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organic matter - Soil constituents that include raw plant residues and microorganisms, along with their decay products and humus, which holds nutrients and gives topsoil its dark color. Organic matter acts as a nutrient "bank account" for plants and soil organisms. Together with fungi, it glues soil particles together to resist erosion.

Related terms: crumb structure


short tops = short roots
How overgrazing affects roots. Canadian researchers kept leaves of a common prairie bunch grass clipped at different levels.

Thomas J. Elpel
patchy overgrazing & overresting
Cattle ignore stale growth while overgrazing neighboring plants. This produces overgrazing and overrest on the same pasture.

overgrazing - Grazing a plant again before it has a chance to fully recover. When grazed, a grass will typically kill off an equivalent mass of roots. It uses the nutrients from these roots to grow new leaves. But if grazed before it has regrown both its root and its leaves, its energy reserves get depleted, and is becomes overgrazed. Continued overgrazing may kill the plant.

Overgrazing can occur

  • When grazers remain too long and regraze the plant when it tries to regrow.
  • When grazers move away, but return too soon and regraze the plant before it finishes growing new leaf and replenishing stored energy.
  • Immediately following dormancy when the plant is growing new leaf from stored energy.
  • When leaf material grown in preparation for the next growing season is grazed from apparently dormant plants, such as cold steppe grasses.

Overgrazing can only happen to individual plants, not rangelands. It is always a function of time rather than number of grazers.

Overgrazing and overrest typically occur side-by-side on the same pasture when continuously stocked at low density. Grazers repeatedly nibble tender new growth, while ungrazed forage gets staler and staler.

Related terms: destructive grazing, regenerative grazing

Related pages: "Grazing and overgrazing"


Joy Livingwell
Overrest killed the center of this plant, leaving a characteristic donut shape. Arid destocked rangeland.

overrest - (Also destructive rest or R.I.P. rest.) Rest of any perennial plant that goes on so long that accumulating old material hampers growth or kills the plant. It occurs mainly in brittle environments where the decay happens slowly. Also called R.I.P. rest. Overrest and overgrazing often take place in the same pasture and even on different parts of the same plant.

Soil surfaces can also become overrested when bare soil forms a hard cap (crust) that keeps out air and water and prevents seeds from germinating. In both cases the main remedy is concentrated animal impact.

Related terms: rest, partial rest, brittleness

Related pages: "Brittleness", "Grazing and overgrazing", "How can grazing heal land?"


overrested plant - A clumped perennial grass plant that has been rested so long that accumulated dead material prevents light from reaching growth points at the plant's base. This hampers new growth and eventually kills the plant. Overrest occurs mainly in brittle environments, where in the absence of large herbivores, decay happens slowly by weathering and oxidation, and dead stems may stand for years.

Related terms: overrest, partial rest

Related pages: "Brittleness", "Grazing and overgrazing", "How can grazing heal land?"



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Posted 23 April 2003
URL: managingwholes.com/glossary/o.htm

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