Riparian Restoration

 

Chambers and Miller, Ch. 9

 

Restoration success depends on understanding:

1) the processes that structure the ecosystem

2) the appropriate temporal and spatial scales

3) the effects of historical and ongoing land use.

 

Livestock grazing is implicated in most disturbances

 

Livestock influence riparian ecosystems by:

 

          1) removing herbage (allowing soil temp to rise and evaporation to increase)

          2) damaging plants by grazing, trampling

          3) altering nutrient cycling by depositing N and removing foliage

          4) compacting soil, which increases runoff and decreases water availability to plants.

 

Other disturbances: roads, recreation

 

There have also been long-term climate effects (drier, warmer).

 

Combined climatic and anthropogenic effects:

 

          1) many streams have become isolated from their floodplains

          2) surface water/ground water interactions have been altered

          3) declines in water tables have resulted in changes in plant species composition

 

 

Spatial Scales

 

Watersheds: drainage basins.

 

Riparian Corridors: integrated networks of stream channels and adjacent floodplains and terraces. 

 

Valley Segments: have semi-uniform slopes, widths and geological materials.

 

Stream Reaches:  have relatively uniform channel morphology, bed materials, bank conditions and woody debris.

 

 

Successful strategies for restoration are at watershed/riparian corridor scale.

 

Projects are at the valley segment/stream reach scale.

 

The most sensitive basins have the quickest and most negative response to disturbance and high-volume runoff.

 

Basin types:

 

Flood dominated    high sensitivity

 

Deeply incised                 low to moderate sensitivity

 

Fan dominated                low to moderate sensitivity

 

Pseudo-stable                  moderate to high sensitivity

 

 

 

 

Briggs, Riparian Ecosystem Recovery, 1996

 

Impacts:

 

          livestock

          recreation

          invasives

          wildlife

 

 

Livestock

 

Grazing may be less the problem than overgrazing.

 

One heavy grazing on sensitive land can be bad

 

          steep slopes

          shallow soils

          low vegetation cover

 

Effects: 

 

          alters plant competition

          decreases soil infiltration

          increases soil erosion

          stream characteristics modified:

                   loss of bank undercuts

                   increased turbidity

 

Livestock Management to decrease riparian impacts

 

          decrease grazing intensity

          rest/rotation

          fencing

          develop upland water sources

 

Re-vegetating livestock-damaged areas

 

          You must first analyze:              1) channel stability

                                                                   2) water availability

 

          Understand the potential for autogenic re-vegetation

 

          Livestock and re-vegetation are not compatible

 

                   Plants palatable to livestock must be protected for the first two growing seasons.

 

                   Non-palatable species should be protected from trampling.

 

Recreation

 

Hiking, camping, off-road vehicles

 

Changes:

          compaction

          loss of vegetation

          lowered organic matter

          increased erosion

          loss of macroporosity

 

ORV’s cause the same changes, only quicker.

 

Managing recreation

 

          adjust use levels

          keep trails and campsites away from sensitive areas (easily disturbed sites, new restorations)

          confine camping to a few sites

          install interpretive signage

 

Do not install a restoration project without controlling use

 

          live stakes may be used as firewood

          seedlings may be run over by vehicles

          irrigation systems may be torn up.

 

Invasives

 

Southwestern invasives include salt cedar (Tamarix), Russian olive (Eleagnus) and Bermuda grass (Cynodon).

 

Usually they come to dominate after hydrology has been modified (salt cedar does well in artificial flow regimes).

 

Invasives negatively impact restoration efforts.

 

Salt cedar control

 

          bulldozer (where there are no natives)

          herbicides

 

Typical control regime

 

          Cut trees down in fall (cut 5 cm above ground)

          Paint cut cambium with Garlon or Tordon within minutes of cutting

          Re-cut and herbicide sprouts within a year.

 

 

 

Wildlife

 

Some wildlife impact restorations

 

          Some eat vegetation:

 

          elk

          white-tailed deer

          beaver

 

          Some will gnaw irrigation lines:

 

          rice rats

          wood rats

          pocket gophers

 

Protecting restoration from wildife:

 

          Provide beaver with alternate food sources

          Build beaver cages out of chicken wire or hardware          cloth

 

Water Availability

 

Revegetating riparian sites characterized by groundwater decline

 

 

Low water availability occurs where groundwater levels are 3m or more below the surface.

 

          Planting riparian plants there is difficult.

 

          Survival rates are low.

 

Sources of decline:

 

          ground water pumping

          impoundment

          agricultural irrigation

          non-native phreatophytes

 

Plant material must be matched to site

 

          Planting riparian species may no longer be practical

          Flood plain spp. may be more appropriate:

                   mesquite, palo verde, hackberry

          Riparian spp. may not have enough water:

                   willows, poplars, walnut, ash

 

Planting Techniques

 

Seedlings may be especially vulnerable to low water availability.

 

Available moisture from spring flooding dries up quickly with onset of summer.

         

          Roots of seedlings must keep up with the retreating zone of soil saturation.

         

          Timing of planting is critical.

 

 

Some techniques that work:

 

          1)  Large poles (poplar trees)

 

                   P. fremontii in this case.

 

                   Use where groundwater is more than 3m deep

 

                   Holes must be dug or “stinger” used.

 

                   Ground must support equipment.

 

                   Drill must go through cobble (not easy).

 

          2) Drilling to groundwater

 

                   Drill 18 cm diameter hole.

 

                   Fill with alluvium.

 

                   Plant tree in hole.

 

                   Irrigate from top.

 

          3)  Irrigating

 

                   Expensive

 

                   Often will not wet soil deeply enough to induce roots to grow to groundwater.

 

                   Must carry on for one or two seasons.

 

Plant more individuals in places likely to have extra available moisture:

 

          secondary channels

 

          depressions

 

          lower-elevation sites

 

Problem: trees planted in wetter sites may also be more flood-prone

 

          Flood energy may disturb vegetation.

 

          Prolonged inundation may kill trees

 

          Even phreatophytes can be damaged under prolonged       flooding.

 

          Fine-grained soils more prone to anaerobiosis.

 

 

Channels

 

Channel instability can degrade associated riparian ecosystems two ways.

 

          1)  Destruction of vegetation through bank erosion.

 

          2)  Dewatering of riparian zone.

 

Developing restoration projects along unstable alluvial stream channels.

 

          Time to implement recovery plans is either 1) before obvious downcutting and erosion have occurred, or          2) after the site has undergone a major erosional event and has begun to stabilize.

 

General categories of strategies:

 

          1) revegetation

 

          2) installation of streambank stabilizing structures.

 

Planting Locations

 

          Planting closest to stream results in the greatest chance of loss due to flood disturbance.

 

          Planting far away from stream results in the greatest chance of vegetation failure due to lack of soil          water.

 

          Best sites include:

 

                   1) just downstream of concave stream reaches (accreting areas)

 

                   2) downstream of large boulders or other obstructions (like logs).

 

          Plant along an elevational gradient so that there is an optimum elevation range along the planting line.

 

          Plant vegetation in the geomorphic position it does          best in.

 

                   Willows go in dynamic landscapes near river channels.

 

                   Catclaw (Acacia gregii) is drought-tolerant and does well on old stream terraces.

 

Revegetation offers several advantages over instream structures.

 

          It is self-maintaining.

 

          Plants may resist a variety of environmental conditions and flood forces.

 

          Plants are cheaper.