Above-ground space sequestration determines competitive success in juvenile beech and spruce trees

A 2-yr phytotron study was conducted to investigate the intra- and inter-specific competitive behaviour of juvenile beech (Fagus sylvatica) and spruce (Picea abies). Competitiveness was analysed by quantifying the resource budgets that occur along structures and within occupied space of relevance for competitive interaction. Ambient and elevated CO(2) and ozone (O(3)) regimes were applied throughout two growing seasons as stressors for provoking changes in resource budgets, growth and allocation to facilitate the competition analysis. The hypothesis tested was that the ability to sequester space at low structural cost will determine the competitive success. Spruce was a stronger competitor than beech, as displayed by its higher above-ground biomass increments in mixed culture compared with monoculture. A crucial factor in the competitive success of spruce was its ability to enlarge crown volume at low structural costs, supporting the hypothesis. Interspecific competition with spruce resulted in a size-independent readjustment of above-ground allocation in beech (reduced leaf : shoot biomass ratio). The efficient use of resources for above-ground space sequestration proved to be a parameter that quantitatively reflects competitiveness.     

Genetic structure in populations of an ancient woodland sedge, Carex sylvatica Hudson, at a regional and local scale

Wood sedge (Carex sylvatica) is a well-known ancient woodland species with a long-term persistent seed bank and a caespitose growth habit. All thirteen isolated Carex sylvatica populations in the Dutch Rhine floodplain (including the river branches Waal and IJssel) were mapped in detail and analysed for genetic variation at a large number of AFLP loci and one microsatellite locus. Across all populations, only 40 % of the sampled individuals (n=216) represented a unique genotype. A high number of the studied patches (spatial clusters of tussocks, 2-10 m in diameter) within populations contained only one or a few genotypes. Identical plants (tussocks) were also found 20-500 m apart and in one case even 1000 m apart. Observed heterozygosity levels (H(O)=0.029) were low, indicating low levels of gene flow, which is in agreement with the selfing nature of other caespitose sedges. Although the number of genotypes in populations is low, these genotypes are genetically very distinct and variation within populations accounted for 55% of the total variation. The absence of a correlation between genetic and geographic distances among populations, and the scattered distribution of genotypes among patches within woodlands, support our hypothesis of rare establishments and subsequent local dispersal within woodlands in this forest floor species, which may benefit from and partly depend on human land use and forest management activities.     

Intraspecific sequence variation of chloroplast DNA among the component species of deciduous broad-leaved forests in Japan

To select appropriate plant materials for a phylogeography of deciduous broad-leaved forests in Japan, we surveyed intraspecific chloroplast DNA variation in 34 species found in these forests. A relatively large number of intraspecific cpDNA variations were detected in ten species: Carpinus japonica (nucleotide diversity π=0.00083), C. laxiflora (π=0.00221), Magnolia obovata (π=0.00134), Lindera triloba (π=0.00255), L. obtusiloba (π=0.00289), Pourthiaea villosa var. leavis (π=0.00263), Acer japonicum (π=0.00170), A. micranthum (π=0.00237), Euonymus oxyphyllus (π=0.00322) and Styrax obassia (π=0.00100).     

Geographical variation in the early regeneration process of Siebold's Beech (Fagus crenata BLUME) in Japan

The causes and timing of seed death in early regeneration process of Siebold's beech (Fagus crenata Blume) was studied at 15 sites along a snowfall gradient in Japan, in order to clarify why the seedling density of the species has geographic difference remarkably. Seed production did not significantly differ along the snowfall gradient. Pre-dispersal seed mortality by insect damage was higher at sites with light snowfall than at sites with heavy snowfall, but this only seemed to be a minor factor influencing the population. A large proportion of the viable nuts that fall in autumn ware killed in winter before germination. Winter mortality was much higher at sites with thin snow cover than that at sites with thick snow cover, and this factor was strongly correlated with the geographic variation of seedling regeneration probability. There was little seed mortality by winter desiccation. The main factor contributing to the geographic difference seemed to be a seed predation by rodents in winter. Deep snow cover may reduce the success of rodents finding seeds in winter. Thus the observed relationship between snowpack depth and early mortality may be due to an indirect effect through the process of seed predation.p>     

A relict population of Fagus grandifolia var. mexicana at the Acatlan Volcano, Mexico: structure, litterfall, phenology and dendroecology

Aim Fagus grandifolia var. mexicana (Martinez) Little has an extraordinarily restricted distribution in the Mexican montane cloud forests. Isolated Fagus (beech) populations have been recorded in less than 10 small areas (2–40 ha) in the eastern Sierra Madre at altitudes from 1400 to 2000 m. The objectives were to determine tree and seedling age, forest structure, phenology, litterfall patterns and the relationship between mast and climatic variables. Location We report on three Fagus stands at the Acatlan Volcano, Veracruz, Mexico. Methods Changes in forest cover were determined using aerial photographs. Within each stand, basal area, density and tree species composition were determined in a 0.1‐ha band transect. Additionally, litterfall production was quantified and phenophases were recorded monthly over a 3‐year period, and 60 tree cores were collected to determine age distribution and tree‐ring growth. Results The forest was atypical in several respects. Fagus was the only dominant tree species in the crater stand, although in the rim and at the top of the volcano it was codominant with other tree species. Juveniles occurred only on the rim, but there was a seedling bank in the crater. Although forest cover in the area increased between 1968 and 1993, the Fagus stands did not change in size. Leaf production peaked in March and April, and leaf fall occurred from October through February. Litterfall production was the highest in November. During mast years, flowering started in February and between mast events there were no flowers or fruits. Minimum temperatures were highly correlated with Fagus litterfall and leaf fall. Seedlings ranged in age from 2 to 18 years and were 13–60 cm tall. Tree cores ranged from 76 to 120 years, but trees were older than the core samples. Main conclusions Although beech is considered a gap regeneration species that reaches the canopy after alternating periods of release and suppression, the trees in the crater were released when less than 1.5 m tall and have suffered few periods of suppression since. The results indicate that the crater stand was established after a severe disturbance destroyed the existing forest. We conclude that the relict beech population should be able to maintain itself, if not severely disturbed by humans or by climatic changes related to global warming.     

The effects of water-level fluctuations on weekly tree growth in a southeastern usa swamp

Annual growth of wetland trees has been shown to be related to variations in hydrologic regimes, however the relationship between water level fluctuations and tree growth throughout the growing season has not been documented. In a study of weekly growth patterns of three wetland tree species in a southeastern forested wetland, transfer function modeling was used to examine relationships between tree growth and the weekly changes in water levels and weekly changes in the atmospheric water balance (precipitation minus potential evapotranspiration). An autoregressive-moving average model was fit to each time series of water-level changes (input series), and the selected model was then used to filter the tree-growth (output) time series. Cross-correlations between each input and output time series were examined and significant relationships between weekly changes in water levels and tree diameter were found for Nyssa sylvatica and Taxodium distichum trees growing at sites with periodic shallow flooding. There were no significant relationships between changing water levels and tree growth in areas with permanent flooding or soil saturation. Further, changes in growth of N. sylvatica, N. aquatica, and T. distichum were significantly cross-correlated with weekly changes in the atmospheric water balance at sites with either periodic or permanent flooding.