Restoration of high species density in calcareous grassland: the role of seed rain and soil seed bank

Abstract. A small-scale restoration experiment concerning a species-rich calcareous grassland was conducted over a 7-yr period. 20 yr of abandonment (1971-1990) resulted in both a strong reduction of the number of species and an absolute dominance of the shrub Crataegus monogyna and the grass Brachypodium pinnatum - which contributed 98% of the above-ground herb phytomass. The plot (3 m x 6 m) was cleared in September 1990 and thereafter yearly mown in autumn. Small soil seed bank samples were taken immediately after clearing and again in the autumn of 1996. The inner part of the plot showed a reduced soil seed bank compared to the plot underneath the vegetation outside the plot in 1990. Six years later an increased number of seeds in the soil in this inside area could be recorded mainly in the upper soil layer, although the amount was only 40% compared to the outside or control area. Ca. 20% of the species present in the restored vegetation were recorded in seed traps during the main seed dispersal period in 1997. Restoration of high species richness in the plot was a fast process during the first few years: from seven species in 1990 towards 39 three years later. This was significantly faster than the restoration process of the calcareous grassland at the same slope 20 yr earlier. This was probably due to the increased size of the community species pool at the site as a result of appropriate management during the last decades. Relative species number increase was highest at the largest scale during this experiment, viz. at the total plot area. The success of restoration of species-rich, dry grassland vegetation largely depends on the interaction between several conditions, e.g. seed availability, either originating from the seed rain or soil seed bank, favourable germination conditions and a successful development to a mature, seed producing individual. Germination and establishment strongly depend on suitable vegetation structure as a result of sustainable management.     

Time and space in the community structure of a species-rich limestone grassland

Abstract. The community structure of a species-rich grassland was investigated at a small spatial scale (0.001 m²), to determine whether evidence suggesting assembly rules could be found in temporal or spatial variation in either species richness or guild proportions. The community was alvar limestone grassland on the island of Öland, Sweden. Three sites were sampled: two lightly grazed, the other recently ungrazed. Plots with and without fertilizer were compared. Evidence was sought for restriction on the ability of species to co-occur within a limited spatial area. Restriction due to a limited number of niches available,‘niche limitation’, could be manifest as lower variance in quadrat richness than expected under a null model (i.e. RV_r, the ratio of observed: expected variance in richness, would be < 1.0). In several cases, RV_r values were significantly < 1.0, even using a patch model to allow for possible spatial variation in the environment. Low RV_r values were found only at the smallest square quadrat size, 10 cm². On Fertilized plots in the years immediately after application of fertilizer, low RV_r could not be demonstrated. Explanations of low RV_r other than niche limitation are considered, such as environmental heterogeneity (present and/or historical) and limitations to the co-occurrence of individual plant modules. Assembly rules based on guild membership were sought by looking at the variance across quadrats in the proportions of species from morphological guilds. An assembly rule would be seen as relatively constant proportion, estimated via RV_gp, the ratio of observed: expected variances in guild proportions. Significant guild proportionality was found in some cases. There was no evidence of guild proportionality in the years after the application of fertilizer. The significant effects in RV_r were more numerous than expected on a random basis, though not observed in every site in every year. Similar trends were seen in RV_gp. At the space/time scales examined, the species in a plant community may be constrained by assembly rules only intermittently, e.g. when resources are more limiting (Wiens 1977). Under this concept, when competition is relaxed, such as following fertilizer application, there is a temporary microhabitat ‘waterhole’ in which more species can coexist, and the assembly rules break down, at least temporarily whilst the species composition adjusts. There was some indication of a return to more deterministic community structure four years after fertilization commenced. Variants of van der Maarel's Carousel model were tested. A Niche-limited Carousel Model (i.e. a model in which there is some limitation in the number of species that can occupy a microsite) would imply restricted variation in richness through time for a single quadrat (temporal RV_r). Overall differences between years in species richness were demonstrated, and their effect removed; after this adjustment there was support for the Niche-limited Carousel Model. The extent of this limitation varied between sites. There were also consistent differences between quadrats in species richness. There was little evidence for constancy of guild proportions through time. The site that showed the strongest community structure in time and space, least year-to-year variation in mean species richness, and least response to fertilizer perturbation, is that on the shallowest soil. Possibly the thin soil results in greater resource limitation, supporting suggestions that assembly rules are stronger when resources are more limited.     

Small-scale plant species turnover in a limestone grassland: the carousel model and some comments on the niche concept

Abstract. This study reports on small-scale changes in the distribution of plant species in a 2.5 m² plot of grazed, species-rich Veronica spicata - Avenula pratensis grassland on shallow, dry, nutrient-poor soil in the Great Alvar area (Stora Alvaret) of southern Öland, southeastern Sweden. Multivari-ate analysis of 0.001 m² and 0.25 m² quadrats within the plot showed that there is little floristic variation without any trend in the plot. Average species richness varied little throughout the study period from 1986 to 1991 with 1986 averages of 7.0 on 0.001m², 16.3 on 0.01 m², and 26.1 on 0.25 m². On 0.001 m²the highest species number found was 12, on 0.01 m², 27. However, cumulative species richness, i.e. species number in the first year plus new species appearing in later years (averaged over 40 quadrats) increased over the same period, on 0.001 m² from 7.0 in 1986 to 14.9 in 1991, and on 0.01 m² from 16.3 to 24.1. Cumulative frequency, i.e. number of quadrats out of 40 where a species occurred in the first year or/and in later years, increased as well; the number of cumulatively highly frequent (> 80%) species increased from 5 in 1986 to 18 in 1991. Species mobility on the scale of the small quadrats used implies both appearance and disappearance from these quadrats. Using six examples, species mobility is shown to vary individualistically, both in rate and degree. We postulate that in homogeneous, grazed, nutrient- and water-deficient environments many species can reach virtually all microsites within the plot, which we express through the idea of the ‘carousel model’. We also question the usefulness of the niche concept and re-interpret it by stating that all species of this plant community have the same habitat niche, while most of them are short-lived and have the same regeneration niche. The essential variation amongst the species is their individual ability to establish or re-establish by making use of favourable conditions appearing in microsites in an unknown, complex spatio-temporal pattern.     

Long-term after effects of fertilization on above-ground phytomass and species diversity in calcareous grassland

Abstract. Long-term after effects on species number and productivity in calcareous grassland were analyzed after cessation of fertilization. Three series of permanent plots were monitored yearly from 1971 to 1993. These series differed in duration of fertilization and in fertilizer composition, notably the amount of nitrogen and phosphorus. Yearly above-ground production decreased in all series after fertilization had been stopped, however at different speeds. The grass/forb ratio also decreased, while species number and Shannon index of diversity (H') increased. In the series where fertilizer treatment was stopped in 1967 (1968-series), productivity and grass/forb ratio decreased equally as in the plots where fertilization with a high nitrogen content was stopped in 1979 (80/Npk-series). However, species number in the plots of the 80/Npk-series increased faster than in the 1968-series. This was probably the result of a higher number of species present in the seed rain from the surrounding vegetation in the period after 1980 than from after 1968. In the plots receiving a high amount of phosphorus (80/nPk series), the productivity decreased more slowly than in the high nitrogen plots (80/Npk-series). At approximately the same total production level, the grass/forb ratio remained higher for another five-year period in the 80/nPk-series. Species number and the Shannon index of diversity increased more slowly in the 80/nPk-series than in the 80/Npk-series. Over a given range of productivity, changes in species number and Shannon index correlated better with the grass/forb ratio than with total above-ground phytomass. Therefore, restoration of species-rich grassland should not only be focused on lowering the yearly production, but also on reducing the grass component of the vegetation.     

Spatial variation in a grassland on soil rich in heavy metals

Abstract. The vegetation in a grassland area in the prefecture of Kilkis (N. Greece), known for its surface Cu-mineralization, was studied. 43 quadrats were established along a transect through an area where the vegetation formed patches of different size. Cover-abundance and frequency estimates for all species were made. Normal Association Analysis revealed five quadrat groups characterized by Trifolium scabrum, Linaria pelisseriana, Anthoxanthum ovatum, Gypsophila muralis and Minuartia hirsuta ssp. falcata. 43 soil samples were analysed for pH, organic C, CaCO₃, total content of Fe, Zn, Pb, Cu, Mn, Ca, Mg, K, Na and soil texture. From a discriminant analysis performed on soil data five soil groups resulted, which are highly related to the five vegetation groups. Thymus sibthorpii, Minuartia hirsuta ssp. falcata and Rumex acetosella are the most important taxa with respect to physiognomy and patchi-ness of the vegetation. The number of species in each group of quadrats is affected by the relative favourableness or severity of the soil conditions. Metal contents, mainly Zn, Cu, Mg and Na, and soil texture are considered to be among the main factors controlling the structure and physiognomy of the vegetation.     

Linear relationships between aboveground biomass and plant cover in low open herbaceous vegetation

Abstract. Four herbaceous plant species of a sand dune area and several herb species of an open early‐successional patch were investigated for the occurrence of a simple relationship between aboveground biomass and plant cover. Without exception linear regressions of aboveground biomass on plant cover were found with slope factors depending on the growth form of the species. These results suggest that (early) growth of herbaceous plants in low and (temporarily) open vegetation is not affected by possible constraints caused by a decreasing ratio of plant cover to aboveground biomass. The obtained linear relationships could be used for rapid non‐destructive determination of aboveground biomass by image‐analysis of cover data.     

Changes in Mediterranean plant succession: old-fields revisited

Abstract. Old-field plots used for a study of succession in Mediterranean France were revisited after 12–14 yr. Our aims were: (1) to verify if predicted patterns of species richness, turnover and composition are confirmed; (2) to compare the development in disturbed plots with that in undisturbed ones; (3) to discuss the impact of management changes. In undisturbed plots species richness and turnover decreased with successional age. Floristic composition changed in a way consistent with the predicted successional development in most plots. Therophytes decreased and phanerophytes increased; anemochorous species decreased and endozoochorous species increased, as expected. In plots disturbed since the first analysis richness decreased with successional age, but generally remained higher than in undisturbed plots. Floristic composition, species turnover and an increase in therophytes indicated changes towards younger successional stages. Thus, disturbance changed succession but not much. This is probably linked with the regeneration abilities typical of mediterranean species, e.g. resprouting. At the landscape scale, richness did not change and species turnover was low. The plots studied were situated in two distinct locations. One had not been disturbed between the two observation periods, while the other is a mosaic of undisturbed and disturbed sites. Observations fitted predictions much more closely at the undisturbed location. We conclude that permanent plot studies are powerful in identifying successional trends and can also provide additional insights into the effects of disturbance some of the mechanisms underlying the dynamics of diversity.     

The vertical distribution of below-ground biomass in grassland communities in relation to grazing regime and habitat characteristics

Abstract. 40 sites, representing different pasture types in Northwest Spain, were sampled in respect of their floristic composition, distribution of above and below-ground biomass and environmental and physical variables. Five plant community types were identified by classification techniques of plant species composition. These communities were then characterized in terms of the percentage of ground covered by herbaceous and shrub vegetation, stones, rocks and gaps as well as their topographic location and characteristics of the shallow soil (pH, organic matter, nitrogen and calcium content). Bio-mass was assessed in terms of above-ground structures, surface crowns and three below-ground layers to a depth of 10 cm. Three types of grazing regime were distinguished: Concentrated Intense Grazing in early spring (CIG), Extended Intense Grazing throughout the spring (EIG), and Non-Intense Grazing (NIG). Grazing regime showed the highest association with plant community type and three broad categories were identified: xeric stressed pastures, which nevertheless received CIG, mesic pastures with EIG, and three kinds of NIG mesic pastures. The xeric communities had the highest proportion of aboveground biomass, as a consequence of their greater proportion of woody perennials. These xeric communities displayed a more gradual reduction in below-ground biomass with depth than mesic pastures, a likely consequence of the low water content in the upper soil layers. The mesic communities had a high concentration of below-ground biomass in the upper layers when they were intensely grazed. However, when grazing was low (i.e. NIG situations), these communities had greater variability in biomass profiles than any of the other pasture types. Possible causes of the patterns in biomass distribution of the intensely grazed pastures are discussed.     

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.     

Impact of cattle dung deposition on the distribution pattern of plant species in an alvar limestone grassland

Abstract. Seed banks in cattle dung, soil under cattle dung and soil under vegetation and growth response of plant species to the changes in soil nitrogen availability were studied in an alvar limestone grassland on Öland, Sweden, in order to analyse the impact of dung deposition and decomposition on the formation of patches of plant species. Results suggest that patches of four plant species could result from cattle dung deposition and decomposition. Impact of dung could proceed in three ways: (1) by changing the relative abundance of species in the soil seed bank under dung, and/or (2) by influencing the deposition of seeds in the dung, and/or (3) by intensifying the growth of some species through nutrient release. Species patches could result from one or more of these aspects. For instance, patches of Arenaria serpyllifolia may be induced by dung deposition because of the dominance of its seeds in dung, while the pattern of Cerastium semidecandrum and Festuca ovina may be due to the abundance of their seeds in the soil seed bank under dung and their positive growth response to increased nitrogen availability.     

Determinants of distribution of six Pinus species in Catalonia,Spain

Abstract. This study explores the determinants of distribution, abundance and regeneration of six Pinus species (P. halepensis, P. nigra, P. pinaster, P. pinea, P. sylvestris and P. uncinata) that occur naturally in Catalonia, northeastern Spain. The aim of this study was to generate accurate predictions of the distribution of each species using simple and readily available environmental variables. We used recursive partitioning and GIS analyses to relate the data base of 10 600 field plots from the Forestry Inventory of Catalonia with abiotic and biotic characteristics of each plot. We present general patterns of distribution, dominance and regeneration for the six species and then focus on P. halepensis, the most abundant pine species in the western Mediterranean Basin. For all six species, the models correctly classified more than 80% of the distribution using abiotic factors, mainly altitude and rainfall variability. Biotic factors such as the basal area of other pine species were necessary to accurately predict patterns of pine species dominance. Biotic factors, especially the basal area of evergreen species (mainly Quercus ilex), were of overriding importance when predicting patterns of seedling occurrence. Potentially important factors such as land use and fire history were of little significance for predicting distribution at the scale of our study. Our models failed to predict accurately which species (and in which numbers) co‐occur with P. halepensis. Factors not included in this study, such as stand age, disturbance (cutting, clearing) and other human‐induced factors, are probably the main determinants of co‐existence patterns.     

Numerical syntaxonomy of the Asplenietalia petrarchae in the Iberian Peninsula

Abstract. A numerical syntaxonomic study of rupicolous vegetation of the Asplenietalia petrarchae in the Iberian Peninsula is described. The study is based on 37 local tables (OSUs) of different rupicolous communities from limestone cliffs found in the eastern half of the Iberian Peninsula. Three classification approaches were followed: (1) ‘hard partition’ techniques, (2) ‘fuzzy partition’ and (3) ordination partition. In order to find a direct solution, we tried an evaluation system based on the inertia associated with a CCA, Canonical Correspondence Analysis, and its relationships with the inertia of a similar CA, Correspondence Analysis. The most effective solutions were found through spatial partitions, and the best partition was obtained with CA considering five segments per axis. Among the fuzzy partitions the best solution was obtained with two clusters and a fuzziness value of 1.20. The best hierarchical partition was Complete Linkage with Chord Distance as a resemblance function. With the GRID procedure applied to the CA diagram, three different groups were distinguished. The first group is related to the Saxifragion boisseriano-reuterani, including five OSUs from Baetic ranges; the second group is very close to the Cosentinio-Lafuenteion rotundifoliae and includes 11 OSUs from thermo-mediterranean areas; the third group, including 21 OSUs basically related to meso-mediterranean areas, is strongly related to the Teucrion buxifolii.     

Small-scale plant dynamics in temperate Themeda triandra grasslands of southeastern Australia

Abstract. Vegetation subjected to two long-term burning regimes (annual or biennial burning) was studied in permanent plots, at two spatial scales: 0.01 m² and 1 m², to determine the small-scale dynamics of plants in temperate Themeda triandra grasslands of southeastern Australia. Species turnover rates were estimated by presence/absence data while species mobility was assessed using cumulative frequency data. While mean species richness did not fluctuate greatly between years, the vegetation was internally dynamic rather than static. Cumulative species richness increased by 50% at both spatial scales and sites over the 4-yr study period. However, few species became cumulatively frequent (i.e. occurred in 80% of plots in the first and/or subsequent years), suggesting that cumulative species richness increases were due to small- or local-scale movements of plants, rather than ‘shifting clouds’ of species moving across the entire site. The vegetation's dynamics did not differ greatly at sites subject to different (frequent) fire intervals. Species turnover and mobility were individualistic, but the dynamics of many species was greater at the smaller spatial scale: 31–48% of the species present at both spatial scales at the two sites had higher turnover rates at the 0.01 m² scale. Similarly, some ‘non-mobile’ species at the 1-m² scale (i.e. ‘constant’ or ‘local’ mobility types), were more mobile at the smaller-scale. Turnover rate and mobility type were strongly associated with life form in some cases, particularly at the annually-burnt site. In general, therophytes (and to a lesser degree, geophytes) were positively associated with high turnover and mobility in most years, while hemicryptophytes were negatively associated with high turnover in many instances. Hemicryptophytes included many species with a range of mobility types and hence, few significant associations between mobility and this life form were found. The previously unrecognized internal dynamics of this community under ‘stable’ management regimes contributes to species coexistence by allowing plants with different dynamics properties to persist in a spatially and temporally unpredictable manner. Frequent burning is presumably the important component driving much of the non-directional, small-scale dynamics because it regularly destroys individual plants and aerial plant parts and creates opportunities for seedling regeneration, whilst permitting the vegetative persistence and spread of established plants in non-light-limited microsites.     

Fine-scale spatio-temporal patterns in a mountain grassland: do species replace each other in a regular fashion?

Abstract. Long-term ‘high spatial resolution’ permanent plot data were used to determine whether fine-scale species replacements in space occur more often than expected on the basis of random processes, and to test whether these replacements are species-specific. Monte Carlo tests were used. There was no indication of significance in associated positive change (species A increased when B increased); the overall number of significant results was not higher than expected on a random basis. For associated negative change, or replacements (species A increased when B decreased) the overall number of significant results was significantly higher than expected. Significant reciprocal replacements between Deschampsia flexuosa, Festuca rubra and Nardus stricta were frequent; changes in Anthoxanthum alpinum and Polygonum bistorta were uncorrelated with changes of the former three. The first three species thus use the ‘same’ space. Both the latter species often reproduce by seeds and their turnover is much higher. The prevalence of negative correlations of changes (i.e. correlation of increase with decrease) supports the concept of an internal structuring within the grassland community.     

Effects of cutting and nitrogen deposition on biodiversity in Cantabrian heathlands

Questions: Does the diversity of heathland vegetation change when subjected to experimental disturbances such as cutting and nitrogen fertilization? Do changes in the vegetation structure negatively affect the regeneration of the dominant species Calluna vulgaris? Is cutting an alternative method of conserving the diversity and maintaining the structure of heathlands in the Cantabrian Mountains? Location: Calluna vulgaris heathlands on the southern slopes of the Cantabrian Mountain range, NW Spain. Methods: A total of 60 plots were treated with different combinations of cutting and twice the estimated atmospheric deposition of nitrogen (56 kg‐N.ha^?1.yr^?1). The changes in the cover values of the species present were monitored over a five year study period. The cover values were used to calculate abundance and species richness. Results: Fertilizing with nitrogen allows biodiversity to increase over time. However, the greatest biodiversity is associated with the cutting plus fertilization treatment, since cutting allows gaps to be opened that are easily colonized by pioneer annual species, while fertilization mainly favours an increase in the mean number of perennial herbs (graminoids and forbs). Increased perennial herb richness also corresponds to a rise in their cover values. The recovery of the dominant woody species in these communities, Calluna vulgaris, is not impeded by the increase in perennial herbs species' cover values. Conclusions: In the Calluna vulgaris heathlands studied, cutting plus fertilization allowed an increase in biodiversity over time. No displacement of the dominant woody species, Calluna vulgaris, is observed due to the presence of the perennial herbs. Cutting patches of heathland is recommended as a mechanism for maintaining high vegetation diversity, when grazing is not possible.     

How do species dominating in succession differ from others?

Abstract. Data on succession were collected from 15 seres starting on bare ground in man-made habitats (i.e. sites disturbed by various mining activities, bulldozed sites, ruderal urban sites, the exposed bottom of a destroyed water reservoir, and abandoned fields), all in the western part of the Czech Republic, Central Europe. The period for which the data on succession were available ranged from 12 to 60 yr. 56 species reaching dominance in some period of succession were selected (the criterion being: at least 25 % cover in at least one year in any sere); they were compared for biological and ecological traits with other species participating in the seres (167 species with at least 1 % cover in at least one year in any sere), and with the Central European flora as a whole. Significant differences between the species dominating in succession and others were found for the following traits: life form, life strategy, pollination mode, and ability of lateral spread. Dominant species differed from the regional flora in distribution of life strategies, pollination mode and immigration status. The results suggest that an ‘ideal successional dominant’ is a tall, wind-pollinated plant, often a geophyte capable of intensive lateral spread, requiring high nutrient supply and sufficient site moisture. The set of traits contributing to achieving dominance by a species in human-made habitats includes both features occurring independently of phylogenies (life strategy, pollination mode, plant height, moisture demands) and those which dominant species probably share due to their common ancestors (nutrient demands, capability of extensive lateral spread).     

Management of a semi‐natural grassland; results from a 15‐year‐old experiment in southern Sweden

Abstract. Vegetation changes in a semi‐natural grassland of wooded meadow type that had been grazed for centuries are described following the introduction of various management regimes: mowing each year, mowing every third year, burning, mechanical removal of woody plants, chemical treatment of woody plants, continuous grazing and abandonment. The experiment was established in southern Sweden in 1972 and has been in progress for 15 years. In 1972, 1980 and 1986 the botanical composition in these plots was investigated in permanent subplots. The study clearly demonstrates that mowing or grazing is necessary to preserve community structure and that mowing is to be preferred in cases where maintaining species richness is of primary concern. Mowing every third year delayed vegetation change and prevented woody species from spreading. Therefore, periodic mowing might be an alternative way to preserve the flora. In contrast, yearly burning does not seem to be a viable management in this type of semi‐natural grassland. To preserve the open landscape regeneration of woody plants has to be prevented. However, in plots where woody plants were removed the typical grassland flora declined. Abandonment resulted in closed forest.     

Effects of germination inhibition on the dynamics of Quercus ilex stands

Abstract. Germination of Quercus ilex L. in coppice stands of this species in the western Mediterranean Basin was examined and a germination inhibitory process is proposed to explain some germination traits. Germination rate and seedling biomass of Q. ilex were greatly modified by watering acorns with various concentrations of aqueous soil extracts from a Q. ilex coppice stand but also when the acorns were sown in soil from Q. ilex coppice stands. In the aqueous extract experiment, Q. ilex germination and seedling weight both decreased as the aqueous extract concentration increased. In the soil type experiment, Q. ilex soil decreased the Q. ilex germination rate. Comparative studies with Q. pubescens germination (this species, replaced by Q. ilex around 5 000 B.P., is assumed to form the climax vegetation of the region) revealed that Q. pubescens was less sensitive to the aqueous extracts and soils of Q. ilex coppice stands. Inhibition of Q. ilex seed germination could be a major reason for the poor seed regeneration and suggested a possible comeback of Q. pubescens.     

Establishment of pasture species on cattle dung: the role of endozoochorous seeds

Abstract. The process of colonization of cattle dung patches and its relation to endozoochorous dispersal is analysed in a Mediterranean pasture. Dung pats dropped in spring and winter were marked, and the vegetation developing on them during the first two years of colonization was followed. The influence of endozoochorous seeds on dung colonization is assessed through the study of: (1) the vegetation on spring and winter dung pats and the seed contents of both, which is abundant in the former and negligible in the latter; and (2) the vegetation on spring dung pats compared with that of the surrounding pasture. The origin of plants growing on dung (either seeds in the manure or in the soil seed bank) was traced by studying dung colonization under controlled conditions in pots with manure put on seed-free sand, and on pasture turf. The results indicate that endozoochorous seeds germinate in manure; they are the main source of recovery in gaps generated by dung pats. The micro-succession involved is independent of the type of pasture. A small-scale spatial pattern results in which gaps of old dung are dominated by endozoochorous species. Thus, dung patches enhance the similarity between grazed communities, and the variation within communities.     

Vertical distribution of below-ground biomass in intensively grazed mesic grasslands

Abstract. Previous work has shown that below-ground biomass is more concentrated in surface soil layers in intensively grazed mesic grasslands than in moderately grazed grasslands. However, since the mesic grasslands previously studied shared similar compositional traits, the question remained whether grasslands with differing species composition, and intensive defoliation, showed similar biomass distribution patterns. Eight grasslands at four sites distributed along an elevational gradient were investigated. The upper and lower zones of a slope were sampled at each site. Four of these grasslands were grazed by livestock and the other four were grazed and mown. Biomass was divided into above-ground, root crown and three root layers. Species composition varied according to management and topography. Annuals and perennial forbs had relatively more above-ground biomass at the upper part of the slopes, while perennial grasses dominated the lower parts. The above-ground biomass and root biomass at 4 — 7 cm depth attained maximum values in the lower, potentially more fertile, parts of the slopes. Crown biomass increased with altitude at the upper part of the slopes. Despite their differences in composition and structure, seven out of the eight stands showed a remarkable concentration of the below-ground biomass near the soil surface, which decreased drastically with soil depth. This pattern is similar to that observed in the intensively grazed mesic communities studied earlier. This similarity was more evident in the more mesic-like grasslands, since it increased from the upper, potentially drier parts of the slopes, to the lower parts, and, when each topographic position was considered separately, from low to high elevation.