LAND- Ecological effects of expanding nitrogen-fixing species in vulnerable ecosystems

Invasive symbiotic nitrogen fixing plant species may affect vegetation of nutrient-poor habitats through competition or through changes in in nutrient cycling and biotic composition of soils. These changes may have a strong impact on vegetation dynamics and succession and symbiotic nitrogen fixers may transform nutrient-poor ecosystems by promoting establishment of both native and invasive species and alter competitive outcomes. Lupinus nootkatensis and Lupinus perennis are both invasive in sand dune systems at Jæren, while Cytisus scoparius have expanded in sand dune - heathland systems at Lista. These expansions have reduced the conservation values of these protected areas calling for management strategies. In this project we aimed to delimitate the genetic origin of Cytisus scoparius populations in SW Norway, document mechanisms and patterns of dispersal in C. scoparius from local to regional scale and how symbiotic nitrogen fixing species affect abiotic and biotic conditions in soils and ecological processes (mainly for Lupinus nootkatensis). Analyses of chemical and biological components of soils and growth experiments were used to investigate the effects of L. nootkatensis on soil conditions and ecological processes. We found that L. nootkatensis had a considerable impact on both chemical and biological conditions on soils, and that these changes had a positive effect on establishment of sand dune vegetation after removal of L. nootkatensis. The major changes were increased mobilization of phosphorus and elevated levels of nitrates in soil. Despite considerable effects of L. nootkatensis on the composition of soil microorganisms (diversity and composition of bacterial 16S ribosomal RNA) and their function (bioassays on different C sources), we only found small effects on soil enzymes and lipid profiles. The changes caused by L. nootkatensis to soils also had a positive effect on establishment of its own seedlings. In addition to a competitive advantage with nitrogen fixation and mobilization of phosphorus in nutrient poor soils, these traits explain the strong invasive ability in this species and the effects it has on soil and vegetation in sand dunes. Based on intensive field mapping from Agder to Hordaland, we established a dispersal model base on climate, distance to houses and a Gauss-field (latent variability) was created for C. scoparius. This species is more common in areas with moist spring (germination), dry summer (flowering and seed set) and warm autumn (growth) and close to houses. C. scoparius has an uneven distribution (Gauss-field) that is not related to distances to houses or climate. The limited natural dispersal indicates that the rapid large scale expansion the last decades are due to anthropogenic activities as planting and soil transport. The availability of suitable symbiotic bacteria seems not to limit the distribution in these species, although symbionts may be important for establishment of C. scoparius under competition with established vegetation. At municipality level, when increasing the number of C. scoparius, the distance to houses decreases, reflecting new infrastructure, time of establishment and a large seed bank. Populations of C. scoparius were found in heathlands at Einarsneset (Lista), but in few other heathlands. At Einarsneset and Mandal C. scoparius were also found in sand dunes, but was not found in sand dunes at Jæren. C. scoparius has a negative effect on number of species in the heathland, and also affect heathland species. C. scoparius should be classified as High Impact (HI) on the black list due to large seedbank, long lifetime of populations and long-distance dispersal by humans. It also replaces local species and is present in vulnerable nature types. To investigate introduction history of Cytisus scoparius to Norway we investigated DNA-variation in the chloroplasts of 27 Norwegian populations sampled in 2012 as well as in 23 Norwegian herbarium specimens from the time period 1889-1998. We also included 19 European populations as references. Results show that we have 7 haplotypes in Norway and four of these are common with European haplotypes. We find no geographic structure among the haplotypes and several populations contain more than one haplotype. From the herbarium specimens we see that several haplotypes are present in Norway already before 1900. We have analysed 20 Norwegian populations for variation in nuclear DNA markers to study genetic structure and gene flow. There is no geographic structure and the variation is not correlated with haplotypic variation. This indicates large amount of gene flow and the populations act as one invasion front. Based on our results we conclude that we do not have a distinct Norwegian population and that Cytisus scoparius have been introduced repeatedly to Norway. The continuing introduction of Cytisus scoparius to Norway very likely contributed to its invasion success.

The establishment of exotic species is recognised as a particular concern in nature management, and especially species affecting plant-soil feedback dynamics as they may alter vegetation development patterns. 'Ecological effects of expanding nitrogen-fixi ng species in vulnerable ecosystems' is a project investigating which factors determine the establishment and expansion of Cytisus and Lupinus in vulnerable nitrogen-limited habitats and the ecological effects of this expansion. We use a spatial model fra mework to predict future distribution and provide knowledge of how different measures can be taken to prevent unwanted expansion and negative ecological effects of invasive species on vulnerable sand dune and heathland ecosystems and species therein. Deta ils on establishment dynamics and local expansion will be provided and the importance of the plant-soil feedback on the vegetation dynamics both before and after control measures investigated. Molecular studies of genetic structuring and diversity of Cyti sus will provide information on the origin and rate of expansion of different populations and elucidate the delicate situation where both native and exotic genotypes of the same species are expanding. The project will make us able to decide whether the re cent range expansions of Cytisus are due to increased invasiveness, increased frequency of introductions, or other processes at landscape level affecting dispersal and establishment. This approach will provide knowledge for improved management at differen t scales addressing adaptive management opportunities for a preventive landscape management of this species.