-growth relationships, were examined in tree rings of four co-occurring tree species from semi-arid Acacia savanna woodlands in Ethiopia. The main purpose of the study was to prove the presence of annual tree rings, evaluate the relationship between radial growth and climate parameters, and evaluate the association of El Niño and drought years in Ethiopia. The results showed that all species studied form distinct growth boundaries, though differences in distinctiveness were revealed among the species. Tree rings of the evergreen Balanites aegyptiaca were separated by vessels surrounding a thin parenchyma band and the growth boundary of the deciduous acacias was characterized by thin parenchyma bands. The mean annual diameter increment ranged from 3.6 to 5.0 mm. Acacia senegal and Acacia seyal showed more enhanced growth than Acacia tortilis and B. aegyptiaca. High positive correlations were found between the tree-ring width chronologies and precipitation data, and all species showed similar response to external climate forcing, which supports the formation of one tree-ring per year. Strong declines in tree-ring width correlated remarkably well with past El Niño Southern Oscillation (ENSO) events and drought/famine periods in Ethiopia. Spectral analysis of the master tree-ring chronology indicated occurrences of periodic drought events, which fall within the spectral peak equivalent to 2-8 years. Our results proved the strong linkage between tree-ring chronologies and climate, which sheds light on the potential of dendrochronological studies developing in Ethiopia. The outcome of this study has important implications for paleoclimatic reconstructions and in restoration of degraded lands.

No abstract

No abstract

Various studies on mangroves and other tall trees rooting in high-salinity water have given compelling evidence that tension is not the only factor in water lifting as thought by plant physiologists. A characteristic feature of these trees is that the tissue cells, the apoplastic space and, in particular, the lumen and the inner walls of many xylem vessels of the roots, the trunk and the branches (up to the apex) contain mucilage. Data on single marine giant algal cells are presented that show that mucilage reduces the chemical activity of water. Longitudinal gradients in the chemical activity of water and interfacial forces are presumably the dominant forces for water lifting. In order to save water on its tortuous pathway to the uppermost foliage trees apparently use different strategies (as revealed by 1 H-NMR imaging), e.g. reduction of the conducting xylem area in the branches at intermediate height by mucilage or interruption of the xylem water columns by gas-filled segments and water lifting through mucilage networks and surface films. Pressure bomb experiments over the entire height of the trees revealed clearly that balancing pressure values cannot be taken as a measure for xylem tension. Such values can be used generally for an estimation of the chemical potential of water in the xylem of leafy twigs under atmospheric pressure, µ w,h=0 , provided that a species-specific "threshold pressure" (depending on wood density, elastic forces of the tissue, hydraulic coupling between xylem and tissue cells, intercellular spaces, cellular osmotic pressure etc.) is subtracted from the balancing pressure values. Transpiration increases the "threshold pressure" considerably and in an unpredictable way. Thus, as shown here, predawn balancing pressure data taken at various heights can yield information about the height dependence of µ w (measured at h=0) under field conditions, particularly when the water content of the xylem is simultaneously determined in a reliable manner (e.g. by the compression/decompression method in combination with centrifugation).

The relationships between annual wood stable carbon isotope composition (d 13 C), dry season midday plant water potential, and annual growth rate were investigated to asses the ability of agroforestry species to adapt to climate changes. 6-8 stem disks from four co-occurring species (Acacia senegal, A. seyal, A. tortilis and Balanites aegyptiaca) were collected for radial growth measurements using tree-ring analysis spanning 1930-2003. Annual d 13 C was measured on three tree disks per species for the period 1970-2002. Midday plant water potential was measured during the dry season. Annual radial growth and midday plant water potential ranged from 0.27 to 9.12 mm and -1.0 to -5.0 MPa, respectively, with statistically significant differences. After correcting annual wood d 13 C for atmospheric changes in d 13 C, carbon isotopic composition ranged from -22.22 to -26.58%. Relationships between d 13 C, radial growth and plant water potentials revealed the interaction of water availability, stomatal conductance, d 13 C values and growth. Two contrasting water use strategies and competitive advantages can be distinguished. Species with lower mean d 13 C values (A. senegal and A. seyal) show high plant water potential and, hence, better growth during moist years. Thus, they indicate low water use efficiency (WUE) and opportunistic water use strategy. On the other hand, species with lower water potentials (A. tortilis and B. aegyptiaca) showed relative better growth performance and less increase in d 13 C in drought years, reflecting their high WUE and conservative water use strategy. These results suggest that d 13 C in tree rings can be useful in estimating historic changes in plant WUE and hence in screening drought tolerant species in the face of expected climate changes, as well as for assessing the functional diversity and risk reduction in mixed vegetation.

The effect of environmental variables on the presence and abundance of tree species in a tropical lowland undisturbed limestone and non-limestone forest in Ben En National Park, Vietnam was investigated. The relationships between 13 environmental variables and 29 tree species with a DBH ≥10 cm, as well as between six 6 physical variables with 26 species of seedling and sapling communities were assessed by canonical correspondence analysis (CCA). Data concerning all tree species ≥10 cm DBH were collected from eighteen 400 m 2 sample plots, while the abundance of regeneration (all individuals ≤5 cm DBH) was counted in fifty 2x20 m strip-plots. The significance of species-environments correlations were tested by distribution-free Monte Carlo tests. The CCA of the 29 examined tree species and 13 environmental variables indicated that the presence and abundance of the tree species were closely related to topographic factors. We may confirm that soil properties including pH, soil moisture content, and soil textures, were the most crucial factor in tree species composition and their distribution. Several species including Pometia pinnata, Amesiodendron chinense, Gironniera cuspidate, Cinnamomum mairei, and Caryodaphnopsis tonkinensis were not controlled by soil properties and topographic variables. The CCA also indicated that the abundance of regeneration tree species at all sites had positive and significant correlations with soil depth, while the occurrence of several other tree species (such as Koilodepas longifolium and Aglaia dasyclada) was positively correlated with a higher slope and rocky outcrop.

As one of the most important mining commodities, coal has been massively exploited as a source of income for the national economy. In general, a coal mining company conducts mining operations in forest areas by employing an open pit mining method. The implementation of an open pit mining method can cause negative environmental impacts, i.e. changes to the forest landscape, reduction in soil quality, reduced biodiversity for both flora and fauna etc. To overcome and mitigate devastating environmental impacts resulting from mining operations in the forest area, land reclamation should be conducted on the ex-mine area. In Indonesia there is still little knowledge on vegetation development and the natural regeneration in mine reclamation areas. Therefore, it is important to understand the stand structure, floristic composition and whether or not the reclaimed mining area can create a good environment for natural regeneration and redevelop into a selfsustaining forest ecosystem. The research was carried out at six stand types, namely five differences age of reclamation areas and secondary natural forest for the comparison. A vegetation inventory was conducted at each stand type covering an area of ±1 ha (total ±6 ha) using a circular plot. Result shows that the stand structure (diameter at breast height, total height, density and basal area) between the reclamation areas were different. Moreover, the reclamation areas with an age greater than four years demonstrate higher mean values for different aspects of stand structure than the secondary natural forest. Conversely, in terms of floristic composition such as species and diversity index, secondary natural forest still had higher mean values than all ages reclamation areas. The older reclamation ages tend to have a higher number of species and diversity index than the younger ages. Natural regenerations were occurred from the first year of reclamation. In general, based on the regression analysis the number of naturally grown species in the seedling, sapling and tree stages tend to increase alongside the rise in reclamation age. These results conclude that the reclamation activities in ex-mine areas have succeeded to create favourable environmental conditions for natural regeneration.

Water availability and salt excess are limiting factors in Mexican mixed pine-oak forest. In order to characterise the acclimatation of native species to these stresses, leaf water (W w ) and osmotic potentials (W s ) of Juniperus flaccida, Pinus pseudostrobus and Quercus canbyi were measured under natural drought and non-drought conditions under two different aspects in the Sierra Madre Oriental. Factorial ANOVA revealed significant differences in W w and W s between two aspects, species and sampling dates. In general, all species showed high predawn and low midday values that declined progressively with increasing drought and soil-water loss. Seasonal and diurnal fluctuation of W w and W s were higher for J. flaccida and Q. canbyi than for P. pseudostrobus. Leaf W w and W s were mainly correlated with soil water content, while W s of P. pseudostrobus were hardly correlated with environmental variables. Thus, species have different strategies to withstand drought. P. pseudostrobus was identified as a species with isohydric water status regulation, while J. flaccida and Q. canbyi presented water potential patterns typical for anisohydric species. The type of water status regulation may be a critical factor for plant survival and mortality in the context of climate change. Nevertheless, for precise conclusions about the advantages and disadvantages of each type, further long-term investigations are required.