Improving Soil Structure to Support Urban Trees

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.

Five functions of soil

Source: The Cooperative Soil Survey http://www.soilsurvey.org/index.asp

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

Habitat for Soil Organisms

• Soil provides habitat for microorganisms, mammals, insects, and reptiles.

• Presence of soil organisms is an indication of healthy, functioning soil.

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)

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

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

Soil Texture: Distribution of Mineral Particles

(USDA NRCS 2012)

• Soil texture = Physical process

– Very difficult to change

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.

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.

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

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!

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

Indicators of Soil Degradation?

June 2012

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

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.

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)

Perennial Vegetation Cover

• Lack of vegetation cover can lead to soil loss.

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-

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

Organic matter

• Decaying grasses, mulch, detached leaves, stems, twigs and fruit of perennial species are good sources of organic matter for the soil.

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

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/

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

Soil compaction

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/

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

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

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

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.

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

Soil Erosion

• Improving soil structure by increasing soil organic matter content can minimize erosion.

• Mulch/ compost

• Allowing vegetation to grow

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.

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

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

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

Questions?

New Yorker January 24, 2000

Riparian Zone Restoration

• Establish passive, no mow zones to improve ecological function

Riparian Zone: The transition between the aquatic and terrestrial

The processes necessary to preserve and create goods or services valued by humans.

Ecosystem function?

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.

Erosion Water Storage

Water Quality

The wider the buffer the greater the function

Passive Restoration

• Allow for natural plant succession to restore ecological function

– Adaptive approach involving intense monitoring

1997 2012

Vegetative Succession

Passive

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

Questions?

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.

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

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

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

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

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

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