Stable carbon isotopes in tree rings of beech: climatic versus site-related influences

 Stable carbon isotopes in tree rings are a promising tool in palaeoclimate research, provided attempts are made to disentangle climatic from local effects (e.g. soil properties, competition, light). The ¹³C/¹²C variations in cellulose of tree rings of beech (Fagus sylvatica) were determined at several sites in the Swiss Central Plateau covering the last 50 years. We chose sites which differ in moisture conditions and sampled cores from four to six trees per site. The mean ¹³C/¹²C series from the different dry sites (distant by up to 40 km) are closely interrelated suggesting a common external cause. Correlation analysis with climate data proved the total precipitation in the months May, June and July to have the strongest effect on the carbon isotopes (r =  – 0.73). This result is in agreement with the commonly used model which relates the isotope discrimination to the water use efficiency. On the other hand, the isotope series of the wet sites are not as well correlated to the climate. At two of the sites (a dry and a humid) tree ring width suddenly increased. We used this effect as a test-case to study the influence of local growth conditions on the climate-isotope relationship. Received: 17 April 1996 / Accepted: 2 September 1996     

On the optimal harvesting of persistent age-structured populations

Summary This paper discusses optimal harvesting policies for age-structured populations harvested with effort independent of age.     

The role of protective understorey in the regeneration system of a heavily browsed woodland

The paper tests an apparent relationship between young understorey of Ilex aquifolium and the presence of seedlings of the canopy species Fagus sylvatica and Quercus species, in heavily browsed woodland in the New Forest, southern England. A small block of woodland was searched and mapped, and the information collected subject to graphical and statistical analyses.Regeneration, though of low frequency, is present and shows non-random patterns of distribution. Older seedlings appear to be located in or near areas of understorey, or near fallen branches, logs, etc. Principal components analysis of woodland characteristics suggests six main habitat types are available to seedlings, and predictions are made about likely regeneration patterns associated with these habitats, according to a model based on the hypothesis of a protective understorey and heavy browsing pressure. Chi-square tests of actual seedling occurrences versus habitat types demonstrate marked associations of regeneration with non-trampled areas, including young Ilex understorey but also other forms of protective barrier. The association is more marked for larger seedlings.The implications for a wider understanding of regeneration processes and community dynamics in heavily browsed forest are discussed. It is concluded that regeneration theories appropriate to such forests are required, since the dominant gap-phase theories are not successful in predicting regeneration patterns when browsing is a major factor.     

Effects of sex,size and substrate on growth and mortality of trees in tropical wet forest

Summary Females and males of three tree species did not differ in growth or mortality over an interval of 9.5 years. Comparing between sexes and across species, there was no consistent pattern of effects of short-term (1 year) growth and fecundity on longer-term gorwth or mortality. Effects of size were significant (but minor) for growth in one species, and were significant for mortality in two species. Soil type affected mortality in one species, but affected growth in all three species. Sex and size are not consistently strong bases for predicting the performance of adult trees.     

Are there seasonal variations of trace element concentrations (Cd,Pb, Zn) in wood of Fagus trees in Germany?

Concentrations of Cd, Pb and Zn were determined in stem wood of beech trees (Fagus sylvatica L.) from 3 sites in northern Germany. Distinct radial distribution patterns of the elements were observed in the xylem. Concentrations of Cd and Pb increased from the youngest, outermost annual rings towards the center of the stem. With Zn intermediate concentrations were observed in the sapwood and higher levels at the center of the stem.Temporal and spatial stability of such distribution patterns in the trunks was investigated. Wood samples taken from the same individual tree in different months of the year were analysed. Marked seasonal variations of mineral concentrations were observed. Also the shape of the distribution patterns of the elements varied with the season. Such variations were larger than those observed with samples taken simultaneously from different sides of the trunk. Furthermore, Pb concentrations in the stem showed variations with height above ground.The results indicate, that radial distribution patterns of Cd, Pb and Zn in xylem rings of beech are not stable. Biomonitoring trace element pollution levels by analysis of beech wood is, thus, questionable. To obtain a reliable historical record of pollution from tree rings, the distribution patterns should be stable over a long period of time. This basic requirement of the dendroanalytical method does not hold for the examined beech. Still, with other tree species and under more favourable conditions the dendroanalytical biomonitoring method may prove valuable.Presented as symposium paper at the V International Congress of Ecology, Yokohama, August 23–30, 1990.     

Comparison of species ordinations resulting from alternative indices of interspecific association and different numbers of included species

Summary Several measures of interspecific association are compared. Dispersion and covariance are limited in value because they respond to the commonness of the species compared. Correlation is not so limited but it responds to discrepancies in commonness among the species. The practical result of these relationships between commonness and association is that only the most common species can occupy periferal positions in a species ordination. Rare species are relegated to positions near the center not on the basis of their phytosociological pattern but simply because of their rarity. Both Cole's index of association and the tetrachoric correlation overcome the problem imposed by the relationship between ordination position and species commonness and they both produce very similar results. The effect of differing numbers of species on the ordination configuration is examined using both Pearson's correlation and Cole's index. The basic pattern of the ordination is set with the first few species when Cole's index is used, however, since rare species are given more weight in the analysis with this index, the addition of several very rare species can change the configuration of the ordination.Nomenclature of species is given in Table 1.Research supported by the Eastern Deciduous Forest Biome Project, US-IBP, funded by the National Science Foundation under Interagency Agreement AG-199, BMS69-01147 A09 with the Energy Research and Development Administration — Oak Ridge National Laboratory. Research also supported by the U.S. Energy Research and Development Administration under contract with the Union Carbide Corporation. Contribution No. 240 from the EDFB, US-IBP. Publication No. 790. Environmental Sciences Division, ORNL.