by James Sottilo
Here’s looking at you, Sustainability.
Today more than ever sustainability is used in our line of work; designing and managing green spaces that reflect the value of the word. It only makes sense that nature remain, as she always has, sustainable.
Over the past several years our team has worked on projects across the United States. These national experiences have exposed us to a variety of natural soils and fauna such as the gumbo clays and wildflower meadows of Southeast Texas, the high silt soils along the Mississippi River, the clay loams of the West Coast and the forests of the Northeast.
Nature by herself always seems to have the answers to the questions we are asking when designing and building new landscapes. It is our job to dissect the ecological behaviors of the landscape, explain them and apply them in our work.
There are times when we believe we have unlocked certain secrets of the Earth and developed efforts unparalleled, but eventually science and/or technology deem these efforts linear or one dimensional when compared to her.
Our efforts are stretching beyond the industrial landscape plane and asking the critical questions to scientists and academics that are not part of the main stream landscape franchise. Foresters for example have a different perspective on certain ecologies, scientists in the management of human microbiology have in-depth knowledge on bacteria and how they grow and respond. Agronomists, who manage thousands of acres of farm land, may look at soil completely different then you and I – yet all of these individuals have insight into the same problems our industry faces such as soil compaction, pH, lack of nutrients, etc.
Soils are the foundation of the landscape and plants are the engineers of the ecosystem. One cannot survive without the other. Questions that we are often faced with include, where does the plant end and the soil begin? Is it realistic to have a specification on soil and second specification on planting? Should both be combined into one specification as a system?
As of now we are still figuring out the answers to those questions but perhaps as we adapt changing paradigms, our soils and plants will shift into performance specifications and eliminate the constant finger pointing when a problem arises with the health of the landscape.
Science and Experience
Nearly 400 million years ago during the Devonian Period, plants and fungi came together to form a symbiosis. Fungi colonize the roots of a plant – the plant then serves as its source of carbon (food) made from photosynthesis, and in return the fungi search out mineral matter for plant nutrients and water. These fungi would also leave behind soil “glues” (Glomalin), substances that help bind sand, silt and clay together to create soil structure and increase carbon sources. Glomalin sequesters atmospheric carbon delivered through the plant generating soil microbial processes that help soil productivity. Glomalin can comprise up to 40 percent of the total carbon found in soil. These cycles also allow for the exchange of gasses and the movement of water – a desired environment for plants to thrive.
This symbiotic relationship between plant, root and fungi is called mycorrhizae and scientists have been studying this dynamic for only a fraction of its existence. Fungi, along with nitrogen fixing bacteria in the soil, have been the main drivers of natural plant growth and health since their arrival on Earth.
In our landscapes we deal with primarily two types of mycorrhiza fungi: 1. arbuscular mycorrhizae (AM) and 2. ectomycorrhizae, depending upon whether or not the hyphae penetrate the root cells. These are formed by two very different types of fungi with very distinct biology. Arbuscular mycorrhizae are found in many crops, ornamentals and trees, i.e. elms. Ectomycorrhizae occur in many trees such as oaks, poplars, willows, pines, spruce, firs and many others. The mycorrhizal fungi are vital for the mineral nutrition of plants, especially phosphorus. Most world plants depend on this beneficial association to complete their life cycles.
1. Arbuscular Mycorrhizae
AM mycorrhiza produce tree-like structures and colonize inside its host’s roots. Fungal hyphae then travel outside the roots to absorb minerals and draw them back to the plant as needed. At the end of the fungal cycle, spores are produced. Spores left in the soil can then be sourced by a new plant root or the ambient fauna to continue the cycle (natural succession).
*Note – AM mycorrhizal fungi spores can range in size from 50-150 um. When looking at most designed soils, many of which tend to be high in sand, most individuals focus on the #60 sieve which is 250 um. I think you can see where I am going with this…
* Riddle – What do you get if 75% of your soil, soil that has little to no structure due to soil blending, is held in a screen that is 250 um and is doused by water from the expensive irrigation system?
* Answer – A very common problem – the leaching of spores smaller than 250 um.
Spores are leached out of that critical 1-6-inch soil layer where roots are growing – roots needed for spore production and the formation of mycorrhizae and sustainability.
Bacteria have a polysaccharide coating around them, so they can survive a bit longer attached to soil particles but eventually will also succumb to leaching stress as well.
We demonstrate this on a 70-year-old golf course that has recently been closed and slated for a new garden landscape. The fairways and roughs are black gumbo clay; years of intense golf course management have destroyed the structure of the soil. Using a soil probe, a solid 20-inch tightly bound clay core was extracted. The same soil found amongst the mature live Oak trees along the fairways had beautiful structure with friable (crumbly) soil aggregates (peds) and a mixture of small and large pores, with deep roots.
At the end of the fairways, high sand greens can be found growing. Interestingly, the fairways and roughs were green – although transitioning from turf grass to weeds – but the high sand greens were completely dormant.
Samples collected and assessed by mycologist, Dr. Efren Cazares indicated that the clay soils averaged 208 AM fungal spores per gram of soil while the sand-based greens averaged 32 spores per gram.
Because of the small size of clay particles, one can hypothesize that the spores accumulated for years while the sand-based soils experienced heavy leaching.
This situation is clearly not a sustainable soil environment and growing system.
Today, data collection and plant response are guiding our soil and plant health design process. This requires extensive ecological assessment and follow up research as well as careful observation and understanding of basic natural behaviors. In the situation described above, there are two roads that one may take in regard to soil – soils can produce green, growing landscapes but require a variety of inputs – large amounts of water and constant applications of biological amendment and often fertilizer, resulting in high energy costs with traditional development.
The second option is to create a native soil profile for the landscape that offers resilient structure. These soils will most likely have more clay (less than 2 um in size) and a stable humus.
2. Ectomycorrhizal Fungi
Ecto-mycorrhizal fungi grow on older succession trees such as oak, beech and spruce species. This type of fungi colonizes the outside of the root with hyphae that travel large distances to find water and nutrients for their host. Oak trees are found growing in savannas as they can handle drier conditions, yet when found in project site or residential landscapes, Oaks often end up being treating for Phytophthora once irrigation systems are turned on.
Ecto-mycorrhizal fungi produce spores on their reproductive structures of many mushrooms. Each mushroom cap can hold millions of spores waiting to be released either by natural forces such as wind or animal consumption and excretion. With climate change and weather shifting patterns, areas not receiving enough rainfall will lack mushroom diversity as moisture is critical. But Mother Nature is smart: she created truffles. Truffles are underground, enclosed fungal fruit-bodies that are filled with spores. Since the spores cannot be transported by wind, they are dependent on animals eating them and dispersing the spores elsewhere.
A new look at dealing with soil compaction …
We were recently presented with a scope of work at a garden that involved using an air spade to make radial trenching throughout 29 mature Gingko trees to help with general health conditions.
Six trees were isolated for sampling; roots were collected for AM colonization and spores. Composite samples of fiber roots were collected from the North, South, East and West side of the trees as well as 500 grams of rhizosphere soil.
Samples were taken along identified radial trenches prior to excavation and immediately following excavation and sent to mycologist, Dr. Efren Cazares for analysis.
Drumroll please – data indicated that all six trees showed a decline in mycorrhizal colonization. In fact, 4 of the 6 trees returned a 60 percent (plus) loss with 5 of the 6 trees indicating a 50 percent loss. Additionally, the spore counts in the soil went from a combined average of 117 per a gram to a combined average of 24 spores to a gram.
Rewind back to our industry’s initial excitement to air spading these trees, when we still thought the efforts would be breaking up compaction, allowing oxygen into the soil and even mixing some fresh compost into the root zone. Data now reported negative impacts on the microbial community, but why?
The fungal filaments of mycorrhizal fungi that are found in soil are microscopic; while they are resilient underground gathering nutrients and water for plants, they cannot withstand the effects of a pneumatic air tool.
In an effort to restore this decrease, the surrounding soil was inoculated with independently tested and viable VAM spores. Follow up testing will be completed at 3 months and 6 months post service to assess the validity of the treatments.
When performed correctly, air tools avoid damaging secondary roots, and the fibrous roots. There are instances where using a pneumatic air tool is the best method such as root collar inspections, trenching throughout a root zone for placement of infrastructure or when root pruning is required. But there is always more to the situation and now it is time to look further and understand that efforts such as air spading and trenching can cause chaos for microscopic ecology and to the plant’s symbiotic relationships. Not only will air spading disrupt fungal hyphae and spore distributions, but like tilling a soil, it often destroys soil structure and causes soil to become denser, reducing pore size and the ability of roots to grow.
While damage to fungi might not have immediate impacts, if large amounts of compounded fungi are dislodged from roots and destroyed, plants will need to dip into their carbon reserves to rebuild. During optimal plant mineralization times of the year, this could have negative impacts on nutrient uptake. With this information, we have seen changes in the dynamics of soil structure and permeability by using plants to solve issues rather than mechanical interference.
Different efforts that can be employed such as cover cropping not only break up compaction, but also creates soil structure and leaves behind the organic residues of the crop, adding to soil health.
Currently the USDA is encouraging farmers to implement cover crop program in association with no-till programs; some states are even offering subsidies to farmers who take this step. The goal is to retain carbon in the soil, stop soil erosion and reduce the loss of nutrients into water.
Food for thought…
The message is that there is still so much we do not know about the connections of the landscape. Nature herself is always in flux and finding new ways to forge sustainability. It is our job as industry professionals, community members and stakeholders of the Earth to keep exploring nature. We should always insist on looking deeper at what is and what will be our environment.
… and if you ever may feel like your visions are muddled, return to nature – she will help guide you.
by James Sottilo, Lead Consultant and Founder, Ecological Landscape Management; Dr. Efren Cazares, Mycologist; Ted Hartsig, Soil Scientist
Ecological Landscape Management
Ted Hartsig, CPSS
Dr. Efren Cazares