Improving Soil Structure to Support Urban Trees

Transcription

1 Improving Soil Structure to Support Urban Trees

2 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.

3 Five functions of soil Source: The Cooperative Soil Survey

4 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

5 Habitat for Soil Organisms Soil provides habitat for microorganisms, mammals, insects, and reptiles. Presence of soil organisms is an indication of healthy, functioning soil.

6 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)

7 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

8 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

9 Soil Texture: Distribution of Mineral Particles Soil texture = Physical process Very difficult to change (USDA NRCS 2012)

10 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.

11 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.

12 Soil Structure Good Soil Structure = Stability Soil becomes less erodible with increase formation of aggregates

13 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!

14 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

15 Indicators of Soil Degradation? June 2012

16 Indicators of Soil Degradation? Loss of Vegetation Cover Reduced organic matter Soil Compaction Reduced Soil Moisture Increased soil erosion/ reduced aggregation Loss of soil organisms June 2012

17 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 soilsplash and erosive forces from rain and surface runoff. Vegetative cover also contributes to below-ground nutrient cycling and water infiltration.

18 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)

19 Perennial Vegetation Cover Lack of vegetation cover can lead to soil loss.

20 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-

21 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

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

23 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

24 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:

25 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

26 Soil compaction

27 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:

28 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

29 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

30 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

31 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.

32 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

33 Soil Erosion Improving soil structure by increasing soil organic matter content can minimize erosion. Mulch/ compost Allowing vegetation to grow

34 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.

35 Soil Organisms Photo taken from the Colorado River Wildlife Sanctuary, a passively restored riparian area designated as water Quality Protection Land, showing fruiting body of mycorrhiza an indication of 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).

36 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

37 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

38 Questions? New Yorker January 24, 2000

39 Riparian Zone Restoration Establish passive, no mow zones to improve ecological function

40 Riparian Zone: The transition between the aquatic and terrestrial

41 Ecosystem function? The processes necessary to preserve and create goods or services valued by humans.

42 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.

43 Erosion Water Storage Water Quality

44 The wider the buffer the greater the function

45 Passive Restoration Allow for natural plant succession to restore ecological function Adaptive approach involving intense monitoring

46 Vegetative Succession

47 Passive

48

49 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

50 Questions?

51 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.

52 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

53 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

54 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

55 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

56 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

57 Rat Bites and Infestation In New Distance to Geographic Feature York City Average # of Bites from Five New York Boroughs Highway 2,381 Waste station 5,816 Subway 1,693 Railroad 1,319 Park 244 Childs et al. 1998