Wednesday, July 23, 2014

Managing Drought Risk on the Ranch

Grass Recovery

Lupines growing in western Nebraska after drought
Lupine population after drought. Image: Pat Reece.

The end of a prolonged severe drought will be memorable. Dense stands of annual plants can give rangelands the appearance of abandoned farmland.

Changes in the appearance of rangeland will be less dramatic as the severity and duration of drought decline.

However, complacency in the aftermath of any scale of drought is hazardous. Cumulative effects of excessive grazing and intermittent drought can change species composition enough to cause measurable long-term declines in herbage production.

Declines in ecological condition are directly linked to the demise of plant species most preferred by livestock. These species, historically referred to as decreasers, are most often tallgrasses or midgrasses that produce the bulk of the forage in historical climax plant communities (HCPC).

When drought ends, vegetation recovery should become a primary management objective.

Effects of Drought

  • Plant mortality increases as severity and duration of drought increase.
  • Plant mortality is highest among shallow rooted species.
  • In summer-grazed pastures, declines in ecological condition are directly linked to the decline of plant species that are most preferred by livestock.
  • Litter and standing plant herbage decline as prolonged drought continues even on nongrazed rangeland. The process is exacerbated by grazing.
  • Declines in protective plant cover reduce hydrologic condition of land surfaces which reduces the efficiency of precipitation.

Characteristics after Drought

  • Drought tolerance and the rate at which native plant communities recover after drought increase as the relative abundance of rhizomatous species increase.
  • Rates at which herbage production potentials recover after drought correspond to pre-drought levels of plant vigor and range condition in individual pastures.
  • When prolonged drought breaks, summer-grazed pastures are often infested with annual weeds and unpalatable perennials.
  • Herbage of unpalatable species may equal or exceed production of palatable species in the first year of recovery.
  • Poisonous range plants may be unusually abundant in the weedy phase of the recovery.

Recommended Management After Drought

  • Restoration of hydrological condition requires a reduction in spring and summer stocking rates.
  • Biologically meaningful rest or deferment needed to enhance recovery of preferred species occurs only when air temperatures and soil water are simultaneously favorable for relatively rapid plant growth.

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