Pasture Productivity Changes In Mongolia

Pasture Productivity Changes In Mongolia

In order to estimate NDVI changes, we have used Two Years Difference method of respective 10 days within 1982-2001. The results showed that, which place had decrease of NDVI compare to previous year and how many years it has repeated within these 20 years. In Fig. 5 have showing the spatial distribution of NDVI changes.

Fig. 5. NDVI changes between
May – August, 1982 – 2001 (3rd 10 day)
In this figure the green color corresponds to no change or increase of NDVI from previous year within 20 years, color yellow to dark red colors showing the frequency of NDVI decrease. Yellow – lower year repetition, red – higher frequency, respectively.

During 20 years study in each 10 day within May to September occurred maximum 9 years had NDVI decreases over Mongolia. Especially, in May in southern and eastern regions, in June, July and in September (not included in Fig. 5) partly in all regions, and in August central and eastern regions had the negative influence on vegetation growth. In 24.4 – 32.7% of all territory occurred one year decrease of NDVI.

From time series, most of changes have been occurred in last decade of June and July, and all September becoming worse than previous years. In Fig. 7. showed 1-3, 3-5, 5-7, and 7-9 years frequency of NDVI decreases in each 10 days within 20 years. Over the Kherlen river basin NDVI decreasing frequency occurred mostly in August and September. The maximum of NDVI decrease was in 9 years over forest steppe and steppe zones.

Fig. 7. Frequency of NDVI decreases in each
10 days of 1982-2001.
NDVI and biomass
In order to integrate NDVI dynamics of each zone with biomass data we have analyzed 20 years NDVI dynamics separated into two decades as, from 1982 to 1991 and from 1992 to 2001. In first period the trend of NDVI in July was increased from 0.31 to 1.39, in August this value changed from -0.72 to 0.87 values per year and in second period it was from 0.96 to -1.61 and from -0.39 to -3.12 values, respectively in July and August within all ecosystems.

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