Tracking pasture conditions and predicting droughts in the Amboseli ecosystem

By David Western,  Victor N. Mose, David Maitumo, Winfridah Kemunto , Erastus Mwaniki, Paul Kasaine, Sunte Kimiti and Samuel Lekanaiya

​Amboseli Conservation Program has been tracking range-land conditions in the Amboseli region since 1976. The tracking measures plant biomass, greenness and grazing pressure in 20 permanent plots each month in the 700 square kilometer area in and around the Amboseli Basin used heavily by livestock and wildlife in the dry season. The methods used and the results of the long-term monitoring have been published in (Western et al., 2015)

We have now developed a simplified method of graphically presenting the range-land tracking data to provide group ranch and grazing committees an early warning system indicating the severity of pasture shortage for each year and month. The method uses grazing pressure on a scale of 0 to 100 as a measure of pasture availability. Zero grazing occurs after good rains and low grazing pressure. To simply the index we use an arrow to indicate the severity of pasture conditions. The arrow in the green range indicates less than a third of the pasture has been grazed down, amber up to two thirds and red severely grazed.

The Illustration 1 below shows the severity of each year from 1976 to 2018. In 1976 pasture was severely grazed down, causing a 50 percent loss of cattle. Grazing pressure was low in the following five years and pastures recovered. From 1982 onward the grazing pressure increases steadily with shorter intervals of recovery until 2009, the worst year on record when the needle indicates an average of 73 percent grazing pressure. In 2009 over 70 percent of livestock, 50 percent of sheep and goats and large numbers of wildebeest, zebra and elephants died of starvation. From 2010 onward the recovery is far poorer and shorter lived than in earlier years due to heavy grazing pressure. By 2017 the grazing pressure needle moved into the second highest level recorded. 2018 would have been as severe as 2009 had the drought not been broken by extremely heavy rains. Despite the heavy rains, pasture conditions are shaping up to be very severe in 2019. 

Illustration 1: The needle in the green zone indicates a good pasture year, in the amber zone a poor year and red zone a severe year when heavy livestock deaths are likely to occur by the end of the year.

Illustration 2: Monthly pasture conditions for 2019 for Amboseli, Eselenkei, Mbirikani and Kimana group ranches.

Illustration 2 shows the monthly pasture conditions for 2019 for Amboseli, Eselenkei, Mbirikani and Kimana group ranches. The needle has already moved into the red zone due to poor short rains and heavy grazing pressure. In the coming dry season Amboseli and all group ranches in the region will experience severe pasture conditions. Unless the region has nonseasonal rains before late September and the pressure relieved by the sale of livestock or outward migration, substantial mortality is likely to occur by October.

 
We will be developing and posting tracking details on livestock body condition, milk yields and market prices over the coming month to improve ACP’s range-land monitoring and projections of the seasonal outlook. Illustration 3 gives a preview of livestock condition and milk production adding weight to the severe outlook for the 2019 long dry season and an early warning of the need for early action to prevent heavy economic losses.

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Illustration 3: Livestock body condition scores and milk yield in the Amboseli ecosytem

References
Western, D., Mose, V.N., Worden, J., Maitumo, D., 2015. Predicting Extreme Droughts in Savannah Africa: A Comparison of Proxy and Direct Measures in Detecting Biomass Fluctuations, Trends and Their Causes. PLoS One 10, e0136516. doi:10.1371/journal.pone.0136516