CHANGES IN THE PLANT COVER OF THE SOLONETZ COMPLEX UNDER DIFFERENT GRAZING PRESSURE IN NORTHERN PRE-CASPIAN REGION

География и геология / 4.Биогеография, биоресурсоведение. биоразнообразие

Novikova N.M., Shadrina M.B., Vyshivkin A.A.

Water problems Institute of Russian Academy of Sciences, Russia

CHANGES IN THE PLANT COVER OF THE SOLONETZ

COMPLEX UNDER DIFFERENT GRAZING PRESSURE IN NORTHERN PRE-CASPIAN REGION

Introduction

The aim of the investigation was to explore the changing of plant cover composition and structure under different grazing pressure. It’s scientifically and practically important problem for the territories of Northern Caspian lowlands, where natural vegetation is the main resource for it’s management.

Materials and methods

The investigations was held at Djanybek scientific station (49°23’ N; 46°47’ E) within dry steppe zone with specific solonetz complex plant cover: communities of Artemisia pauciflora+Kochia prostrata on micro elevations with colonetz soils, Tanacetum achilleifolium + Festuca valesiaca on the slopes of micro elevations with light chestnut soils and Stipa sareptana + S. lessingiana – Jurinea multiflora + Galatella villosa on the dark colored meadow chestnut soils of depressions. Method of investigation – tracing transect along gradient of grazing pressure increasing from preserved site to one with overgrazing. Along the transect with the plant communities changing the following parameters were registered in 7 time replication: species composition, plant height, general projective cover, width of humuя horizon, depth of carbonates. Increase of distance from preserved area to overgrazed one is considered as grazing pressure increasing. Thus at the statistical analysis the distance from preserved area to overgrased one is accepted as a measure of grazing pressure - the more distance - the stronger impact.

A comprehensive analysis of geobotanical data allowed identifying the similarity degree of the species composition between all the key sites; Jakkar formula in ECOL was applied for these purposes. Plant species and their behavior under grazing pressure, the succession of plant communities affected by grazing in different relief elements and changes in vegetation productivity have been studied as well.

Results and discussion

Relief changes along transect. The surface of the territory under study is permanently elevating from south-southwest to north-northeast what coincids with inclination of the entire territory. The total excess in absolute altitude is 160cm along transect, the latter being 2114m in length. Meso-and microelements of the relief are clearly seen: the key sites 1 and 3 reveal large depressions, slopes and elevations are dissected by a great amount of small ones. In key sites 2 and 4 mesorelief represents an elevation slope with some depression mesoforms. Such microrelief dissection should be considered as a result of overgrazing what is indicated in B.D. Abaturov’s studies (2001).

Changes in the vegetation status along the grazing pressure gradientt. The transect being stretched from the area of nature reserve to that suffered from overgrazing reveals changes in the vegetation status induced by influence of this factor.

Total projective covering is a very important feature of plant communities: the highest values (55-58%) are marked for key sites under low and moderate grazing pressure in the mid-summer as the period of intensive plant growth and development. For key sites under moderate and heavy grazing pressure the low values (17-28%) are observed at the end of the vegetation period. The maximum of projective covering (51%) is on micro-elevations within the area of nature reserve. The projective covering in micro-depressions is considerably higher during the vegetation period being maximum in the area of nature reserve (83-79%). Low values (44-42%) are specific for the key site under moderate grazing pressure. The total projective covering changes from 30 to 60% in the major part of the profile and from 10 to 60% in its last section.

Number of plant species. Maximum of plant species (12) is observed in June in depressions of nature reserve, their minimum (2 plant species in the same month) – on micro-elevation suffered from heavy grazing. The average value of this index accounts for 7 in depressions and 4 on micro-elevations during the entire period of observations. This feature displays trend to decreasing its values depending on grazing pressure (Fig.1A) .

The plant height along transect becomes lower due to increasing the grazing pressure (Fig. 1B). The correlation coefficient (r = -0.5) speaks about statistically valuable negative correlation. In the area of nature reserve the plant height is 0.3m reaching 0.5m in some cases. It doesn’t exceed 0.1m in the last profile section.

The quantitative parameters of correlation between the main features of plant communities including total projective covering, number of plant species and the height are statistically reliable (95%), thus showing trends in vegetation changes along the gradient of grazing pressure - a tendency to decreasing the values of all the parameters.

Plant species depending on grazing pressure. In a result of many years of geobotanical investigations 5 groups of plant species met within key sites due to there frequency of occurence were determined. The first group – preferred grazing includes 3 species of annual and biennial plants, which are absent in the nature reserve but presented at the territory used for grazing. The second group – indifferent to grazing, consists of 15 plant species (Artemisia vulgaris, Kochia prostrata, Leymus ramosus et all) and is present in all the key sites including the area of nature reserve. The third group – not resistant to overgrazing, contains 3 plant species of different ecology including Camphorosma monspeliaca, Ferula nuda, Salvia tesquicola. The group 4 – resistant to low grazing, includes 14 plant species (Stipa capillata, Koeleria cristata) spread in the area of nature reserve and in that used for low grazing and absolutely absent in the area under heavy grazing pressure. The fifth group consists of 10 no resistance to grazing plant species, which are distribted only in the area of nature reserve. Among them are Tulipa biflora, Ornithogalum fisherianum, Delphinium puniceum, Veronica spicata.

Fig.1 Change of characteristics of plant communities along a transect from a preserved area to an area with very high pasture pressure: A – amount of species at the sites, B – height of plants at the sites.

Based upon the descriptions of plant communities for every key site along transect a summary scheme has been compiled to reflect their succession beginning with the area of nature reserve to that suffered from overgrazing. The overgrazing leads to adverse changes in the ecological status of biotopes: the soil surface layer gets compacted, its capillarity is increased promoting higher water evaporation, the soil becomes drier. Permanent grazing of the overground phytomass serves as a cause of soil depletion and succession of plant communities.

Conclusions

Since the 1950s the solonetz complex within the territory of Dzhanybek experimental station has retained its spartial heterogeneity (Kamenetskaya I.V., Gordeeva T.K., I.V. Larin. 1955, Gordeeva T.K., I.V. Larin. 1965) represented by Kochia prostrata, Artemisia pauciflora plant communities on micro elevations, Tanacetum achilleifolium, Leymus ramosus and Agropyron desertorum communities on the slopes, gramineous and herbs plant communities in micro depressions. Under overgrazing the plant cover structure becomes less heterogenious due to disappearing plant communities so specific for slopes.

The plant communities along transect display their succession depending on increasing the grazing pressure on different microrelief elements. In key sites suffered from heavy grazing the dominated annual plant species such as Petrosimonia triandra, Ceratocarpus arenarius, Ceratocarpus testiculata are capable for preventing the soil degradation.

The transect method allowed to obtain data on the quantitative dependences and to show a decrease of plant height, species abundance and total projective covering along the grazing pressure gradient. The most succesful plant communities are marked in the area used for low grazing.

The plant species distributed only in nature reserve and being absent in the other pastures are referred to the group of those threatened and the nature reserve of Dzhanybek experimental station contributes to their preservation.

A detail study of relief at the given territory allowed concluding that the microrelief is superposed above mesorelief of the solonetz complex. Micro-elevations or micro-depressions exert a considerable effect on the development of edaphic processes and those connected with water migration in particular. It would be desirable to typify the areas of different mesorelief how it was shown in D.L. Mozeson’s publication (1955). The morphometric characteristics of the territory under consideration indicate that the microrelief seems highly dissected in areas affected by heavy grazing.

References

Abaturov B.D. 2001. Ecological consequences of grazing for desert ecosystems // In: Ecological Processes in arid biogeocoenoses. Moscow: Nauka. Pp. 57-83

Gordeeva T.K., I.V. Larin. 1965. Natural vegetation in the semi-desert of Northen Pre-Caspian region as a fodder base for livestock breeding Moscow, Nauka. 160 p.

Kamenetskaya I.V., Gordeeva T.K., I.V. Larin. 1955. Structure and dynamics of natural vegetation at the territory of Dzhanybek experimental station // Proceed. Inst. of Forest Sci. Moscow: Nauka. Vol. 25. Pp. 175-211.

Mozeson D.L. 1955. Microrelief in the northwestern part of Pre-Caspian lowland and its influence on the surface runoff // Proceed. Forest Inst. V. 25. Pp. 55-65.

Tcherepanov S.K. 1995. Vascular plants in Russia and adjacent countries. St-Petersburg: Publ. House My Family. 245 p.