In this article we will discuss about:- 1. Definition to Clonal Forestry 2. Applications of Clonal Forestry 3. Implementation Programme 4. Advantages 5. Disadvantages.
Definition to Clonal Forestry:
Vegetative propagation can be used for large scale propagation of identified and tested clones with valuable properties. Such extended use of superior clones, is referred to as clonal forestry. Clonal forestry refers to the large-scale deployment of relatively few (10 to 50), known-superior clones that have proven their superiority in clonal tests. Clonal forestry can be defined as ‘the deployment of tested clones.
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The chief difference between clonal propagation and bulk propagation is in terms of the number of genotypes involved and the proven superiority of clone used in clonal forestry. The genotype effect consists of two components: additive and non-additive. Through sexual propagation, while it is easy to pyramid additive effects, due to recombination of the parental genotypes, the non- additive effects cannot be exploited.
The potential to utilize non-additive effects is one of the attractive features of clonal forestry, since it offers possibilities of capturing additional genetic gain. Clonal forestry would then increase the genetic gain realized in the production forest compared with bulk propagation due to the use of tested genotypes. Clonal propagation offers a chance to propagate a superior genotype that would be lost through sexual reproduction.
Applications of Clonal Forestry:
Clonal forestry in tree breeding programme has been emerging as a strong attraction to the traditional seed orchard breeding system. It is now recognized that most efficient genetic improvement to trees can happen by combining the controlled breeding of highly selected parents with the clonal magnification of the very best offspring from each cross. Clonal forestry has been recognized as a method offering huge potential benefits in terms of tree improvement gains, uniformity and ‘customization’.
The key to clonal forestry is the ability to propagate selected, superior proven clones on a large scale. Through clonal forestry it is possible to deploy some unique reliable genotypes continually for many years, even several rotations and the possibility to adopt clone-specific management practices including matching clones to specific site types and optimizing silvicultural regimes for different clones.
Clonal forestry would be relevant under certain conditions namely:
(1) When high performing individuals, proven as such through careful screening and evaluation in field tests are available.
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(2) When there is sufficient number of superior clones which can be mass propagated in equal numbers of each clone in order to maintain a “variation in space”, new, possibly partly overlapping sets of clones, must be used each year.
(3) When more productive and more resistant clones are continuously injected into the planting programmes, through continuous genetic improvement programmes in order to maintain “variation in time”.
One of the fundamental requirements for initiation of a clonal forestry programme is sufficiently refined cloning technique for the species. Angiosperms have been mostly into clonal forestry, since, the cloning techniques were well established in many of them. Propagation of trees vegetatively was originally used for the species which reproduced vegetatively under natural condition such as Poplars, Cryptomeria etc. Clonal plantations of Cryptomeria have been grown in Japan since the 1400s to provide an alternative to the use of natural forests.
Later on, many researchers multiplied the selected superior trees, mostly through cuttings and grafting for use in seed orchard and also to preserve germplasm in banks. The interest in clonal forestry increased primarily due to improvement in vegetative propagation techniques in particular, the refinement of the procedures for rooting of cutting and other methods of somatic propagation. Recently, techniques have been developed in many forest tree species for large-scale propagation from cuttings at costs similar to those of seedlings.
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There has been growing interest in using the techniques of clonal forestry and thereby, exploiting the considerable amount of genetic variability already existing in the natural populations of forest tree species that have been amenable to vegetative propagation and partly because of tremendous yield improvement by adopting the clonal forestry approaches.
The most widespread use of clonal plantings has been with the willow family (Salicaceae), involving willow (Salix) and poplar (Populus) species and hybrids. Several species in the genus Eucalyptus, especially Eucalyptus grandis and several of its interspecific hybrids in many tropical and sub-tropical countries have also been subjected to clonal forestry. Cryptomeria japonica, mainly in Japan and Picea abies in Europe are further examples of successful clonal forestry programs. More applications of clonal forestry like in Christmas tree and landscaping in urban settings are being made.
Clonal forestry is not a breeding strategy, but an operational option. Hence, an important requirement for a successful clonal forestry programme is the existence of an underlying breeding program of selection, breeding and testing to identify clones of ever-increasing genetic merit.
Development of superior clonal lines which involves establishment of long term genetic testing of clonal lines developed through breeding programmes is a pre-requisite for initiating clonal forestry programme. This has to be constant process involving constant up gradation of clones in use, incorporating the results of the ongoing breeding programme. Techniques aimed at early selection will be an added asset in the development of a successful clonal forestry programme.
Implementation of a Clonal Forestry Programme:
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The important steps in implementation of a clonal forestry programme are as detailed below:
i. Selection of Trees for Clonal Propagation:
The selection criterion for clones varies with species, object of management and the end use. Selection of genetically true to type clone is done after correct identification and proper labeling. Generally, a dominant tree with good apical dominance, free from pests and diseases and free from genetical disorders with a history of superior phenotypic performance is selected. Clones can be specifically chosen to exploit different ecological niches on the merit of different mechanisms for resistance to a particular pest; and/or to increase genetic diversity of traits observed.
ii. Number of Clones to be Selected:
The number of clones to be selected depends on rotation age, intensity of forest management, genetic variability of the species and clones involved, the likely risks and the acceptable loss levels. The number of selected clones is based on the criteria that we should achieve the greatest improvement by selecting only the best clones within acceptable limits of the dangers of destructive losses in the forest.
Hence, the safe and reasonable number of clones is recommended to be 7 – 30. In a stress affected area, more number of clones should be used. There are special conditions such as, severe insect or disease infested areas or very severe environment where in, very few clones may be justified.
iii. Clonal Maintenance:
The selected clones have to be maintained and multiplied under strict sanitary conditions to prevent reinfection. Measures should also be taken for immediate detection of any reinfection or any change in the original stock.
iv. Clonal Multiplication:
Identified superior clones of proven quality are assembled in an isolated area with proper labeling. These clones are vegetatively multiplied on a large scale after establishing under field condition. Large-scale plantations can be raised from clones obtained from clonal multiplication area.
v. Clonal Testing:
To identify suitable clones for deployment, systematic screening of clones for productivity attributes and their adoptability to adverse environment is necessary. Testing of clones should be done under multi locations with sufficient number of ramets from each clone. Testing of clones at multiple test sites provides information on adoptability of clones in varying environmental conditions.
White et al (2007) has given the following sequences for a typical clonal forestry programme. The program starts with the establishment of clonal trials on several sites in the planting zone to test the clones for suitability. Each test site can contain multiple ramets with large numbers of clones. These ramets are planted in randomized, replicated designs, usually in single tree plots to facilitate the precise ranking of clones. At appropriate selection age, measurements taken in the tests are used to predict clonal genetic values.
The best ones are used for operational deployment. If there is substantial clone x site interaction, then specific clones are chosen for deployment to particular types of sites within the planting zone. The selected clones are then asexually propagated on a large scale, to produce plantlets for operational forestation.
These plantlets have the same genotypes as the selected clones. Later on, with increased experience with selected clones, clone specific management prescriptions in all phases (nursery, plantation and processing facility) can be developed with concomitant cost savings and gains in efficiency of operation.
Advantages of Clonal Forestry:
The greatest advantages in clonal forestry are derived from use of selected superior clones that are reproduced and deployed true-to-type in operational forestry. Clonal forestry offers the only option for complete capture of non-additive genetic variance and since, the deployed clones retain their entire genetic composition. Through clonal forestry, it is possible to exploit genotype x environment interaction through site-specific deployment of tested clones to edaphoclimatic conditions in which they are known to perform well.
Hence, clonal forestry offers the greatest potential to deliver the benefits of the best genotypes from a controlled cross. Clonal forestry ensures maximum genetic gains from selecting and mass- producing best individuals. This is the best method for early deployment of improved material for commercial purpose and saves time.
Clonal forestry can ensure enhanced plantation productivity and economic benefits by mass propagating superior plants in the breeding programme. It can lead to increased productivity in the forests. There can also be substantial economic gain by ensuring better return on investment in both operational forestry and for breeding programme. This can also mean that less land need to be devoted to production forestry and more forest land available to meet environmental (e.g. increased biodiversity) and social (e.g. recreation) requirements.
Relative uniformity of clonal forests offers commercial advantages for the market, for the forest manager and for the plant producer. Overall performance of the clones can be very close matching with particular soil and cultural environments that optimize commercial utility of the clonal forests. Clonally forestry will ensure that all the trees reach harvestable stage at the same time and with the same morphological and chemical characteristics.
There will be increased predictability and repeatability of the crop. Organizations desiring uniform plantations to reduce costs of harvest and produce more uniform products can even establish monoclonal plantations in which a single clone can be planted over the entire extent.
Disadvantages of Clonal Forestry:
Although there are many advantages for clonal forestry, there are a large number of disadvantages and concerns in adopting clonal forestry. The most important disadvantage is the problems created due to reduced genetic diversity. Reduction in genetic diversity can make the crop highly vulnerable stresses like to pests and diseases that the crop may not be exposed till then.
The unpredictability in clone x environment interaction could be a serious disadvantage for a long term venture like forestry, where changes in ecosystem condition is possible and loss of adaptation to long term survival would be a major drawback. This disadvantage however, could be partly avoided by increasing the use of superior clones. Apart from this, genetic diversity has a better ecological advantage as different niches in a site is used up more efficiently.
Moreover, such a diverse crop will offer more niches for other living beings too. Social and political risks, including public perceptions are some other disadvantages of clonal forestry. Worries about monoclonal forestry can limit the legally permitted and publically acceptable areas of vegetative propagation in forestry. Generally uniformity in forests is aesthetically poor and socially unacceptable.