… maybe they aren’t quite that black-and-white about it, but … trying to plant our way out of global warming is going to have some so-far-underappreciated side effects.
Planting trees to absorb carbon and reduce the threat of climate change could cause a range of new environmental problems.
… tree plantations can dramatically reduce water availability, remove nutrients from soil and increase its salinity. … better planning is needed to assess the environmental costs and benefits of planting trees to mitigate climate change.
… it is important to think carefully about where and what people plant, particularly where water resources are scarce.
Scientists: Planting trees bad for environment
IEMA (2005)
https://www.iema.net/resources/news/2005/12/28/scientists-planting-trees-bad-for-environment
OK, so maybe they aren’t quite that black-and-white about it, but scientists whose work is described in today’s issue of Nature suggest that trying to plant our way out of global warming is going to have some so-far-underappreciated side effects.
Planting trees to absorb carbon and reduce the threat of climate change could cause a range of new environmental problems, researchers warn.
In a global study published today (23 December) in Science, the researchers say tree plantations can dramatically reduce water availability, remove nutrients from soil and increase its salinity. They say better planning is needed to assess the environmental costs and benefits of planting trees to mitigate climate change.
“The purpose of our paper isn’t to suggest that plantations are bad,” says lead author Robert Jackson of Duke University, United States.
“Rather, we are saying it is important to think carefully about where and what people plant, particularly where water resources are scarce.”
Climate change is partly caused by increased concentrations of the gas carbon dioxide in the atmosphere. Planting trees can help limit climate change because, as trees grow, they absorb large amounts of carbon from the atmosphere, and store it in their tissues. Tree planting is set to increase in developing countries as ‘carbon trading’ initiatives such as the Clean Development Mechanism of the Kyoto Protocol get underway. But young trees use up considerably more water than crops or pastures. This can decrease the flow of water in nearby streams or dry them out completely. By absorbing more nutrients than other types of vegetation, trees can also change the chemical make-up of soil.
“They take up ‘good’ nutrients, such as nitrogen, calcium, and potassium, and leave behind others, such as sodium, that can increase salinity,” explains Jackson. Trees can also deplete shallow underground supplies of freshwater, drawing up deeper salty water and potentially affecting local drinking water supplies, as has happened in parts of Argentina. But Jackson points out that tree plantations have also benefited regions such as Africa’s Sahel, where trees can improve water quality.
Plantations also help reduce erosion and nutrient and pesticide runoff when croplands are replaced with trees. He adds that wetter regions in developing countries may be the best place for new plantations.
Trading water for carbon with biological carbon sequestration
Robert B Jackson, Esteban G Jobbágy, Roni Avissar, Somnath Baidya Roy, Damian J Barrett, Charles W Cook, Kathleen A Farley, David C le Maitre, Bruce A McCarl, Brian C Murray
(2005)
https://pubmed.ncbi.nlm.nih.gov/16373572/
Carbon sequestration strategies highlight tree plantations without considering their full environmental consequences. We combined field research, synthesis of more than 600 observations, and climate and economic modeling to document substantial losses in stream flow, and increased soil salinization and acidification, with afforestation. Plantations decreased stream flow by 227 millimeters per year globally (52%), with 13% of streams drying completely for at least 1 year. Regional modeling of U.S. plantation scenarios suggests that climate feedbacks are unlikely to offset such water losses and could exacerbate them. Plantations can help control groundwater recharge and upwelling but reduce stream flow and salinize and acidify some soils.
Effects of afforestation on water yield: a global synthesiswith implications for policy
Kathleen A. Farley, Esteban G Jobbágy, Robert B Jackson
(2005)
https://www.academia.edu/22300769/Effects_of_afforestation_on_water_yield_a_global_synthesis_with_implications_for_policy
Carbon sequestration programs, including afforestation and reforestation, are gainingattention globally and will alter many ecosystem processes, including water yield. Someprevious analyses have addressed deforestation and water yield, while the effects ofafforestation on water yield have been considered for some regions. However, to our knowledge no systematic global analysis of the effects of afforestation on water yieldhas been undertaken. To assess and predict these effects globally, we analyzed 26catchment data sets with 504 observations, including annual runoff and low flow. Weexamined changes in the context of several variables, including original vegetation type,plantation species, plantation age, and mean annual precipitation (MAP). All of thesevariables should be useful for understanding and modeling the effects of afforestationon water yield. We found that annual runoff was reduced on average by 44% (±3%) and31% (±2%) when grasslands and shrublands were afforested, respectively. Eucalyptshad a larger impact than other tree species in afforested grasslands (P=0.002), reducingrunoff (90) by 75% (±10%), compared with a 40% (±3%) average decrease with pines.Runoff losses increased significantly with plantation age for at least 20 years after planting, whether expressed as absolute changes (mm) or as a proportion of predictedrunoff (%) (P<0.001). For grasslands, absolute reductions in annual runoff were greatestat wetter sites, but proportional reductions were significantly larger in drier sites(P<0.01 and P<0.001, respectively). Afforestation effects on low flow were similar tothose on total annual flow, but proportional reductions were even larger for low flow(P<0.001). These results clearly demonstrate that reductions in runoff can be expectedfollowing afforestation of grasslands and shrublands and may be most severe in drier regions. Our results suggest that, in a region where natural runoff is less than 10% ofMAP, afforestation should result in a complete loss of runoff; where natural runoff is30% of precipitation, it will likely be cut by half or more when trees are planted. Thepossibility that afforestation could cause or intensify water shortages in many locationsis a tradeoff that should be explicitly addressed in carbon sequestration programs.
Robert Jackson
https://nicholas.duke.edu/people/faculty/jackson
Robert B. Jackson is the Nicholas Chair of Global Environmental Change in the Earth and Ocean Sciences Division of the Nicholas School of the Environment and a professor in the Biology Department. His research examines how people affect the earth, including studies of the global carbon and water cycles, biosphere/atmosphere interactions, energy use, and global change.
Rob Jackson received his B.S. degree in Chemical Engineering from Rice University (1983). He worked four years for the Dow Chemical Company before obtaining M.S. degrees in Ecology (1990) and Statistics (1992) and a Ph.D. in Ecology (1992) at Utah State University. He was a Department of Energy Distinguished Postdoctoral Fellow for Global Change at Stanford University and an assistant professor at the University of Texas before joining the Duke faculty in 1999. He is currently Director of Duke’s Center on Global Change and Duke’s Stable Isotope Mass Spectrometry Laboratory. In his quest for solutions to global warming, he also directs the Department of Energy-funded National Institute for Climate Change Research for the southeastern U.S. and co-directed the Climate Change Policy Partnership, working with energy and utility corporations to find practical strategies to combat climate change.
Jackson has received numerous awards, including the Murray F. Buell Award from the Ecological Society of America, a 1999 Presidential Early Career Award in Science and Engineering from the National Science Foundation (one of 19 scientists honored at the White House by President Clinton), a Fellow in the American Geophysical Union, and inclusion in the top 0.5% of most cited scientific researchers (http://www.isihighlycited.com/). His 150+ peer-reviewed scientific publications have been cited more than 15,000 and 25,000 times in Web of Science and Google Scholar, respectively. His trade book on global change, The Earth Remains Forever, was published in October of 2002. His first children’s book, “Animal Mischief”, was published in March of 2006 by Boyds Mills Press, the trade arm of Highlights Magazine for children. Its sequel, “Weekend Mischief”, appeared in 2010.
Jackson’s research has been covered in various newspapers and magazines, such as the Boston Globe, New York Times, Washington Post, USA Today, Scientific American, and BusinessWeek, and on national public radio, including the syndicated programs “Morning Edition”, “All Things Considered”, “Marketplace”, “The Tavis Smiley Show”, “The Next 200 Years”, and “Earth and Sky” (for which he was a science advisor and scriptwriter). He conceived and organized the Janus Fellowship, an annual undergraduate award to encourage the study of an environmental problem from diverse perspectives; 1999’s first recipient traveled down the Nile River to examine water use and water policy in Egypt.
Tree-planting projects may not be so green
· Knock-on effect thwarts carbon offsetting plan
· Attempts to undo CO2 damage a short-term fix
by James Randerson
(2005)
https://www.theguardian.com/environment/2005/dec/23/frontpagenews.climatechange
Brides and grooms do it. Transatlantic travellers do it. And you might even be getting it for Christmas. Neutralising your carbon emissions is becoming the must-do activity for the eco-conscious citizen. But now an international team of scientists has raised an unexpected objection: some tree-planting projects may, they suggest, be doing more harm than good.
Carbon offsetting allows people to pay someone else to atone for their climate sins by soaking up the CO2 that they produce. And with the consequences of global warming becoming more apparent, more Britons are opting to undo their personal share of the damage.
Last year companies and individuals in the UK spent around £4m offsetting carbon emissions. The Kyoto protocol allows member countries to do the same through carbon trading.
But it seems the guilt-free option is not as simple as writing a cheque and leaving it to someone else to sort out. Researchers have found that planting trees to soak up carbon can have detrimental knock on effects. “I believe we haven’t thought through the consequences of this,” says team-member Robert Jackson at Duke University in North Carolina, “I think the policy could backfire on us, but it will take decades to play out.”
His team pooled more than 500 separate yearly observations from studies from five continents which compared planted areas with plots nearby that did not have trees. They report in Science that the plantations had a drastic effect on stream flow. By sucking water out of the ground and evaporating it from their leaves the trees reduced flow by half. And 13% of streams dried up for at least a year. This would have effects downstream where less water would be available for plants and animals.
The team found that nutrients in the soil were also affected by tree planting. Calcium, magnesium and potassium were all depleted while sodium was enriched, meaning that plantation soil was more salty on average. All of these changes would affect the range of plant species.
Dr Jackson says the two most common plantation species are pines and eucalyptus trees. These fast-growing species rapidly suck CO2 out of the atmosphere, but they result in monoculture forests which support a meagre range of biodiversity. Dr Jackson stresses that planting trees is not a bad thing per se, but schemes that are not well thought through can be environmentally harmful.
Tree-planting has always been a controversial method of soaking up CO2 because it is little more than a short term fix. Once the trees die they rot, releasing the carbon back into the atmosphere. “We are buying a few decades to transform our economies,” says Dr Jackson.
Chris Field, an ecologist at the Carnegie Institution of Washington in Stanford, California, agrees. “It is not a slam dunk in terms of providing the kind of carbon benefit we would like to have,” he says, “In the long run, solving the carbon problem is going to be more about reducing emissions rather than storage.”
So where does this leave the eco-minded citizen who wants to tread a lighter carbon footprint? “Start by doing what you can yourself,” says Tom Delay, chief executive of the Carbon Trust, a government funded company that is charged with helping UK businesses reduce their carbon emissions. “Most of the actions you can take will save you money as well as have a climate benefit.” So installing energy saving light bulbs, insulating the loft or using the car less is a good start.
When it comes to buying a carbon offset, things get more tricky. “It’s something of a wild west at the moment,” says Bill Sneyd, operations direction of The Carbon Neutral Company (formerly known as Future Forests), the UK’s largest company selling carbon offsets. This year it planted just under 300 hectares (750 acres) of new forest. Their plantations are planted with 90% native species, but he says the range of tree-planting options on offer vary widely in their knock-on effects on environment.
Tom Morton, director of Climate Care, a not-for-profit organisation based in Oxford, says tree planting is often the form of carbon offset that is most recognisable with the public. “These are often the easiest projects for people to understand.” But he believes the biggest gains will come through new technologies. Four fifths of Climate Care’s funding goes into supporting energy efficient or low-carbon technologies, for example training people in Madagascar to use energy efficient cooking stoves.
Conscience money
How to ease your climate conscience and neutralise your carbon emissions
· If you want to support forestry make sure the plantation will use native species/promote biodiversity
· Make sure it is protected from future logging or fire
· When donating to a company offering carbon offset projects check the cash is actually needed to get the project off the ground · Check the project has the support of local people · Ensure it represents a cost effective way of reducing carbon – has a responsible company or not-for-profit organisation audited the project?
· Consider supporting other carbon reduction options, such as funding energy efficient equipment or businesses selling low carbon technology
Why planting trees is not the solution to global warming
Guardian
(2005)
https://www.theguardian.com/environment/2005/dec/27/guardianletters.climatechange
**
The Guardian is correct to point out the problems of tree planting as an off-the-shelf “solution” to global warming (Tree-planting projects may not be so green, December 23). But the problems of carbon-offset forestry far exceed reducing stream flow, changing soil chemistry and unreliable rates of carbon absorption. Large-scale forest plantations also impact negatively on biodiversity.
Moreover, forest plantations create various social and political problems for people in developing countries who may be prevented from gaining access to land needed for food production, or who may be prevented from collecting forest products for food, medicines, fuel or trading purposes. In Brazil, for example, local people have formed the Green Desert Network to counter industrial tree plantations. And in November 2005, representatives of organisations from Africa, Asia, Latin America, Europe and the US issued a declaration at the Brazilian city of Vitoria to support the rights of local people against land closure resulting from plantation forestry. The Uruguay-based NGO the World Rainforest Movement (wrm.org.uy) publishes further information about these struggles.
Many environmental consultancies in Europe and North America like to point out the possible benefits of tree planting as a way to offset carbon emissions, and some even suggest this can help prevent the destruction of rainforests. The reality is different. The best way to counter global warming is to reduce greenhouse gas emissions at source through greater energy efficiency and reduced consumption, rather than creating various ecological and social problems by creating plantations in poor countries.
Dr Tim Forsyth
Development Studies Institute, LSE
**
By omitting any reference to the underlying soil, your correspondent tells only half of the carbon story. Trees, like other forms of vegetation, deposit carbon below ground, a proportion of which is stabilised for hundreds of years. The potential to do this varies between soils and will be greater in sandy mineral rather than peaty soils. Similarly, the impact of trees on mineral nutrients is not as negative as the article suggests, as nutrients are recycled through the litter and also intercepted from aerosols in the atmosphere. Compared to the total contents of major nutrients in a mineral soil, the quantity in the tree crop is small.
The controversy revolves around a “quick fix” approach to atmospheric CO2; the choice of fast-growing species such as eucalypts containing volatile compounds raises issues such as susceptibility to fire and damaging effects on soil. Forest management and harvesting methods to optimise the stabilisation of carbon in soils as well as trees offer a long-term alternative that should not be ignored.
Berwyn Williams
Westhill, Aberdeenshire
**
Offsetting carbon emissions by planting new forests lasts only as long as the trees are standing, because stored carbon is released back into the atmosphere as the forest biomass decomposes after logging. That is true unless you plant the forest again after you cut it down. Over a few decades, the landscape then permanently stores a certain amount of carbon – as long as you keep replanting – while also providing timber and (with more smart choices) habitat for wildlife.
The solution to the temporary nature of carbon sequestration in planted forests is thus simple: make logging without replanting subject to a carbon emissions permit. With carbon trading, the price of a permit will be high in 30 years’ time when the trees are harvested (unless we’ve solved our carbon addiction and live in a low-C economy), providing a healthy incentive for the forest’s owners to replant and to continue replanting until greenhouse gas pollution is no longer an issue.
Dr Mark Smith
East Kilbride, S Lanarkshire