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Rapid Invasion of Fraxinus ornus L. Along the Herault River System in Southern France: The Importance of Seed Dispersal by Water
Abstract
To document the range extension of a plant species in a region in which it was previously absent, we have examined the distribution pattern of Fraxinus ornus L. 65 years after its introduction to the Herault River in southern France. Censuses of flowering individuals showed that Fraxinus ornus successfully colonized, but remained mainly restricted to, flood-disturbed riparian habitats in the Herault River system. The present distribution of this species showed that it spread along the river system at an average rate of 970 m/yr. We suggest that this very rapid spread, of a usually wind-dispersed species, has resulted from water transport of seeds during periodic flooding in autumn.
... However, it can also grow in regions where temperatures are more extreme, including a large scale of different altitudes. Due to its ability to spread spontaneously, it even shows apparent expansive properties (Thébaud & Debussche, 1991;Gojdičová et al., 2002). ...
... However, the above mentioned characteristics of manna ash also represent a strong potential for its undesirable expansion. This undesirable expansive behaviour of manna ash has already been studied in several regions of Europe (Thébaud & Debussche, 1991;Giovannini et al., 1992;Wallnofer et al., 2008) including South-Western Slovakia (Hegedüsová & Senko, 2011). ...
... The most striking example of the expansive behaviour of manna ash is probably its expansion along the Hérault River in Southern France (Thébaud & Debussche, 1991) Here, manna ash spreads along the watercourse and outcompetes most of the other, native species. Thus, its fruits are dispersed by water, analogous to the fruit and seed of many harmful invasive plants (Richardson et al., 2007;Aguiar & Ferreira, 2013). ...
Manna ash (Fraxinus ornus L.) is a Mediterranean shrub or a small tree with the northern limit of its natural range in central Europe. At the same time, it is also a tree species which, due to its considerable tolerance to high temperatures and lack of moisture, as well as some expansive properties, could be expected to increase its range in the coming decades as a result of the changing climate and the associated spontaneous spread. The paper summarizes the results of several years of our research, during which we evaluated the following growth and reproductive characteristics: (1) phenological traits and the length of the growing season, (2) the intensity and evenness of fruiting, and (3) the numbers of individuals and stems according to the height categories. In addition, the species composition of vegetation cover was analysed on the sites with the occurrence of manna ash. Observations were made in two autochthonous populations of manna ash in Southern Slovakia and one allochthonous population in its central region. The onset of spring vegetative and generative phenophases showed a noticeable latitudinal trend during our observations (2015‒2019). In Central Slovakia, flowering and leafing of manna ash occurred on average more than two weeks later than in its southernmost region. The “Central Slovakian” population of manna ash was also characterised by the earliest onset of autumn vegetative phenophases and the lowest total length of the growing season. Despite these trends, flowering and fruiting in this population were relatively regular ‒ in contrast to the other two sites, it was observed every year. In this locality, we also observed the highest total numbers of individuals and stems in all the height categories and the markedly decreased occurrence of competing species. The achieved results point out to the considerable vigour and high reproductive ability of the allochthonous population of manna ash outside its natural range and the natural range of its most important competitors.
... Using the immersion device shown in Fig. 2, we simulate transport by the river of both scarified and unscarified seeds. We assess the effect of immersion duration (15,35, and 55 days). As a control treatment, we germinate seeds in water without any movement. ...
Background
The silver wattle Acacia dealbata is a fast-growing tree from Australia that has become naturalised in different regions of the world, attaining invasive status in most of them. In Chile, A. dealbata reaches large abundances along banks and floodplains of invaded fluvial systems, suggesting that rivers may act as a vector for seed dispersal. As hydrochory has not been documented previously in this species, the aim of this study is to evaluate the potential for water dispersal of seeds of this invasive tree along rivers.
Methods
Seed samples from rivers were collected at three sites along two A. dealbata -invaded rivers within the Cachapoal basin, central Chile. Number of seeds collected was contrasted versus hydraulic and local conditions with RDA. Seed buoyancy and sedimentation velocity were determined and compared between sites with an ANCOVA. Finally, the probability of seed germination after long periods of immersion in water was assessed, simulating transport conditions in the flow. Germination results were tested with a GLM.
Results
Results indicate that increasing abundance of A. dealbata seeds in the flow is related to the level of turbulence of the flow. Seeds display high floatability but their sedimentation velocity is high when they do sink. Finally, silver wattle seeds can germinate after long periods (many weeks) of immersion in water; however, their probability of germination depends to a large extent on whether seeds are scarified or not.
Conclusions
Based on the evidence collected, we suggest that the seeds of A. dealbata have the necessary traits to be dispersed by rivers, this being the first research testing this hypothesis. The success of hydrochory of A. dealbata would depend on river flow turbulence, and whether there are natural mechanisms for scarifying the seeds either before or during transport. The proposed methodology can be used to assess river hydrochory for any tree species.
... Indeed, dust seeds, as well as seeds which are haired or have a pappus, are more likely to germinate after water transport, while anemochory with winged diaspores is negatively correlated with survival. We should not forget the relativity of this statement, as there are examples of large and wing-seeded species where hydrochory is recognised as an important additional way of long-distance dispersal (e.g., Fraxinus ornus,Thébaud & Debussche, 1991).Myrmecochory is a very specific adaptation and true (obligate) myrmecochorous species can hardly profit from other dispersal vectors ...
We studied seed transport in the Upper Eider River (Northern Germany). Our main questions were: Diaspores of what species are transported in the river and which of them remain viable after the drift? Could functional species traits be used as predictors for the survival of plant propagules in course of water transport?
The water body of the Upper Eider River was sampled for plant diaspores at two bridges with each four traps changed weekly during the whole year. Samples were separated into two equal groups. Each two samples per bridge and week were dried and seeds were counted manually. The other two samples were spread on sterilized soil for germination. Species composition and community weighted trait means were compared for dried samples (total transport) and seedlings (germinated after drift). About half of the species and 1/10 of the seeds were able to survive hydrochorous transport. Species traits (community weighted means) were not reliable predictors for survival of species during the hydrochorous transport, but the majority of traits reflect the differences between the transport pools of seeds and seedlings. Small seed size, ruderal life strategy and high light preference correlate positively with germinability after the drift, while large-seeded species adapted to endozoochory tend to lose viability during hydrochory. Dispersal of terrestrial plants with running water in the studied small river system is a highly stochastic event. We didn’t find evidences that specific adaptations to hydrochory significantly contribute to its success. Nevertheless, a few functional traits can increase the probability for the species to pass through the ecological filter “hydrochory”. Among those traits are (i) small seed size (less vulnerability for mechanical stress), (ii) generalist dispersal mode, less dependent on other particular vectors, and (iii) ruderal life strategy.
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... Due to high phenotypic plasticity, F. ornus can even be invasive in some locations. Thébaud and Debussche (1991) reported that after the first introduction of F. ornus into southern France in 1920, it spread along the riverbeds of the Hérault and Vis Rivers through seed propagation by water and air at 970 m per year. ...
Key message
Native Fraxinus ornus cohabits with the alien invasive species Ailanthus altissima. This work aims to give an insight into the distinction of functional traits, which relate to species invasiveness.
Abstract
Fraxinus ornus cohabits with the alien species Ailanthus altissima, which is invasive throughout Europe and North America. This work studied ecophysiological response of two cohabiting species and their leaf and bark traits to contribute to understanding A. altissima invasiveness. We compared the radiation-use and water-use efficiency following 6 months of good water supply as opposed to a pronounced water shortage in two cohabiting species. Leaf anatomical properties were studied, and their differences in leaf and bark biochemical and optical properties were examined. The two species differed significantly in leaf morphology, but less so for leaf biochemistry. This latter differed more in comparison from two precipitation levels within the same species. Compared to F. ornus, the A. altissima leaves were thicker, with thicker epidermal and palisade layers, and less numerous, but larger, stomata. A. altissima had higher effective photochemical efficiency and maintained a more favourable water potential despite higher stomatal conductance with high precipitation, meanwhile there were no significant differences of ecophysiological responses in low precipitation. There were only small differences between the two species for the leaf optical properties, while they differed significantly for the bark optical properties. We show that pigments have an important role in defining bark reflectance, and that differences in bark spectral signatures provide a basis for the distinction between these two species for remote sensing.
... Many authors describe the sources and causes of invasive behaviour of trees (plants) as a form of their life strategy (e.g. Thébaud and Debussche, 1991;Eliáš, 1997Eliáš, , 2009Richardson et al., 2000;Pyšek et al., 2002;Warren, 2007;Medvecká et al., 2012;and others). Biological invasive assumptions include: big amount of seeds and diaspora, broad ecological adaptability, high allelopathic behaviour in succession, no or rare occurrence of diseases and pests, the way of seed spreading (mainly anemochores and hydrochores), root shoots and polycormone sprouting ability, neglected or incorrect management of invasive woody plant species (Drake et al., 1989;Kelbel, 2012;Head, 2017). ...
Supuka, J., Tóth, A., Bihuňová, M., Verešová, M., Šinka K., 2020. Alien and native woody plants in scattered vegetation in agricultural landscape. Folia Oecologica, 47 (2): 109-120. The woody plant species composition has been evaluated in three cadastral territories of southwestern Slo-vakia, together in 77 habitats of non-forest woody vegetation (NFWV). A total of 43 tree species have been identified; 8 of them were alien and 5 species were cultural fruit trees. In total 20 shrub species were identified , out of which 3 were alien. Three woody species are classified as invasive according to the law in Slova-kia: Acer negundo L., Ailanthus altissima (Mill.) Swingle, and Lycium barbarum L. They occurred only in 2, maximum in 4 of the evaluated habitats. The most occurring alien tree species Robinia pseudoacacia L. was generally identified in 58 habitats and in 48 habitats, with an incidence over 40% and dominance index of 70.6. The second most occurring alien tree Populus × canadensis had a dominance index of 8.3. The dominant native trees in NFWV were Acer campestre L., Fraxinus excelsior L., Quercus robur L., Salix fragilis L. with the dominance index of 1-5 only.
... Similarly, disturbances can also aid invader establishment by removing native predators, parasites, or competitors that provide biotic resistance to invasion (Kotanen 1997, Lafferty & Kuris 2005 or by creating environmental conditions that favor invaders over natives (Byers 2002, Ruhí et al. 2016. Disturbances can also disperse exotic propagules to new locations and facilitate their colonization of previously inaccessible areas; for instance, floods transport invasive plant seeds to new riparian plant communities (Thébaud & Debussche 1991). Although positive associations between disturbance and invasion are well-documented, disturbance can also impede invasion by harming invaders, hindering their dispersal, or perhaps by disrupting facilitative interactions with resident species (Smith & Knapp 1999, Flynn et al. 2010. ...
Disturbances often have positive, direct effects on invasions by dispersing propagules or creating environmental conditions that favor invasive species. However, disturbances that alter interactions between resident and invading species could also affect invasion success. In northeast Florida, the black mangrove Avicennia germinans is expanding into salt marshes, where it interacts with the dead litter (wrack) of the native marsh cordgrass Spartina alterniflora . From 2015-2017, we performed monthly surveys before and after 2 hurricanes in 3 marsh microhabitats (bare sediment, vegetation, wrack) to quantify mangrove propagule and seedling densities. Wrack increased propagule retention up to 10 times relative to other microhabitats. Hurricanes did not directly harm mangrove propagules or seedlings. However, storm surge relocated wrack to upland environments, which indirectly inhibited mangroves by temporarily disrupting the facilitative effects of wrack on propagule recruitment and exposing intertidal bare patches that decreased propagule retention and seedling establishment. Wrack remained absent from intertidal areas for 1-3 mo. Because hurricane season overlaps with propagule recruitment, hurricane timing and wrack return time to intertidal areas influence the degree that hurricanes disrupt wrack-mangrove interactions. We demonstrate that large-scale disturbances can negatively and indirectly affect invader recruitment by altering interactions with resident species.
... As well as, dispersal of sexual propagules may determine the level of gene flow within and among populations, thus affecting adaptation (Eminniyaz et al., 2013). Deposition of weed seeds in irrigation canals and rivers is one of the important and very rapid ways of dispersing seeds of some invasive plants (Thebaud and Debussche, 1991). ...
Seed longevity under different environmental conditions is considered as one of the most important factors in the spread and persistence of an exotic species. The Experiments were conducted to determine seed persistence in soil, effects of submergence in water, flooding of the soil, and high temperatures on germination and viability of spotted spurge (Chamaesyce maculata) and wild poinsettia (Euphorbia heterophylla) as two exotic species in different regions of Golestan province. Spotted spurge seeds buried at depth of 10 cm maintained their viability above 95% after a year, while wild poinsettia seeds were destroyed completely after exhuming the soil. Seeds of both species were unable to germinate under submergence, but 92% of the spotted spurge seeds remained viable under this condition for 14 d. No germination was observed after 9 weeks submersion. Submersion duration drastically affected seed germination of wild poinsettia, so that no germination occurred after 6 d submersion. Twelve days after flooding, spotted spurge emergence decreased by 57% compared to the control. Ten percentage of wild poinsettia seedlings emerged when flooding was kept up to 12 d after sowing, while control had 96% emergence. Germination of spotted spurge seeds subjected to 140 oC for 5 min was 5%. Viability of wild poinsettia seed was completely lost at 120 and 140 C for 5 min. These results suggest that spotted spurge is capable of forming persistent seedbank. Seeds of spotted spurge were partially tolerant to submersion in water, but wild poinsettia seed are susceptible to submergence. The burning of crop residue could also prevent augmenting the soil seed bank of both species.
The flood pulse is the main driving force influencing river floodplain ecosystems. The dominant role of the flood pulse on the success of non-native species (NNSs) is what differentiates floodplains from other ecosystems, in terms of invasion. In this review, I discuss some patterns related to the performance of NNSs in response to the flood pulse. First, floods connect floodplain habitats and spread propagules of NNSs, causing ‘propagule pulses’ in these ecosystems. After the establishment of NNSs, floodplains may function as steppingstones for future invasions, because propagule pulses enhance invasions in nearby landscapes. Second, the flood pulse changes environmental filters, with consequences for invasion success and for the coexistence of native and NNSs. Flooding represents a disturbance that enhances the success of some NNSs by reducing biotic resistance and changing resource availability, but diminishes the success of others. Drought enhances the invasion success mainly of NNSs that colonize the aquatic-terrestrial transition zone. Third, impacts caused by river regulation and global changes alter the flood pulse, which in turn affects invasion success. There is a great degree of idiosyncrasy in these patterns, but they pose a broad perspective that helps to understand and manage NNSs in floodplains.
1. Macrophytes play important functional roles in river ecosystems, providing habitat
and food, as well as influencing flow, water chemistry, and sediment dynamics.
They also represent an important component of river biodiversity.
2. Artificial river barriers have the potential to disrupt macrophyte dispersal, and
compromise their distribution and persistence, but little information is available
compared to barrier impacts on fish and macroinvertebrates. Here, we review the
mechanisms supporting dispersal of river macrophytes in rivers and evaluate the
nature of barrier impacts on macrophytes.
3. Hydrochory (dispersal of propagules by water) is the principal mechanism of downstream
dispersal, while zoochory (dispersal of propagules by animals) is likely to be
the most important vector of upstream dispersal and inter-catchment transport.
4. Most studies have focused on the impact of large structures such as dams, and the
findings indicate the impact is highly context dependent. Slow-flowing habitats
upstream of dams can act as traps to drifting propagules and thereby interrupt hydrochory.
However, the consequences of interrupted hydrochory for downstream
populations are unclear. River regulation can result in lower macrophyte diversity,
although the lentic habitats associated with reservoirs can also favour an increase
in the abundance and richness of macrophyte communities.
5. Instream barriers are unlikely to affect zoochory by birds directly, but barriers
are well known to restrict fish movements, so there is considerable potential for
barriers to disrupt zoochory by fish, although no empirical study has specifically
examined this possibility.
6. There is a paucity of studies examining the impacts of low-head barriers on macrophyte
dispersal. Given the influence of macrophytes on river processes, we call
for further research into barrier impacts on macrophyte population dynamics in
order to gain a better understanding of the consequences of river fragmentation
for fluvial communities and ecosystem functioning.
Cecropia peltata L., an early successional neotropical tree species, was introduced in Malaysia in the 1950s. Although the Azteca ants with which it is usually associated in the mainland neotropics are not present in Malaysia, Cecropia trees grow faster, suffer less herbivore damage, and are less often liana-laden than sympatric Malaysian pioneer tree species. These findings cause us to further evaluate the Cecropia-Azteca relationship and to consider other attributes of Cecropia that reduce its susceptibility to both vines and herbivores. Interpretation of the data on rates of leaf loss to herbivores is complicated, however, by the recency of Cecropia introduction and by the observation that native early successional trees at our study site in Malaysia suffered much less herbivory than native early successional trees on Barro Colorado Island in Panama and possibly elsewhere in the neotropics. Finally, substantial variation among individuals in the production of ant-related structures (trichilia and Mullerian bodies) was observed in Malaysia, variation that is presumably masked in the mainland neotropics.
Fossil pollen was used to map American beech (Fagus grandifolia) populations in Wisconsin and Michigan during the last 8000 yr. Among questions addressed were: (1) What were routes and rates of range expansion? (2) Did range expansion follow a @'wave-front@' model or occur by coalescene of outliers? (3) Has the range of beech been determined by environmental tolerance or by dispersal rate? Presettlement distributions were mapped from survey records. Range expansion was reconstructed using pollen diagrams from 34 sites, most in a 30-50 km grid. We show beech moving through southern Michigan into Wisconsin and Michigan's Upper Peninsula. During much of the last 8000 yr the range of beech was relatively stable and presumably environmentally controlled. Brief delays may have been occasioned by dispersal barriers. Range expansions occurred during the last millennium, as well as 3000-2500 yr ago and 8000-5000 yr ago. Several separate colonizations across Lake Michigan formed temporary outliers. No other past outliers were detected, although modern outliers are known; however, even with closely spaced sites, outliers may have been undetected.
Persistent distribution patterns of woody vegetation within the bottomland forest of Passage Creek, Virginia, were related to fluvial landforms, channel geometry, streamflow characteristics, and sediment-size characteristics. Distinct species distributional patterns were found on four common fluvial geomorphic landforms: depositional bar, active-channel shelf, floodplain, and terrace. Independent hydrologic characteristics (flow duration and flood frequency) were determined for each of the landforms. Vegetation patterns appear to develop more as a result of hydrologic processes associated with each fluvial landform rather than from sediment-size characteristics. -from Authors
During the Holocene boreal and temperate tree species advanced into deglaciated regions of North America at rates averaging 100-400 m per year. The mechanisms are examined by which shade-tolerant, long-lived and generally slow-growing late-successional tree species (beech Fagus grandifolia and hemlock Tsuga canadensis) were able to extend their ranges rapidly and to invade forest communities. -from Author
The interaction between spread of a plant species and its population growth rate is discussed. Three parameters, population growth rate at an infection site, fractional loss by dispersal and the distance this fraction can move were used to build a simple model of spread. The effect of changes in these parameters on rates of spread, patterns of spread and total population growth rate were examined using simulation. There was no simple arithmetic relationship between the parameters, spread and total population growth rate because of spatial limitations on the spreading population. Rates of total population growth tended to be exponential and rates of spread linear. /// Обсуждается взаимосвязь между распространением видов растений и скоростью роста их популяций. Три параметра, скороств роста популяции на зараженном участке, частичная потеря при расселении и дистанция этой потери могут измениться при использовании их для построения простой модели распространения. Влияние изменений этих параметров на скорость распространения, характер распространения и обшую скорость роста популяции проверяли методом моделирования. Не найдено простой арифметической зависимости между параметрами, распространением и средней скоростью роста популяции в результате пространственного ограничения, расселяющейся популяции. Колебания скорости роста популяции имеют тенденцию к форме эксдоненциальной кривой, а скорости расселения - к линейной.
Vegetation was classified and mapped along the small meandering River Kamajohka in peatlands in northernmost Finland. The results show a mosaic of thirteen communities, mainly woody grasslands and mire types. They may be schematically arranged into a developmental order that represents the flood-controlled successions on well-drained and poorly-drained areas. Channel migration largely determines the boundaries between vegetation groups, and river migration is a natural perturbative factor that causes continuous site turnover. All of the current floodplain vegetation has originated from riparian primary successions, and all riparian vegetation may be destroyed by further river erosion. Some vascular plants benefit from special habitats created by river channel migration, though flood influences (duration and magnitude) are probably the most important factors affecting species distribution. Six recent channel abandonments illustrate the heterogenous nature of sedimentary patterns and vegetation successions; they are important components of the vegetation mosaic along the river.
Experiments with seeds of the guanacaste tree, E. cyclocarpum (Jacq.) Griseb., indicate that scarification of the seed testa may be more beneficial than heat treatments in stimulating rapid germination but that a humid environment and warm tropical temperatures are completely adequate for this process. Based on these data, the possibility that megafauna served and presently serve as principal agents of seed dispersal is questioned. Dissemination by water (hydrochory) is suggested as an alternate strategy.
The small perennial monkey flower Mimulus guttatus is common to mesic habitats in the Wasatch Mountains of Utah. Field and laboratory experiments suggest that seeds can be carried over long distances by flowing water but not by wind; pollen transport appears to be localized. Two indicators of genetic differentiation, crossing barriers and morphological dissimilarity, varied substantially between populations in the Big Cottonwood Canyon area near Salt Lake City. This variation was explained more by differences in physical environment than by barriers to gene flow through seed dispersal, but multiple regressions explained little of the variation overall. Thus plants appear to retain some similarity because of similar selective regimes imposed by the physical environment, but random processes associated with rapid extinction and reestablishment of populations probably influence local patterns of microevolution strongly.
(1) Salix setchelliana is a prostrate clonal willow that grows peripherally from a horizontal root system. Vertical shoots are typically 5-20 cm tall. The growth and demography of shoots and clones have been examined in Denali National Park, Alaska, and have been related to the transitory gravel bar habitat. (2) Shoot emergence and death rates, measured along two river systems, did not show significant year to year variability, but were affected by position within a clone. Shoot death, but not shoot emergence, differed between the patches sampled. Shoot survivorship curves are log linear. (3) Patch survivorship, measured in one river system, averaged 95% per year. Clonal expansion rates averaged 0.25 and 0.19 m year-1 at the two locations examined. Clones vary in their percentage of expanding versus non-expanding edges; the non-expanding edges are associated with old channel banks or gravel with large rocks and large shrubs. Clonal segments broken off by migrating river channels appear to be able to serve as long-distance propagules. (4) S. setchelliana exhibits rapid radial spread, reducing the likelihood of genet extinction in its transitory habitat.
The importance of hydrochory, or seed dispersal by water, to the regeneration of Taxodium distichum (bald cypress) and Nyssa aquatica (water tupelo) as examined in a forested floodplain of the Savannah River in South Carolina. Seedfall and dispersal by water were quantified for 2 yr using floating seed traps. Water depth, surface velocity, and flow direction were monitored over the same period. Seedfall for bald cypress and water tupelo occurred primarily from early fall throughout the winter, when water levels were rising in the swamp. Extended buoyancy periods for newly released seeds and fruits (bald cypress: 42 @+ 37 d; water tupelo: 85 @+ 36 d) prolonged dispersal for both species. Flowing water transported experimentally released seeds long distances, but in a uniform direction, and concentrated them nonrandomly against logs, trees, knees, and other emergent substrates. An examination of the soil seed banks in five microsite types supported the results of the seed transport study. Lowest woody seed densities occurred in the open areas, and highest seed densities occurred in sediments adjacent to emergent substrates such as logs. Additionally, elevated water levels of 1-2 m caused by short-term, high-discharge floods scoured seeds of Nyssa sylvatica var. biflora, Quercus spp., Liquidambar styraciflua, Pinus taeda, and other species from adjacent bottomland hardwood communities and transported them into the bald cypress-water tupelo forest. We conclude that elevated water levels, which occur during late fall when seeds are released, influence the distribution of bald cypress and water tupelo seeds and their availability for recruitment. Short-term, deeper floods may also be important for seed transport among bottomland hardwood communities that are spatially separated or differ in species composition.