DISTURBANCE

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DISTURBANCE OTHER FACTORS

• The Effect of Disturbance on Weed Populations
  along Roadsides, Right of Ways, and Easements
• Rod Cook, La Plata County Weed Manager

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Background Growing Days in Southwest Colorado

• Avg. last Frost (50 chance) May 25
• Avg. first Frost (50 chance) Sept. 22
• Avg. 120 frost free nights (1/3 of the year)
• Avg. 245 frosty ones (2/3 of the year)
• SW Colorado has a short growing season

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SW CO Annual Precipitation

• Top of San Juans 60 in. zone
• Purgatory Ski Area in a 25-40 in. zone
• Durango is in a 16-20 in. zone
• Cortez in a 12-16 in. zone
• 4 Corners is in a 7 in. zone
• Annual Precip. in the lower elevations for
  growing plants is low without supplemental
  irrigation
• SW Colorado is a cold, dry, high mountain desert
  with a short growing season

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SW CO Soil Nutrition

• In most places Soil Nutrients are below what is
  required to grow healthy grasses.
• Historic desert conditions do not provide for
  high organic matter and soil nutrients required
  to grow robust plants

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SW CO has Fragile Lands

• SW Colorado generally has shallow or very little
  top soil
• Some areas have minimal top soil
• Top soil sources are limited or non-existent
• We have fragile lands that scar easily and take
  decades for desirable vegetation to repair on its
  own.

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Weed Invasion Competition

• Weed invasion is generally caused by some
  previous activity or event on the site i.e.
  disturbance of some sort, recent or historic.
• Most times, weeds do not invade healthy,
  established balanced plant communities.

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Two Classes of Weeds

• I. Simple, Early Colonizers are weeds that
  inhabit waste areas or disturbed sites. A weedy
  and commonly introduced plant growing where the
  vegetational cover has been interrupted.
• II. Complex, Stress Tolerator. A weed that can
  survive a single stress or multiple stresses.
  Can become established and spread on disturbed or
  non-disturbed sites. Over time, can dominate the
  site or become a monoculture precluding all other
  vegetation. Can even crowd out simple weeds.

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Webster Definitions

• Which definition best fits Disturb?
• To interfere with or interrupt
• To alter the position or arrangement
• To break up or damage
• To destroy the tranquility or composure
• To throw into disorder

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Definition Successional Domination

• Successional A group, type, or series that
  succeeds or displaces another
• Domination Supremacy or preeminence over
  another
• In the plant world, Successional
  Domination may take several years, several
  decades or several centuries to achieve a
  balanced plant community.

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The Slow Silent Battle

• In the plant world, competition is not as evident
  in stable plant communities.
• On disturbed sites, the race is on to determine
  which plant(s) will eventually dominate.
• This is where successional domination comes into
  play.

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Preventing Weed Invasion

• Making best land management decisions that
  minimize disturbance and reduce the potential for
  weed invasion. Example Deep Plowing
• Evaluating and managing existing plant health.
• Managing for weeds you dont have is the cheapest
  form of control.

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Disturbance, Natural

• Geological rock falls, landslides, earthquake
• Meteorological hurricane, tornado, hail, heavy
  rain
• Hydrological floods, avalanches
• Drought
• Fire

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Disturbance, Animal Caused

• Overgrazing
• Hoof compaction
• Rolling
• Large herd trails
• Pocket gophers
• Prairie dog colonies

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Disturbance, Human Caused

• OHV, dirt bikes, Mt. bikes
• Vehicle soil compaction
• Heavy equipment construction
• Imported soils filled with debris (or weed seeds)
• Excessive cultivation practices
• Snow removal

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Disturbance Keep in mind that some disturbances
are avoidable, and some are not and we do the
best we can with them.

• Some Photo Examples

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Geological
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Drought

• 2002 Drought SW Colorado
• 500 year event
• 1.3 inches of precipitation January-July
• D-4 (Extreme Drought)
• Trees were measuring 7 moisture
• Kiln dried lumber products are 14

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Fire

• Missionary Ridge Fire Event
• June 9- 2002
• Burned for 40 days
• 72,962 Acres burned
• 56 homes destroyed

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Hydrological Floods

• Topsoil removal and erosion
• Can be a major disturbance event
• Is this a bad thing?

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Overgrazing, hoof compaction, animal caused
disturbance
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No Grazing or Mowing

• Makes grass plants un-challenged and unproductive
  over time.
• Then become subject to weed invasion

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Pocket Gophers, P. dogs

• Pocket gophers eat grass, shrub and tree roots
  causing damage or death.
• P. dogs eat their weight in grass daily (5 lbs)
• 12 dogs A 60 lb. bale of hay daily
• They overgraze and weeds invade

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Heavy Equipment Construction

• Major disturbance
• Soil compaction
• Equipment moves weed seed infested clay soils
  around

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Imported Dirt with Debris

• Usually is not top soil
• Sometimes filled with rock or concrete
• Difficult to establish desirable vegetation

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Excessive Cultivation Practices
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Snow Removal

• Can be a major roadside disturbance

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What observations can be taken from the following
photo?
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Thank You,

Rod Cook

www.laplataweeds.org