---

Contents:

How relevant are ecologically equivalent species and vacant niches to the invasive potential of introduced woody plants ?

Binggeli, P.  University of Ulster, Coleraine, North Ireland

 The widespread occurrence of invasive woody plants as well as their ability to displace native vegetation on oceanic islands would suggest that species disharmony, the flora`s lack of competitive ability or the existence of vacant niches may explain, at least to some degree, islands susceptibility to invasions. A review of the known instances of invasive woody plants in both island and continental settings does not provide a firm answer to the relevance of ecological equivalence and vacant niches to invasion failure or success.

Spread of neophytic trees and shrubs in South-Western Germany

Böcker, R. & Dirk, M. Universität Hohenheim, Stuttgart, Germany

 The spread and dispersal of neophytic species were studied in south western Germany and experiments on their biology were conducted. Some of the species are growing as agriophytes (mixing with the natural vegetation, sensu LOHMEYER & SUKOPP 1992). The following species were studied: Ailanthus altissima, Robinia pseudoacacia, Paulownia tomentosa, Prunus serotina, Buddleja davidii and others.
 Results on vegetation types formed by these species, biology and growth strategies are submitted.
 The dynamics of flora and vegetation have been studied and analyzed for a long time in differet areas, normally dealing with the indigenous flora and their distribution. Newcoming shrub species got more and more in the center of interest in the beginning of this century. Already in those days problems arising by the introduction of neophytic species were recognized.
 Baden-Württemberg in south-western Germany has very variable geological and climatical properties. The southern Rhine-valley is the warmest area all over Germany, so many of the aliens shrubs and trees here have very good growing conditions.
 The majority of aliens (more than 4000) introduced into our gardens and landscape do not form a problem but the few which escape from cultivation can invade our semi-natural and man made ecosystems. We know very little about the process of invading because up to the moment no monitoring programs exist by which the speed of invasion is precisely documented. The agriophytic species (in south-west Germany we have more than 120 species, LOHMEYER & SUKOPP 1992) are able to mix up with our natural plant communities. The newcomers must be observed in a critical way. The progress of invasion has to be documented and on the other hand the measures and methods of control must be derived.

 Tree and shrub species (beside the already mentionend) being in continuous spread in south west Germany are: Acer negundo, Aesculus hippocastanum, Amelanchier alnifolia, A. lamarckii, Berberis thunbergii, Buddleja davidii, Castanea sativa, Cornus sericea, Cotoneaster div. spec., Cryptomeria japonica, Fraxinus pennsylvanica, Koelreuteria paniculata, Laburnum anagyroides, Mahonia aquifolium, Prunus laurocerasus, Prunus serotina, Pseudotsuga menziesii, Quercus rubra, Rhus typhina, Rosa rugosa. With some of these most common ones, seed experiments on different substrates were performed the last three years.

(Im)migration of Cyperus esculentus in Europe

ter Borg, S.J.  Wageningen Agricultural University, Netherlands

 In the early seventies Cyperus esculentus was introduced in the Netherlands, as a contaminant of gladiolus bulbs, probably collected in the USA. It soon became a problem in agriculture, due to the extensive production of rhizomes and tubers. We studied the intraspecific variation and distinguished four varieties. This information allowed us to state that one var. had been in southern Europe from old times, two had been introduced in the Netherlands, from where they may have spread to Belgium and Germany, but the fourth, with the widest distribution in Europe had already been brought to France, (with gladiolus ?) in 1947. This taxon, C. esculentus var. leptostachyus, still seems to migrate; the most recent report came from Hungary, where it may have been introduced with maize seeds. In France, by now it is locally common in the natural vegetation on the Loire banks.

Ecology and diffusion dynamics of Eclipta prostrata (L.) L. in Sardinia (Italy)

Brundu, G., Satta, V. & Venditti, T.  Università di Sassari, Italy

 Eclipta prostrata (L.) L. is an annual aquatic emergent plant. It has a wide geographical distribution, mainly in the tropical and temperate-hot areas. From California it has spread to the southern part of the United States, in Africa and Eastern Asia. Growing quite exclusively in wet sites like channels it has become an aggressive weed in many rice fields. As a result of rice cultivation, this plant has extended its distribution area in the south of Europe.
 It was first recorded in Italy in 1902 and the plant was described as Eclipta alba (L.) Hasskarl var. neapolitana Terraciano, at Campi Flegrei, Bagnoli, Posillipo and on the shores of Lake Averno.
 In spite of further field researches, there were no further finds in these stations. It was however found in Lazio in 1958 and in Sicily in 1992. These new reports were not confirmed subsequently, thus the species still has not a definite distribution in Italy.
 It was first recorded in Sardinia in 1988. The author emphasized that the species was well suited to the climate of south Sardinia, and that the ecological needs of the plant, as far as germination and growing were concerned, were sub-optimally satisfied.
 E. prostrata grows in Sardinia following the cycle of rice cultivation, starting from July.  The rise in temperature, together with a great availability of water in the rice-field, creates a micro climate of subtropical-kind and the plant flowers until October. The prostrate-ascending growth form promotes the natural tendency to produce roots from secondary shoots of the stem. As a result the plant can form big tufts, isolated or in wide colonies.
 The rice fields, in which the weed grows, lie in soils locally called "Gregori" which are typic palexeralfs, according to USDA Soil Taxonomy. These soils, present in the Campidano plain, are rich of pebbles, have a high content of clay and are not well suited for many agricultural uses with the exception of rice cultivation.
 The colonisation process starts from the raised banks, were the plant grows vigorously. From here it moves to the rice field (camera) during the dry phase of cultivation, shortly before harvesting, especially when other weeds have been eliminated by means of herbicides. Apart from competing directly with the rice plants, the alien is very harmful because its still-green mass clogs the operating mechanisms of the harvesting machines.
 There is a significant damage to production and, in addition, the weed may be spread to other agricultural areas of Sardinia and Italy, because many of the rice field in the Island are seed-fields.
 The weed finds refuge in the raised banks of artificial channels and in the wet areas surroundings the fields. Its growth is helped by inadequate and/or inefficient cleaning of the channels and so it grows undisturbed during the summer period.
 Control techniques should not be limited only to cultivation areas. As a general rule, the spreading of E. prostrata in Sardinia has been favoured by negligence. Since the first records, restricted to few stations, the plant has today invaded almost all the rice fields in the Island.

The cases of threatened indigenous plants invasion into anthropogenous ecotopes

Burda, R.I.  Donetsk Botanical Gardens, Donetsk, Ukraine

 By way of illustration of three oligotope species a tendency to colonize nonstandard anthropogenous ecotopes, shown by alien populations of indigenous species, which belong to a category of vulnerable, because of natural or anthropogenous reasons, is being observed. In this respect the most significant is the south Black sea coast endemic, a component of the psammophyte - halophyte floristic complex Gypsophilla paulii Klok. It has widely spread within Ukraine especially in its south-east by way of expansion in technogenous ecotopes. It has been repeatedly found by us in abundant populations in the industrial sites of metallurgic and chemical plants, along railroads in Donbass cities.
 In the south - east of Ukraine Cephalanthera longifolia (L.) Fritsch, a Euroasian species of broad - leaved woods, has been observed only in the flood-lands of the Seversky Donets in the mouth of the river Krasnaya. In the Red Book of Ukraine its distribution is confined by the latitude of Kiev. It has been recorded by us in the Donets ridge in the ravine oak-woods “Stupki” near Chasov Yar (nor more than 20 individuals) and in the reserved territory “Velikoanadolsky” in the Azov sea area. The latter population we regard as an alien one because the wood of Velikoanadol is a completely artificial forest - plantation in the former herbaceous-fescue-needle-grass steppes. C. longifolia grows in the plantations of Quercus robur a quantity is up to 55 thousand individuals.
 In the Red Book of Ukraine Platanthera bifolia (L.) Rich., an Euroasian species of broad - leaved forest is not reported for our latitude. However, according to our data it grows in flood-land oakgroves along the Seversky Donets and in ravines of the Donets hills. But its populations are scanty (up to 30 - 50 specimens) and inhibited. The exception is P. bifolia in the Makaticha gully, which numbers more than 1000 specimens. An intensive spread of this species in this habitat occurs in the oak-maple plantations which are 45 - 50 years old.
 How to evaluate these cases: as natural ways of renewal of a disappearing species or as a “floristic falsification” causing a further anthropogenous transformation of ecosystems ?

Naturalization process of Pinus halepensis Mill. in Sardinia (Italy)

Camarda, I., Brundu, G., Satta, V. & Venditti, T. Università di Sassari,Italy

 The diffusion of plants made by man is a process difficult to control, especially for those ones which have some economic interest. For some plants that have been used for human purposes since ancient times, it is often quite problematic to assess the original distribution area.
 One of these is Pinus halepensis Miller, whose natural distribution area, although discontinuous, is spread along the coast of many countries of the Mediterranean basin.
 In Sardinia, the oldest known nuclei are in the south-west coastal area, i.e. on the island of S. Pietro and along the gulf of Porto Pino.
The island of S. Pietro is mainly made up of effusive rocks. After the presence of Carthaginians and Romans, it was left uninhabited until 1737. Afterwards, it was populated by a colony of Genoese sailors, who found quite large woods of this species on the island on their arrival.
 Aleppo pine is an heliophilous and thermophilous species that prefers calcareous soils. It requires little and it is well fitted to the variable Mediterranean climate. The serotinous cones are adapted to fire and the high temperatures promote the seed escape and  the anemochory dispersal, and improve the germination rate. Thus, many authors have highlighted its capacity to recolonise burned sites in many areas of the Mediterranean.
 Fires are not, in fact, a good explanation for the colonisation processes that we describe for some areas of Sardinia. They are much more likely to be related to fitness to nutrient-poor soils with scarce vegetation cover, when the competition with other species is low.
 In the surroundings of Sassari, on Miocene Limestone, this process of colonisation is in progress and is not related to previous fires. As a result of the abandonment of olive grove cultivation and of cessation of soil tillage, there has been a vegetative regrowth of the wild rootstocks and large clumps of wild olive trees (Olea europaea L. var. sylvestris Brot.) have formed. Soil tillage, traditionally carried out in spring and in summer, was a serious obstacle to the colonisation of the fields by the species of the macchia and by Pinus seedlings. Now, by contrast, the following species are able to cover the soil to a great extent: Pistacia lentiscus L., Rhamnus alaternus L., Olea europaea L. var. sylvestris Brot., Lonicera implexa Aiton, Rubia peregrina L., Smilax aspera L., Asparagus acutifolius L., Spartium junceum L., Anagyrys foetida L., Ruta chalepensis L., Cistus incanus L. and P. halepensis.
 In these sites, the physionomy of the vegetation is made up of two layers, dominated respectively by wild olive and Cistus plants. The young plants of Aleppo pine are from 1 to 15 years old, the oldest ones are about 3-4 metres high and they produce cones regularly.
 A similar evident process of colonisation is present along the road cuttings, around Sassari. This process is also active, even if less evident, in a few similar habitats along the Island.
 In the absence of certain paleobotanical evidence, it is difficult to decide if the Aleppo pine is truly native to Sardinia. In spite of its presence since ancient times, the diffusion remained restricted.  The colonisation is not present in sites that would seems favourable to the process and where Aleppo pine has been successfully introduced by means of reforestation. The natural process of colonisation, in the case of Sardinia, cannot be easily understood. It is not directly related to fires, while bare lands and abandoned cultivated fields are strictly linked to colonisation processes.
 

Fruit and seed production in Gleditsia triacanthos

Colombo-Speroni, F. & de Viana, M.L.  Universidad Nacional de Salta, Argentina

Gleditsia triacanthos is a legume that invades the montane forest gaps in North Western Argentina. Invasion success dependes on both: the features of the environment and the biological characteristics of the alien plants (seed production, dispersal, estabilishment and ability to maintain a viable population). We studied G. triacanthos fruit and seed production in four invaded gaps, sampling ten adult trees in each one. Fruit production starts at 10 cm DAP and there are no further increments in production with DAP. However, fruit weight decreses with DAP while seed number per fruit increases. These results agree with the characteristics proposed by Rajmanek and Richarson (1996) for invasive species, such as early fruit production that remains constant allover its life cycle. On the other hand, there are no significant differences in fruit and seed production nor in seed number per fruit between patches; that support the Choes`s hypothesis about the species conservative characteristic of reproductive traits. These results are compared with other invasive species.

Rate of invasion of Impatiens glandulifera Royle in the middle section of Odra river valley

Dajdok, Z., Aniol-Kwiatkowska, J. & Kaçki, Z.  Wroclaw University, Poland

 In many European countries Impatiens glandulifera becomes more and more common not only in ruderal but also seminatural or even natural habitats. The rate of expansion of this neophyt in Poland seems to be smaller than for example in the Czech Republic, but in fact there is lack of findings of the real number of its localities in our country.
 I. glandulifera has been recorded both from the springs of Odra river, and the mouth of this river as well, but till the early 70th there were no recorded localities on the territory of the middle section of Odra valley. During 3-year researches we have found almost 20 new localities of this species along 30 km part of Odra valley (between two towns: Olawa and Wroclaw) and many more in ruderal habitats near villages. Himalayan Balsam rivals there with both native and other alien plant species. Some individuals of the I. glandulifera have been recorded in such plant communities like: Polygono-Bidentetum, Calystegio-Archangelicetum litoralis, Cuscuto-Convolvuletum, Phalaridetum arundinaceae and Urtico-Calystegietum. It was found also in riverside forests of Alno-Padion. But the biggest and most dense stands of I. glandulifera were classified as Impatienti-Calystegietum (MOOR 1958) Soó 1971, which prefers semi-shaded borders of forests, not far from the river. Habitat conditions of different localities of the species have been compared using ecological indicators of light, moisture, trophic conditions, acidity, soil dispersion, and humus content.

Medieval castles as centers of spread of non-native plant species

Dehnen-Schmutz, K. Technische Universität, Berlin, Germany

 In the Middle Ages (11th -13th cent.) many castles were built on top of hills and rocks to have an optimal strategic position. Since that time non-native species had the chance to establish in the vegetation around the castles. Waste, castle-gardens and visitors are the main sources of diaspores.
 Plant species of walls and rocks of 56 medieval castles in South and South-Eastern Germany were investigated showing in summary 372 vascular plant species and ferns, 25 % were non-native species (91 species).
 It was found that the position of the castles to the next settlement has an influence on the number of species. Castles in a settlement had less species on the whole than castles nearby or far away, but the number of hemerochore species was higher. The sites in the settlement had more neophytes than archaeophytes, whereas outside more archaeophytes than neophytes occurred. Also actual intensive used castles had more neophytes in contrast to un-used castles.

A critique of the general approach to invasive plant species

Edwards, K.  Institute of Botany, Trebon, Czech Republic

 It is assumed that the establishment and spread of non-native, invasive plant species results in decreased diversity of native flora and fauna, possibly threatening rare and/or endangered species, and may change ecosystem processes. Accidental and deliberate introductions of these species also is leading to the homogenization of the world's communities, blurring the boundaries between biogeographical realms.  While many examples exist for invasive animal species in support of the first two arguments, such data are much less numerous for plant species. Usually, management actions are initiated against invasive plant species before ecological studies are conducted to determine the ecological values and problems of these species.
 Management actions should be based on sound ecological information; the lack of such information for most invasive plant species means that such studies should become a priority.  In addition, management focuses mostly on controlling a particular invasive species and not on the disturbance which allowed it to establish originally; such management considers the effects of environmental degragation, but not the cause.  A more holistic approach is recommended, placing the invasive species within an ecosystem context and incorporating larger spatial and temporal scales than are normally considered. Such an approach requires obtaining data about these upper level processes before formulating and implementing a management plan.

The successful strategy of the expansive alien plant species Bunias orientalis L. - I. The role of anthropogenic disturbance

Dietz, H., Steinlein, Th. & Ullmann, I.  Universität Würzburg, Germany

 Within the last three decades the alien (east-European) colonizer plant species Bunias orientalis L. (Brassicaceae) has spread rapidly in several agricultural regions of Central Europe, potentially posing a threat for farmers and species-rich plant communities. Although it lacks clonal growth, the polycarpic perennial B. orientalis is able to quickly establish dominance stands. In search for the key factors underlying the high colonization ability of the species the population structure and dynamics were comparatively studied in sites with differing disturbance regimes.
 B. orientalis profits from anthropogenic disturbance in every stage of its life-cycle, particularly from widespread features such as moving or manipulation of top-soil. Its ability to effectively expoit the transiently high resource availability following disturbance is based on high recruitment rates, rapid seedling growth, rapid and extensive regeneration of established individuals, vegetative propagation via root fragments, increased reproductive output in the year after disturbance and reduced mortality. These opportunistic traits lead to rapid space pre-emption following disturbance events, favouring both, new establishment to dominance stands and stand persistence. We, therefore, hypothesize further spreading of the species under the present anthropogenic disturbance regimes.

Biological control of leafy spurge, Euphorbia esula, an economic and ecologically sensitive approach to control an exotic weed in the United States.

Hansen, R.W. & Richard, R.D.  USDA, APHIS, PPQ, Bozeman, MT
Parker, P.E. & Wendel, L.E.  USDA, APHIS, PPQ, Mission, TX

 Leafy spurge, Euphorbia esula , Euphorbiaceae, is a perennial plant native to Eurasia originally documented in the United States in 1827. Since that time, leafy spurge has become widespread in the west, midwestern, and northeastern areas of the United States. Economically, leafy spurge has caused a substantial adverse economic impact upon the farm and ranching community. Annual primary and secondary economic costs associated with leafy spurge on grazing lands in the Northern Great Plains for 1995 is estimated to exceed $144 million. Since 1988, the United States Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine (USDA, APHIS, PPQ) has conducted a classical biological control implementation program against leafy spurge in the United States.  Nine Eurasian insect species have been imported and released in 188 counties in 19 states. The most successful established insects (Aphthona spp.) now allow for massive collection and redistribution to new locations nationally. Data from permanent transects are presented from two separate grassland locations in Montana infested with leafy spurge. These data show declines in leafy spurge stem density and leafy spurge canopy cover, and increases in grass cover, over time due to Aphthona spp. biological control agents. The benefits of classical biological control of leafy spurge are far reaching. Classical biological control of leafy spurge has demonstrated itself to be ecologically sensitive to native plants and the environment.

Invasion history and ecology of Pinus strobus in the Elbe Sandstone Mountains

Hadincová, V. Botanical Institute, Pruhonice, Czech Republic

 An alien north American pine species Pinus strobus has been cultivated in the Elbe Sandstone Mountains area (so called Saxon-Bohemian Switzerland, Czech Republic) since the end of the 18th century. According to our survey, however, its more frequent spontaneous regeneration started as late as at the turn of the 1960s and 1970s, and was followed by a massive invasion in the  1990s.  The relic pine forests (alliance Dicrano-Pinion, ass. Dicrano-Pinetum) which skirt rock edges are the plant communities most endangered by the invasion. P. strobus spread also into scrub and rock communities. New stands with P. strobus are dense and shady and have thick detritus layer because of the slow needle decomposition during two first years after they drop down and because of the large needle production. Under such conditions, native understory vascular plant species dissapear.
In our study we compared those characteristic of P. strobus and P. sylvestris which could explain the invasion success of  the former. The results can be summarized as follows:

(1) Final number of germinated seeds was not influenced by the needle extract of both species but the germination of P. strobus was delayed.

(2) In the glasshouse experiment, seedlings of both species grew best when cultivated under low nutrient concentrations and under pH 6.2 and 4.0. Both very low and high nutrient concentration and  pH value suppressed P. strobus seedlings  less than P. sylvestris one.

(3) In cultivated forests, young trees and 50 years old trees of P. strobus grew faster than  those of P. sylvestris.

Comparative study of Pinus strobus L. and Pinus sylvestris L.: growth at different soil pH and nutrient levels

Hanzélyová, D. University of South Bohemia, Ceské Budìjovice, Czech Republic

 The invasion of Pinus strobus into the forest ecosystems of northern Bohemia, Czech Republic, occurring during the last 20 years, has probably several reasons. Quite important can be the changes of habitat conditions on some sites as a consequence of a high nitrogen deposition and soil acidification. The main aim of the present study is a comparative assessment of conditions affecting seedling establishment in P. strobus - an invasive species originating from N. America, and P. sylvestris - a native  European species. Seedlings of both species were grown under different conditions of pH and nutrient supply.
 The seedlings were cultivated in a greenhouse in nutrient solutions with pH = 2.7, 4.0 and 6.2 - all at nutrient level of 2x basic nutrient solution (BNS, INGESTAD & KÄHR 1985) respectively, and in solutions with added nutrient levels: distilled water, BNS, 2x BNS, 4x BNS and 6x BNS (all at pH= 6.2). The influence was investigated of the experimental treatments on the dry weight of shoots and roots, the ratio between root and shoot dry weight (R/S ratio), and the relative growth rate (RGR) of the seedlings, their survival, number of lateral branches and dormancy of apical buds. Significant differences were found between the growth and development of P. strobus and P. sylvestris seedlings. P. strobus seedlings were less sensitive both to low pH (pH = 2.7) and high nutrient levels (4x BNS and 6x BNS). The seedling biomass and RGR were significantly higher in P. sylvestris than in P. strobus grown under favourable conditions (pH = 4.0 or 6.2 and 2x BNS). Under unfavourable conditions (pH = 2.7, distilled water or 6x BNS) the total dry weight and R/S were similar in both species, but P. sylvestris  seedlings had a significantly higher mortality. The conditions of cultivation influenced the onset of dormancy in the apical buds and the number of  branches formed by both species. Their seedlings grown at pH = 2.7 or in distilled water formed either no branches at all or (seldom) only one branch; their apical buds developed one month later than in the other treatments. The average number of branches formed by one seedling was one in P. strobus  and two to three in P. sylvestris. The results  of this study show that under unfavourable conditions (low soil acidity and/or very high or very low concentrations of nutrients in the soil) the establishment  and subsequent growth are more probable in P. strobus seedlings than in those of P. sylvestris.

Habitats of Lythrum salicaria in the Trebon basin biosphere reserve in comparison with the species secondary habitats in North America

Hanzélyová, D., Kvet, J.  University of South Bohemia, Budijovice, Czech Republic
Edwards, K.    Institute of Botany, Trebon, Czech Republic

Environmental characteristics (soil nutrients and water levels) and species lists were used to compare wetland habitats in central Europe and the U.S. with Lythrum salicaria. Relevs were used to generate species lists, which were then used to classify the European communities. L. salicaria is a native species of European wetlands but is an aggressive invader of temperate North American wetlands. We hypothesized that biotic characteristics (e.g. mean shoot height and shoot density per unit area) would differ between invasive and native populations, as well as species composition and richness. Environmental characteristics would be important in explaining the differences in biotic characteristics between different habitats but that U.S. and European L. salicaria would grow in similar habitat conditions.

Invasive plants and biodiversity conservation in the East Usambaras, Tanzania - status and management implications

Johansson, S.G East Usambara Catchment Forest Project, Tanga, Tanzania
Katigula, M.I.L. Inst. f. Aerospace Survey & Earth Sciences, Enschede, Netherlands

 The East Usambara rain forests in Tanzania is one of the global biodiversity hot spots and centres of plant diversity. They secure the water supply in the Tanga area, and local people depend on the forests for many of their needs. In 1902 an Agricultural and Biological research station was founded in Amani. By 1914 close to 1,000 different species and varieties had been introduced, including several potential invasive species. In the 1980’s, when commercial harvesting and pit sawing was at its peak, the invasive behaviour of Maesopsis eminii raised considerable concern as a potential threat to the forests and the biodiversity in the East Usambaras. Other species which raised concern were e.g. Clidemia hirta and Lantana camara. In 1987 commercial harvesting was banned while a pit sawing moratorium was introduced in 1989. The East Usambara Catchment Forestry Project, supported by the Finnish government, has worked since 1990 with the mission to protect the East Usambara forests and establish a nature reserve in Amani. As a result of the project efforts disturbance, especially within Amani Nature Reserve (ANR), has been contained. Studies have been made to up-date the status of invasive species in ANR. According to these studies disturbance was the major factor promoting the spread of Maesopsis eminii. They also suggest that Maesopsis, which is a pioneer species, easily colonises disturbed sites but that spread is effectively controlled by containing disturbance. It is also appears that regeneration of primary forest species is developing under the stands of Maesopsis, suggesting that it would be replaced by indigenous species in the progress of succession. From a management perspective it is very difficult to contain Maesopsis because it so easily re-colonises sites which are disturbed, e.g. through harvesting of the species, while simultaneously, attaining an acceptable regeneration of primary forest species through interventions is difficult and costly. It is also next to impossible to contain its spread in the non-protected forest areas, where agriculture and forest clearing provides continuous sites for colonisation. At present the most appropriate management strategy is to control disturbance which in any event is of primary importance for the conservation area. It also appears that while spreading easily, species such as Clidemia hirta, Lantana camara, do not pose any major threat and do not warrant any specific actions apart from monitoring. The potential threat of Psidium cattleianum, introduced early by the Germans, has also been noted although there are no clear signs of a visible spreading of the species. Since it has been introduced only on few restricted sites an effort to remove it using experience from Mauritius could be considered, while monitoring of the situation is important.

Invasive alien plants along watercourses of the Ruhr area

Keil, P. Universität Bochum, Germany

 Flora and vegetation of the riparian area of the River Ruhr and the Rhine-Herne-Canal (RHK), both in western Ruhrgebiet (North-Rhine-Westphalia, Germany) were studied in the early 1990s. All native and non-native species were recorded. The results show that among 603 recorded species 148 (24,5 %) were neophytes. The neophytes can be subdivided in 41,7 % epecophytes, 30,5 % agriophtys, 8,6 % synanthropic species and 18,5 % ephemerophytes. The most frequent invasive species with a wide distribution in the study area are Impatiens glandulifera, Reynoutria japonica, Bidens frondosa, Heracleum mantegazzianum, Solidago gigantea, Acorus calamus, Senecio inaequidens and Angelica archangelica ssp. litoralis. In the local frequency of these species some differences are obvious. For example, at the Ruhr Impatiens glandulifera, Bidens frondosa and Acorus calamus are found almost in the whole riparian area, while at the RHK these neophytes are much rarer. On the other hand, Reynoutria japonica, Solidago gigantea and Senecio inaequidens show an equal frequency at the Ruhr and at the RHK. Some rare but biogeographic interesting invaders in the study area are Coronopus didymus, Bromus tectorum, Cardaria draba, Datura stramonium, Ficus carica, Hordeum jubatum, Inula graveolens, Mimulus guttatus, Rapistrum rugosum and Sisymbrium loeselii.
 The results agree with other studies of riversystems (for example Elbe, BRANDES & SANDER 1995; Weser, BRANDES & OPPERMANN 1994; Oker, OPPERMANN & BRANDES 1993). - Compared to the flora of cities (for example Essen, REIDEL 1989; Berlin, SUKOPP ET AL. 1981; Halle, KLOTZ 1984; Bochum, SCHULTE 1984) or industrial areas (DETTMAR 1992, REIDL 1993) in Germany, the proportion of invasive alien plants in this study area was relatively low.

Stress on invasive alien plants: simulated herbivory and competition

Klipfel, St.  Universität Göttingen, Germany

 This study compared growth patterns of invasive alien plants under stress in introduced and indigenous populations of seven plant species. Different reactions to herbivory or competitive stress in introduced and indigenous populations could not be proved. However introduced populations produced more dry biomass than indigenous populations. Therefore this investigation supports the hypothesis that invasive alien plants invest more resources in growth and less in defense after a lag-phase of genetical adaptation to lower herbivory pressure.

Population-ecological determinants of spread in Atriplex sagittata

Mandák, B. & Pyšek, P. Botanical Institute, Prùhonice, Czech Republic

 It is generally accepted that  Atriplex sagittata (Chenopodiaceae) is a species alien to Central Europe, although the time of immigration is perceived differently in particular countries, e.g. it is considered an archaeophyte in Czech Republic and neophyte in Germany. This species has been remarkably successful in the last decades, becoming a dominant of ruderal communities as well as a serious weed of arable land. History of its spread as it is reflected in modern data sources (floristics, herbaria) is analysed and compared with the records from medieval settlements. A detailed study of  population biological characteristics, with special reference to the heterocarpy (production of different types of fruit), has been carried out and these data are used to interpret the spreading pattern found. Possible role of particular seed types and their contribution  to the invasive potential of A. sagittata are discussed.

Invasion of the accidentally introduced tropical alga Caulerpa taxifolia in the Mediterranean Sea

MEYER, U.     Freie Universität Berlin, Germany
MEINESZ, A. & DE VAUGELAS, J.  Université de Nice-Sophia Antipolis, France.

 The green alga Caulerpa taxifolia (Vahl) C. Agardh (Chlorophyta, Ulvophyceae) is a siphonous alga. It forms erect feathered fronds originating from horizontal stolons which are attached to the substratum by rhizoidal pillars. This alga usually occurs in the tropical warm waters of the Atlantic Ocean, the Red Sea, the Pacific and the Indian Ocean. In 1984, individuals of C. taxifolia were first observed in the Mediterranean Sea in front of the coast of Monaco, occupying an area of 1 m2. Five years later, the colony had developed to a surface of one hectare. The spread of this invasive alga has been progressing rapidly since its accidental introduction and the invaded sites have extended along the northern parts of the Mediterranean Sea. At the end of 1996, the total area more or less affected by the invasive alga was estimated at 3096 hectares, with 77 recorded stations along the Mediterranean coasts of France, Monaco, Spain, Italy and even Croatia.
 The rapid spread of C. taxifolia is due to 2 main causes: first, to the vegetative reproduction by fragmentation of the thallus and local dissemination of the fragments (which do not float but tend to sink when detached) as well as by ramification and growth of the stolons (maximum: 1860 mm in 10 months); second, to the dissemination at a wider range occurring through transport of algal fragments over long distances by boat anchors or fishing material. This tropical green alga produces several toxins (such as the terpene caulerpenyne), and has very few herbivorous consumers. C. taxifolia forms dense and durable covers on the sea bed with more than 5000 fronds per square meter at depths ranging from 2,5 to > 50 meters. Living individuals of the introduced alga have been found in the Mediterranean Sea at a depth of 99 m. This introduced alga presents ubiquistic characteristics, such as its capacity to colonize all kinds of substrates of the infralittoral zone (rock, sand, mud, gravels, seagrass beds). Furthermore, it can be encountered in exposed sites as well as in sheltered locations and has been observed in clear waters as well as in harbours or polluted environments. C. taxifolia constitutes a vigorous alien plant in the Mediterranean environment, where it is well established and now threatens most littoral ecoystems.
 The C. taxifolia individuals of the Mediterranean Sea present characteristics different from those of the original tropical form:

? in opposition to the individuals of tropical origin that have never been found in zones with a mean water temperature lower than 20°C, the Mediterranean individuals resist to water temperatures as low as 10°C;
? only releasing of male gametes has been observed so far in the Mediterranean form of C. taxifolia (monoic thalli in tropical waters);
? in the introduced Mediterranean individuals, the algal fronds can reach a length of up to 80 cm, but the tropical C. taxifolia  fronds rarely reach 20 cm;
? the Mediterranean form builds dense and durable meadows with up to 5000 fronds per square meter, whereas the tropical individuals occur only sparsely in small patches.

 Serious changes have been encountered since the introduction of C. taxifolia in the Mediterranean Sea, as the tropical alga is altering the endemic algal communities by an impoverishment of the species diversity. There has also been a noted decline in sea urchin populations and an impact on the ichthyofauna. A major ecological risk constitutes the invasion of the seagrass meadows of P. oceanica by the introduced alga, where the invasive C. taxifolia acts not only on the physiology and the morphology of this fragile marine phanerogam but also on the functional processes of the seagrass ecosystem. The invasion of C. taxifolia in the Mediterranean Sea constitutes therefore a major threat to all types of littoral Mediterranean ecosystems.

Poster: no Abstract

Environmental factors influencing plant invasions on the landscape scale

Mihulka, St.  University of South Bohemia, Ceské Budijovice, Czech Rebublik
 

Colonisation of an urban motorway embankment by Buddleja davidii Franch. in Northern Ireland

Paterson, J.P.H. & Cooper, A.  University of Ulster, Northern Ireland

 An elevated motorway with steep embankments consisting of crushed graywacke quarry stone (grizzly) has been constructed in Belfast (Northern Ireland). The embankments, which are moisture deficient during the summer months, have recently been planted with  tree species, most of which are native to Ireland. Buddleja davidii, a native of China, is colonising the embankments. It's spread appears to be influenced by the location of an established seed source associated with a derelict urban site, the direction of traffic flow (slipstream effect) and prevailing wind direction. The age (time since construction) of the embankments does not appear to have an effect on the establishment success of  B. davidii, which has higher growth rates (1-2 m yr -1) than planted tree species (0.05-0.5 m yr -1).

Pohl-Orf, M., Brand, U. & Bartsch, D. Universität Aachen, Germany

 With the introduction of new genes in cultivated plants that do not normally occur in its species or in its crossable relatives, the evolutionary principle of mutation and selection is accelerated in a way that can not be expected under natural conditions. The distribution of beet, Beta vulgaris, is ecologically limited due to their low competitiveness and susceptibility to a number of plant pathogens and phytophagous animals. Therefore, an escape of transgenic sugar beet attributes is more reliable through gene flow into populations of beet relatives than the escape of the transgenic sugar beet plant itself. It is important to emphasise that all cultivated and wild varieties of the beet (sugar beet, swiss chard, red beet or fodder beet) belong to the same species. That implies that there should be no barrier for outcrossing of fixed genetical qualities within this species. In our studies, the potential ecological advantage of virus resistance was assessed under conditions of virus infection and no virus infection. At experimental field test sites where virus was present, results showed a small but detectable ecological advantage of the genetically engineered trait. The biosafety of genetically engineered crops depend on the gene flow consequences on wild relatives. We attempt to assess what the likely fitness consequence might be of introgression of the transgene into wild beets growing near Italian seed beet production areas.

Poster: no Abstract

Ecological characteristic of Uzhgorod synanthropic flora (Ukraine)

Protopopova, V. & Miroslav, S.  Academy of Science, Kiev, Ukraine

Early growth and mortality in Impatiens glandulifera

Prowse, A.J.  Bolton Institute, Bolton, United Kingdom

 Seedlings in wild populations of Impatiens glandulifera were individually tagged and mortality recorded. High mortality rates were found which varied according to habitat and locally competing species. Major causes of mortality at the seedling stage were identified as slug predation, disease and (under tree canopies) physical damage from rainfall. Highest mortality rates occurred during the period between mid-May and the beginning of July. Plant height was found to be a good indicator of plant performance.

Röttgermann, M. & Steinlein, T.  Universität Bielefeld, Germany
Dietz, H.      Universität Würzburg, Germany

 Bunias orientalis, a perennial Brassicaceae, was introduced to Central Europe in the 18th century, entering a period of rapid spread within the last two decades, especially on roadside and distrubed locations. Earlier experiments in 1995 showed that B. orientalis has a strongly reduced performance under dense canopies with high plant competition. In a field study high regrowth under varying mowing intensities (i.e. different cutting heights) indicates, that B. orientalis is well adapted to disturbed sites and dominant stands and can develop on these locations. In an experiment with different mowing regimes vegetative growth parameters were studied for evaluating the performance of B. orientalis.
 Our results demonstrate that B. orientalis shows many typical traits of a successful colonizing plant species:
? The dominant structure of B. orientalis stands was not adversely affected by moderate mowing regimes (i.e. 2-3 times a year) on three different roadsides. The proportion of above-ground biomass to total standing crop was not significantly altered by an increase in mowing or seasonal effects (ANOVA, Tukey test) independent of the nutrient availability at different sites.
? The relative growth rate (RGR) of B. orientalis is highest under intensive mowing regimes (cutting height of 0 cm above ground). Under lower mowing-intensity (cutting height of 10 cm above ground) the relative growth rates decrease. Furthermore under a high intensity of mowing the RGR is higher if B. orientalis was mowed twice a year.
? Dominance stands with maximal vegetative and reproductive performance occur predominantly at locations with medium to high nitrogen supply and medium disturbance regimes.

Insect herbivory on invasive plants: Rhagoletis meigenii infestation on the alien invader Mahonia aquifolium and the native host Berberis vulgaris

Soldaat, L.L. & Auge, H.  UFZ - Leipzig-Halle, Germany

Oregon grape, Mahonia aquifolium (Berberidaceae), a fleshy-fruited shrub from western North America, now successfully invades semi-natural habitats in Western and Central Europe. Invasive Mahonia populations are infested by an indigenous fruit fly, Rhagoletis meigenii (Diptera, Tephritidae), a specialist pre-dispersal seed predator of the native and phylogenetically related barberry, Berberis vulgaris (Berberidaceae). Generally, infestation by Rhagoletis is much higher in the invasive than in the native host plant. Mean seed weight is the same in both host plants. However, due to the higher number of seeds per fruit food availability (total seed weight per fruit) is ca. 3 x higher in Mahonia fruits than in Berberis fruits. We hypothesize that the carrying capacity for Rhagoletis populations is much higher in the invasive host plant than in the native one because of the higher food availability.
In both host species ca. 50% of the ovules do not develop into ripe seeds. In Berberis this loss is mainly caused by abortion of ovules and seeds, whereas seed loss due to predation by Rhagoletis is much stronger in Mahonia than in Berberis. Long distance dispersal of Mahonia, and to a lesser extent local population increase, depend on seeds. Therefore, seed predation by Rhagoletis could slow down the invasion process.
In addition to the direct reduction of seed production Rhagoletis infestation facilitates fungal infection of the fruit. Frugivorous birds responsible for seed dispersal may avoid infected fruits as in other plant - frugivore systems. Thus insect herbivory may also have an indirect effect on seed dispersal and on the Mahonia invasion.

Invasion of North-American Blueberries (Vaccinium corymbosum x angustifolium) in Northern Germany

Schepker, H. & Kowarik, I.  Universität Hannover, Germany

 About 200 years after the first introduction of Vaccinium angustifolium und Vaccinium corymbosum to Germany, hybrids of these species escape frequently from commercial plantations in Niedersachsen (northern Germany). The invaded ecosystems include pine plantations, bogs, ditches and other linear biotopes. The evaluation of the blueberry invasions has to be differentiated: Only in bogs, conflicts with nature conservation are obvious. In pine plantations, however, the blueberries may even enhance the value for recreational activities.

Why can aliens plants prevail: growth patterns of Bunias orientalis underlying its rising dominance in some native plant assemblages

Steinlein, Th., Röttgermann, M.  Universität Bielefeld, Germany
Dietz, H.     Universität Würzburg, Germany

 The polycarpic perennial Bunias orientalis L. (Brassicaceae) introduced to Central Europe in the 18th century recently entered a phase of rapid spread accompanied by sudden establishments of extensive dominance stands mainly on roadside locations. We studied vegetation structure and expansion rate of B. orientalis stands and performed a series of experiments to investigate key factors that underlie the colonizing and establishment of B. orientalis. Reiterated observations exposed a high current expansion rate of B. orientalis populations and vegetation surveys of B. orientalis stands showed that these stands were mainly composed of Artemisietea and Arrhenateretea species. Regeneration experiments with root fragments revealed high regeneration capacities: root fragments of 3 cm length showed 93 % regeneration, varying water content (10 - 50 % water loss) and separation into root cortex and root stele yielded regeneration of 30 to 50 %. Vegetative growth parameters were studied in two controlled growth experiments with elevated nutrient availabilities. B. orientalis exhibited a high sensitivity to nutrient addition and rosette sizes of maximal 90 cm were reached. Biomass was comparable or even higher that that of native ruderals (Arctium tomentosum, Cirsium vulgare and Rumex obtusifolius) grown in the same experiment. Measurements of reproductive parameters revealed a high reproductive effort (0.2 to 0.45 g g-1) even under intense mowing regimes, resulting in a dense seed bank with maximal values of about 400 fruits (? 550 seeds) l-1 soil.
We conclude that:
? Long distance dispersal mostly occurs along traffic ways via highly regenerative root fragments in soil or dispersal by means of soil containing fruits.
? Establishment and rapid development of dominance stands is supported by high growth rates and a high reproductive effort.
? Local spread of initial metapopulations, i.e. short distance propagation is promoted by a high fruit set and high germination rates.

Regularities of emergence, distribution and invasion of alien species in the south-east of Ukraine

Tokhtar, V.K.  Donetsk Botanical Garden, Donetsk, Ukraine

 As a result of the investigations of the Ukrainian south eastern alien flora we have found 54 new adventive species. 4 of them have been reported for the Eastern-European plain for the first time (Ipomoea lacunosa L., Polygonum rigidum B. Skvorts., Pseudosaponaria pilosa (Huds.) Ikonn., Sesbania exaltata (Raf.) Schlecht., Oenothera wienii Renner ex Rostanski, Phalaris brachystachys Link., Polygonum argyrocoleon Steud. ex G. Kuntze, Sida spinosa L., Rubus macrophyllus Weihe et Nees).
 The aim of this study was to observe a further way of these species, which have been recently brought to our region, and to reveal regularities of the spontaneous, as it might seem process of emergence and distribution of alien species. For this purpose according to different features we have compared specific compositions of 5 categories of species:
? registered in the quarantine documents for imported loads, i.e. which have been brought into our region
? found for the first time
? which have spread into new habitats
? which have been colonophytes
? naturalized

This allowed us to elucidate some peculiarities of invasive plants. The specific compositions of the drifted and found alien species do not always coincide. Because, on the one hand, not all diaspores of migrating plants can be registered by the state quarantine inspection, on the other hand a number of species get into the south-east of our country in some other ways. Nevertheless, we have already found 21 out of 51 invasive species. The emergence of the rest of species is easy to prognosticate.
 The analysis of plants by their origin has shown that 33 north-american species are regularly brought into our region, 23 have been recently found by us, 12 of them have been discovered in new habitats and 3 have completely naturalized.
 Thus, our investigations have shown that prognostication of a number of alien species emergence in the south-east of Ukraine is a real task.
 A comparative analysis of plant species which are at different stages of naturalization allows to elucidate changes of quantitative features of these groups of plants. Under the conditions of the south-east of Ukraine mainly annual and biannual xeromesophytes, anemochores of the Poaceae family, of the north-american and european origin, which have the european-north-american and european-mediterranian-iranian-turanian types of area, have spread into new habitats.
 The success of the species invasion is also determinated by mechanisms of propagation systems. They may completely differ in different groups of species, however it is important for them to provide considerable variability for the populations of invaded species or to favour formation of adapted microspecies as in the case with species of the Oenothera L. genus. During naturalization the amplitude of variability of quantitative morphological features of populations of an alien type may weaken.
 So these data and the previous results, obtained while investigating some model invasive species (genera Amaranthus L., Oenothera L., Xanthium L.) allow to conclude:
1.) In the process of drift and naturalization of alien species a selection of species and biotypes which “correspond” to regional flora takes place. During naturalization the coefficient of populations features variation in some species of alien plants may decrease. In the course of this divergent evolutionary detached populations of alien species are being formed.

2.) The success of species invasion depends not so much on quantitaive factors (intensiveness and recurrence of drift) but rather on biological pecularities of species (including mechanisms of propagations systems), ecological conditions of different geographical territories, economic reasons.

Poster: no Abstract

The routes of plant migrations on the North Podlasie lowlands
(NE Poland)

Wolkowycki, D.  Warsaw University, Poland