Degradation-restoration: defining a safe space

Work with the Scottish Ecological Design Association (SEDA) over the past year [1] led to an invited, short article in SEDA’s autumn 2021 magazine [2]. The topic chosen was the integrity of ecosystems, their degradation through mismanagement and their possible restoration. This short article expands on some of the topics raised in the article.

Transitions in the state of land

Production ecosystems can be placed in one or more categories defining their state on a scale of degradation and regeneration. All agriculture and forestry began through change in a primary or original ecosystem (1) that was largely untouched by human activity. In many places, the original was slowly transformed into production land (boxes 2, 3). Some such systems have remained in production for hundreds, even thousands of years. More generally, sustainable production gave way to extractive production, which if intensified reduced the functioning of the system to the point where it could no longer support economic output (5). Land might have further degraded to a state that no longer supported agriculture and forestry (6). An alternative route from (1) to (6) is through rapid and excessive exploitation, as is happening in parts of the world that have lost primary ecosystems in only a few decades.

Figure 1. Transitions in land use from natural ecosystems (1) to systems managed for economic output (2, 3, 4), to exhausted or degraded land (5, 6), and then through regeneration to sustainable production (2, 3) or through wilding to a system much removed from (7) or similar to (8) the original. Brown arrows represent degradation, green arrows regeneration, dashed arrows a difficult transition and uncertain outcome. Green boxes – where productive land in agriculture and forestry should be.

Many past civilisations have reached 5 or 6 and then faded away as they lost the ability to produce essential food and materials. Others have decided to repair and regenerate ecological processes. Regeneration might attempt – where the land and climate permit – to move back from 4 or 5 to a sustainable state, whether extensive production (2, low management input per unit area) or sustainable, economic production (3).

Relative stability in categories 2 and 3 is possible in many different soils and climates (some examples in Figure 2) but the prevailing trend in much of agriculture and forestry has been continued transition from 3 to 4, 5 and 6.

Figure 2. Examples of productive land use in categories 2 and 3: upper left, c’wise, wetland rice, northern Laos; seasonal hill grazing, Slovenia; terraced vegetable fields, Burma (Myanmar); and mixed woodland and grazing, Romania (photographs by the author).

Recognising that land has degraded to 4 or 5 is a first and necessary step to regeneration. The Improvements in Scotland after 1700 accepted that much land had been exhausted of nutrients and found ways to re-stock soil. In the 1800s, the design and trialling of complex ‘grass’ seed mixtures, comprising grasses. legumes and other dicot plants, aimed to improve nutrition of both the soil and the livestock that fed on the grass [3].

An even greater challenge is to move severely degraded land back towards the primary state (from 6 or 5 to 2). That is possible but it takes a long time, decades, centuries. Some shifting cultivation in Asia is in many respects of this type. The forest is felled and burned, crops are grown on the nutrients from the trees, and after a few years, agriculture moves to a new area, the land left to return to scrub or forest. Shifting cultivation of course needs a lot of land and a small population to feed and when those conditions are met, can be sustainable to a degree. In many cases, the land simply cannot get back – for example, its soil might have been lost, its functional biodiversity extinct – and it ends up in what is here termed a reduced system, a desert for example (7).

Proportioned stores and flows

Natural ecosystems evolved to balance their ‘flows’ and ‘stores’. The big universal flows of solar radiation and water allow plant life to turn carbon dioxide in the air to living matter – the basis of an ecosystem store. Microbes and small animals feed on the plant products, creating a more diverse store and allowing it to combine with the earth’s inorganic materials, to create soil or coral, for example. A balanced ecosystem can last for millennia, but the balance is delicate.

The problem for land management and restoration is that main flows of energy and matter are very large compared to the stores. One of the crucial functions of an ecosystem’s store, therefore, is to regulate the flows that sustain it. In a perennial forest or grassland, high solar radiation is balanced by evaporation of water through vegetation to achieve an equable temperature, and layers of vegetation shield soil from the most intense rain. The store also allows a system to survive through adversity, whether seasonal dryness or flooding.

The problem is very simply illustrated in Fig. 3, which represents, on the left, a well-regulated system and on the right, one exhausted to destruction. The box shows the store, and the large downward arrow represents the main flows into the system. The store captures and partitions some of the flows (internal circular arrows) but most of the flows pass through the system. On the left, the large store is able to partition the inflows through several different outflow channels, whereas on the right the small store is ineffective to a degree that the inflow passes through in a single large outflow.

Figure 3. Diagrams to represent and ecosystem ‘store’ (box) and the flows of energy and matter (arrows) in systems that are left, well proportioned (large store compared to inflow and many dissipating outflows) and right, degraded (small store compared to inflow and single outflow).

In a place that experiences, for example, high inflows of rainwater, the left-hand diagram might represent be a multi-storied tree-crop system that collects and holds water, then channels the excess through evaporation, drainage, soil-surface flow and transpiration through the plants (e.g., Fig. 4 right); whereas the right hand box could be a degraded, weakly structured and sparse vegetation that intercepts little of the water, which then hits the soil and flows off mainly as surface wash, eroding soil at the same time (e.g., Fig. 4 left).

Figure 4. Examples of tea plantations in the same region of Sri Lanka, the right hand one able to contain, use and dissipate high flows of solar radiation and water, the right hand one unable to do so and losing its soil. The difference is due entirely to management. (Photographs by the author).

Scientific study can inform ecosystem restoration by quantifying the stores and flows in a system, assessing the current status of the system compared to a sustainable ideal and defining feasible transitions in Figure 1.

International efforts in restoration have been boosted this year by the UN’s Decade of Ecosystem Restoration 2021-2030 and its 10 Guiding principles [4] and by the Society for Ecological Restoration’s [5] intensified political activity, particularly in Europe, both of which will have further coverage on this web site.

Sources | links

[1] Background to the Scottish Ecological Design Associations set of 6 Land Conversations: Land Conversations – first ideas, SEDA Land Conversations – matrix and decision tree, and later in the year, a summary of the online discussion hosted with the John Muir Trust: Carbon tax land conversation?

[2] Sustainable Design for Ecosystem Restoration by G R Squire in SEDA Magazine Autumn 2021.

[3] Grass seed mixtures of 1800s Scotland are described on this site at Grass mix diversity a century past and the Agrostographia.

[4] UN Decade of Ecosystem Restoration 2021-2030 at and the UN’s 10 Principles that Underpin Ecosystem Restoration

[5] Society for Ecological Restoration (SER)