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The term reforestation is synonymous with reforestation and refers to the introduction of forest mass into land that already had it in a relatively short time. However, the term forestation refers…
RESTORATION: SPECIES CHOICE
- Concept and Objectives
- Species selection
- Introduction of exotic species
1. CONCEPT AND OBJECTIVES
The term reforestation is synonymous with reforestation and refers to the introduction of forest mass into land that already had it in a relatively short time. However, the term afforestation refers to the introduction of a forest mass in places where that type of vegetation has never existed. Reforestation can be defined as the “set of techniques that need to be applied to create a forest mass, made up of woody plant species (trees or shrubs), which “is stable with the environment, in a terrain whose current vegetation is ineffective to a greater or lesser degree depending on the use assigned to the territory, and that, by adopting the desired characteristics, meets the purposes demanded of it” (Serrada, 1995). /span>
Forest mass is understood as the “set of woody plants that occupy a relatively large area and that interact between their components (they live in thickets), that evolve in relation to their environment and that is the object of treatment to obtain benefits from it” (Serrada, 1995). According to the definition, the fact that the forest mass is stable in the environment over time implies that its survival, development and reproduction do not depend on human intervention constant or intense, although sporadic silvicultural treatments are carried out (pest and disease control, pruning, thinning, fire protection, etc.).
On the other hand, the concept of reforestation has implicit objectives, the establishment of which constitutes the first step to follow when carrying out a project of this nature. In general terms, these objectives can be included in one of the following groups: producer objectives and protective objectives, giving rise to productive and protective repopulations, respectively. The first are oriented towards the production of raw materials or direct goods (fruit, wood, cork, etc.) and the second arise when the claims refer to obtaining indirect benefits derived from the simple existence of the mass (protection of the soil, wildlife conservation, etc.). It is the latter that are imposed in Spanish repopulations, intended to defend the soil from water or wind erosion, improve the conditions for the development of wildlife, etc.
- CHOICE OF SPECIES
The choice of the species will be made based on the previously established objective and the initial state of the land to be repopulated or season. This process is carried out in three stages: the first two select the species compatible with the station, taking into account ecological factors and the third consists of choosing from those selected in the previous two phases, taking into account economic criteria.
Once the species or species have been chosen, their ecotype or origin must be indicated, that is, where the seeds come from, so that the seeds are detailed and homologated with the destination station. ecological factors and that forecasts can be established about the characteristics of the mass to be created. When in the country producing the seed of the requested species there are studies regarding the geographical delimitation of the different origins, the key to this classification must be provided (García Salmerón, 1991). The widely distributed species or Linnaean species will present greater genetic variability than those with a more restricted distribution, Jordanian species, given the variability of the environment throughout their natural area.
In the first stage, the ecological factors to be considered, following an orderly selective process, are: phytogeographic factors, climatic factors, physiographic factors and edaphic factors.
Phytogeography or Botanical Geography studies the geographical distribution of plant species. Therefore, the first step will be to draw up a list of native species, along with ecologically compatible exotic ones.
The climatic factors to take into account are: radiation, precipitation, temperatures and air movement. The effects of these factors on photosynthesis and, ultimately, on development, must be considered globally and not individually, which is why it is necessary to have a Climate Index or Climate Study that quantifies the capacity of a climate to produce biomass. Methodologies based on phytoclimatic classifications can be used using climodiagrams (Allue, 1990) or bioclimatic diagrams (Montero de Burgos and González Rebollar, 1982; García Salmerón, 1980). The selective process using the bioclimatic diagram is as follows (García Salmerón, 1991):
– The first selection is made by admitting all species whose IBS (Dry Bioclimatic Intensity) is equal to or greater than the seasonal IBS.
– The second selection uses the thermal factor, taking into account its influence on photosynthetic activity. The climatically optimal station, from a thermal point of view, will be the one that has a free basic temperature equal to the optimal one, having completed the selection. However, this does not happen frequently, so we usually proceed as follows:
* The species are discarded when TmE-Eme>1 ºC, Tme being the optimal basic temperature of the species and TmE that of the station.
* The case in which Tme>TmE is preferable to Tme
– If there is more than one usable species left after applying the two previous criteria, the one with the highest production will be selected, when the repopulation is productive, or the most appropriate for fighting. against water erosion, if it is a protective repopulation. When it comes to mountainous terrain, the data collected at a nearby weather station only approximately reflects its climatology, so the factors must be taken into account. physiographic parameters of altitude, orientation and slope, given their influence on climatic factors. Altitude influences through temperature, precipitation and radiation. Likewise, the thermal gradient with altitude depends on the orientation of the slope and the orographic system and the rainfall gradient depends on the general orographic situation.
When it comes to forest vegetation, edaphic factors have less influence than climatic factors, except in extreme cases, due to the plasticity of this type of vegetation: nutritional requirements are minor, since wood is composed mainly of the elements that air and water can supply and, in the case of Linnaean species, the degree of adaptation to edaphic conditions is high when the rest of the environmental conditions are favorable. . The soil characteristics that are truly important are those that in a certain way replace the climate: a high water retention capacity and easy transfer of moisture from wet to dry periods, equivalent to precipitation in the transfer period; Depth replaces precipitation, since it allows water to be extracted from greater depths, when the upper layers have reached their withering point. These properties, water retention capacity and depth, can be modified to a certain extent in a favorable way, through soil preparatory work. However, the soil will be studied from two points of view:
– Degree of evolution or degradation, to obtain information about the impact of repopulation, its future evolution after repopulation and the possible improvement of its properties.
– Interpretation of the following parameters: depth, stoniness, texture, structure, organic matter content, electrical conductivity of the soil solution, active limestone content and reaction (pH) .
Once these characteristics are known, they are compared with the needs of the selected species, discarding those for which the soil is limiting. The presence of active limestone, permeability and salinity are the characteristics that are most frequently determining.
Interesting methodologies to follow are: the one proposed by Elena Rosselló et al. (1990) and the analysis of integrated edaphoclimatic factors for the choice of species developed by Gandullo and Sánchez Palomares (1994).
In the second stage of selection, the biological factors will be taken into account, which include: phytosociological factors, competition factors with the current vegetation, the possibility of mycorrhization, behavior against pests, diseases and predators, and indirect anthropozoic influences.
The study of phytosociological factors involves knowledge of the current floristic composition of the terrain, which informs about seasonal conditions, the climatic plant association and the state of degradation of the vegetation.
It will be necessary to determine which of the selected species will establish unacceptable competition with the current vegetation. With respect to mycorrhization, this is guaranteed by the inoculations carried out in the nursery. As for pests and diseases, some species can be discarded due to their low resistance. The human factor, on the other hand, may be incompatible indirectly through its activity and, especially, that of an industrial nature.
In the third stage, economic selection criteria will be applied to the list made during the two previous stages. In Spain, given the prevailing conditions of intense summer drought combined with great soil degradation, it is common that at the end of the second stage this list is reduced to a single species. The application of the aforementioned economic criteria is carried out in direct relation to the objective of repopulation.
Among the economic factors that directly influence profitability are: establishment costs and technical and administrative procedures, losses due to agents or susceptibility to those not considered in the factors biological, the amount of growth and the usefulness and value of the products.
Regardless of profitability, there are indirect economic factors that can advise the choice of a species and that are usually related to the extrinsic conditions of the forest: distance from the market for certain products, structure of the raw materials transformation industry, availability of labor, etc.
Sometimes there are economic reasons linked to the need to have a product with certain technological characteristics, for strategic reasons of different kinds. Thus, technological factors can refer to: the characteristics of the product itself because it is better suited to a specific industry, or due to the market demand situation, etc.
- INTRODUCTION OF EXOTIC SPECIES
An exotic species is considered to be one for which the vector of its propagules when introduced outside its natural habitat is man.
Its use may be considered in the following cases:
– When the spontaneous vegetation is poor in its development and, therefore, of very little profitability.
– When the native species is technologically inappropriate for the demands of a given industry.
– When there is no native species that is completely satisfactory for vegetating in a given season.
The stages to follow in the selection process will be the same as for native species, with special emphasis on:
– The risks of pests and diseases, since indigenous pathogens can present greater virulence compared to new species, or new pathogens, in the event that they are transferred with the species will lack natural enemies in the introduction zone.
– The scarcity of genetic variability.
– The scarcity of genetic variability.
– The risks of frost.
However, once the ecological factors between the area of origin and introduction have been positively approved, an exotic species will have to meet the following requirements:
– That its use represents an advantage over native species.
– That its introduction does not entail irreversible damage: edaphic alterations, important alterations in the water cycle, uncontrolled spread, etc.
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