Forest Gardens and Land Stability
The lesson of the land
Upon the cliffs where green grass lay,
A man looked out in bleak dismay.
His land was slipping to the sea,
A price paid for his legacy.
He carved the earth, he kept it bare,
A lawn so neat, yet unaware,
That roots were lost, that rain ran free,
That soil would fall without a tree.
The mower screamed, a roar of death,
A choking cloud, a toxic breath.
The grass stood still, but could not save
The slumping land from water’s wave.
But in the quiet, soft and small,
A squirrel worked beyond the sprawl.
It buried nuts with knowing hand,
A rebel in this broken land.
And as the seasons passed him by,
The man beheld the trees grow high.
Their roots held fast, their leaves drew rain,
The earth stood firm, the cliffs remained.
No mower hummed, no tree burned,
The man had watched, the man had learned.
He let the forest take its place,
And found himself in nature’s grace.
Gavin Roberts.
There's hope for slopes
A forest garden is a natural ally in preventing landslips. Diverse root systems stabilise the soil, while dense planting intercepts rainfall, reducing runoff and erosion. In this way, it protects fragile landscapes while contributing to the resilience of the wider environment.
A forest garden offers a compelling alternative to the outdated grass desert. This vibrant, multi-layered ecosystem mimics natural woodland, offering beauty and productivity in equal measure. Fruit and nut trees form a protective canopy, while shrubs, herbs, and climbers weave together to create a lush and abundant under-storey. Each layer works in harmony, nurturing biodiversity and establishing a self-sustaining system. By adopting such regenerative landscapes, we not only support the natural world but also create resilient spaces that nourish both people and fragile lands.
Beyond its ecological value, a forest garden is a feast for the senses. The interplay of colours, textures, and seasonal changes makes it a living artwork. Its beauty is not just aesthetic but deeply meaningful, providing a refuge for wildlife. By planting fruit and nut trees, berry bushes, and perennial vegetables, a forest garden yields an abundance of fresh, nutritious food. This abundance feeds not only the body but also the soul, offering a sense of connection, purpose, and wellbeing that conventional gardens often lack. A forest garden is more than a garden, it is a declaration of care, creativity, and hope for the future.
Nature-Based Solutions for Landslip Mitigation: Harnessing the Power of Forests to Stabilise Slopes and Manage Water"
Land management practices have the greatest impact on how water moves and behaves in the environment, directly influencing the potential for flooding and landslips. Poor domestic choices in vulnerable areas, such as maintaining formal lawns, removing trees and vegetation, or adding excessive hard surfaces, can significantly increase the likelihood of landslips.
Water is the primary cause of most landslides because it significantly reduces the stability of slopes by altering the physical and mechanical properties of soils. When rainwater infiltrates the soil behind fragile slopes, it increases pore water pressure which is the pressure of water in the gaps between soil or rock particles. Excessive ground water pressure reduces the soils shear strength and can trigger a landslip.
The most effective long-term strategy to reduce landslips and flooding is through nature-based solutions (NBS), which harness the power of ecosystems to manage water and stabilise landscapes. These solutions work with natural processes, offering sustainable, cost-effective, and environmentally friendly alternatives to traditional engineering methods. Here's how they work:
Tree and plant roots play a crucial role in stabilising soil and preventing landslips through a combination of physical and biochemical mechanisms:
1. Mechanical Anchoring
Root Networks: Roots create an extensive, interconnected network that binds soil particles together. This network resists the force of gravity and external stresses like water flow or wind.
Penetration Depth: Deep roots, particularly from trees, anchor the soil layers into stable subsoil or bedrock, reducing the likelihood of a landslip. Shallow, fibrous roots of shrubs and ground cover plants secure the topsoil, preventing surface erosion.
2. Increased Shear Strength
Roots increase the shear strength of soil by reinforcing it. When soil is subjected to shear stress, roots act as a physical barrier, preventing soil particles from sliding over each other.
3. Water Absorption and Drainage
Plants and trees absorb significant amounts of water through their roots, reducing soil saturation. Lower water content decreases the likelihood of soil becoming heavy and unstable, which are key triggers of landslips.
4. Erosion Prevention
The root systems of plants hold topsoil in place, protecting it from being washed away by rain or surface water runoff. This helps maintain the soil structure and prevents destabilisation of slopes.
5. Biochemical Effects
Roots secrete organic compounds that bind soil particles together, forming aggregates. These aggregates enhance soil cohesion, making it more resistant to erosion and landslips.
6. Creation of Vegetative Cover
The canopy of trees and plants reduces the direct impact of raindrops on the soil, minimising surface erosion and the loosening of soil particles.
Example in Nature
In hilly areas and coastal slopes, forests are crucial for slope stabilisation. When deforestation occurs, the absence of root systems often leads to increased landslides and soil erosion.
In summary, roots act as a natural engineering system that interlocks soil layers, drains excess water, and maintains the structural integrity of slopes. This interconnected process is vital for landslip prevention and ecosystem stability.
INTERCEPTION by forests play a significant role in reducing landslides.
Interception is the amount of rain that is intercepted by a tree and plants and then evaporated back into the atmosphere. The multiple layers of a forest catch rainfall temporarily with branches, leaves and understory. The sun and wind carry the moisture away, like drying clothes on a windy day. Through the summer a forest transpires huge amounts of ground water, lowering the water level before winter rain returns. This natural process buffers rapid ground water pressure, and is one of the most effective ways to mitigate landslip.
Interception figures and water retention capabilities extend beyond the canopy to include components like dead and decaying wood, mulches, and organic matter. These elements contribute significantly to the hydrological balance in forest ecosystems. Here's how they factor in:
Rainfall Interception and Retention by Forest Floor Components
Dead and Decaying Wood:
Interception and Retention: 5-20% of annual rainfall, depending on the volume and type of wood.
Decaying logs and stumps act like sponges, soaking up water during rainfall.
The high porosity of decomposed wood allows it to absorb and hold water, gradually releasing it into the atmosphere.
Mulches (Leaf Litter and Organic Debris):
Interception: 10-30% of annual rainfall in areas with thick litter layers.
Mulches act as a sponge, absorbing rain then drying out in preparation for the next rain event
Retained water slowly infiltrates the soil, supporting gradual groundwater recharge and maintaining moisture for plant roots.
Soil Fertility and Organic Matter:
High organic matter content increases soil's water-holding capacity by 30-50%, depending on the soil type.
Fertile, humus-rich soils can absorb and retain more water, reducing surface runoff and soil erosion.
Organic matter improves soil structure, facilitating better infiltration and storage.
Decomposing material releases nutrients into the soil, maintaining forest health and vigour.
Combined Interception and Retention in Forest Ecosystems
Canopy Contribution: 15-40% of annual rainfall.
Forest Floor (Mulch, Deadwood, and Organic Layer): 15-50%, varying with layer thickness and decomposition rates.
Total System Contribution: Forest ecosystems can intercept and retain 30-70% of annual rainfall, depending on forest type and health.
Transpiration
Transpiration, the process by which trees and plants release water vapour through their leaves, plays a significant role in reducing groundwater levels as vegetation draws water from the soil. From spring to autumn a single mature tree can transpire up to 2 tonnes of water per day. The combined effect of a forest is effective at lowering the water table. This reduction delays the soil's saturation point when winter rains return, thereby decreasing the likelihood of landslip.
Community Mulch Service: A Practical Approach to Landslip Mitigation
Twenty-one years ago, I drove onto a piece of land that began a journey, one that continues today. The land had suffered from land slippage, partly due to inappropriate land practices both onsite and on neighbouring properties. Excessive lawns and increasing domestic discharge from more residents had pushed groundwater pressure past a critical threshold, causing instability.
Lawns, in particular, are unsuitable for fragile slopes. Regular mowing depletes soil fertility, reducing its ability to absorb and hold rainwater. Unlike natural ecosystems, lawns provide zero rain interception, allowing all rain to pass through to add to ground water pressure. In contrast, fertile woodlands intercept 30–70% of annual rainfall. Slopes behind known landslips should be encouraged to regenerate with woodland cover, which improves fertility and stabilises the land.
The hydrological benefits of vegetation come from its ability to extract water from the soil and intercept rainfall, allowing a portion of it to evaporate before reaching the ground. Deep-rooted plants help reduce pore-water pressure by drawing moisture from the soil and transpiring it through their leaves. These effects lower overall soil moisture content and delay soil saturation, reducing the risk of landslides.
Managing Water with Vegetation at Permaculture Island
The site covers 1.6 acres (6,475 square meters) and receives an average 900mm of rainfall per year, contributing 5,827 tonnes of rain water annually. By prioritising trees, shrubs, ground covers, deep mulches, and fertile soils, we can intercept up to 70% of the rainfall, preventing up to 4,079 tonnes of water from reaching fragile cliffs.
One of the first challenges was to remedy soil fertility, the site's dense clay soil, which lacked the necessary structure to absorb and retain water effectively. The solution was to apply raw organic mulch to the surface of the land which rapidly improves soil fertility, absorbs rainfall, and enhances evaporation back into the atmosphere. However, large quantities were needed, so we turned to the local community.
Community Involvement and System Growth
A free garden waste drop-off was introduced, encouraging locals to contribute organic material that would otherwise be discarded. This not only improved our soil fertility but also nurtured community interest in the project. Over time, community engagement grew into tours, courses, and hands-on participation, reinforcing the shared benefits of the system. Garden waste also became an essential food source for our animals, creating a closed-loop system that benefited everyone involved. People felt connected to a meaningful cause, knowing their contributions directly supported a unique and sustainable venture.
The project’s success, particularly during the hardships of COVID-19, led to another major development, a land vehicle to transport mulch. We purchased a used an electric golf buggy and adapted it for better use. A suspension upgrade and large off-road tires improved its ride and traction, while a fabricated rear flatbed allowed it to carry ton bags of mulch and wood chip. A simple modification transformed the flatbed into a pickup-style hauler: by placing a rubber sheet underneath the load, unloading became quick and effortless.
A Model Worth Repeating
This evolving system has demonstrated a repeatable model for mitigating land instability while enhancing fertility, biodiversity, and community engagement. The knowledge gained through observation and hands-on experience is now shared widely, empowering others to apply similar principles.
This journey, built on whole-system thinking and community support, is ongoing.
I wholeheartedly believe that what we have created here can inspire real change elsewhere.
