Accurate crop yield predictions from modelling tree-crop interactions in gliricidia-maize agroforestry
Accurate crop yield predictions from modelling tree-crop interactions in gliricidia-maize agroforestry
22 August, 2017
FTA COMMUNICATIONS TEAM
Agroforestry systems, containing mixtures of trees and crops, are often promoted because the net effect of interactions between woody and herbaceous components is thought to be positive if evaluated over the long term. From a modelling perspective, agroforestry has received much less attention than monocultures. However, for the potential of agroforestry to impact food security in Africa to be fully evaluated, models are required that accurately predict crop yields in the presence of trees.
The positive effects of the fertiliser tree gliricidia (Gliricidia sepium) on maize (Zea mays) are well documented and use of this tree-crop combination to increase crop production is expanding in several African countries. Simulation of gliricidia-maize interactions can complement field trials by predicting crop response across a broader range of contexts than can be achieved by experimentation alone. We tested a model developed within the APSIM framework. APSIM models are widely used for one dimensional (1D), process-based simulation of crops such as maize and wheat in monoculture. The Next Generation version of APSIM was used here to test a 2D agroforestry model where maize growth and yield varied spatially in response to interactions with gliricidia.
The simulations were done using data for gliricidia-maize interactions over two years (short-term) in Kenya and 11 years (long-term) in Malawi, with differing proportions of trees and crops and contrasting management. Predictions were compared with observations for maize grain yield, and soil water content. Simulations in Kenya were in agreement with observed yields reflecting lower observed maize germination in rows close to gliricidia. Soil water content was also adequately simulated, except for a tendency for slower simulated drying of the soil profile each season. Simulated maize yields in Malawi were also in agreement with observations.
Trends in soil carbon over a decade were similar to those measured, but could not be statistically evaluated. These results show that the agroforestry model in APSIM Next Generation adequately represented tree-crop interactions in these two contrasting agro-ecological conditions and agroforestry practices. Further testing of the model is warranted to explore tree-crop interactions under a wider range of environmental conditions.
Gendered Responses to Drought in Yunnan Province, China
Gendered Responses to Drought in Yunnan Province, China
21 August, 2017
FTA COMMUNICATIONS TEAM
Vulnerability to and perceptions of climate change may be significantly affected by gender. However, in China, gender is rarely addressed in climate adaption or resource management strategies. This paper demonstrates the relevance of gender in responses to climate change in the mountainous province of Yunnan in southwest China.
Based on surveys undertaken during a record-breaking drought, the paper explores how women and men in a village in Baoshan Prefecture differ in their perceptions of and responses to drought, and how the changing roles of women and men in the home and the community are influencing water management at the village level.
Our results show that despite the increasingly active role of women in managing water during the drought, they are excluded from community-level decision-making about water. The paper argues that given the importance of gender differences in perceptions of and responses to drought, the lack of a gender perspective in Chinese policy may undermine efforts to support local resource management and climate adaptation.
Can agroforestry landscapes reduce the risk of floods?
Can agroforestry landscapes reduce the risk of floods?
Floods become a normal part of life when floodplains are converted. Photo by ICRAF
FTA COMMUNICATIONS TEAM
There is a lack of evidence of the effects of trees on reducing, or worsening, floods. Arguments continue about whether the research results that do exist from small-scale studies also apply at larger scales. A new technique is proving useful for finding evidence and better predicting trees’ role in flood mitigation.
Not surprisingly, humans have found the subject of floods of compelling interest, especially the extent to which removing trees from a watershed increases or decreases the risk of flooding. The pros and cons of deforestation have been hotly debated over the last 100 years and the basic concepts go back 2000 years.
The debate oscillates between strong over-generalizations — encapsulated in statements such as ‘forests are good for any aspect of water’ — to disbelief in anything not supported by strong evidence.
For CGIAR Research Program on Forests, Trees and Agroforestry (FTA) scientist Meine van Noordwijk of the World Agroforestry Centre (ICRAF), the challenge in the debate is properly understanding things at scale. Does deforestation increase the risk of flooding from small to large scales — and even can any flood be attributed to removing or adding trees — or is the evidence primarily valid only at the scale of measurement and not necessarily beyond?
For example, can the results of research in a small catchment be applied across a much larger landscape and help to decide whether more or less trees are needed to reduce flooding, or whether they have any effect at all?
A new article in the journal, Hydrology and Earth System Science, explores the middle ground in the debate and offers scientists an easier way of predicting river flow from rainfall and, consequently, the likelihood of flooding.
It is correlated with two metrics that have been used before: a ‘flashiness’ index as indicator of catchment health; and a ‘base flow’ metric that represents the opposite aspect of continued flow in dry periods. The empirical relationship between these two metrics depends on the context: terrain and details of rainfall patterns. The flow persistence metric can be derived from any period of consistent river flow measurements.
Of course, the more data, the more accurate the estimates will be but data requirements are much less than for the models that have been used so far. This is a good step in the right direction for better understanding how catchments work and how flooding can be reduced.
“Good quality data on river flow is scarce for many tropical watersheds,” said Van Noordwijk, lead author of the study, “so we need to first of all rely on consistency of interpretation and robust indicators of ‘buffering’ as the key process linking floods to rainfall. What we presented is a simple metric called ‘flow persistence’. Where its value is high, it means that only a small fraction of peak rainfall comes to the river the same day; when it is low, peak river flow will be high but will rapidly decline after that.”
Co-author Betha Lusiana, who heads ICRAF’s ecological modelling unit in Indonesia, explained that, “When we applied this method to cases in Southeast Asia, we found that annual variations in rainfall are such that effects of land cover on river flow in anything other than a small catchment can only be asserted statistically with long-term data. Lack of evidence of effects is not the same as evidence of lack of effects, as Sherlock Holmes already noted.”
There is a lot of interest in “restoration”, but we need metrics of where it is most relevant. The Flow Persistence method makes it easier for scientists to gather and analyse data extrapolate it across whole landscapes. This improves the ability to predict effect on river flow, and the potential for flooding, if trees in the form of agroforests are put back into large-scale, deforested landscapes.
This, too, is an area of research which hasn’t been fully studied at large scale yet such knowledge is in increasing demand to meet the needs of the various global programs aimed at rehabilitating the many millions of hectares of degraded landscapes.
“When forests are removed and the land is used for agriculture or other purposes, we observed that the flow persistence decreases when the soils no longer absorb all the rain,” explained Lisa Tanika, who is ICRAF’s hydrologist in Indonesia, “whereas agroforestation, which returns trees to the landscape, can induce a restoration of hydrological functions but it will take 5-to-10 years to see the effects.”
Being able to predict more accurately the restoration of such functions that are provided by different combinations of tree species in landscapes increasingly stressed by extremes of climate will increase the efficiency and effectiveness of rehabilitation programs.
The findings come at an appropriate time, following on from a recent, ground-breaking symposium that brought to the world’s attention the importance of forests and agroforests in the production of atmospheric moisture, a role second only to the world’s oceans in the global water cycle.
“Rather than think of trees only as things that soak up carbon and reduce the harmful effects of greenhouse gases, which is how international bodies like the United Nations Framework Convention on Climate Change see them,” argued Van Noordwijk, who was a key presenter at the symposium.
“We need to shift the focus to their role in the water cycle, something especially important for an increasingly hot and dry world. The Flow Persistence metric is a small but important part of such a shift.”
Connecting the dots between forests, water and climate
Connecting the dots between forests, water and climate
Left to right: Meine van Noordwijk, Chief Science Advisor of the World Agroforestry Centre, and Vincent Gitz, Director of the CGIAR Programme on Forests, Trees and Agroforestry, talking with the audience in Bogor, Indonesia as part of the virtual symposium. Photo: World Agroforestry Centre/Riky Hilmansyah
More than 500 people from around the world tuned in on 21 and 22 March 2017 to Cool Insights for a Hot World, a virtual symposium to engage with scientists in a discussion about the links between forests, water and climate, on the International Day of Forests and World Water Day, respectively.
Scientists from the fields of biology, chemistry, climate science, geology, hydrology and social science, spoke with one voice in calling for greater attention to be paid to the vital role of trees in the water cycle. The functionality of trees is of great importance given forests’ ability to produce moisture that is then transported from one area to another by winds, eventually falling as rain far from its source and crossing national boundaries on the way.
That the geopolitical consequences of deforestation in one country can exert a serious impact on rainfall in another country did not go unnoticed. The scientists recommended the establishment of regional bodies to manage ‘precipitation-sheds’, areas that generate moisture into the atmosphere, in order to mitigate potential conflict arising from mismanagement of the forests that make up precipitation-sheds.
Jointly hosted by the World Agroforestry Centre and the Center for International Forestry Research, the symposium explored the interconnectedness of forests and water in addressing climate change, drawing on a recent study, Trees, forests and water: cool insights for a hot world. A key takeaway from the study showed that where rain is produced and where it falls both have wide a ranging impact on the security of water supplies and food production as well as the ability of nations to adapt to, and mitigate, climate change.
Call to action
Forests and trees’ critical role in global, regional and national water cycles is second only to the influence of the world’s oceans. Yet, this is mostly left off global discourse on climate change, which largely focuses on forests and trees as carbon stocks and sinks as part of national actions to reduce emissions of greenhouse gases.
At the local level, the planting of trees is an immediate action easily available to householders, farmers and urban dwellers, one that contributes to cooling the Earth through the moisture released by trees through evapotranspiration. Tree-planting need not wait for global agreements to be in place, the scientists noted.
The symposium was organized under the aegis of the CGIAR Research Program on Forests, Trees and Agroforestry. Participating scientists included David Ellison (Swedish University of Agricultural Sciences), Cindy Morris (French National Institute for Agricultural Research), Michael Marshall (World Agroforestry Centre), Aster Gebrekirstos (World Agroforestry Centre and Erlangen University), Meine van Noordwijk (World Agroforestry Centre and Wageningen University), Jan Pokorný (ENKI, Czech Republic); Douglas Sheil (Norwegian University of Life Sciences), Victoria Gutierrez (WeForest), Daniel Murdiyarso (Center for International Forestry Research and Bogor Agricultural University) and Elaine Springgay (Food and Agriculture Organization of the United Nations).
Learn more about forests and trees and their role in the water cycle
Since Rio 1992 and the climate convention, climate policy has put a “mitigation” sticker – with the associated pressure – on forests and land use for their role in climate, emphasizing the carbon stored in forests and peat soil, and the capacity of trees to sequester carbon.
This triggered a lot of scientific work and publications, including by FTA scientists, on the best pathways to strengthen the role of forests and trees in climate mitigation. Attention was given to integration with other dimensions (‘cobenefits’ and ‘safeguards’) beyond carbon measures, especially social and economic dimensions.
It also triggered many debates, in science and in policy, as to whether or not this was the right approach, such as the recurrent debates about land-use and forestry-related loopholes in the necessary climate action in the energy sector.
However, this perspective on forests and climate change might well change radically. And the change may not come from carbon, but from water.
What is this new light? The findings of the review, with the level of confidence of underlying scientific evidence – assessed in the symposium – are the following:
Trees influence local temperature through high transpiration rates, and remote sensing and infrared tools exist for visualizing this effect (very high confidence).
Forests recharge atmospheric moisture and regional evapotranspiration responds to tree-cover transitions (very high confidence).
Vegetation and trees influence cloud formation and trigger rainfall via bioprecipitation effects (high confidence).
Historical evidence from tree rings and their isotopic composition shows decadal variation and local influences of land use on local rainfall and climate (medium confidence).
Rainbow (atmospheric) water bookkeeping combined with prevailing winds shows continental-scale teleconnections on all tropical continents. Forests enable cascading transport of water vapor over distant locations, and therefore rain, far from the sea (high confidence).
Forests, as biotic pumps, attract air and moisture flows, and the loss of forests can create a tipping point turning wet climates to dry climates (medium confidence).
Trees and forests can improve groundwater recharge, with the existence of an optimum level of tree cover for that effect (high confidence).
To sum up: forests and trees are drivers of key mechanisms that govern the water cycle, atmospheric moisture, precipitation and climate at the local, regional and continental levels. In other words, forests and trees can help manage the water cycle not only from the well-known watershed perspective, but from a precipitation-shed perspective, with key implications for climate regulation. Geopolitical implications are huge: Who has the right to influence rainfall elsewhere? Yet, that happens every day, according to the new hydroclimate paradigms.
Altogether, these findings have significant implications for policy and action, and for research – particularly for FTA research – and what it can do or the tools it can provide to inform and underpin this new agenda.
The first implication is for climate research itself, to better understand “where does rain come from?” with a priority challenge of better incorporating the above processes in general circulation models. This would inter alia lead to the improvement of the projection of precipitation and its variability, and to a better estimation of the magnitude of the effects by which forests – and land use – contribute to the processes that determine winds and rain in different regions. We need to better quantify the extent of relevant hydroclimatic relations between trees, forests and climate.
In climate policy, it calls for a threefold change of narrative:
Carbon sequestration and mitigation, rather than being the main focus, are to be seen as cobenefits of climate action in landscapes.
Adaptation of forests is important, but even more important is the role that forests and trees will play for the adaptation of agriculture, food security, water security and livelihoods, as well as to avoid ecosystems experiencing tipping points.
The top-down policy perspective on forests (their role in the global carbon cycle, absorbing the world’s excess CO2) is shifting to a bottom-up policy perspective (their role in the water cycle and in localized climates).
This triple change of narrative calls for research to look into integrated approaches to revisit the currently segregated mitigation-versus-adaptation frameworks (including related procedures and funding), especially from the perspective of the implementation of the NDCs, many of which include a range of targets for sustainable forest management, including afforestation, reforestation and forest restoration.
It will further interrogate REDD+ and call for research to help establishing measurable metrics to quantify the role of forests with regard to adaptation benefits on different scales, from local and national to regional and continental. More broadly, it will call on research to assist in the refinement of existing and new climate change policy frameworks, building on the adaptation article (Article 7) of the Paris Agreement, in order to ensure synergies with and within the SDGs.
Importantly, it will also put back the mitigation focus on fossil fuels and the energy sector, contributing to ending the often counterproductive land carbon “loophole” debate, while at the same time giving even more emphasis to the roles of land use, forests and trees for climate regulation.
These findings can help better understand – or avoid mistakes on – what to plant where and how or what natural regeneration to assist. They provide a hydroclimatic rationale over and above the current carbo-climate metrics of performance for tree-based landscape restoration.
They call for research to provide more information on plant functional attributes (as a source of nucleating particles for biological generation of rainfall) across climates and ecozones. They also call for research to provide tools that include a hydroclimatic perspective for stakeholders to better assess the costs and benefits of action including not only downstream benefits, but also those beyond the watershed, downwind, complemented by economic and social analysis.
Integrated landscape policies
Here the question is how to organize land use on different scales for water and climate. More effective, tailored information (including maps, transfer functions, remote sensing and visualization tools) on the location-specific nature of atmospheric moisture, rainfall and their sources can lead to improved integrated water, land and climate policies in the forest-rural-urban continuum.
This would lead to water policies going beyond the watersheds, toward “precipitationsheds.” Research should look into what institutional mechanisms and incentive schemes would account for such land/water teleconnections, and remote impacts from where actual land use, tree planting or removal decisions are made.
This research gives a new perspective on the role of forests and trees from continental to farm scale for food production and food security. Here research should strive for a better understanding of the decadal scale variation in rainfall and its origins (oceanic/terrestrial), to contextualize current climate and yield variability and support landscape-level ‘climate-smart’ options.
It can document and quantify the role of forests that generate rainfall in teleconnected but distant areas (including “bread baskets”). Finally, on a more local scale, it can provide new insights on how to integrate trees and forests in agriculture/crop systems.
Sustainable Development Goals
A last domain relates to the achievement of the SDGs. Expanding our interpretation of the development targets to embrace the concept of a land-food-water-energy-climate-biodiversity nexus on the landscape scale could provide a better point of reference than existing segregated policies. Research should provide operational insights on the use of forests and trees – fully embracing their relationship with water – in achieving and connecting the SDGs. It should aim for actionable, concrete and easy-to-grasp solutions for multiple objectives, and guidance on forests, trees and land-use options are part of them.
It is not often in research that efforts lead to considering possible “changes of theory” and such-wide ranging implications. The next challenge for research is both internal and external: for us to better quantify and assess the magnitude of these relations, providing clarity about uncertainties and validity domains (including on the diversity of local-specific situations), and to avoid oversimplification.
This will enable us to pursue our quest for strengthening the knowledge base, while being credible enough not to delay the opening of new avenues for action, with clarity on current evidence, (un)certainties, and policy and development implications.
New research has revealed a multitude of ways in which forests create rain and cool local climates, urging a closer look at forests’ capabilities beyond just climate change mitigation.
In a recent paper, 22 researchers from as many diverse institutions, call for a paradigm shift in the way the international community views forests and trees, from a carbon-centric model to one that recognizes their importance in cross-continental water cycles, as well as at the local scale.
“People are used to hearing the idea that forests are really important, but we now have a much deeper insight into why the loss of forest cover can have such a huge impact on water availability- especially for people downwind,” says study co-author Douglas Sheil from the Norwegian University of Life Sciences.
“The links are so much stronger than people previously thought. And if policymakers and land use planners are not aware of that, that’s a huge shortfall in decision making.”
So what exactly do we now know about forests and water?
Forests help raindrops form
Every day, forests replenish the supply of water vapour in the atmosphere. They draw up water through their roots, and release it from their leaves via transpiration. Along with evaporation from oceans and other water bodies, this is what drives the water cycle and charges the atmosphere with water vapor.
“The process is so powerful that it can be seen from space,” says co-author David Gaveau from the Center for International Forestry Research (CIFOR). “If you look at satellite images [above] of the Amazon, central Africa, or Southeast Asia, you can see these flashes of water vapor bubbling up.”
“We use the phrase ‘lungs of the planet’ all the time, but here you can really see this natural rhythm of forests actually breathing water vapor into the atmosphere.”
Recent studies have shown that as much as 70 percent of the atmospheric moisture generated over land areas comes from plants (as opposed to evaporation from lakes or rivers) – much more than previously thought.
In addition, new research has revealed that forests also play a key role in water vapor actually forming clouds and then falling as rain.
Trees emit aerosols that contain tiny biological particles – fungal spores, pollen, microorganisms and general biological debris – that are swept up into the atmosphere. Rain can only fall when atmospheric water condensates into droplets, and these tiny particles make that easier by providing surfaces for the water to condense onto.
Some of these plant-based microorganisms even help water molecules to freeze at higher temperatures – a crucial step for cloud formation in temperate zones.
“These particles are incredibly important for the occurrence of rainfall in the first place,” says the study’s lead author David Ellison, from Ellison Consulting and the Swedish University of Agricultural Sciences. “If they’re missing, rainfall might not occur, or will occur less frequently.”
Trees can actually increase local water availability
Though the accepted orthodoxy is that trees remove water from catchments, and that planting trees reduces water availability for local people, another “game-changing” study has turned that assumption on its head.
“In a water-short environment, where people are digging their wells ever deeper because the groundwater is disappearing, it was believed that there’s a trade-off between planting trees and the water people need,” says Sheil. “A lot of donors have avoided supporting tree-planting in arid parts of the world because they see this as a conflict.”
But research conducted by Ulrik Ilstedt from the Swedish University of Agricultural Sciences, one of the study’s co-authors, has shown that in dry landscapes, trees (at some densities) can actually increase the availability of water, by assisting with groundwater recharge.
“What Ulrik has showed is that in the drylands of Africa, if you start planting trees you get an initial rise in the amount water in the landscape, because the trees actually use less water than the amount of additional water they allow to infiltrate through the soil,” Sheil says.
Tree roots – and the animals they attract like ants, termites and worms – help to create holes in the soil for the water to flow through.
“It’s pretty exciting,” says Sheil. “In huge areas of Africa, people can now start to plant trees. If you’re only interested in carbon, there are still lots of carbon benefits,” he says. “This is a win-win in every sense.”
Forests cool locally and globally
In tropical and temperate regions, forests cool the earth’s surface. It’s not just that they provide shade – the water they transpire also cools the air nearby.
“One single tree is equivalent to two air conditioners, and can reduce the temperature by up to 2 degrees,” says study author Daniel Murdiyarso, from CIFOR.
Maintaining tree cover can therefore reduce high temperatures and buffer some of the extremes likely to arise with climate change, the authors say.
The effect can even be seen in urban environments, says Gaveau. “We all feel it – if you go to the park on a hot day, and you go under a tree, you’ll feel the cooling effect.”
Forests may draw moisture into the heart of continents
The authors also draw attention to a recent theory that proposes that forests create winds, bringing rain into the heart of continents – and that without continuous forest cover from the coast to the interior, rainfall would drastically diminish.
The ‘biotic pump’ theory includes physical mechanisms not present in current climate models, and still hasn’t been proven, but scientists from CIFOR believe it is credible.
The model proposes that forests generate low atmospheric pressure, sucking moist air inland from the ocean, creating a positive feedback loop.
“One value of this theory is that it allows us to explain how we can get really high rainfall in the interior of continents – the Amazon Basin in South America and the Congo Basin in Africa – when the original source of water, the ocean, is so far from where the rain is falling,” says Sheil.
Another of the study’s authors, Dominick Spracklen, has previously showed that across most of the tropics, air that has passed over extensive vegetation in the preceding few days produces at least twice as much rain as air that has passed over little vegetation – showing the immediate effect of deforestation on rainfall patterns.
Forests affect water availability downwind – not just downstream
The atmospheric moisture generated by forests doesn’t just stay in the local catchment. In fact, most of it is blown by prevailing winds into other regions, countries, or even continents.
“The more that you remove forests and other vegetation cover from terrestrial surfaces, the more you damage that cross-continental water transport,” says Ellison.
That has geo-political consequences that are not yet well understood.
“We want people to start to think in terms of ‘upwind and downwind’ dynamics. Where does your water come from, and how much does the catchment basin that you’re a part of contribute to downwind rainfall?”
“If you’re a land-use planner or a water management planner, what happens if you remove forests? How does that impact people downwind? If you’re in a catchment with a declining water supply, how might you influence that through upwind interventions?”
These questions require extensive collaboration between countries, new institutional frameworks that don’t currently exist, and new ways of thinking about water catchments.
For example, an international partnership called the Nile River Basin Initiative currently only includes the countries that are part of the actual Nile catchment basin and use its water, Ellison says. But the central African countries where the rain comes from are not involved.
“So then the question becomes, who should be involved in the management of a catchment basin, if the source countries for the moisture are somewhere else? How can they be included? Can you get them to recognise that what goes on in their country may be closely connect to what happens in yours?”
“You can easily understand how this leads to dilemmas,” he says.
A call to action
The link between forests and climate is intuitive, and easily understood by everyone, says Gaveau. “When you look at the morning mist rising from a forest, you see that forests are transpiring water vapor. If you sit under a tree on a hot day in a city, you’ll feel cooler.”
“At the moment, the nexus between forests and water is sort of treated as a co-benefit to the carbon story, but it should be front and center. Carbon can seem abstract to many people, but a glass of drinking water – that’s a tangible thing.”
Given the mounting scientific evidence for just how strong this connection is, the study’s numerous authors have issued a “call to action”.
We need a new way of looking at forests that prioritizes water, they argue – even within the global climate change framework.
Protecting forests to ensure access to water will inevitably also increase carbon storage, mitigate climate change, and have other immediate benefits, says Murdiyarso.
“If you are talking about carbon, you will see the results in 15, 50, or 100 years. But we see these cycling processes of water every day.”
“Hopefully, this approach can shift the paradigm, and the course of the debate on climate change adaptation and mitigation.”
Anyone who has walked outside on a sunny day knows that forests and trees matter for temperature, humidity and wind speed. Planting trees speaks to concerns about climate change, but the directly important aspects of the tree-climate relationships have so far been overlooked in climate policy where it relates to forest.
Click here for more information on the Virtual Symposium on forests, climate and water on International Day of Forests, 21 March, and World Water Day, 22 March.
That, at least, is the conclusion of a new review. The authors suggest that the global conversation on trees, forests and climate needs to be turned on its head: the direct effects via rainfall and cooling may be more important than the well-studied effects through the global carbon balance.
Yet, current climate policy only recognizes the latter. While farmers understand that trees cool their homes, livestock and crops, they had to learn the complex and abstract language of greenhouse gasses and carbon stocks if they wanted to be part of climate mitigation efforts. Not anymore, if the new perspectives become widely accepted.
In the review, published in the journal Global Environmental Change, the 22 authors provide examples for the planet-cooling benefits of trees. Scientists found evidence for the widespread perception that trees and forests also influence rainfall. As such, the review insists that water, and not carbon, should become the primary motivation for adding and preserving trees in landscapes.
“Carbon sequestration is a co-benefit of the precipitation-recycling and cooling power of trees. As trees process and redistribute water, they simultaneously cool planetary surfaces”, says Dr David Ellison, lead author of the study.
“Some of the more refined details of how forests affect rainfall are still being discussed among scientists of different disciplines and backgrounds. But the direct relevance of trees and forests for protecting and intensifying the hydrologic cycle, associated cooling and the sharing of atmospheric moisture with downwind locations is beyond reasonable doubt.”
Trees are giant air conditioners with no power bills. They use solar energy to convert water into vapour, thereby cooling their surroundings. On a hot day the surface temperature of a forest—in an example discussed in the paper—is similar to that of a nearby lake, while a dry patch of meadow or a tarmac road in the vicinity are more than 20 °C hotter. The cooling power equivalent is around 70 kWh for every 100 liter of water transpired, similar to the output of two home air-conditioning units.
“There are important implications for practice, as we can no longer simply focus on carbon sequestration to mitigate or adapt to climate change”, says Dr Victoria Gutierrez, Chief Science Officer of the WeForest NGO that supports forest landscape restoration efforts in tropical countries, and co-author of the study.
“For organizations and agencies working to restore forest ecosystems for climate and people, it is crucial that we pay greater attention to the sustainability of the water processing and cooling aspects of the trees.”
Planting trees has long been an expression of intent to do something of substance in the climate change debate; scientists have found a new rationale for this.
As they cool the planet, trees may also promote rainfall. Two ingredients for rainfall are: i) water vapour in the atmosphere to which trees and wetlands contribute importantly and in quantities that can be measured, and ii) a starting point for condensation of vapour into cloud droplets and rain drops. Trees are a source of volatile compounds that can become cloud condensation nuclei and trees are also a source of bacteria that form ice nuclei.
“In clean, dust-free air, cloud droplets may cool down to -40 °C, high up in the atmosphere, before freezing occurs if there are no ice nuclei present that can catalyse freezing”, says Dr. Cindy Morris, one of the co-authors. “But trees and forests release ‘ice nuclei’ into the atmosphere including certain fungal spores, pollen and bacteria that can initiate rainfall at much warmer temperatures, sometimes as warm as -4 °C. This means that rain initiation can take place more readily in low-altitude clouds.”
As forests modify and contribute to the atmospheric flows of moist air they influence downwind rainfall. While coasts derive most of their rainfall from oceanic evaporation, downwind continental surfaces are increasingly dependent on upwind terrestrial sources of atmospheric moisture. On average 40% of rainfall over land is recycled from evapotranspiration over land surfaces.
Important examples of long-distance dependencies have been documented between the Congo basin and East Africa providing rain to the Ethiopian Highlands and the Sahel; the Amazon supporting rain in NW Argentina; and mainland Southeast Asia feeding atmospheric moisture to China. In all these cases, major changes in tree cover can break the chain and reduce precipitation in downwind basins.
“Where most water studies have focused on the ‘blue water’ in rivers and the ‘green water’ used by plants, water in the atmosphere is now recognized as ‘rainbow water’”, says Meine van Noordwijk, co-author, Chief Scientist with the World Agroforestry Centre (ICRAF) and Coordinator of the landscape theme of the CGIAR Research Program on Forests, Trees and Agroforestry. “The policy arena may have to adjust to the idea that rainfall is not simply the result of large scale air mass movements, but depends importantly on how upwind neighbours care for their forests.
“Reliable rainfall in the continental interiors of Africa and South America, as well as in other downwind locations, may depend on maintaining relatively intact and continuous tree cover from upwind coasts. The geopolitics of these relations can become a source of conflict, but can also lead to new types of cooperation.”
With these and more fascinating “cool insights” and evidence from research, the authors point out that there is a strong basis for a hydro-climate policy that involves forests and trees. This policy would be much wider than what has so far been shaped by scientific understanding of the greenhouse-gas dominated climate and been incorporated in international agreements.
The review concludes with a cry to action on forests, water and climate: “Climate policy must take these water-processing, cooling and rainfall-generating effects of trees and forests more explicitly into account.”
Significant revision of national, regional and continental climate change mitigation and adaptation strategies are urgent as next steps.
Read full review article: Ellison D, Morris CE, Locatelli B, Sheil D, Cohen J, Murdiyarso D, Gutierrez V, van Noordwijk M, Creed IF, Pokorny J, Gaveau D, Spracklen D, Tobella AB, Ilstedt U, Teuling R, Gebrehiwot SG, Sands DC, Muys B, Verbist B, Springgay E, Sugandi Y, Sullivan CA. 2017. Trees, forests and water: cool insights for a hot world. Global Environmental Change. http://www.cifor.org/library/6408/trees-forests-and-water-cool-insights-for-a-hot-world/
The 22 authors are from the Swedish University of Agricultural Sciences (SLU); Ellison Consulting; France’s National Institute for Agricultural Research (INRA); Montana State University; France’s Institute for Agricultural Research for Development (CIRAD); Center for International Forestry Research (CIFOR); Norwegian University of Life Sciences; University of Texas-Austin; Bogor Agricultural University; WeForest; World Agroforestry Centre (ICRAF); Western University, Canada; ENKI-Czech Republic; University of Leeds; Wageningen University & Research; Addis Ababa University; Uppsala University; KU Leuven – Belgium; FAO; and Southern Cross University -Australia.
In Peru, the Andes used to be home to biting poverty but are far more prosperous today. Their indigenous inhabitants benefited from land reform, and successive governments have invested in roads, municipalities and even sports grounds. Nevertheless, there is much to worry about. The environment is profoundly fragile, its degradation threatening economic growth.
Sarah-Lan Mathez-Stiefel from the World Agroforestry Centre (ICRAF) is researching the mountains’ trees. Over half the water in the Amazon watershed comes from Andean forests. But they are fragmented, neglected and a fraction of what they once were. On farms, exotic trees have supplanted native ones.
In Ancash, Mathez-Stiefel, who is also a Senior Research Scientist at the Centre for Development and Environment (CDE) in Bern, meets experts on social and environmental change. “In Peru we’ve done well on production but less on environment,” says Pedro Estrada, who heads ALLPA, an NGO based in the town of Huari.
Looking across at a group of women in traditional hats and big skirts and at a poster for a bullfight with matadors from Colombia, Estrada says. “It’s striking to see indigenous women eating in restaurants, and twenty years ago, no one would have had ten soles to see a bull fight. Today more money circulates in the economy.”
Other informed commentators also appreciate Peru’s progress but worry deeply about its sustainability. Dr. David Vidal, who directs Peru’s National Research Institute on Glaciers and Mountain Ecosystems, describes how “the glaciers in the Andes have dangerously retreated – 40% since the 1970s”.
Robert Lopez, who is chief of the 340,000 ha Huascaran National Park, is worried that the park’s 41 sub-watersheds are overlooked, especially in light of Peru’s water crisis. “We have to see the park as a water bank that produces water.”
Lopez has just 26 rangers. Yet the park holds most of Peru’s glaciers and lies in the world’s highest tropical mountain chain, the Cordillera Blanca. Rivers that start in the park flow to the Amazon as well as Peru’s hot arid Pacific coast where large farms rely on their water to produce the exports that have helped make Peru a middle income country. Income per person is now $12,000 a year.
The growth of jobs elsewhere in Peru partly explains the threat. “When the park was created in 1975, government gave rights to the people who were using it,” says Lopez. “But they were meant to periodically withdraw to let it recover. This broke down 10-15 years ago. Mining dynamized the economy, pulling men out of cattle. They now just roam, compacting soil and stopping regeneration.”
Glacier expert Dr. Vidal says “In the last 20 years, there has been an abandonment of agriculture towards mining, medium cities, and the coast. In agriculture, you can earn 10-12 soles a day, in mining 40-70. What type of reforestation can we do? Plantations have been planted but we need to think about how to make them deliver more ecosystem services and improve water infiltration.”
Mathez-Stiefel has documented changes in highland villages. One was a vast hacienda 40 years ago with Argentine livestock. Until land reform in the 1970s, its Quechua-speaking inhabitants were serfs who surrendered animals as tithe to the landowner. Transport was by mules, houses were straw, and education took place in a church rather than a school.
Since then, as in most of Peru, where 40% of the population has moved out of poverty since 2000, a great deal has improved. The village now belongs to the community and has houses of cement, potable water, a health center, a kindergarten, primary and secondary school, and electricity. Nationally, 91.4% of dwellings in Peru have electricity, 74.2% in rural areas.
“Some people say land reform was rushed, and there have been attempts to reverse it,” says ALPA’s Estrada, whose grandfather’s own 40 hectares were given to his workers in the reform. “But people are much better off because of it. The system was unjust. There are still communities in the jungle that are made up of people who fled peon status in the Andes.”
However, Mathez-Stiefel has found less positive change – more extreme weather and crop disease, less forest and indigenous tree cover, the virtual disappearance of llamas and other camelids, and depopulation, particularly the flight of men.
Anthropologist Teófilo Altamirano from Peru’s Catholic University calls internal migration “the major transformational force of the past 60 years” in the Andes. Today just 30% of Peruvians live in the mountains, half the figure before. Other ICRAF research has found that about 15% of people in the Amazon are Quechua speakers, a sign of the number of indigenous people that have left the highlands.
Mathez-Stiefel believes trees can address the interlinked challenges of climate, water, energy, diet and livelihoods. “The Andes is dominated by eucalyptus but there is also a rich array of traditional agroforestry practices and indigenous species. One of the most exciting is quenuales, a tree which lives where nothing else lives – up to 15,000 feet.”
“Quenuales (Polylepsis spp.) are uniquely suited to store water in upper basins,” says literature at the Huascaran National Park. “The leaves and bark absorb water, thus creating very humid zones in which there is development of mosses, lichens and fungi. The water absorbed is deposited underground and feeds the region’s ponds. The roots prevent erosion and landslides to lower areas.”
Increasingly aware of its importance, government has begun restoring quenuales. Farmer Margarita Rubina, 42, approves. “It’s a sturdy hedge and protects the house from wind and its branches are good for cooking,” she says. Dressed traditionally, in many ways, she represents the new Andes. Guinea pigs run around her feet on her earth floor. But her children study in schools in town. And where Rubino once had a herd of criollos, descendants of the small stocky cattle brought by the Spaniards 500 years ago, she now has four exotic cows and sells cheese. Mathez-Stiefel and Estrada discuss if planting protein-rich fodder trees might raise her output of milk.
“The rural world has not been seen as an opportunity for life,” says the vet, whose family has been Andean for 300 years. “We need to improve rural identity. Youth do not want to repeat the lives of their parents. But a dignified comfortable life is possible here. Agroforestry is super interesting”
Mathez-Stiefel has work ahead but has clearly found allies.
Her research to characterize Andean villages was a collaboration between ICRAF and the Andean Forest Program funded by the Swiss Agency for Development and Cooperation (SDC). It forms part of the CGIAR Research Program on Forests, Trees and Agroforestry.
“Agroforestry as micro-nexus for the SDGs”: the right moment to make a strong case for agroforestry science
“Agroforestry as micro-nexus for the SDGs”: the right moment to make a strong case for agroforestry science
Rubber agroforestry in Nigeria: a farmer checks his beehive. Photo: Julius Atia (World Agroforestry Centre)
By Kerstin Reisdorf
The World Agroforestry Centre (ICRAF) has a lot to offer to help developing countries reach the Sustainable Development Goals (SDGs) and should make agroforestry exemplary for a nexus of different land use-issues. This was one of the main messages of ICRAF’s Science Week 2016. But there are challenges, participants agreed, such as fostering cross-sectoral approaches with the right science.Director General Tony Simons expressed satisfaction that agroforestry was gaining more recognition, e.g. the French agriculture ministry just released an agroforestry development plan.The 120 scientists also debated the “refreshing” of ICRAF’s strategy in the light of the SDGs and the climate agenda, before it will be handed over to the Board in November. Plenaries also dealt with hypotheses to guide ICRAF’s science, and land restoration, among others. As is customary, field trips were organized to show the work of ICRAF partners.
Silos no more
“Integration is at the core of what needs to happen to make the SDGs work,” said Peter Minang, Leader, Environmental Services research unit Domain at ICRAF. Division of land uses into different sectors, as it is today, has to be overcome to drive the nexus of food, water, energy plus the factor income. He deplored that in governance “there is no bonus for agriculture and forestry working together” when cross-sectoral action was key to really make progress on the way to reaching the SDGs and to address trade-offs and create synergies at the landscape level.
Scientists need to ask questions on how agroforestry compares to other land uses and how it supports the process towards integrated action by also meeting other objectives within the landscape, Minang added. Trade-offs and conflicts between land users have to be managed so that synergies can be created. These processes need negotiation support and this is “where our work really comes in handy, as it provides the evidence that is needed.”
“We have to do a bit more work on finance,” Minang said. There are two aspects of finance to enable the nexus approach, blended finance from multiple sources, and performance-based finance. He gave the example of the pilot project DRYAD on community in Cameroon. “You put in public money as a start-up process that generates a sustainable land-use-based enterprise.” This money is tied to the recipients’ meeting their deliverables.
Insights from agroforestry
His theme of integration was echoed by guest speaker Alexander Müller, Study Lead TEEBAgriFood, hosted at UNEP. “The silo orientation of the past is not going to solve the problems of the future.” An integrated approach would help to look at the competition for natural resources everywhere. He argued for a participatory approach, bringing together scientists and the people in the landscape to identify the issues.
But the interdependency of the elements food, water, energy plus income was also relevant at the global level, e.g. biofuels have an impact on the landscape but are also closely related to global trade, he added.
Müller, who is also a Member of the German Council for Sustainable Development (RNE), sees agroforestry as “kind of a micro nexus” for the SDGs, because in agroforestry one has to deal with food, energy, water and income.
With its capacity to analyze problems and present evidence for solutions, “ICRAF has a lot to offer,” he said. “Why not use the insights gained from agroforestry to present the management of natural resources at the landscape level in an integrated way and make it part of the successful implementation of the SDGs.”
Deputy Director General Research, Ravi Prabhu urged his colleagues to come up with “liberating hypotheses”. “We are not going to get a nexus approach unless we tackle the barriers,” he warned. The barriers could be structural, i.e. lie in the ways that societies are organized.
To break down the barriers on the way to a nexus approach it needs a revolution—from the researchers in a context of agriculture in and for development, Prabhu said. ICRAF has to define hypotheses to address the nexus of food, water, energy plus income if it wants to be part of the solution.
Integration starts with data sharing
Valentina Robiglio, a Landscape Ecology and Climate Change Specialist in Latin America, called on her colleagues to promote intergovernmental cooperation by encouraging all units within a government to work off the same data. “That would be a start towards more integration,” she said.
Overall, the “nexus” discussion on the last day of the annual meeting was somewhat exemplary for the current discourse at ICRAF. Many other important debates took place in the sub-plenaries, and a recurring theme was—in simple terms—how does ICRAF produce relevant science?
View from outside
The donor perspective was brought into the discussion by Steve Twomlow from the International Fund for Agricultural Development (IFAD): He urged scientists first of all to communicate their work to the users in much simpler terms.
View from the ground
Post-doctoral fellow Mary Njenga brought in the perspective from the ground by reminding the audience that rural women in Africa are in need of safe energy sources while facing a myriad of constraints; starting with the time they spend on collecting firewood, a recurring shortage of woodfuel and the health hazard from indoor cooking fumes, to name only a few.
She suggested to include bioenergy production in the CGIAR FTA, under Climate change mitigation and adaptation. “The big question is: How can we sustainably produce bioenergy in developing countries?” Njenga said. The aim would be to realize an integrated food and bioenergy production policy and practice. Her message was underpinned by a film on women in Kenya’s West Aberdares, produced by Stockholm Environment Institute.
By Deanna Ramsay, originally published at CIFOR’s Forests News
It is not often that a study completely upends a prevailing view, and, in doing so, offers hope of improving the lives of hundreds of millions of people.
But that is exactly what research under the CGIAR Program on Forests, Trees and Agroforestry, recently published in Scientific Reports, has done for the understanding of trees and water in dry regions.
In arid places where water is scarce, the planting of trees is often discouraged out of the belief that trees always reduce the availability of much-needed water.
Yet scientists working in Burkina Faso found that when a certain number of trees are present, the amount of groundwater recharge is actually maximized.
The study is a “game changer”, according to one of the study’s authors, Douglas Sheil, professor at the Norwegian University of Life Sciences and a senior research associate with the Center for International Forestry Research (CIFOR).
“We don’t get so many scientific studies in our lives where we see such a potential shift in how we do something,” Sheil said.
“It is very dramatic in the sense that it totally overturns the way we had looked at trees and water availability.”
WET WET WET
Previously, few studies had examined tree cover in the tropics or what effect scattered, or intermediate, tree cover might have on water yields.
Drawing on the idea that trees can improve the movement of water in soil, the scientists worked with an ‘optimum tree cover theory’ that would provide for the maximum amount of groundwater recharge.
The research bridges two contrasting views on forests and water: the ‘trade-off theory’ and the ‘sponge theory’, explained Aida Bargués Tobella of the Swedish University of Agricultural Sciences, one of the study’s lead authors.
The ‘sponge theory’ holds that forests soak up water during the rainy season and slowly release it during the dry season, thereby sustaining stream flow during dry periods, whereas the ‘trade-off theory’—which has become the dominant paradigm—holds that more trees equals less water.
“Both perceptions are true to some extent, but what we show is that the net effect of trees on groundwater recharge depends on the degree of tree cover,” Bargués Tobella said.
“So trees can improve groundwater recharge to a point.”
By testing groundwater levels both near and far from trees in a typical semi-arid landscape over several years, the researchers found that an intermediate amount of tree cover created conditions in which more water was available than if there were no trees or a large number of them.
“Without trees, these sensitive tropical soils lose their large pores, which are responsible for leading water down into the ground quickly,” said Ulrik Ilstedt of the Swedish University of Agricultural Sciences (SLU), the study’s other lead author.
“Without these pores, the water flows away on the soil surface or is trapped in the compact soil surface and evaporates.”
“With that said, if there are too many trees, they will still consume more water than what is gained by their soil improvement.”
Other factors that also affect water availability include tree species, soil quality and type, and climate.
This study was done on a type of soil that is widespread in the tropics, but there are other types of less sensitive soils that would not have produced the same positive effects, according to Ilstedt.
However, some 70 percent of the semi-arid tropics have soils similar to those used for this research, he added.
“The most important point of our study is to show that a trade-off between water and tree cover doesn’t always exist, and that more trees can actually improve groundwater recharge,” Bargués Tobella said.
“This means that people could benefit from the many goods and services that trees provide while also seeing improved water availability.”
The benefits of trees in the seasonally dry tropics for people in their daily lives are myriad and varied.
In particular, in the study area of Saponé in Burkina Faso, Shea trees dominate: the more Shea trees there are, the more nuts local people can sell.
Trees also support erosion control and climate change mitigation.
“With greater tree cover, there are also benefits like biodiversity, carbon and wood fuel that were being denied before,” Sheil said.
“Large areas of the arid tropics actually have no tree cover, and having more trees would be advantageous, as it would give people more access to fuelwood, fruit and many other benefits.”
The findings from the study enable people to control and manage such conditions by planting more trees, Sheil added, noting that it presented an opportunity for donor organizations to start working to support land management that facilitated the planting of trees in water-deprived areas.
Goal Number Six of the recently agreed upon Sustainable Development Goals (SDGs) is to increase access to clean water, with the recognition that water is a basic human requirement.
Landscapes such as those studied in Burkina Faso house some of the world’s poorest people, where, as the study notes, limited water not only constrains food production, nutrition and health, but also reduces opportunities for education, work and improved livelihoods.
The finding that increased tree cover in tropical dry regions could increase people’s access to water could therefore have a major impact on their lives, the researchers believe.
“The study needs to repeated in other sites as the optimal tree cover will vary with conditions, and with the species involved, but there is no good reason not to expect similar results in other parts of the tropics,” Sheil said. “I think this will have global significance.”
This research forms part of the CGIAR Research Program on Forests, Trees and Agroforestry.