THE SIGNIFICANCE OF SUMMER PRECIPITATION IN THE NORTHERN GREAT PLAINS

Authors: Heitschmidt, Rodney; Vermeire, Lance

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2005
Publication Date: 2/1/2006
Citation: Heitschmidt, R.K., Vermeire, L.T. 2006. The significance of summer precipitation in the northern great plains. Society for Range Management Meeting Abstracts #160.

Interpretive Summary: Drought is an inher4nt trait of most rangelands, and although drought is expected to occur on a fairly regular basis, managers are often ill prepared for drought. This is probably in part because rangeland managers are eternal optimists when it comes to expected precipitation. Although this optimism is a necessary character trait for rangeland managers to maintain a healthy mental state, they also need to face reality. To this end, they need to address 2 fundamental questions relative to drought management. The first question is – what is the probability that substantial precipitation will be received over the time period of concern, and the second question is – if it does rain, what will the impact be on current year’s herbage production? The objective of this study was to address the second question. Our hypothesis was that herbage growth response to above normal summer precipitation (i.e., 2x in July and August) will be quite limited in the Northern Great Plains because of limited response capacity. Study plots were 5 x 10-m non-weighing lysimeters. Treatments were established using a combination of simulated droughts, using an automated rainout shelter, and irrigation. Treatments were: 1) spring drought (i.e., 1 May-1 July) followed by amvient precipitation thereafter; 2) spring drought followed by amvient precipitation thereafter plus summer irrigation (i.e., July and August); 3) ambient precipitation only; and 4) ambient precipitation plus summer irrigation. Study revealed that substantial herbage production can be expected in this region during summer if substantial precipitation is received. This is primarly because of the positive growth response of a single species, that being blue grama (Bouteloua gracilis (H.B.K.) Lag. Es Griffiths) a warm-season, short-, perennial grass species. However, long-term weather data shows the probability of receiving 2x normal precipitation in bot July and August (i.e., our irrigation treatments) is 0.01% (1%). Thus, although these rangeland possess the capacity to respond favorably to “dry season” precipitation, the probability of receiving said precipitation insures levels of ecological and economic risks remains high.

Technical Abstract: Drought is an inherent trait of most rangelands, and although drought is expected to occur on a fairly regular basis, managers are often ill prepared for drought. This is probably in part because rangeland managers are eternal optimists when it comes to expected precipitation. Although this optimism is a necessary character trait for rangeland managers to maintain a healthy mental state, they also need to face reality. To this end, they need to address 2 fundamental questions relative to drought management. The first question is – what is the probability that substantial precipitation will be received over the time period of concern, and the second question is – if it does rain, what will the impact be on current year’s herbage production? The objective of this study was to address the second question. Our hypothesis was that herbage growth response to above normal summer precipitation (i.e., 2x in July and August) will be quite limited in the Northern Great Plains because of limited response capacity. Study plots were 5 x 10-m non-weighing lysimeters. Treatments were established using a combination of simulated droughts, using an automated rainout shelter, and irrigation. Treatments were: 1) spring drought (i.e., 1 May-1 July) followed by ambient precipitation thereafter; 2) spring drought followed by ambient precipitation thereafter plus summer irrigation (i.e., July and August); 3) ambient precipitation only; and 4) ambient precipitation plus summer irrigation. Study revealed that substantial herbage production can be expected in this region during summer if substantial precipitation is received. This is primarily because of the positive growth response of a single species, that being blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths) a warm-season, short-, perennial grass species. However, long-term weather data shows the probability of receiving 2x normal precipitation in both July and August (i.e., our irrigation treatments) is 0.01% (1%). Thus, although these rangeland possess the capacity to respond favorably to “dry season” precipitation, the probability of receiving said precipitation insures levels of ecological and economic risks remains high.