E. Dana Sanchez (1), Juan Mota Poveda (1), Mario Sanz Elorza (2) and Eduardo Sobrino Vesperinas (3)

(1) Departamento de Biologìa Vegetal y Ecologìa. Escuela Politècnica Superior. Universidad de Almerìa. E-04120. Almerìa
Spain.
edana@ualm.es
(2) Gerencia Territorial del Catastro. Avenida Fernandez Ladrede, 28. 40002. Segovia.
Spain
(3) Departamento de Producciòn Vegetal Botanica y Protecciòn Vegetal. Escuela Tècnica Superior de Ingenieros Agrònomos. 28040. Madrid.
Spain
esobrino@pvb.etsia.upm.es

As a result of the increasing importance of exotic plants invasions, evaluation of alien flora in every country has became a necessary goal. In order to reach this aim, floristic lists, in wich other kind of information is recorded (as the extension degree in every territory or morphological and ecological characteristics of every species) should be a prioritary objetive.
For pushing this kind of research, the "Exotic Plants Database National Research Project" has been recently developed in Spain and its goal is to quantify and to study the alien flora of this country. Seventeen items allow us the recording of any information concerning any species. Our contribution here is based on this National Research Proyect and is an advance for the knowledgement concerning the exotic flora in the southeastern of Spain. The study area is Almerìa province (8,774 km2), a territory with a high landscapes diversity, wich has a wide altitudinal variation range in only few km. We may consider Almerìa province as representative enough of other sea-side regions in southeastern Spain; the goal of this paper is to reduce the multiple factors involved in the differences among invassiveness characteristics of  alien plant species in order to get a few parameters easier to use, and wich allow to improve prevention strategies for avoiding further plants invasions.
Our preliminary results show that about 300 exotic species (about the 10% of the total flora) may be found in this territory, although rather fewer show invassive behaviour. Paleo and Neotropical terophytic species showed the strongest invassive character and were the most numerous group. Hence, the prevention strategies should be focused on this group. The results also showed the high invading power of those southafrican species, mainly chamephytes and phanerophytes, and the lower invading power of the Chinese and Japanese species.
Finally, we remark the needing use of autochtonous flora, in sustitution of alien one.

Susan Donaldson (1) and Ellen Swensen

(1) University of Nevada Cooperative Extension PO Box 11130, Reno, NV 89520
U.S.A.
(775) 784-4848 (phone)
(775) 784-4881 (fax)
sdonalds@agnt1.ag.unr.edu

Tall whitetop (Lepidium latifolium) is a non-native weed from Eurasia that has invaded sensitive wetland and riparian sites in the western United States. The plant was first positively identified in the Lake Tahoe Basin in 1997, with anecdotal reports of infestation dating back to the early 1990s. Lake Tahoe is a unique national treasure famed for its unusual water clarity and surrounding beauty. Pressures from development and urbanization have resulted in an accelerated rate of eutrophication and resultant algae growth. It has been estimated that during the last 30 years, clarity as measured by secchi disks has decreased at a rate of more than one foot per year. Current research suggests that the lake is phosphorus limited, with erosion and sediment transport increasing phosphorus loads to the lake. Efforts to control erosion include construction best management practices, limits on growth, and preservation of streamside environment zones.
Tall whitetop forms colonies that dominate entire fields or wetlands. The name "tall whitetop" comes from the clusters of small white flowers produced from June through September. This weed expands by creeping underground roots that send up shoots to form new plants.
The weed is spread in a number of ways. It commonly travels in rivers and irrigation systems over long distances as seeds and rhizomes from eroded banks. Seeds and rhizomes are also spread in contaminated fill dirt or topsoil during construction and landscaping. They may be picked up and distributed to uninfested areas on tires and all types of equipment. Contaminated straw used in erosion control projects also moves this weed.
Tall whitetop is difficult to control due to its competitive nature and rapidly spreading roots. Research is underway at the Agricultural Research Service in Reno, Nevada to determine optimal control methods. Mechanical methods, including digging, mowing, tilling, mulching or shading have proved ineffective for control of established stands. To date, no biological control agent has been identified for this weed. In most cases, chemical applications provide the only effective control. In most cases, controls must be practiced over several years, and competitive vegetation must become established if the weed is to be controlled. Since tall whitetop prefers to grow in wet areas, extreme care is needed to avoid contaminating waterways with pesticides. Because tall whitetop has the potential to destroy sensitive streamside environment zones that are essential to the protection of Lake Tahoe's clarity, an effort was begun immediately to locate and map the weed throughout the Basin.
During the summer of 1998, a public awareness campaign was mounted by the University of Nevada Cooperative Extension and MAster Gardener intern Ellen Swensen. Local media ran stories on radio, television, and in local newspapers, and posters were placed in strategic locations. On August 15, 1998, the public was asked to call one of four locations, to report suspected locations of the weed. From these reports, 35 tall whitetop infested sites were identified, confirmed and mapped in the Tahoe Basin. The size of these infestations ranges from one plant to one-half acre dominated by tall whitetop. While the weed is found throughout the Basin, the largest infestation sites involve riparian areas adjacent to Trout Creek in South Lake Tahoe, a tributary to Lake Tahoe. There are several other infestation sites in the South Shore area as well as a number of sites at North Shore's Incline Village. Many of these sites fall within priority 1 and 2 watersheds critical to preserving the Lake's water clarity. At many of these sites, there is a co-incidence of straw bale usage and tall whitetop infestation. It seems likely that seeds or plant parts are entering via these erosion-control bales. The bi-state Tahoe Regional Planning Agency is aware of this issue and has changed their policies to require use of certified weed-free straw.
The current phase involves the implementation of site-specific control recommendations developed with the assistance of USDA/ARS. Local residents will be urged to "Adopt-a-Spot" for long term monitoring of control efforts. As the Lahontan Regional Water Quality Control Board has set a zero tolerance standard for pesticides in Lake Tahoe water, any chemical applications will have to be carefully controlled and monitored. Tall whitetop is a designated noxious weed in the state of Nevada, but is currently "B" listed in California, placing it lower on the list of priorities. In order to have any chance of successfully eradicating tall whitetop in the Lake Tahoe Basin, it must become a #1 priority for all Basin residents and agencies.

Marianne Erneberg

National Environmental Research Institute, Dept. of Terrestrial Ecology, Vejlsoevej 25, 8600 Silkeborg
Denmark
Phone: +45 89 20 17 87. Fax: +45 89 20 14 13
mae@dmu.dk

Many crop species are able to grow and persist in non-cultivated habitats and this has given rise to a general concern about the effects of escaped crops. To improve properties favourable for cultivation, crop species are undergoing constant selection in breeding programs. Presumably, crops selected towards increased disease resistance may achieve an increased invasiveness as several researchers have argued that diseases are among the most important barriers to invasion.

To test this hypothesis, a manipulative field experiment set up as a full factorial block design was carried out to investigate the effects of fungal plant disease on artificially introduced and naturally occurring perennial ryegrass, Lolium perenne. Soil disturbance was included as a treatment in order to asses the importance of creating additional microsites suitable for establishment. Two cultivars of L. perenne differing in their susceptibility to crown rust, Puccinia coronata, were broadcast to experimental plots at four different types of grassland sites.

The preliminary results from the first year of measurement show that additional seeds did not increase the total cover of L. perenne at sites where L. perenne was already occurring. Contrary to expectations, the existing L. perenne populations responded to addition of disease by increasing in cover. Lolium perenne was successfully established at two sites with no existing population of the species. This establishment was dependent on neither the disease nor on the variety added. Disturbance had a significant effect on establishment only when biomass of the vegetation was high and the level of natural soil disturbance low. Data from the second year of measurements will also be presented.
 

M. Dalila Espirito Santo and P. Arsènio

Instituto Superior de Agronomia, Departamento de Protecao de Plantas e de Fitoecologia, 1349-018 Lisboa
Portugal
dalilaesanto@isa.utl.pt
arseniop@isa.utl.pt

The Hakea Schrader genus is mainly represented by evergreen xerophytical trees or shrubs, being represented in Portugal by the species H. sericea Schrader and H. salicifolia (Vent.) B. L. Burtt. Both are originary from Australia and where introduced in Portugal to form fencelines or windbreaks. The second species is particularly well adapted to windy seashores. Both species have revealed a highly invasive character, having the authors often seen H. sericea infestating Eucaliptus woodlands. The expansion of these taxa populations is largely enhanced by forest fires, because fire facilitates the opening of the ligneous follicles, as well as seed sprouting. H. salicifolia is very similar to an Acacia schrub, differing from this one because of the redish tips of its leaves, especcially at young ages. It constitutes one of the main problems nowadays, in Serra de Sintra, where it is especially abundant (mostly on the South slope).
The authors present the general distribition of the two taxa and their relation the ecological characteristics in wich they occour.

Key-words: Hakea sericea, Hakea salicifolia, ligneous weeds, ecology, Portugal.

Tereza Francirkova

Faculty of Biological Sciences, University of South Bohemia Branisovska 31
Ceske Budejovice, CZ - 370 05
Czech Republic
tereza.francirkova@tix.bf.jcu.cz

Rudbeckia laciniata belongs to the North American species first introduced to Europe as an ornamental plant. It became spreading outside gardens in the 1850s and 1860s. The species occurs as a characteristic component of the vegetation along rivers and brooks. Outside Europe, the species is invasive in Japan. The aim of this work was to clarify mechanisms leading to the incorporation of this invasive alien into natural communities, considering both vegetative and generative reproduction. Possibility of restriction of already established R. laciniata populations was experimentally tested.
As for generative reproduction, seed germination was tested in a greenhouse experiment with respect to the type of winter storage of seeds. In all types of storage, the germination was about 40 %. Seed germination was also tested under field conditions. Germination and seedling survivorship in differently treated plots (control, mowing and plots with sod turned upside down) was checked during 1997 and 1998 (and will be checked in 1999 as well). Phenological observations were made during 1998. The changing numbers of leaves in rosettes and on stems are correlated to the shoot mortality during vegetation season. Two peaks of mortality were observed - the first one responding to self-thinning during shoot sprouting from rosettes, and the second one corresponding to senescence in the end of vegetation season. Established populations of R. laciniata were subjected to mowing of different intensities. After two vegetation seasons, there were no significant changes in community structure, implying the necessity of long-term management.
Low germination and incapability of recruitment in undisturbed sites indicate that generative reproduction doesn't provide the species with enough possibilities to incorporate into natural communities. The relatively small role of generative reproduction is apparently compensated by vegetative spread.

Tauleigne Gomes, C., Draper, D. and Rossell, A.

Museu, Laboratorio e Jardim Botanico da Universidade de Lisboa
Rua da Escola PolitÈcnica, 58
1250-102 Lisboa
Portugal
ctgomes@fc.ul.pt
ddarper@fc.ul.pt

The aim of this work is to evaluate the alteration in floristic diversity caused by Carpobrotus edulis (L.) N. E. BR. growth on the autochthone vegetation of the protected area, the arquipelago "Reserva Natural das Berlengas". This protected area is located on the portuguese Estremadura littoral (39° 24' 49'' N e 9° 30' 29'' W) and is formed by rocky islands. The height of the islands is under 100 m and Berlenga, the largest island has an area of 76 ha. A seasonally occuped fishermen village is located in this island and the others are uninhabited.

In the 50's Carpobrotus edulis as been introducted in order to avoid the overthrow of rocks in the leasure areas of the island, it as been planted in two islands, Berlenga and Farilho Grande and has successfully established. Presently Carpobrotus edulis as spread out over the cliffs and hillsides mainly in those with south exposition. Spontaneous occurences of this specie have been observed in three other islands of the arquipelago. Carpobrotus edulis establishes a monospecific cover that obstructs the occurrence of the autochthone vegetation. The Flora of this protected area consists of around a hundred species mainly annuals and few perennials, three species are endemics from the arquipelago.

Linear transepts were done in order to collect the data, they were made inside and outside the area covered with Carpobrotus edulis, in both islands Berlenga and Farilho Grande.

The results allow to obtain a quantitative appreciation of the frequency reduction and covering area of the native Flora. They also indicate that Carpobrotus edulis presents a different soil occupation pattern on the differents islands.
 

Hadincova Vera

Institute of  Botany, Academy of  Sciences of the Czech Republic, CZ-252 43 Pruhonice
Czech Republic
Tel.: 0042-2-71015256; Fax: 0042-2-67750031
hadincova@ibot.cas.cz,

The North American pine species Pinus strobus  L. became a pest in different sandstone areas in the Czech Republic. It invades into forests of Pinus sylvestris L., both native and cultivated. The study was hold in the Elbe River Sandstone Mountains where the  invasion is the most advanced.
As the favourable reproduction strategy of P. strobus is supposed to be responsible for its great success, the seedling and sapling growth of both pine species was compared in different habitats in the field and in the common garden. Localities were not far from a seed source of both pine species.

Field study
More Pinus sylvestris saplings survived and grew better only at the sunny and extremely dry localities represented by the ass. Dicrano-Pinetum. A lot of saplings of P. strobus survived at not so extremely dry and sunny localities and in cultivated pine forests and they grew faster there. At the humid and shady localities hardly any saplings of Pinus sylvestris survived.

Common garden study
Seedlings and saplings were cultivated in the soil taken from the field with both P.sylvestris and P. strobus litter on the soil surface, under optimum light and soil humidity conditions. P. sylvestris grew better in comparison with P. strobus: more seeds germinated, the seedlings developed higher biomass, trunks were taller, cotyledons were longer. Saplings were taller and produced more branches and terminal buds.
The kind of the litter on the soil surface influenced significantly more parameters of Pinus sylvestris then P. strobus: All of P. sylvestris seedling parameters exhibited lower values when cultivated in P. strobus litter. P. strobus was negatively influenced by its own litter only in the number of seedlings.
It could be concluded: Pinus sylvestris would grow better at more favourable stands then are those at which it prevails in the field - windy, dry and sunny rock tops and rock plateau edges. But at not so exposed localities a lot of Pinus strobus saplings appear making a dense undercanopy layer and causing the habitat is shady. Such environment suppress P. sylvestris sapling growth and survival.

Keith R. Edwards (1) and Dasa Hanzelyova (2)

(1) Institute of Botany, 145 Dukelska, CZ-37982 Trebon
Czech Republic
Tel: 420-333-721156
keith@butbn.cas.cz
(2) Biological Faculty, University of South Bohemia, 31 Branisovska, CZ-37005 Ceske Budejovice
Czech Republic
hanzely@bio.bf.jcu.cz

Lythrum salicaria, native to Eurasia, has successfully colonized and established in temperate North American wetlands. The success of L. salicaria in North America may be the result of the rapid evolution of non-native populations into a more competitive genotype, compared to native Eurasian populations.
Based on the results of a field study, a three year long (1996-1998) common garden experiment, using a full factorial design, was devised to test the possibility that the native and non-native populations used in the initial study are different genotypes. Plants from one non-native U.S. (Indiana Dunes) and two native European (Opatovicky, Czech Republic; Gbelce, Slovak Republic) populations were subjected to one of three nutrient (nutrient-poor, intermediate, nutrient-rich) and one of two water level (saturated, unsaturated) treatments.  Plants were grown in sand in tubs at the Institute of Botany in Trebon, Czech Republic, with plants in a particular tub subjected to similar treatment conditions.  Measurements included flower phenology, susceptibility to herbivory, shoot height, stem number per plant, and dry weight biomass allocation.  We hypothesized that non-native U.S. plants should be taller, flower later, have lower reproductive effort, and more biomass allocated to growth, than plants from native European populations.
Native European plants flowered earlier in the growing season than the U.S. plants, especially when growing in nutrient-rich conditions. There was a much greater difference between plants from Slovakia and the U.S. plants, than between the Opatovicky and U.S. plants.  Insect herbivores, which attacked the plants naturally, did not have a preference for native or non-native plants. Also, there were no significant differences in shoot height or stem number between the U.S. and European populations, when subjected to similar treatment conditions. Reproductive effort was greater for European plants, but the differences were significant only between the U.S. and Slovakian populations. Similarly, U.S. plants allocated more biomass to roots, but, again, differences were significant only when comparing the U.S. and Slovakian populations.

The results of this experiment are counter to what is predicted by theory. While there are significant differences in some life history and growth traits between native and non-native populations of L. salicaria, mainly the populations tested grew in a similar manner. Any conclusions also appear to depend on which populations are being compared and in the conditions in which they are grown.

Dása Hanzélyová

University of South Bohemia, Faculty of Biological Sciences, Braniöovská 31, Èeské Budìjovice, 370 05 CZ
Czech Republic
hanzely@tix.bf.jcu.cz

Lythrum salicaria L., an herbaceous perennial native to Europe and Asia, is recognized as an aggressive invasive species of North America wetlands. In the present paper, 26 invasive and 32 native populations of L. salicaria  were compared in conditions of their growing habitats (native populations in Tøeboò Biosphere reserve – South Bohemia, Czech Republic and invasive populations in Indiana Dunes National Lakeshore – Indiana, USA). Basic population characteristics (shoot density, fertility etc.), plant life history traits (average height, plant architecture etc.) and stand characteristics (water level, irradiance) were quantified in native and invasive locations. Additionally, phytocoenological releves were taken to evaluate the frequency of co-occurring species in the primary and secondary regions.
Shoot density and fertility were significantly greater in invasive populations than in native ones. Invasive plants grew taller with more lateral branches, supporting the idea of increased competitive ability of those plants in plant communities.
Lythrum salicaria occurs in a wide variety of habitat conditions in both native and invaded areas; from very dry locations along railroads to deep water in lakes or ponds. Statistically, invasive plants occurred more often on stands with deep water and very scattered vegetation.
Invasive L. salicaria populations were more often monocultural (often connected with deep water), which is very rare in native populations, as the native plants seem to prefer more disturbed stands in ditches along roads. Native stands in the Czech Republic  had higher species diversity than invasive stands in the U.S. On the other hand, plants in native populations were apparently more negatively affected by herbivores than plants in invasive populations. Other differences and facts found in plant, population and  stand characteristics are discussed in the paper.

Bonnie L. Harper-Lore

Federal Highway Administration/USDOT
400 Seventh Street SW, Washington D.C. 20590
U.S.A.
Tel. 651-291-6104
Bonnie.Harper-Lore@fhwa.dot.gov

Past and Present Highway rights-of-way on interstate and State highways covers more than 10 million acres of land in the United States. When invasive plant species are found on those rights-of-way, the plants threaten our and our neighbors land. Non-native invasive plants do not respect political boundaries; and so we cannot limit ourselves to boundary solutions. We need to work together. Over the years, how we care for roadside right-of-way (ROW) has been similar from State to State. Our history goes something like this:
1930's - unwritten front yard policy. The development of roadsides was a natural goal following road construction, improved automobiles and public demand. Jesse M. Bennett wrote a book, *Roadsides, the Front Yard of the Nation* in response. He wrote *what is really desired, however, is attractive and useful roadsides which can be obtained by preserving or creating a natural or an approach to a natural condition in keeping with the adjacent or surrounding country. And the significant thing about this is that to follow a natural development is outright economy in road maintenance.* Unfortunately it was the title of his book, not his words that were unofficially adopted as policy. Mowing to a *front yard* look occurred nationwide.
1950's - agricultural approach. With the development of herbicides came another tool.
The mow-spray combination continued to achieve that front yard look. The State highway agencies had concluded by this time that *the look* was what the public wanted.
1970's - ecological approach. The energy crunch of this era halted this labor-intensive, fossil-fuel eating, maintenance approach. Yes, economic restraints led to ecological solutions during this decade. Less mowing and spraying had positive effects: increased wildlife habitat, enhanced natural beauty, saved maintenance dollars...and the public did not complain.
1990's - ecological approach and IRVM unite! Not all States embraced this common sense maintenance method. Because safety will always be the number one priority for transportation*s decision-making, many States did maintenance 50's style. The 90's fiscal constraints pressured those traditional approaches. Roadside managers sought affordable solutions that were environmentally responsible. The result was an idea that emerged from Iowa, Integrated Roadside Vegetation Management (IRVM). IRVM meant being site specific with methods and tools that fit each segment of roadside. When IRVM was explained to the public, the public embraced it.
Into 2000 - Pulling Together. But problems of vegetation management have been complicated by State and Federal Laws or absence of them, as well as weed population explosions. Often it is the highway agency that is blamed for the transport and planting of invasive species. This paper will explain current policy changes that have resulted from the signing of an Executive Order on February 3, 1999 by President Clinton to address invasive species across all agencies across the country, including highway ROW.

Frank Hays

United States National Park Service, Grand Canyon National Park, PO Box 129, Grand Canyon, Arizona, 86023,
U.S.A.
Tel. 520-638-7857
Frank.Hays@NPS.GOV

Did I here you correctly? You are asking park visitors to give up vacation time to hack at "non-native invasive" plants? Although the idea seems a bit far-fetched on paper, using volunteers to complete habitat restoration projects is an idea whose time has come. It is obvious that many people are truly interested in giving something back to their national parks.

Grand Canyon National Park's Habitat Restoration Team (HRT) program is an innovative approach to introducing the public to the joy of eradicating non-native species. Grand Canyon's "ground-breaking" technique was developed to involve park visitors in the effort to control some of the park's 140 known alien plant species. The program also provides a medium for educating the public about natural ecosystems, native and alien species, and ecological diversity.

The program is designed to take advantage of as many volunteers as possible. Scheduled small-scale projects are available for park visitors; organized groups are recruited and scheduled for larger projects; and participation by local schools is actively sought after and encouraged. Since its inception five years ago, the program has blossomed to over 14,000 volunteer hours in 1998.

Short-term projects are scheduled on a daily basis. During each 1.5-hour session, visitors are given a brief orientation to the issues on non-native plants and habitat restoration. After the orientation, the volunteers proceed to a work site to complete a restoration project. The projects generally involved removal of alien species and replacement with a native species.

The second component of the HRT program took advantage of organized groups to complete large-scale projects. These groups usually stayed at the park for several days and ranged in size from 10 to 100 people. The groups were scheduled several months in advance so that all necessary planning and environmental compliance requirements could be met.

Habitat restoration needs are not going to disappear. In these times of diminishing budgets, innovative approaches to solving problems need to be developed. Habitat Restoration Teams take advantage of a tremendous pool of talented and eager volunteers.

Tina Heger

Lehrstuhl für Landschaftsœkologie, TU München (Technical University Munich), Am Hochanger 6 - D-85350 Freising-Weihenstephan
Germany
Phone: +49-(0)8161-71-4149
Fax: +49-(0)8161-71-4427
tina@dec.loek.agrar.tu-muenchen.de
http://www.loek.agrar.tu-muenchen.de/loek/persons/heger/heger.html

Analysing the causes and mechanisms of biological invasions, different approaches have been followed in the past. One of the most common approaches is the search for certain attributes, which make species invasive. Another approach is to look for abiotic or biotic conditions making a site or a community resistant (or especially prone) to invasions. A third approach is to consider the possibilities for an organism to get transported as being crucial for the process of an invasion.
It has already been stated that none of these approaches is appropriate to explain every single process of invasion. To get to an explanation of the causes and mechanisms of invasions, it is necessary to consider not just one of these decisive factors (attributes of the invading species, characteristics of the invaded ecosystems, modes of transportation), but all of them. Trying to combine the different approaches brings about the problem of handling the complexity of the invasion process.
A possibility to get over this problem will be presented in the paper. It will be demonstrated, that the interpretation of the invasion process as a sequence of barriers, which must be overcome for a successful invasion, is a helpful tool in understanding the invasion process. It is possible to find typical crucial situations within the invasion process, which may cause the failure of an invading species. For every one of these crucial situations there are special favourable attributes, which make it possible for a species to succeed in the crucial situation.

L. Henderson

ARC - Plant Protection Research Institute; stationed at National Botanical Institute, Private Bag X101, Pretoria 0001
South Africa.
Tel.: +27  12 804 3200
Fax: +27 12 804 3211
LH@nbipre.nbi. ac.za

The Southern African Plant Invaders Atlas (SAPIA) is a mapping project, launched in 1994, to collate information on the distribution, abundance and habitat types of alien invasive plants in southern Africa. The SAPIA database is a computerised catalogue of some 40 000 locality records of more than 400 naturalised alien plant species. The database incorporates records gathered by about 180 participants between 1994 and 1998 and from roadside surveys conducted by the author between 1979 and 1993. Among its many uses, SAPIA can assist biological control programmes, in particular the more recent ones, in several ways.  Information on the geographical distributions and ecological requirements of invasive plants in their introduced range can ensure that biological control agents are brought from comparable habitats in their country of origin so as to optimise the chances of establishment and efficacy. Early detection of new invaders and new foci of spread allows implementation of biological control at an early stage of invasion with the potential to pre-empt severe problems.  In the long term, SAPIA will also provide an historical record of the spread of invaders and can thereby be used to monitor the effectiveness of introduced biological control agents. Although biological control programmes against weeds have been ongoing in South Africa for some 80 years prior to the advent of SAPIA, baseline data generated by this initiative should prove particularly useful in the case of new programmes.

Betsy Hickey and Bruce Osborne

Botany Department, University College Dublin, Belfield, Dublin 4
Ireland
Betsy.Hickey@ucd.ie
Bruce.Osborne@ucd.ie

In the west of Ireland invasion by the N-fixing, alien species Gunnera tinctoria has lead to changes in community composition. This results in the formation of almost monospecific stands of G. tinctoria, with a fragmentary ground flora, comprising between ~ 22 and 40 higher plant species. Only 3 to 14 of the 22 to 40 species present were common to both colonised and uncolonised areas. Few surviving seedlings of G. tinctoria were found in either colonised or uncolonised areas even though individual plants of G. tinctoria are capable of producing ~760,000 seeds annually. Examination of colonised plots indicated that only ~ 0.1% of the potential seeds produced germinated and, of these, at most 3% (22 to 33 seedlings m-2) over wintered successfully (Fig. 1a). In contrast, significantly less seedlings of all the other species were present in the colonised plots, and few of these survived (Fig. 1b).

Fig.1. Total number of seedlings of G. tinctoria (a) and associated species (b) in colonised
 
 

plots ( • = well-drained site; _ = poorly drained site).
We investigated the reasons for the poor germination and survival of seedlings beneath the G. tinctoria canopy. Two assessments of the seed-bank of colonised plots were carried out over 2 consecutive years in the greenhouse, under exposed and shade conditions with differing watering regimes, using soil collected before (Feb-Mar) significant growth of G. tinctoria had occurred. Under these conditions only 1 to 4 additional species were found, indicating that few species fail to germinate under natural conditions. However the number of species were significantly reduced (9-18), suggesting significant recruitment into the colonised plots prior to canopy closure. Of the seedlings present those of G. tinctoria dominated the population with peak values between May and June when the canopy is almost developed (Table 1).

Table 1. Numbers of seedlings of G. tinctoria grown under greenhouse conditions given optimal (+ H2O) and sub-optimal (– H2O) amounts of water.

                Numbers of G. tinctoria seedlings
                                     (m-2)
Month Shade + H2O Shade - H2O Open + H2O Open - H2O
March   268  318 204    178   459   726 484   561
April 5873  3337 5770  4127   7515  4650 6828  4115
June 6471  3681 6140  4076 8547  3107 8217  6242

Although water supply and shading influence seedling germination, with the lowest germination under shade, this did not account for the approximately 90% reduction in germination, in the field beneath the G. tinctoria canopy. Seedling numbers of the other species were significantly less (120-140 m2), with a seasonal pattern and magnitude comparable to the field results (Fig 1b). On the basis of these results there is little evidence for any additional factors inhibiting the germination of these species in the colonised plots.
 

Carol Horvitz (1) and Anotny Koop (2)

(1) Institut National d'Horticole, 49045 Angers
France
carolhorvitz@miami.edu
(2) University of Miami, Coral Gables, FL 33124
U.S.A.

After disturbances such as tree falls, fires and hurricanes, vines sometimes constitute an initial sere that temporarily provides cover. They may grow rapidly over the ground and ameliorate harsh heat and light as well as preventing erosion; they may create conditions favorable for the establishment of trees. On the other hand, vines may cover gap areas too intensively and for a prolonged period, shading out any potential sources of forest regeneration. We investigate the role of non-indigenous vs indigenous vines in forest succession with five years of experimental data on vine cover and forest regeneration from tropical hardwood forests of southern Florida after Hurricane Andrew. To facilitate the natural regeneration process, managers removed non-indigenous vines from some forest areas. Recruitment of native seedlings and saplings was higher in areas from which non-indigenous vines had been removed. Recruitment of non-indigenous vines was shade tolerant in contrast to native vine recruitment. Also, our results indicate that non-indigenous vines strangled gaps more often than native vines. A model incorporating these effects indicates that non-indigenous vines dramatically altered the spatiotemporal pattern of recruitment sites.
 

Heinke Jaeger (1), Alan Tye (2), Albrecht Gerlach (3)

(1) Department of plant ecology, Oldenburg University, Oldenburg University, AG Pflanzenoekologie, Postfach 2503, 26111 Oldenburg
Germany
Ph: 0049 441 7983794, fax: +441 798 3331
heinke@hrz2.uni-oldenburg.de
(2) Department of Plants and Invertebrates, Charles Darwin Research Station
Isla Santa Cruz, Galapagos
Ecuador, S.A.
atye@fcdarwin.org.ec
(3) Department of plant ecology, Oldenburg University
Germany
bot.garten@uni-oldenburg.de

This quantitative study evaluates the impact of Cinchona pubescens (syn. C. succirubra) (Red Quinine Tree) on the native vegetation in the Miconia- and Fern-Sedge zones in the highlands of Santa Cruz Island (Galapagos). Percentage cover of all species occurring in this area was measured in plots suffering from a range of invasion by Cinchona and by means of transects around individual Cinchona trees.

Though investigations in plots did not reveal significant differences between grades of invasion, measurements around individual Cinchona trees displayed drastic reductions in all species and especies groups' concerned when comparing the outer area with the area under the tree's canopy. In the Miconia zone, cover of the endemic shrub Miconia robinsoniana was reduced by almost half when these two areas were compared. In the Fern-Sedge zone the species especially affected included the native grasses and the endemic herbaceous species Justicia galapagana and Pilea baurii, which were significantly reduced in their cover. In general, vegetation of the Fern-Sedge zone was more adversely affected by the presence of Cinchona pubescens than that of the Miconia zone. This is probably due to the fact that species in the Miconia zone are already shade adapted to a certain degree as they are adapted to live under the relatively dense canopy of the Miconia population when in healthy condition. An analysis of historical records for the Cinchona invasion for the last 20 years, showed that the originally treeless highlands of Santa Cruz will be entirely covered with Cinchona if no control of the invader is implemented. It is recommended to keep the Miconia zone free of Cinchona, since this is a unique vegetation zone and the area is limited, so that an eradication is feasible. In the Fern-Sedge zone, prioritized areas should be established which will be intensively, since native and endemic species are adversely affected in this zone.

Furthermore the seed-producing trees should be controlled in the Fern-Sedge zone, since the light wind-born seeds are easily distributed and cause a continuous infestation with Cinchona pubescens in other areas or a reinfestation of areas already controlled.
By means of permanent vegetation quadrats, a long-term sustainable monitoring project was established to study the ecology of the invasion by Cinchona and the biological characteristics that account for its invasive character (e.g. phenology, growth, vegetative reproduction).

Jan Jedlicka

University of South Bohemia, Biological Sciencies, Department of Botany, Branisovská 31
Ceské Budejovice 370 05
Czech Republic
jedlicka@tix.bf.jcu.cz

Perennial North-American members of the genus Aster L. have become very common in the Middle Europe, especially in the lowlands and disturbed sites such as urban abandoned areas, road and railway ditches. These invasive Asters were tested on their seeds germination capacity, the main character of the generative reproduction.
Mature achenes were taken from wild growing Asters in three macrolocalities in the Czech Republic. Ten samples of achenes were germinated after three differnt treatments: immediately after ripening in the autumn, after cool storage at 5 °C and storage at room temperature. The experiments shows that Asters haven’t a primary dormanci and can germinate immediately after ripening in the autumn. The percentage of germinating achenes is approximately correlated with the percentage of mature achenes and can reach a relatively high value (about 70% in three samples) after using all treatments. The relatively low value of germinating achenes (about 10% in two samples) can be due to different enviromental conditions, or the hybrid origin of sampling plants. Nevertheless the taxonomical origin of Asters growing in the area of the Czech Republic (also in the Middle Europe) haven’t been clarified.

V. Juarez and A. Cazòn

Cátedra de Química Orgánica. Facultad de Ciencias Naturales. Universidad Nacional de Salta. Buenos Aires 177, 4400, Salta
Argentina
cazon@ciunsa.edu.ar

In the last decades, the studies of biological invasions has increased, as one of the components of global change and biodiversity loss. The northwestern of Argentina is affected by Tithonia tubaeformis invasion, a plant from Mexico. It appeared in the Lerma Valley (Salta, Argentina) in 1978, and is found as weed in corn, sorghum and bean crops. The invasion success of this plant is related to its reproductive rate that produces more than 3,000 fruits by plant. The objective of this work is the study of autotoxic chemical compounds produced by this plant. Dry tissues of the inflorescence, leaf and stem were macerated separately in distilled water and the extraction of the compounds was conducted following Heisey (1996). Triplicates, following a randomized design in a germination chamber, using 20 seeds per container ran bioassays. Each container was moistened with the different extracts separately. There was a significant inhibition of germination with the chloroformic extracts from stems and leaves. From these extracts a TLC chromatography was conducted in silica gel and the presence of flavonoids was detected.

A.D. Kendle and J.E. Rose

The University of Reading School of Plant Sciences, Whiteknights, Reading RG6 6AS
United Kingdom
Tel +44 118 9318071 Fax +44 118 975 0630
A.D.Kendle@reading.ac.uk
J.E.Rose@reading.ac.uk

Saint Helena Island, South Atlantic, has a long history of mis-management of natural resources. Loss and fragmentation of the natural vegetation began in the early 1500s with the release of feral goats and tree removal for firewood and timber. Today wastelands of bare soil and sparse, mostly exotic scrub, cover over 60% of the island. Indigenous semi-natural forest covers less than one per cent of the country, occurring only in isolated remnants and are given statutory protection as Crown Lands (Maunder et al, 1995).

The native flora of St Helena consisted of about 70 species of flowering plants and ferns, 60 of which are endemic in 10 endemic genera. This makes it one of the most important islands for biodiversity in the world. Many of the plants are relicts of a primitive flora that was once widespread and that colonised the island perhaps 10 million years ago (Cronk, 1989). Today approximately 50% of these natives are extinct from the island. In parallel with this decline, introductions of economically important plants have increased the number of species significantly together with an accidental increase in weeds and invertebrate pests. The flora now consists of about 320 species, of which 260 (86%) are naturalized aliens.

The last feral goats were culled in the 1960s (Cronk, 1986) and the regeneration of vegetation on the barren areas is now clearly progressing. Areas devoid of trees just twenty years ago now show a developing covering of sparse scrub. However the opportunities and trends now presented are complex. A careful analysis is required of whether the revegetation can be influenced by intervention, the nature of the species and communities that are developing, and the ways in which sustainable use can be made of the new land use opportunities.

The key colonists on the regenerating scrublands include several weeds of global importance such as Opuntia species, Lantana camara and Schinus terebinthifolius. Is it possible that the recovery from desertification is as big a threat to St Helena than the original degradation was? To be able to make a realistic assessment of the weed threat requires addressing the issue of what the concept of 'weed' really means in the heavily degraded environment of the St Helena Wastes. For a plant to be a real weed on the island there has to be a target for it to impact against, it needs to be expected to cause significant harm and it needs to be a species for which eradication or control is challenging. The challenge on St Helena is to predict these impacts or problems for ecosystems that are as yet unformed, and to identify which weeds will be likely to remain problems rather than representing a temporary successional stage.

The following threats may result on St Helena through the growth of undesirable shrubs: soil quality degradation; excessive water use; encouragement of spread of invertebrate pests (Lantana is a host for Orthyzia insignis that has threatened endemic relict woodlands); competitive threat to pasture land species; competitive threat to forestry land species; human health effects (Schinus terebinthifolius has been linked to respiratory diseases); livestock health effects (poisonous plants); honey spoiling; development of a fire risk; weed threat to endemic plant refuges (this has international as well as local significance).

In contrast many of the invading plants play an important role in substrate development and soil stabilisation. In the 1970s biological controls were introduced to attack Opuntia and Lantana and this has lead to an increase in erosion and the redevelopment of instability on slopes above housing (Kendle, 1995).

Amidst growing global concern about invasive species there is a great temptation to see the dominance of non-native species on St Helena as in itself a problem that needs to be tackled, but this would present the people of the island with an impossible challenge. The future ecology of St Helena will inevitably be based on a combination of natives and non-natives. Alien species can not be condemned just because of their non-native origin or even rate of spread, rather a functional classification of the effects and behaviour of each species is required.

References
Cronk Q.C B. (1989) The past and present vegetation of St Helena. Journal of Biogeography 16 47-64
Kendle, A.D. (1995) Soil Conservation and Restoration on St Helena Island. St. Helena: The Overseas Development Administration for the Government of St Helena, l27pp
Maunder M., Upson T. Spooner, B. and Kendle A.D. (1995) Saint Helena: Sustainable Development and Conservation of a Highly Degraded Island Ecosystem. In: Vitousek, D. (ed) Islands: Ecological Studies, vol 115. Heidelberg: Springer-Verlag, 206-217.

Stefan Klipfel and Teja Tscharntke

Fachgebiet Agraoekologie, University Goettingen, Waldweg 26 - D-37077 Goettingen
Germany
Tel.: 0049-0551-392111
Fax: 0049-0551-398806
s.klipfel@uaoe.gwdg.de

Success of alien plant invasions is often attributed to the release from natural enemies. In this study we examined whether invasive alien plants host fewer herbivorous species than indigenous plants. Furthermore we analyzed herbivorous pressure on both plant groups. Endophagous insects in leaves, stems, and fruits were examined in 10 invasive and 10 indigenous plant species. Indigenous plant species were chosen carefully in order to maximize similarity of the paired invasive and indigenous species considering distribution, plant architecture, taxonomy and ecology. Results showed that invasive alien plants hosted fewer species of herbivores than indigenous control plants. Difference in species diversity between both groups increased when parasitoids were taken into account. Moreover attack rate of herbivores was significantly lower on invasive plants and herbivorous insects reached significant higher abundances on indigenous control plants.
 

S. Klotz, Harald Auge and Roland Brandl

UFZ Centre for Environmental Research Leipzig-Halle, Department of Community Ecology, Theodor-Lieser-Straße 4, D-06120 Halle
Germany
Phone ++49 - 3 45 - 55 85 302; Fax ++49 - 55 85 329
klotz@oesa.ufz.de;
http://www.ufz.de/spb/bioz/index.e.html

One major component of biological invasions is the interaction of invasive species with native organisms, for instance the interaction between alien plants and native herbivores, pathogens and parasites. Because of the high diversity of alien plant species, parks and gardens may provide suitable model systems to evaluate possible effects of plant invasions across the food web. The aim of our case study is to identify factors determining the colonization of alien trees in the City Park of Mendoza (Argentina) by Ligaria cuneifolia (R. and P.) Tieghem (Loranthaceae), a widespread hemi-parasitic mistletoe of arid regions in Argentina. Using a multi-factorial approach, we test if the incidence of L. cuneifolia on alien park trees depends on (1) the taxonomic isolation of the tree species, (2) the abundance of the tree species in the park, and (3) the nitrogen concentration in the trees.

Ingo Kowarik

Technical University of Berlin, Institute of Ecology and Biology, Rothenburgstr. 12, D 12165 Berlin
Germany
Tel. +49 30 314 71372, Fax +49 30 314 71355
maurjfcd@mailszrs.zrz.tu-berlin.de

Which traits of an alien species and which of the recipient ecosystems decide the success of an invasion? There is a still increasing knowledge on these classic questions of invasion biology. Save predictions on the performance of alien plant species are however still limited. This may be only partly due to incomplete knowledge on biological characteristics of species and habitats. This paper stresses the role of different types of man-made interactions on the performance of plant invasions. In addition to factors ascribed to species and to habitats, human interference should be recognised as a third set of factors that may determine the success or failure of invasions.

Piotr Kunstler

Department of Environmental Botany,Warsaw University, Al Ujazdowskie 4 00-478 Warsaw
Poland
Tel. +48 22 621 27 09. Fax: +48 22 622 66 46
kunstler@ulmus.bot.uw.edu.pl

Acer negundo (ash-leaved maple) has been recognized as a very agressive antropophyte in the Central Europe. It is a widespread and common tree in  the floodplain zone of the Vistula River. The aim of this study was to determine the influence of ash-leaved maple on riparian scrub and forest plant cover. The species composition of scrub and forest communities was analysed along a hundred kilometre stretch of the Vistula course. The Braun-Blanquet method was used on 100 (400 square metre) sample plots. The detail structure analysis was conducted on twelve 1000 square metre plots.
Crown-projection, height and diameters of tree and shrub layers were studied on plots holding different cover of ash-leaved maple individuals. Although A. negundo forms communities dominated by itself two-way indicator species analysis showed that environmental factors were still mainly responsible for species distribution on the floodplain. In additon the presence of A. negundo was connected with geomorphological configuration which was a typical habitat of willow-poplar forests. The influence of ash-leaved maple on invaded communities is manifested in the reduction of species richness of shrub and herb layers. Compared to other woody native species it forms very asymmetric crowns.
This is caused by strong tendency of A. negundo to polycormonic growth that enables it to fill in empty spaces created by natural or anthropogenic disasters. Secondary communities dominated by ash-leaved maple are poor in species with lower shrub and tree densities and lower average height.