ALBERT

Beschreibung: Aims Theory suggests that species perform best at intermediate densities, where density-dependent facilitation and antagonism are balanced, but empirical evidence is scarce, particularly in plants. In a self-incompatible perennial herb ( Saussurea nigrescens ), whose recruitment heavily relies on seed output, we test whether both intraspecific facilitation and antagonism significantly affect seed production, resulting in highest seed yield at an intermediate capitulum density. Methods Plots with different S. nigrescens densities were sampled in an Eastern Tibetan meadow during the growing season of 2012 to investigate the relationships between capitulum density and pollinator visitation rate, seed set ratio, parasite ratio, seed damage ratio, and capitulum size. Both simple linear and quadratic models were employed to determine the shape of relationships. Important Findings In line with general theory, hump-shaped relationships of capitulum density versus seed set ratio and number of florets per capitulum indicate intraspecific facilitation in sparse populations, which can be attributed to positive density-dependent pollinator visitation and the amelioration of detrimental physical factors. However, the proportion of seeds damaged by pre-dispersal predators increased monotonically with capitulum density, which may have—in combination with increased intraspecific competition for light and soil nutrients—resulted in density-dependent antagonism. Both positive and negative density-dependent agents acted simultaneously throughout the density range investigated and led to the highest seed yield at intermediate density levels in the Tibetan lotus. More efforts concurrently exploring the two effects are needed to facilitate understanding species abundance and community structure.

Beschreibung: Aims Vegetation sampling employing observers is prone to both inter-observer and intra-observer error. Three types of errors are common: (i) overlooking error (i.e. not observing species actually present), (ii) misidentification error (i.e. not correctly identifying species) and (iii) estimation error (i.e. not accurately estimating abundance). I conducted a literature review of 59 articles that provided quantitative estimates or statistical inferences regarding observer error in vegetation studies. Important Findings Almost all studies (92%) that tested for a statistically significant effect of observer error found at least one significant comparison. In surveys of species composition, mean pseudoturnover (the percentage of species overlooked by one observer but not another) was 10–30%. Species misidentification rates were on the order of 5–10%. The mean coefficient of variation (CV) among observers in surveys of vegetation cover was often several hundred % for species with low cover, although CVs of 25–50% were more representative of species with mean covers of 〉50%. A variety of metrics and indices (including commonly used diversity indices) and multivariate data analysis techniques (including ordinations and classifications) were found to be sensitive to observer error. Sources of error commonly include both characteristics of the vegetation (e.g. small size of populations, rarity, morphology, phenology) and attributes of the observers (e.g. mental fatigue, personal biases, differences in experience, physical stress). The use of multiple observers, additional training including active feedback approaches, and continual evaluation and calibration among observers are recommended as strategies to reduce observer error in vegetation surveys.

Beschreibung: Aims Understanding relationships between vegetation and environments is of importance for ecosystem restoration and management. However, information on how environments influence the floristic patterns of shrublands is lack, especially in the subtropical China. In this study, we explored how environments regulate species composition of shrublands at landscape scale in mid-subtropical China. Methods We investigated species composition and measured the climate and soil environments for 207 shrubland plots in mid-subtropical China (24°39'–30°08'N, 108°47'–114°15'E). We applied a hierarchical cluster analysis and indicator species analysis based on the Bray–Curtis similarity index to identify the main shrubland types and employed principal coordinate analysis (PCoA) to explore the relationship between floristic composition and environment. Important Findings We identified four shrubland types occurring in different environmental conditions. Montane shrubland, dominated by species suitable for cool climates (e.g. Rhododendron simsii ), were distributed in steep areas at comparatively high altitudes; foothill shrubland, dominated by mesophilous species (e.g. Loropetalum chinense ), were distributed in low mountains and hills; pioneer shrubland, dominated by fast grow and short-life cycles species (e.g. Rhus chinensis ), were distributed at low altitudes with dense population; and finally, limestone shrubland, dominated by calcicole plants (e.g. Coriaria nepalensis ), were distributed in the extensive karst areas. Communities occurring in high pH soils were completely separated from those in low pH soils according to the hierarchical cluster analysis. PCoA ordination associated the four types with distinct edaphic and climatic gradients. Soil pH explained 63.3% of variation in PCoA, followed by soil depth and soil bulk density.

Beschreibung: Aims The loss of canopy trees associated with forest decline can greatly influence the species composition and structure of a forest and have major impacts on the ecosystem. We studied the changes in forest composition and structure 1 and 5 years following nearly total canopy mortality on several hundreds of hectares of xeric oak forests in south-central United States. Because the forests were within an ecotonal vegetation type composed of a mosaic of forest, savanna and grassland, we sought to learn whether forest decline areas would recover to forest or change to more open savanna and grassland conditions in the landscape pattern of vegetation. Because low intensity fire shaped the vegetation type, we sought to learn whether fire would keep the decline areas open. Methods The study was conducted in a xeric oak forest in east-central Oklahoma, USA. Randomly located vegetation and regeneration surveys were conducted in decline and non-decline stands 1 and 5 years following nearly total canopy mortality. Diameter at breast height (DBH), regeneration and sprout origin were recorded for all woody species. Important Findings The major canopy species post oak ( Quercus stellata Wangenh.), blackjack oak ( Quercus marilandica Muenchh.) and black hickory ( Carya texana Buckl.) suffered 85–92% mortality; however, minor canopy components experienced limited mortality. Mortality affected all size classes of canopy trees except those below 5cm breast height diameter. There was abundant regeneration of all species and fire seemed to maintain a high level of sprouting. Decline appeared to decrease the relative importance of stump sprouting and increase other types including root sprouts. Decline areas had abundant true seedlings, with stem origin from a root with the same diameter as the stem, which is very unusual for xeric oak forests. Regeneration height in decline areas was twice that of non-decline forests. Our findings suggest that forest decline may lead to: (i) reduced oak dominance and species change in the canopy, (ii) change in reproduction type to increase success of true seedlings and maintain genetic diversity of oaks.

Beschreibung: Aims To assess the role of moisture in phenological timing in the mediterranean coastal flora of Baja California, and specifically to assess the role of coastal fog and ocean-derived moisture in plant phenology. Moisture seems to be the primary driver of flowering times and durations at the arid end of the mediterranean-climate region, where rainfall is often sporadic (temperature and day length can be expected to play a much lesser role as they are not growth limiting). We aimed to understand: What factors drive climatic variation between sites? Are there general flowering patterns allowing us to identify phenological categories? Do flowering patterns vary in relation to site-specific weather? and most importantly, does maritime influence on weather affect flowering dynamics in coastal mediterranean ecosystems? Methods The southernmost extent of the California Floristic Province (in Baja California, Mexico) is a biological diversity hotspot of high endemism and conservation value, with two steep moisture gradients: rainfall (N–S) and coastal fogs (W–E), providing an ideal study system. We installed five weather stations across the moisture gradients, recording data hourly. We monitored flowering phenology in the square kilometer surrounding each weather station from 2010 to 2013. About 86 plant taxa were monitored across the five sites, every 6–8 weeks. Averaged climatic data is presented with general trends in flowering, and specific flowering syndromes were observed. Data for flowering intensity across the sites was analyzed using a principal components analysis. Important Findings Data analysis demonstrates a general seasonal pattern in flowering times, but distinct differences in local weather and phenology between the five study sites. Three flowering syndromes are revealed in the flora: (i) water responders or spring bloomers, (ii) day-length responders or fall-blooming taxa and (iii) aseasonal bloomers with no seasonal affinity. The two moisture gradients are the strongest drivers of flowering times. Inland sites showed higher phenological variation than coastal sites where seasonality is dampened by ocean-derived moisture, which extends and buffers perennial plant phenology and is a probable driver of local endemism. Phenological controls vary globally with climate and geography; moisture is the primary driver of phenology in mediterranean climates and fog is an important climatic variable in coastal Mexico.

Beschreibung: Aims The aim of the study was to discover what set of variables best explains the transition from warm to mesic forest vegetation. Based on various variables grouped into sets (geomorphological, ecological, structural, soil characteristics and chorological), six models were built and tested by generalized additive mixed models (GAMMs). We assumed that each set of variables has different explanatory power. Our aim was to compare the six different models (sets of variables), to test which model best explains the species turnover in forest communities along the transition between warm and mesic temperate forests and to try to find reasons for the different explanatory power of the models. Methods The research took place in the southern part of the Balkan Peninsula. Field sampling was done according to standard methods. The gradient from warm to mesic forests was defined as the turnover of species and evaluated by projection of samples on the first unconstrained DCA axis. Geomorphological, ecological, structural and soil characteristics, together with chorological sets of variables, were regressed on the turnover of species composition. Based on the five sets of variables, six models were constructed and tested by generalized additive mixed models. Important Findings Ecological conditions best explain the change of forest communities along the gradient; evolution and the development of vegetation reflected in chorotypes are also of high importance; geomorphology and structure seem not to change so dramatically and soil shows the least significant differences of all. Ecological variables are the most important set of variables in the transition between warm and mesic temperate forests but eco-evolutionary dynamics after the Pleistocene should also be taken into consideration.

Beschreibung: Aims Increasing evidence worldwide indicates that high mountain regions are not immune to invasion by alien plants. Here, we aimed to address whether three major woody invaders of low-mountain areas are constrained to lower altitudes due to climatic restrictions or just by low propagule pressure. We hypothesize that the increasing climatic harshness towards higher altitudes restricts seedling establishment and survival of these woody invaders and thus their potential for altitudinal expansion. Methods The study was carried out in the Sierras Grandes Mountains, Córdoba, central Argentina (32º50'S, 64º90'W). We addressed the hypothesis with an experimental approach, dissociating the effect of the environmental gradient from that of propagule pressure, by discarding the influence of seed sources. We translocated seeds of Gleditsia triacanthos L. , Ligustrum lucidum W.T. Aiton. and Pyracantha angustifolia (Franch.) C.K.Schneid. along the altitudinal gradient (from 900 to 2700 m asl). Seven sites were selected along the altitudinal gradient, spaced every 200–400 m. Three plots (4 x 4 m) were selected within each altitudinal site and excluded from livestock; 100 seeds of each species were sown within each plot (6300 seeds in total). Seedling emergence and survival was monitored during two growing seasons and soil temperature and moisture was recorded as well. The field experiment was complemented with lab assays. Important Findings Climate along this altitudinal gradient might be least restrictive at mid elevations, as a result of the intersection between opposite soil temperature and moisture gradients. Sown seeds germinated along the whole altitudinal gradient and seedlings successfully established and over-wintered well above their current altitudinal distribution (up to 2200 m for Ligustrum and 2400 m for Gleditsia and Pyracantha ). Additional lab assays confirmed field patterns and gave some insights into contrasting regeneration strategies between these invaders that might help to overcome stochastic environmental constraints in the germination stage. Overall, seedlings of three major woody invaders of low-mountain woodlands can establish and survive at higher elevations than their current distribution. In contrast to natives, they seem to be broad climate tolerators, rather than specialized stress tolerators, capable of germinating and growing across a wide elevational range. While long-term experiments might be necessary to fully address the potentials for altitudinal expansion, out results on early lifecycle stage suggest that the invaders studied here would have mostly a dispersal barrier rather than a climate barrier to establish in the upper belt of the Sierras Grandes.

Beschreibung: Aims The diversity–productivity relationship is one of the most critical questions in ecology and can be altered by environmental factors. Hydrological fluctuation affects growth of wetland plants, and such effects vary with plant species. Therefore, we hypothesized that hydrological fluctuation changes effects of species richness on productivity of wetland plant communities. Methods We constructed wetland plant communities consisting of three or six wetland plant species and subjected them to hydrological fluctuation (i.e. gradually changing water level) of two frequencies and two ranges, with unchanged water level as the control. We measured height, root and shoot dry mass of each plant at harvest. Important Findings Hydrological fluctuation significantly decreased biomass of wetland plant communities, which was due to impacts of fluctuation range, but not those of fluctuation frequency. Community biomass was significantly higher when species richness was higher, and such an effect did not depend on hydrological fluctuation. Therefore, hydrological fluctuation can decrease the productivity of wetland plant communities but may not alter the diversity–productivity relationship.

Beschreibung: Aims We aimed at determining differences in the leaf spectral signatures of plant species groups growing in habitats along the hydrological gradient of an intermittent wetland and to define leaf traits that explain their variability. We want to contribute to the understanding of the causes for plant spectrum variability at leaf and community levels. Methods We measured leaf reflectance spectra (300–887nm) of representative plant species from different habitats and analyzed spectral differences among species groups. To explain leaf spectra variability within a group, we performed detailed analyses of leaf morphological and biochemical traits in selected species. Important Findings The reflectance spectra of the different species groups differed most in the green, yellow and red spectral ranges. The reflectance spectra of submerged leaves of hydrophytes with simple structures were explained by their biochemical traits (carotenoids), while for more complex aerial leaves, morphological traits were more important. In submerged and natant leaves of amphiphytes, total mesophyll and spongy tissue thickness were the most important traits, and these explained 44% and 47%, respectively, of the spectrum variability of each plant group. In general, the redundancy analysis biplots show that samples of different plant species colonizing the same habitat form separate clusters and are related to the explanatory variables in different ways. The redundancy analysis biplots of helophytes and wet meadow species show clustering of graminoids and dicots into two distinct groups. Leaf encrustation (prickle hair properties and epidermis thickness) is important for graminoids, while leaf thickness and specific leaf area have more important roles in dicots. Our results show that knowledge of the species composition and leaf traits is necessary to interpret the reflectance spectra of such plant communities.

Beschreibung: Aims The physiological responses during dormancy removal and multi-phasic germination were investigated in seeds of Paeonia corsica (Paeoniaceae). Methods Seeds of P. corsica were incubated in the light at a range of temperatures (10–25 and 25/10°C), without any pre-treatment, after W (3 months at 25°C), C (3 months at 5°C) and W + C (3 months at 25°C followed by 3 months at 5°C) stratification, and a GA 3 treatment (250 mg·l –1 in the germination substrate). Embryo growth, time from testa to endosperm rupture and radicle emergence were assessed as separate phases. Epicotyl–plumule emergence was evaluated incubating the germinated seeds at 15°C for 2 weeks, at 5 and 25°C for 2 months on agar water before transplanting to the soil substrate at 10, 15 and 20°C and at 15°C for 2 months on the surface agar water with GA 3 . Important Findings Embryo growth, testa rupture, endosperm rupture (radicle emergence) and growth of the epicotyl were identified as four sequential steps in seeds of P. corsica . Gibberellic acid alone and warm stratification followed by 15°C promoted embryo growth and subsequent seed germination. Cold stratification induced secondary dormancy, even when applied after warm stratification. After radicle emergence, epicotyl–plumule emergence was delayed for ca. 3 months. Mean time of epicotyl–plumule emergence was positively affected by cold stratification (2 months at 5°C) and GA 3 . P. corsica seeds exhibited differential temperature sensitivity for the four sequential steps in the removal of dormancy and germination processes that resulted in the precise and optimal timing of seedling emergence.