Long‐term vegetation changes in experimentally grazed and ungrazed back‐barrier marshes in the Wadden Sea

Abstract. Vegetation succession in three back‐barrier salt marshes in the Wadden Sea was studied using a data set comprising 25 years of vegetation development recorded at permanent quadrats. The effect of livestock grazing on succession was assessed by comparing quadrats where grazing was experimentally prevented or imposed. We studied changes at the species level as well as at the level of the plant community. Special attention is given to effects on plant species richness and community characteristics that are relevant for lagomorphs (hares and rabbits) and geese. Inundation frequency and grazing were most important in explaining the variation in species abundance data. The three marshes studied overlap in the occurrence of different plant communities and the observed patterns were consistent between them. Clear differences in frequency and abundance of plant species were observed related to grazing. Most plant species had a greater incidence in grazed treatments. Species richness increased with elevation, and was 1.5 to 2 × higher in the grazed salt marsh. Grazing negatively influenced Atriplex portulacoides and Elymus athericus, whereas Puccinellia maritima and Festuca rubra showed a positive response. The communities dominated by Elymus athericus, Artemisia maritima and Atriplex portulacoides were restricted to the ungrazed marsh. Communities dominated by Puccinellia maritima, Juncus gerardi and Festuca rubra predominantly occurred at grazed sites. As small vertebrate herbivores prefer these plants and communities for foraging, livestock grazing thus facilitates for them.     

Osmoregulation in halophytic higher plants: a comparative study of soluble carbohydrates, polyols, betaines and free proline

Abstract. The levels of soluble carbohydrates, polyols, betaines and free proline have been determined in different organs of sixteen plants collected on coastal salt marshes. Among the carbohydrates, sucrose, fructose and glucose accumulated at quite high levels. Sucrose is particularly abundant in the monocots Juncus maritima, Phragmites communis and Scirpus maritimus. Maltose is quite abundant in Atriplex hastata and rhamnose in Plantago maritima roots. High levels of polyols were detected in Aster tripolium, Juncus maritimus, Plantago maritima and Phragmites communis. According to their capacity to accumulate carbohydrates and (or) nitrogenous solutes, halophytic higher plants can be divided into three main groups: (1) species producing high levels of soluble carbohydrates only, (2) species accumulating both carbohydrates and nitrogenous compounds, (3) species producing more nitrogenous solutes than soluble carbohydrates. The possible functions of these various organic solutes, including a role in equalizing the relative water potentials of cytoplasm and vacuole and to lower the internal potential, are discussed.     

Na+/H+ antiport activity in tonoplast vesicles from roots of the salt-tolerant Plantago maritima and the salt-sensitive Plantago media

Plantago species differ in their strategy towards salt stress, a major difference being the uptake and distribution of Na⁺ ions. A salt-sensitive ( Plantago media L.) and a salt-tolerant ( P. maritima L.) species were compared with respect to Na⁺/H⁺ antiport activities at the tonoplast. After exposure of the plants to 50 m M NaCl for 6 days isolated tonoplast vesicles of P. maritima showed Na⁺/H⁺ antiport activity with saturation kinetics and a K_m of 2.4 m M Na⁺, NaCl-grown P. media and the control plants of both species showed no antiport activity. Selectivity of the antiport system for Na⁺ was high and was determined by adding different chloride salts after formation of a Δ pH in the vesicles. Specific tonoplast ATPase activities were similar in the two species and did not alter after exposure to NaCl stress.     

四种植物粘液繁殖体粘液的比较研究

对百里香(Thymus serpyllum)、平车前(Plantago depressa)、盐生车前(P．maritima)、野亚麻(Linum stelleroides)进行了粘液繁殖体粘液情况比较．以在水浸和浇水条件下植物种子粘沙量的多少衡量粘液量．结果表明,对于不同浸水时间处理,野亚麻和平车前未表现明显差异,盐生车前和百里香有随浸泡时间加长而粘液溶出量增多的趋势．对于不同浇水量处理,4种植物均有随浇水量增多而粘液增多的倾向．浸泡80min后,盐生车前种子的粘液粘沙使重量达原重的60多倍,平车前种子达原重的10倍左右,百里香和野亚麻种子达原重的4～6倍左右．浇水8mm后,盐生车前种子的粘液粘沙使重量达原重的20多倍,平车前种子达原重的6～10倍左右,百里香和野亚麻种子达原重的2～7倍左右．将各种处理平均,得到各种植物粘沙种子百分率为：野亚麻67．7％,百里香94．5％,平车前97．7％,盐生车前99．5％．     

Long-term changes (1953–1990) in the salt marsh vegetation at the Boschplaat on Terschelling in relation to sedimentation and flooding

Long-term vegetation changes in permanent plots along two transects from the low to the high salt marsh at the Boschplaat on Terschelling between 1953 and 1990, were analysed in relation to sedimentation and flooding. In both transects, the number of plant species decreased between 1953 and 1990. In lower parts of the two transects the dominant plant species of the vegetation changed from Puccinellia maritima in 1953/54 to Limonium vulgare in 1980 to Atriplex portulacoides in 1990. The increase in A. portulacoides between 1980 and 1990 coincided with an increase in the thickness of the silt layer, caused by a sedimentation rate of about 5 mm per year. This sedimentation led to an increase in elevation but not to large changes in flooding frequency between 1953 and 1990, probably due to a sea level rise during the same period.In the higher parts of the salt-marsh transects Elymus athericus strongly increased and this species became dominant in 1980 and 1990. In these parts of the salt marsh, a small increase in elevation, in thickness of the silt layer, and in flooding frequency occurred between 1953 and 1990.The described changes in vegetation are discussed in terms of general succession of salt-marsh vegetation in relation to flooding and sedimentation.     

Species properties and recovery from disturbance: Forest herbs buried by volcanic tephra

Question: How do forest herb species differ from each other in their spatial and temporal dynamics during recovery from volcanic disturbance, and how are dynamics related to species traits? Location: Northeast of Mount St. Helens, Washington, USA. Methods: Following deposition of volcanic tephra in 1980, we measured herb density and cover in permanent 1‐m² plots during 1980‐2005 in three old‐growth forests with differing tephra depths. For 26 species, we calculated the frequency of plots with residuals (individuals that survived the eruption) versus re‐establishment on the tephra, timing of establishment, turnover, influence of nearby conspecific plants, importance of three components of cover increase, and relationship of flowering frequency to succession. Results: Tephra depth affected species behavior. Deep tephra produced fewer residuals, a greater increase in shoot size, and more shoot turnover; favored species that established late; and allowed establishment of early seral herbs. Nearby presence of conspecifics increased permanence of first establishment and rate of plot occupancy. Most species spread significantly in deep tephra but not in shallow tephra. Among species, frequency of flowering increased with fewer residuals, later establishment, and higher turnover. Species behavior seldom differed among growth forms based on leaf longevity and vegetative spread. Conclusion: Population dynamics at the small‐plot scale differed from those of the entire population. The timing and permanency of establishment and mechanism of expansion differed among species and with tephra depth. There was some consistency among species with similar habitat breadth and degree of flowering, but little consistency associated with the usual growth form classification.     

Male sterility, protogyny, and pollen-pistil interference in Plantago maritima (Plantaginaceae), a wind-pollinated, self-incompatible perennial

Evolution and maintenance of male sterility in seed plants can be explained by the maternal inheritance of mitochondria, which encode the trait, and by adaptive functions that enhance female fecundity in male-sterile compared to hermaphrodite individuals. Protogyny and male sterility can independently decrease the negative effect of pollen-pistil interference in self-incompatible species. In Plantago maritima, which possesses both traits, protogyny increases seed set in hermaphrodite individuals. This is shown both by a significantly positive association between seed set and retarded dehiscence of the anthers and by a more than 50% reduction in seed set following self-pollination. Male sterility does not seem to increase seed set further, as female and hermaphrodite plants do not differ significantly in mean seed set per capsule. Bagging experiments demonstrate strong self-incompatibility in the study populations. Hence, in P. maritima male sterility seems neither to prevent selfing nor to reduce the effect of pollen-pistil interference. Females had significantly larger stigmas than hermaphrodites, but seed set varied negatively with stigma length among females, indicating that the evolution of unisexuality in P. maritima is not due to prefertilization sex allocation. I therefore conclude that the genetical system of nucleocytoplasmic determination of gender is the main cause for maintenance of male sterility in P. maritima.     

The impact of some environmental factors on the establishment of Plantago maritima seedlings and juveniles along a distributional gradient

The establishment of Plantago maritima seedlings and juveniles along a distributional gradient was investigated with pantograph technique. Mortality was closely dependent on vegetational characters such as cover, height of vegetation and amount of litter. Superimposed on these factors was mortality due to flooding. The density dependent mortality of seedlings was also investigated. The number of surrounding seedlings seemed to be of vital importance for survival, i.e. self thinning occurred most likely as a result of competition for light. The establishment and survival of seedlings cannot fully explain the distribution of adults.     

Unpreferred plants affect patch choice and spatial distribution of European brown hares

Many herbivore species prefer to forage on patches of intermediate biomass. Plant quality and forage efficiency are predicted to decrease with increasing plant standing crop which explains the lower preference of the herbivore. However, often is ignored that on the long-term, plant species composition is predicted to change with increasing plant standing crop. The amount of low-quality, unpreferred food plants increases with increasing plant standing crop. In the present study the effects of unpreferred plants on patch choice and distribution of European brown hare in a salt-marsh system were studied. In one experiment, unpreferred plants were removed from plots. In the second experiment, plots were planted with different densities of an unpreferred artificial plant. Removal of unpreferred plants increased hare-grazing pressure more than fivefold compared to unmanipulated plots. Planting of unpreferred plants reduced hare-grazing pressure, with a significant reduction of grazing already occurring at low unpreferred plant density. Spatial distribution of hares within this salt-marsh system was related to spatial arrangement of unpreferred plants. Hare-grazing intensity decreased strongly with increasing abundance of unpreferred plants despite a high abundance of principal food plants. The results of this study indicate that plant species replacement is an important factor determining patch choice and spatial distribution of hares next to changing plant quality. Increasing abundance of unpreferred plant species can strengthen the decreasing patch quality with increasing standing crop and can decrease grazing intensity when preferred food plants are still abundantly present.     

Characteristics of seedling survival in habitats of hill and gully slopes in hill-gully Loess Plateau region of northern Shaanxi

Aims Seedling is the fundament of vegetation restoration succession and plays a very important role in ecosystems. The objective of this paper was to explore the characteristics of seedling survival in habitats of hill and gully slopes in a hill-gully Loess Plateau region.
Methods Fifteen permanent plots in Zhifanggou and Songjiagou watershed in Ansai County were established for sentinel dynamic monitoring, and one-way ANOVA and hierarchical cluster analysis were used to analyze seedling density and survival rate in different habitats.
Important findings There were significant differences in the characteristics of seedling survival among different habitats, with smaller seedling density and higher survival rates observed on the sunny slopes and larger seedling density but lower survival rate found on the shady slopes. In competition for survival, Artemisia gmelinii, Potentilla tanacetifolia, and Heteropappus altaicus etc. took advantage of quality and were characterized by a higher seedling survival rate, while Artemisia scoparia, Ixeris chinensis, Siphonostegia chinensis etc. adopted a strategy of “quantity” and characterized by a higher seedling density. The same species in different habitats had different survival curves, and the same survival curves in different habitats applied to different species. The seedlings of Artemisia gmelinii, Potentilla tanacetifolia, Stipa bungeana, Heteropappus altaicus, and Lespedeza davurica etc. had a strong survival capability in the rainy season and were easy to overwinter successfully, whereas the seedling survival capability in Artemisia scoparia, Dracocephalum moldavica, and Artemisia hedinii etc. was strong priorto the rainy season but weak in winter. The characteristics of seedling survival in different micro-environments also differed. A change in micro-environment affected seedling growth, survival, and overwintering to some extent. Thus, a proper tending for seedlings according to the survival characteristics of species is conducive to the seedling establishment and vegetation succession in the hill-gully Loess Plateau region.     

Flood‐deposited wood creates regeneration niches for riparian vegetation on a semi‐arid South African river

Question : The formation of large woody debris (LWD) piles during floods has significant impacts on riparian succession through pioneering plants often establishing in association with wood. We assess the importance of LWD for seed regeneration of riparian plants after a century‐scale flood disturbance in a semi‐arid environment. Location : The Sabie River within Kruger National Park in the semi‐arid northeast of South Africa. Methods : Our approach was to quantify the riparian soil seed bank, to record the frequency of establishment of riparian plants in woody debris piles, and to conduct experimental out‐plantings of common riparian trees in plots with and without LWD. Results : We found the abundance and diversity of seedlings were higher in soils taken from wood piles than from open reference areas, and most seedlings were herbaceous species. Surveys indicated that numbers of seedlings recorded within woody debris were significantly greater than in open reference areas or within established vegetation. Seedling establishment in various cover‐types also varied for different riparian tree species. Experimental out‐planting of seedlings of two riparian tree species (Philenoptera violacea and Combretum erythrophyllum) revealed that, after 433 days, planted seedlings survived only in woody debris piles. Conclusion : LWD formed after a large flood creates heterogeneous patches that may influence post‐disturbance regeneration of riparian vegetation by providing a variety of environmental niches for seedlings establishment. We suspect that higher seedling survival in LWD is due to increased moisture (particularly in the dry season) and nutrients, and protection from seasonal flooding and herbivory.     

Threats and benefits of invasive alien plant species on pollinators

Invasive alien plant species are usually disliked due to their high pressure on native communities. However, their ecological effects on pollinators are complex: some species provide abundant floral resources, boosting the number of pollinators, while they often disrupt plant-pollinator interactions by outcompeting native plants. Our direct knowledge is mainly based on single-species studies, while understanding the mechanism of these complex ecological interactions needs multi-species field-based approaches. It is also imperative to clarify the pros and cons of invasive plants and drivers of invasion from the perspective of pollinators. We conducted a standard protocol-driven regional study in Central and Eastern Europe, comparing 6-7 invaded and non-invaded sites of 12 herbaceous invasive plant species. We sampled floral resources, bees, and hoverflies before and during the flowering of the invasive plants. We analysed the effects of plant invasion at the invasive plant species level and in combined analyses, and tested whether the life span (perennial vs. annual) and flowering time (early-, middle-, and late-flowering) of invasive plants affect the abundance, species richness, diversity and species composition of native plants and pollinators. The combined analyses showed lower abundance and species richness of flowering plants and pollinators before, and higher abundance of both during the flowering of invasive plants in invaded sites. However, invasive plants had significant species-specific effects. Perennial invasive plants had a stronger negative impact on floral resources and pollinators already before their flowering compared to annuals. Flowering time of invasive plants affected the pollinator guilds differently. We suggest that in certain critical time periods of the year, invasive plants might provide the dominant foraging resources for pollinators in an invaded ecosystem. But, they also often cause significant losses in native floral resources over the year. Instead of simple eradication, careful preparation and consideration might be needed during removal of invasive plants.     

Specific leaf area as a superior predictor of changes in field layer abundance during forest succession

Question : How accurately can a suite of suggested functional traits predict plant species response to succession from semi‐open woodland to closed deciduous canopy forest? Location : Southeastern Sweden. Methods : Abundance of 46 field‐layer plant species in a temperate deciduous forest, measured as frequency of occupied plots, was estimated in 1961, 1970 and 2003. Abundance change over time across species was tested for correlations with functional traits and literature information on habitat preference. Results : Increase in abundance was positively correlated with specific leaf area (SLA), weakly negatively correlated with seed mass and not significantly correlated with plant height or start, peak and length of the flowering period. Change in abundance was correlated with the Ellenberg light indicator value, whereas no correlations were found with Ellenberg values for nitrogen, calcium and moisture, or forest preference according to the literature. Conclusions : SLA was a better predictor of how field layer plants responded to succession from semi‐open woodland to closed canopy forest than empirically‐derived measures of habitat preference. The same holds for SLA in relation to seed size, indicating that interactions in the established life‐cycle phase are more important than the recruitment phase for species response to succession.     

Dynamics of Plantago maritima along a distributional gradient: A demographic study

The dynamics of a Plantago maritima population was studied along a distributional gradient on a sea shore meadow during four years. The dynamics of the population varied along the gradient. In the lower parts there was a high flux with high mortality due to flooding but also a higher reproductive effort and good establishment. In the upper parts the flux was slower with lower reproductive effort and lower seedling success but instead longer lifespans. Population growth in these upper areas was primarily restricted by competition for light which prevented flowering and lowered the seedling success. Both cover values and the number of species decreased seawards and consequently the strength of competition. Simultaneously the risk of flooding increased. Thus the density peak was found at the intersect of these two variables. The plants showed differences in behaviour along the gradient in reproductive effort, growth rate, phenology etc. Whether this variation was phenotypical or genotypical is not known.     

Diversity of climbing seed plants and their reproductive habit in a karst seasonal rain forest in Nonggang,Guangxi, China

Aims Diversity of climbing seed plants and their reproductive habits and characteristics are central for the understanding of community structure and dynamics of forests and hence are important for forest protection. However, little is known about the climbing seed plants in northern tropical karst seasonal rain forests. Here, using the data of the species diversity and reproductive habits of climbing seed plants in Nonggang, Guangxi, China, we aim to 1) explore the species diversity and distribution of climbing seed plants in northern tropical karst seasonal rain forests, 2) study the flowering and fruiting phenology and 3) the associations of reproductive characteristics to the environment. Methods Species composition, preferred habitat, flowering time, fruiting time and fruit types of climbing seed plants were surveyed. The seasonality of flowering and fruiting were analyzed by concentration ratio and circular distribution. Climbing seed plants were divided into three groups according to their growth forms and places in spatial forest structure: bush ropes, herbaceous vines and lianas. Monthly flowering ratios, fruiting ratios, fruit types and their ratios in different groups were determined. These relationships of flowering ratio, fruiting ratio, fruit type and its ratio to meteorological factors were investigated using Pearson correlation analysis. Important findings There were a total of 333 species of climbing seed plants in Nonggang karst seasonal rain forest, belonging to 145 genera and 56 families. Bush ropes, herbaceous vines and lianas contained 119, 88 and 126 species, respectively. At species level, herbaceous vines were more abundance in valleys, while bush ropes and lianas were more abundance on slopes. Flowering and fruiting of climbing seed plants occurred seasonally, with flowering peaking in April to September, while fruiting peaking in July to December. The seasonality of flowering and fruiting in bush ropes was weaker than in herbaceous vines and lianas. Flowering ratio was significantly positively correlated with rainfall and air temperature, which suggest that flowering peaks in monsoon season. Peak time for fruiting was about three months later than the peak time of flowering, around the end of monsoon season. The ratio of samara species to all fruiting species in lianas was significantly positively correlated with wind speed, but negatively correlated with rainfall and air temperature. It showed that samara in lianas tended to occur in dry season with high wind speed. In conclusion, species diversity and the seasonal features of reproduction of climbing seed plants in Nonggang karst seasonal rain forest were closely related to the spatial and temporal variations of habitat resources.     

Effects of selective grazing by cattle on the reproduction of Plantago maritima

The grazing areas of cattle in a Baltic sea-shore meadow changed during the summer. The effects of this on the demography of Plantago maritima was studied. This species is distributed over most parts of the area and suffers differently from grazing in different areas. It was found that the losses of flowers due to grazing, was severe and that the density peak of Plantago maritima coincides with the least grazing intensity. Flower-spikes established in different time-periods are disproportionally represented as seed-dispersers and this may be of importance in regeneration since early and late flowers bear seeds of different size.     

Long day plants and the response to global warming: rapid evolutionary change in day length sensitivity is possible in wild beet

Day length is a key factor in flowering induction in many plant species in a seasonal environment with flowering induction usually happening at shorter day lengths in lower latitudes. Now, the climate changes systematically at a considerable speed due to global warming. As a consequence, earlier flowering will be selected for in long day plants by favouring a lower threshold for day length sensitivity, on the condition of available genetic variability. Here, we show that there is considerable genetic variation for day length sensitivity in our study species, the seabeet Beta vulgaris subsp. maritima. In the northernmost natural populations without vernalization requirement, in southwest France, the necessary day length for flowering induction could be reduced by artificial selection in <10 generations from >13 h to <11 h, the latter value corresponding to populations in the Beta-species complex from Northern Africa and the eastern part of the Mediterranean tested under the same conditions. A quantitative genetic analysis provided evidence of a gradual change without detectable major genes. Additional experiments were carried out to separate the response to photoperiod from age and energy effects. A certain effect of energy availability has been found, whereas age effects could be excluded. These results indicate a considerable potential for evolutionary change in adjusting flowering time in a changing climate.     

Flowering phenology as a functional trait in a tallgrass prairie

? The timing of flowering is a critical component of the ecology of plants and has the potential to structure plant communities. Yet, we know little about how the timing of flowering relates to other functional traits, species abundance, and average environmental conditions. ? Here, we assessed first flowering dates (FFDs) in a North American tallgrass prairie (Konza Prairie) for 431 herbaceous species and compared them with a series of other functional traits, environmental metrics, and species abundance across ecological contrasts. ? The pattern of FFDs among the species of the Konza grassland was shaped by local climate, can be linked to resource use by species, and patterns of species abundance across the landscape. Peak FFD for the community occurred when soils were typically both warm and wet, while relatively few species began flowering when soils tended to be the driest. Compared with late-flowering species, species that flowered early had lower leaf tissue density and were more abundant on uplands than lowlands. ? Flowering phenology can contribute to the structuring of grassland communities, but was largely independent of most functional traits. Therefore, selection for flowering phenology may be independent of general resource strategies.     

Smaller species experience mild adversity under shading in an old‐field plant community

Plant competition experiments commonly suggest that larger species have an advantage, primarily in terms of light acquisition. However, within crowded natural vegetation, where competition evidently impacts fitness, most resident species are relatively small. It remains unclear, therefore, whether the size advantage observed in controlled experiments is normally realized in habitats where competition is most intense. We characterized the light environment and tested for evidence of a size advantage in competition for light in an old‐field plant community composed of perennial herbaceous species. We investigated whether larger species contributed to reduced light penetration (i.e., greater shading), and examined the impact of shade on smaller species by testing whether their abundance and richness were lower in plots with less light penetration. Light penetration in plots ranged from 0.3% to 72.4%. Significant effects were more common when analyses focused on small plants that reached reproduction (i.e., flowering rooted units); focusing on only flowering plants (i.e., excluding nonflowering rooted units) can clarify community patterns. Plots with a greater mean species height had significantly lower light penetration, and plots with lower light penetration had significantly lower flowering abundance and richness of small species. However, the impact of shade on the flowering abundance and richness of small species was relatively small (R ² values between 8% and 15%) and depended on how we defined “small species.” Synthesis: Our results confirm that light penetration in herbaceous vegetation can be comparable to levels seen in forests, that plots with taller species cast more shade, and that flowering smaller species are less abundant and diverse in plots where light penetration is low. However, variation in mean plot height explained less than 10% of variation in light penetration, and light penetration explained between 5 and 15% of variation in the flowering abundance and richness of small species. Coupled with the fact that flowering small species were present even within the most heavily shaded plots, our results suggest that any advantage in light competition by large species is limited. One explanation is that at least some small species in these communities are shade‐tolerant. Shade tolerance in predominantly herbaceous communities, particularly among small plant species, requires further research.     

陕北撂荒地上优势蒿类叶片解剖结构及其生态适应性

对陕北丘陵区撂荒地上处于自然恢复演替不同时期的3种优势种蒿类铁杆蒿（Artemisia gmelinii Web．）、茭蒿（Artemisia giraldii Pamp．）、猪毛蒿（Artemisia scoparia）的叶片解剖结构进行了观察研究的结果表明,随着演替序列的发展,3种蒿类的栅栏组织随演替时间的推移呈现出全栅型-环栅型-过渡型的趋势,叶片解剖结构说明越靠近演替前期的蒿类对干旱的适应性越强。此外,3种蒿类的栅栏组织排列都很紧密,表皮细胞排列不规则,且具有表皮毛和腺毛等旱生适应结构;在猪毛蒿和茭蒿中还发现了特化的气腔结构。这些特征均能说明这些蒿类植物具有很好的抗旱适应性,作为环境改造的先锋物种,它们在当地的自然植被恢复演替中起着积极的正向推动作用。