Tag Archive for: ecological landscaping

‘Leave the Leaves’ — Yes, But Why and How?

A million.

That’s how many microorganisms can live in a soil sample that would fit in a bottlecap.

They’re nature’s decomposers: microscopic, beneficial fungi and bacteria that form the foundation of the food web. They make soils fertile, providing various food sources for plants and animals alike.

But they don’t live in soil unless they, too, have something to eat.

 

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Enter “leave the leaves.” Some homeowners employ it as a low-impact mulching method — harvesting free soil-enriching resources by doing almost nothing.

Fallen leaves can insulate roots, trigger nutrient cycling, and create shelter for a wide range of insects and invertebrates. Birds and squirrels use the litter as nesting material, and whatever’s left can help conceal seeds from them.

But Maas Verde wanted to go deeper. So we asked:

    • What effects does leaf litter cause in soils and wildlife communities?

    • How does it impact the environment on larger scales?

    • What do we lose when we remove leaf litter from the landscape?

And if we do “leave the leaves,” how can we tell that we are causing a positive effect?

Researchers are still studying the impact leaf litter makes on soils and biota at large. But we do know that this unassuming natural byproduct can build biodiversity, create soil resilience, and increase ecosystem function.

“The leaf layer protects and nourishes the soil, enables rainwater to filter into the ground, harbors seeds, and provides hiding places for woodland animals,” the American Museum of Natural History writes. “Without it, the woodlands would be unable to exist and reproduce.”

Not bad for a renewable resource that ends up in landfills at rates up to 10 million tons each year.

Natural Leaf Recycling in the Landscape

When a tree loses a leaf, it starts a recycling process.

a small plant sprouting amid leaf litter(Photo/Marc Opperman)

The first step in this process is senescence, which is the aging of leaves. As sunlight on a tree decreases, it begins to reabsorb nutrients from its photosynthesizing structures. Proper tree maintenance, including pruning and trimming, can help ensure that trees receive adequate sunlight and nutrients, promoting healthy leaf growth and senescence. The tree first pulls nitrogen and minerals back from its leaves. This triggers a hormonal response that causes the leaf to start detaching from the tree.

Fall colors start popping as the tree reabsorbs chlorophyll from its leaves. Finally, the leaf detaches, usually influenced by wind and other disturbances.

Once the leaf drifts to the soil, it joins an unsung but vital group of the food web: the decomposers. These heavy-lifting fungi and bacteria complete the food chain.

Decomposers break down organic materials like decaying plants and leaves into simple compounds like phosphorus and nitrogen, creating viable, nutrient-rich soil. Many varieties of microbes and fungi belong to this group.

 

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Along with nutrients, they also expel CO2 and water into the soil for future plant and animal generations.

They and their leaf litter habitat are existential in forests and landscapes.

“Forest litter, including fallen leaves, twigs, seeds, and other woody debris, is the link between forest and soil systems. [T]he leaf litter is the main component, accounting for more than 70% of the litter.”

Guizhou Normal University, ‘Leaf litter chemistry and its effects on soil microorganisms in different ages of Zanthoxylum planispinum var. Dintanensis,’ 2023

The nutrients they produce can act as fast-uptake food sources. Nitrogen and phosphorus are cornerstone ingredients in many fertilizers. They generally belong in the landscape in abundance.

Why Not Mulch?

Is leaf litter mulch? No, but Maas Verde recommends adding leaf litter along with wood mulch. Soil organisms need varied food sources to thrive, and leaves contain key nutritional components that wood does not.

Imagine a cyclist. The athlete needs a platform of robust, protein-rich meals for long-term strength and stamina. But during a ride, their needs are completely different — here, they require simple sugars for fast-burning energy.

Basically, this is the difference between wood mulch and leaf litter as food for soil organisms.

Wood mulches contain very high amounts of lignin. This is the compound that reinforces plant cell walls, making them sturdy enough to create structures like trees.

Lignin helps create fibrous woody tissues, like this oak stem; (photo/Fayette A. Reynolds, M.S., via Flickr)

Soil bacteria and fungi can digest lignin — but they can’t do it very fast. On the other hand, leaf litter is a highly bioavailable food source for these creatures. The nitrogen and phosphorus in fallen leaves can provide quick bursts of growth.

This helps diverse bacterial and fungal colonies propagate, which increases ecosystem resilience.

 

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How Leaf Litter Shelters Insects and Protects Roots

Why should you leave your leaves? So the plants that were put in during landscaping can thrive.

But leaf litter also creates critical habitat for a wide range of invertebrates. Many insects like cicadas, worms, and beetles depend on leaf litter for larval habitat and overwintering.

That’s also the case with bumblebees, which are the only pollinators for potatoes, blueberries, and tomatoes.

Bumblebee “gynes,” or young queens, spend winter burrowed under warm leaf litter. When one emerges, she can produce a colony of up to 800 pollinating workers.

Some key functions the leaves provide for these animals are soil decompaction and temperature insulation.

Leaf litter insulates the soil and the roots and organisms in it, creating more stable temperatures. This helps plants develop healthy roots, which loosen the soil. It results in better conditions for insects and increases water absorbency, which mitigates pollution, erosion, and floods.

The opposite conditions — bare, compacted soils where water can’t penetrate — often host damaging chain reactions.

In these soils, the American Museum of Natural History writes, “it is difficult for rainwater to filter into the soil. When soil is compacted, the pore spaces in the soil collapse, making it difficult for water to penetrate and making air less available.”

Bare soils also fluctuate in temperature more readily than covered ones. And dry soils like those in Central Texas can heat and cool faster than wetter soils.

Consistency in soil temperature supports healthier plant and animal populations. Biodiversity strongly depends on these animals which, like soil fungi and bacteria, play a key role in the food web.

Generally, biodiverse ecosystems are healthy ecosystems — capable of supporting a wide range of life.

a nesting bird in a field with grass and stonesGround-nesting birds like killdeers protect and camouflage their eggs with litter components, and feed on insects and worms; (photo/Marc Carlson via Flickr)

How To Apply Leaf Litter to the Landscape

Of course, the easiest way to use leaf litter on any landscape is to simply not move the leaves from where they fall.

You may want to use them more strategically. You can use them to cover bare soil in beds or lawns, jump-starting the process of improving soils there. You can also insulate plants with leaves, including trees. (Protective structures around trees should be rings — never mulch volcanoes!)

Keep in mind that each tree on your landscape is actively using its falling leaves to support its own health. So Maas Verde wouldn’t recommend transporting all of your leaves between spots. From a land management perspective, “leave the leaves” should literally apply on each landscape.

Several inches of cover should be plenty for trees. Planted beds can take less.

Deeper leaf cover can yield higher soil benefits, depending on conditions.

Finally, try to make sure your soil cover doesn’t get compacted. Mulches or leaf litter can turn into matted surfaces that won’t allow water and air to reach the soil.

Simply choose a small area of soil cover and dig it up with your fingers or a trowel. It should release under light pressure and not come out in clumps.

To loosen your soil cover, use a twist tiller. Work it moderately, several inches deep across the whole surface until you’ve broken it up.

“What you’re doing is infusing oxygen into the system that probably wasn’t there before,” said Maas Verde president and founder Ted Maas. “Thick mulch thatch can prevent infiltration — so what you’re doing when you aerate these materials is kick-starting the process for the microbes inside.”

How Can We Tell if Leaf Litter is Working?

Like many creative ideas, enriching a landscape with leaf litter is only as good as its results.

One of the central goals of this method is to cultivate soil microbes and fungi. But these organisms are tiny, and even huge communities of them leave very little visual trace.

On top of that, they also need time to cause their effect. How can you measure the impact of using leaf litter?

For one, Maas Verde recommends long-term seasonal monitoring. You’ll want to do this over multiple seasons or years. To start, set up a camera spot. This should be a convenient, out-of-the-way place that overlooks your landscape or yard — like a fence corner or deck.

Mark it with a flag, T-post, or similar item and start snapping a few photos each season. Keeping track of every plant on a landscape can be harder than you might think — but plant spread can be a general marker of soil health.

Sometimes a desired species will propagate in one area, then pop up in another one nearby (Maas Verde recommends native plants under virtually all circumstances). When desired plants “move” around a landscape like this, it can indicate improving soil conditions.

a thermometer at 160 degreesHot conditions inside this leaf compost pile indicate microbe activity; (photo/Marc Opperman)

However, the information you’ll get from these observations is anecdotal and may not pertain directly to healthier soil. Changing light conditions, seasonal variances, and species competition are factors, too.

A targeted soil test is the only way to measure bacterial and fungal content in soils. Multiple groups provide these resources. Choose a regional specialist, like Texas A&M or Austin’s Rhizos.

Or take the short route — which, in this case, is letting nature take over. Without leaf litter to provide ecological services like nutrient cycling, soil will soon lack nutrients and plants will suffer.

The American Natural History Museum simplified it:

“New plants sprout from the nutrient-rich soil. The cycle begins again.”

What is Ecological Landscaping?

Ecological landscaping seeks to implement a vision of human-designed outdoor spaces that integrate into natural processes. In action, it leverages natural sciences to create healthy communities of diverse native plants and wildlife.

It promotes the costless ecological benefits that support all life. And it satisfies human needs and aesthetics.

Ecological landscaping works to restore any ecosystem by fostering healthy soil and supporting pollinators. It can resolve trenchant infrastructure shortfalls. Examples include heat islands and wasteful stormwater drainage in urban areas, and soil erosion and monoculturing in rural areas. It can also ease pressure on existing, engineered solutions to these problems.

Finally, it can result in colorful, attractive landscapes.

a planted rain garden with a birdbath, both filled with waterFunctional and appealing

Designers of ecological landscapes seek to plan communities as unified systems where natural and manufactured components work together. Arguably, every landscape design must integrate into a “novel ecosystem” — a system of biotic, abiotic, and social components defined by human influence.

The key goals of these landscapes serve the three pillars of sustainability: economic, social, and environmental benefits. The main factors the ecological landscaper must consider are soil restoration, species biodiversity, and plant propagation. All these measures build educational and social opportunities, and support functioning economies in the long term.

two workers prepare a plant bedPhoto: Marc Opperman

“Ecology-based design emphasizes stimulating growth of soil biotic populations and maximizing above and below-ground biodiversity. Specific methods and materials vary by site,” said Rick Martinson, Ph.D. in Horticulture and owner of WinterCreek Restoration & Nursery. “But every design strives to create a fully functional landscape that doesn’t rely on artificial inputs.”

Prioritizing ‘Ecosystem Services’

Imagine a typical city or suburb. Blocks are laid out in squares, lined with impermeable structures that reflect heat and do not absorb water. Natural materials are relegated to the medians, margins, and other in-between spaces.

A typical suburbPhoto: Harry Thomas via Pexels

In this standard format, cities are linear designs that usually consume water and produce waste at high rates. Stormwater flows faster over hard surfaces, causing erosion and depositing pollutants downstream.

The overall effect is to interrupt nature’s cyclical, filtering processes.

an illustration showing how cities affect natural water cyclesIllustration: University of Florida Institute of Food and Agricultural Sciences

These impervious designs also obstruct the flow of “ecosystem services.”

These free, nature-provided functions are the reason all human life exists. They allow life on multiple levels, from growing food to filtering water, controlling disease, and supporting recreational and cultural opportunities.

ecosystem services categories including provisioning, regulating, cultural, and supporting

Infrastructure that ignores or restricts ecosystem services fails to capitalize on these vital, zero-cost resources. But ecological landscape designers can remediate these deficiencies. The critical path is to harness natural elements to perform infrastructural functions (called “green infrastructure”).

an illustration desribing a rain gardenPhoto: thewatershedproject.org

One common example of green infrastructure design is a rain garden, a landscape structure that mimics natural water cycling. Rain gardens can cause stormwater to infiltrate soils and recharge aquifers, reducing flood and pollution hazards that most impermeable drainage structures worsen.

Even more simply, trees, vegetation, and green roofs can reduce heat island effects. They shade reflective surfaces, deflect solar radiation, and regulate atmospheric moisture.

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Biodiversity is Key

But creating healthier plant communities is more complex than just installing more green things. Biodiversity among species is a major driver of ecosystem structure and function. So intentional species selection is critical to any ecological landscaper’s plant plan.

As well-designed plant communities mature, they tend to increase in resilience and benefit. Consider the rain garden below (swipe right for seasonal progress).

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Every size ecosystem needs a wide variety of species to function beneficially. In fact, a non-biodiverse environment could not produce any of the ecosystem services listed above.

We need multiple species of pollinators for food production. Plant communities with multiple cohabitating species resist disease better, limiting failure. Stronger plant communities retain and enrich soil, limiting flooding and supporting resource security. And research has established links between exposure to nature and mental well-being. (The Royal Society further explains these concepts in a colorful 90-second read.)

Landscapes like rain gardens, butterfly gardens, and even hardscape projects should include diverse plantings. Designers should prioritize native species, because these plants have adapted to their local ecosystem for thousands of generations.

Yes, we mainly live in novel ecosystems. But these changes point even more directly to the benefits of native plants.

“Seven to eight generations of human management have affected most soils in our area,” explained Ted Maas, president and founder of Maas Verde. “We can perform amendments, but that creates human influence, too. So plants that have adapted to these soils over long periods of time are more likely to thrive.”

As Martinson points out, “fully functional landscapes” are the goal. The effective ecological landscape designer considers links between all species at a site. This also factors in migratory and resident wildlife, including insects and soil biota.

Monarchs on Gregg’s mistflower (top); Ruby-throated hummingbirds on lantana. Photos: Texas Parks and Wildlife Department, Travis Audubon

Soil Health and Long-Term Benefits

Creating human-friendly systems where plant communities also thrive is the overarching goal of ecological landscaping. But the benefits of these landscapes must propagate in the soil first.

Many areas, urban and rural, experience deeply degraded soil conditions due to a range of causes. Ecological landscaping needs to address erosion and sterility in soils.

An example of gully erosion, in which fast-moving water removes soils by cutting channels in landscapes

Virtually all sites that have undergone conventional construction or industrial-scale agriculture exhibit these conditions.

At a typical construction site, crews prepare the area by scraping away vegetation and topsoil down to a depth of several yards. Materials that replace it are usually impermeable (concrete, asphalt) or do not support the site’s original ecology.

This creates several problems. Applying hard surfaces over soil compacts it, increasing erosion and runoff and decreasing nutrient exchange. And plants that are unsuited to their location tend to root poorly, require chemical treatments, or fail.

Roots naturally decompact and aerate soils. Decomposition and water infiltration in soils stimulate nutrient cycling, and biodiversity of species builds resilience against stressors. Ecological landscaping performs these functions.

Illustration: Institute for Local Self-Reliance

This generates lasting resilience, leading to long-term resource security in communities. Once the system establishes itself, it becomes more valuable as it propagates.

An ecological landscape is “an investment that tends to increase in value as plants grow and become more self-sufficient. Studies have shown that capital costs can be reduced by 15 to 80 percent by using green infrastructure in stormwater management, paving, and landscaping,” Oregon State University’s Gail Langelotto and Singe Danler explain.

Maintenance costs represent one clear example of these savings. Since native plants are adapted to their site, they require little chemical treatment or irrigation (if any).

‘Rethinking’ Landscape Design

Traditional landscapes conform to traditional human infrastructure designs — linear, decoupled from natural processes, and waste-producing. Ecological landscapes will alter these designs and perform new, integrated functions within the novel ecosystems that result.

A bioswale on an urban street. Photo: Department of Energy & Environment

“Ecological landscaping does not necessarily replicate natural landscapes, although it may include parts of them; rather, it incorporates natural systems and processes into a human-centered design. By rethinking landscape design and modifying some of its objectives, we can make use of the many services natural ecosystems freely provide, often more efficiently and economically than built systems.”

-S. Danler, G. Langellotto

The quantifiable benefits of ecological landscaping are substantially unknown, mainly because the trade is so nascent. While its rudimentary principles have existed for well over half a century (it’s not functionally wrong to think of the Barton Creek Greenbelt as one giant rain garden), the industry is young.

Ecosystems need time to develop and mature, and society needs time to accept change. People generally like it when their surroundings seem cohesive and conform to the status quo. Transitioning the aesthetic ideal of a landscape from the conventional lawn (perfectly manicured but often dysfunctional) to the native plant garden (wilder but functional) will take time.

A conventional turfgrass lawn and plantings (left) and rain garden (right)

Installing ecological landscapes at scale can ease this pain point. More importantly, linking more naturally landscaped areas together makes the habitat far more viable for the plants and wildlife it hosts.

Ecological landscapes can look different, or messy, but design techniques like critical species selection and clean edging can add intentionality. Below grade, the soil will store the benefits of increased biodiversity and erosion control for future generations.

Maas Verde believes creating aesthetic, functioning landscapes will spark widespread adoption of these re-imagined structures. And that through this process, we can restore ecosystems.