Diaspore Weight Research Articles

The functional composition of the neophytic flora changes in response to environmental conditions along a rural-urban gradient

Compared to rural environments, cities are known to be extraordinarily rich in plant species. In particular, the proportion of alien plant species is higher in urban areas. This is attributed to specific urban conditions, which provide a large variety of habitats due to high geological heterogeneity. It can also be attributed to the role of cities as centres for plant introductions and the consequential increased propagule pressure. Neophytes, alien plant species introduced after the discovery of the Americas, appear to contribute especially strongly to the increased proportion of alien plants in cities. To investigate whether the plant traits of neophytes can be explained by environmental variables, we modelled the composition of their pollination types and growth forms as well as their diaspore weight and the onset of flowering in response to a selection of climatic, geological, land cover and traffic network variables with data from Germany. To test for a specific urban effect, we included their interactions with the area of urban land use.In general, we found that climatic variables were the most important predictors for all traits. However, when considering interactions with urbanisation, non-climatic variables, which often were not significant as the main effect, remained in the final models. This points to an existing ‘urban effect’. However, it is much smaller compared to the purely climatic effects. We conclude that interferences and alterations mainly related to urbanisation and human activity in general are responsible for the different ecological processes found in cities compared to rural areas. In addition, we argue that considering functional traits is an appropriate way to identify the ecological mechanisms related to urbanisation.

Divergent Tree Communities across Ridge, Cliff, and Talus Relate to an Association between Diaspore Weight and Micro-Topography at Mohonk Preserve, New York

Ecological study of cliff environments has steadily increased in the last three decades. However, plant communities on many cliffs have yet to be investigated, and there remains uncertainty about the mechanisms that drive vegetation patterns on cliffs. On the Trapps cliff, a renowned rock-climbing destination within Mohonk Preserve, New York, we recorded tree species and surface micro-topography (“sloping.” “level,” “incut”) along seven rappel transects. In two study areas, we also sampled the ridge and talus areas above and below the cliff transects, and in one of those areas, we included a separate lateral survey along a prominent ledge on the cliff. We used estimated diaspore (seed or fruit) weights and chi-square analyses to test for association between diaspore weight class and topographic categories across the entire study. The cliff tree communities were dominated by mature pitch pine (Pinus rigida) and more frequent but smaller-diameter sweet birch (Betula lenta). Sweet birch, a species with lightweight, wind-dispersed seeds, was disproportionately frequent on the cliff and on sloping surfaces on the cliff, while heavier, gravity-dispersed diaspore species (especially oaks) were underrepresented on the cliff in general, but disproportionately associated with level micro-topography on the cliff. Our results suggest that diaspore weight and associated dispersal mechanisms may play a role in the assembly of cliff tree communities that are divergent from the ridge above, or talus below. Management implications include protecting adjacent plant communities (ridge, talus) that are likely diaspore sources that sustain plant communities on cliffs.

High potential of sub-Mediterranean dry grasslands for sheep epizoochory

AbstractThere is a general decline of grasslands across Europe due to habitat loss and degradation. Ensuring plant dispersal thus becomes a key process for preserving grassland patches in all scales. We examined diaspore dispersal by sheep epizoochory in the pastures of the North Adriatic Karst (NW Slovenia) and determined the qualitative and quantitative features of diaspores in fur. We recorded 25,650 diaspores of 141 plant taxa (with 107 taxa and 23,350 diaspores determined to species level), using three different methods: (i) the “whole-coat method”, (ii) the “part-of-thecoat method” and (iii) a “seedling emergence method”. A comparison of these techniques revealed that the “wholecoat method” provided the highest number of diaspores and plant species. All diaspores were clustered into five emergent groups based on seven functional traits (diaspore weight, length, width, height, volume, specific weight and the diaspore surface structure). Our research revealed that sheep represent an important dispersal vector, since about half of the plant species recorded in the pastures were found as diaspores in fur. This study contributes to knowledge about the modes of seed dispersal in seminatural grasslands. Taking into account that livestock play a key role in vegetation dynamics, understanding their effects on seed dispersal is essential for conservation and restoration of these species-rich grassland communities.

Simple Traits among Diaspore Weight/Number, Plant Height and Ability of Vegetative Propagation

Several expected correlations among followed internal plant traits were confirmed using the dataset of 492 herbaceous species from the temporal zone of Central Europe. Average diaspore weight (seed mass), reproductive capacity of population (number of produced diaspores), species height, and ability of lateral spread were the plant traits considered. The evident correlations were confirmed among all investigated traits: (i) The reproductive capacity of population negatively correlated with diaspore weight, plant height, and vegetative propagation. The diaspore weight and their number are closely correlated and co-adapted. (ii) Bigger plant species produce bigger diaspores. These trends are obvious at the inter- and intra-family levels. (iii) Larger plant species showed higher ability to vegetative propagation.

Colonization of recent coniferous versus deciduous forest stands by vascular plants at the local scale

Abstract.Questions: 1. Are there differences among species in their preference for coniferous vs. deciduous forest? 2. Are tree and shrub species better colonizers of recent forest stands than herbaceous species? 3. Do colonization patterns of plant species groups depend on tree species composition?Location: Three deciduous and one coniferous recent forest areas in Brandenburg, NE Germany.Methods: In 34 and 21 transects in coniferous and deciduous stands, respectively, we studied the occurrence and percentage cover of vascular plants in a total of 150 plots in ancient stands, 315 in recent stands and 55 at the ecotone. Habitat preference, diaspore weight, generative dispersal potential and clonal extension were used to explain mechanisms of local migration. Regression analysis was conducted to test whether migration distance was related to species’ life‐history traits.Results: 25 species were significantly associated with ancient stands and ten species were significantly more frequent in recent stands. Tree and shrub species were good colonizers of recent coniferous and deciduous stands. In the coniferous stands, all herbaceous species showed a strong dispersal limitation during colonization, whereas in the deciduous stands generalist species may have survived in the grasslands which were present prior to afforestation.Conclusions: The fast colonization of recent stands by trees and shrubs can be explained by their effective dispersal via wind and animals. This, and the comparably efficient migration of herbaceous forest specialists into recent coniferous stands, implies that the conversion of coniferous into deciduous stands adjacent to ancient deciduous forests is promising even without planting of trees.

Upward migration of vascular plants following a climate warming trend in the Alps

The aim of this study was to understand (1) whether warmer climatic conditions affected the vascular plant species composition, (2) the magnitude and rate of altitudinal changes in species distributions, and (3) whether an upward migration of alpine plants is connected to wind dispersal of diaspores. We compared historical records (1954–1958) with results from recent plant surveys (2003–2005) from alpine to nival ecosystems in the Rhaetian Alps, N-Italy. The presence of all vascular plant species and their maximum altitude were recorded along a continuous altitudinal transect of 730 m. An increase in species richness from 153 to 166 species was observed. Moreover, 52 species were recorded from altitudes 30–430 m higher than their 1950s limits, which corresponds to a median migration rate of 23.9 m/decade. In order to explain the observed migrations, the species wind-dispersal ability (diaspore weight and morphology) and the air temperature variation from 1926 to 2003 were considered. Species with more pronounced altitudinal shifts possess lighter diaspores. The highest increase in species richness was found between 2800 and 3100 m a.s.l.; this appears to be related to an estimated shift of the permafrost limit by +240 m during the last 50 years. The mean air temperature in the region rose by +1.6 °C in summer and by +1.1 °C in winter within this period. Climate warming is therefore considered as a primary cause of the observed upward migration of high mountain plants. Calculated altitudinal migration rates, however, varied remarkably among species. This would imply differential abilities of species to persist in an increasingly warmer climate. Species-specific conservation measures, including ex situ conservation, may therefore be required. Mit dieser Studie sollte untersucht werden (1) ob wärmere klimatische Bedingungen die Artenzusammensetzung beeinflussen, (2) der Umfang und die Rate von Änderungen in der Artenverteilung hinsichtlich der Höhe, und (3) ob eine Aufwärtswanderung von alpinen Pflanzen mit der Windverbreitung von Diasporen zusammenhängt. Wir verglichen historische Listen (1954–1958) mit den Ergebnissen rezenter Pflanzenaufnahmen (2003–2005) von alpinen bis nivalen Ökosystemen in den Rätischen Alpen (Nord-Italien). Das Auftreten aller Gefäßpflanzen und ihre maximale Höhe wurden entlang eines Höhentransekts von 730 m registriert. Eine Zunahme von 153 auf 166 Arten wurde beobachtet. Darüberhinaus wurden 52 Arten in Höhen festgestellt, die 30 bis 430 m oberhalb der Grenzen von 1950 lagen. Dies entspricht einer mittleren Wanderungsgeschwindigkeit von 23.9 m/Dekade. Um die beobachteten Wanderungen zu erklären, wurden die Windausbreitungsfähigkeit der Arten (Gewicht und Morphologie der Diasporen) und die Temperaturänderungen von 1926 bis 2003 betrachtet. Arten mit deutlicheren Höhenverschiebungen besitzen leichtere Diasporen. Die größte Zunahme des Artenreichtums wurde zwischen 2800 und 3100 m N.N. festgestellt. Dies scheint mit der geschätzten Verschiebung der Permafrostgrenze um +240 m in den letzten 50 Jahren zusammenzuhängen. In diesem Zeitraum stieg die mittlere Lufttemperatur in der Region um 1.6 °C im Sommer und 1.1 °C im Winter. Die Klimaerwärmung wird somit als die primäre Ursache für die Aufwärtswanderung der Hochgebirgspflanzen angesehen. Die errechneten Wandergeschwindigkeiten variierten indessen stark zwischen den Arten. Dies impliziert unterschiedliche Fähigkeiten der Arten in einem immer wärmeren Klima zu überleben. Artspezifische Schutzmaßnahmen, einschließlich Artenschutz ex situ, könnten notwendig sein.

Comparative study of growth parameters on diaspores and seedlings between populations of Bromus setifolius from Patagonia, differing in Neotyphodium endophyte infection

Bromus setifolius Presl., a native perennial grass, is widely spread in the harsh environment of Patagonia, Argentina. This grass can be associated with Neotyphodium Glenn, Bacon et Hanlin endophytes which are related to aerial tissues of these plants and never show external signs of infection. Endophyte presence of certain grasses improves abiotic and biotic stress resistance, productivity or reproduction in their hosts. To compare and contrast natural populations of B. setifolius differing in endophyte infection diaspore weight of seven populations was registered. In addition, emergence and growth parameters of seedlings, dry weight, leaf length and mortality rate were measured. For this purpose, two independents assays were conducted under controlled environmental conditions, using an infected (E+) and an uninfected (E–) population in each one. Most of the analysed parameters differed between E+ and E– populations, being significantly greater in E+ populations. Populations with percentage of endophyte infection between 0% and 100% presented intermediate mean diaspore weight. These results could suggest an adaptive advantage of infected plants as a consequence of endophyte presence.

Spontaneous Establishment of Woody Plants in Central European Derelict Sites and their Potential for Reclamation

AbstractThe performance of woody plants was analyzed in 15 successional seres starting at bare ground in central European manmade habitats. The total cover of woody species after 10 years of succession was significantly related neither to initial soil moisture nor to nitrogen (expressed using Ellenberg indicator values). But the comparison of seres indicates that establishment of woody plants was easier under moderate environmental conditions and retarded in extreme habitats (dry, nutrient‐poor, or acid). The arrival of the first woody plants was delayed in dry sites. No significant differences were found between primary and secondary seres, either with respect to the total cover of woody plants reached after 10 years of succession or considering the time of their arrival. In total, 24 woody species (10 shrubs and 14 trees) appeared in the series investigated. Their successional performance (in terms of the number of seres in which the species occurred and maximum cover reached in any sere) was not related to species traits (life strategy, type of mycorrhizae, mode of dispersal, diaspore weight), except for the regeneration strategy, species with seasonal regeneration by seeds were capable of creating higher cover. Betula pendula (European birch) was the most successful species in spontaneous succession, especially on moist sites. Practical suggestions for the management of particular habitats (sites disturbed by mining, sites reclaimed after acid rain deforestation, urban sites, abandoned fields) are provided regarding the establishment of woody plants.

Postdispersal survivorship of north Queensland rainforest seeds and fruits: Effects of forest, habitat and species

Abstract Diaspore (seed and/or fruit) survivorship of 12 species of North Queensland rainforest trees was monitored over a 4 week period in two rainforests on the Atherton Tableland, north Queensland, Australia, with replicated sites in forest interiors, canopy gaps, forest edges and adjacent pastures. General linear modelling was used to estimate the relative importance of forest site, habitat, species and diaspore type on survival.The probability of survival varied significantly among species, between habitat, forest and diaspore types. Survival averaged 41.2% at day 28, was greater in one forest (Curtain Fig, 56.1%) than the other (Lamins Hill, 25.3%) and was apparently inversely related to the abundance of rodents. In both forests, survival declined in the order: pasture ≥ forest edge ≥ forest interior = canopy gap. A lack of significant difference between the forest interior and canopy gap is consistent with findings in other rainforest sites within Australia, but contrasts with most results from other continents. The study also indicated that diaspore weight was an important intrinsic variable affecting survival, the predators (mostly rodents) taking small to moderately large diaspores rather than the very large ones.

Geographic Ranges of Plant Species in Relation to Dispersal Morphology, Growth Form and Diaspore Weight

We investigated the relationship of geographic range to growth form, dispersal morphology and diaspore weight within three comparative databases of 219-325 native species from arid central Australia, semi-arid western NSW and maritime Sydney. Geographic range was measured as the number of regions occupied. In the arid and semi-arid floras, but not in the maritime flora, species adapted for dispersal by vertebrates (mainly birds) tended to occupy more regions than species adapted for dispersal by other means. The same pattern occurred within four major families (Chenopodiaceae, Myoporaceae, Mimosaceae and Solanaceae), and thus was not a product of differences between families. We suggest that lineages with adaptations for long-range dispersal may have undergone a lesser incidence of geographic speciation, within the arid and semi-arid flora.

Seed Size and Shape Predict Persistence in Soil

An understanding of seed persistence in the soil is important to vegetation management and weed control, but experimental collection of seed bank data is tedious and expensive. We report a rapid, simple method for predicting seed persistence in the soil. The method is tested on a range of British, mostly herbaceous, species. Diaspore (seed or fruit) weight is plotted against variance of the three linear dimensions of the diaspore. All diaspores within an area of the graph defined by a maximum weight and variance are persistent in the soil. The critical weight is the same for fruits and seeds, but the critical variance of diaspore dimensions appears slightly higher for fruits. The great majority of diaspores outside this region are short lived, and the relatively few ambiguous cases can be resolved by reference to habitat (...)

Diaspore Weight, Dispersal, Growth Form and Perenniality of Central Australian Plants

Diaspore weight and dispersal were measured in 229 plant species of the central Australian arid zone. The frequency distribution of log diaspore sizes was unimodal, as has been observed for other habitats. the quantity of reserve (embryon plus endosperm) stored in the seed was related to the weight of the dispersal unit. Reserve weight was greater for woody species than for herbaceous species. Within each growth form, there was no clear relationship between perenniality and reserve weight. Most graminoids were wind dispersed, and elaiosomes for and dispersal were more common among the woody species (...)

Diaspore Size, Shape, and Fall Behavior in Wind-Dispersed Plant Species

Seeds and fruit of 38 anemochorous species were dropped in still air to simulate their descent under natural conditions. Fall rate and lateral distance were recorded as indices of wind-borne dispersal capability. Differences in fall rates among plumed species were dependent on interspecific variation in diaspore weight and plume area, while fall rates of winged species were strongly differentiated by contrasting wing shapes. In Acer platanoides and Asclepias syriaca, representing wing and plume architectures, respectively, the range of diaspore weight was artificially extended by removing embryos or adding lead weights. In both of these species, rate of descent of altered diaspores was controlled by weight relative to wing or plume area. The wing morphology of A. platanoides showed lower fall rates than the plumed A. syriaca above 45 mg, while the plume morphology of A. syriaca achieved lower fall rates below this weight. Compared with wide variation in diaspore weight, members of the Compositae showed relatively low variation in plume loading (diaspore weight/plume area) and fall speed. These observations suggest functional and phyletic constraints on diaspore architecture. Such constraints may limit evolutionary change in diaspore size and performance.

DIASPORE SIZE, SHAPE, AND FALL BEHAVIOR IN WIND‐DISPERSED PLANT SPECIES

Seeds and fruit of 38 anemochorous species were dropped in still air to simulate their descent under natural conditions. Fall rate and lateral distance were recorded as indices of wind‐borne dispersal capability. Differences in fall rates among plumed species were dependent on interspecific variation in diaspore weight and plume area, while fall rates of winged species were strongly differentiated by contrasting wing shapes. In Acer platanoides and Asclepias syriaca, representing wing and plume architectures, respectively, the range of diaspore weight was artificially extended by removing embryos or adding lead weights. In both of these species, rate of descent of altered diaspores was controlled by weight relative to wing or plume area. The wing morphology of A. platanoides showed lower fall rates than the plumed A. syriaca above 45 mg, while the plume morphology of A. syriaca achieved lower fall rates below this weight. Compared with wide variation in diaspore weight, members of the Compositae showed relatively low variation in plume loading (diaspore weight/plume area) and fall speed. These observations suggest functional and phyletic constraints on diaspore architecture. Such constraints may limit evolutionary change in diaspore size and performance.

DISPERSAL ABILITIES OF SEVEN SPARSE AND COMMON GRASSES FROM A MISSOURI PRAIRIE

Seven grass species on an abundance continuum from common to sparse on a Missouri tall‐grass prairie were examined for two diaspore traits (morphology and weight), for three dispersal traits (terminal velocity, and mean and maximum lateral movement propagules released in still air from a height of 1 m), and for two parental traits (culm biomass at maturity and culm height at dispersal). Dispersal ability, measured in the laboratory as the lateral movement of propagules in the upper 5% (right tail) of the distribution of distances, is inversely correlated (rs = –0.94) with biomass abundance. Under constant conditions, seeds of sparse species travel farther than seeds of common species. Dispersal ability is more closely related to a populational attribute (abundance) than to a more proximate characteristic (diaspore weight). Diaspore weight is closely related (rs = 0.97) to culm biomass of the parent, in apparently simple allometry, and more weakly related (rs = 0.71) to biomass abundance. Large parents make large seeds. The sparsest species, which is small in stature, has light (0.08 to 0.19 mg), flattened diaspores with low terminal velocities (82 to 87 cm sec−‐1) and achieves lateral movement (up to 460 mm) by tumbling and gliding. Species of intermediate abundance have intermediate stature and diaspore weight (1.0 to 1.8 mg), unornamented propagules, high terminal velocities (191 to 209 cm sec−‐1) and intermediate dispersal ability (up to 388 mm). The three most common species have heavy propagules (2.2 to 2.8 mg), ornamented with long hairs. Although the ornamentation slows fall (96 to 194 cm sec−‐1), it acts as a “guide parachute,” orienting the propagule so that it falls nearly straight downward. The common species, which morphologically appear adapted to longer dispersal, achieve little lateral movement (up to 235 mm) under laboratory conditions. Terminal velocity is a misleading descriptor of dispersal because diaspores with similar terminal velocities have differing movement patterns. When diaspores of two species (one tall common species and one short sparse species) are released in still air from their natural height, differences in maximum fall distance observed under constant height of release are lost. When dispersal is observed in the field by means of sticky seed traps, the slopes of the dispersal curves (regression coefficient of ln‐transformed number of seeds caught on distance from the clump) do not differ from common and sparse species, despite the fact that seeds of the common species are released from greater heights. The orderly differences in dispersal behavior among species due to subtleties of morphology observed under laboratory conditions are masked in nature.

Abundance and diaspore weight in rare and common prairie grasses.

Abundance (g/m2) and diaspore weight are positively correlated in seven species of perennial grasses that occur in prairies. The rare grasses (<10.0 g/m2) have light dispersal units (0.06 to 1.76 mg); the common grasses (>10.0 g/m2) have heavy dispersal units (2.23 to 2.80 mg). This result is the first reported differentiating trait between related rare and common organisms occurring in same habitat.Three hypotheses that explain this phenomenon are compared; the third most likely holds. First, rare grasses may be rare because their small seeds are less successful in establishment than those of common grasses. Second, if the persistence of small populations is marginal, rare grasses may devote less energy (or other currency) to seed production. Third, rare grasses may be colonizers of spatially and temporally rare microsites appropriate for growth and thus have seeds adapted for longer distance dispersal than those of common grasses. This last hypothesis suggests a new pathway for the evolution of weeds.