Soil seed bank and floristic diversity in a forest‐grassland mosaic in southern Spain

Abstract. Soil seed bank and floristic diversity were studied in a forest of Quercus suber, a forest of Quercus canariensis and a grassland, forming a vegetation mosaic in Los Alcornocales Natural Park, southern Spain. The soil seed bank was estimated by the germination technique. In each community patch, diversity, woody species cover and herbaceous species frequency was measured. Three biodiversity components – species richness, endemism and taxonomic singularity – were considered in the vegetation and the seed bank. Forest patches had a soil seed bank of ca. 11 200–14 100 seed.m^?2 and their composition had low resemblance to (epigeal) vegetation. The grassland patch had a more dense seed bank (ca. 31 800 seed.m^?2) and a higher index of similarity with vegetation, compared with the forests nearby. The complete forest diversity was 71–78 species on 0.1 ha, including 12–15 species found only in the seed bank; the grassland species richness was higher (113 species on 0.1 ha). We discuss the role of soil seed banks in the vegetation dynamics and in the complete plant biodiversity of the mosaic landscape studied.     

A resampling approach for evaluating effects of pasture abandonment on subalpine plant species diversity

Abstract. The decline of species‐rich semi‐natural calcareous grasslands is a major conservation problem throughout Europe. Maintenance of traditional animal husbandry is often recommended as an important management strategy. However, results that underpin such management recommendations were derived predominantly from lowland studies and may not be easily applicable to high mountain areas. In this study we analyse the importance of traditional low‐intensity summer farming (cattle grazing) for vascular plant species diversity of a subalpine region in the northern calcareous Alps in Austria by resampling from an existing dataset on its vegetation. Results indicate a significant long term decline of plant species diversity following abandonment at the landscape scale. In contrast, within‐community effects of pasture abandonment on plant species diversity are equivocal and strongly depend on the plant community. We suppose these differences to be due to diet preferences of cattle as well as to the differential importance of competition for structuring the respective communities. From our results we infer that the main mechanism by which pasture abandonment affects vascular plant species diversity, at least during the first ca. 100 yr documented here, are not local‐scale competitive exclusion processes within persisting communities. Instead, post‐abandonment successional community displacements that cause a landscape scale homogenization of the vegetation cover seem to be primarily responsible for a decline of species diversity. We conclude, that successful management of vascular plant species diversity in subalpine regions of the Northeastern Calcareous Alps will depend on the maintenance of large scale pasture systems with a spatially variable disturbance regime.     

Seed-shedding in a Scottish heath community

Abstract. For a 28-week period in late 1987 and early 1988, a study of seed-shedding by several heath species was carried out at the Muir of Dinnet in northeastern Scotland. The dominant species in the heath is Calluna vulgaris. Seed-shedding in Calluna began in early September 1987 and was completed in April 1988, with the period of maximum shedding falling between early November and late December 1987. The total numbers of seeds/m² deposited in stands of Calluna in its four growth-phases were: pioneer, 18 910; building, 169010; mature, 198580; degenerate, 33900. Substantial loss of potential seeds results from the shedding of immature flowers. A control area close to, but outside the area of Calluna dominance had a deposition rate of 770 Calluna seeds/m², indicating sufficient seed to colonise nearby available habitats. Seed rain was also recorded for several other heathland species: Erica cinerea, E. tetralix, Carex spp. and Betula pendula. Seeds of Erica cinerea were deposited in all the Calluna stands, 32670/m² in the pioneer stand, 17600/m² in building, 3720/m² in mature, 210/m² in degenerate (120/m² in the control area). Numbers were greatest at the start of the sampling period, declining thereafter. This applied also to Betula seeds. Erica tetralix occurred in the degenerate Calluna stand and yielded 640 seeds/m² (400/m² in the control area). Seeds of Carex spp. were obtained in the control: 4110/m². The method of sampling has a significant effect on the figures obtained. A method using tube collectors, emptied frequently, is recommended.     

Plant functional types in coastal foredunes in relation to environmental stress and disturbance

Abstract. The foredune vegetation in the Gulf of Cadiz (SW Spain, S Portugal) was studied by means of morphological characters and functional traits of plants. The 55 vascular species recorded in the area were classified into three functional types: Type I consists mainly of winter annuals of moderate size with soft leaves, showing no presumed adaptations to the dune environment. Plants of Type II are mostly perennials with a below-ground spreading root network and leaves with presumed adaptations to coastal environmental stress. Type III includes plants mostly capable of being dispersed by sea-water and of withstanding sand burial. In relatively unstable soil, Type II and Type III plants were found to be more abundant, their relative proportion depending on the dominance of accretion/erosion processes. Increasing cover of Type I plants was associated with relatively more stable soils. The ratios in occurrences of the three types can be used as an indicator of foredune dynamics.     

Species richness and composition of amphibians and reptiles in a fragmented forest landscape in northeastern Bolivia

We quantified patterns of species richness and species composition of frogs and reptiles (lizards and snakes) among three habitats (continuous forest, forest islands, and a seasonally flooded savannah) and between forest island size and isolation classes in a floristic transition zone in northeastern Santa Cruz Department, Bolivia. Species richness was similar across macrohabitats, as was faunal composition of forested habitats, although savannah harbored a distinct herpetofauna. On forest islands, richness and composition of forest frogs was largely related to isolation, whereas reptiles were affected by both isolation and habitat. The observation that isolation rather than area was the primary driver of distribution patterns on forest islands stands in contrast to many studies, and may be a function of (1) the greater range in forest island isolation values compared to area or (2) the long history of isolation in this landscape.     

Effects of age and distance on the composition of mixed deciduous forest fragments in an agricultural landscape

Abstract. Forest patches in central Belgium were inventoried twice for the presence or absence of forest plant species to study the effects of age and distance on species composition. All forests in the study area were subdivided based on their land use history. To avoid effects of autocorrelated environmental characteristics on species composition, habitat homogeneity was indirectly investigated using a TWINSPAN classification of the vegetation data. Two major habitats (alluvial and non‐alluvial forests) were distinguished and analysed separately. Patterns of species composition were investigated at the landscape level using Mantel tests. Species composition similarity measures were calculated between all pairs of fragments based on the floristic data. A highly significant correlation was found between species composition similarity and inter‐patch distance. Difference in age, which we used as a measure for habitat quality, was less important in explaining species composition patterns. The effects of spatial configuration became significant when difference in age was accounted for, and a partial correlation was calculated between inter‐patch distance and species composition similarity. Different results were found for alluvial and non‐alluvial forest types. Alluvial forests were more influenced by the spatial configuration than the non‐alluvial. For the non‐alluvial forest type effects measured with the difference in age between forest fragments obscured the effects of inter‐patch distance. Based on our findings we suggest that species composition is not only internally generated, but external processes such as differential colonization caused by varying degrees of isolation may be of overriding importance.     

Patterns of ecological,chorological and taxonomic diversity at both sides of the Strait of Gibraltar

Abstract. Diversity relations in Mediterranean heathlands and the understorey of oak woodlands on sandstone-derived substrates were studied at both sides of the Strait of Gibraltar. Trends in species composition and cover were analysed by Detrended Correspondence Analysis; the first axis, assumed to reflect a main environmental gradient, was used to analyse the patterns of three aspects of community diversity. Species richness, i.e. number of species along a 100-m transect, shows a humpbacked trend along the gradient, with the highest values in the understorey of evergreen Quercus suber woodlands, associated with soils of intermediate fertility and moisture status. The number of endemic species is highest in open heathlands, associated with more extreme conditions of acid, infertile soils on exposed ridges. The taxonomic singularity, as measured by the inverse of the average number of species per genus at each site, is highest at the most fertile and moist sites occupied by semideciduous Q. canariensis woodlands. A comparison between northern (Spanish) and southern (Moroccan) sides of the Strait of Gibraltar shows a general concordance of the trends of woody plant communities along the main environmental gradient. However, significant differences of the southern samples are: (1) lack of some differential, habitat-specific species and greater abundance of widespread generalists; and (2) a general reduction in species diversity, number of endemics and taxonomic singularity. We interpret these differences as affected partly by the smaller extent and fragmentation of sandstone areas in the south, and partly by the higher impact of slashing and grazing there.     

Seed bank classification and its importance for the restoration of species-rich flood-meadows

Abstract. This paper focuses on the persistence of seeds in the seed bank of a formerly fertilized flood-meadow into which seeds from an original Alopecurus pratensis-Sanguisorba officinalis community have been introduced. The longevity of seeds in the seed bank of the original community is also estimated. The established vegetation was compared with the seed bank, as divided into two layers (0 - 5 cm and 5–10 cm); this allowed a classification of species into three groups, with (1) transient, (2) short-term persistent and (3) long-term persistent seed bank. The majority of the species of the unfertilized flood-meadow community have a transient or short-term persistent seed bank with seeds showing a large variance in shape i.e. flattened or elongate. Because of this, the characteristic flood-meadow species will disappear soon after the beginning of fertilizer application and will not re-establish from the seed bank, once the fertilizer application is ceased. The formerly fertilized flood-meadow contains many ruderal and arable weed species, the seeds of which tend to be compact or round. Significantly more seeds were found in the seed bank of the formerly fertilized flood-meadow under cattle-grazing than under sheep-grazing and no grazing.     

An experimental study of the impact of seasonal sheep grazing on formerly fertilized grassland

Abstract. The effects of grazing upon the composition of a grassland were examined in a replicated grazing experiment with sheep over eight years. Grazing was controlled to produce two levels of grazing in each of winter, spring and summer, combined in a 2×2×2 factorial experimental design. Particular species were either increased or decreased by winter grazing while, in general, dicotyledonous species were favoured by grazing in both winter and spring. A model fitting the main effects of grazing in three seasons showed the importance of grazing in winter and spring to achieve sward diversification.     

农业区域市化对植物多样性的影响：遵化的研究

选择河北省遵化市(39°55'～40°22'N,117°34'～118°14'E),调查了城郊和乡村在东南西北4个方向上以及市区的植物多样性,同时考察了不同取样点土壤养分的差异结果表明,西部和北部接近,而东部和南部的土壤养分特殊,城郊与乡村明显差异;西部物种丰富度低于其它方向,而南部最高,这种差异由草本造成;城市与东南西北4个方向的生物多样性差异明显;城市植物多样性与城郊和乡村呈现梯度变化;本研究统计的物种总数只有126种,而与之同纬度的北京东灵山区却有高等植物997种.城市化的影响是引进了一些观赏物种,区域地形和土壤养分等自然特征的影响微弱.     

An index of functional diversity

Abstract. Functional diversity has been seen as the key to predicting the stability, invasibility, resource capture, nutrient cycling and productivity of communities. However, it has been unclear how to estimate it. Ten criteria for an index of functional diversity are developed. These include that it should reflect the range of characters present and the abundance of the species with those characters in the community, and be unaffected by the measurement units used or by the number of species. An index that meets all ten criteria, FD_var, is investigated. It is based on the variance in characters, weighted by the abundance of the species with those characters. Tested with artificial and randomly generated data, it showed reasonable use of the 0 ‐ 1 range (mean 0.60, range 0.0009 ‐ 0.975) and intuitive behaviour. Tested with field data from eight sites in New Zealand, it gave a good spread of values (mean 0.65, range across sites 0.34 ‐ 0.84), showed good ability to distinguish between the communities and its performance was ecologically intuitive. Illustrative correlations are made with mean annual temperature and soil fertility, determined by a bio‐assay. FD_var is recommended for general use.     

Epiphytic lichen diversity in old-growth and managed Picea abies stands in southern Finland

Abstract. Epiphytic and epixylic lichens were surveyed on 15 1-ha plots in mature Picea abies-dominated boreal forests in southern Finland. The sample plots were classified into three groups according to the age of the dominant tree stand and recent signs of cutting: (1) early mature managed, ‘EM’ (95 -109 yr), (2) late mature managed, ‘LM’ (126 - 145 yr) and (3) old-growth, ‘OG’ (129 - 198 yr). Two data sets on epiphytic and epixylic lichens were recorded from each plot: (1) species on basal trunks and branches of Picea abies and (2) species on all available woody substrates, including basal parts of all tree species, saplings, snags, logs and stumps. 142 epiphytic and epixylic lichen species were found, of which 83 (58%) occurred on P. abies. Mean total numbers of species per sample plot were 69 in EM, 78 in LM and 88 in OG plots, species number on P. abies were 47, 56, and 54 respectively. The LM plots had lower species numbers than OG plots, mainly due to the lack of old Populus tremula trees, but they had higher species number than the EM plots mainly due to the higher age of Picea abies. Differences in species composition, both within and between the three groups, were small. The results suggest that the epiphytic and epixylic lichen diversity in a managed stand can be increased by prolonging the rotation of the stand to >120 yr and by increasing the diversity of habitats in the stand.     

Effects of selective logging on tree diversity,composition and plant functional type patterns in a Bornean rain forest

Abstract. The effects of selective logging on tree diversity, changes in tree species composition and plant functional types were studied with the use of seven permanent plots in virgin and in logged forest. All plots were located in a lowland dipterocarp rain forest in East Kalimantan on the island of Borneo. Just after logging and during the following 20 yr tree diversity measured as Fishers’α was not significantly affected in logged forest plots. Temporal shifts in tree species composition were analysed with Principal Component Analysis (PCA). Logged forest plots had much larger changes over time than virgin forest plots. In the smallest diameter class, some logged forest plots showed a distinct trajectory in PCA space compared to virgin forest plots, while in larger diameter classes movement of logged plots in PCA space was random. This suggests that there is no predetermined community to which logged forest plots tend to shift when recovering from logging. We found a significant negative correlation between diameter increments and the species‐specific wood densities of tree species. Species‐specific wood density and potential tree height were used to assign species to five PFTs. As expected, logging increased the fraction of softwood stems in small diameter classes. In the largest diameter classes (≥ 50 cm DBH) a strong decrease of softwood emergent stems was found in logged forest plots. After more than 20 yr no recruitment was found of softwood emergent stems in selectively logged forest.     

Climatic discrimination of Mediterranean broad-leaved sclerophyllous and deciduous forests in central Spain

Abstract. Climatic differences between three types of deciduous (Quercus pyrenaica) and three types of sclerophyllous (Quercus rotundifolia) Mediterranean forests in the Spanish Sistema Central were analyzed by means of Canonical Discriminant Analysis and Jancey's Discriminant Analysis, applied in successive steps to data from 252 meteorological stations. Climatic data included temperature and precipitation records as well as bioclimatic indices. Discriminant analysis was applied to broad-leaved sclerophyllous and deciduous forest communities sampled at each meteorological station using phytosociological methods. Annual and seasonal (summer, spring) water availability are the most important factor controlling the distribution of the two physiognomic forest types; southwestern associations of Quercus pyrenaica and Q. rotundifolia differ from their colder homologues by annual and monthly temperatures; western associations were separated from eastern ones in terms of annual and seasonal precipitation gradients. Discriminant analysis was a good technique to explore climatic gradients not shown by other general ordination or classification methods.     

Sex ratio in populations of Silene otites in relation to vegetation cover,population size and fungal infection

Abstract. In contrast to populations of most dioecious Silene species (which usually are female-biased), populations of Silene otites have been frequently reported to be male-biased. We describe sex ratio variation in 34 natural S. otites populations in Central Germany in relation to vegetation cover, population size and fungal infection. The overall sex ratio was unbiased in 1994 and only slightly male-biased in 1995. Sex ratio varied among the populations from 26.6 % to 72.6 % females. The sex ratio of small populations varied strongly due to stochastic processes. Furthermore, we found that populations in habitats with high vegetation cover contained a higher percentage of females. Hermaphroditic plants, theoretically, could increase male bias as they only produce male or hermaphroditic offspring. Their frequency in the populations, however, was far too low to affect sex ratio. In 1994 12.1 % and in 1995 17.0 % of the plants were infected by the smut fungus Ustilago major. Disease incidence in the population was not related to sex ratio, suggesting equal susceptibility of males and females. The sex ratio of partially infected plants did not deviate from the population sex ratio, both under field conditions and in a greenhouse laboratory experiment. The results suggest that the frequently reported male bias in Silene otites populations is not a general pattern, but is mainly caused by environmental conditions.     

Effects of soil erosion on the floristic composition of plant communities on marl in northeast Spain

Abstract. This study explored the validity of three responses of vegetation to increased soil erosion: reduction of vegetation cover, number of species and reduced substitution of species. 201 relevés, including edaphic and geomorphological data, were surveyed in the intensely eroded Eocene marls of the Prepyrenees (NE Spain). Changes in plant species’ presence in relevés from different degradation stages were compared. The level of vegetation degradation was defined as the total phanerogam cover which, in the studied area, was correlated to the degree of soil erosion. The considered trends were validated. Reduction of phanerogam cover and species number were gradual from low to high‐eroded areas. Vegetation degradation explained 48% of the species number variance. In the later stages of degradation a significant substitution of species was not observed, only a lower frequency of occurrence of several species that appeared in the whole set of relevés. Through the process of degradation, 47% of species displayed significantly reduced frequencies as degradation increased, none showed a significant increase in frequency. It is concluded that there are no characteristic species in these plant communities that survive in the severely eroded marls. Among the few species that had increased in frequency, most only colonised favourable micro‐environments.     

Trends and fluctuations in species abundance and richness in Mediterranean annual pastures

Abstract. Floristic data collected from permanent plots during 14 consecutive years are used to model the frequency of the 62 most abundant species in relation to post-ploughing succession, topography and rainfall in annual Mediterranean grasslands located in a Quercus rotundifolia dehesa. The interannual dynamics of species richness are also analysed. From 1980 to 1993, presence/absence data of grassland species were noted in five 20 cm X 20 cm permanent quadrats placed at random in 1980 in 14 permanent plots on a south-facing slope along the topographic gradient. Weekly autumn rainfall data over the 14 years were analysed using a profile attributes index and Hybrid Multidimensional Scaling to arrange the years according to their autumn rainfall pattern. Generalized Linear Models were used to fit the species richness and species frequency according to topographic position, age since the last ploughing episode, total rainfall in the growing season and autumn rainfall pattern using a forward stepwise procedure. The richness model includes all of these variables, and reveals a relatively high goodness-of-fit (71 %). The fact that the meteorological factors play a key role in modelling richness forces us to include them if we wish to use richness as an indicator of the degree of disturbance in these highly fluctuating annual pastures. Models of species dynamics show that although roughly 33 % of the species have a successional behaviour, the majority are more dependent on temporal heterogeneity associated with rainfall or spatial heterogeneity linked to the topographic gradient.     

Lignotuber size of Erica australis and its relationship with soil resources

Abstract. It has been proposed that resprouting after a disturbance would be favoured under conditions of low soil resource availability. In lignotuberous plants of Mediterranean‐type areas, successful resprouting after disturbances such as fire depends on the size of the lignotuber, but little is known about the role of soil resources in determining the relative size of this organ. In this work we tested whether the relative size of the lignotuber in the resprouting shrub Erica australis is related to the availability of soil resources. At each of 13 different sites in Spain, 10 plants were chosen and the sizes of their various parts (above‐ and below‐ground) measured. Additionally, at each site we evaluated soil fertility, foliar N and P concentrations and plant water potential in the middle of the summer. The relationships between lignotuber dimensions and the various plant parts were assessed. In all cases, significant differences between sites were found indicating consistent differences in lignotuber size across the range of plant sizes. This was particularly the case when lignotuber dimensions were expressed as a function of foliar biomass. Lignotuber dimensions relative to foliar biomass were positively correlated with soil pH and negatively with plant water potentials in midsummer. There were, however, no clear relationships between lignotuber relative dimensions and soil N and P contents or other measures of site productivity. In summary, lignotubers were not smaller at more productive sites, in fact they were relatively larger at sites where soils were less acidic, but where plant water conditions were less favourable. These findings contradict predictions made based on current theory on the role of soil fertility allocation to resprouting.