Drivers of Land Degradation

Land Degradation

“Land degradation” is the reduction or loss of the biological or economic productivity and complexity of cropland, pasture, forest and woodlands. This may result from a combination of land uses and processes, including those arising from human activities and habitation patterns. Land degradation may take the form of

soil erosion caused by wind and/or water;
deterioration of the physical, chemical and biological or economic properties of soil; and
long-term loss of natural vegetation.

Land degradation is commonly caused by the mismanagement or over-exploitation of land resources.

Land degradation is a major global environmental issue of this century because of its adverse impact on agronomic productivity, the environment, and its effect on food security and the quality of life. Land degradation is happening at an alarming pace and is affecting regions inhabited by over one-third of the global population. This phenomenon contributes to a dramatic decline in the productivity of croplands and rangelands worldwide, thereby, threatening food security and environmental quality.

Drivers of Land Degradation

Three broad, inter-related groups of factors drive land degradation: biophysical factors that determine how land is used; institutional factors that govern broader land use policies; and socioeconomic factors that affect the demand for and management of land.

In general, land use change that results in land degradation is driven by multiple, interacting elements, from the local to the global scales. Over the coming decades, a decrease in the availability of productive land will be compounded by competition between land uses. Global estimates of the amount of degraded land vary widely, from 1 billion to 6 billion hectares, which illustrates both the scale of the problem and the need for more accurate data. The critical drivers include: agriculture and forestry; urbanization; and mining and quarrying.

Agriculture is by far the largest human use of land, covering roughly 38 per cent of land surface, not including Greenland and Antarctica. The area used for agriculture is still expanding, currently at the expense of natural forests and grasslands. Although the net area devoted to agriculture continues to expand, this expansion masks the loss of land due to agricultural land degradation and abandonment that results from soil loss, erosion, nutrient depletion, and salinization. Soil degradation is a key factor undermining food security. Soils can be degraded over time either qualitatively (e.g., salinization) and quantitatively (e.g., erosion). There are several major types of soil degradation processes.

The share of the global population expected to live in cities is projected to grow by around 2.5 billion people by 2050. Such growth often results in urban sprawl, with built-up land spilling over in some cases onto fertile soils and farmland, resulting in a permanent loss of arable land. Globally, about 2-3 per cent of the land area is currently urbanized; this is expected to increase to 4-5 per cent by 2050. Built-up areas in developing country cities, meanwhile, are projected to increase threefold by 2030. Urbanization is projected to cause the loss of between 1.6 and 3.3 million hectares of prime agricultural land per year in the period between 2000 and 2030. In addition to using land directly (“land take”), urban populations have a footprint that spreads far beyond the boundaries of the city. Tropical deforestation has, for instance, been positively correlated with urban population growth and agricultural exports.

Drivers of land degradation in Malta

Agricultural land covers 48% of the Maltese islands and is its predominant land use. In 2011, the primary productive agriculture and fisheries sectors produced 1.8% of the National gross domestic product (GDP) and in 2010 the agricultural sector employed 10.6% of the financially active Maltese population. Agriculture is therefore a key economic production centre and plays a key role in Malta’s long-term food-provision and food security.

Agricultural practices have a significant impact on an area’s susceptibility to land degradation. Appropriate management may sustain key ecosystem services and agricultural productivity. On the contrary, inadequate measures may degrade natural resources and reduce crop yields. The Maltese agricultural sector faces significant economic, social and physical challenges that limit agricultural revenue. Such challenges include the relatively small agricultural parcel sizes (an issue exacerbated by land fragmentation) and poor soil quality.

In marginally profitable or entirely uneconomic situations agricultural land is abandoned. In Malta, such scenarios are common in valley margin terraced slopes. These areas require regular maintenance of rubble walls, are difficult to access and are of small size. In Malta, significant expanses of sloping valley margins were reclaimed for agricultural use. The creation of valley margin terraced slopes involved the use of rubble material for levelling, infilling with soil and the construction of rubble walls to retain soil. The resulting anthropogenic landscape may be maintained under continued agricultural management. However, abandoned terraced fields do not receive the required rubble wall maintenance and consequently soils retained by these structures are rapidly eroded, transported and deposited downslope. This dynamic is eroding the thin soils artificially deposited in the flanks of valleys, and over time reducing the agricultural capacity of such areas. The last, also demonstrates the importance and need for continued agricultural land management.

Calculated National annual soil loss using the revised Universal Soil Loss Equation (rUSLE) indicates that 61.01km2, 19:33% of total National land area, are at risk of moderate to severe soil erosion. Maltese central and north-eastern areas show the lowest erosion risk. These areas are characterised by relatively flat topographies, good land management and erosion control measures. Maltese north-western and Gozitan areas are characterised by a large range in erosion rates. Within this area, low erosion risk occurs in plateaus comprising low topographic gradients, and the application of good land management and erosion control measures. Plateau flanks typically consist of exceptionally high erosion rates, characterised by high topographic gradients, inappropriate cultivation practices and poor erosion control measures. Steeply inclined plateau flanks demonstrating low erosion risk are associated with areas demonstrating adequate vegetation cover, and effective management and conservation practices.

Average annual soil loss (t ha-1 yr-1) in the Maltese Islands following RUSLE equation (Sultana, 2015)

Numerically modelled soil erosion volumes in Maltese agricultural areas were estimated at 766.278 m3/yr costing 7.98M€/yr to replace, as derived from a study applying GIS numerical modelling approach. The model calculates that the average owner incurs 1170€/0.01 km2/yr on soil replacement and soil improvement requirements. With an average yearly economic revenue of 1720€/0.01 km2/yr, this cost benefit imbalance may force agricultural land owners to not replace eroded soils. Over time, as a result of soil erosion, an increasingly large proportion of agricultural land may no longer suitable for agricultural purposes. Over 50 years, 1.53 km2 (0.5% of Maltese area) of agricultural land may be depleted of soil, incurring an average national agricultural revenue loss of 0.26 M€ per year. Soil erosion rates, and associated economic implications, may be mitigated with cost effective management practices. Two such practices include conservation tillage, which offers various economic advantages to farmers, and the restoration of breaches in slope-facing rubble walls in areas subject to soil erosion. The latter may require an investment of 11.94M€ at the National scale or 1,600€ by the average agricultural landowner. Both measures contribute towards the sustainable use of Maltese agricultural areas and maintaining key associated ecosystems services.

Map of Maltese Islands showing soil depth loss - 50 years

50 Year % soil depth removed	Area (km2)
0 – 10%	41.32
10 – 20%	17.19
20 – 30 %	6.66
30 – 40%	3.20
40 – 50%	1.81
50 – 60%	1.14
60 – 70%	0.74
70 – 80%	0.52
80 – 90%	0.42
90 – 94%	0.10
95%+	1.53
% MT agric. area lost	0.5

Map of Maltese Islands showing soil depth loss - 100 years

100 Year % soil depth removed	Area (km2)
0 – 10%	19.62
10 – 20%	21.75
20 – 30 %	10.83
30 – 40%	6.35
40 – 50%	3.97
50 – 60%	2.67
60 – 70%	1.97
70 – 80%	1.23
80 – 90%	1.05
90 – 94%	0.29
95%+	4.90
% MT agric. area lost	1.6

Map of Maltese Islands showing soil depth loss - 500 years

500 Year % soil depth removed	Area (km2)
0 – 10%	0.10
10 – 20%	1.82
20 – 30 %	5.19
30 – 40%	6.10
40 – 50%	6.41
50 – 60%	5.58
60 – 70%	5.02
70 – 80%	4.34
80 – 90%	3.43
90 – 94%	1.36
95%+	35.28
% MT agric. area lost	11.2

50, 100, 500 year (top to bottom) erosion maps showing % (of total) soil depth eroded. Area in black marks agricultural land with 95% + soil eroded; considered as containing insufficient soil depth to support agricultural practices. Tables to the right of images indicate the total National land area affected by the soil loss percentage category (Sultana, 2016).

Not all Maltese agricultural areas undertake the same erosion risk. Maltese central, south-eastern and north-eastern agricultural areas demonstrate the lowest risk of erosion. These areas are characterised by relatively flat topographies and adequately maintained soil erosion structures. The Maltese north-western and Gozitan areas are most susceptible to soil erosion. These zones are characterised by a large range in erosion rates. Within the area, low erosion risk occurs in plateaus comprising low topographic gradients. Plateau flanks and valley sides typically demonstrate exceptionally high erosion rates and are characterised by high topographic gradients, inadequate cultivation practices and poor erosion control measures.

Maltese agricultural land is subject to various socioeconomic conditions that constrain net farm income. As a consequence a number of agricultural areas, once financially viable, are now less so. Having lost their economic potential, marginally profitable agricultural areas were abandoned. In Malta, such areas are common in valley margin terraced slopes which contain soil retaining rubble walls. These structures require regular maintenance, which is no longer carried out when agricultural land is abandoned. As soil retaining rubble walls on sloping surfaces gradually deteriorate, they are breached and gravitational processes rapidly transport the retained soils downslope to more stable areas.

To ensure continued sustainable agricultural land use, eroded soils need to be replaced. This process increases farming costs and reduces net agricultural earnings. In addition to soil replenishment, soil erosion degrades the remaining in situ soil requiring the addition of chemical soil supplements to maintain crop yields. These costs are termed on-site costs. As a consequence of the above interacting factors, soil erosion has been identified as a prevailing land degradation process that poses a significant threat to continued agricultural land use.

Soil erosion rates, and associated economic implications, can be mitigated with cost effective agricultural cover and management practices. Soil conservation practices may be cheaper to set up and maintain than the continuous replacement of eroded soils. This approach increases the economic viability of agricultural exploits within areas subject to soil erosion and ensures sustainable, continued, use of such areas. Two cost-effective agricultural management methods in particular can reduce soil erosion, maintain soil quality and preserve agriculture associated ecosystem services. The first, conservation tillage and no-till farming techniques, seek to minimise soil disruption and retain at least 30% of the previous crop residues. This process protects soil from erosion and promotes soil productivity and also provides farmers with various direct economic incentives. The second is the restoration and maintenance of soil retaining rubble walls.