Bruce J. Zobel

Genetics of wood production

1 The Role of Genetics in Wood Production-General Concepts.- 1.1 Background Information.- 1.2 Categorization of Wood and Trees.- 1.3 Wood Properties of Importance.- 1.3.1 Wood Density (Specific Gravity).- 1.3.1.1 The Genetics of Wood Density in Conifers - General Introduction.- 1.3.1.2 The Genetics of Wood Density in Hardwoods - General Introduction.- 1.3.2 Other Wood Properties.- 1.4 The Causes and Types of Wood Variation.- 1.4.1 Importance and Magnitude of Wood Variation.- 1.4.2 Assessing Genetic Improvements.- 1.4.2.1 Strength of Inheritance - General.- 1.5 Environmental vs. Genetic Influence on Wood.- 1.6 Literature on the Inheritance of Wood.- 1.7 Summary.- 2 Genetic Controls in Wood Formation.- 2.1 Controls Influencing Wood Development.- 2.1.1 The Kinds and Strength of Genetic Control in Wood.- 2.1.1.1 The Measurement of Genetic Control.- 2.1.1.2 The Change of Genetic Control with Tree Age - Juvenile and Mature Wood.- 2.1.1.3 The Environmental Control.- 2.1.1.4 Reaction with the Environment - Genotype x Environment Interaction.- 2.2 The Value of Genetic Differences in Wood.- 2.3 Summary.- 3 Sampling and Analysis in Genetic Studies on Wood.- 3.1 Making Wood Studies - Sampling Methods.- 3.2 Size of Sample.- 3.3 Location and Age of Sample.- 3.3.1 Estimating Whole Tree Specific Gravity Values from a Single Sampling Point.- 3.3.1.1 Age of Wood-Juvenile to Mature Wood Correlations.- 3.3.1.2 Removing Extractives.- 3.4 Obtaining Wood Samples.- 3.5 Methods of Determining Wood Density.- 3.6 Methods of Determining Other Wood Properties.- 3.6.1 Spiral Grain.- 3.6.2 Tracheids and Fibers.- 3.6.3 Moisture Content.- 3.6.4 Pulp Yield.- 3.7 Indirect Selection for Wood and Pulp Properties.- Appendix Table 3.1 Some methods used to determine wood density in trees.- Appendix Table 3.2 Some methods that have been used to determine spiral grain.- 4 The Importance of Wood Density (Specific Gravity) and Its Component Parts.- 4.1 General Concepts and the Importance of Wood Density.- 4.1.1 Earlywood and Latewood.- 4.1.1.1 The Ratio of Latewood to Earlywood and Its Value.- 4.1.1.2 Inheritance in Earlywood and Latewood.- 4.1.1.3 Wall Thickness.- 4.2 The Effect of Genetic Manipulation of Wood Density on the Final Product - General.- 4.2.1 The Effect of Wood Density on the Final Product for Conifers.- 4.2.2 The Effect of Wood Density on the Final Product for Hardwoods.- 4.2.2.1 Wood Density in the Diffuse-Porous Hardwoods.- 4.2.2.2 Wood Density in the Ring-Porous Hardwoods.- 4.2.2.3 The Effect of Rays and Vessels.- 4.3 Summary.- 5 The Genetics of Wood Density.- 5.1 General.- 5.2 The Genetic Control of Wood. Density in *the Conifers.- 5.2.1 Hard Pines.- 5.2.2 Soft Pines.- 5.2.3 Other Conifers of Major Importance.- 5.2.3.1 The Spruces and Firs.- 5.2.3.2 Douglas-Fir and Larch.- 5.2.4 Other Conifers of Minor Importance.- 5.3 The Genetic Control of Wood Density in Hardwoods.- 5.4 Genetic Gains in Wood Density Using Vegetative Propagation and Coppice.- 5.5 Inheritance of Within-Tree Variation in Wood Density.- 5.6 Summary.- 6 Inheritance of the Cellular Components of Wood, Cellulose Yield and Pulp and Paper Products.- 6.1 General Concepts.- 6.1.1 Variability and its Causes.- 6.2 Cells of the Hardwoods.- 6.2.1 Fiber Length.- 6.2.2 Fiber Diameter, Wall Thickness, and Percentage of Cell Types.- 6.2.3 Vessels and Rays.- 6.3 Cells of the Conifers.- 6.3.1 Tracheid Length.- 6.3.2 Other Tracheid Characteristics.- 6.4 Cellulose Yield and Pulp and Paper Products.- 6.5 Summary.- 7 Grain, Fibril Patterns, and Internal Defects.- 7.1 General.- 7.2 Spiral Grain.- 7.2.1 Interlocked Grain.- 7.3 Microfibrillar Angle.- 7.4 Miscellaneous Wood Grain Patterns, Figured Wood.- 7.5 Reaction Wood.- 7.6 Cracks, Shake, and Other Internal Defects.- 7.7 Summary.- 8 Tree Form and Internal Tree Characteristics.- 8.1 Introductory Comments.- 8.2 Stem. Form and Branching.- 8.2.1 Stem Straightness and Sinuosity.- 8.2.2 Stem Taper.- 8.2.3 Branching Characteristics.- 8.3 Juvenile Wood and Genetics.- 8.3.1 Juvenile to Mature Wood Transition.- 8.3.2 Changing the Properties of Juvenile Wood.- 8.4 Chemistry of Wood.- 8.4.1 Cellulose and Lignin.- 8.4.2 Extractives and Gum Yields.- 8.4.3 Heartwood.- 8.4.4 Other Chemicals.- 8.5 Miscellaneous Traits.- 8.5.1 Moisture Content.- 8.5.2 Bark Characteristics.- 8.5.3 Wood Color.- 8.6 Summary.- 9 Wood Genetics Related to Provenance and Seed Source.- 9.1 The Meaning of Provenance and Seed Source.- 9.1.1 Provenance, Geographic Source, or Geographic Race.- 9.1.2 Confusion and Complexity of Terms.- 9.1.3 Assessment of the Wood of Provenances.- 9.2 The Overall Effect of Provenance.- 9.2.1 Genetic Differences in Wood Properties Among Provenances of the Hard Pines.- 9.2.2 Genetic Differences in Wood Properties Among Provenances in Conifers Other Than the Hard Pines.- 9.2.3 The Importance of Provenance in Determining the Wood Properties of Hardwoods.- 9.3 S Summary.- 10 Correlations Among Wood Properties and with Growth Rate.- 10.1 General Concepts.- 10.2 Growth Rate and Wood Properties.- 10.2.1 Growth Rate and Wood Density.- 10.2.2 Growth Rate and Other Wood Properties.- 10.3 Wood Property Relationships in the Conifers.- 10.4 Relationships Among Wood Properties in Hardwoods.- 10.5 Relationship of the Wood Properties of Coppice, Rooted Cuttings, and Grafts to Donor Trees.- 10.6 Wood Property Relationships Between Chemical Composition and Pulp Properties.- 10.7 Summary.- 11 The Genetics of Miscellaneous Factors That Affect Wood.- 11.1 What Are Miscellaneous Factors?.- 11.2 Diseases and Insects.- 11.2.1 Diseases.- 11.2.1.1 Wood Decay and Discoloration.- 11.2.1.2 Other Effects of Disease.- 11.2.2 Insects.- 11.3. Wood Uniformity.- 11.4 Hybridization to Change Wood Properties.- 11.5 Effects of Polyploidy on Wood.- 11.6 The Effect of Tissue Culture and Biotechnology.- 11.7 Wood for Energy.- 11.8 Summary.- 12 Determination of Wood Properties to Be Used in a Tree Improvement Program.- 12.1 Using Genetic Information.- 12.2 Selection of Trees for a Genetics Program.- 12.2.1 Considerations for Selection.- 12.2.2 Opportunity for Early Selection.- 12.3 Choice of Wood Properties - What Should Be Included?.- 12.4 Summary.- 13 Improvement in Wood by Using Genetics.- 13.1 Current and Future Usage of Genetics to Change Wood.- 13.1.1 When to Employ Genetics.- 13.2 Examples of Changes in Wood by the Use of Genetics.- 13.2.1 The Hard Pines.- 13.2.2 Other Conifers.- 13.2.3 Temperate Hardwoods.- 13.2.4 Tropical Hardwoods.- 13.2.4.1 Eucalypts.- 13.3 Improving Wood When There Is a Negative Correlation with Growth Rate.- 13.4 Summary.- References.- Species Index.

The changing quality of the world wood supply

SummaryThe reasons for changes in wood quality and utilization are related to the trends toward harvesting smaller, younger and lower-quality timber, wider use of formerly waste wood, unconventional uses of wood, and improved forest management and new wood manufacturing techniques.1.An unequal distribution of timber along with increasing costs of forest ownership and management is forcing short-rotation forestry, which results in small-sized timber, low-quality wood, and a high proportion of juvenile wood and knots. This is true for almost all forest regions although it has been most evident in tropical plantations. The economic pressures for short-rotation ages will become increasingly great, especially in those areas where a timber imbalance in age class distribution occurs.2.Especially in the Tropics, many forestry organizations are planting exotic species on a massive scale and are producing a large volume of “different” wood. The trend toward using exotics is very strong. The trees attain a merchantable size at young ages, with thinning being standard; this produces a large proportion of juvenile wood. Such wood is not desirable for some products, based on current quality criteria, and may be distinctly different from the wood that the same species produces in its indigenous environment. Huge amounts of it are now becoming available, requiring a reassessment of both manufacturing techniques and product type and quality.3.Better utilization in forest harvesting operations results in the use of mill residues of bark and sawdust and forest residues of bark, limbs, leaves, stumps and roots that formerly were considered to be waste. There is also greater utilization of previously unwanted species, including some which were once considered to be of limited value and often were destroyed during regeneration programs. Of great importance are the technological developments that are enabling a greater utilization of the grossly differing woods found growing together in tropical forests, rather than using only a few species and destroying the rest.4.Wood quality is very responsive to both silvicultural and genetic manipulation. The improvements possible in wood will partially offset some quality declines caused by young wood and lower quality trees. The quickest and easiest method of changing wood quality is to control age of harvest.5.New industries are developing which use wood as a source of energy and organic chemicals. In some areas, wood for energy is primarily obtained from large forests being planted solely for energy needs and is secondarily obtained as a salvage product from the forest. From 20 to 50% of the wood harvested in the world is for firewood, which often results in a marked reduction of the quality of the wood used for industrial purposes. Currently some research is focused to grow trees which will yield improved energy and chemicals.6.New manufacturing techniques, such as oriented strand-board and the endgluing of short, clear wood segments from low-quality logs, are enabling the production of high-quality products from low-quality timber. These manufacturing techniques result in products that differ markedly from those previously available but they are stable and of excellent quality. However, a strong sales program will be needed to assure acceptance of the different products.

Genetic manipulation of wood of the southern pines including chemical characteristics

SummaryA review of possible changes in wood morphology through genetic manipulation of the southern pines showed that:1.Significant changes can be obtained by modifying tree form, growth rate and disease resistance.(a)Compression wood can be reduced by developing straighter trees. The inheritance of straightness is so strong that one generation of selection has resulted in enough improvement to enable deemphasis of this characteristic in second-generation breeding.(b)Branch size affects the final product by knot volume and the associated compression wood, included bark and resin; it is moderately genetically controlled.(c)Use of disease-resistant trees not only results in greater wood volume but in higher quality wood. Logs infected with fusiform rust give lower pulp yields and lower mullen and tensile strength in the paper.(d)Growth rate has a limited effect on wood qualities in mature loblolly pine. It is possible to have fast growth combined with either high or low specific gravity wood, since these characteristics are not closely related genetically.2.Inheritance of wood qualities per se is strong enough to obtain meaningful changes in both yield and quality of pulp and paper.(a)Wood specific gravity, which is really a complex of several characteristics, has responded well to selection. Specific gravity differences affect yield, quality and cost from harvesting to the end product.(b)Cell wall thickness appears to be the most important morphological characteristic that affects pulp and paper qualities; it is moderately genetically controlled directly and also controlled through specific gravity.(c)Pulp yield per unit volume increases when specific gravity is increased; also, 1 to 7 percent greater yields are found per unit weight dry wood.(d)Parent trees with juvenile wood of high or low specific gravity produce progeny with juvenile wood similar to the parents. Pulping tests showed high gravity juvenile wood had characteristics similar to mill run chips.(e)Moisture content inheritance closely parallels that of specific gravity.(f)All important wood morphological characteristics tested are under enough genetic control to obtain useful gains. A review of the inheritance of chemical characteristics revealed the existence of few definitive studies. Cellulose yield is inherited in such a manner that selection will not be effective, whereas, oppositely, resin content is inherited in a manner allowing gains to be made through selection. Because of the relationship between chemical characteristics and wood morphological characteristics such as specific gravity, breeding for one will generally affect the other.A previously unreported study of six trees from six control-pollinated families, all of which had the same mother but different fathers, showed that the sugar contents of the six families were essentially constant; glucose varied from 65 to 70 percent but this difference was not statistically meaningful. Polysaccharide differences were not closely related to specific gravity. Because of the close relationship between morphological and chemical characteristics it is the authors opinion that breeding for chemical differences should be limited to those instances in which it is specially useful for yield improvement.It is possible to manipulate wood in a desired direction by breeding for characteristics that affect wood or by breeding for the wood characteristics directly. Enough is now known about the effect of differing wood properties on the final product so that the worth of changes obtained can be assessed in terms of economic or utilization values.

Gene conservation — as viewed by a forest tree breeder

Abstract There is very great interest in, and need for, action relative to the conservation of gene resources of forest trees. This paper presents the views of a tree breeder as to the needs and methods available for species on which genetic manipulation is underway. It is emphasized that conservation for applied programs is usually for gene complexes rather than for single genes. The need to preserve adaptability and pest resistance is emphasized, and methods are suggested for doing this. The controversy as to what genes or gene complexes should be saved is briefly covered. Emphasis is placed on alternative methods of saving gene complexes in addition to large acreages in situ; this involves gene packaging and storage in clone banks or by other means. The alternative of conserving characteristics of a provenance as a unit versus characteristics of individual trees is emphasized. The need for gene conservation for continued progress in tree breeding is great, requiring solid, long-range planning so that the plant breeder can meet his objectives in the long term. Decisions based on vague desires to ‘save everything’ or based on emotion without solid biological support must be avoided.

Effect of fertilization on growth and quality characteristics of loblolly pine

Abstract The effect of fertilization of loblolly pine ( Pinus taeda L.) and its interaction with genotype was studied for six characteristics (DBH, height, volume, fusiform rust infection, crown form and bole straightness) in four 8-year-old control-pollinated progeny tests, located in the Coastal Plain of North Carolina. Fertilizer (superphosphate, potassium, and dolomitic lime) was applied the first spring after outplanting and re-applied the spring of the third growing season. Results showed that fertilizer had a significant effect on growth characteristics over all progeny tests and increased fusiform rust infection in three out of four progeny tests; in only one of the four progeny tests were crown and straightness significantly (negatively) affected. In no case was a fertilizer × genotype interaction of significant importance found, indicating that genotypes selected for good growth and form under non-fertilized conditions can generally be used under fertilized conditions with expectation of good performance.

Variation Within and Among Trees

Perhaps the subject most widely studied in forestry with respect to wood is the variability within and among trees. Both are large; this provides an advantage to the forester for developing better wood, especially since inheritance patterns of wood properties are usually strong, and silvicultural practices can influence wood. However, it is a distinct disadvantage to the user who encounters problems in developing efficient methods for the manufacture of variable woods. Often the user of wood must “overbuild” in the sense that the construction must be designed for the weaker, not the stronger wood members, so that much potential strength is “wasted”.

Wood Variation and Wood Properties

Wood, a most useful substance, varies greatly. Wood properties are changing throughout the world (Zobel et al 1983) and the magnitude and causes of the changes must be known. The importance of wood properties to the final product is becoming better known; one example is the relationship of the morphology of loblolly pine (Pinus taeda) tracheids and the paper made from them, as discussed by Barefoot et al. (1970). The subject of cell morphology and usefulness for the final product was covered in a general way by Keating (1983). Before the causes and control of wood variation are discussed, it is necessary to know just what wood is.

The Effect of Silvicultural Practices on Wood Properties

The major activity of the silviculturist is geared toward changing growth patterns of the tree in the desired direction; for example, Schmidtling (1973) obtained an eightfold increase in yield in the southern pines after 9 years by fertilization and cultivation. As a result of the growth differences, wood properties often are affected. The changes that will occur in wood are not always predictable, and the silviculturist cannot be certain whether one will even occur. Most foresters assume that a varied growth pattern resulting from forest management will not affect the wood produced. This attitude has developed largely because there have been few good studies that have been underway long enough to determine the true effect of silvicultural activities on wood.

Characteristics of Juvenile Wood

There are many characteristics of juvenile wood, described by investigators such as Knigge and Koltzenburg (1965), Foelkel et al. (1976), Thomas (1984), Zobel and Talbert (1984), Krahmer (1986), and Zobel and van Buijtenen (1989). The general attitude of most foresters is that juvenile wood is undesirable. As shown below, this is not always true and currently, with new methods of manufacturing, juvenile wood is sometimes preferred. Such wood has now been accepted as a general part of the wood supply to the industry and steps are being taken to learn how best to use it. The characteristics of juvenile wood, and how they affect the final product, are covered in several sections of this book.

The Effect of Growth Rate on Wood Properties

Perhaps no aspect of wood quality variation and its control has been more discussed and debated than the effect of growth rate on wood properties (Fig. 5.1). For example, concern was expressed for several species of southern pines many years ago by Paul (1927) that free and fast growth would produce wood that would have characteristics unsuitable for quality products. The need and future for fast-growing trees was emphasized by Bingham (1983). It is evident that forestry is moving in that direction and the kind of wood produced by harvesting fast-growing trees at young ages will have to be accepted. As Zobel (1980b) states: “the proportion of trees from fast grown plantations of both conifers and hardwoods will continue to increase until it will predominate in the next quarter-century. Therefore, the industry must learn to use it effectively; just complaining about how different it is from what it has been using is not good enough. Wood from fast-grown plantations is not necessarily ‘bad wood’ but certainly it is different, especially in the conifers.” In his discussion of variation in wood quality, Hillis (1983) emphasizes that the effect of compound interest on final timber growing costs will place future emphasis on rapid growth and shorter rotations. In the future it seems inevitable that the forest industry will have to defer to the economic realities and accept rapid growth unless it can be proved that the consequences are so marked as to reduce the present net value of the forest crop.