Technician checks on genetically modified peach and apple "orchards". Each dish holds experimental trees grown from lab-cultured cells to which researchers have given new genes. Source: USDA.
A genetically modified tree (GMt, GM tree, genetically engineered tree, GE tree or transgenic tree) is a tree whose DNA has been modified using genetic engineering techniques. In most cases the aim is to introduce a novel trait to the plant which does not occur naturally within the species. Examples include resistance to certain pests, diseases, environmental conditions, and herbicide tolerance, or the alteration of lignin levels in order to reduce pulping costs.
Genetically modified forest trees are not yet approved ("deregulated") for commercial use with the exception of insect-resistant poplar trees in China[1][2] and one case of GM Eucalyptus in Brazil.[3] Several genetically modified forest tree species are undergoing field trials for deregulation, and much of the research is being carried out by the pulp and paper industry, primarily with the intention of increasing the productivity of existing tree stock.[4] Certain genetically modified orchard tree species have been deregulated for commercial use in the United States including the papaya and plum.[5] The development, testing and use of GM trees remains at an early stage in comparison to GM crops.[6]
Research
Research into genetically modified trees has been ongoing since 1988.[7] Concerns surrounding the biosafety implications of releasing genetically modified trees into the wild have held back regulatory approval of GM forest trees. This concern is exemplified in the Convention on Biological Diversity's stance:
The Conference of the Parties, Recognising the uncertainties related to the potential environmental and socio-economic impacts, including long term and trans-boundary impacts, of genetically modified trees on global forest biological diversity, as well as on the livelihoods of indigenous and local communities, and given the absence of reliable data and of capacity in some countries to undertake risk assessments and to evaluate those potential impacts, recommends parties to take a precautionary approach when addressing the issue of genetically modified trees.[8]
A precondition for further commercialization of GM forest trees is likely to be their complete sterility.[6][9] Plantation trees remain phenotypically similar to their wild cousins in that most are the product of no more than three generations of artificial selection, therefore, the risk of transgene escape by pollination with compatible wild species is high.[10] One of the most credible science-based concerns with GM trees is their potential for wide dispersal of seed and pollen.[11] The fact that pine pollen travels long distances is well established, moving up to 3,000 kilometers from its source.[12] Additionally, many tree species reproduce for a long time before being harvested.[13] In combination these factors have led some to believe that GM trees are worthy of special environmental considerations over GM crops.[14] Ensuring sterility for GM trees has proven elusive, but efforts are being made.[15] While tree geneticist Steve Strauss predicted that complete containment might be possible by 2020, many questions remain.[16]
Proposed uses
GM trees under experimental development have been modified with traits intended to provide benefit to industry, foresters or consumers. Due to high regulatory and research costs, the majority of genetically modified trees in silviculture consist of plantation trees, such as eucalyptus, poplar, and pine.
Lignin alteration
Several companies and organizations (including ArborGen,[17] GLBRC,[18] ...) in the pulp and paper industry are interested in utilizing GM technology to alter the lignin content of plantation trees (particularly eucalyptus and poplar trees[19]). It is estimated that reducing lignin in plantation trees by genetic modification could reduce pulping costs by up to $15 per cubic metre.[20] Lignin removal from wood fibres conventionally relies on costly and environmentally hazardous chemicals.[21] By developing low-lignin GM trees it is hoped that pulping and bleaching processes will require fewer inputs,[22] therefore, mills supplied by low-lignin GM trees may have a reduced impact on their surrounding ecosystems and communities.[23] However, it is argued that reductions in lignin may compromise the structural integrity of the plant, thereby making it more susceptible to wind, snow, pathogens and disease,[24] which could necessitate pesticide use exceeding that on traditional plantations.[25] This has proven correct, and an alternative approach followed by the University of Columbia was developed. This approach was to introduce chemically labile linkages instead (by inserting a gene from the plant Angelica sinensis), which allows the lignin to break down much more easy.[26] Due to this new approach, the lignin from the trees not only easily breaks apart when treated with a mild base at temperatures of 100 degrees C, but the trees also maintained their growth potential and strength.[27]
Frost tolerance
Genetic modification can allow trees to cope with abiotic stresses such that their geographic range is broadened.[28] Freeze-tolerant GM eucalyptus trees for use in southern US plantations are currently being tested in open air sites with such an objective in mind. ArborGen, a tree biotechnology company and joint venture of pulp and paper firms Rubicon (New Zealand), MeadWestvaco (US) and International Paper (US)[29] is leading this research.[30] Until now the cultivation of eucalyptus has only been possible on the southern tip of Florida, freeze-tolerance would substantially extend the cultivation range northwards.[31]
Reduced vigour
Orchard trees require a rootstock with reduced vigour to allow them to remain small.
Genetic modification could allow the elimination of the rootstock, by making the tree less vigorous, hence reducing its height when fully mature. Research is being done into which genes are responsible for the vigour in orchard trees (such as apples, pears, ...).[32][33]
Accelerated growth
In Brazil, field trials of fast growing GM eucalyptus are currently underway, they were set to conclude in 2015–2016 with commercialization to result.[34]FuturaGene, a biotechnology company owned by Suzano, a Brazilian pulp and paper company, has been leading this research. Stanley Hirsch, chief executive of FuturaGene has stated: "Our trees grow faster and thicker. We are ahead of everyone. We have shown we can increase the yields and growth rates of trees more than anything grown by traditional breeding."[35] The company is looking to reduce harvest cycles from 7 to 5.5 years with 20-30% more mass than conventional eucalyptus.[35] There is concern that such objectives may further exacerbate the negative impacts of plantation forestry. Increased water and soil nutrient demand from faster growing species may lead to irrecoverable losses in site productivity and further impinge upon neighbouring communities and ecosystems.[36][37][38] Researchers at the University of Manchester's Faculty of Life Sciences modified two genes in poplar trees, called PXY and CLE, which are responsible for the rate of cell division in tree trunks. As a result, the trees are growing twice as fast as normal, and also end up being taller, wider and with more leaves.[39]
Disease resistance
Ecologically motivated research into genetic modification is underway. There are ongoing schemes that aim to foster disease resistance in trees such as the American chestnut[40] (see Chestnut blight) and the English elm[41] (see Dutch elm disease) for the purpose of their reintroduction to the wild. Specific diseases have reduced the populations of these emblematic species to the extent that they are mostly lost in the wild. Genetic modification is being pursued concurrently with traditional breeding techniques in an attempt to endow these species with disease resistance.[42]
Current uses
Poplars in China
In 2002 China's State Forestry Administration approved GM poplar trees for commercial use.[43] Subsequently, 1.4 million Bt (insecticide) producing GM poplars were planted in China. They were planted both for their wood and as part of China's 'Green Wall' project, which aims to impede desertification.[44] Reports indicate that the GM poplars have spread beyond the area of original planting [45] and that contamination of native poplars with the Bt gene is occurring.[46] There is concern with these developments, particularly because the pesticide producing trait may impart a positive selective advantage on the poplar, allowing it a high level of invasiveness.[47]
Living Carbon in the USA
Living Carbon, an American biotechnology company founded in 2019, has developed genetically engineered hybrid poplar trees aimed at enhancing carbon sequestration. These trees have been modified to improve photosynthetic efficiency, enabling them to capture more carbon dioxide (CO₂) and produce greater woody biomass than conventional trees. Living Carbon’s mission is to leverage technology to combat climate change while promoting biodiversity and restoring degraded ecosystems.[48][49]
Development and Deployment
Living Carbon’s genetically modified trees were first planted in a bottomland forest in Georgia, USA, in February 2023. Early field trials indicated that these trees achieved a 53% increase in above-ground biomass compared to control groups, enabling them to absorb 27% more carbon.[49] The company generates revenue by selling carbon credits derived from these forests to individuals and businesses seeking to offset greenhouse gas emissions.[50]
Benefits and Potential
Supporters of Living Carbon’s approach highlight its potential to contribute to global climate solutions, particularly if deployed on a large scale. The modified trees are targeted for use in afforestation and reforestation projects on degraded land, where they can aid in carbon capture and ecosystem restoration without displacing native species. These projects also aim to enhance biodiversity while addressing environmental degradation.[51]
Controversies and Challenges
The deployment of genetically modified trees has been met with skepticism. Critics, including some forestry and genetic experts, question whether the trees will meet carbon absorption expectations outside controlled laboratory settings. Concerns have also been raised about the potential ecological risks, such as the unintended spread of genetically modified traits to wild tree populations, which could disrupt native ecosystems.[52][53]
Maddie Hall, co-founder of Living Carbon, has addressed these concerns, emphasizing the urgency of climate action and the limitations of waiting for natural evolutionary processes to improve tree resilience. However, experts note that achieving success in lab or greenhouse trials does not guarantee similar outcomes in complex, natural environments.[54]
^Wang, H. (2004). "The state of genetically modified forest trees in China"(PDF). Preliminary Review of Biotechnology in Forestry, Including Genetic Modification, Forest Genetic Resources Working Paper Forest Resources Development Service, Forest Resources Division. Rome, Italy. FAO: 96.[permanent dead link]
^Strauss, S.H. (2009). "Strangled at birth? Forest biotech and the Convention on Biological Diversity". Nature Biotechnology. 27 (6): 519–27. doi:10.1038/nbt0609-519. PMID19513052.
^Williams, C.G. (2010). "Long-distance pine pollen still germinates after meso-scale dispersal". American Journal of Botany. 97 (5): 846–855. doi:10.3732/ajb.0900255. PMID21622450.
^James, R.R. (1997). "Utilizing a social ethic toward the environment in assessing genetically engineered insect-resistance in trees". Agriculture and Human Values. 14 (3): 237–249. doi:10.1023/A:1007408811726. S2CID153218540.
^Doering, D. S. (2001). "Will the Marketplace See the Sustainable Forest for the Transgenic Trees?"(PDF). Proceedings of the First International Symposium on Ecological and Societal Aspects of Transgenic Plantations: 70–81. Archived from the original(PDF) on 2 February 2014. Retrieved 25 January 2014. The communities at or near the plantations and the paper mills may receive a net environmental benefit of cleaner water and air in their communities. (p. 73)
^Meilan, R. (2007). "Manipulating Lignin Biosynthesis to Improve Populus as a Bio-Energy Feedstock"(PDF). Institute of Forest Biotechnology, Genetically Engineered Forest Trees - Identifying Priorities for Ecological Risk Assessment: 55–61. Archived from the original(PDF) on 2 February 2014. Retrieved 25 January 2014. Some scientists believe ... that reducing lignin content may lead to increases in cellulose content. But critics argue that reductions in lignin will compromise the structural integrity of the plant and make it more susceptible to pathogens, and diseases. (p. 59)
^Hall, C. (2007). "GM technology in forestry: lessons from the GM food 'debate'". International Journal of Biotechnology. 9 (5): 436–447. doi:10.1504/ijbt.2007.014270. Archived from the original on 2014-02-02. Retrieved 2014-01-25. Altering the quality or quantity of lignin may have significant impacts on the survival abilities of the tree, such as impairing its pest or disease resistance and necessitating the use of additional pesticides.
^Wilkerson, C. G.; Mansfield, S. D.; Lu, F.; Withers, S.; Park, J.-Y.; Karlen, S. D.; Gonzales-Vigil, E.; Padmakshan, D.; Unda, F.; Rencoret, J.; Ralph, J. (2014). "Monolignol Ferulate Transferase Introduces Chemically Labile Linkages into the Lignin Backbone". Science. 344 (6179): 90–93. Bibcode:2014Sci...344...90W. doi:10.1126/science.1250161. hdl:10261/95743. PMID24700858. S2CID25429319.
^Harfouche, A.; et al. (2011). "Tree genetic engineering and applications to sustainable forestry and biomass production". Trends in Biotechnology. 29 (1): 9–17. doi:10.1016/j.tibtech.2010.09.003. PMID20970211. ArborGen is a joint venture between International Paper Company (USA) MeadWestvaco (USA) and Rubicon Limited (New Zealand) (p.13)
^"Deliberate release of genetically modified trees An abundance of poplars". GMO Safety. 1 June 2012. Archived from the original on 2 February 2014. Retrieved 27 January 2014. A gene has been introduced into the trees that makes them less sensitive to cold. Until now cultivation of eucalyptus in the US was only possible on the southern tip of Florida; frost tolerance could mean that cultivation would be possible in other parts of the USA.
^Gerber, J.F. (2011). "Conflicts over industrial tree plantations in the South: Who, how and why?". Global Environmental Change. 21 (1): 165–176. Bibcode:2011GEC....21..165G. doi:10.1016/j.gloenvcha.2010.09.005. Fast-wood plantations tend to destabilize water cycles provoking reduced water flow throughout the year, the disappearance of streams during the dry season, and damages to other (agro-)ecosystems (p.167)
^Owusu, R.A. (1999). "GM technology in the forest sector - A scoping study for WWF"(PDF). WWF. Archived(PDF) from the original on 2014-02-01. Retrieved 2014-01-25. Biotechnology may inadvertently become yet another driver for inappropriate plantation development. Increased soil nutrient and water demand of fast growing species on short rotations could lead to irrecoverable loss of site productivity. (p.5)
^Nottingham, S. (2002). Genescapes - The Ecology of Genetic Engineering. Zed Books. ISBN9781842770375. Archived from the original on 2024-05-04. Retrieved 2021-05-29. fast-growing transgenic trees will make additional demands on soil nutrients and water, with consequences for the long-term fertility of soils. Substantial fertilizer inputs might be necessary to maintain high yields
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^Powell, William (March 2014) "the American Chestnut's Genetic Rebirth", Scientific American, Volume 310, Number 3, Page 52
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^Then, C.; Hamberger, S. (2010). "Genetically engineered trees – a ticking "time bomb"?"(PDF). Testbiotech. Archived(PDF) from the original on 2014-02-01. Retrieved 2014-01-29. Bt poplars are grown alongside non-transgenic trees, possibly delaying the emergence of resistances. If this is the case, the transgenic poplars will have higher fitness in comparison to the other trees, thus conceivably fostering their invasiveness in the mid or even long-term. (p.16)
