Study the effects of rainfall and vegetation to halt the disappearance of the Mediterranean soil

An investigation by the Department of Agronomy of the University of Cordoba contemplates precipitation and vegetation cover variables to predict the appearance of gullies.

The appearance of gullies is one of the most common soil erosion problems in Mediterranean environments. Gullies are ditches or incisions produced by water draining off the surface of the soil. The formation of this type of trench affects more arid soils, naturally more sensitive to the negative impacts of erosion, and is becoming one of the main concerns of farmers in the Mediterranean region.

In low rainfall conditions, vegetation cover has an important effect in preventing the formation of gullies on the ground, but once rainfall increases it becomes the element that controls the formation of gullies. Faced with a year of high rainfall and a vegetation cover of less than 25%, it would be very difficult to avoid the incision of the gully.

This conclusion is reached by the research group of the Department of Agronomy of the University of Cordoba, coordinated by Professor Tom Vanwalleghem, after studying the appearance of gullies in the Cordovan countryside between 1956 and 2013, using aerial photos.

To predict the exact location of the gully, until now, the relationship between the local slope and the drainage area of the topographic thresholds had been taken into account, paying little attention to the variation of these thresholds over time.

The research from which these data are extracted is based on the study of the topographic thresholds of ravines formed in olive groves and arable crops between 1956 and 2013 in the western countryside of the Guadalquivir basin, analyzing the impact that rainfall, land use, and vegetation cover have had on the variation of these thresholds.

Thus, although there is not too much variation in the topographic thresholds for olive groves and arable crops, it is observed how the thresholds change over time and how this dynamic is linked to the characteristics of vegetation cover and rain.

To anticipate the formation of gullies or to foresee the exact place where the new ravines will appear is one of the ways to fight against the high figures of soil loss caused by this phenomenon which, in addition to causing serious damage to the farmer, threatens the biodiversity and sustainability of soils.

This is why Vanwalleghem raised the need to develop a standardized system to evaluate the predisposition of soils to the incidence of gullies using as a tool the memory that keeps the landscape. In this way, it will be easier to adapt soil management techniques and conservation measures for each specific area.

Deciduous trees should be pruned in their dormancy period, which in Mediterranean climates and in similar mild climates, means towards the end of winter. They should not be pruned in spring, as pruning causes the sap to rise in the plant “blood”, thus depleting the valuable energy and nutrients of the tree. If you have missed the boat, wait until next year or prune very lightly in summer.

On the other hand, broad-leaved evergreens and trees from tropical or subtropical climates are probably sensitive to cold and late frost and can suffer serious damage if pruned too early in the year. They should not be touched until all possibility of frost has passed.

In Mediterranean climates, spring is the best time for pruning as it anticipates the beginning of the growing season. It does not make much sense to allow the tree to spend energy on a new growth only to eliminate it a month later.

Unlike shrubs and bushes, the goal of landscape tree pruning is to develop and maintain the natural shape of the tree. For this reason, it is a mistake to shorten the branches, as this impairs the natural “flow” of the tree.

Instead, branches and entire limbs should be removed at their base, which is where the branch is attached to the main trunk or a thicker branch. An exception is when a stem sprouts forward on a long, thin branch that is out of proportion with the rest of the tree’s branches. It is best to cut such stems.

Pruning Fruit Trees

There is considerable confusion among home gardeners as to the best way to prune their fruit trees. It is common to see the cut branches as if the tree were a rose bush or some other flowering shrub. This is a technique taken from agriculture where the farmer is more interested in maximizing yields than in maintaining the natural appearance and beauty of the tree.

In my opinion, garden trees are ornamental, landscape elements in the first place, and fruit suppliers in the second place. In fact, pruning fruit trees as if it were a tree landscape (i.e., removing a few branches altogether) gives the best of both worlds: a dignified, natural-looking specimen that produces enough fruit to meet the needs of an average family.

The health of the tree

Another reason for not pruning fruit trees according to the agricultural method is the long-term health of the tree. Persistent pruning, which involves the removal of large volumes of material, depletes the tree’s energy potential and makes it more susceptible to pests and diseases. Remember that the tree, whether fruitful or not, is the most precious element in the garden, and that pruning should be carried out with the utmost care, conservatism and common sense.