Genetic conservation of forest tree species

Natural ecosystems represent an immeasurable source of current and potential genetic resources for man, both as a direct source of products and producing other services. A large part of these resources has been irreversibly destroyed, even before they are fully known, requiring urgent measures for their conservation. Furthermore, the exploitation of these resources has led to the depredation of ecosystems, with profound changes to them and disastrous consequences for the environment (KAGEYAMA, 1987).

The devastation of Brazilian forests has reached alarming proportions in all biomes, placing many species of microorganisms, animals and plants at risk of extinction. Human competition and disordered growth are possibly the main reasons for habitat destruction.

The ability of species to survive this situation depends on the greatest possible spatial heterogeneity in the constitution of these habitats. The constant removal of native tree species and the exploratory cultivation of some commercial species in monoculture have caused erosion in biodiversity in the various ecosystems spread across the country.

Studies began with native tree species, mainly from the end of the 80s, when some research centers began to pay attention to the conservation of genetic resources (FREITAS, et al., 2005).

Genetic conservation consists of a technical process, based on scientific bases, of permanent maintenance of the diversity and genetic variability of germplasm under special conditions, for the purposes of species preservation and genetic improvement. Therefore, there are strategies to save species in danger of extinction: in situ and ex situ conservation.

Forest Fragmentation

Brazilian forests have been undergoing an accelerated process of fragmentation, mainly as a result of urban expansion and activities linked to population growth. Thus, fragmentation is a process resulting from human action, which has two main components: the reduction of the area of ​​a large and continuous habitat, and the division of the remaining habitat into smaller fragments.

The reduction in the size of the fragments and their isolation in the form of islands trigger some ecological and population genetic processes with potentially disastrous consequences (ISHIHATA, 1999).

Fragmentation introduces a series of new factors into the evolutionary history of natural populations of plants and animals. These changes affect the demographic parameters of mortality and birth rates of different species differently and, therefore, the structure and dynamics of ecosystems. In the case of tree species, changes in the abundance of pollinators, dispersers, predators and pathogens alter seedling recruitment rates; and fires and microclimatic changes, which affect the edges of the fragments more intensely, alter tree mortality rates.

Forest fragmentation, in addition to reproductively isolating individuals that contain only a small sample of the gene pool of the original population (genetic bottleneck), can cause continuous loss of alleles due to genetic drift, if the remaining population remains isolated for several generations (SOUZA, 1997 ). In this small population, genetic drift can occur in the short term, which means having the frequencies of its genes move away from those of the original population, even leading to the loss of alleles. In the long term, there may still be an increase in inbreeding, resulting from the greater probability of self-fertilization and crossings between related individuals (KAGEYAMA, et al., 1998), which may reduce survival capacity in addition to adaptive capacity, fertility, vigor, size and productivity, among others (RITLAND, 1996).

This shows that the fragmentation process, triggered by the exploitation of natural forests to provide food, well-being and a better quality of life for a continually growing human population, is based on the unsustainable use of natural resources, particularly biodiversity. The result of this, in the long term, points to a situation completely opposite to that desired, ranging from a fatal deterioration in the quality of life, in the best of cases, to the total exhaustion of the means of human survival.

In this sense, attitudes have been taken with the aim of quantifying this impact and defining appropriate conservation strategies for ecosystems under intense exploitation (AZEVEDO, 2007).

Genetic conservation

Conservation is defined as the management by man of the biosphere so that it can produce the greatest sustainable benefit to current generations, while maintaining its potential to satisfy the needs and aspirations of future generations. In this sense, conservation is positive and encompasses the preservation, maintenance, sustainable use, restoration and improvement of the natural environment. The conservation strategy depends on the nature of the material, the objective and scope of conservation. The nature of the material involves the duration of the total cycle, mode of reproduction, size of the individuals and whether the material is domesticated or not. Furthermore, time (short, medium and long term) and the location where conservation will be carried out must also be considered (NASS, et al., 2001).

In tree species, each species must be represented by viable populations and this depends on the existence of broad genetic variability that allows adjustments to environmental changes over generations. Basically, there are two conservation strategies called in situ and ex situ, which are not exclusive and should be considered complementary (KAGEYAMA, et al., 2001).

Knowledge of the genetic structure of populations is understood as the fundamental step in carrying out conservation programs. Data generated by population genetics research can be used to define conservation units and priorities for the management of genetic resources, indicating areas and populations of greater or lesser importance for the preservation of taxa in question and allowing the development of effective strategies for conservation (CAVALLARI,

2004).

In situ genetic conservation

In in situ conservation, species are left in their natural habitats and the objective is to conserve as much of the number of alleles and/or the diversity of genotypes as possible so that evolution occurs continuously. This is important in generating new genes and genotypes, particularly in response to environmental changes and to confer resistance to newly developed types of pathogens; as well as for selection to occur continuously, also including coevolution between plants, animals and microorganisms. The benefit of this practice is the conservation of much more biodiversity, in an entire ecosystem, than just through samples of

germplasm of a species. Its disadvantage is that the germplasm cannot be used efficiently, as it is not available to be explored quickly (HAYAWARD and HAMILTON, 1997).

One of the interests of in situ conservation is to maintain genetic diversity within wild populations in natural or semi-natural forests, having the great advantage of allowing genetic processes such as gene flow within the species of interest (YOUNG and BOYLE, 2000).

Ex situ genetic conservation

Ex situ conservation refers to the maintenance of genes or gene complexes in artificial conditions, outside their natural habitat. This type of conservation can be done through permanent collections of pollen, seeds, tissue cultures, or plant collections maintained in the field, among others (PAIVA and VALOIS, 2001). The objective of ex situ conservation is to maintain representative samples of populations, that is, with enough alleles and gene combinations so that, after being characterized, evaluated and multiplied, they can be used for improvement.

genetic or related research (LLEIRAS, 1992).

The maintenance of ex situ populations has proven to be an important form of intervention in the conservation of biological diversity, given the growing number of species threatened with extinction. The programs have contributed to maintaining the genetic variability of populations, thus ensuring the permanence of species that would otherwise be unavailable to future generations. Populations can also serve as a stock of individuals for possible reintroductions or increasing the size of wild populations.

The closing thought

Given the devastation of forests caused by human demand for forest resources and food production, the effective conservation of native tree species is extremely important. To avoid the extinction of species that are important both ecologically and for humans, conservation strategies must be designed. The in situ Conservation of tropical trees is in a way more interesting because it maintains all biodiversity and its relationships in an ecosystem as a whole, but combined with ex situ conservation it becomes a powerful tool in the conservation of forest essences on the verge of extinction. Conservation studies on trees are increasingly relevant in terms of preserving, maintaining, restoring and improving the natural environment and also guaranteeing genetic resources and greater sustainable benefit for current and future generations.

Hélio Sandoval Junqueira Mendes1, Deise Reis de Paula2

1Biologist,

, 2 Biologist, FCAV/UNESP

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