Stormwater Restoration: The Plants Matter

A Fairfax County, VA, publication
Department of Public Works and Environmental Services
Working for You!
Stormwater Restoration:
The Plants Matter . . .
October 2016

Stormwater Planning Division
Stormwater Restoration: The Plants Matter
The role of vegetation in stream health
Difficult Run after a flood.

Stormwater Restoration: The Plants Matter.
The role of vegetation in stream health
• Ecosystem Function (from Natural Resources Conservation Service)
– Water quality
– Energy transfer
– Hydrology & Base Flow
– Downstream flooding
– Nutrient cycling
– Terrestrial wildlife
– Benthics

The role of vegetation: beyond engineering
• Meet BOS Objectives
– 2007 Adopt “Natural Landscaping
Guidelines for Maintenance and
Planting” on public lands
– 2015 Initiative to support bees
• Aesthetics
– Wild versus tended
– Front door/ back door/open
woodland
– HOA versus public lands

The role of vegetation: regulations
• Regulatory Requirements:
– Army Corps Nationwide Permit
– EPA/State –
• MS4 Permits/credits for land use
– State E&S (erosion and sediment)
– FFXCO - Chesapeake Bay Preservation Ordinance
• requires 200/100/1089
– FFXCO PFM - Urban Forestry Goals, Chapter 12
• 10-year tree canopy goals

The role of vegetation: structural diversity
• Functioning ecosystems include multiple layers
– Soil profile
– Herbaceous
– Shrub
– Understory
– Overstory

The role of vegetation: species diversity
• Functioning ecosystems include multiple
guilds
– Overstory vs. understory vs. herbaceous
– Grass vs. flower
– Annual vs. perennial
– Male vs. female (e.g. Acer negundo, Salix sp., Populus
sp.)
– Native vs. non-native
– N-fixers
– Calcium sequesters
– Carbon storage

The role of vegetation

Current vegetation monitoring: goals
• Protect our investment of about $750,000/year (11% of budget)
• Meet contractual warranty goals (slight variation):
– 85% planted woody survivorship
– <20% non-native herbaceous
– 0% highly invasive herbaceous (including stiltgrass)
• After warranty ends
– Basins are moved to MSMD - MEND
– Streams
• COE: monitor yearly until the permit is closed for 1 to 5 years
• Summer 2016 – 54 sites with 2 or 3 action items, often requiring
follow up actions

How do we currently measure?
– Nationwide Permit
• Visual inspection
– Warranty
• Loosely measured in the past
• Now using systematic transects
– point intercept herbaceous
monitoring and woody plots
– Monitoring effort >=10%
• Direct counts if needed based on size
– Progress
• Gaining acceptance from vendors
• and county Utilities Design/Construction
division (UDCD)
• to hold contractors to CD’s
• Using ESRI Collector in the field to
integrate our data with county partners
South Lakes High School in 2016

Monitoring results
• Success of past projects (at least 2 years off warranty):
• Stabilized site?: yes, but largely by non-natives
• Canopy cover: low survival of small size woody plants
• Herbaceous Cover: largely invasive
• Current projects under warranty (13 projects) :
• 85% planted woody survivorship: 57% are compliant
• <20% non-native herbaceous: 57% are compliant
• 0% highly invasive herbaceous: 0% are compliant (due to stiltgrass)
• Failure impacts the short term and long term success:
• Non-compliance results in costly re-plantings by contractor
• Or if post warranty, by Stormwater Planning Division
Bridle Path in 2016

10-years post installation
Low survivorship of small woody plant material
Lack of diversity in herbaceous layer – high invasive herbaceous
Stiltgrass dominant at Clarke’s Landing

Two years post installation
Heavy shade and compaction
Poor herbaceous cover at Miller Heights outfall

Quality of live stake stock and bank compaction
Lack of invasive treatment within initial contract
Poor success of live stakes at Banks property

Herbaceous cover improves with time but stiltgrass still problematic
Poor survival of small size woody plants
Successful herbaceous cover at Big Rocky Run

Success was evident early. Low replacements and minimal invasive plants.
Combination of factors including size, design, landscape contractor and plant quality?
Success of live stake and tublings at Pohick Creek Tributary (at Guinea)

Six months post installation
Improved: contractor expectation and performance, UDCD support
Success of tree and shrub installation at Daventry

Vegetation monitoring: early outcomes
Outcomes:
• Some older sites have less than 10% of the original trees planted at
10 years, which calls into question our compliance
• Non-native invasive species and deer are ongoing challenges
• Results of monitoring are used to inform the design process and
• Clarify the construction documents and expectations for contractors
• Enforcing warranty is now leading to better outcomes
Still missing:
• Ecosystem function is not measured. Survivorship and herbaceous
cover have not been found to be predictive of ecosystem function
Pohick
at Guinea
in 2016

What does stormwater restoration mean?
“The overall secret is that water, soil, animals and plants all interact, and restoration has
to address them all as critical components of a complex ecosystem.”
(Joy Zedler, 2014)
“Meeting performance standards does not guarantee that functions and services are
being replaced” (after Wes Hudson, 2016)
“If you build it, will they come?” (Suzy Foster, 2016)
Stormwater Restoration: create a stable, functioning system and associated habitats to
return community or ecosystem function to a degraded, or degradable, feature

How does vegetative monitoring help?
• If the plants are alive at the end of
warranty
• Tracks species and stock type success
• Tracks contractor specific success
• Overstory Trees – 300/acre @ 10 years
Most sites on track to meet goal
• Two species & minimum 35 feet wide
Most sites meet goal
• Vegetated (minimize bare earth)
Sites meet goal
Species % survival
Diospyrus virginiana 96%
Magnolia virginiana 93%
Amelanchier candensis 93%
Quercus palustris 92%
Amelanchier arborea 90%
Quercus bicolor 89%
Acer rubrum 87%
Platanus occidentalis 84%
Betula nigra 83%
Cornus amomum 83%

What does the data look like?
• Metrics are to support
questions associated with
warranty
– Success of woodies
– Herbaceous cover
– Highly invasive plants
Overst
ory
Under
story Shrub
Live
Stake
300
Trees
Native
Herba
ceous
Non-
Native
Highly
Invasi
ve Bare
Meth
od
Armfield 79 Good
Patch
es DC
Autumnwood 110 66 67 3 20 10OM
Banks 118 48 71 861 27 30 37 6NM
Big Rocky Run 374 10 15 3 418 47 11 36 6OM
Cinnamon Oaks 80 DC
Daventry 193 120 83 1934 18 29 10 43NM
Flatlick Confluence 66 35 5 46 12
NM/D
C
Government
Center Stream 151 33 966 19 3 66 12NM
Loftridge 0 50 0 0 50 5 40 5
Estim
ate
Miller Heights 36 31 28 485 17 8 10 65NM
Paul Springs 171 65 30 0 1771 17 45 4 34NM
Pohick @ Guinea 72 29 73 1076 61 1 16 22NM
R-17 87 50 DC
Rabbit Branch 46 15 33 516 52 3 39 6NM
Reston 41 207 95.5 1 35 3 25 37OM
Sandy Run 57 34Low Med-High DC
Schneider Branch 277 72 62 1088 15 54 2 29NM
South Lakes HS 189 45 65 1158 45 18 1 35NM
Tripps Run 243 45 51 29 276 50 12 19 19OM
Wakefield Run 210 68 47 1084 70 6 18 6NM
Wolf Trap 43 6 30 441 25 31 30 14OM

Diving into the data: part one
Can our data answer which sites are a “success”?
– Not really
– But we can
• support request for additional work under warranty
• inform our designs
• validate an ‘index of success’ – e.g. is our best professional judgment validated
by objective measurements?
• drive how we answer the question “which sites are a success”

Diving into the data: part two
• Used statistical techniques to validate creation/use of a
qualitative or semi-quantitative index for success (SMMI5).
– Best professional judgment (BPJ) of 3 SWPD botanists
– Variable scores in magnitude, but all scored sites in the same direction
• Used linear and multivariate techniques to compare warranty
monitoring (and other) metrics to SMMI5.
– Best predictors of overstory success are:
• Coverage of overstory and lack of ‘Highly Invasive’
– Best predictors of the BPJ – SMMI5 rating were:
• Tree counts (300 trees) and native herbaceous vegetation

Vegetative monitoring community trends
Overstory/Non-harmful Harmful non-native
Trees/ShrubsHerbaceousCover

Diving into the data: part three
• Good sites appear to be grouped – possibly similar drivers –
some of the worst sites spread out
• Relationships appear to be between:
– Non-native species cover
– Herbaceous cover
– Overstory survivorship

What will make our ecosystems “successful”?
Indicators of restoration “success”
• Low invasive species cover
• Sites should remain forested for at least
40 years (easements)
• Sites have distinct and recognizable
riparian community
• Site quality should be within top ? percent of
riparian areas
Hollin Hills neighborhood, scoping walk in 2016

What will make our ecosystems “successful”?
Recommendations:
• Measure site conditions
• Amend (e.g. sulfur, hydrogel) where appropriate
• Alter plant palette based on site conditions
• Alter plant size, density and type to increase survivorship
Wakefield Run in 2016

Measurements of ecosystem function
• Woody biomass/canopy*
• Woody survivorship and/or colonization*
• Bare earth, leaf litter* (new and time to decay)
• Soil characters (nutrients, organic matter, bulk density)
• Coarse woody debris
• Floristic Quality Index and/or Plant Stewardship Index
• Fungus/bacteria ratio
• Keystone predator – e.g. spiders
*Others are pursuing this question, too. This is an excellent opportunity for building
partnerships

Why?
A better understanding of our ability to direct restoration to
successful outcomes will protect our investment, promote
better ecosystem development and create functional
replacement systems.
Wakefield Run: at substantial completion in 2014 and in 2016

Next steps
• Explore the data we have
• Refine functions to measure
• Refine criteria for success
• Determine sample size and
frequency
• Maximize partnerships
• Implementation plan
Bridle Path in 2016

Additional Information
For additional information, please contact
www.fairfaxcounty.gov/dpwes
Irene Haske, Public Information Officer, Public Works and Environmental Services,
Fairfax County, Virginia
703-324-5500, TTY 711

Stormwater Restoration: The Plants Matter

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Stormwater Restoration: The Plants Matter

Similar to Stormwater Restoration: The Plants Matter (20)

More from Fairfax County

More from Fairfax County (20)

Recently uploaded

Recently uploaded (12)

Stormwater Restoration: The Plants Matter