Tree Improvement, Tree Selection and Tree Provenance

Introduction

The tree improvement concept comprises two components viz. Phenotype improvement and genotype improvement.  The three terms commonly used in tree improvement are: Forest tree breeding, Forest genetics and Forest tree improvement. Forest tree breeding activities deal with solving some specific problems or produce a desired product such as development of post resistance or strains of possessing superior wood quality.  In Forest genetics the activities are restricted to genetic studies of forest trees.  Forest tree improvement indicates the improvement of overall yield and quality of forest products by combining the forest management activities, with control of parentage.  Tree improvement includes the practices of silviculture and tree breeding meant to enhance total yield.  Tree improvement is an additional tool of silviculture that deals with genetic make up of the tree to be used in forest practices.

The main objectives of Tree improvement are to maximize the gain per unit time and space through selection and development of improved genotypes and to maintain large and diverse genetic base for continuing successful Tree improvement programs for many generations. Forest trees are wild and least influenced by human activities; however there is an opportunity to make improvement in such races. In tree species large variability exists which may be owing to geographic (provenance) sources, stand and sites and geographic variation is important for its survival and adaptability. Individual tree variability has economic importance such as clear bole stem and specific gravity.

Advantage of Tree Improvement:

1. Change in genetic make up of the tree in permanent.
2. The genetic material can be kept intact for indefinite time by means of vegetative propagation.
3. Great genetic variability is present in tree stand which can not be changed greatly by human action.
4. The wide genetic variation enables wider adaptability.

Limitations of Tree Improvement:

1. Large area is required for storage of desired genetic material for testing. 
2. Size of the trees also creates problems to carry out different breeding activities height and diameter measurement, seed collection etc.
3. Cost and effort of producing new seed crops per year is high.
4. Different trees possess different growth curves.  Therefore, juvenile and mature correlations are not satisfactory for growth characteristics.
5. Lack of seeds of known and desired genetic background.
6. Requirement of good, permanent record, because tree improvement is a long term process. 

Selection of Tree species and traits to be improved:

1. Demand for plantation of the species
2. Economic value of the species
3. Amount of genetic variation within the species
4. Cost of breeding production vs economic value and gain.
5. R and D conducted by other organization.

Methods of tree improvement: 

The active elements of forest tree genetics and improvement are the following: 

1. Assessments of original genetic variability 
2. Selection of desirable genotypes and phenotypes
3. Development of trees or population containing desirable genotypes and phenotypes 
4. Capture of the benefits derived from genetic improvement. 

Provenance tests

Tree improvement program involves all practices designed to produce genetically superior trees. The most important step in any tree improvement program is the right choice of the species followed by the selection of suitable provenance within the species.  It is necessary to conduct species and provenance tests before making the right choice of species and provenance for a specific site. 

The objectives of species or provenance selection is to identify a suitable species and search for the desirable genes or gene combinations accumulated over the generations in a particular population in that species. 

In selection procedure for species or provenance, whether set out classical or, for plantation forestry the following criteria have great significance. 

1. Adaptation to climatic and edaphic condition.
2. Resistance to pest and diseases 
3. Productivity
4. Quality 

The tree improvement programs are started at species level; however, these may be initiated at provenance level if the species is already identified.  Genetic grain can rarely be accomplished directly by individual tree selection without first selecting the provenance.   

Species Testing: 

Species elimination phase: 

1. Compare the performance of a large number of different species on one or a number of sites. 
2. Duration of trials is commonly 0.1 to 0.2 times the rotation age. 
3. About 20 to 40 species could be tested in the initial stage. 
4. Continued the introduction of small number of species and eliminate the low performance species. 

Growth phase/Species- testing phase: 

1. It is adaptability phase 
2. This phase is the comparison of restricted number of promising species selected or the basis of previous experiment. 
3. Properly designed lay out for statistical analysis. 
4. Plots must be large enough to enable reliable assessment.  The expected final size of the tree is important. 
5. Promising potential species are tested and compare in largest plots for longer periods (0.25 to 0.5 times) the estimated rotation length.

Species proving phase/ Pilot Plantation: 

1. Statistically valid experimental design is needed i.e. proper blocking replications, randomization, plot size etc. 
2. Plots must be large enough to provide data or growth and yield for full rotation.
3. Other management techniques may be taken up for testing viz. 
   1. Different types of nursery stock and nursery method 
   2. Different method of ground preparation
   3. Different planting methods 
   4. Spacing and thinning trials 
   5. Different weeding intensities 
   6. Pruning trials, 
   7. Fertilizer and herbicide trials. 

Provenance Testing: 

After the selection of most suitable species, the question is of the source or location of collecting seed for large scale afforestation programs. 

Seeds from different eco-environments in the species distribution range are collected for testing on distinct sites to find out most suitable ones.  The ideal sequence of provenance-testing trials is initiated from preliminary testing stage followed by intensive testing with suitable experimental design. 

1. Range- wide Provenance Phase; 
   1. The objective of the phase is to determine the extent and pattern of variation among provenances of a species 
   2. About 10-30 provenances are suggested at the stage according the range of geographical distribution and climatic variation in the species. 
   3. Testing lasts for a duration of 0.25 to 0.5 times of the rotation age. 

1. Restricted Provenance phase 
   1. The objective of this phase is to find out sub regions and ultimately provenances most suited to the sites under test
   2. Sometime, the differences to be detected between the provenances may be small or even within a small geographic sub-region; large differences in performance may exist. So, statistical experimental design is necessary. 
   3. Generally 3-5 provenances are tested for duration of 0.5 to 1.0 times of the estimated rotation at appropriate size of plots. 
   4. This phase often run concurrently with species proving phase
   5. Local land races and other geographical races should be included whenever possible. 

Provenance – Proving Phase 

1. At this stage 1 or 2 provenance will be usually selected 
2. Procedure is as species –proving phase.

Pilot planting; 

1. Pilot plantation in large areas often established. 
2. Such plantations may demonstrate the viability for planned programs.
3. Provide an opportunity for carrying out many trials for the improvement in management system and cultural techniques for tree improvement. 

Sources of Variation

The first thing to do for tree improvement program is to determine the amount, cause and nature of variation that is present in the species of interest and learn how to use it. Assessing of variation requires time and effort of tree improver.  During the study of variation in forest trees one find lot of diversity in nature.  The diversity is more in native species.  The place of origin of a species is the place of diversity.  The diversity or variation is the major factor for bringing about changes to make the species adaptive to a particular environment and help them to change with the changing environment for their survival.  As such, some species are growing in plains and hilly tract under different environmental condition.  The natural variations are the result of continuous environmental selection for generations.  The variation observed differs phenotypically and genetically.  These variations are important source for tree breeder to improve a species through selection and hybridization.  The variation can be successfully utilized for the adaptability of a species to a particular area e. g. cold hardiness, drought resistance etc.  The variations can help in checking the epidemic caused by insect damage, in checking pathogen or a virus attack and in the selection of suitable genotypes for different end uses of a species. 

Zobel et al, 1960, have grouped the variation for wood properties in forest trees as geographic variation, site variation within provenances, Stand variation within sites, individual tree variations with stands and the variability within individual trees. 

Types of variation 

1. Environmental variations
2. Genetic variations.

Environmental variations

1. It is the result of nature's variability in rainfall, temperature, wind, soil depth, humidity.
2. Human interfere also create these variations by creating micro environment for example, establishing industries, canals dams, roads. 
3. These variations are ecological variations, racial variations and ecotypes variation. 

Genetic Variation: 

1. Wood quality and tree form are major source of genetic variations
2. Genetic variations are of two types. 
   1. Additive
   2. Non additive 
3. Many tree characters are believed to be under the control of additive variance, for example specific gravity of wood, clear bole. 
4. Dominant gene governs the trait.  However, dominant gene or recessive genes are allelic to each other. 
5. Dominant genes express both homozygous and heterozygous state.  Where as recessive gene express only in homozygous state. 
6. Epistasis variance is due to interaction among gene loci. 

Causes of Variations: 

Environment:

1. Depending on environment there are xerophytes, hydrophytes species.
2. Teaks have also different races suitable for dry areas and wet areas. 
3. Due change in environment, races and ecotypes are developed to become adaptive to that particular environment. 

Geographic: 

1. Longitude, latitude and altitude bring changes in species. 
2. As altitude change species remain same but genotypes charges to adapt. 

Genetic: 

1. The change in gene frequency from one generation to another brings greater variability. 
2. These variations are caused by 
   1. Mating system 
   2. Mutations
   3. Polyploidy
   4. Gene flow 

Mating system

1. Cross-pollination increases heterozygous population
2. Self pollination increases homozygous population. 
3. Most of the forest trees are cross pollinated and hence they have more variations e. g Eucalyptus and Poplar. 

Mutation: 

1. It is sudden change in genotypes 
2. It helps in maintaining variability in species. 
3. Mutations are classified as 

1. Cytoplasmic mutation 

   Hereditary changes that arise in cytoplasm and transmitted by it are called cytoplasmic mutation. 

2. Nuclear mutation 

   It occurs due to change in chromosome number.  They are of the following types. 

Gene Mutation: 

1. Genes are situated on the chromosome in large number and are stable. 
2. Due to mutation some changes occur in gene.  This is the gene mutation. 

Chromosomal Mutation: 

1. Genes are arranged on a chromosome and number and sequence of position of chromosome are stable. 
2. The change in number and sequences of chromosome within ?without affecting mutation is known as chromosomal mutation. 

Somatic Mutation: 

1. Changes occurred in the cells of or actively growing organism, except the germ cell is a somatic mutation. 
2. These mutations exist in vegetative propagation. 

Genomatic mutations: 

1. A change in chromosome number is called genomatic mutation or polyploidy. 

Polyploidy 

1. As a result of change in chromosomes, or increase in chromosome number in some multiple of the haploid number commonly takes place.  This phenomenon is called polyploidy.

Gene Flow: 

1. Migration of gene from one population to another through crossing is called gene flow 
2. Gene migration takes place either through seeds or introducing of trails, when the out crossing takes place with the original population.

Man Made Variation:

1. Clear felling in large area causes gene erosion.
2. Introduction of new variations to recover the area.
3. Variation also created during the process of research and trials. 

Plus Tree Selection

Sustainable forest management is crucial to sustain yield through the application of improved silviculture methods. At present there is a gap between production and demand of forest products. So, some immediate remedial measure to control ecological disasters and increase the forest product is required. To meet this challenge we have to save and improve existing forests and raise large scale plantations in depleted areas using genetically superior indigenous and exotic fast growing species.  The selection program must be followed by progeny testing of the selected phenotypes, to determine, the actual genetic worth of the tree, because the genetic effects are transmitted from parents to offspring but not those of the environment. To achieve the maximum gains per unit area per unit time, there is a strong need for immediate selection superior phenotypes.  The criteria and procedure for the selection of the right tree, and testing of its progeny is important. 

Method of plus tree selection; 

1. Selection of plus tree should not be haphazard, it has to be done with systematic procedure
2. Tree selection should be made from a maximum possible stands.
3. The candidate trees are selected from the good stands.
4. Economically important traits are considered for selection. 
5. Sometime a single trait selection (Tandem selection) for specific purposes is considered. 
6. Tandem selection is the selection practiced for one trait at a time until satisfactory improvement is achieved.  However, efforts are made towards improvement until each has seen improved to the desired level. 
7. Tow kinds of forest stands of unknown pedigree, e. g even aged wild stand or plantation and uneven aged scattered mixed species. 
8. Both types of stands require different first generation selection procedures. 
9. Selection methods are: 
   1. Comparisons tree method 
   2. Independent culling method
   3. Total score method
   4. Regression method
10. Individual tree selection is best in pure even aged natural stands or plantations.
11. Comparisons tree method does not work when trees are grown in uneven aged stands 
12. Independent culling method is more efficient in uneven aged stands for multi trait selection. 
13. Other important methods of selection for uneven aged stands are mother tree selection.

Evaluating Plus/candidate

Comparison Method: 

1. Suitable for plantations and natural stands of uniform age 
2. The comparison is made under economic importance and the traits 
3. Comparison trees are selected from dominant or co dominant crown with similar age
4. Effectiveness of the method can be improved by increasing the member of comparison trees. 
5. Candidate tree is designated as a plus tree, if it proves superior to the comparison trees, otherwise rejected. 

Precautions for candidate-tree selection; 

1. Systematic search for plus tree selection must concentrated on good stands
2. Selection should be done from uniform age and site condition
3. Isolated or border trees are excluded 
4. Age of tree should be half of rotation 
5. Not more than 3 to 4 trees are selected per hectare.
6. Candidate trees are selected from upper crown in a stands
7. Comparison trees are selected near from the candidate tree. 
8. Candidate tree should be 5% superior to height and 20% in dhb 
9. Candidate tree must be free from pest and disease.
10. Stem should not be crooked bole. 
11. Trees should be good seed production capacity 
12. Select few trees (30/40) from large part of species distribution
13. Trait of economic significance should be determined by the objective of plus tree selection. 
14. Trait selection should be arranged according to economic priority. 
15. Record ownership, geographical information and map of the area of plus tree selection. 

Independent culling method. 

1. It is the selection made from all characters but reflect all individuals that fail to meet the minimum selection standard of any one trait 
2. It fix the minimum acceptable standard, below which are eliminated. 
3. This is useful for uneven aged stands in a large area, where comparison trees are not available to candidate trees. 

Total score Method: 

1. Selection done for all traits by using some kind of a total score by combining together the scores of each component character.
2. Each character is assigned a score from 0 to 5, 5 with most desirable
3. Individual tree with the highest total score are kept for candidate trees and seem of total scores above some arbitrary fixed limits are selected as plus trees, otherwise rejected. 
4. Since the traits considered may not be equally important economically, so different weightage need to be provided to the trait characters. 
5. Weightage given depends on economic value, heritability and correlation between different traits. 

Regression Method. 

1. This method is applicable for uneven aged on mixed forests 
2. A regression line is developed for a stand or site to tree age.
3. The sampling requires of different ages. 
4. Different regressions are developed for different sites. 
5. Once the regression line is developed, candidate tree values are plotted against the regression line, the trees that most minimum selection standards or above regression lines are selected as plus trees, others falling below regression line are rejected.
6. Regression line is for a particular species and site. 
7. It has been used to select superior trees in hard wood forest stands.
8. Major drawback is that it could not be used whose age is not know. 

Mother tree selection: 

1. Mother tree selection is best if there is no need of large amount of improve seeds immediately 
2. This method is best in a degraded stands with few good phenotypes are available but not comparison trees. 
3. It locates good tree, but not of minimum selection standard. 
4. It is suitable for short rotation hardwood species. 

Selection traits: 

1. Stem:  Height, diameter, forking, straightness, tapers, bark thickness 
2. Branches: Number , diameter, angle, distribution
3. Crown:  Length, width, foliage, symmetry 
4. Wood:  density, fiber , dimensions, grain workability 
5. Phyto chemicals: yield, composition, quality 
6. Adaptation: Environmental factors, tolerance to pest and pathogen attack. 
   1. Clonal Seed orchards on vegetative orchards (CSO) 

Seed Orchards

Large scale forestation requires large quantity of improved planting sock.  Insufficient seed supply of suitable species. is often a bottleneck of planting program.  Genetically, improved quality seed has a major impact on the benefits from plantation forestry. The production of good quality seed ensures well adapted and genetically desirable planting stocks.  The production of genetically superior seeds can be obtained form 'seed orchard'.  The production of improved planting stocks is obtained by two ways one is establishment of seed orchards and another is macro and micro propagation.  The widely adapted method is the establishment of seed orchard for genetic gain in shorter time of tree improvement. 

Zobel et al, 1958, define the seed orchard as a plantation of genetically superior trees, isolated to reduce pollination from genetically inferior outside source and intensively managed to produce frequent abundant easily harvested

 seed crops.  It is established by setting out clones or seedlings progeny of trees selected for desired characteristics. 

Feilberg Seogard, 1975, define a seed orchard as a plantation of selected clones or progenies, which is isolated or managed to avoid or reduced pollination from outside sources and managed to produce frequent, abundant and easily harvested crops of seed.  Seed orchards are not always for genetic improvement, but also be used for the production of sees that is adequately required to a specific planting location. 

Kinds of Seed Orchards;

There are various kinds of seed orchard, but mainly classified into three broad class as. 

1. Seedling Seed orchards (ss0) 
2. Extensive seedling seed orchards (Esso)

Clonal seed orchard/vegetative orchards; 

It is most common type used world wide.  In clonal seed orchards the vegetative material, graft, cutting and plantlets derived form tissue culture, of selected phenotypes. Plus trees are planted in the areas with good isolation under the condition favorite to flowering with fertilization and managed for the production of maximum amount of seeds.  

Without progeny Testing: 

1. Tree selection or wild on planted stand and grafting of scions on the root stocks to establish used orchards.
2. NO progeny testing
3. It is important for gene conservation if the nature population is in danger. 

Progeny Tested: 

1. It contains large number of clones obtained through plus tree selection and grafting.
2. The undesired trees removed from the orchard, it is called ‘Progeny tested colonel seed orchard’.

1.  Seedling –seed 

In this orchard, progenies from open or controlled pollination of selected phenotypes are planted at normal plantation spacing. This thinning or rouging must be done before starting abandoned seed production on collection: 

From Open Pollination: 

In some cases progeny trial can be corrected into seedling seed orchard.  But it is not good to carry out both testing and seed production or the site. 

Controlled Pollinations: 

1. Controlled pollination is performed on original parents or their grafting in the clone bank after the selection of plus trees. 
2. Progenies obtained from these pollinations are than established for plantations. 

Planning of Seed orchards; 

Seed orchards are a major component of most tree improvement programs involving breeding. Important factors to be considered when planning an orchard program are: 

1. Biology of the species 
2. Choice of the breeding method
3. The use of combined or separate breeding or seed production population 
4. Combining progeny testing; 

Location, Establishment and Management of Seed orchard: 

It is concerned with maximizing the production of seed of high genetic and physiological quality as soon as possible. 

1. Location
2. Macro-Micro climate
3. Soil and Topography
4. Pollen –dilution zone 

Seed orchard Management: 

1. Soil management 
2. Orchard surface
3. Orchard fertilization
4. Irrigation 
5. Pest problem
6. Other Management method to increase flowering
7. Protection
8. Seed orchard Records

Disadvantages or Problems of Hybridization in Forestry

Problems exists in hybridization of trees in comparison to annual crops:

1. The species are perennial cross pollinated and heterozygous. in nature
2. First flowering is quite late, which varies from 3yrs to 90yrs
3. Homozygous or pure lines are not available in trees. 
4. The size of the flowering trees in term of height and diameter. 
5. desiccation of band pollinated buds occurs in the ordinary bags in the absence of proper aeration. To prevent this special types of crossing or hybridization bags are required. 
6. Before controlled crossing is attempted fertility of pollen and receptivity of stigma for better and successful results, highly skilled knowledge is required. 
7. Once the flowering period is missed, complete one year is lost.  This floral biology of the species and genera need to be studied beforehand. 
8. More time is required for harvesting the crosses.  Therefore, care is to be taken for using durable metal or aluminum label having all details with date of controlled crossing to avoid mistakes and confusion. 

Advantages of Hybridization in Forestry

1. In most of the tree species or genera, provenances or individual plus trees in which controlled crossing or hybridization by hand or nature is done, hybrid vigor has been observed.  As this phenomenon is present in trees, it can be utilized for the following condition. 
2. Heterosis can help in improving the productivity in comparison with parent species and also in reducing rotation age. 
3. Expression of maternity can be observed based on morphological traits in the field , facilitating alternate row planting of 2 spp.  Side by side, avoiding cumber some methodology of controlled crossing and thus saving time, money and efforts. 
4. Production of triploids or haploids by taking aid of induced polyploidy. 

Pre-Requisites for Hybridization and Precautions. 

Before attempting hybridization, information on the following aspects is essential.

1. Whether the spp. belong to the crossable series, classes or, genotypes or chromosomal acceptability or not. 
2. Species or genera are cross pollinated or self pollinated
3. Near relatives should not be crossed to avoid inbreeding depression.
4. Proper selection female and male parents should be made. 
5. Identification of the source and location of female and male parents is essentially preferred in inter or intra specific on provenances or crossing work. 
6. Information on heritability for genotypic improvement is an essential in gradient for the program of hybridization. 
7. Knowledge of floral biology of the female and male parents, in inter provenances or specific or genera crosses are being attempted. 
8. Availability of grafting techniques and tissue culture. 
9. Information on ploidy level of the female and male parents. 
10. Survey collection and establishment of germplasm. 

Types of Hybrids 

Interspecific. 

Interspecific hybrids are produced when crosses are attempted between different species of a genus, if two species 'A' and 'B' are to be crossed, each species is used simultaneously as female and male , it will provide in formation on better combination as well as on maternal effect. 

Intraspecific 

Intraspecific hybrids are produced when crosses are attempted within different individuals of the same species i.e. between two superior selected trees, between plus trees, between provenances, between individuals of different ploidy levels to produce triploids or tetraploids etc.  or between mutants and normal tree to transfer the desired traits or traits like disease resistance 

Inter generic: 

Inter generic hybrids are produced when crosses are attempted between individuals belonging to different genera like wheat and rye, radish and turnip, tomato and potato etc., though it is difficult to get success through conventional methods but ' Biotechnology' has made it possible through 'Somatic hybridization"  .