Houston Arboretum and Nature Center, Phase 1
Landscape Performance Benefits
- Reduces average annual runoff within 1 mile of the site by an estimated 7% (580 acre-ft) as compared to a scenario where the site was instead developed in a similar way to the surrounding area.
- Reduces chemical pollutants by an estimated 13% (498,104 lbs), bacterial pollutants by 16% (553,728 million coliforms), and overall pollutant load by 14% as compared to a scenario where the site was instead developed in a similar way to the surrounding area.
- Reduces overall metal-based pollutant load from parking lot runoff by 16% as compared to pollutant reductions achieved by more conventional green infrastructure at a comparable parking lot.
- Supports essential flood management for the City of Houston. If the site had been developed instead of being maintained as a green space, during the 2015 Memorial Day flood an additional 83,963 cu meters of water (approximately 34 Olympic-size swimming pools) would have run off into the Buffalo Bayou. Peak flow reduction within the HANC for the Memorial Day flood was 67%, and peak flow reduction for the 2016 Tax Day flood was 75%.
- Provides habitat for at least 133 observed bird species. Of 9 bird species with more than 5 individuals observed, 67% show an increasing trend in number of individuals after the HANC renovation (from 2019 to 2021).
- Provides habitat for at least 9 observed amphibian species. Of 6 amphibian species with more than 5 individuals observed, 50% show an increasing trend in number of individuals after the HANC renovation (from 2019 to 2021).
- Provides habitat for at least 9 observed mammal species. Of 6 mammal species with more than 5 individuals observed, 50% show an increasing trend in number of individuals after the HANC renovation (from 2019 to 2021). Species of Greatest Conservation Need observed on-site include the hoary bat, Eastern red bat, Northern yellow bat, and swamp rabbit.
- Provides habitat for at least 465 observed insect species. Of 90 insect species with more than 5 individuals observed, 40% show an increasing trend (59% of which are pollinators) in number of individuals observed after the HANC renovation (from 2019 to 2021).
- Increases plant species richness in the prairie with at least 22 newly planted species, achieving a Shannon Index value of 2.79, which is 34% higher (1.83 to 2.79) and a Reciprocal Simpson Index value that is 263% higher (5.64 to 29.49) than if the site had been replanted with individual trees and lawn.
- Contributes to a reduction in urban heat island effect by decreasing air temperatures in vegetated areas by 0.54 °C (0.94 °F) on average, reducing wet bulb globe temperature by up to 1.5 °C (12.7 °F), and increasing relative humidity by up to 4.9% as compared to hard surfaces nearby.
- Reused salvaged materials including wood for parking stops, field stations, and mulch as well as 50,000 plant plugs collected from the field, saving an estimated $240,500 in new materials.
- Supports increased visitorship, with over 1.6 million visitors from January 2019 to March 2022. Compared to 2016, which was the year before restoration, visitors increased by 151% in the first year after renovation completion (2019), 271% in the second year after renovation completion (2020), and 222% in the third year after renovation completion (2021).
- Reduces anxiety as reported by 137 visitors while moving through the site. Over 40% of visitors reported feeling very calm, relaxed, and content and more than 65% reported not being tense, upset, or worried at all. Overall anxiety was significantly negatively correlated with perceived naturalness of the scenery/zone.
- Offers restorative experiences according to 365 surveyed visitors who agreed that the HANC provides a sense of being away (92%), fascination (87%), coherence--having orderly scenes and activities (61%), scope--serving as a world of its own (85%), and compatibility--ease of moving around (83%).
- Provides desirable nature experiences, with 365 surveyed visitors identifying nature (17%), trails (13%), and plants and vegetation (11%) as their favorite aspects of the HANC.
- Increased average property value within 1 mile by 42% during the beginning period of the HANC renovation (2010-2015), which is 24% higher than average property value for the period before the renovation (2005-2010). Property values increased by 13% and 14% from 2015-2020 and 2020-2022, respectively.
- Generates an estimated $27,200 annually in additional parking revenue, driven by goat management and burning and their appeal to visitors, even after covering the costs of these approaches.
- Generates parking revenue, with a 151% increase in revenue in the first year after renovation (2019), 271% in the second year after renovation (2020), and 222% in the third year after renovation (2021), as compared to pre-renovation parking revenue from 2016.
- Contributes to a 43% average increase in median property tax revenue for owner-occupied homes in the surrounding census tracts before and after the construction of the HANC, while median property tax revenue for Harris County as a whole increased by only 7% over the same period.
At a Glance
Design Workshop; Reed Hilderbrand
Former Land Use
4501 Woodway Drive
Houston, Texas 77024
65 acres (Phase 1 implementation within 155-acre master plan)
Phase 1 completed 2018; ravine opened May 2019
The Houston Arboretum and Nature Center (HANC) is located six miles from downtown Houston, Texas. Natural disasters previously caused substantial tree canopy die-off in the HANC. Instead of reforesting the arboretum to its previous state, endemic grasslands were restored to reflect ecosystems native to the Houston area. The 65-acre first phase of the project restored the site’s ravine landscape and created 20 acres of prairie and savanna ecosystems with native plant species to educate visitors on the natural Gulf Coast environment. To increase site resiliency to future natural disasters, the HANC has two wetlands to manage stormwater, and the site’s former riparian ecology (historically ravaged by floods) was restored. The new trail system, which is set at a high elevation, avoids seasonal flooding, facilitates the flow of water, and gives visitors the opportunity to re-engage with the ravine landscape.
- Shift to a more sustainable savanna ecosystem that is more characteristic of coastal prairie landscapes instead of replanting/reforesting the arboretum in order to prevent tree mortality and the need to repeatedly replace trees.
- Sequester carbon through roots of herbaceous species within the prairie and savanna.
- Retain and absorb stormwater within HANC’s landscape instead of allowing it to run off into Buffalo Bayou to prevent flooding.
- Create and improve diverse habitats for pollinators, birds, mammals, and insects.
- Save on irrigation costs by drawing from stormwater retention ponds and using native plants.
- Control invasive species by utilizing goats and controlled burns to save on long-term environmental management costs.
- Provide environmental education for people of all ages and serve the 10,000 elementary school students who visit the grounds annually to participate in education programs about science and conservation.
- Support an increased number of mission-based educational programs focused on the site’s new resilience to droughts and floods as well as the provision of ecosystem services.
- Increase the number of annual volunteers who help with restoration efforts.
- Improve equitable access to green space around the site.
- Promote active and passive recreation.
- The arboretum features 25 acres of prairie and savanna ecosystems with an average of 21.6 plant species per square meter that reflect the native ecosystems of the Houston area. These native plants are also able to withstand natural disasters such as drought, flooding, and freezing. Visitors can pass through the savanna ecosystems and reach out to touch the plants as they walk on narrow crushed decomposed granite paths.
- Newly planted native savanna and prairie species include sunflowers, liatris, bluestem grasses, coreopsis, gaillardia, and basket-flower. Plants on site support wildlife, with 52% of species providing fruit and seed sources, 29% serving as nectar sources, 58% providing larval host habitat, 9% supporting biological control, and 15% providing native bee nesting material or structure.
- 7 acres of woodland were restored through the removal of woody invasive species (including early successional trees) to expose the native herbaceous understory layer as well as the integration of new tree species.
- 8 acres of the ravine (which accommodates a tributary to Buffalo Bayou) were restored and stabilized to withstand flood events and reduce erosion. Target species such as graminoids and dwarf palmetto were increased in number, and jute netting was used to better establish plant communities and control erosion.
- The new trail system, including an expanded boardwalk of fiberglass decking and 2 large bridges, gives visitors the opportunity to re-engage with the ravine landscape. 2 bridges were replaced at significantly higher elevations at 2 ravine crossing locations to handle flow velocity and reduce flooding and channel erosion. All materials were selected and engineered to withstand heavy floods.
- 18,548 linear ft of trails give visitors access to areas of the site that were not accessible before the renovation, including the lowest areas of the ravine. This is an increase from the previously existing 7,857 linear ft of trails, but it also represents a reduction in the overall area of trails from 71,417 to 61,042 sf, the result of adjusting the width of the trails to more appropriate sizes for various areas and uses. Trail widths vary from 3 ft wide to the 20-ft-wide display walk which doubles as a fire lane. However, most trails are in the 4- to 6-ft range. Trails in the savanna prairie and around the parking loop are 3 ft wide to allow visitors to directly experience the landscape.
- 2.54-acre and 1.19-acre detention ponds were added as part of a new parking loop and arrival experience. These wetland ponds serve many functions, including the detention and reuse of stormwater for irrigation as well as providing habitat for insects, amphibians, and birds. A plug mix was used in wetland ponds because a seed mix would not have established with water constantly flushing through the system. Coir matting on the slopes holds plugs in place.
- Salvaged materials make up 5.11% of total materials used in order to reduce the need to manufacture and ship new products to the site.
- Invasive plants in the 11.75-acre planted area are controlled by “goat grazing” and controlled burns.
Converting areas of trees damaged by natural disasters to prairie/savanna ecosystems through seeding will save an estimated $2,832,000 in potential replacement costs and water savings over the next 15 years as compared to the original strategy of replanting the HANC with individual trees and lawn. The projected 15-year cost savings on plant materials and installation labor is $934,00 and cost savings on water is $1.9 million when comparing the prairie/savanna seeding and plugs to the original strategy of trees and lawn.
- During the design process (prior to construction), the site experienced floods during the Memorial Day Flood of 2015 and Hurricane Harvey in 2017, which damaged many existing bridges and washed out several of the trails. The design team quickly realized that the light structures with cable rail details that were originally proposed for ravine bridges and boardwalks would not be resilient against the torrents of water produced by regular flooding. The design team engaged a geofluvial morphologist to design a more stable watercourse and reorient and elevate the bridges at two ravine crossing locations. Boardwalks were redesigned with weathering steel and marine-grade fiberglass decking.
- Starting in 2015, the design team used test plots for the savanna seeding to understand the conditions needed for the plants to thrive and inform the development of specifications during design and documentation. This early pilot indicated that a large volume of new soil was not necessary, and that the existing soils with 1 in of amended compost were adequate. This saved a significant amount of money across the site and reduced the amount of imported materials required.
- The design team observed that seeding in the ravine—no matter how steep or gentle the slope—was ineffective without erosion control measures to keep seeds from washing away with strong rains. Jute mesh was used to stabilize the banks and plantings, and seeding was supplemented with plugs which grew more quickly and helped hold the slopes.
- The contractors did not clear the tanks that held the native seed mix before seeding. Due to this, the seed that was initially broadcast on the site was contaminated with turf grass seed. Invasive turf grasses took hold, requiring scraping and reseeding. This highlights the importance of requiring full cleanup before seeding to reduce the potential for invasive species to enter a site.
Ravine Bridges: Pioneer Bridges - Trailblazer
Decking: Aqua Grate fiberglass pedestrian grating by Fibergrate
Bike Racks: City of Houston donation
Trash and Recycling Receptacles: Home Depot
Compost Bins: Custom built
Light Poles: Structura
Light Fixtures, Uplights, and Light Bollards: Bega
Metal: Weathering Steel
Bridge Wood: Theory
Fence: McNichols quality square weave wire mesh
Cable: Keystone Steel and Wire Co.
Fence Hardware: Stay-Tuff Fence MFG Inc.
Filter Fabric: Ten Cate Nicolon
Landscape Architects: Design Workshop, Inc. and Reed Hilderbrand Landscape Architects
Other Consultant: Lady Bird Johnson Wildflower Center, Department of Ecological Research & Design
Civil and Structural Engineering: Walter P Moore
Operations and Maintenance: ETM Associates, LLC
Forestry Management: Dr. W. Todd Watson, PhD, BCMA
Historical Research: SWCA Environmental Consultants
Architecture Design Architect (new administrative building): Lake | Flato
Civil Engineering: Frayre Engineering & Consulting, PLLC
Ravine Restoration and Fluvial Geomorphologist: HydroGeo Designs LLC
Irrigation and Soils Engineering: Jeffrey L. Bruce & Company, LLC
Electrical Engineer: E&C Engineers & Consultants Inc.
Architect of Record (maintenance facility and existing administrative building): Kendall/Heaton Associates, Inc.
Design Architect (renovation of existing administrative building): Leslie Elkins
Role of the Landscape Architect
The landscape architects, working in collaboration, administered comprehensive landscape architecture services for planning, design, and construction, collaborating closely with an extensive consultant team and leading coordination with the client and multiple agencies. Site design, grading, and planting design; paving and layout; and materials were completed and detailed by the landscape architects.