Problem faced in Forest Genetics

Bibek Subedi
M.Sc. Forestry, IOF, Pokhara Campus, TU
Email: [email protected]

Introduction to Forest Genetics

Forest genetics is the study of hereditary variation in forest trees.  Hereditary differences are those which are caused by the genes and/or cytoplasm within the tree. They are predetermined at the time the seed is formed, and in that sense are opposed to differences that are caused by the external environment. However, it is a mistake to speak of most tree characteristics as being strictly under either genetic or environmental control. Most commercially important traits are controlled by both internal and external factors. An example is the growth rate, which can be increased by breeding for faster growth or by culture. Also, many genetically controlled traits may be more evident in one environment than another. For example, genetic differences in frost resistance will not be evident when trees are planted in a frost-free region but may be very important when the same trees are planted in an area subject to low temperatures during the growing season.

Trees are composed of cells, some living and some dead. Each living cell consists of an outer "cell wall," a fluid called the "cytoplasm," and a "nucleus" surrounded by the cytoplasm. Among other things the nucleus contains "chromosomes." The chromosomes are of special interest genetically because they carry the bulk of the genetic information and transmit that information from one cell generation to the next. They are nearly constant in number throughout the vegetative cells of a tree or of an entire species. A chromosome is a long, thread-like structure consisting of deoxyribonucleic acid (DNA) and a protein sheath. The DNA is the active genetic material and is a very long molecule composed of two spiral strands. Each strand is composed of four organic bases (cytosine, C; guanine, G; adenine, A; and thymine, T) and attached sugar radicals. One such base and its attached sugar radical is called a "nucleotide." The nucleotides in a single strand are tightly joined together by phosphate radicals. The two spiral strands are held together more loosely by hydrogen bonds. 

Forest tree improvement is the application of forest genetics to practice. Usually, this is accomplished by testing various wild types and determining which will grow best when planted on specific sites. In more advanced programs, this is accomplished by breeding, e.g., for increased growth rate, increased resistance to pests. The new varieties are then planted. 

Basic genetic principles are the same for trees, men, and fruit flies. But inheritance patterns and methods of experimentation vary considerably among these groups. Thus, forest genetics is a distinct field of endeavor, having its own problems. (Wright, 2012) 

Fig. Structure of Gene

Problems that are peculiar to forest genetics: 

With their unique life-history traits, such as longevity, late attainment of reproductive maturity, greater opportunity for accumulation of mutations, and their range of mating and dispersal systems, forest trees pose many challenges for genetics research and their practical application (Williams and Savolainen, 1996). Such problems are unique to the characteristics of a tree and are hence different from genetics study conducted in other organisms like agricultural crops or animals. 

Some of the problems that are peculiar to forest genetics are: 

i. Forest genetics uses indirect evidence: 

Most characteristics are under the control of genes and the environment. Genes are sub-microscopic parts of a cell. Even with an electron microscope they cannot be seen and identified as "good" and "bad." Instead, they must be identified by indirect means—by growing the offspring of a tree and observing the characteristics of the offspring. Thus, progeny tests are integral parts of forest genetics research. By a progeny test is meant the growth of different species, different races, or the offspring of different trees under similar conditions in a replicated experiment. Then if one particular progeny grows faster than the others it is safe to assume that growth rate is under genetic control. Or, if one particular progeny has longer needle than the others it is safe to assume that needle length is under genetic control. 

ii. Uncertainty and the need for continuous experimentation: 

Most forest genetics research leads to some generalizations such as "tall trees produce faster-growing offspring" or "trees from southern climates grow faster." Each such generalization is usually for a single species.  But these rules are rarely absolute. Nearly always there is a certain amount of unexplained variation. Because of these uncertainties, continued experimentation is an integral part of most practical as well as theoretical tree improvement programs. 

iii. The time element: 

Trees are long-lived organisms that require several years to produce seed, unlike agricultural plants which are mainly annual or perennial with the short life cycle. Hence forest geneticists have to live with the problem and to adjust their procedures to compensate for the fact that they work with long-lived perennials rather than herbs. 

iv. Scarcity of basic genetic information: 

Since trees are difficult test organisms, we lack basic genetic information of even the best-studied plants. According to the country reports prepared for The State of the World’s Forest Genetic Resources, approximately 2400 species are actively managed in forestry. The total count of forest species, however, remains inconclusive. Only approximately 700 tree species are subject to some level of selection and improvement globally, and progeny tests have been established for no more than two-thirds of these species. In addition, a number of non-planted trees species have been studied, mainly using molecular markers. Assuming a total global count of at least 80,000 tree species, little more than 1 percent of the tree species have been subject to genetic study, and less than 1 percent have been studied with the aim of improving resources for human use. Undoubtedly many not yet studied species have untapped potential that could be realized given sufficient resources, interest, and survival of sufficiently diverse populations.  

Genetics problems brought upon by Human Activities 

i. Deforestation and Fragmentation: 

Given the current worldwide pervasiveness of habitat fragmentation, integrating the conservation of essential ecosystem processes with human population needs is urgently needed since they have colliding objectives (Henle et al. 2004).  Fragmentation of natural ecosystems may have obvious results, such as the elimination of species, but there may also be less immediate effects on the longer-term viability of species through the modification of ecological and genetic processes within and among populations. 

More specifically, forest fragmentation may be seen as having three main effects: 

1. Reduction in the numbers of individual trees, 
2. Reduction of population sizes as individuals are restricted to smaller forest fragments, and 
3. Spatial isolation of remaining populations and individuals within nonforest land-use matrixes (Young and Boyle, 2000). 

The genetic consequences of fragmentation may be seen in losses of diversity at population and species levels, in interpopulation structural modifications and in increased inbreeding. Such changes may reflect the effect of non-random sampling, short-term genetic effects (genetic bottlenecks and modified gene flow), or longer-term outcomes like genetic drift. However, the occurrence and extent of such predicted changes will depend in large measure on the degree to which deforestation is random, and on whether the physical fragmentation of the forest is reflected in the segregation of the remnant forest into genetically isolated patches. (Boshier and Amaral, 2004) 

ii. Logging: 

The genetic impact of logging on regeneration depends on the size at which trees start reproducing and on the proportion of reproductive trees after logging. 

When there is species selective logging i.e. large trees of preferred species are felled, the remaining trees might have less genetic quality and their reproduction will ultimately decrease the overall quality of the stand. (Boshier and Amaral, 2004) 

iii. Climate change: 

Thomas et al. (2004) have shown through modeling that between 18 and 35 percent of the world’s animal and plant species are on the path or committed to extinction due to climate change, and this figure does not take into account interactions with other threats; these authors have also shown that the threat to survival of species from climate change is much greater than the threat from habitat loss, with some variation depending on the biome under consideration. Climate change in addition to pollution has been steadily altering forest genes and their impacts can be detrimental to the long run. 

iv. Genetic pollution: 

A significant but largely unquantified risk to FGR conservation and use is the uncontrolled and undocumented mixing of gene pools of forest tree species. This can occur within species, whereby genetically diversified local populations, which may possess valuable attributes, interbreed with non-local germplasm introduced for planted forest establishment. Hybridization of local and introduced gene pools may reduce local adaptation in subsequent tree generations (Millar and Libby, 1989; Palmberg-Lerche, 1999). Mixing of gene pools can also inadvertently lead to the incorporation of undesirable genes, resulting in diminished economic value for production forests and vastly complicating and increasing the costs of tree breeding. Interbreeding can also occur when formerly allopatric (geographically isolated) related species are brought together. If the taxa are not fully reproductively isolated and share the same flowering times and pollinators, then hybridization is likely; if the resulting progeny 

are fertile and are not selected against, then the eventual outcome can be loss of a species through assimilation (CGRF, 2014) 

v. Invasive species: 

Invasive species, including plants, insect pests and microbial pathogens, are increasingly being identified and noted as major threats to ecosystem integrity and individual species, including trees. They can significantly alter the genetic composition of the ecosystem and can even drive a species to extinction. 

Genetics problems in context to Nepal 

It is fair to say that not much consideration is done in regard to the genetic field. Some advances have been made agricultural plants but not much has been done in regards to the tree.  

Policy tools and instruments are essential along with preventive measures to address the loss of genetic diversity of tree species.  To this end, the government has prepared the National Biodiversity Strategy (NBS), 2002 which highlights an overview of Nepal’s biodiversity along with major achievements, gaps, and future strategies. NBS emphasized on the inventory of the species in the protected areas and throughout the country. A species conservation plan that focuses on the keystone species is pressed concerned of the NBS. Following NBS, numerous policies such as wetland, rangeland, etc. have been developed and implemented accordingly. Forest Act 2076 has provision to protect species which are likely to be threatened. Other than national policies, the government is adhering to international treaties such as CITES. However, the actual implementation of such a policy is not done efficiently. 

Similarly, while developing protected areas, only ecosystem and species levels are considered and genetic consideration is not done. Moreover, inadequate representation of the PA’s i.e.  PA’s represents only 80 of the total 118 ecosystems is also a pressing issue. 

Ex-situ conservation in Nepal basically focuses on conventional approaches viz. tissue culture, Breeding Seed Orchards (BSOs), botanical gardens, arboretum and gene bank. Institute of Forestry has established a pinnatum at its premises in Hetauda to conserve and study the pine forests from different regions in a single place. There is one plant tissue culture laboratory at National Herbarium and Plant Laboratories, Godawari which was established in 1976. Over the period, 115 plant species have been cultured and scientific protocols have been developed including orchids, agricultural, horticultural, forestry, ornamental and medicinal plants. The government has established 11 botanical gardens in different physiographic regions with a focus on landscape development for education and research, aesthetic and recreational purposes. TISC has established breeding seed orchards in different districts to conserve the genetic resources of many species such as Dalbergia sissoo and D. latifolia. But, TISC has now been discontinued because of lack of funding. These are the only instances of genetic works done in Nepal which are abysmally low.  

Besides, inadequate funds and trained human resources, lack of taxonomist, rapid pace of genetic diversity loss, insufficient equipment and lack of an implementation plan is a major issue. In addition, there is lack of comprehensive inventory regarding the status of forest species. (MFSC, 2012) 

Now is the due time to give utmost consideration to improving genetical knowledge and tools to conserve biodiversity and improve the livelihood of the people. 

References: 

• Boshier, D., & Amaral, W. (2004). Threats to forest ecosystems and challenges for the conservation and sustainable use of forest genetic resources. Challenges in managing forest genetic resources for livelihoods. IPGRI, Rome, 7-22. 
• Commission on Genetic Resources for Food. (2014). The State of the World's Forest Genetic Resources. Food & Agriculture Org. 
• Henle, K., Davies, K. F., Kleyer, M., Margules, C., & Settele, J. (2004). Predictors of species sensitivity to fragmentation. Biodiversity & Conservation, 13(1), 207-251. 
• MFSC. (2012). Country Report on the State of Forest Genetic Resources-Nepal. GON. 
• Millar, C. I., & Libby, W. J. (1989). Disneyland or native ecosystem: genetics and the restorationist. Ecological Restoration, 7(1), 18-24. 
• Palmberg-Lerche, C. (1999). Conservation and management of forest genetic resources. Journal of Tropical Forest Science, 286-302. 
• Thomas, C. D., Cameron, A., Green, R. E., Bakkenes, M., Beaumont, L. J., Collingham, Y. C., ... & Hughes, L. (2004). Extinction risk from climate change. Nature, 427(6970), 145. 
• Williams, C. G., & Savolainen, O. (1996). Inbreeding depression in conifers: implications for breeding strategy. Forest Science, 42(1), 102-117. 
• Wright, J. (2012). Introduction to forest genetics. Elsevier. 
• Young, A., Boyle, T., & Brown, T. (1996). The population genetic consequences of habitat fragmentation for plants. Trends in ecology & evolution, 11(10), 413-418.