The effect of grazing and weather conditions on the productivity of Tyva dry steppes, Russia

Abstract

The aim of the study. To investigate specifics of plant production process in steppe pastures in Tyva.

Location and place of the study. The study was performed in 1998-2000 and  2008-2010 in five pasture ecosystems in the Ubsu-Nur depression in Tyva, Russia.

Methodology. Field and laboratory work was carried out to assess the biological productivity of pasture ecosystems employing conventional geobotanical, botanical and ecological methods.

Main results. The study showed that all characteristics of production process change with grazing pressure and weather conditions of  the year. The highest grazing pressure was observed at the Erzin pasture, whereas the lowest pressure was found at the  Yamaalyg one. The green phytomass stock (G) at the  Erzin pasture during all years varied within 0.3–0.6 Mg ha^-1, whereas the living belowground stock (R) during six years ranged 4.5–11.5 Mg ha^-1. The Yamaalyg pasture had the lowest and the highest G of 0.5 and 1.1 Mg ha^-1, respectively, with the minimal and maximal R estimates of 7.8 and 20.1 Mg ha^-1, respectively. Therefore it was concluded that both under the highest (Erzin) and lowest (Yamaalyg) grazing pressure the between-years dynamics (over six years) may change as much as 2–3 times. Phytomass production was shown to vary much more. The aboveground production (ANP) at Erzin pasture was found to change from 0.4 to 1.2 Mg ha^-1yr^-1, i.e.3-fold. At the Yamaalyg pasture ANP changed 1.2 to 2.0 Mg ha^-1yr^-1. The belowground phytomass production (BNP) was shown to vary much more as compared with the aboveground production: from 2.7 to 24.5 Mg ha^-1yr^-1. Some production characteristics were shown to be weather-associated. At one and the same pasture (Onchalaan), depending on the weather conditions, ANP and BNP were found to vary 4 times, i.e. from 0.9 to 3.7 Mg ha^-1yr^-1  and from 4 to 18 Mg ha^-1yr^-1, respectively. The highest grazing pressure resulted in less yearly variation, as ANP ranged 0.4–0.8 Mg ha^-1yr^-1, and BNP ranged 5–8 Mg ha^-1yr^-1. Such lesser variation was apparently due to the higher resilience of the dominating herbs and grasses to grazing. Analysis of the influence of weather conditions showed that abundant summer precipitation resulted in the highest ANP estimates. No correlation was revealed between BNP and weather conditions. Overall seasonal hydrothermal conditions, such as warm and wet autumn of the preceeding year and rainy summer of the current year) were beneficial for the aboveground plant production.

Conclusion. The phytomass stock the in grazed dry steppes of Tyva was found to vary more as compared with phytomass production. Belowground production showed especially drastic changes from year to year. Increased ANP almost always results in decreased belowground living phytomass stock and often in decreased BNP due to modified nitrogen turnover under grazing. The BNP estimate is extremely volatile and does not follow the aboveground phytomass dynamics.The highest BNP in 2008  could not be attributed only to weather conditions, being most likely due to the increased solar radiation. Spatial and temporal dynamics of the phytomass production showed that the maximal green phytomass and dead belowground phytomass stocks, as well as ANP, displayed greater spatial variation as compared with the temporal one. Overall we conclude that despite different methods to study phytomass production, its spatial and temporal variation is about the same.