TECTONIC SAFARI

The project area is a 112 acre linear stretch of land 2 1/2 miles south of the United States Capitol building. 

Part of the land in the project area is within a interstitial wildlife corridor surrounded by dense urbanization.

The site was heavily forested through the early 1900's. Overtime the land was fragmented by urban development.

Today few patches of forested areas are left around the project area
What's left of the natural landscape is largely protected by the National Park Service.

At this link you can access the research paper published in the 2017 International Conference on Ecology & Transportation conference proceedings.

Like many cities, DC's regulatory agencies realize the value of natural land and are beginning to develop policies to better preserve and shore up whats left of these resources.

Currently DC doesn't have many policies or guidelines in place to support pollinators or create sustainable natural habitats. This project was and exploration into what could be required to do so.
 

Over the past 150 years the site has transitioned from a large hardwood forest; then was partially occupied by tenement farmlands; in the mid 17th century the site was host to a Civil War defense network with two forts in or directly adjacent to the project area; and most recently the land around the site was developed into Federal and private lands.

Today the project area sits between a military base on the west and Shepherd Parkway, a 205 acre mixed forest managed by NPS on the south and east. The northern boundary of the site meets the St. Elizabeths West campus.

In the early  2000's the US Congress passed legislation to build the new DHS campus on the grounds of the historic St. Elizabeths campus.

It was determined that the projected traffic demands would be a major burden on the existing highways and local roads.

The Access Road project developed from the need to alleviate future traffic demands on the existing highway infrastructure.

The 364 acre DHS campus recently began construction and completed its first major building, the USCG facility, in 2013.

The images at the top of the screen show the West campus master plan. most of the master plan landscape was design by Anropogon LAB also has a few landscape project on campus.

The Access Road will be built to serve the subsequent phases of campus development.

The new roadway spur will connect to the south-western most point of the West Campus, bridging the new local roads with the existing highway.

The images on the bottom of the screen show the point of connection at the campus and images of the adjacent Access Road project area.

This is a view looking south towards the point of connection between the future access road and the existing city infrastructure.

In the background you can see Shepherd Parkway abutting the southern edge of the West Campus.

On the left of the image is the edge of the U.S. Coast Guard Headquarters

We entered the conference under the banner of collaboration, so before we get into the design process I think its important briefly mention the complexity of the collaborative process in this job.

Our client was the GSA, although we were required to coordinate with and receive approval from many governing agencies because the project overlapped several jurisdictions.

Both the roadway alignments and the landscape went through several rounds of reviews from these consulting parties and municipal agencies before final approval.

At this point in the job the concerns were mainly about how much of the  national park services land was required to build the roads; what the extends of the environmental impact were and how much revegetation was necessary.

After satisfying the Local and Federal requirements our team at LAB brought on The Xerces Society to aid in the development of a plant lists that worked to support pollinators across the varying conditions of the site.

The project has several layers of infrastructure and vegetation that are intertwined across the mile and a half project area. At is foundation are the roadway alignments.

The stormwater infrastructure consisted of LID facilities, bioswales and dry detention basins. these facilities were integrated in the design to accept runoff.

Planting zones were developed inbetween the new and existing infrastructure as part of the revegetation efforts and the canopy was reincorporated to the maximum extent practicable. This helped to stitch the site back into Shepherd Parkway.

A shared-use path was designed under the canopy to allow pedestrians to travel across the site.

The section below shows the typical relationships between the infrastructure and open spaces.

In this deep section cut we can see the typical relationships between the edge of the NPS parcel, the stormwater facility and the open space between the infrastructure.

The retaining walls the separate the NPS land from the Districts land vary almost equally between cut and fill along this edge. The walls undulate up and down between +25' and -30' sometimes opening up vast views under the canopy into the forested parkway.

As we approached the planting design, we decided to base our selections on three key criteria: local ecology, conditions on-site, and spatial structure, tying into the surrounding context.

Because of our goal of developing a sustainable site that supports pollinators we decided to orient the planting palette towards natives.

When we began developing the planting palette for the project we started by looking towards the larger physiogeographic region.

Our research found that Washington, D.C. and the project site are at the intersection on the Piedmont and the Coastal Pain. This has a significant impact on the planting.

With Xerces Society, LAB developed a database of plant communities within 40 miles of DC using research from the Virginia Department of Recreation.

The list on the left of the screen shows the communities in the database which were adapted for the project.

After creating the database we began to look more closely at the site conditions to determine how to organize the site.

The topography of the larger project area goes from steep and hilly to relatively low and flat from east to west. The red section markers show the new augmented topography over the existing grey topo in the diagrams on the right.

The Access Road and Shared-Use path are at the intersection of the floodplain and plateau. This analysis revealed us the challenge of bridging the natural landscape from the manufactured landscape.

At this point we also began to think of how can we make the canopy and understory plantings in the project be productive for pollinators while also relating to the vehicular and pedestrian scales.

After developing a better spatial understanding of the site we began looking at the projects conditional criteria.

To analyze the ecological and conditional conditions, we made a 3D model of the site, and ran various scripts to analyze the sun-shade conditions in the top image, and the hydrologic flows in the second image. Blue is wet, yellow is dry. These two diagrams revealed a number of micro climates across the site that became the basis for future planting zones. We also looked at soil. The sections at the bottom show the varying conditions of cut and fill along the shared-use path. In the bio-retention areas here and across the site, we have a very well-draining sand-based soil, while the native site soils are clay based and slow draining. Additionally, we had to consider in each planting area, their proximity to roads, which determines their exposure to salt and pollution. Finally, in the clover leaf interchange area and linear medians, we knew maintenance would be conducted by mowing, dictating that we use a seeding method for planting, while in the linear LID bioretention facility adjacent to the shared-use path, maintenance would be by hand, and we therefore could plant potted plants from nursery stock. So, with all of these conditions in mind, we were able to define different zones on-site as 'wet, sunny, ponding and depressed', or 'dry, part-shade, well drained, and elevated' for example. 

Here we have our third criteria: Spatial Structure. This is where we get to wear our landscape architect hats. Instead of defining space with walls and ceilings, we like to do it with hedges and canopies. Because the site is so divided by all of the roads, we wanted to use the interstitial spaces to visually form connections across the landscape. This led us to create a kind of gradient. In the north-south gradient along the shared use path, in the top image, the structural criteria moves from an open condition in the neighborhood (think lawn and street trees) to the forested character of Shepherd Parkway. Everywhere we connect back to the neighborhood, we want to relate to its structural character. In the east-west continuum, we are moving from the open nature of the Potomac River floodplain, which is also very developed in this case, to again, Shepherd Parkway, which is a forested portion of the riparian uplands. Working from these gradients, we developed four structural criteria, which have ecological implications. 'Open' is grass and perennial landscape with no trees, such as a meadow or a marsh. 'Edge' is a wooded savanna type environment, grass dominated with some trees. 'Transition' is a scrubland or a heath, shrub dominated with trees, and 'Enclosed' is a completely forested environment with overstory, understory, and groundplane layers. 

In order to create our on-site planting zones, we overlaid the conditional and structural criteria. Don't worry about the letters and numbers now - as you can see there are a lot of zones - we ended up with 19 different zones, some repeat. We knew we needed to respect the conditional micro-climates across the site, and at the same time, we wanted to encourage a specific spatial character. On top of that, we drew from our ecological criteria - the database we had created based on research - to match an appropriate local ecological type with each zone. This was really a practical kind of reverse engineering. Rather than forcing a native ecological type that historically should be on this site, we instead looked at the proposed, future, conditions, which are quite alien, and then looked at a pallet of natural communities to pick the one that's best suited and may have the best chance of survival. 

We'll go into the details of each zone in a moment. But here's a preview of what happened. The result of our methodology was a very rich and diverse plant palette. The list on the left is for the nursery stock alone. It's an even longer list with the seed mixes. The diagram on the right shows seasonal interest month by month. One key thing for us to consider was consistent bloom time. Pollinators need pollen and nectar resources from early spring to late fall, and it's important not to have any gaps, or your local population could die. 

In the interchanges dry detention basins and highway median plantings, are where seeding and mowing are to occur, which of course dictated our seed mixes in combination with trees.

This is an enlarged potion of the plan in the interchange area, and a section cut through this piece of the site. What this shows is the spatial relationships between the Open, edge, and enclosed zones - what we are calling the ecotone. 

So this chart and diagram show all of the seed mix zones in the interchange and highway medians. The A types are dryer conditions, and the C types are wetter. Each zone has a defined set of structural, conditional, and ecological criteria. For example, A1 is open, dry and sunny, and has been matched with Piedmont Prairies.

These diagrams show the textural aspects of the plantings in each zone, along with their seasonal colors, and where they are located on-site. The idea in these zones was to paint the site in large swaths of color and texture, to be experience by vehicle. Because they are seed mixes being maintained by mowing, the intention is that over time they may mix and mingle. These are also the zones that are packing the biggest punch in terms of area for pollinator resources and habitat creation.

So, how did we choose the plants? Kelly Gill from The Xerces Society was really indispensable in helping us to refine these lists. We would develop initial lists based on our criteria and send them over to her for comments, and she would advise based on availability, maintenance issues, establishment, and proportion of grasses to perennials.

Here we are looking at the A1 zone in detail. This is based on the Piedmont Prairie, and as such, Little Bluestem is the dominant grass. However, 55% of the mix is a diverse group of perennials. You can see the overlapping bloomtimes in the table on the right. Additional features Kelly was helping us to select for include high quality nectar and pollen, nesting opportunities, larval host plants, and vegetative structure for refuge and overwintering. She also helped us to select annuals and short lived perennials to provide ground cover while the slower growing and longer lived perennials grow in. In this case it was partridge pea.

These are the zones we developed for the 4' wide LID bioretention planter that flanks the shared-use path. These are the areas planted with nursery stock, rather than a seeding application, and they are to be maintained by hand seasonally.

The table and diagram below outline each of the zones along the shared use path. Again, they each have a set of structural, conditional, and ecological criteria.

Unlike the interchange and median areas, we did not wat these plantings to shift and move over time. So, instead of 10-15 species in a seed mix, we were aiming for 5-8 recognizable species in a group that could be maintained as such over time. We wanted these distinct zones to call attention to themselves, particularly at the transition between zones. Here we are showing two of our enclosed zones where they meet, and even though the structural criteria is similar, the textures are strikingly different. 

Similarly, here we have an edge and a transition zone meeting. Again, the textures and feel should change and be noticeable to the passersby. 

Now we'll look at each zone individually. This is the only fully open zone along the shared-use path. It was necessitated because the tie-backs did not leave enough room for the soil volume needed for trees. This zone is based on Rocky Bars & Shores.

This is an edge zone, so grass dominated with trees. It's based on Oak-Hickory Woods and Savannas.

This is a transition zone that's very distinct because of the evergreen pine canopy, and in fact it's ecologically based on pine/scrub oak sandhills, a very dry condition.

This is very distinct from the last zone, though it is also a transition, with a shrub-dominated groundplane. The plantings are based on piedmont/mountain swamp forest. This is a much wetter condition.

This is another wet transition zone, based again on rocky bars and shores, but this time with a canopy of river birch. We're excited about these types in the LID zone because we feel their well-draining soil is really mimicked by the DDOT standard soil spec we are using here.

This acid oak-hickory forest zone is an enclosed structural typology. It shows how we had to make some substitutions. White Oak and Dogwood would be the classic combination here. We substituted Swamp White Oak because it's a smaller species, and perhaps better adapted to the LID condition. 

In this Oak-Heath Forest zone, we included two types of monarda to extend the bloom time.

This coastal plain/piedmont bottomland forest zone will be an interesting one to watch, because it's based very strictly on the VA DCR species. As you can see it also has a very distinct red and white color palette. As landscape architects, we of course want to emphasize this, but what's really interesting here is that the palette is coming from the ecological type itself. 

The planting selections for this zone were drawn from a plant survey of Shepherd Parkway. Though not one of VA DCR's scientifically defined natural plant communities, we felt it was important to connect with and reference the neighboring species.

This is an enclosed zone based on oak-hickory woods. 

Here we have 12 of our 19 zones displayed, drawn from 11 of our 16 natural plant communities. Our hope is that these plant lists can be published and used in the Mid-Atlantic area, and that our methodology can be shared with other landscape architects. We see the project as a testing ground to see how these lists perform, so that they can be further refined. What we've delivered to the client includes planting plans, planting schedules, maintenance guidelines, planting calendars, seeding methods, and establishment methods. When built, the Access Road will be the largest LID facility in DC and the first large-scale constructed meadow. We would love to see the site used for education and further research into pollinator habitat and natural plant communities.

The Flora of the District of Columbia project was created to serve as a comprehensive visual guide on the native and naturalized vegetation of the greater Washington area. The matrix developed for this project provides a tool for plant identification and curation by landscape architects, planers, urban designers, horticulturists and avocational users.

The matrix include data on in leaf duration, flowering times, fruiting times, winter interest, planting times, habitat, inundation tolerances, light requirements and soil conditions.

The metrics show which specific region each of the flora and fauna can be found in nature and what the ideal landscape usage is. The chart also shows the height, spread and growth rate of each species.

Ten years of Washington, DC weather data was averaged out to show the typical temperature, inundation, wind and barometric pressure. This was included to show the correlation between the annual weather conditions and the leaf durations of each species.

The typical in leaf periods, bloom times and colors were plotted out across the psychometric calendar.

The winter interest for each plant can be seen on the chart in the fall color and duration of leaf and stems.

The fruit color and duration is illustrated to show which species have wildlife value for birds. 

Over 100 years of bird monitoring data was collected from the Auduban Society to plot the most optimal times to see the birds of DC in the wild.

This chart measures the frequency that each bird species is typically spotted in Washington, DC. The relative occurrence and seasonal timing was plotted across the calendar.