Does Germination Success Differ with Respect to Seed Mass and Germination Season? Experimental Testing of Plant Functional Trait Responses to Grassland Management

BACKGROUND AND AIMS: Plant functional trait responses to processes such as grassland management have been analysed frequently; however, the scaling-up from individual traits to the outcomes of vegetation dynamics has seldom been tested. In this experiment, germination success was studied with respect to the relationships between grassland management (mowing and grazing), as well as abandonment, and two traits that are relevant for seedling recruitment: seed mass and germination season. On the basis of discussions in the literature and indirect trait analyses in our previous studies, the following hypotheses are proposed: (1) with respect to seed mass, mowing and grazing favour the germination of small seeds, whereas after abandonment the germination success of larger seeds is higher; and (2) with respect to germination season, mowing and grazing favour autumn-germinating seeds, whereas succession promotes spring-germinating seeds. METHODS: The germination experiment took place in a semi-natural, dry grassland in north-east Germany. Seeds of eight herbaceous species that differ with respect to seed mass and germination season were sown in mown, grazed and abandoned plots. Germination success was documented during the following year. KEY RESULTS AND CONCLUSIONS: Contrary to the hypothesis, germination of small seeds was not promoted by mowing or grazing and they germinated relatively more often than expected in the abandoned plots. A relationship between abandonment and gaps of bare soil below the vegetation cover that favour germination of small seeds was likely, but could not be proved statistically. It is possible that the small seeds suffered less from predation. Mowing favoured autumn germination, which could be explained by the removal of biomass in late summer. Contrary to our expectation, there was relatively more spring germination after grazing than after mowing, yet vegetation height was smallest in spring. Generally, germination season was found to be related to the temporal occurrence of favourable light conditions.     

Effects of experimental and real land use on seedling recruitment of six fen species

Seedling emergence and early establishment of six fen species differing in seed mass and growth form were investigated under experimental land use with changed vegetation structure and under real land use in a calcareous fen. Seeds of all six species were sown in plots with different experimental land-use treatments: summer and autumn mowing with or without litter removal, trampling and abandonment. Additionally, emergence and survival of experimentally sown seeds was investigated under real land use on adjacent sites managed by mowing, grazing, intense trampling or abandonment.On abandoned plots and on plots without litter removal of the land-use experiment, emergence rates of all species were negatively affected either by high litter and moss cover or by tall canopy. No differences were found between autumn and summer mowing. Gap creation by experimental trampling did not increase germination rate. Under real land use, establishment of seedlings of most species was positively affected by litter cover and tall canopy. Trampling, in contrast, had a severe negative effect on seedling survival.The investigated species differed in their germination ability which was tested in the germination chamber and in their response to land use. Succisa pratensis with the highest seed mass germinated well in the chamber and in the field more or less regardless of land use. The low germination rate of Parnassia palustris in the germination chamber indicated a limitation of viable seeds. In the field, however, seedling emergence was additionally limited by microsite availability. Seeds of Serratula tinctoria and Primula farinosa germinated well in the germination chamber, but seedling recruitment in the field was hampered in the presence of a high litter or moss cover. Seeds of Tofieldia calyculata and Pinguicula vulgaris were strongly dependent on the availability of suitable microsites in the field. They hardly germinated under natural conditions, in spite of a high number of germinable seeds in the germination chamber.     

Seedling recruitment of Succisella inflexa in fen meadows: Importance of seed and microsite availability

Abstract. The effects of different forms of land use on germination and establishment of the rare fen species Succisella inflexa were investigated in seed introduction experiments in a mown and an abandoned fen meadow in SE Germany. Treatments included abandonment, mowing in fall and mowing with creation of gaps in the moss and litter layer. Floating capacity of seeds was tested in order to estimate potential dispersal by water. On the mown meadow, gaps had a slightly positive effect on germination rates, while greatly increasing seedling survival until the next spring. At the abandoned site, litter inhibited germination, whereas mosses had a negative effect on germination and a positive effect on survival rates during the first year after germination. Both germination and seedling establishment were negatively affected by the presence of slug herbivores. On the abandoned site, no seedlings at all survived until the next spring. Even though seeds of Succisella inflexa were capable to float for several weeks and to germinate thereafter, the situation at the field sites indicates that longdistance dispersal is highly unlikely. Our results showed that not only direct effects of abandonment, such as accumulation of litter, may have led to poor germination and poor seedling establishment of the species. Additionally, indirect consequences of changes in land use, such as higher seedling herbivory by slugs and successional vegetation changes due to abandonment, were important in determining habitat quality and availability of microsites for seedling recruitment. Furthermore, early mowing imposed seed limitation on plant populations.     

Mechanisms controlling establishment of the non‐bradysporous Banksia integrifolia (Coast Banksia) in an unburnt coastal woodland

Abstract Remnant stands of the non‐bradysporous Banksia integrifolia on the Mornington Peninsula, Victoria appear to be in decline due to old age and other unknown factors. Many stands have been unburnt for >55‐100 years and there is little evidence of successful regeneration by seed. The cause(s) for this lack of recruitment are unclear. In the present study we quantified (i) seed production and germinability in four remnant forests in the region; (ii) the microsite conditions necessary for seedling emergence; and (iii) the effect of herbivore browsing on early seedling survival in order to understand this apparent recruitment failure. Despite large intra‐annual variation, no evidence was found that old forest trees do not produce viable seed. Emergence and survival of seedlings were not inhibited by the presence of groundlayer vegetation. Rather, vegetation facilitated early seedling survival by providing protection from browsing. Seedling transplants exhibited extremely high mortality (≥75%) due to browsing and summer soil desiccation and these factors appear to be major contributors to the lack of recruitment at the study site. Stand‐replacing recruitment is therefore considered to remain unlikely under the present conditions. Developing fire and/or grazing management regimes will be necessary to conserve the structural integrity of these coastal ecosystems.     

The effect of management on productivity,litter accumulation and seedling recruitment in a Carpathian mountain grassland

The management regime may have a significant impact on the productivity and dynamics of grasslands, but the causal relationships influencing grassland conservation value are still not completely understood. Changes of selected community characteristics, such as standing crop, proportion of forbs in the standing crop, litter amount, litter decomposition and seedling recruitment, were investigated in a 4 year manipulative experiment in a mountain grassland in Slovakia. The aim of the research was to compare changes in newly abandoned sites and sites where restoration measures were applied after 20 years of abandonment. The sites were located in areas containing two vegetation types of the Arrhenatherion alliance (wet Poo-Trisetetum and dry Anthoxantho–Agrostietum) with different moisture regimes. The expected increase of the standing crop after abandonment was rather slow, and more pronounced towards the end of the experiment, and in the wet meadow type (~30% increase). The restoration mowing promoted forb proportions in the biomass, but it did not decrease the standing biomass in the restored grasslands. Strong litter accumulation after abandonment was observed in subsequent years after abandonment, when the amount of litter increased about 100% in abandoned plots. Decrease in litter was also significant after the start of restoration mowing (a decrease from 258 to 159 g m⁻² in wet type and from 287 to 147 g m⁻² in dry type was noted). Accumulated litter was negatively correlated to seedling recruitment (r = −0.63 at the end of the experiment). The litterbag experiment showed that the wet type has a higher rate of decomposition, with 20% more biomass decomposed during the litter-bag experiment. The experiment confirmed a negative role of litter accumulation on seedling recruitment, with the number of seedlings per m² decreasing from 413 to 321 individuals in the abandoned wet-type site. This may lead to a decrease in species richness. Mowing along with raking of mowed biomass may be a useful tool to restore degraded mountain grasslands and to remove accumulated litter from the stands.     

Year-round cattle and horse grazing supports the restoration of abandoned,dry sandy grassland and heathland communities by supressing Calamagrostis epigejos and enhancing species richness

The spread of competitive grasses, changes in species composition and vegetation structure are direct consequences of grassland and heathland abandonment. As an alternative to more costly management measures such as traditional pastoralism, year-round low-intensity grazing with large herbivores is increasingly used to restore and maintain semi-open habitats. However, the suitability of this grazing regime has not yet been investigated for long-abandoned, highly degraded but nutrient-poor sandy grassland and heathland communities. In particular, it is unclear if year-round grazing is suitable for preventing the further spread of highly competitive grasses such as Calamagrostis epigejos while simultaneously maintaining or improving characteristic species richness and vegetation structure. Hence, we conducted a comprehensive field study on two spatial scales (plot-level: 25 m², macroplot-level: 1 ha) to analyse the impacts of year-round low-intensity cattle and horse grazing on the development of the highly competitive grass Calamagrostis epigejos, as well as the vegetation structure and plant species richness of long-abandoned but nutrient-poor dry sandy grassland and heathland communities, their mosaics and Calamagrostis stands within an 800 ha heathland between 2008 and 2015. Finally, we assessed the local conservation status of the habitat types after seven years of grazing in comparison to long-abandoned sites.Grazing successfully reduced the coverage of Calamagrostis epigejos, whereby Calamagrostis stands developed towards species-rich sandy grasslands after seven years of grazing. In addition, the quality of the vegetation structure was improved by enhancing the proportion of bare soil, while litter and grass cover, litter thickness and height of the field layer as well as the coverage of ruderal indicators were significantly reduced on grazed sites in comparison to ungrazed sites in 2015. Moreover, we found an overall positive grazing effect on species richness: Total species number, number of target species as well as subordinated target species significantly increased within the vegetation types over time.Thus, year-round low-intensity cattle and horse grazing is a suitable management tool for restoring, maintaining and even improving long-abandoned, nutrient-poor sandy grassland and heathland communities, and thus to enhance the local conservation status of the habitat types. However, if there is a high initial cover of woody species (e.g. shrubs, tree rejuvenation), then an extensive shrub and tree clearance will be necessary, with manual shrub cutting being crucial to reduce the heavy regrowth of the woody species. In addition, a one-time mowing should be implemented in highly degraded heaths to facilitate the vegetative rejuvenation of degenerate stands of Calluna vulgaris, thus improving its attractiveness for the grazing animals.     

Feathermoss seedbeds facilitate black spruce seedling recruitment in the forest–tundra ecotone (Labrador,Canada)

As climate warms, conifers are expected to expand their ranges into alpine tundra where ecological factors such as seedbed availability, and post‐dispersal seed and seedling predation may control local recruitment. Seedbed composition may influence microhabitat, nutrients, physical structure, and predation level and, therefore, affect the success of conifer recruitment, thereby providing the template for future expansion. In the boreal forest, seedbed–seedling competition dominates such that seedbed removal increases black spruce recruitment. In the harsher climate of the Mealy Mountains boreal forest–tundra ecotone (Labrador, Canada) the Stress gradient hypothesis (SGH) predicts that facilitation may dominate seedbed–seedling interactions. This study investigated potential mechanisms of seedbed facilitation (temperature, water, nutrients, physical protection) in three conifer seedbeds (Pleurozium schreberi, Cladonia spp., bare soil) and examined whether seed predation and/or seedling herbivory varied among seedbeds over three years. Seed emergence was low overall (< 10% on all treatments), but highest on Pleurozium (6.3%), followed by bare ground (4.6%) and Cladonia (0.3%). Facilitation was observed between Pleurozium and black spruce as seedling height increase (31%) and survival (55%) were highest; herbivory, seed predation and overwinter mortality were lowest compared to both Cladonia and bare ground seedbeds. Unlike in the closed canopy boreal forest, seedlings recruited poorly on bare soil as seedling height increase and survival were 20.5% and 26%. Temperature and water availability were similar across seedbeds, while nutrient availability was higher on Pleurozium. The physical structure of Pleurozium likely protects first to third‐year seedlings from temperature extremes and predators. As climate warms and seed availability increases, Pleurozium may facilitate black spruce recruitment and treeline expansion.     

Long‐term effects of the abandonment of grazing on steppe‐like grasslands

Question: What are the consequences of grazing abandonment on the Stipa lessingiana dominated steppe‐like grasslands? What is the relative importance of management and environmental factors in causing variation in species composition and abundance in the continuously grazed and abandoned grassland stands? Location: Transylvanian Lowland, Romania. Methods: Repeated vegetation mapping of a grassland stand, where grazing was abandoned 35 years ago; re‐sampling six grassland stands surveyed 29–57 years ago. For revealing long‐term changes in species composition and rank abundance PCoA ordination was applied. The relative importance of management and environmental factors in structuring vegetation were explored by CCA ordination. Diversity, evenness and the relative number and abundance of red‐listed species were compared between managed and abandoned stands. Results: Our results pointed out that grasslands which were formerly grazed and dominated by S. lessingiana, in the long‐term absence of grazing, have been transformed into a S. pulcherrima dominated type. Management, probably by creating bare surfaces and preventing litter accumulation, had the strongest effect on the species composition and abundance in the grasslands. Abandoned grassland stands had lower diversity and evenness compared to continuously grazed stands. While at the same time, the relative number of threatened, rare species did not differ between managed and abandoned sites. Conclusion: Maintaining extensively grazed, as well as un‐managed, Stipa dominated grasslands would be important in order to create various habitat conditions for plant species, especially threatened and rare species, and promote diversity on the landscape scale.     

Flooding and grazing promote germination and seedling establishment in the perennial grass Paspalum dilatatum

Seed germination and seedling emergence are key processes for population recruitment. Flooding and grazing are disturbances forming gaps that may strongly influence recruitment patterns in space and time, but their combined effects and action mechanisms have rarely been addressed. In this study we analysed the effects of microhabitat conditions associated with winter flooding and spring‐summer defoliation on seed germination and seedling establishment of Paspalum dilatatum, a dominant perennial C₄ grass in native grasslands of the Flooding Pampa, Argentina. The dynamics of seedling emergence from natural seed banks and buried seeds was studied in a factorial experiment with flooding and defoliation treatments applied to soil monoliths (mesocosms) collected from natural grassland. Additional laboratory experiments were applied to investigate seed germination under different combinations of temperature, light quality and simulated flooding. Seed germination and seedling emergence of P. dilatatum were promoted by flooding and high intensity defoliation. Gaps generated by flooding were maintained by high intensity defoliation exercising a synergistic effect on survival seedlings. Flooding resulted in the breaking of seed dormancy and higher germination rates associated with alternating temperature and the activation of the phytochrome system. Our results indicate that microhabitat conditions associated with the disturbances forming gaps, such as flooding and heavy grazing, synergistically promote the recruitment process of this dominant grass species.     

Shifts in N and P Budgets of Heathland Ecosystems: Effects of Management and Atmospheric Inputs

In the present study we analyzed the combined effects of management (grazing, mowing, prescribed burning, sod-cutting) and atmospheric deposition on N and P budgets of heathland ecosystems (Lüneburger Heide nature reserve; N Germany). We hypothesize that management measures such as grazing and mowing can accelerate a deposition-induced imbalance of N and P pools as a result of a disproportionally high output of P. We analyzed management and deposition affected input–output flows of N and P and related them to changes in the nutritional status of Calluna vulgaris 5 years after treatment application. We found that grazing and mowing caused the highest net loss of P due to high P concentrations in the aboveground biomass. In contrast, prescribed burning only slightly affected P pools, as P remained in the system due to ash deposition. Management-mediated effects on N and P pools were mirrored in the nutritional status of Calluna vulgaris: at the grazed and mown sites, the P content of current season’s shoots significantly decreased within 5 years after treatments, whereas the N content remained unchanged. We conclude that grazing and mowing can accelerate declining availability of P and, thus, accelerate a deposition-induced shift from N- to P-limited plant growth in the medium term. In the face of ongoing atmospheric N loads management schemes need to combine high- and low-intensity measures to maintain both a diverse structure and balanced nutrient budgets in the long term.     

Grazing buffers the effect of climate change on the species diversity of seedlings in an alpine meadow on the Tibetan Plateau

Climate change predominated by warming over the past decades has affected plant biodiversity, distribution, and ecosystem functioning in alpine grasslands. Yet, little is known about the interactive effect of climate change and grazing on biodiversity and ecosystem functioning. Here, we conducted a vegetation translocation experiment (ten soil‐vegetation blocks were translocated from high‐altitudinal site 3,245 m to low‐altitudinal site 3,045 m) combined with grazing treatment in an alpine meadow on the Tibetan Plateau. The results showed that (a) translocation induced effect of climate change from harsh, high‐altitudinal site to benign, low‐altitudinal site significantly promoted species richness, and density of asexual and sexual seedling, with an increase in the proportion of asexual recruitment to sexual recruitment; (b) grazing decreased the proportion of asexual seedling to sexual recruitment within community, led to a shift in the dominant plant functional groups from graminoids and legumes to forbs; and (c) grazing partly offset the increased species richness of seedling, but not seedling density, induced by climate change. These findings suggest that moderate grazing may buffer the effect of climate change on the plant community composition, and thus, functional role in alpine meadows. Further understanding the influence of climate change on grassland ecosystems needs to consider the non‐additive effect of grazing and climate change to sustainability of grassland services.     

Intrinsic biotic factors and microsite conditions drive seedling survival in a species with masting reproduction

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Year-to-year Oscillations in Demography of the Strictly Biennial <Emphasis Type="Italic">Pedicularis sylvatica</Emphasis> and Effects of Experimental Disturbances

In 1998–2001, I studied disturbance effects on the population structure and dynamics of a grassland strict biennial Pedicularis sylvatica, and on the species demography (monthly dynamics of seedling recruitment in 1998 and within- and between-year survival in 1998–2000). In two Czech populations, I established three experimental disturbance regimes: (1) a gap treatment, that simulated grazing by clipping vegetation and creating small gaps, (2) a mowing treatment, where I clipped the vegetation, and (3) a no management treatment, where I left the vegetation untreated. The number of recruiting seedlings varied greatly by year, and demographic structure of populations showed significant year-to-year oscillations in mean seedling numbers, from low (3 ± 0.7 s.e. per 0.25 m² plot) to high (103 ± 20). Inversely in the same years and plots, mean adult numbers in populations oscillated from high (12 ± 2) to low (0.7 ± 0.3). Disturbance effects were only important for seedling recruitment in early census dates in all years. In 1998, most seedlings recruited in April–May in gaps in both sites, but most died before winter. Within- and between-year survival was not affected by disturbance regimes but fluctuated significantly among years. Between-year survival increased with increasing size of the overwintering bud and was higher in disturbance treatments. Since the oscillations in population structure did not significantly vary in response to experimental disturbances, population dynamics may be driven endogenously rather than by disturbance events. The weak disturbance effects on species demography may also indicate population resilience to changes in habitat quality. However, since disturbances promoted seedling recruitment, grazing or mowing regimes are strongly recommended, as they create regeneration opportunities and maintain habitat quality, meeting the species long-term conservation goals.     

Fire and flood: Soil‐stored seed bank and germination ecology in the endangered Carrington Falls Grevillea (Grevillea rivularis,Proteaceae)

Abstract Seed germination is dependent on the interaction between the dormancy state of a seed and the presence of favourable environmental conditions. Thus, the spectacular pulse of seedling recruitment in many Australian vegetation communities following disturbances such as fire can be attributed to changes in microsite conditions and/or the dormancy‐breaking effect of the disturbance on accumulated seed banks. Grevillea rivularis is a threatened species endemic to the area immediately above Carrington Falls in the NSW Southern Highlands. Most of the population is confined to the riparian vegetation zone in woodland and heath, and is therefore subject to periodic disturbance from fire and flood. For this species, a pulse of seedling recruitment has been recorded after fire, flood and mechanical soil disturbance. The aims of this study were to examine the density and vertical distribution of the soil‐stored seed bank and to investigate the role of heat and scarification as cues for germination of fresh and soil‐stored seed. There was a large seed bank under the canopies of established individuals (194 ± 73 seeds m^?2) and most seeds were found in the 0–2 cm and leaf‐litter layers of the soil profile. The germination response of soil‐stored and fresh seed was examined using a hierarchical series of laboratory experiments. Seeds of G. rivularis showed marked dormancy polymorphism. Thirty‐six percent of soil‐stored seed germinated without treatment, whereas no untreated fresh seeds germinated. Scarification or heating caused significant germination of dormant soil‐stored seed, but only scarification resulted in germination of dormant fresh seeds. These results highlight important differences in the dormancy state of soil‐stored and fresh seed. Thus, being a riparian species in a fire‐prone environment, the dormancy mechanisms in seeds of G. rivularis suit this species to disturbance by both fire and flood.     

The impact of grazing on plant communities,plant populations and soil conditions on salt marshes

Grazing an abandoned salt marsh causes retrogressive succession, since mid salt-marsh communities change into lower salt-marsh communities. Grazing and mowing are compared in detail. Both management practices enhance species diversity in an abandoned salt marsh. This can be attributed to the removal of litter. The finding that lower salt-marsh species appear more with grazing than with mowing or abandoning is not related to a higher soil salinity as compared to mowing or abandoning, but probably to locally baring of the soil by grazing animals. Only species of pioneer or unstable environments seem to have a persistent seed bank, for other species seed dispersal seems to be a limiting factor for their establishment.Nomenclature follows Heukels & van Ooststroom (1977) for species; Westhoff & den Held (1969) for syntaxa.Mrs R. Rusthoven analyzed the soil samples, Mr E. Leeuwinga drawed the figures, and Mrs J. O'Brien corrected the English text.     

Restorative mowing on an abandoned semi‐natural meadow: short‐term and predicted long‐term effects

Abstract. When management, in the form of cattle grazing and mowing, ceases the abundance of competitively superior plant species tends to increase in abandoned semi‐natural meadows. Litter accumulation elevates the soil nutrient levels and hinders seedling recruitment. We surveyed changes in plant cover and species composition of a formerly grazed meadow in permanent plots for six years. Some plots were unmown, while others were mown and raked annually in August. The cover of grasses decreased and herb cover remained unchanged regardless of the treatment. Mowing and raking significantly reduced litter accumulation and increased the number of ground layer species. The expected long‐term effects of abandonment and restorative mowing were studied by calculating the transition probabilities for unmown and mown plots and simulating the course of succession as projected by the transition matrices. During a simulation period of 30 yr, abandonment led to (1) a decrease in the cover of small herbs, (2) a slight increase in the cover of tall herbs and (3) a slight decrease in the cover of grasses. In contrast, the cover of small herbs on the mown plots remained unchanged or slightly increased during the course of simulation. These results suggest that mowing late in the season is primarily a management tool for the maintenance of the existing species diversity and composition. However, it may not be an effective restorative tool to induce overall changes in the resident vegetation of abandoned grass‐dominated meadows. Grazing or mowing early in the season may be more effective in this respect. Consequently, mowing early or, alternatively, late in the season may provide management strategies for the maintenance and restoration of species diversity, respectively.     

Response of a rare herb (Trioncinia retroflexa) from semi‐arid tropical grassland to occasional fire and grazing

Trioncinia retroflexa (Asteraceae) is a rare perennial herb endemic to Dichanthium‐dominated grasslands on basaltic soils in central Queensland. Trioncinia lives for approximately 5 years and some seed remains viable in the soil for at least 18 months. Population densities increased sixfold over 4 years, coinciding with recovery during a period of above‐average rainfall after a 4‐year drought preceding this study. The species’ lifespan, which can exceed 5 years, coupled with its extended seed‐bank viability ensures that populations can endure drought despite low levels of seedling recruitment. The restricted occurrence of the species to spasmodically grazed stock routes provides evidence that Trioncinia is sensitive to the continuous grazing that typically occurs in paddocks. The hypothesis that the species requires occasional disturbance for survival was experimentally tested. Recruitment was depressed with burning and inflorescence production enhanced with both burning and simulated intense spasmodic grazing after the first application of treatments. However, these effects were not evident after a second application of the treatments and there were no significant effects of treatment on population densities at the completion of the 4‐year experiment. Although not requisite, sporadic dry‐season grazing and burning of these areas would appear to be compatible with the survival of Trioncinia. This project highlights the value of stock routes for rare plant conservation.     

Do we need livestock grazing to promote <Emphasis Type="Italic">Polylepis australis</Emphasis> tree recruitment in the Central Argentinean Mountains?

South American Polylepis mountain forests are endangered due to centuries of logging, fire clearance, and intensive livestock grazing. Polylepis australis (Rosaceae) dominates the tree canopy in the Central Argentinean Mountains, where livestock have been excluded or reduced to very low densities over wide areas. Lowered plant and bird diversity in these abandoned grazing areas suggest that some livestock grazing may be beneficial for conservation purposes. Our study aimed to determine whether this may also be true for forest regeneration. In 300 plots of 1 m² distributed in sub-regions of high to moderate grazing pressure as well as grazing exclusion, we recorded the presence of P. australis seedlings and grazing indicators. Topographical parameters as well as vegetation and soil characteristics were also assessed. Seedling frequencies were highest in the region with moderate grazing, intermediate with grazing exclusion, and the lowest with high grazing pressures. Logistic regression models revealed that seedling occurrence was highest close to seeder trees, with intermediate litter coverage and at intermediate altitudes above sea level. Since grazing ultimately affects seeder tree occurrence through browsing and reduces litter cover and predominates in higher areas, we conclude that grazing is an important driving factor for P. australis regeneration. We confirm previous studies determining high grazing pressure to be detrimental for P. australis regeneration, but also provide data suggesting that its complete exclusion may not be recommendable either. Management should aim to alternate between a moderate grazing intensity to promote seedling recruitment, with subsequent exclusion to accelerate the growth of the established seedlings.     

Vegetation changes following sheep grazing in abandoned mountain meadows

Abstract. Sheep grazing was investigated as an alternative to traditional management of meadows in the Krkono?e Mts. Until the second World War these meadows were mown in mid‐summer and grazed by cattle for the rest of the season. Subsequent abandonment of the meadows has resulted in decreasing species richness. Degradation phases of the former communities have been replacing the original species‐rich vegetation. Significant changes were apparent six years after the introduction of sheep grazing. In grazed plots the proportion of dominant herbs (Polygonum bistorta and Hypericum maculatum) decreased and grasses (Deschampsia cespitosa, Festuca rubra, Agrostis capillaris, Anthoxanthum alpinum) increased. The increase in grasses was positively correlated with an increase in several herbs. The proportion of some herbs increased despite being selectively grazed (Adenostyles alliariae, Melandrium rubrum, Veratrum lobelianum). Any losses caused by grazing of mature plants were probably compensated by successful seedling establishment. Cessation of grazing resulted in significant changes in vegetation within three years. The cover of nitrophilous tall herbs and grasses (e.g. Rumex alpestris, Holcus mollis, Deschampsia cespitosa, Geranium sylvaticum) increased in the abandoned plots. In the plots grazed for nine years cover of species‐rich mountain meadow species increased (e.g. fine‐leaved grasses, Campanula bohemica, Potentilla aurea, Viola lutea, Silene vulgaris). The main conservation risk is the expansion of a competitive species with low palatability, Deschampsia cespitosa. This species can be suppressed by a combination of grazing and mowing. In order for grazing to be effective, the number of sheep should be proportional to meadow production. This may be difficult to maintain as production is variable and is impossible to predict at the beginning of a growing season. A large part of the biomass may thus remain intact in some years. Negative effects of grazing may be, at least partly, eliminated by a combination of cutting and grazing.     

The Nature of Seedling Assemblages in a Fragmented Tropical Landscape: Implications for Forest Regeneration

Whether aging forest fragments are able to recover original assemblages or progressively move toward impoverished successional stages remains as an open question. This study tested the hypothesis that seedling assemblages in forest fragments differ from those across mature forest stands and examined to what extent the uncovered patterns supported the notion that edge‐affected habitats tend to support impoverished tree assemblages dominated by pioneer species. We contrasted a series of small forest remnants (3–91 ha) to old‐growth stands located in the largest (ca 3500 ha) and best preserved forest remnant in northeastern Brazil and found that tree seedling assemblages inhabiting forest fragments exhibited reduced species richness (up to 50%) at different spatial scales in comparison to seedling assemblages in mature forest and adult assemblages in both fragments and mature forest stands. Moreover, ordination analyses clearly segregated fragment seedling assemblages in taxonomic/functional terms and segregation correlated to the richness of pioneer species. Seedlings of pioneer species and those bearing medium‐sized seeds (0.6–1.5 cm) increased in fragments, whereas large‐seeded species (1.5–3.0 cm) were reduced by more than a half. Such a multiple‐scale replacement of the old‐growth flora by pioneers was also confirmed by an indicator species analysis and the resulting pioneer indicator species. Our results suggest that small forest fragments support impoverished and distorted seedling assemblages. This floristic/functional drift implies that forest remnants or edge‐affected habitats tend to be dominated by a small set of pioneer tree species rather than supporting a substantial portion of the old‐growth flora as do mature forest stands.