by James Sottilo, Ecologist/Arborist; Dr. Efren Cazares, Mycologist; Ted Hartsig, Soil Scientist
Introduction
Our team began the day reviewing the landscape of Expedia’s anticipated waterfront campus with Michal Kapitulnik, Tim Kirby and Heath House of Surfacedesign, Inc. Our mission – find the potential of current site soil for repurposing. Reusing native soil profiles in future blends can have a tremendous impact on future plant acclimation and site maturity. The campus presented a contrasting ecology. Certain areas of vegetation were lush and dense while other areas displayed brown, drying turf; it was clear to the team where our attention would be needed – right?
Exploring the vibrant sections of vegetation, soil was dark, rich and moist to a depth of 14-inches. Its observable characteristics were rated as productive and ideas for soil reuse and logistics were already being explored.
Taking a few steps into neighboring areas, the look of the landscape began to change. A particular section of grassland was going dormant due to irrigation having been turned off as the site was pending demo and construction. Rooting in this area was measured at 4-inches and the soil profile was a fine sand and clay mix. Another section of land, deemed the Rectangle of Death, had dying to dead grass cover; the soil was a sandy gavel mix with obvious signs of compaction.
The three landscape sections were identified and recorded. The team took their time collecting soil profiles as well as root samples for a health analysis. Now, we wait.
. . .
As results came back, the team began piecing together the data to finalize an approach – except the picture that was forming was not at all what we thought the landscape had advertised.
The dense, vegetative areas of the landscape were indeed thriving with a high microbial biomass of 541 ug/G. The grassland area nearing dormancy returned a 381 ug/G. And rounding out the group – the Rectangle of Death, with its sparse grasses and declining health, delivered a 265 ug/G microbial biomass. Microbial results were as expected as dormant to dying plants do not release large amounts of exudates to feed the microbial biomass such as healthy plants do.
Now, here is where it gets really interesting. Results regarding the measurement of VAM mycorrhizal spores per gram of soil were shocking. About 95% of vascular plant species in the world belong to families that typically form mycorrhizae with specialized mycorrhizal fungi. These fungi are essential components of ecosystem dynamics and involved in many biological interrelationships. Vegetative areas measured 16 spores per gram of soil – Good. The grassland returned 67 spores per gram – Excellent, and the Rectangle of Death tested at 132 spores per gram of soil – Really Excellent. These data points had now completely altered our anticipated plan and changed our train of thought. How could a dying ecology return such high measurements?
The Science
Microbial biomass (MB) is a great indicator of plant health, especially when recorded on a systematized schedule. In our experience, MB readings can change dramatically in just days as soil microbiology flows with the natural cycles of the earth. It is so important to understand photosynthesis; the process creates the carbohydrates, sugars and proteins living organisms need to develop and grow. Plants use 20-70 percent of these food sources to fuel leaf expansion, twig growth, root growth and so on. The remaining 30-80 percent of foods leak out of roots (exudates) to feed and encourage the symbionts in the soil.
These behaviors explain why the biomass readings were higher in the healthy vegetation when compared to the dormant and dying vegetation. Plant cycles are capable of driving the rhizospheric microbial biomass.
Onto the VAM spore results. In a healthy ecology, both plants and their associated mycorrhizal fungi process efficiently as carbon and minerals are appropriately available to a plant for growth and development. Stressed systems begin to process differently; more of a plant’s carbon source and general energies are used to build fungi and increase mycorrhizae so that more nutrients can be supplied back to the plant. Just as plants tend to produce more seeds when stressed, plants also trigger an increase in mycorrhizal spore production to colonize a plant as it prepares for an anticipated generational shift.
In reviewing the data once more, post initial shock, one cannot help but smile as we realize the natural efforts of nature. The earth around us is incredibly connected and concerned with the future of its health. Healthy conditions promote dynamic biomass communities to cycle nutrients back with little additional force to continue life. Stressed and/or dying plants, as seen in both the grassland and Rectangle of Death landscapes, generate the necessary behaviors and materials to help foster the next generation – seeds above ground and spores below ground.
A New Approach
It was decided to keep the lush vegetation and soil in its current state until the interior portion of the campus was completed. The grassland soil will be used as fill material to build various landforms throughout the project site.
The Rectangle of Death soil was harvested to a 10-inch depth and has been placed in small piles at the designated soil blending facility where it will be seeded with various cover crops such as Clover for nitrogen and Sorghum to aid in producing additional spores during the growing season. Once soil blending phases approach, these recycled, native profiles will be developed into organic inoculum materials and evenly dispersed into each new soil blend. The inoculum will be able to reintroduce multiple species of native spores to future landscape VAM plants, increasing plant survival and long-term sustainability.
Food for Thought – Commercial, over-the-counter mycorrhizal spores offer few species that can be commercially cultured, and the quality of these products may vary. In order to guarantee a higher rate of success, materials should be tested by an independent lab for quantity and viability prior to application.
Looking Forward
We anticipate testing the base materials, the new soil blends and the new landscape every three months for data collection and health tracking. Once the project is completed, we will remain as part of the management team to study how the system develops as the campus become active.
As resiliency and sustainability become a driving force in design, landscape Architects have a great opportunity to expand upon the current model of soil science and embrace it. In implementing practices for repurposing whole ecologies, efforts to increase native pollinators and native soil/plant biology as well as help protect, preserve and acclimate new landscapes becomes a reality. Projects become more inspired as they transform over time while keeping a multi-generational legacy.
by James Sottilo, Lead Consultant and Founder, Ecological Landscape Management; Dr. Efren Cazares, Mycologist; Ted Hartsig, Soil Scientist
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