Forces of Change

Range Change Factors

Grazing

Fire

Invasive Species

Weather/Climate

Human Activities

Goal of ecosystem management

Efficiently capture sunlight

Reduce losses of nutrients and water from system

Forces of Ecosystem Change

Immigration and establishment of plants

Competition between plants

Fire

Grazing

Site modification

Stabilization

How does grazing affect plants

Some plants are extremely sensitive to grazing (A)

Most plants are somewhat tolerant of grazing (B)

A few plants actually benefit from grazing, especially light grazing (C )

How does fire affect plants

Some plants are extremely sensitive to fire (A)

Most plants are somewhat tolerant of fire (B)

Other plants actually benefit from fire especially light fire (C )

Location of Growing Points – Grasses

Also called:

Buds

Meristems

As long as the growing point is present growth continues.

If removed - growth stops and new growth has to initiate from a dormant bud.

Location depends on season

Early in the growing season - close to the ground and protected.

As the season progresses - elevates and subject to removal.

Stolon

Rhizome

Apical Meristem

Axillary Buds

Meristem Location of Growing Points – Shrubs & Trees

May have basal buds and be able to resprout from base after fire

Differences between fire & grazing?

Fire

Not selective for specific plants

Removes dead and live tissue

Forbs and shrubs initiate growth outermost points

Insulating bark Serotinous Cones

Produces heat

Recycles nutrients in inorganic form

Recycles nutrients in a relatively even layer across the landscape

Patchiness on a landscape scale

Most likely in dry-hot season

May create hydrophobic soil layer but, doesn’t yield compaction

Generally reduces seed viability, though some seeds require fire to be viable.

Grazing

Selects palatable over unpalatable

Live tissue preferentially removed

No heat produced

Recycles nutrients in organic (feces) and inorganic (urine) forms

Recycles nutrient in patches

Patchiness on a plant-scale

Occurs year round

Can cause compaction through hoof action

Generally reduces seed viability though some seeds require consumption to become viable

Weather/Climate

Most important factor in long-term changes to rangeland plant communities

Normal variation

Year-to-year (annual)

Long-Term

Drought

Impacts on plant composition

Exotic of Introduced Species

Definition: “plants that are not native to a region that have been brought in either intentionally or unintentionally”

Invasive vs. weed

Response to disturbance

How do they increase?

Negative environmental impacts

Invasive Species

Species that that increase in a community in a way the suppresses other plants in the community and reduces there abundance or fitness.

Can native or introduced

Negative environmental impacts

Have characteristics, such as high seed production or root sprouting, that allow them to increase with disturbance.

Human Activities

Included development, recreation, subdivision

Humans affects other forces of nature

Invasion

Fire

Grazing

Climate/weather?

Current Issue of Ecological Change:

The “Pristine Dream” - many environmentally concerned people wish that rangelands could return to pristine conditions similar to what Lewis and Clark observed.

Possible or Not?

Sustainability (or Sustained-yield) is the concept that we can graze or otherwise use the rangeland resource in such a way as to not jeopardize future productivity.

Possible or Not?

Biodiversity (or Biological Diversity) is an attribute that describes for the variety of organisms the genetic variation they contain and the variety of communities, ecosystems and landscape pattern in which they occur.

Believed that more diverse ecosystems are generally more stable and able to cope with disturbance than less diverse ecosystems.

Many agencies and environmental organizations espouse the concept that we should manage for high biodiversity.

Yes or No?