1. International Conference on Multi Function of Wetland Systems June 26-29 2007 Legnaro (Pd) - Italy Buffer strip plant community changes over a 10-year period and consequences on the effectiveness of agricultural pollution reduction Monica Vianello *, Maria Clara Zuin ** and Giuseppe Zanin * DAAPV Padova University IBAF CNR *DAAPV, Università degli Studi di Padova, Agripolis, Viale dell’Università 16, 35020 Legnaro (PD) ** IBAF-CNR, Sezione di Legnaro, Agripolis, Viale dell’Università 16, 35020 Legnaro (PD) Introduction Buffer strips (BS) are an efficient and economical way to reduce the adverse environmental impacts of agricultural pratices. Most of the literature on BS deals with their capacity to retain and transform nutrients and herbicides. Non-agricultural habitats are critical for the conservation of biological diversity and ecological processes on farmland, but field boundary plant communities are affected by agrochemical drift and runoff. Few data are available on changes in the plant community of sown BS and their possible effects on buffer performance. The effect of different types of BS in reducing runoff volume, suspended solids, nutrients and herbicides from a cultivated area was assessed in a field experiment conducted in north-eastern Italy during 1998-2007. BS were created to obtain multifunctional effects: wood production, landscape improvement, reduction of non-point source pollution due to nutrient and herbicide runoff, and increased biodiversity. Plant cover and floral surveys of the BS were conducted to investigate BS plant community changes and relate them to BS performance in reducing agricultural pollution (Borin et al., 2005; Vianello et al., 2005). The qualitative results of a 10-year study are discussed. Materials and Methods The experimental site is a 200 m x 35 m rectangular field, with a 1.8% slope down towards a ditch, on the Padova University Experimental Farm in the Po Valley, north-eastern Italy (45°12’N, 11°58’E, altitude 6 m a.s.l.). Four types of BS, one grassed and three wooded, were created in 1997 between cropland and ditch. The grassed BS was sown with Festuca arundinacea Schreber (at a density of 30 kg ha-1); the wooded BS were sown with F. arundinacea Schreber and planted with 1 to 2 rows of regularly alternating Viburnum opulus L. shrubs and Platanus hybrida Brot. trees (Table 1). BS management practices were mowing of herbaceous cover at least twice during the growing season leaving the mowings in situ, and thinning of plane tree offshoots, with the aim of management at minimal expense. The first tree coppicing was done in November 2003. To investigate plant community changes over time and relate them to BS performance, plant cover and flora surveys have been conducted prior to mowing each year since 2001. Results and Discussion The closed canopy created by shrubs and trees caused a progressive decline of herbaceous cover. 3G showed the highest cover values while, among the wooded BS, those with the more closed canopy, i.e. 3G1R and 6G2R, showed the lowest (Figure 1). Since 1997, when only Festuca arundinacea was growing, total species number increased to 116: 40.5% composed of weeds derived from the soil seed-bank and the remaining 59.5% species of undisturbed soils. The highest species richness were observed in the wooded BS in 2005, with a maximum of 62 in 3G1R, 49 in 6G1R and 67 in 6G2R (Figure 1). The lowest species richness recorded in 6G1R was due to the wider herbaceous area. Conclusions The studied BS are artificial systems, regularly disturbed by BS and nearby cropland management practices. The consequence is a lack of advance in the vegetation succession with the disappearance of shrub and tree seedlings in the wooded BS, a harbour for bird dispersal species: colonization is possible, but survival of late successional species is ultimately hindered by the environmental conditions in the BS. Attention needs to be paid to the dispersal and propagation of some species (Cirsium arvense, Conyza canadensis, Veronica persica, Lactuca serriola, Equisetum arvense, Bromus sterilis, etc…) which were a large component (12.7%) of the plant community in the studied BS and also potential weeds. A previous study (Vianello et al., 2005) highlighted the diminished BS effect in reducing herbicide runoff as a consequence of herbaceous cover reduction; but the changes in botanical composition of the plant community are also important: in fact the non-continuous presence of annual species could reduce the filtering and adsorption capacity of the BS. Moreover it is also important to evaluate the effect of litter in pesticide loss, according to Margoum et al., 2006. Appropriate BS management is required to ensure agricultural activities, BS trapping efficiency and biodiversity conservation on farmland, as example biodiversity enhancing could be obtained avoiding to mow close to the rows where ornithocore species could grow. References Borin M., Vianello M., Morari F., Zanin G. (2005). Effectiveness of a buffer strip in removing runoff pollutants from a cultivated field in North-East Italy. Agr. Ecosyst. Environ. 105, 101-114. Vianello M., Vischetti C., Scarponi L., Zanin G. (2005). Herbicide losses in runoff events from a field with a low slope: Role of a vegetative filter strip. Chemosphere 61, 717-725. Margoum C., Malessard C., Gouy V., 2006. Investigation of various physico-chemical and environmental parameter influence on pesticide sorption to ditch bed substratum by means of experimental design. Chemosphere 63, 1835-1841. Acknowledgement The authors would thank Mrs Marisa Golo, Mr Paolo Cadin and Mr Giovanni Favaron for their help in the field collecting data, Mr Francesco Osele and the BAUM for having being possible the authors meetings. The effect of the coppicing done in winter 2003, and the resulting light increase was observed in 2005 in the wooded BS with the highest values of herbaceous cover and number of species (Figure 1). In the wooded BS the surveys showed a conspicuous but ephemeral number of ornithocore species (i.e. Rubus caesius, Duchesnea indica, Crataegus monogyna, Ficus carica, Morus alba, Punica granatum, Prunus avium, etc…), which belong mainly to the nanophanerophyte and phanerophyte biological groups (Table 1). Buffer strip coppicing - winter 2003Buffer strip after coppicing - 2004Buffer strip - 1998Buffer strip - spring 2003 Canopy evolution and coppicing effect Table 1: BS types and mean of 10 years of plant community biological groups and seed dispersal. 3G = 3m grass; 3G1R = 3m grass + 1 row; 6G1R = 6m grass + 1 row; 6G2R = 6 m grass + 2 rows B:barochore;A:anemochore;Z:zoochore;Th:therophyte;H:hemicryptophyte;G:geophyte;NPh:nanophanerophyte;Ph:phanerophyte Figure 1: Time pattern of herbaceous cover percentage (continuous line) and species richness (discontinuous line). is 3G; is 3G1R; is 6G1R; is 6G2R. Cover (%) n. Species Loss in biodiversity Bryonia dioica Jacq.Ficus carica L.Celtis australis L.Rosa sp. Prunus avium L.Parthenocissus quinquefolia (L.) PlanchonVitis vinifera L.Punica granatum L.Juglans regia L.Humulus lupulus L. Rubus caesius L. & Sambucus nigra L. Crataegus monogyna L. Ulmus minor Miller Duchesnea indica (Andrews) Focke