INFLUENCE OF THE ENVIRONMENTAL AND AGRONOMIC FACTORS IN THE BOTANICAL COMPOSITION OF PASTURES FROM GALICIA (NW SPAIN) - M.I. Fraga, J.C. Baleato and L.R. Calvo

Departamento de Biología Vegetal, Facultad de Biología, Universidad de Santiago de Compostela, 15706 Santiago de Compostela, Spain

SUMMARY

Floral inventories were carried out on 110 pastures in 14 different Galician areas. Of the 143 species recorded, only 63 were regionally or locally important species, according to their frequencies and mean abundance. For these species an evaluation of relationships was made among species as well as between species and environmental and agronomic variables, using a canonical correspondence analysis. Moreover, the species ecological behaviour was investigated by ecological profile analysis.

Keywords: ecological behaviour, ecological profile, pasture species

INTRODUCTION

Native pasture species have an ecological behaviour according to environmental and agricultural factors that are often heterogeneous. In spite of these, species can generally grow under a wide range of environmental factors. Some reveal preference for particular environmental conditions; as a result, these species can be considered as field indicators of that condition and can be useful for simple and quick field analysis of pasture environmental variables. Conversely, cultivars of sown species are generally adapted to favourable culture conditions and have a very narrow ecological amplitude, hence indigenous species growing together with sown cultivars are more interesting in terms of their ecological behaviour. This paper is intended to improve the knowledge about the ecological behaviour of native and sown species of Galician pastures.

MATERIAL AND METHODS

A total of 110 pasture plots (sown and permanent) were selected in 14 of the most important areas for forage production throughout Galicia, in order to sample main ecological and management factors. Floral inventories, with visual estimation of abundance of all recorded species (number of individuals per m² in the plot) were drawn up in 1997. In addition, environmental and agronomic plot variables were analysed. The Canoco computer program (Ter Braak, 1988) was used for relating the pasture botanical composition to their environment. For this analysis a canonical correspondence technique was utilized. The estimation method was based on weighted averaging. Furthermore, the ecological behaviour of the main Galician pasture species was analysed by their ecological profiles of weighted frequencies, using Perfeco computer program (Fraga and Martinez, 1993).

Table 1. Main species preference for agronomic factors, according their ecological profiles.

Y: Yes, N: NO, **-Strong preference. *- Preference. Ind- Indifferent. Other species in Figure 1: Achillea millefolium (ACHMI), Amaranthus blitum (AMABL), Amaranthus hybridus (AMAHY), Coleostephus myconis (COLMY), Conyza canadensis(CONCA),, Erodium moschatum(EROMO), Geranium robertianum(GERRO), Fumaria muralis (FUMMU),, Urtica dioica(URTDI), Pteridium aquilinum(PTEAQ), Polygonum persicaria(POLPE), Rumex pulcher(RUMPU).

Figure 1. Diagram based on canonical correspondence analysis. See species abbreviations in Table 2.

RESULTS

Of the 143 species recorded, only 63 were regionally or locally important species, according to their frequencies and mean abundance, the remaining 80 species were considered as “accidental” in Galician pastures. Ecological behaviour was analysed for the most frequent 63 species.

The results of canonical correspondence analysis are shown in Table 1 and Figure 1. Some variables analysed at the beginning of this survey were omitted later, because they had negligible variance, collinearity was detected, or their correlation coefficients with ordination axis were very low. At the end, ten variables were enough to account for 71.2 percent of variance, using four ordination axes. These variables are shown in Table 1; seven of them are agronomic factors.

Although most of the species showed broad ecological amplitude for the factors analysed, some of them have shown more favourable or unfavourable tendencies for any particular variable state. This allowed setting up species clusters for species with similar ecological behaviour with respect to one or more variables. In this way, Figure 1 shows, at the top, a cluster of species closely related to permanent pasture conditions: no manure, fertilizer or liming and grazing management (Cirsium vulgare, Centaurea nigra, Prunella vulgaris, Agrostis stolonifera). The group of Agrostis capillaris, Lolium perenne and Holcus lanatus is mainly characterized by no liming practice.

Sown species Lolium multiflorum and Dactylis glomerata are in the middle of the ordination diagram, close to fertilization and cutting/grazing centroids, because they have shown preference for those management practices. Similar ecological behaviour was observed for native Polygonum lapathifolium, Stellaria media, Capsella bursa-pastoris, Spergula arvensis, Echinochloa crus-gallii and Amaranthus blitum.

Trifolium repens and Trifolium pratense did not show clear preferences for any particular pasture condition. This result could have been caused by the fact that in this study, indigenous and wild biotypes were analysed together. More comprehensive studies are necessary to determine the ecological behaviour of these wild and sown species. Cyperus esculentus, Arrhenatherum elatius and Digitaria sanguinalis take advantage over other pasture species, when herbicides were used.

These results could be useful as new information about ecological behaviour of the main Galician pasture species, although most of these species showed only medium indicator value.

REFERENCES

Fraga, M.I. & Martinez, A. 1993. Perfeco: Programa informático para análisis del comportamiento de especies de malas hierbas. Actas Reunión Sociedad Española de Malherbología: 114-117.

Ter Braak, J.F. 1988. Canoco, version 2.2. Technical report LWA-88-02. Ed. Ministerie van Landbouw en Vesserij.