In this activity, students will learn how traditional methods of artificial selection and modern methods of bioengineering have been used in an
attempt to improve the quality of forests products worldwide. Students will investigate both the risks and benefits of genetically modifying trees.
102 project learning tree Exploring Environmental Issues: BioTechnology ©AmericAn Forest FoundAtion
background
About 30 percent of the land surface of Earth is occupied by forests, which play an enormous role in our climate, local habitat, culture, and consump- tion. Trees are responsible for recycling nutrients such as nitrogen, sulfur, phosphorus, and carbon and decontaminating wastes that have accumu- lated in the soil, water, and air. Trees play a major role in the water cycle, slowing down surface run- off, drawing water through their roots, and return- ing moisture to the atmosphere through transpira- tion. Forests, along with grasslands, shrubs, and other autotrophs, absorb solar radiation to pro- vide the basis of the food chain; regulate abiotic factors such as wind, temperature, and moisture; and offer habitat, nutrients, and renewable sup- plies of many organisms.
Global use of wood removed from forests1
Today, 50 percent of wood worldwide is used as fuel for cooking fires and home heating or for run- ning boilers for electricity or steam. Because of the conversion of tropical forests to agriculture, our planet’s forests are shrinking at an annual rate of 140,000 square kilometers.2 There is an increasing price to pay in energy, effort, and education lost as young children and women travel farther each day to collect firewood for daily cooking and heat. Of the forests that are cleared annually, 90 per- cent are in the tropical regions where people seek money for immediate use from the sale of this wood and the land that it occupies. Humans have been breeding trees for more than a thousand years to produce organisms that are better suited to specific uses.3 Artificial selection techniques and forest management have provided solutions that
reduce human demands on forests worldwide so that smaller amounts of land can be used to pro- vide an abundance of wood products in a manner that is sustainable for centuries to come.
Biotechnology in the Historical Management of Forests4
Biotechnology was used as early as 6,000
years ago when people began planting fruit tree orchards and ornamental gardens with select spe- cies that displayed desired traits. Agriculture was well on its way by that time, and the biotechnology of artificial selection for specific traits was seen in food crops and animal breeding. Tree reforestation practices began as early as 2,300 years ago in Egypt to reduce erosion and to offset the demand for firewood, but it wasn’t until the 13th century that civilizations began selecting specific high-quality trees to use for reforestation.
Tree improvement techniques, which began in ear- nest worldwide in the 19th century, moved deeper into the practices of biotechnology while using results from experiments in inbreeding and out-
crossing, cross-pollination, and the introduc-
tion of nonnative tree species. It was determined that trees that combined the gene pools of two separate populations often yielded more desirable
progeny. Further experimentation revealed that hybrids (offspring from selected parents of the
same species or two related species) could be bred to provide desirable traits such as better lumber, more fruit, or faster growth.
Hybrids, both intraspecific and interspecific, became the focus of 20th-century forest improve- ment techniques. Backcrosses, the offspring of two different parental lineages that are pollinated with other trees from the lineage of a single parent for one or more generations, were used to rein- force the majority of the traits of one parent while maintaining one or more desirable traits from the opposite parent (see part B and the case study of the American chestnut for a more detailed exam- ple). Hybridization techniques became the basis of
seed orchards using select superior trees, called
“plus” trees, to create entire orchards of offspring from various select parents. These seed orchards were then culled to remove the lesser individuals, Fuel 50% Lumber 30% Paper 20%
leaving entire forests of the choice plus the tree offspring that could interbreed and could provide seeds for reforestation or for initiation of forests in other areas.
During the 1950s, the seed orchard method of developing large populations of highly selected trees was introduced to the United States, and sci- entists across the country began developing seed orchards for native species that could be grown in this country. Early on, it became apparent that limiting the gene pool and planting monocul-
tures increased a forest’s susceptibility to disease.
Those forests also had a more simplistic ecosystem that allowed pest species to proliferate without the complex niche structure that would harbor a range of predatory species. In an attempt to rem- edy the problem of limited gene pools, scientists introduced new plus trees periodically to enlarge the gene pool of the offspring trees and to allow gene flow from a greater outcrossing population. The other problems with single-species forests— such as competition and depletion of certain soil nutrients, the loss of ecosystem diversity and com- plexity, and a decrease in aesthetic value of a less diverse forest—continue to be issues.
Creating seed orchards required grafting the tops of plus trees to existing mature trees for harvesting seeds at ground level and then raising the prog- eny of those seeds to adulthood until the progeny too produced seeds. This method was time-con- suming. By the mid-20th century, scientists began combining seed orchard methods with vegetative
reproduction while using root cuttings to quickly
obtain several genetically identical trees from a single individual. This process provides genetic
clones that can be planted en masse at any loca-
tion to reforest an area with trees that have already undergone extensive artificial selection techniques. Furthermore, some clonal forests could be plant- ed from cuttings made from any part of the plant by using tissue cultures so scientists could choose the desired state of maturity for the new forest. Choosing the desired state of maturity either allowed trees to jump past a juvenile stage—if needed—so the trees could avoid damage from a pest species or allowed reproductively mature plants to bear fruit immediately.
Biotechnology in Forest
Management in the 21st Century
Although transgenic species are not used in the vast majority of commercial forestry in North America today, the industry is beginning to see a place for this new technology in coming years. Transgenic species have genes inserted into their developing cells that are designed to resist pest species or herbicide applications; to tolerate drought, salt, or other environmental stresses; and to increase desirable properties by introducing genes that could directly affect wood production or other economically viable qualities.5 The geneti- cally engineered varieties can be used to reduce erosion in specific areas or to serve as wind- breaks for agricultural land. Scientists use DNA
fingerprints on individual trees to analyze their genome, to trace weak genes, or to target desir-
able ones. Relationships of ancestry and taxonomy are being resolved so hybrid crosses can become calculated successes.
Issues of Costs and Benefits
Many believe that sustainable, commercial forestry is being implemented across the landscape today and that it has the ability to protect biodiverse areas, water quality, and wildlife habitat, particular- ly when compared with other land use alternatives (e.g., residential development and agriculture). Intensive management and use of fast-growing non–genetically engineered trees are techniques that are predominantly used today.
Advances in biotechnology (bioengineering) that may become more widely used as we move further into the 21st century have raised some concerns for many scientists. Concerns are rooted in the new risks that such transgenic plants pose. Pest resistance to the genes that were introduced to deter those species may eventually lead to new generations of insects and pathogens that are immune to the novel gene. Because the pollen of plants is highly mobile, the introduced gene will be found in surrounding populations of closely related plants through cross-pollination. In addi- tion, both the transgenic and selected species can increase a tree’s potential for invasive reproduc- tion, thereby allowing it to outcompete native spe- cies and to reduce overall biodiversity.
104 project learning tree Exploring Environmental Issues: BioTechnology ©AmericAn Forest FoundAtion The biodiversity problems associated with a mon-
oculture continue to challenge scientists as soils become depleted through intraspecific competi- tion and as ecological complexity is compromised.6 However, if tree plantations were used to meet all the world’s need for forest products, those planta- tions would make up only 5 percent of the total land mass, freeing millions of acres for preserves and biologically diverse habitats.7 In many parts of the world, including the United States, sustainable commercial forestry is successfully implemented using intensive management and fast-growing, non–genetically engineered trees, thus yielding a forest where trees can be harvested and where bio- diversity, water quality, and wildlife habitat are pro- tected. However, in many regions of the world, the natural forest has been removed for human use of the land (e.g., tropical forests that have been har- vested, burned, and converted to farmland that is typically productive for only 1–3 years) so there is no longer a sustainable source of timber.
One perspective holds that if humans made the choice to introduce fast-growing bioengineered species on marginal and degraded farmland and pastureland that was already accessible by roads, then natural buffers would be in place between wild forests and tree plantations to reduce the chance of having introduced genes escape from their planted host. This setup would also keep new roads from being built into pristine areas, therefore limiting human encroachment and habi- tat degradation. Another perspective is to perform experimental trials before broad implementation in order to test the risk of crossbreeding and gene escape. Such solutions would still call for monitor- ing and oversight, but they might reduce the pres- sure being placed on the old-growth forests and dwindling forests that are being used by the poor to meet their basic needs.
With the size of the human population, our per- sonal, economic, and political choices in the com- ing century will greatly affect the air, soil, and water quality around the world. With advances in biotechnology that apply to forestry and manage- ment of public and private land, it will be neces- sary to have a citizenry that is informed and ready to participate in the decision-making process.
endnotes
1. G. Tyler Miller, Living in the Environment (Pacific Grove, CA: Brooks/Cole Thompson Learning, 2002).
2. World Resource Institute, 2000.
3. D. Rowland Burdon and William J. Libby,
Genetically Modified Forests: From Stone Age to Modern Biotechnology (Durham, NC: Forest
History Society, 2006). 4. Ibid.
5. Ibid. 6. Ibid.
7. Miller, Living in the Environment.