Improving Soil Structure to Support Urban Trees · Soil Aggregate • Soil aggregates are produced...
Transcript of Improving Soil Structure to Support Urban Trees · Soil Aggregate • Soil aggregates are produced...
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Improving Soil Structure to Support Urban Trees
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What's the difference between Soil and Dirt?
• “Soil is something you pay for and dirt is something you sweep away.”
• Soil has value, provides functions necessary for human survival.
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Five functions of soil
Source: The Cooperative Soil Survey http://www.soilsurvey.org/index.asp
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Plant Growth
• Soil provides a physical substance that supports plants and enhances plant growth.
• Soil provides plants– Nutrients (18 essential)
– Aeration (oxygen)
– Water
– Physical support
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Habitat for Soil Organisms
• Soil provides habitat for microorganisms, mammals, insects, and reptiles.
• Presence of soil organisms is an indication of healthy, functioning soil.
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Water Quantity and Quality
• Healthy functioning soil acts as a sponge.– Recharge groundwater
– Provide stream flow
– Water for plants
• Filter out pollutants– Plants
– Microorganisms
– Adsorption (particle binding)
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Nutrient Recycling
• Organic matter breaks down to form humus.
– Humus = Compost
– Holds moisture• 80-90% of it’s weight
– Provides nutrients for plants/soil organisms
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What is soil?
• Unconsolidated mineral and organic matter on the Earth's surface that can be used as a medium for plant growth (USDA NRCS August 2012).
Pidwirny 2006
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Soil Texture: Distribution of Mineral Particles
(USDA NRCS 2012)
• Soil texture = Physical process
– Very difficult to change
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Soil Structure
• Mineral particles (sand, silt, clay) combined with organic matter to form larger, secondary particles called aggregates.
– Soil structure = Physical and biological processes.
• Biological processes are more easily disrupted.
– Altered soil structure is the first sign of reduced ecological function.
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Soil Aggregate
• Soil aggregates are produced by soil microbial activity, the amount and composition of the soil organic and mineral components, diversity and structure of aboveground plant community, and disturbance history.
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Soil Structure
• Good Soil Structure = Stability
– Soil becomes less erodible with increase formation of aggregates
http://www.consumer.org.nz/reports/soil-quality/check-your-soil-condition
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Soil not Dirt!
• Dirt is the physical without the biological
– Dirt can have texture but lacks structure
• Soil is where the physical and biological meet.
– Minerals (Sand, Silt, Clay) + Organic Matter (Humus, Roots, Organisms)
• Soil Is Alive!
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Questions?
• “We abuse land because we regard it as a commodity belonging to us. When we see land as a community to which we belong, we may begin to use it with love and respect”.-Aldo Leopold- 1948
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Indicators of Soil Degradation?
June 2012
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Indicators of Soil Degradation?
June 2012
• Loss of Vegetation Cover
• Reduced organic matter
• Soil Compaction
• Reduced Soil Moisture
• Increased soil erosion/ reduced aggregation
• Loss of soil organisms
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Perennial Vegetation Cover
• Healthy functioning soils will host an abundant and diverse assemblage of perennial vegetation (plants that live more than a few years).
• Soil not covered by vegetation is more prone to soil-splash and erosive forces from rain and surface runoff.
• Vegetative cover also contributes to below-ground nutrient cycling and water infiltration.
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Perennial Vegetation Cover
• The taller the plant is above the ground the deeper its roots will penetrate below ground.
– Erosion Control
– Nutrient Cycling
– Water Infiltration
Source: Nueces River Authority, Your Remarkable Riparian 2010
Texas Switchgrass (Panicum virgatum)
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Perennial Vegetation Cover
• Lack of vegetation cover can lead to soil loss.
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Quote Time
• “With the disappearance of forests all is changed…. The face of the earth is no longer a sponge, but a dust heap, and the floods which the waters of the sky pour over it hurry swiftly along the slopes, carrying in suspension vast quantities of earthly particles.”
-George Perkins, 1864-
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Organic matter
• Is strongly related to the concentration of carbon, nitrogen and other elements stored in the surface soil layers (Tongway and Ludwig 2011).
– Organic Matter = Plant Food
• Increasing soil organic matter content can increase:
– Topsoil depth,
– soil porosity,
– water infiltration and nutrient cycling
– improve soil stability over time• Aggregates and soil structure
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Organic matter
• Decaying grasses, mulch, detached leaves, stems, twigs and fruit of perennial species are good sources of organic matter for the soil.
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Mulching
• Conserves water, reducing soil moisture evaporation.
• Helps reduce soil erosion
• Reduces surface water runoff
• Increases groundwater infiltration
• Regulates soil temperature
• Fertilizes the soil
• Reduce soil compaction
Apply mulch 3-4 inches deep and 4-5 inches away from base of tree
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Soil compaction
• Soil compaction : is one of the most discerning variables separating healthy forest soil cover from degraded turf grass (Pouyat et al. 2007).
• Increasing soil compaction can reduce the soil’s ability to function for structural support, water and solute movement, and restrict root growth (USDA 2008).
Source: http://www.dpi.nsw.gov.au/
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Austin Riparian Zone Data
• The city of Austin found a significant increase in soil compaction at mowed vs. un-mowed (natural) sites.
– Mowed sites = 458 PSI
– Un-mowed = 183 PSI
Mowed Riparian Zone Un-mowed Riparian Zone
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Soil compaction
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Soil compaction
• Compaction can result in shallow rooted plants and poor plant growth, reduced vegetative cover, increased erosion, and reduction in water infiltration (USDA 2008).
– Improvements can be gained by reducing disturbance from vehicle and foot traffic and increasing soil organic matter content.
Source: http://www.dpi.nsw.gov.au/
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Soil Moisture
• Has been shown to be negatively correlated to urban land-use (Gift et al. 2010).
– Less moisture in urban environments
• Hydrologic changes associated with urbanization often result in lower water tables and drier more aerobic soil conditions.
• Impervious surface = increased runoff/ less infiltration
• Continued vegetation removal results in reduced organic matter content and loss of soils water holding capacity.– Organic Matter = Hummus = 80-90% water content
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Austin Riparian Zone Data
• The city of Austin found a significant decrease in soil moisture at mowed vs. un-mowed (natural) sites.
– Mowed sites = 60% surface soil moisture
– Un-mowed = 77% surface soil moisture
Mowed Riparian Zone Un-mowed Riparian Zone
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Soil Moisture
• Improving soil moisture by increasing vegetation cover, and organic matter inputs, such as mulch, can improve nutrient cycling and plant growth.
Decaying grasses, mulch, detached leaves, stems, twigs
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Soil Erosion
• Good Soil Structure = Stability
– Increase formation of aggregates = Less erosion• Formation of soil aggregates require adequate soil organic matter.
– Soil organic matter = humus, tree roots and soil organisms.
• Aggregate stability or erosion potential: is the measure of soil aggregates resistance to external destructive forces such as wind and water.
– The greater the percentage of stable soil aggregates, the less erodible the soil will be.
– Erosion can be used as an indicator of reduced aggregate percentage and a loss in soil function.
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Austin Riparian Zone Data
• The city of Austin found increased bank instability (erosion) at mowed vs. un-mowed (natural) sites.
– Mowed sites = 38% bank instability
– Un-mowed = 23% bank instability
Shows evidence of soil erosion and lack of soil aggregate percentage on the banks of Tannehill Creek at Bartholomew Park in Austin, Texas.
Mowed Riparian Zone Un-mowed Riparian Zone
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Soil Erosion
• Improving soil structure by increasing soil organic matter content can minimize erosion.
• Mulch/ compost
• Allowing vegetation to grow
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Soil Organisms
• Presence of algae, fungi, lichens, mosses, liverworts and mushrooms and earthworms can be an indication of improved soil conditions.
– Increased nutrient cycling, organic matter content, and aggregate percentage).
– Earthworm abundances between 10 and 50 worms per square foot are considered adequate for soil function.
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Soil Organisms
Photo taken from the Colorado River Wildlife Sanctuary, a passively restored riparian area designated as water Quality Protection Land, showingfruiting body of mycorrhiza an indicationof recovering soil conditions.
Earthworm abundance can be used as a tool to assess different environmental impacts such as tillage operations, soil pollution, pesticide and fertilizer inputs, compaction, industrial pollution, etc…(Paoletti 1999).
http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html
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Soil Organisms
• Increase the abundance of soil organisms:
– ↑organic matter content,
– ↑ root biomass• Let vegetation grow
– ↓soil compaction
– ↓ use of pesticides, herbicides, and fungicides,
• Healthy Soil = Live Soil
http://courses.be.washington.edu/LARCH/433/2012_winter_vermiculture_and_vermicomposting/definition.htm
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Summary
• Soil is alive, providing functions essential for humans– Medium for plant growth– Water quantity and quality– Habitat for soil organisms– Nutrient recycling– Engineering medium
• Improving soil health and function– Increasing organic matter inputs– Moisture retention– Increasing vegetative cover– Reducing soil compaction and erosion potential– Creating habitat for soil organisms
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Questions?
New Yorker January 24, 2000
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Riparian Zone Restoration
• Establish passive, no mow zones to improve ecological function
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Riparian Zone: The transition between the aquatic and terrestrial
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The processes necessary to preserve and create goods or services valued by humans.
Ecosystem function?
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Healthy Riparian Buffers Provide
• Filtering of overland flow, removing pollutants
• Prevention of stream bank erosion.
• Slowing of flow, reducing downstream flooding.
• Absorption of water, providing for baseflow in streams.
• Shade, reducing water temperatures.
• Reduced mowing and maintenance by City staff.
• Reduction City’s carbon footprint via both sequestration and reduced emissions.
• A greenbelt forest and stream amenity with diverse tree and plant communities for walkers, hikers and wildlife observers.
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Erosion Water Storage
Water Quality
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The wider the buffer the greater the function
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Passive Restoration
• Allow for natural plant succession to restore ecological function
– Adaptive approach involving intense monitoring
1997 2012
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Vegetative Succession
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Passive
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Restoration Approach
• Establish a “no mow” area along the stream channel with a goal of a 50 foot riparian buffer (25 ft on each side of creek). • This is a flexible buffer, depending on trails, park infrastructure, access
areas and/or view corridors.
• Allow for passive plant growth in entire buffer area, with additional active plantings where necessary, (native grass, wildflowers, and woody species) following site assessments.
• Periodic trash clean-up, triggered WPD Trash index score
• Periodic “weed/invasive management” to address nuisance problems that may arise
• Educational and demarcation signage where appropriate
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Questions?
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Restoration Sites
• Bartholomew Park
• Bull Creek District Park
• Givens Park
• Lady Bird Lake, downstream/east of I35
• Commons Ford Park
• Blunn Creek Greenbelt, upstream of Monroe
• Little Stacy
• Big Stacy
• Dittmar Park
• Buttermilk Greenbelt
• Dottie Jordon Park
• Boggy Creek Greenbelt
• Gillis Park
• Robert E. Lee (small channel along R.E. Lee drive)
• Tarrytown Park
• North Star Greenbelt
• Reed Park
• Battlebend Greenbelt
• Shoal Creek Greenbelt at 2222/Northland
• Boggy Creek between Cherrywood and 38 ½ St.
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Vegetation = Lower Crime
Crime rates for 98 apartment buildings in Chicago with varying levels of nearby vegetation were compared. The greener a building’s surroundings were, the fewer crimes reported.
Kuo and Sullivan 2001
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Mosquitoes
• Mosquitoes breed in stagnant pools
– Increased water flow reduces mosquito habitat
• Research shows that mosquito density decreases in the presence of vegetation and predators.
– Predators = damselflies, dragonflies, diving beetles
Healthy riparian systems with adequate vegetation, increased flow and improved habitat can reduce mosquito abundance
Leisnham et al. 2005
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Cool surrounding area
• Covering 40% of Austin with trees would lower peak summer temperatures by as much as 2°F
– Riparian buffers have been shown to effectively decrease surrounding air temperature up to 7°F
Dong et al. 1998
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Increase home values
• A property directly adjacent to the Barton Creek Greenbelt was associated with a significant $44,332 (20.2%) rise in property value compared to all homes in the Barton area
– Barton, Lost Creek, and Travis neighborhoods
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Snakes
Cause # Annual Texas Fatalities
Heart Disease 38,493
Cancer 35,618
Cerebrovascular disease 9,550
Accidents 9,455
Respiratory diseases 8,858
Lightning Strikes 6.4
Snake bites 1-2
Texas Department of State Health Services 2011
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Rat Bites and Infestation In New York City
Childs et al. 1998
Distance to Geographic Feature
Average # of Bites from Five New York Boroughs
Highway 2,381
Waste station 5,816
Subway 1,693
Railroad 1,319
Park 244