Combating Land Degradation by Minimal Intervention - University of ...
Combating Land Degradation by Minimal Intervention - University of ...
Combating Land Degradation by Minimal Intervention - University of ...
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Sixth Framework Programme<br />
<strong>Combating</strong> <strong>Land</strong> <strong>Degradation</strong><br />
<strong>by</strong> <strong>Minimal</strong> <strong>Intervention</strong>:<br />
The Connectivity Reduction Approach<br />
Written and Edited <strong>by</strong> the RECONDES Project Team
Introduction and context<br />
Desertifi cation and its related problems <strong>of</strong> soil erosion and land degradation are<br />
identifi ed <strong>by</strong> the European Union as becoming one <strong>of</strong> their largest environmental<br />
problems as a result <strong>of</strong> global change.<br />
Soil erosion and land degradation have negative ‘on-site’ and ‘<strong>of</strong>f-site’ effects: on<br />
the fi elds the topsoil is being removed <strong>by</strong> water fl owing over the soil surface. These<br />
‘on-site’ processes lead to a decrease in soil quality as most nutrients are present<br />
in the topsoil. So erosion leads to impoverishment <strong>of</strong> the soil, but it also deteriorates<br />
the water absorbing properties <strong>of</strong> the soil, reducing infi ltration <strong>of</strong> water into the soil.<br />
Therefore, eroded soils <strong>of</strong>ten give higher amounts <strong>of</strong> run<strong>of</strong>f than non-degraded soils.<br />
The soil material, including the nutrients it contains, as well as the increased amounts<br />
<strong>of</strong> water, are transported downwards through the catchment, where the soil may<br />
be deposited in reservoirs, eventually silting them up. In the case <strong>of</strong> fl ooding, the<br />
sediment may also be deposited in urban areas causing direct damage to buildings<br />
and roads and even to humans. These ‘<strong>of</strong>f-site’ effects are a second negative effect<br />
<strong>of</strong> land degradation in upland areas.<br />
The aim <strong>of</strong> these guidelines is to present novel and effective sustainable measures to<br />
reduce the on-site problems <strong>of</strong> land degradation in two ways:<br />
• identifi cation <strong>of</strong> ‘hotspots’ in the landscape where run<strong>of</strong>f occurs, increasing soil<br />
degradation.<br />
• application <strong>of</strong> environmentally sound and effective revegetation strategies on the<br />
identifi ed hotspots using suitable plant species.<br />
This approach is different from other approaches in that it identifi es hotspots and<br />
focuses on the application <strong>of</strong> appropriate vegetation species to these areas, whereas<br />
in other approaches measures are applied across the entire landscape.<br />
Vegetation has several positive effects: its roots reduce erosion <strong>by</strong> holding the soil<br />
together, the stems and leaves obstruct water fl ow so lowering fl ow velocities and<br />
the ability to carry sediments, and furthermore infi ltration <strong>of</strong> water into the soil is<br />
enhanced under the vegetation. The placement <strong>of</strong> vegetation in hotspots should be<br />
adjusted in such a way that these positive effects are maximized. Also, the most<br />
suitable vegetation species should be selected, which are adapted to the environment<br />
where they are being applied, and that also have the largest effects with regard<br />
to their rooting system and their above-ground canopy and stem structure. The<br />
resistance and resilience <strong>of</strong> the vegetation to fl ow conditions is also considered as the<br />
vegetation application should be a sustainable strategy to reduce on-site degradation<br />
problems. In this way, not only ‘on-site’ degradation is being reduced, but also ‘<strong>of</strong>fsite’<br />
problems are being reduced. Furthermore, this remediation strategy is a ‘green’<br />
and environmentally sound solution to degradation problems in dryland regions.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 1
Processes <strong>of</strong> land degradation<br />
<strong>Land</strong> degradation is a reduction or loss <strong>of</strong> the biological productivity and complexity resulting from land uses or<br />
from natural and human driven processes such as soil erosion caused <strong>by</strong> wind and/or water; deterioration <strong>of</strong> soil<br />
properties; and loss <strong>of</strong> natural vegetation. When land degradation occurs in arid to dry sub-humid areas then it is<br />
called desertifi cation. More specifi cally, land degradation includes soil erosion, soil acidifi cation/salinization, fertility<br />
depletion, soil crusting, compaction, reduction in soil organic carbon, in biomass and loss <strong>of</strong> biodiversity. Here, we<br />
will examine some <strong>of</strong> the aspects related to processes <strong>of</strong> run<strong>of</strong>f generation, sediment production and export and<br />
the role <strong>of</strong> vegetation in counteracting these processes.<br />
Run<strong>of</strong>f generation and soil erosion<br />
In arid to dry sub-humid areas overland fl ow normally occurs when rainfall intensity exceeds the rate at which water<br />
infi ltrates into the soil. This process can be promoted <strong>by</strong> the destruction <strong>of</strong> soil aggregates (if present) and the<br />
packing <strong>of</strong> soil particles (sealing and crusting). One <strong>of</strong> the main factors in causing this decrease in infi ltration rate<br />
is raindrop impact on bare soils with low vegetation cover. When rain exceeds infi ltration, water begins to move<br />
following local slope gradient. During this phase soil splashed <strong>by</strong> raindrops is entrained <strong>by</strong> the fl ow and removed<br />
from the spot, so that mineral particles and organic matter are exported. Once concentrated, run<strong>of</strong>f moves faster<br />
and can erode the soil, incising the landscape. Now the level <strong>of</strong> damages is increased. Mineral particles and organic<br />
matter are exported in larger quantities, while the incision further facilitates concentrated fl ow to erode and transport<br />
more sediment. In this way rills and gullies can form.<br />
When thunderstorms occur, even if they are rare, they can produce a large amount <strong>of</strong> water in a short time span<br />
across local areas. This excess <strong>of</strong> water, assisted <strong>by</strong> a network <strong>of</strong> small rills, gullies, and channels, can produce<br />
fl ooding. Of course, this occurs in all climates, but the problems are more severe in dryland areas where soil is <strong>of</strong>ten<br />
bare and more exposed to erosion. Moreover, dryland areas require more time to recover from the shock <strong>of</strong> intense<br />
rainfalls because all the processes <strong>of</strong> soil formation and <strong>of</strong> vegetation re-establishment in severely eroded sites are<br />
slower than in more humid environments, counteracted as they are <strong>by</strong> scarcity <strong>of</strong> water and recurrent droughts.<br />
It is evident that vegetation plays an important role in opposing these processes <strong>of</strong> erosion and land degradation.<br />
Plants locally protect the soil surface from the impact <strong>of</strong> rain drops, their canopy reducing or completely wiping<br />
out their destructive and erosive power (no aggregate destruction, no raindrop splashed soil lost to overland fl ow).<br />
Moreover plants protect the soil from direct solar radiation. This is benefi cial for the local ecosystem which can host<br />
more biological activity which means in the long run, more active soil forming processes, particularly the formation<br />
<strong>of</strong> new stable soil aggregates. The roots, with both their physical action and positive infl uence on soil mineral and<br />
nutrient levels, further improve soil resistance to erosion. All this also promotes porosity and macro-porosity with<br />
strong benefi cial effects on infi ltration rate (and water availability to plants on the site). Finally, plants locally increase<br />
hydraulic resistance to water movement causing sediment deposition and decreasing the erosivity <strong>of</strong> run<strong>of</strong>f.<br />
2 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
Hotspots<br />
Hotspots are places that, unless properly managed, can be severely eroded (or receive excessive sedimentation)<br />
and begin a process <strong>of</strong> export <strong>of</strong> unwanted sediment. Examples are river and gully banks where river processes,<br />
wall collapse and run<strong>of</strong>f from upslope areas can trigger the creation <strong>of</strong> a new headcut that will then retreat upslope<br />
and/or sidewise to the main water course (Figure 1).<br />
As another example, semi-arid agricultural terraces with a counter slope at the end <strong>of</strong> their sub-horizontal surfaces<br />
work as collector <strong>of</strong> run<strong>of</strong>f from large areas. If not properly managed, water can spill over the counter-slope (or<br />
undercut the system <strong>by</strong> tunnelling), concentrating large amounts <strong>of</strong> run<strong>of</strong>f and increasing connectivity (Figure 2).<br />
Generally hotspots can be managed locally <strong>by</strong>, for example, protecting them with vegetation. This can decrease the<br />
amount <strong>of</strong> water that will be transmitted downslope and even stop sediment transport. Other protection measures<br />
can be based on reducing the amount <strong>of</strong> run<strong>of</strong>f and sediment from upslope, for example intercepting run<strong>of</strong>f and<br />
sediment in several places where local fl ux concentration can still be managed effectively and possibly at a lower<br />
cost. Most <strong>of</strong> the sediment is lost from these hotspots in the landscape. Therefore, if they can be identifi ed they can<br />
be targeted for action.<br />
Figure 1 Example <strong>of</strong> hotspot: Gully headcut retreating upslope into fi eld.<br />
Figure 2 Example <strong>of</strong> hotspot: Spill over <strong>of</strong> water at terrace counter-slope, leading to export <strong>of</strong> sediments.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 3
Principles <strong>of</strong> approach and methods<br />
Sustainability<br />
Any techniques <strong>of</strong> land, water or soil management that are applied need to be sustainable. This means that they<br />
can be maintained and continued over a long time without causing detrimental consequences, without decreasing<br />
quality <strong>of</strong> life or environment, and without causing markedly increased costs that would not otherwise be incurred.<br />
Ideally, they should be self-maintaining. They should allow the use <strong>of</strong> the land in a way that suits the conditions<br />
and landuse. The methods may need to allow for adaptation as conditions change, for example due to global<br />
warming.<br />
Connectivity<br />
This is a term which means the extent to which parts <strong>of</strong> the landscape are connected, or the extent to which there<br />
are pathways which can be identifi ed in the landscape. These pathways or connections are primarily the fl ow <strong>of</strong><br />
water and the movement <strong>of</strong> sediment. Water will naturally fl ow down slope and down through channels and it will<br />
transport sediment with it if it can pick up sediment (erosion) and has suffi cient energy to carry it. Pathways <strong>of</strong> water<br />
will continue until the water runs out or it reaches an end point <strong>of</strong> the catchment. Sediment will be carried until the<br />
water runs out or until all the sediment is deposited due to the setting. These endpoints represent ends <strong>of</strong> pathways.<br />
If this is part way down a slope or down a channel then this means the pathways are not continuous throughout the<br />
drainage basin (catchment). The longer these pathways, the further away water and sediment will be removed from<br />
the slopes, causing a decrease in fertility <strong>of</strong> the soil, and causing problems downstream.<br />
The main aim <strong>of</strong> the conservation practices recommended here is to minimise connectivity, particularly <strong>of</strong> sediment,<br />
so reducing soil loss. Many modern land use practices have tended to increase the connectivity, causing increased<br />
soil erosion problems. The idea here is to use vegetation in these pathways to reduce the connectivity.<br />
Vegetation effects<br />
The main idea is to identify the locations and conditions where vegetation could be increased or could be encouraged<br />
to grow. Suitable types <strong>of</strong> plants also need to be identifi ed. Vegetation is used because it can prevent erosion or soil<br />
loss <strong>by</strong> increasing the resistance <strong>of</strong> the soil to removal. Again, many <strong>of</strong> the problems are due to a lack <strong>of</strong> vegetation<br />
cover or a decrease from former conditions. The presence <strong>of</strong> vegetation can also encourage infi ltration <strong>of</strong> water into<br />
soil, keeping the water on the slope. Once vegetation is established it can help to create better conditions for further<br />
growth <strong>by</strong> adding organic matter. This also increases the stability <strong>of</strong> the soil to erosion.<br />
Strategic placement <strong>of</strong> vegetation<br />
The idea <strong>of</strong> the use <strong>of</strong> vegetation to manage soil erosion as part <strong>of</strong> conservation management is not new. What<br />
is new here is the idea <strong>of</strong> placing the vegetation in particular locations. These are the locations where it will have<br />
maximum effect. They are in the pathways <strong>of</strong> fl ow <strong>of</strong> water and sediment. The methods involve identifying where<br />
in the landscape it would be most benefi cial to establish vegetation. This will be cheaper to establish than trying<br />
to plant everywhere, as has been done in many reforestation schemes. It also means the rest <strong>of</strong> the land can still<br />
be used.<br />
Scales <strong>of</strong> application<br />
These planting strategies can be applied at a variety <strong>of</strong> scales, as is shown in the next section. They can be applied<br />
at the scale <strong>of</strong> a fi eld or part <strong>of</strong> a terraced slope, or in an area <strong>of</strong> existing reforestation. They can be assessed also<br />
at the scale <strong>of</strong> the whole hillslope. The link between the hillslope and the channel is an important point <strong>of</strong> potential<br />
control. Strategies may also be applied within channels, though mostly small channels.<br />
4 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
Types <strong>of</strong> environment<br />
These approaches and techniques are deigned for application in areas which are prone to soil erosion and in<br />
which vegetation tends to be sparse but can grow. Obviously, vegetation can be made to grow where there is an<br />
adequate supply <strong>of</strong> water and other resources and environmental conditions are not limiting. The approach should<br />
be sustainable so that the vegetation will grow under natural rainfall and water supply conditions <strong>of</strong> the location. The<br />
initial designs are suited to dryland environments <strong>of</strong> the Mediterranean region <strong>of</strong> southern Europe, particularly on<br />
s<strong>of</strong>t rock areas such as marl bedrock. These are areas with a long tradition <strong>of</strong> agriculture and much traditional use<br />
<strong>of</strong> agricultural terraces on steeper slopes. This is the type <strong>of</strong> landscape which is used in the illustrations. It is based<br />
on research in southern Spain.<br />
Steps in approach<br />
In the following pages, further details are given on the problems <strong>of</strong> erosion arising in different areas <strong>of</strong> the landscape<br />
and vegetation strategies which may be taken to address these problems. Using the information presented in this<br />
booklet, the following steps are recommended for developing a revegetation plan:<br />
1. Identify pathways or connectivity within area<br />
2. Identify particular locations or hotspots where erosion tends to occur<br />
3. Assess the conditions for growth <strong>of</strong> plants in relation to a few factors<br />
4. Identify the types <strong>of</strong> plants that would grow there<br />
5. Identify additional techniques that are needed to enable plants to grow or establish<br />
6. Implement the techniques<br />
7. Plant seeds or seedlings<br />
Step 1. Identify pathways or connectivity within area<br />
Step 2. Identify particular locations or ‘hotspots’ where<br />
erosion tends to occur<br />
Step 3. Assess the conditions for growth <strong>of</strong> plants in<br />
relation to a few factors<br />
Step 4. Identify the types <strong>of</strong> plants that would grow there<br />
Step 5. Identify additional techniques that are needed to<br />
enable plants to grow or establish<br />
Step 6. Implement the techniques<br />
Step 7. Plant seeds or seedlings<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 5
Reforested land<br />
Problems <strong>of</strong> soil erosion and land degradation on reforested land<br />
Extensive reforestation works have been carried out across Spain and other parts <strong>of</strong> the Mediterranean using<br />
terracing to reduce run<strong>of</strong>f and improve soil water availability for plants with the objective <strong>of</strong> controlling soil erosion in<br />
degraded areas. As a consequence, large areas have been topographically altered and covered <strong>by</strong> homogeneous,<br />
even-aged coniferous forest (primarily Pinus halepensis). However, reforestation has not always been successful<br />
and it is now realised that past methods <strong>of</strong> construction may contribute to the development <strong>of</strong> erosional problems.<br />
Defective terraces, which are not perpendicular to the slope, act as fast run<strong>of</strong>f pathways (Figure 3). Local defaults<br />
in terraces act as points for fl ow to concentrate, resulting in further erosion. With time, old reforestation terraces<br />
collapse, increasing connectivity in these lands (Figure 4).<br />
The construction <strong>of</strong> terraces and side banks not only dramatically alters the topography <strong>of</strong> the landscape, but also<br />
negatively impacts the establishment <strong>of</strong> plant cover and plant biodiversity.<br />
A<br />
Figure 3 Terracing can increase hydrological connectivity <strong>of</strong> reforested lands:<br />
(A) Terraces not-perpendicular to slope act as collector and fast run<strong>of</strong>f paths.<br />
(B) Failures <strong>of</strong> terrace embankments are the origin <strong>of</strong> headwater gullies.<br />
Figure 4 Torrential run<strong>of</strong>f events and active headwater erosion processes can destroy terraces and trigger land degradation.<br />
6 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH<br />
B
A medium term survival rate <strong>of</strong> 50% has been reported in studies <strong>of</strong> Pinus halepensis reforestations in semiarid<br />
Mediterranean environments. While some studies suggest that planted forest may improve soil properties in decades,<br />
others have found lower soil organic content and nutrient concentration under Pinus plantations than in adjacent<br />
shrublands. Vegetation colonization on the side banks is also very low (Figure 5).<br />
A B<br />
Figure 5 Example <strong>of</strong> poor, slow re-colonization process on side bank caused <strong>by</strong> terracing: (A) Contrasting view <strong>of</strong> reforested and natural<br />
slopes. (B) Detail <strong>of</strong> planted terrace (Te); side bank (artifi cial talus Tn) and non-altered natural slope (Ta).<br />
Studies in SE Spain reveal that after 30 years the side<br />
bank is hardly colonized, and bare soil is 12 times<br />
more frequent than on the terrace. The species pool<br />
is also severely depleted, species richness is less than<br />
half than in original slopes (Figure 6). The layer <strong>of</strong> litter<br />
which forms under Pinus halepensis also inhibits the<br />
germination <strong>of</strong> seeds and growth <strong>of</strong> seedlings, hence<br />
hampering the development <strong>of</strong> an understorey layer.<br />
Figure 6 Planted forests show a low species diversity. The common<br />
hypothesis that planted forest will foster vegetation<br />
dynamics fails in dry semi-arid environments.<br />
Vegetation strategies to mitigate erosion and reduce connectivity<br />
The following three vegetation strategies are recommended to correct negative impacts and reduce connectivity in<br />
Reforested <strong>Land</strong>s.<br />
1. Vegetation should be planted where the rills originate, where terraces are collapsing or across terraces not<br />
perpendicular to slope as these will form zones <strong>of</strong> run<strong>of</strong>f during rainfall events.<br />
2. Side banks are much more extensive structures. Massive plantations <strong>of</strong> vegetation are expensive, and mostly<br />
unsuccessful because <strong>of</strong> the harsh conditions. Encouraging spontaneous or induced colonization should be<br />
the focus <strong>of</strong> the works. Microstructures built with natural barriers like wood, debris and stones should be<br />
established on the side banks in order to promote the trapping <strong>of</strong> water, nutrients and seeds. Conditions could<br />
be further improved <strong>by</strong> local addition <strong>of</strong> organic amendments (to improve soil infi ltration and nutrient status) and<br />
seeding with side-bank adapted species.<br />
3. In mature forests, some manipulation <strong>of</strong> litter layer and seeding <strong>of</strong> shrubs and grasses should encourage<br />
understorey development. This should be especially targeted at areas between trees that function as contributing<br />
headwater areas <strong>of</strong> rills and gullies.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 7
Rainfed croplands<br />
Problems <strong>of</strong> soil erosion and land degradation on croplands<br />
Overland fl ow removes soil material from the fi eld and causes the collapse <strong>of</strong> terraces: the sparse vegetation cover<br />
fails to protect the soil against intense rainfall. On shallow soils, prolonged erosion may lead to a decrease in soil<br />
productivity and yield. Run<strong>of</strong>f concentrates in the valley bottom, on dirt roads and on access tracks <strong>of</strong> terraces.<br />
Figure 7 Erosion in fi eld and export <strong>of</strong><br />
sediments.<br />
Figure 8 Gully formed in bare fi eld. Figure 9 Erosion along track connecting<br />
two fi elds.<br />
Vegetation strategies to mitigate erosion and reduce connectivity<br />
An effective way to reduce erosion problems is to cover the soil during the rainy season. Depending on the water<br />
availability, cover crops can be grown throughout the fi eld, limited to strips perpendicular to the slope or in buffer<br />
strips along the fi eld border (Figure 10).<br />
A B C<br />
Figure 10 Different types <strong>of</strong> cover crops can be considered, including (A) weeds, (B) legumes and (C) grass species.<br />
In semi-arid areas, where competition for water with the main crop is crucial, it may be necessary to limit the growth<br />
<strong>of</strong> cover crops to terrace/fi eld access tracks and valley bottoms. The cover crops can be killed <strong>by</strong> tillage in spring.<br />
In the case <strong>of</strong> chemical weeding, the plant residue is left as mulch, keeping the soil covered as much as possible.<br />
8 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
The selection and application <strong>of</strong> specifi c vegetation measures should be done at the sub-catchment level, taking<br />
into account the local climate, landscape and cropping systems. Figure 11 shows priority areas to be protected<br />
during the rainy season. The side bank <strong>of</strong> earth terraces can be stabilised <strong>by</strong> natural vegetation. This is a common<br />
and quite effective practice in many areas.<br />
Figure 11 Priority areas to be protected during the rainy season: terraced orchards/vineyards when competition for water is high (left),<br />
orchards on steep slopes (middle) and sloping cereal fi elds (right).<br />
Table 1 Major benefi ts <strong>of</strong> vegetation strategies.<br />
Vegetation strategies Benefi ts<br />
Cover crops/vegetation strips • Effective protection against soil degradation and loss <strong>of</strong> soil<br />
productivity<br />
• Increased infi ltration <strong>of</strong> rain water<br />
• Improvement <strong>of</strong> soil structure<br />
• The mulch left after chemical weeding prolongs the period <strong>of</strong> soil<br />
protection and decreases water loss <strong>by</strong> evaporation<br />
Grassed waterways • Reduced risk <strong>of</strong> gully formation<br />
• Reduction <strong>of</strong> run<strong>of</strong>f volume and peak discharge at (sub)catchment<br />
level<br />
Water availability for cover crops<br />
The water availability for cover crops in rainfed cropping<br />
systems strongly depends on the local climate. Figure<br />
12 shows the effect <strong>of</strong> climate on the tree canopy cover<br />
in olive orchards. The possibilities for cover crops are<br />
clearly more restricted in, for example, Southeast Spain<br />
(300 mm annual rainfall) than in Central Italy (700 mm<br />
annual rainfall).<br />
Figure 12 Effect <strong>of</strong> climate on tree canopy cover in orchards.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 9
Abandoned and semi-natural areas<br />
Problems <strong>of</strong> soil erosion and land degradation on abandoned and semi-natural areas<br />
The focus <strong>of</strong> the section is on abandoned lands, since these are more disturbed and are therefore more prone to<br />
land degradation. However, also in semi-natural areas land degradation can be a problem, although most erosion<br />
is considered to be ‘natural erosion’, which is almost inevitable because <strong>of</strong> the topographic position or erodible<br />
substrate. An example <strong>of</strong> degraded semi-natural areas is Stipa shrublands on marls (Figure 13). Semi-natural lands<br />
may especially be vulnerable to accelerated degradation when rills and gullies encroach from surrounding arable<br />
and abandoned fi elds. This expansion should be prevented as much as possible.<br />
Figure 13 Degraded Stipa shrubland. Figure 14 Soil crust on recently abandoned fi eld.<br />
Abandoned fi elds in semi-arid areas can be vulnerable to erosion because <strong>of</strong> the slow vegetation recovery and<br />
unfavourable soil properties. The combination <strong>of</strong> a low vegetation cover and the absence <strong>of</strong> ploughing lead to the<br />
formation <strong>of</strong> soil crusts (Figure 14), which decreases the infi ltration capacity <strong>of</strong> the soil. This causes an increase<br />
in overland fl ow and may lead to rill and gully erosion when the run<strong>of</strong>f becomes concentrated. Many fi elds are<br />
terraced or have earth dams to retain water and once the fi elds are abandoned these soil and water conservation<br />
structures are no longer maintained. This increases the risk <strong>of</strong> terrace failure due to gully erosion (Figure 15) and piping<br />
(Figure 16) and once the terrace structures are broken the connectivity increases, which increases the risk that lower<br />
lying terrace walls will also collapse.<br />
Figure 15 Gully initiation on abandoned fi eld. Figure 16 Piping on abandoned grape fi eld.<br />
10 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
Vegetation strategies to mitigate erosion and reduce connectivity<br />
Two types <strong>of</strong> vegetation strategies can be distinguished<br />
to mitigate the degradation processes in these lands:<br />
(1) increase <strong>of</strong> vegetation cover on the fi eld, which<br />
should decrease the occurrence <strong>of</strong> concentrated run<strong>of</strong>f,<br />
and (2) planting <strong>of</strong> vegetation on critical spots with<br />
concentrated fl ow. The fi rst strategy also includes the<br />
maintenance <strong>of</strong> soil and water conservation structures<br />
until the vegetation on the terraces has suffi ciently<br />
recovered, e.g. restoration <strong>of</strong> terrace walls after heavy<br />
rainfall and construction <strong>of</strong> small dikes around existing<br />
gullies (Figure 17).<br />
A vegetation cover <strong>of</strong> more than 30% already decreases<br />
run<strong>of</strong>f considerably. To obtain a quick establishment <strong>of</strong><br />
vegetation cover perennial species with a fast growth<br />
rate, good vegetation cover and the ability to improve<br />
the soil properties should be used. Additional seeding<br />
and amendment <strong>of</strong> organic material can stimulate<br />
vegetation recovery.<br />
Figure 17 Small dike around deep gully.<br />
The second strategy focuses on the prevention <strong>of</strong> terrace failure and development or expansion <strong>of</strong> gully and rill<br />
erosion <strong>by</strong> planting vegetation on spots where concentrated fl ow can be expected. The water fl ow pattern can be<br />
easily identifi ed in the landscape. The locations where lines <strong>of</strong> concentrated fl ow coincide with a change in gradient<br />
(e.g. terrace wall) are hotspots for erosion (Figure 18). To mitigate concentrated fl ow erosion the root system <strong>of</strong> the<br />
vegetation is very important and especially grass roots appear to be very effective. Some native species that may<br />
be planted in these hotspots are grasses like Lygeum spartum, Brachypodium retusum and Stipa tenacissima in<br />
combination with deeper rooted shrubs like Anthyllis cytisoides, Atriplex halimus or Salsola genistoides.<br />
Figure 18 Map <strong>of</strong> abandoned terraced fi elds with fl ow paths and observed terrace failures (red points). These can be mitigated <strong>by</strong> planting<br />
vegetation, e.g. Lygeum spartum (right), in areas with concentrated fl ow just before the terrace wall.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 11
Hillslopes and gullies<br />
Problems <strong>of</strong> gully erosion<br />
Concentrated fl ow zones are hotspots in the landscape where gullies can develop and where large volumes <strong>of</strong><br />
sediment can be eroded. Several studies indicate that gully erosion may be responsible for up to 80% <strong>of</strong> total soil<br />
losses due to water erosion, whereas the area affected <strong>by</strong> gully erosion <strong>of</strong>ten only operates on less than 5%. In<br />
addition, once developed, gullies increase run<strong>of</strong>f and sediment connectivity in landscapes, there<strong>by</strong> transferring run<strong>of</strong>f<br />
and sediment rapidly from uplands to lowlands. The location <strong>of</strong> potential gullies is controlled <strong>by</strong> local topography<br />
(i.e. slope gradient and drainage area). Hotspot areas in the landscape where gully erosion is <strong>of</strong>ten a problem include<br />
existing channels, abandoned croplands and steep badland slopes under semi-natural vegetation.<br />
A B<br />
Figure 19 Illustration <strong>of</strong> a bank gully (A), which developed in an abandoned terrace and a permanent gully (B) in rangeland on loam soils.<br />
Vegetation strategies to mitigate erosion and reduce connectivity<br />
On croplands<br />
In addition to grass stems, which reduce run<strong>of</strong>f velocity, grass roots increase the topsoil resistance to concentrated<br />
fl ow erosion to a large extent and also prevent soil blocks from sliding <strong>by</strong> increasing the soil cohesion (Figure 20).<br />
It is therefore recommended to establish grass buffer strips or grassed waterways where run<strong>of</strong>f concentrates or at<br />
the downslope border <strong>of</strong> a fi eld.<br />
Downslope direction<br />
Figure 20 Illustration <strong>of</strong> Brachypodium retusum roots reinforcing the<br />
topsoil and preventing shallow mass movements on the<br />
gully wall.<br />
Figure 21 Plan view <strong>of</strong> fi eld with concentrated fl ow zone and<br />
erosion channel (bold line). Double drilling the zone <strong>of</strong><br />
concentrated fl ow in an ideal situation: i.e. the zone <strong>of</strong><br />
concentrated fl ow is drilled fi rst, then the entire fi eld.<br />
12 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
Double drilling <strong>of</strong> wheat or cover crops increases the resistance <strong>of</strong> topsoils to concentrated fl ow erosion (Figure 21).<br />
Studies have shown an average reduction in soil loss <strong>of</strong> 25% for double-drilled compared to single-drilled topsoils.<br />
On slopes with semi-natural vegetation<br />
Planting species in rows perpendicular to the fl ow direction will provide an optimal resistance to channel erosion and<br />
a better ability to trap sediments and organic debris compared to species planted at random or in rows parallel to<br />
the fl ow direction (Figure 22). Grasses such as Stipa tenacissima, Lygeum spartum and Helictotrichon fi lifolium are<br />
very effective for stabilizing steep slopes.<br />
Figure 22 Species planted in rows perpendicular to the fl ow direction. Example given for Stipa tenacissima tussocks on steep slopes.<br />
• Establish vegetation on gully fl oors. Gullies covered with at least 50% vegetation with high trapping effectiveness<br />
(e.g. Juncus acutus, Figure 23) in the gully fl oor as a percentage <strong>of</strong> total gully fl oor surface become inactive.<br />
• Establish vegetation barriers in gullies to further prevent soil loss. For example, vegetation barrier downslope,<br />
covering only 20% <strong>of</strong> a marly plot, can be suffi cient to trap all the sediments eroded upslope.<br />
Figure 23 Illustration <strong>of</strong> a Juncus acutus clump trapping organic debris and sediment.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 13
Channels<br />
Problems <strong>of</strong> soil erosion and land degradation in channels<br />
Channels form major pathways for sediments eroded from agricultural lands <strong>by</strong> gullies. The erosional activity <strong>of</strong><br />
gullies and channels are closely linked. As the channel erodes its bed, this erosion migrates upstream, leading to the<br />
extension <strong>of</strong> gully networks and creation <strong>of</strong> new gullies. Gullies may also form through the channel eroding its banks<br />
and adjacent valley walls. Four erosion hotspots are identifi ed in channels: bank gullies, valley walls, tributaries and<br />
the channel bed itself (Figure 24). In order to reduce the occurrence <strong>of</strong> erosion in channels, vegetation strategies<br />
need to be effective in decreasing excessive sediment supply from source areas, however also maintain suffi cient<br />
balance <strong>of</strong> run<strong>of</strong>f and sediment supply so as not to create new erosion areas.<br />
Incoming gully<br />
Figure 24 Hotspots <strong>of</strong> erosion that develop in association with channels.<br />
Vegetation strategies to mitigate erosion and reduce connectivity<br />
Some prior understanding <strong>of</strong> relations in the channel is required in order to assess suitable locations for strategies.<br />
The present status <strong>of</strong> the channel can be assessed <strong>by</strong> dividing it into a number <strong>of</strong> reaches, and classifying each<br />
reach into one <strong>of</strong> three zones:<br />
• Erosion zones are characterised as sediment supply areas.<br />
• Transfer zones link erosion and deposition zones; whilst they may also be a source <strong>of</strong> sediments their major<br />
function is to fl ush supplied sediments downstream.<br />
• Deposition zones are areas where sediments are deposited.<br />
Eroding banks<br />
and valley walls<br />
Eroding channel bed<br />
Consideration needs to be given to:<br />
• the nature <strong>of</strong> sediment supply and magnitude <strong>of</strong> fl ows within each zone, as this will guide plant selection;<br />
• the infl uence increased vegetation may have in reducing fl ow capacity <strong>of</strong> the channel and decreasing sediment<br />
supply to downstream areas (potential to cause a fl ood or erosion problem).<br />
A number <strong>of</strong> different vegetation strategies may be applied to the identifi ed erosion hotspots. These are outlined in<br />
Table 2 with reference to Figure 25.<br />
14 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
Table 2 Potential vegetation strategies applied to hotspots.<br />
Hotspot Vegetation strategies<br />
Bank gullies • Reduce fl ows through diversion <strong>of</strong> run<strong>of</strong>f from gully. Check condition <strong>of</strong> terrace banks and<br />
repair if necessary. Plant with grasses like Lygeum spartum, Brachypodium retusum and<br />
Stipa tenacissima in combination with more deeper rooted shrubs like Anthyllis cytisoides,<br />
Atriplex halimus or Salsola genistoides. Increase ground cover in fl ow lines to create<br />
grassed waterways and consider planting cover crops in fi elds.<br />
• Encourage deposition <strong>of</strong> fans and sedimentation before channel. Vegetate fans at base <strong>of</strong><br />
gully walls. Plant Lygeum spartum.<br />
Valley walls • Encourage deposition <strong>of</strong> fans and sedimentation at base <strong>of</strong> valley walls. Vegetate fans<br />
and base <strong>of</strong> valley walls. Plant with Stipa tenacissima, Lygeum spartum and Juncus<br />
acutus.<br />
Tributaries • Encourage vegetation at base <strong>of</strong> channel. Vegetate on raised areas <strong>of</strong> the bed. Plant<br />
Nerium oleander on coarse gravels and Tamarix canariensis on fi ne substrates. Build small<br />
log boulder structures to trap sediments and vegetate with Lygeum spartum and Tamarix<br />
canariensis.<br />
• Divert fl ow at confl uences. Build small log/boulder structures to trap sediments and<br />
vegetate with Lygeum spartum and Tamarix canariensis.<br />
Channel<br />
bed<br />
• Encourage more vegetation in areas with sediment. Where there is no sediment deposited,<br />
but obvious sources and transfer in zone, encourage deposition <strong>by</strong> planting vegetation<br />
upstream. This may need additional obstructions to cause initial deposition e.g. boulders<br />
or logs. Plant Nerium oleander on coarse gravels and combination <strong>of</strong> Lygeum spartum<br />
and Tamarix canariensis on fi ne substrates.<br />
Vegetate fans and<br />
base <strong>of</strong> valley/gully<br />
walls<br />
Check condition <strong>of</strong> terrace<br />
banks and increase ground<br />
cover in fl ow lines<br />
Build small log/boulder<br />
structures to trap sediments<br />
and vegetate<br />
Figure 25 <strong>Land</strong>scape diagram showing distribution <strong>of</strong> vegetation measures to reduce erosion and sediment connectivity along channels.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 15
Small catchments<br />
Problems <strong>of</strong> soil erosion and land degradation in small catchments<br />
Whilst erosion may start as a very small feature in the landscape (i.e. bank collapse, rilling across a fi eld) if nothing is<br />
done to control the erosion, it can quickly develop into a major problem that has signifi cant on-site (soil impoverishment)<br />
and <strong>of</strong>f-site impacts (silting up <strong>of</strong> reservoirs, increased fl ooding). Once pathways begin to form, they serve to further<br />
concentrate erosive fl ows. Small isolated areas <strong>of</strong> erosion (bank failure and rills) may link up and form larger erosion<br />
problems (gullies) that are much more diffi cult to control.<br />
Developing vegetation strategies to address problems<br />
Hotspots and pathways need to be identifi ed in the landscape. This identifi cation should begin at the smallest scale<br />
<strong>of</strong> the individual fi eld/terrace bank but should extend up to the scale <strong>of</strong> the small catchment. Vegetation strategies<br />
should be applied to hotspots and pathways with the aim <strong>of</strong> increasing the resistance <strong>of</strong> the soils to erosion and<br />
reducing the supply <strong>of</strong> sediments to downstream areas.<br />
Identification <strong>of</strong> hotspots and pathways<br />
Hotspots are locations <strong>of</strong> concentrated erosion and appear as points <strong>of</strong> high soil loss. The location <strong>of</strong> hotspot areas<br />
and pathways may be easily recognised <strong>by</strong> the landowner as they will <strong>of</strong>ten coincide with areas where continued<br />
maintenance is required after there has been signifi cant rainfall. The following is a list <strong>of</strong> some <strong>of</strong> the areas in the<br />
landscape where erosion hotspots and pathways tend to develop:<br />
• Natural depressions/drainage areas and where there is a marked increase in gradient.<br />
• Terraces where bank failures frequently occur or terraces that generate signifi cant run<strong>of</strong>f leading to the formation<br />
<strong>of</strong> rills/gullies.<br />
• Tracks and hardened areas where signifi cant run<strong>of</strong>f takes place during a rainfall event.<br />
• Abandoned lands where terrace/bank structures are in a state <strong>of</strong> decay due to lack <strong>of</strong> maintenance.<br />
Vegetation strategies to mitigate erosion and reduce connectivity<br />
As preceding sections have shown, a range <strong>of</strong> vegetation strategies may be applied to these hotspots and pathways.<br />
In the following example, these hotspots and pathways are identifi ed and a series <strong>of</strong> vegetation strategies are<br />
suggested to address the erosional problems associated with these areas.<br />
Figure 26A Mapped connectivity strategies that may be applied to the<br />
sub-catchment to reduce erosion and connectivity.<br />
Example: Sub-catchment <strong>of</strong> Cárcavo,<br />
SE Spain<br />
This is based on a small sub-catchment area <strong>of</strong><br />
Cárcavo, SE Spain. The map on the left (Figure<br />
26A) shows an outline <strong>of</strong> the fi eld terraces and a<br />
track crossing the catchment. The area is mostly a<br />
mixture <strong>of</strong> almond and olive trees with a small area<br />
<strong>of</strong> abandoned land. Pathways <strong>of</strong> run<strong>of</strong>f and erosion<br />
occurring in several events (red arrows) and areas<br />
where sediments were deposited (grey areas) are<br />
shown. The steep uplands and area <strong>of</strong> abandoned<br />
land were a signifi cant source <strong>of</strong> run<strong>of</strong>f. Many <strong>of</strong> the<br />
larger rills commenced immediately east <strong>of</strong> the road,<br />
with connecting pathways following the natural<br />
drainage line that exists in the landscape. There was<br />
also signifi cant run<strong>of</strong>f along the elongated terraces<br />
as they are not constructed on the contour.<br />
16 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
The map on the right (Figure 26B) gives an outline<br />
<strong>of</strong> the suggested strategies that should be applied<br />
to the hotspot areas and pathways to reduce the<br />
potential connectivity in the landscape. These can<br />
be summarised as follows:<br />
• Establish more vegetation on terrace banks.<br />
Suitable species include grasses like Lygeum<br />
spartum, Brachypodium retusum and Stipa<br />
tenacissima in combination with more deeper<br />
rooted shubs like Anthyllis cytisoides, Atriplex<br />
halimus or Salsola genistoides.<br />
• Plant vegetation on fl at terraces <strong>of</strong> abandoned<br />
lands and vegetate banks. Suitable species<br />
include Lygeum spartum, Brachypodium retusum<br />
and Stipa tenacissima.<br />
• Plant cover crops in tree lanes <strong>of</strong> all fi elds in winter<br />
time (cover up to 50% <strong>of</strong> fi eld area). Planted<br />
cover crops should follow the contour as much<br />
as possible. Recommend planting winter annuals<br />
and weeds.<br />
• Plant vegetation at sides <strong>of</strong> tracks. Suitable<br />
species include Brachypodium retusum.<br />
• Plant vegetation along the natural drainage line<br />
(grassed waterway). Suitable grass species<br />
include Brachypodium retusum. Where water<br />
accumulates plant Juncus sp.<br />
Figure 26B Vegetation strategies that may be applied to the subcatchment<br />
to reduce erosion and connectivity.<br />
Types <strong>of</strong> plants, strategies for planting and growth<br />
Selection <strong>of</strong> plants<br />
In choosing plants and developing a vegetation strategy to reduce erosion and sediment connectivity, consideration<br />
is given to the characteristics <strong>of</strong> the plants themselves and the location <strong>of</strong> the hotspots in the landscape where the<br />
strategy is to be applied. Desirable plant characteristics are: dense rooting system; high threshold for removal; ability<br />
to trap water and sediments; perennial or persistent; quick growth rate; germinates or propagates easily; endemic<br />
species that are not invasive; ability to withstand drought and an ability to grow in a range <strong>of</strong> substrates. Based on<br />
detailed studies, a list <strong>of</strong> plants which may be considered for developing vegetation strategies has been developed<br />
and is outlined in Table 3, overleaf.<br />
Suitability for different types <strong>of</strong> location<br />
While a mixture <strong>of</strong> grasses and shrubs are recommended for stabilising side-banks and increasing cover in Reforested<br />
and Abandoned <strong>Land</strong>s, it is predominantly grasses that are recommended for reducing erosion and connectivity in<br />
the other land-units (Croplands, Hillslopes and Gullies and Channels). In large gullies and channels the use <strong>of</strong> shrub<br />
Nerium oleander and Tamarix canariensis should also be considered, for their high resistance to erosion, potential<br />
to decrease fl ow velocities and trapping <strong>of</strong> sediments.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 17
Table 3 Potential plants to form part <strong>of</strong> vegetation strategies and be applied to land unit hotspots.<br />
<strong>Land</strong>-unit Types <strong>of</strong> plants<br />
Reforested<br />
land<br />
Grasses (Stipa tenacissima and Brachypodium retusum, Helictotrichon fi lifolium) and shrubs (side<br />
bank: Salsola genistoides, other hotspots: Rosmarinus <strong>of</strong>fi cinalis, Anthyllis cytisoides [fi rst step],<br />
Rhamnus lycioides, Pistacia lentiscus [second step]).<br />
Croplands Weeds, legumes and grass species.<br />
Abandoned<br />
lands<br />
Hillslopes<br />
and<br />
gullies<br />
Grasses (Lygeum spartum, Brachypodium retusum and Stipa tenacissima) in combination with<br />
more deeper rooted shrubs (Anthyllis cytisoides, Atriplex halimus or Salsola genistoides) on<br />
terrace wall.<br />
Grasses (Stipa tenacissima, Lygeum spartum, Helictotrichon fi lifolium) and shrubs (Salsola<br />
genistoides) on steep slopes. Grass species (Brachypodium retusum) and reed species (Juncus<br />
acutus) to vegetate drainage lines. For stabilizing gully fl oors a combination <strong>of</strong> grasses (Lygeum<br />
spartum, Stipa tenacissima, Brachypodium retusum), deep rooted shrubs (Salsola genistoides,<br />
Anthyllis cytisoides, Atriplex halimus) or trees (Tamarix canariensis) should be considered.<br />
Channels Grasses (Lygeum spartum) on fans. Grasses (Stipa tenacissima, Lygeum spartum) and trees<br />
(Tamarix canariensis) to stabilise valley walls. Larger tributaries/channels, consider either trees/<br />
shrubs (Fine substrate – Tamarix canariensis, Coarse substrate – Nerium oleander) and grasses<br />
(Lygeum spartum). Where water accumulates plant Juncus sp. and Phragmites australis.<br />
Note: For Sub-catchments, break up into land-units listed above and then select appropriate plants.<br />
Methods <strong>of</strong> seeding, planting and encouraging growth<br />
One <strong>of</strong> the main challenges in new approaches to soil restoration is how to deal with the lack <strong>of</strong> knowledge on how<br />
these plants may be used. In fact, the set <strong>of</strong> species that have traditionally been used is small and if new species<br />
have to be used, experience on nursery, transplant and soil preparation techniques have to be developed, in order to<br />
increase success. An alternative and complementary approach would consist <strong>of</strong> <strong>by</strong>-passing nursery steps and directly<br />
sowing seeds on favourable microsites which are naturally available or artifi cially created using structures.<br />
Grasses and shrubs may be planted directly on defective terraces in Reforested <strong>Land</strong>s. Planting may be more<br />
successful, particularly on side banks if small microstructures are built to promote trapping <strong>of</strong> water, nutrients and<br />
sediments. To counteract the negative effects <strong>of</strong> the pine litter layer, this may be removed to encourage growth <strong>of</strong><br />
seeded grasses and shrubs. The use <strong>of</strong> cover crops to cover the fi elds during the rainy season will reduce erosion in<br />
these fi elds. A range <strong>of</strong> weed, legume and grass cover crops can be considered, though potential costs <strong>of</strong> application<br />
can be avoided if weed species are used. In Cárcavo it is recommended that cover crops should not exceed 50% <strong>of</strong><br />
the fi eld and be restricted to the lanes between the trees. Where water supply is limited, further consideration may<br />
be given to only planting cover crops along drainage lines, edges <strong>of</strong> fi elds or along access tracks.<br />
Ongoing maintenance <strong>of</strong> water conservation structures (terraces and side banks) is important for decreasing<br />
connectivity, maximizing water usage and increasing vegetation cover in abandoned lands as well as reforested<br />
lands and croplands. Repair <strong>of</strong> failed terrace banks, planting grasses and shrubs on reformed banks and in areas<br />
<strong>of</strong> concentrated fl ow is required. Where natural drainage lines are evident in the landscape, whilst these also<br />
represent hotspot areas, they also form areas where water and nutrients are transmitted, providing ideal conditions<br />
for the establishment <strong>of</strong> grassed waterways. Improvements in the effectiveness <strong>of</strong> grassed waterways have been<br />
documented where double drilling techniques have been used.<br />
18 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
In seeking to reduce erosion and connectivity to channels, strategies are better applied further up in the headwaters<br />
in smaller catchments. Areas <strong>of</strong> deposition, and in particular where there are fi ne sediments are locations where<br />
grasses should be encouraged and planted. The use <strong>of</strong> structural interventions to alter conditions that favour<br />
vegetation establishment may be required in channels, in the situation where there is insuffi cient substrate for<br />
planting. Time is then given for sediments to be deposited behind these structures prior to planting; the ponding <strong>of</strong><br />
water behind the structure can also be benefi cial for improving conditions for plant establishment. In larger channels,<br />
efforts should focus on planting <strong>of</strong> larger shrubs and trees, as these will have the effect <strong>of</strong> reducing fl ow velocities<br />
and hence increasing the potential for sediment storage. While large vegetation could reduce fl ow velocity, overall it<br />
is regarded as reducing fl ood capacity because <strong>of</strong> reduced velocities and increased infi ltration, and hence trade<strong>of</strong>fs<br />
need to be considered.<br />
Summary and recommendations<br />
Summary<br />
This booklet comprises a set <strong>of</strong> guidelines that have been compiled based on detailed studies <strong>of</strong> vegetation and its<br />
positive effects in mitigating erosion and reducing connectivity at a range <strong>of</strong> scales. The purpose <strong>of</strong> these guidelines<br />
is to provide information on how problems <strong>of</strong> soil erosion and land degradation may be controlled <strong>by</strong> the application<br />
<strong>of</strong> innovative vegetation strategies with existing soil conservation measures. These strategies target specifi cally<br />
those hotspot areas in the landscape where erosion is a problem at present, or which, if improperly managed, will<br />
become a signifi cant problem. The approach is different from other approaches in that it identifi es hotspots and<br />
focuses on the application <strong>of</strong> appropriate vegetation species to these areas, whereas other approaches are applied<br />
across the entire landscape. These guidelines are suitable to dryland environments <strong>of</strong> the Mediterranean region <strong>of</strong><br />
southern Europe, and they are based on research in SE Spain.<br />
Recommendations<br />
These guidelines should be used to develop vegetation strategies to mitigate erosion and land degradation at the<br />
small catchment scale. More specifi c recommendations that apply to particular land unit and hotspots are listed<br />
below:<br />
• In Reforested <strong>Land</strong>s, microstructures which trap sediments and nutrients could be applied to the side banks and<br />
on terraces the needle litter layer removed to improve vegetation establishment.<br />
• On Abandoned <strong>Land</strong>s existing terraces should be maintained and failures repaired after events. Dense rooted<br />
grasses should be planted on reformed banks and in areas <strong>of</strong> concentrated fl ow.<br />
• Consider correcting terraces that are not constructed on the contour and breaking up long terraces, as these<br />
concentrate run<strong>of</strong>f and contribute to erosion problems downslope.<br />
• Establish winter cover crops in access lanes between trees, but cover should not exceed 50% <strong>of</strong> terrace. Cover<br />
crops should then be killed <strong>of</strong>f at the end <strong>of</strong> the winter period.<br />
• Plant vegetation cover along edges <strong>of</strong> tracks, particularly where these cross a drainage line or gradient changes<br />
such that the track begins to concentrate run<strong>of</strong>f.<br />
• Where there are natural drainage lines crossing fi elds establish grassed waterways. Double drilling techniques<br />
should also be used when seeding these areas. Establish vegetation on gully fl oors.<br />
• In small channels, revegetation efforts should focus on planting grasses in areas where there are fi ne sediment inputs.<br />
Small structures may be built to promote deposition and improve conditions for vegetation establishment.<br />
• In larger channels, efforts should focus on establishing larger shrubs and trees as these will have a greater effect in<br />
reducing fl ow velocities and trapping sediments, therefore reducing sediment connectivity to areas downstream.<br />
COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH 19
Contribution <strong>of</strong> RECONDES project to policy<br />
Much research has been undertaken within the European Union (EU) to understand the processes <strong>of</strong> land degradation<br />
and desertifi cation, to develop tools for modelling these processes and predicting impacts under future scenarios<br />
<strong>of</strong> climate and land use change, and to develop early warning systems and assessment <strong>of</strong> vulnerability. The<br />
research is now moving on to address the development <strong>of</strong> approaches and methods <strong>of</strong> combating and mitigating<br />
desertifi cation. The RECONDES project is a contribution to this, under the Sustainable Development, Global Change<br />
and Ecosystems Programme <strong>of</strong> Framework 6.<br />
The project RECONDES is entitled ‘Conditions for Restoration and Mitigation <strong>of</strong> Desertifi ed Areas Using Vegetation’.<br />
The focus <strong>of</strong> RECONDES is the mitigation <strong>of</strong> desertifi cation <strong>by</strong> the means <strong>of</strong> innovative techniques using vegetation<br />
in specifi c landscape confi gurations prone to severe degradation processes. Its major objective was to produce<br />
practical guidelines on the conditions for use <strong>of</strong> vegetation in areas vulnerable to desertifi cation, taking into account<br />
spatial variability in geomorphological and human-driven processes related to degradation and desertifi cation.<br />
These guidelines build upon present knowledge <strong>of</strong> degradation and desertifi cation processes and combine this<br />
with ecological knowledge about vegetation to consider strategies for land management at a variety <strong>of</strong> scales.<br />
Successful land management requires a holistic approach and the integration <strong>of</strong> many disciplines. These guidelines<br />
have been written mainly <strong>by</strong> ecologists, geomorphologists, hydrologists, soil scientists, modellers and those with an<br />
involvement with policy and its application.<br />
The RECONDES Project contributes directly to the objectives <strong>of</strong> the Global Change and Ecosystems Sub-Priority<br />
<strong>by</strong> providing major support to the EU Strategy for Sustainable Development. The innovative knowledge and<br />
products, resulting from the scientifi c and technological enhancement <strong>of</strong> the scientifi c state <strong>of</strong> the art include upscaling<br />
approaches, new sustainable and environmentally sound eco-engineering methodologies and appraisals for<br />
effective management strategies. These products support the world-wide scale strategies (Johannesburg Summit<br />
on Sustainable Development, 2002) and strengthen the knowledge for its future orientation. The development in the<br />
project RECONDES <strong>of</strong> guidelines to mitigate desertifi cation <strong>by</strong> sustainable practices including the use <strong>of</strong> vegetation<br />
is specifi cally devoted to the new EU 6th Environmental Action Plan. These guidelines aim explicitly at solving<br />
problems at the source, preventing <strong>of</strong>f-site problems.<br />
The project results also contribute to the priorities set under the UN Convention to Combat Desertifi cation<br />
(UNCCD, 1994) and are very suitable for adoption in the Action Plans that are being designed on national or regional<br />
level.<br />
20 COMBATING LAND DEGRADATION BY MINIMAL INTERVENTION: THE CONNECTIVITY REDUCTION APPROACH
Contributors:<br />
www.port.ac.uk/research/recondes/<br />
MD2029 0507<br />
<strong>University</strong> <strong>of</strong> Portsmouth Pr<strong>of</strong> Janet Hooke<br />
Department <strong>of</strong> Geography Dr Peter Sandercock<br />
Buckingham Building, Lion Terrace Dr Miguel Marchamalo Sacristán<br />
Portsmouth, P01 3HE, United Kingdom<br />
Tel: +44 23 9284 2482<br />
Fax: +44 23 9284 2512<br />
Email: janet.hooke@port.ac.uk<br />
Universite Catholique de Louvain Pr<strong>of</strong>. Bas van Wesemael<br />
Geography Department André Meerkerk<br />
Place Louis Pasteur 3, Louvain-la-Neuve<br />
1348, Belgium<br />
Tel: +32 1047 2056<br />
Fax: +32 1047 2877<br />
Email: vanwesemael@geog.ucl.ac.be<br />
Consiglio Nazionale Delle Ricerche Dr Dino Torri<br />
Istituto Di Ricerca Per La Protezione Idrogeologica Dr Lorenzo Borselli<br />
Unità Staccata di Firenze (IRPI-FI) Dr M. Pilar Salvador Sanchis<br />
Piazzale delle Cascine 15/28, Dr Marta S. Yañez<br />
Firenze, 50144, Italy<br />
Tel: +39 055 328 8290<br />
Fax: +39 055 321 148<br />
Email: dino.torri@irpi.cnr.it<br />
Consejo Superior de Investigaciones Cientifi cas Dr Victor Castillo<br />
Centro de Edafologia y Biologia Aplicada del Segura (CEBAS) Dr Gonzalo González Barberá<br />
Department <strong>of</strong> Soil and Water Conservation José Antonio Navarro<br />
Campus Universitario de Espinardo Dr José Ignacio Querejeta Mercader<br />
Murcia, 30100, PO Box 164, Spain<br />
Tel: +34 968 396 349<br />
Fax: +34 968 396 213<br />
Email: victor@cebas.csic.es<br />
Dr Carolina Boix-Fayos<br />
Universiteit van Amsterdam Dr Erik Cammeraat<br />
Instituut voor Biodiversiteit en Ecosysteem Dynamica (IBED) – Ir. Jan Peter Lesschen<br />
Universiteit van Amsterdam, Nieuwe Achtergracht 166<br />
NL 1018 WV, Amsterdam<br />
Tel: +31 20 525 5890<br />
Fax: +31 20 525 7431<br />
Email: lcammera@science.uva.nl<br />
Katholieke Universiteit Leuven Pr<strong>of</strong>. Jean Poesen<br />
Physical and Regional Geography Research Group Sarah De Baets<br />
K.U. Leuven, GEO-INSTITUTE<br />
Celestijnenlaan 200 E, B-3001 Heverlee, Belgium<br />
Tel: +32 1632 6425<br />
Fax: +32 1632 2980<br />
Email: jean.poesen@geo.kuleuven.ac.be<br />
The RECONDES project is funded <strong>by</strong> the European Commission,<br />
Directorate-General <strong>of</strong> Research, Global Change and<br />
Desertifi cation Programme. Project No. GOCE-CT-2003-505361.<br />
Produced <strong>by</strong> <strong>University</strong> <strong>of</strong> Portsmouth, 2007<br />
Sixth Framework Programme