Maatalouden tutkimuskeskus, Tuhoeläintutkimuslaitos, Tikkurila
Maatalouden tutkimuskeskus, Tuhoeläintutkimuslaitos, Tikkurila
This investigation was carried out on July 2—14, 1961 in the commune of Laihia, situated in western Finland southeast of the city of Vaasa. The region is level and the soil type is compact clay (fine sand plus clay). As a result, there is poor natural drainage of the land, and consequently it has been necessary to dig a system of parallel open drainage ditches at intervals of 10—11 metres. The total width of the ditches with the bordering uncultivated edges of the field strips (ditch banks) is about 1.0–2.0 metres (Fig. 1). Eighteen farms in this region were selected for investigation (Fig. 2). The fields of spring cereals chosen for the study were those which contained at least one internal drainage ditch which had not been treated with herbicides during the year of the study and whose edges had not been cut before the time of the investigation. A total of 49 such fields were studied. Four circular sample plots with an area of 0.25 sq.m were selected in the cultivated strips in each field; these plots were located at least one metre from the edge of the strip. In addition to each of these sample plots, another plot of the same size but quadratic in shape was taken from the nearest edge of the strip bordering an internal ditch in the field. There were thus a total of 196 sample plots in the strips proper and the same number in the strip edges. Estimations were made on the cover of the various species of vascular plants growing in each plot. The cover degrees used were +, 1, 2, 3, – – – 10, 20, 30, – – – 100 %. At the time of the estimation, some plants were so young that it was not possible to determine them to species. The Galeopsis and the perennial Poa species were identified when possible, but they are also presented in the tables as combined groups. The same was done in the case of the Rumex acetosa – R. acetosella group. Of the fields investigated, 21 were situated on peat soil, 12 on clay soil and 16 on such thin peat soil that the underlying clay was to a varying degree mixed in the plough layer. This latter category of soils is termed peat-clay in the present study. At first the number of plant species rose rapidly as the number of investigated fields increased. The rise was slowed down in the cultivated strips earlier than in the edges (Fig. 3). The addition of 34 more cultivated strips to the 49 already investigated in the present study would have increased the number of species by only 9. In an area of 4 x 0.25 sq.m there were an average of 17.5 species on the cultivated strips and 20.9 in the edges bordering the ditches. The cultivated strips included 7 peat soil species, 2 peat-clay, and 21 clay soil species (Table 1). The peat-c layspecies are those which occurred significantly more frequently on peat-clay soil than on peat soil plus clay soil. In the case of the strip edges, the number of peat species was 9, peat-clay 6 and clay species 19 (Table 2). The previous crop had an effect on the botanical composition of the fields. On the strips where spring cereals were cultivated, it was found that the frequency percentage of 7 species or species groups was greater after spring cereal than after ley, while the reverse was true for 9 species (Table 3). Also on the uncultivated egdes of the strips there was a difference: the frequency percentage of 4 species or groups was greater after spring cereal than after ley, and that of 6 species respectively smaller (Table 4). The species more common after spring cereal than after ley were – both on the strips and the edges – generally annuals, while species increased after ley were mainly perennials. From time to time some of the most commonly cultivated plants in the region occurred as weeds in the fields investigated. Phleum pratense, as well as possibly also Poa pratensis and Trifolium pratense, are usually cultivated on peat soils (cf. Tables 1 and 5), but they apparently have a better competitive ability on clay soils, since they are more common on the strip edges of cay soils than on those of peat soils (Table 2). Following JALAS and JUUSELA (13) the different phases of the crop rotation have been considered to belong to same vegetation unit, called stand (»association») , The partial stands which can be differentiated in the different years are called annual (partial) stands in this study. In addition, seasonal partial stands can be differentiated from each annual stand. In the cultivated strips the Ranunculus repens – Deschampsia caespitosa stand, occurring on peat soils, can be distinguished. During the spring cereal phase of rotation it is represented by the Avena sativa – Phleum pratense – Rumex acetosella annual stand. This annual stand is characterized by the peat soil species shown in Table 1. All the species found in the partial stand are listed in the columns 1 and 5 of Table 5. On clay soil the Elytrigia repens – Stellaria media stand is differentiated in the field strips. In the spring cereal phase the Hordeum vulgare – Viola arvensis – Spergula arvensis annual stand is found. The characteristic species for this annual stand are given in Table 1 and all the species encountered are shown in columns 3 and 7 of Table 5. There are approximately equal numbers of annual and perennial species in the annual stands in spring cereal phase, but the cover of the annuals is greater than that of the perennials. There is variation in the partial stand depending upon the previous crop (cf. Table 3). In the ditch banks on peat soils the Deschampsia caespitosa – Rumex acetosa stand occurs. The characteristic species for this stand are the peat soil species listed in Table 2. All of the species encountered in this stand are given in columns 9 and 13 of Table 5. On clay soils the Phleum pretense – Trifolium repens stand is differentiated. The clay soil species occurring in the strip edges are characteristic for this stand (Table 2). The species found are shown in columns 11 and 15 of Table 5. Perennial species comprise 90 % of the total number of species in the peat soil stand and 76 % in the clay soil stand. Similarly, the cover of the perennials is greater than that of the annuals. Variations from year to year are so small that it was not considered necessary to differentiate annual stands. In Table 5 are shown the frequency and cover percentages of the plant species found on the strips and edges of spring cereal fields on different soil types, A total of 78 species of vascular plants were encountered in the sample plots on the strips and 112 on the edges. The number of species occurring on both strips and edges was 64, on strips alone 14 and on edges alone 48. The distribution of the species into frequency percentage classes is shown in Fig. 4 and into cover percentage classes in Fig. 5. There is a positive correlation between the numbers of species found in the 4 x 0.25 sq.m sampling area on the strips proper and in a similar area on the strip edges (Fig. 6). In comparing the plant species on the field strips proper and their edges, Sørensen’s (36) quotient of similarity was used. In this equation QS = (∑2c)/(∑(a + b) ∙ 100, in which a = the average cover percentage of the species in a certain spring cereal field strip, b = the average cover percentage of the same species in the corresponding edge, and c = the smaller of the two above values (a and b). If the average cover percentage of the species was »+», it was given the value 0.1 in the calculations. The quotient was applied in a similar way by HANSON and DAHL (6) and JALAS and JUUSELA (13). Table 5, column 17 presents the QS values for all of the species. These values are seen to be generally quite small. The symbol »+» means that the species occurred both on the strips proper and on the edges, but in different fields. There is accordingly no great similarity between the kinds of plants growing in the cultivated strips of ditched spring cereal fields and in the edges bordering the ditches; this is because the species are mainly annuals in the fields proper and perennials in the edges. The most similarity occurs in the case of certain of the perennial species. The species composition of the field edges appears to be more similar to that of hay fields (cf. 26) than to that of spring cereal fields.
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