Erosion Control: Stabilise Before You Plant

Why Erosion Control Comes First

There is no point planting trees on a slope that is actively losing soil. Every rain event strips away the very substrate your seedlings need to root into, carrying topsoil, seeds, and nutrients downhill into watercourses where they become pollution rather than fertility. On severely degraded land, erosion rates can exceed fifty tonnes of soil per hectare per year. At that rate, you are planting into a disappearing resource. Stabilisation must precede planting, or planting will fail.

Erosion operates through several mechanisms, and understanding which ones dominate your site determines which control methods to deploy. Sheet erosion removes a thin, uniform layer of soil across a slope during rainfall and is easy to miss because the damage is invisible until the topsoil is gone. Rill erosion concentrates water into small channels that cut progressively deeper with each storm. Gully erosion is rill erosion that has escalated beyond the point where normal tillage or vegetation can repair it, producing channels metres deep that expand with every flood. Wind erosion removes dry, unprotected soil particles and is a primary concern in arid and semi-arid landscapes.

A thorough site assessment identifies which erosion types are active and where the worst damage is occurring. Tackle the most severe erosion first. A single active gully can undo restoration work across an entire hillside by undercutting the root zone of new plantings and depositing sediment over established vegetation downslope. Stabilising that gully may be more important than planting a thousand trees.

Passive Methods

Passive erosion control uses inert materials to slow water, trap sediment, and protect bare soil while vegetation establishes. These methods work immediately upon installation, which is their great advantage over living methods that take weeks or months to become effective.

Jute netting is one of the most versatile tools available. Laid flat over bare soil and pinned with stakes, it breaks the impact of raindrops, slows surface water flow, and holds soil particles in place. Because jute is biodegradable, it decomposes over one to three years, by which time vegetation should have established through its mesh. Coir logs, cylindrical rolls of coconut fibre, are placed along contour lines on slopes to intercept sheet flow and trap sediment behind them. They function as miniature dams, creating flat terraces of accumulated soil where seeds germinate and roots establish. Like jute, coir is biodegradable and becomes part of the soil organic matter as it breaks down.

Straw wattles serve a similar function to coir logs but are cheaper and easier to source in many regions. Bound bundles of straw are staked along contour lines, slowing water and trapping sediment. On steeper slopes, combine wattles with jute netting between them for comprehensive coverage. Rock check dams placed in rills and small gullies slow concentrated water flow, causing sediment to deposit behind the dam and gradually filling the channel. Check dams are a permanent intervention and are particularly effective in arid landscapes where biodegradable materials dry out and blow away before they can do their job.

Living Methods

Living erosion control uses plants whose root systems bind soil, whose canopy intercepts rainfall, and whose organic matter builds soil structure over time. The advantage of living methods is that they are self-sustaining and self-repairing: a jute net eventually rots, but a well-established grass sward gets stronger every year.

Vetiver grass is arguably the single most effective living erosion control tool on the planet. Planted in dense hedgerows along contour lines, vetiver's massive root system, which can penetrate three metres or more into the soil, anchors the slope while its stiff, upright leaves slow surface water flow and trap sediment. Vetiver does not spread by runners or seed in most climates, so it stays where you plant it. Over time, sediment trapped behind vetiver hedgerows creates natural terraces, progressively flattening the slope and reducing erosion to near zero.

Willow stakes driven into moist slopes root readily and grow into dense living fences that stabilise banks and trap sediment. Willows are particularly effective along watercourse banks where their dense root mats hold soil against the scouring force of flowing water. In tropical regions, species like Gliricidia and Leucaena can be established from large cuttings in the same way. These are nitrogen-fixing species that simultaneously stabilise soil and enrich it, accelerating the transition to conditions that support a wider range of plants.

Integrating With Earthworks

Erosion control does not operate in isolation. It works best as part of an integrated water management strategy that includes swales, check dams, and rain gardens. Swales dug on contour intercept sheet flow and infiltrate it into the soil, reducing the volume of water running across the surface below them. Check dams in gullies and drainage channels slow concentrated flow and trap sediment. Together, these earthworks and erosion control measures turn a site that is haemorrhaging soil and water into one that captures and retains both.

The sequence matters. Install earthworks and passive erosion control first, during the dry season when ground disturbance will not trigger new erosion. Then plant living erosion control species into and around the passive structures as the growing season begins. The passive materials hold the line while the living materials establish. By the time the jute and coir decompose, roots have taken over the stabilisation role.

On large restoration sites, Geoff Lawton's work in the Jordan Valley demonstrated how integrating swales, mulch, and pioneer tree planting can reverse severe erosion on desert hillsides within a few years. The swales captured scarce rainfall, the mulch protected bare soil between swales, and the trees provided permanent root stabilisation and organic matter input. The principle applies everywhere: slow the water, protect the soil, establish living cover, and let the biology take over.

When to Plant

The temptation to start planting trees immediately is understandable but often counterproductive. On actively eroding sites, seedlings planted into unstabilised ground face washing out, burial by sediment, or exposure of their roots as soil erodes around them. Survival rates on unstabilised slopes can be as low as ten to twenty percent, wasting money, effort, and the biological capital of the seedlings themselves.

Wait until passive and living erosion control measures have had at least one full wet season to prove themselves. If the jute is holding, the check dams are trapping sediment, and the vetiver hedgerows are rooting in, the site is ready for tree planting. Plant into the stabilised zones between erosion control structures, where trapped sediment has created pockets of deeper, more fertile soil. These microsites give seedlings the best possible start.

On the most severely degraded sites, a full year of erosion control before any tree planting is not wasted time. It is an investment that multiplies the survival rate and growth rate of every subsequent planting. Wangari Maathai's Green Belt Movement understood this implicitly: community nurseries grew seedlings during the months when the planting sites were being prepared with terracing and erosion control, so that when planting day came, the ground was ready to receive them.