Patterns of net primary production changes in eurasian steppes

The aim of the study. The aim of the study was to analyze changes in the above-ground (ANP), below-ground (BNP) and total net primary production (NPP), expressed in dry matter, in meadow, true and dry steppes along the latitudinal (from 56o to 43o N) and longitudinal (from 36o to 116o E) gradients. Methodology. Production characteristics of 32 steppes (9 meadow, 14 true and 9 dry steppes), obtained by the same method of minimal estimate, were analyzed. Main results. The ANP value in meadow steppes decreases from 10,2 to 3,1 t/ha per year, in true steppes from 6,7 to 0,7 t/ha per year and in dry steppes from 3,7 to 0,6 t/ha per year. The value of BNP in meadow steppes varies from 26,8 to 10,1 t/ha per year; in true steppes - from 25.7 to 7.7 t/ha per year; and in dry steppes - from 24,8 to 4,9 t/ha per year. The BNP changes from West to East were found not to follow the ANP changes: a decrease in ANP may be accompanied by an increase in BNP. According to the ANP estimates the analyzed steppes can be grouped as following: 1) ANP from 10 to 5; 2) ANP from 5 to 3; 3) ANP from 3 to 1; 4) ANP less than 1 t/ha per year. The first group is located between 56o and 51o NL and includes six meadow steppes and one true steppe. The second group includes all three types of steppes (three meadow, six true and one dry steppe) between 56o and 50o N. The third group of steppes, between 54° and 43° NL, consists of six true and seven dry steppes. At 50°N one true and one dry steppes are located with the smallest ANP. The first and the second groups are located in the same territory (from 56o to 50o N) and include both meadow and true steppes. About 70% of the meadow and half of the true steppes are characterized by the ANP ranging from 6.7 to 3.1 t/ha per year. In the northern part of the explored zone there are highly productive meadow steppes, whereas in its southern part there are true steppes with both high and low production. The third group of steppes, with production from 3 to 1 t/ha per year, includes seven low-productive true and eight dry steppes. The average ANP of true and dry steppes of this group are similar (2,2 t/ha per year). Consequently, the area from 54° to 43°N can be considered as a zone of dry steppes. Conclusion. There are no separate zones of meadow and real steppes, but there is a steppe zone that includes meadow and true steppes. The proposed division of the steppes and their zoning is made on the basis of ANP, which is the most important characteristic of any ecosystem.