New species of Passiflora subg. Plectostemma and subg. Tacsonia (Passifloraceae)

Five new species of Passiflora subgenera Plectostemma and Tacsonia from Ecuador are described, viz. P. discophora, P. monadelpha, P. subpurpurea, P. hirtiflora and P. sanctaebarbarae . Section Discophora of subg. Plectostemma is proposed.     

Vegetation types and patterns in Senegal based on multivariate analysis of field and NOAA-AVHRR satellite data

Abstract. Woody vegetation was studied in 44 sites in Senegal. Species composition and density were analysed with TWINSPAN and Canonical Correspondence Analysis; 16 vegetation types were defined. A supervised, multispectral and multitemporal classification of day and night, dry season NOAA-AVHRR imagery was used to identify their distribution with a classification accuracy ranging from 60–100%.     

Effects of species partition on explanatory variables in direct gradient analysis - a case study from Senegal

Abstract. Species-environment data from Senegal, West Africa, are used to study the effects of partition of a large species data set into subsets corresponding to rare and common species respectively. The original data set contains 129 woody plant species from 909 plots and 60 explanatory variables. By applying Canonical Correspondence Analysis to data subsets, marked differences in the forward-selected variables were detected. The highest resemblance was found between the complete species set and the common species subset. Only one of eight selected variables was common to all species and the rare species groups. These findings were tested with partial ordination, applying the selected variables from the original species group (Vb), as variables and covariables to the analyses of common and rare species. For the common species this application resulted in a constrained ordination with higher eigenvalues as compared to the set of variables selected with reference to the common species group. Using the rare species group, the application of Vb gave a much lower sum of eigenvalues than did the ordination with selected variables based on the rare species group only. Evidently, the set of variables selected on the basis of the rare species data were more significant. Hence, the resulting gradients depend on the frequency of the species. Gradient analysis is apparently only valid for groups of species with closely resembling characteristics. This implies that different functional types of species, with different distributions and abundances, respond individually to environmental variation. Extrapolating deduced gradients from one species group to another maybe risky, particularly when used in vegetation modelling.     

Vegetation in Danish beech forests: the importance of soil,microclimate and management factors,evaluated by variation partitioning

The importance of management regime on floristic variation (mosses and vascular plants) in four Danish beech forests was investigated. Sixty-four blocks were sampled, representing beech stands of different age and management types. Nineteen potential explanatory variables were recorded and tested with Monte-Carlo tests and Canonical Correspondence Analysis. In addition results were evaluated by use of Detrended Correspondence Analysis. Explanatory variables were divided into three groups; soil, microclimatic and management parameters. The amount of variation explained by each group of variables was calculated by use of variation partitioning. The group consisting of management variables explained most variation, on local as well as regional scale. Management related variables explained more variation in vegetation than any other variables together. This indicates the importance of management as determining species composition in Danish beech forests. Management related variables explained most variation on local scale. On a regional scale, soil parameters explained the major part of the variation. The results suggest that thirty years without management are sufficient to change species composition significantly, as compared to managed forests.     

Sahelian woody vegetation in Sénégal

Structure and composition of woody vegetation in Sahelian forest types (not including riparian and riverine types) were studied in Sénégal. The application of classification and ordination resulted in the recognition of seven distinctive woody community types, related to soil and precipitation gradients. The described vegetation types only contained four strictly Saharan species, the rest being of Sahelian and Soudanean affinity, so a floristic change from savanna to desert vegetation after two decades of drought could not be confirmed. Tree density was lower in the northern part than earlier, possibly an indication of degradation. Rejuvenation was greatest at the northernmost arenosolic stations, but low in the southern, ferrouginous areas. This presumably demonstrates the resilience of North-Sahelian vegetation, at the moment being in a dynamic rejuvenation phase, after a period of adverse conditions.     

Estimation of plant species richness from systematically placed plots in a managed forest ecosystem

A Danish managed forest of 325 hectares was sampled for plant species richness in a regular 100 × 100 m grid using four nested quadrates of 2, 4, 25, and 200 m², respectively, at each sample point. The survey resulted in total counts of 161, 171, 224, and 289 species depending on size of quadrates. A list of more than 370 species, however, was accumulated for the forest based on the present study, the literature, and additional personal observations. It was shown that species richness estimators and especially the log-log estimator resulted in improved estimates of species richness. It was also shown that a search strategy in which plots with high habitat diversity in the immediate neighbourhood or plots close to forest roads were chosen first was more effective than a random search strategy. The random strategy, on the other hand, was more efficient than emphasising core areas of major habitat types in the beginning of the search. The study has clearly demonstrated that a managed forest ecosystem with its mixture of open areas and different stands can harbour a very high plant species diversity (in this case ca. 25% of the total Danish flora in only 325 hectare). It is also shown, however, how difficult and time consuming it is to count all species in a heterogeneous ecosystem.     

Vegetation structure and diversity of an ancient temperate deciduous forest in SW Denmark

Bolderslev Skov (113 ha) is the largest contiguous ancient forest remnant in Denmark. The forest has been preserved since 1998 as a strict non-intervention forest reserve. We studied vegetation structure, floristic gradients, and diversity of the forest in 50 plots of 100 m² placed according to a restricted random sampling design. Dominant tree species were Fagus sylvatica, Fraxinus excelsior, Tilia cordata and Quercus robur, which in most parts of the forest form a mixed canopy. Most stands appeared to be of moderate age, 55-80 years old, and large old trees were rare. pH in association with light and thickness of the litter layer were the most important factors in explaining floristic gradients in the forest. Soil moisture (dry to mesic) was not strongly correlated with DCA axes for neither tree nor field layer, but had a significant effect on the distribution of a number of herb species. Forest structure was not important in explaining species distributions. Field layer species richness showed a positive relationship with the pH-gradient. At the scale of 1m² plots we also found a highly significant negative relationship between field layer species richness and the plot-wise Ellenberg indicator value for nitrogen availability. Structure of the tree layer had little effect on field layer species richness. The mixed composition, long continuity, and presence of a high proportion of the regional species pool assigns a high conservation value to Bolderslev Skov and makes it an important site for future studies of the dynamic properties, niche preferences, and inter-specific competition of temperate deciduous forest species. This revised version was published online in June 2006 with corrections to the Cover Date.