WEED PROBLEMS IN CONSERVATION FALLOWS BY SOWN
WILDFLOWER MIXTURES
KROMP, B.1, SCHMID, R. 1
Key words: nature conservation, wildfl ower strips, seed-mixtures, harmful weeds
Abstract
Since 2001, the Viennese Programme of Contracted Nature Conservation “Biotope Farmland” aims at increasing nature conservation value as well as functional biodiversity of farmland in the urban area of Vienna. Farmers voluntarily contract with the Municipal Department of Environmental Protection to take arable fi elds out of production and convert it into nature conservation areas by appropriate cultivation measures like mulching and mowing. One of the following successional types is allotted to the fi elds: “Nature Conservation Fallow” with sown wildfl ower-mixture, “Weed Conservation Field” with sown rye- and-weed mixture and “Species-rich Dry Meadow”. At present, a total of 72 fi elds with an acreage of 33.2 hectares are contracted. 58 fi elds (81%) of the fi elds are cultivated by 14 conventional farms, 14 (19%) by 4 organic ones. In accompanying research performed by Bio Forschung Austria, the vegetational succession is recorded continuously for adapting management methods as well as detecting upcoming of weeds potentially threatening adjacent fi elds, especially organic ones. Up to now, no weed problems arose due to sown wildfl ower mixtures successfully suppressing harmful weed species.
Introduction
Due to longtime intensive fertilization and area-wide herbicide application (Maurer et al. 2003) arable landscape (approx. 5,200 hectares) in the urban area of Vienna has a low nature conservation value. In 2001, the Viennese Programme of contracted nature conservation “Biotope Farmland” was started. It aims at increasing general biodiversity in arable landscape, creating living space of endangered species as well as enhancing functional biodiversity in terms of pest antagonists and pollinators. Furtheron, it contributes towards maintaining of farmers income as well as improving the recreational value of arable landscape. For that, fi elds are taken out of cultivation and evaluated for their potential of development for conservation purposes by Bio Forschung Austria. If accepted, the farmer contracts with the Municipal Department of Nature Conservation for subsidy to cultivate the fi eld according to one of the following management schemes: “Nature Conservation Fallow” with initially sown wildfl ower-mixtures (at present covering 48 fi elds with a total acreage of 21.3 hectares), “Weed Conservation Fields” with a yearly sown mixture of weed seeds and rye as cover crop (at present 2 fi elds with 1.6 hectares) and
1 Bio Forschung Austria, Rinnboeckstr. 15, 1110 Wien, Austria, E-Mail [email protected],
“Species-rich Dry Meadows” (spontaneous fallow vegetation, managed by mowing; at present 22 fi elds, totalling 10.3 hectares).
The programme has been developed in a “bottom-up” approach: the cultivation schemes and the compatibility of management measures with e.g. the available farm machinery as well as the procedure of contracting and the level of subsidies have been discussed prior to implementation of the programme with representatives of Viennese arable farmers. Thereby, a high level of acceptance and readiness for participation was ensured. With special emphasis on the potential threat of weed problems, the accompanying research performed by Bio Forschung Austria consists of a continuous observation of vegetational succession in all conservation fi elds by inspecting them twice a year. Additionally, in seven selected sites representative of the three management schemes the vegetation has been monitored annually. In this paper, vegetation results of two “Nature Conservation Fallows” are presented.
Materials and Methods
The two investigated sites “Stammersdorf 1” (0.37 hectares; highly fertile, dry chernozem on loess; loamy sand) and “Breitenlee” (0.54 hectares, middle fertile, dry tchernozem on limy, loess-like fi ne sediments; sandy silt to loamy sand) are situated in Vienna North (average yearly temperature 11°C, yearly precipitation 518mm; 2003–2008) and followed longtime, intensive arable cropping. In early April 2000, a seed mixture (“Voitsauer Wildblumenmischung”, www. wildblumensaatgut.at), consisting of up to 60 diff erent segetal and ruderal domestic fl owering species was sown in a fi ne seed bed and rolled. The vegetation was recorded according to Braun- Blanquet, adapted by estimating the plant coverage in 1% steps. The recordings were performed end of May/beginning of June each year from 2000 until 2007 in six 6 x 4 m plots in each fi eld. The plant species were classifi ed for origin from sown seed-mixture or autochthonous seed bank, life span, biotope requirements and red list status.
Results and Discussion
In both sites, a species-rich vegetation was recorded over the years (Table 1). The higher number of total species found in the site Stammersdorf 1 is due to being embedded in a diverse cultivated landscape with crop fi elds, grassy fallows, fi eld margins, hedges and woodland plots whereas Breitenlee is isolated in an intensively cropped area poor in uncultivated landscape structures. In Stammersdorf 1, 34 % of plant species originated from the sown mixture compared to 38% in Breitenlee, in a few cases it remained unclear though if a species germinated from the sown mixture or from the autochthonous seed bank. Due to the rich surroundings, 57% of the recorded 26 red list species were autochthonous in Stammersdorf 1 (e.g. Ajuga chamaepitys) compared to only 40% of 20 in Breitenlee.
Nevertheless, Breitenlee proved to have a high conservation value for wildlife biodiversity, e.g. in wild bees: due the warm, sandy habitat character of the site some rare, stenocio-eremophilic and psammophilic species were found in 2004 (e.g. Eucera pollinosa, Andrena limata), some of them following host plants from the sown mixture (e.g. Colletes fodiens and C. similis on Tanacetum vulgare) (Pachinger 2004, unpubl.). Likewise, in both sites rich carabid assemblages containing rare xerothermophilic elements were recorded (Kromp et al. 2004).
Since the prevention of weed problems in adjacent arable fi elds is considered crucial for acceptance of nature conservation schemes by farmers, the composition of the wildfl ower seed- mixture sown is intended for suppressing autochthonous annual as well as perennial harmful arable weed species. In Fig. 1, the vegetational succession is shown in terms of plant coverages of life span types. In the fi rst year, annual weeds prevailed with a high amount of sown Agrostemma githago and Bromus secalinus. In the second year, sown biennials like Isatis tinctoria and Malva sylvestris took over as well as the perennial grasses Lolium perenne and Dayctylis glomerata. The dominance of biennials (mainly the sown Melilotus offi cinalis and the autochthonous Carduus acanthoides) from 2003 to 2005 refl ect a disturbance of the site by construction vehicles due to erection of a wind turbine in 2002. From the sixth year onwards, perennial grasses and herbs (e.g. Tanacetum vulgare) were predominating.
In Table 2, the average coverages of potentially harmful weeds are provided. From the annual autochthonous weeds, Amaranthus retrofl exus and Chenopodium album only occurred in the fi rst year of fallow whereas Tripleurospermum inodorum showed higher coverage in the fi rst and third year of succession, possibly due to the disturbance in 2002 mentioned above. The problematic perennial weed Cirsium arvense occurred in the fallow from 2002 onwards but in low densities only.
Similar low densities of harmful weeds also were recorded in Stammersdorf 1, with exception of Agropyron repens covering over 40% in the fourth year of succession but decreasing again in Tab. 1: Total number of species, species originating form the sown mixture and red list species recorded in two conservation fallows in Vienna North from 2000 until 2007
Conservation fallows Total nr. of plant species
recorded
Species originating from the sown mixture
Red list species
Stammersdorf 1 161 55 26
Breitenlee 141 54 20
Figure 1: Vegetational succession in the nature conservation fallow Breitenlee/Vienna North: coverages of annual, biennial and perennial plant species from 2000 to 2007
the following years to around 20%. In Switzerland, Eggenschwiler (2003) found signifi cantly lower coverages of A. repens and C. arvense in sown mixtures compared to spontaneously vegetated fallows. Sown mixtures proved itself with regard to both weed suppression as well as high fl oristic diversity, especially in previous intensively cropped arable sites with impoverished seed banks. The development of conservation fallows over the years decisively depended on the successful establishment of the sowings (Pfi ff ner and Schaff ner 2000, Günter 2000).
Conclusions
In Vienna, spontaneously vegetated fallows on sites with high soil fertility usually are dominated by undesirable plant species like A. repens, Bromus sterilis and C. arvense. So for implementation of nature conservation fallows, seed mixtures are considered useful in previous intensively farmed arable fi elds with impoverished autochthonous seed banks.
Acknowledgments
This research was supported by the Municipial Department of Environmental Protection of the City of Vienna.
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Tab. 2: Average plant coverage (%) of undesirable weed species in the conservation fallow Breitenlee in Vienna North from 2000 until 2007
Weed species 2000 2001 2002 2003 2004 2005 2006 2007
Amaranthus retrofl exus <1
Chenopodium album 29 <1 1
Tripleurospermum inodorum 16 7 27 4 2 1 1 <1