Biological invasions are considered an increasing threat to biodiversity, but the underlying principles are poorly known. Also the way changes in the global climate will affect invasions is not well understood. The aim of the current project is to develop an improved mechanistic framework to (a priori) establish which communities are most susceptible to being invaded (‘invasibility’) and which species are expected to become invasive (‘invasiveness’) under given conditions. The project mainly focuses on grasslands since grasses have been responsible for some of the most harmful invasions in the past.

With respect to invasibility we investigate how the plant diversity of resident communities acts as a promotor or resistance to invasion, but also how diversity itself is modified by establishment of invasive species. By exposing plant stands to simulated heat waves (infrared irradiation experiments), it will be assessed to what extent climatic extremes facilitate invasion by inducing mortality and gap formation. Changes in key ecosystem processes (photosynthesis, respiration, evapotranspiration) associated with such climatic disruptions and with subsequent gap-mediated invasion are also studied. This allows to estimate the resistance and resilience of grasslands to disturbances which affect the carbon balance. A further aim of the project is to better characterise the physiological/morphological basis of the susceptibility of individual species to extreme heat and drought events, as a key to predicting which grasslands are most robust in a future climate. A probabilistic model on the influence of diversity on ecosystem functioning under extreme conditions (developed in PODO I) is used to analyse the data.

With respect to invasiveness we want to identify factors critical to survival in the low-light conditions typical of gaps in dense grasslands. Competition for nutrients between invaders and neighbouring plants is also considered. We will not focus on known invaders but rather screen a range of species of unknown invasiveness. Technically, invasion is simulated in highly controlled, synthesised model ecosystems to study mainly the phases of initial establishment and persistence of invading species. This is complemented by field experiments covering longer time scales. In one of these experiments spontaneous invaders are monitored in 288 recently installed field plots, covering a large number of combinations of initial species diversity and management (fertilizer supply rate and mowing frequency).

A primary driver of biological invasions is land use change. Agricultural policies in Western Europe are developing towards reduction of unsustainable intensive farming and promotion of biodiversity in agricultural land, but it is uncertain how this will affect biological invasions. We investigate this question for the recent trend of field borders. The latter are installed on arable land to buffer nutrient and biocide efflux from crops and are considered to become new ‘reservoirs’ of biodiversity in our fragmented landscapes. However, because their installation represents a severe disturbance and because species influx in field borders is not intensively controlled, they could become future hot spots for invasion. First, we will compare a series of methods to maximise diversity in field borders (spontaneous introgression of vegetation, sowing with commerical seeds vs. local seeds, etc.). Next, the invasibility of field borders is tested by introducing the species examined in our model ecosystems. The aim is to devise management options which minimise risks of invasion, both into field borders and from field borders into arable land.

The overall goal of the project is to provide a better scientific foundation for protective strategies towards biological invasions in grasslands and field borders, so that management policies can eventually become pro-active rather than curative today.


Methodology

UIA:
1) Underlying mechanisms of establishment of invading species.
Eight grass species acting both as invader and as invaded system. One monoculture per species, each with 8 predetermined gaps to insert seeds of the 8 possible invaders. Measurements on invaders: germination; survival; growth rate etc. Measurements on invaded monocultures to determine invasibility (e.g. photosynthetic active radiation (PAR) in the gaps).

2) Effect of species diversity and climatic extremes on invasion.
24 different synthesized plant communities with species number varying from 1 to 8. Three replicates sets develop undisturbedly; the 3 others are exposed to a simulated heat wave. The 3 most aggressive species of Exp 1. are inserted as invaders in gaps. Measurements: gap conditions; invader survival/growth; critical traits for invasiveness/ invasibility; changes in ecosystem processes.

3) Predicting which grasslands are sensitive to climatic extremes.
Species are experimentally exposed to heat/drought stress in the field (FATI-system), to investigate the physiological/morphological basis of sensitivity to climatic extremes.

RUG:
1) Creation of diversity reservoirs in field borders.
Four different plant communities are installed under 3 managements (2 cuts with no, 1 time or 2 times removal of the cuts):

a) spontaneous vegetation;
b) commercial blend of grasses, leguminous plants and field flowers;
c) same as b) but covered with the mown and chopped product from a botanically species-rich roadside in the neighbourhood;
d) locally bred grasses and dicots assembled in the neighbourhood.

Measurements: characterization of the seed bank; seed rain captation and determination; biomass production and quality; species presence, abundance and shifts; PAR; mineral status of soil and vegetation; incidence and development of weeds, pests and diseases in the crops.

2) Effect of light and disturbance on invasion.
Field border plots are installed along a tree lane consisting of 2 rows of very uniform 50- year-old beeches, east-west oriented offering a sunny and a shady side. Investigated factors: light effect and disturbance effect (passage of a tractor in the middle of the plots) on selected invaders inserted in the border plots.


Interaction between the different partners

The research teams study different aspects of diversity and biological invasion: UIA the theoretical ecological foundations and RUG the application in field borders in order to optimize diversity management. The interaction will focus on the integration of the more artificial detail experiments of UIA with the information from the field experiments of RUG.


Expected results and/or products

- Publication in peer-reviewed international journals
- Presentation of results on national and international fora (conferences, ...)
- Construction of a web site describing the objectives and results of the project
- Contribution to databases (IWETO, OSTC, the database ‘Understanding and conserving biodiversity in Europe’)
- Submission of the project as Core Project of IGBP-GCTE Focus 4
- Participation to the Global Invasive Species Programme (GISP)
- Development of a mathematical model


Partners

Activities

- UIA - PLECO:
Research in plant ecophysiology, physical ecology, crop micrometeorology, ecosystem physiology, plant sociology, and landscape ecology. Over the past decades the group has been involved in impact studies on acid rain, elevated CO2 concentrations, global warming, ultraviolet-B, changes in biodiversity and biological invasion. Experimental research is often coupled to existing or newly developed models.

- RUG - Plant production:
The department focuses its research into plant breeding; farming systems: monocultures versus crop rotation; research into grassland and forage crops; extensivation of grassland systems. The objective trough out all research items is the development of a sustainable agriculture, supported by divergent research activities and concepts.


Coordinates/Details

- Promotor: Prof. Dr. Ivan Nijs
Onderzoeksgroep Planten- en Vegetatie-ecologie (PLECO)
Universiteit Antwerpen (UIA), Departement Biologie
Universiteitsplein 1, B-2610 Wilrijk
Tel: +32 (0)3 820 22 57; Fax: +32 (0)3 820 22 71
e-mail: inijs@uia.ua.ac.be

- Promotor: Prof. Dr. ir. Dirk Reheul
Faculteit Landbouwkundige en Toegepaste Biologische Wetenschappen
Vakgroep Plantaardige Productie
Universiteit Gent (RUG)
Coupure Links 653, B-9000 Ghent
Tel: +32 (0)9 264 60 96, Fax: +32 (0)9 264 62 24
e-mail: dirk.reheul@rug.ac.be


Users Committee

- Barenbrug-Maes, seed company
- V.T.I. Agriculture and Horticulture Institute: education in agriculture and horticulture; refresher courses; experimental plots
- Ministry of the Flemmish Community, A.L.T. Division Agriculture and Horticulture
- Province West-Flanders