stormwater restoration: the plants matter

A Fairfax County, VA, publication

Department of Public Works and Environmental ServicesWorking 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 installationLow survivorship of small woody plant material

Lack of diversity in herbaceous layer – high invasive herbaceous



Stiltgrass dominant at Clarke’s Landing

Two years post installationHeavy shade and compaction



Poor herbaceous cover at Miller Heights outfall

Two years post installationQuality of live stake stock and bank compactionLack of invasive treatment within initial contract



Poor success of live stakes at Banks property

Two years post installationHerbaceous cover improves with time but stiltgrass still problematic

Poor survival of small size woody plants



Successful herbaceous cover at Big Rocky Run

Two years post installationSuccess 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 installationImproved: 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

Overstory

Understory Shrub

Live Stake

300 Trees

Native Herbaceous

Non-Native

Highly Invasive Bare

Method

Armfield 79 GoodPatches DC

Autumnwood 110 66 67 3 20 10 OMBanks 118 48 71 861 27 30 37 6 NMBig Rocky Run 374 10 15 3 418 47 11 36 6 OMCinnamon Oaks 80 DCDaventry 193 120 83 1934 18 29 10 43 NM

Flatlick Confluence 66 35 5 46 12NM/DC

Government Center Stream 151 33 966 19 3 66 12 NM

Loftridge 0 50 0 0 50 5 40 5Estimate

Miller Heights 36 31 28 485 17 8 10 65 NMPaul Springs 171 65 30 0 1771 17 45 4 34 NMPohick @ Guinea 72 29 73 1076 61 1 16 22 NMR-17 87 50 DCRabbit Branch 46 15 33 516 52 3 39 6 NMReston 41 207 95.5 1 35 3 25 37 OMSandy Run 57 34 Low Med-High DCSchneider Branch 277 72 62 1088 15 54 2 29 NMSouth Lakes HS 189 45 65 1158 45 18 1 35 NMTripps Run 243 45 51 29 276 50 12 19 19 OMWakefield Run 210 68 47 1084 70 6 18 6 NMWolf Trap 43 6 30 441 25 31 30 14 OM



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

Tree

s/Sh

rubs

Her

bace

ous C

over



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

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