by Rastislav Skalsky, Ecosystems Services and Management Program, International Institute for Applied Systems Analysis
As growers, we know soil is important. It supports plants, and provides nutrients and water for them to grow. But do we all appreciate how crucial the role of soil is in continuously supplying plants with water, even when it hasn’t rained for a few days or even weeks, even without extra water being added via watering?
Soil is like a sponge. It can retain rain water and, if it is not taken up by plants, soil can store it for a long time. We can feel the water in soil as soil moisture. Try it — take and hold a lump (clod) of soil — if it is wet it will leave a spot on your palm. If it’s only moist then it will feel cold — cooler than the air around. And if the soil is dry, it will feel a little warm.
Soil moisture not only can be felt, but it can also be measured — in the lab, or directly in the field with professional or low-cost soil moisture sensors.
Soil moisture in general indicates how much water is contained by the soil. But it is not always the case that soil which feels moist or wet is able to support plants. It could happen that, despite feeling moist, the soil simply does not hold enough water, or holds the water too tightly for the plants to extract it. Or the opposite, soil can sometimes contain too much water. To understand how this works, one has to learn more about how water is stored in the soil.
Water is bound to soil by physical forces. Some forces are too weak to hold water in the plant root zone and water percolates to deeper layers, where plants can no longer reach it. Other forces can be too strong, preventing water from being retrieved by the roots.
If soil moisture is measured at one place over time, it can reveal its seasonal dynamics. Having estimated important soil water content thresholds (FS — full saturation, FC — field capacity, PDA — point of decreased availability, and WP — wilting point) for that particular site, e.g. based on soil texture test or measurement, one can easily interpret if the measured soil moisture and say if there was enough water or not to fully support plants with water and air. In this particular case of sandy 0–30 cm deep topsoil from Slovakia, it was never wet enough to cause oxygen stress for plants, — in fact it never reached state of all capillary voids filled with water (FC). On the other hand, each summer the topsoil moisture dropped below the point of decreased availability (PDA), even got close to the wilting point or went through (WP), which means that during those periods plants suffered drought conditions.
Thresholds In order to describe this behavior in more useful terms, plant ecologists and soil hydrologists came up with couple of important soil water content thresholds (Figure 1). These thresholds, also called “soil moisture ecological intervals”, define how easily plants can get the water out of the soil.
We speak about full saturation of soil when all empty spaces (pores/voids) are completely filled with water. Full saturation of the soil with water prevents air entering into the soil. Yet there is no force holding water in the soil. Roots need air as well as water so, if this situation continues, it eventually causes oxygen stress for most of the common plants because roots simply cannot breathe.
Soil also has different types of pores. Larger ones, which are called “gravitational pores”, are filled with water only when the soil is saturated and otherwise drains freely, and smaller ones called “capillary pores” which are small enough in size to prevent water from percolating down the soil profile by gravitation. These smaller pores can hold water even in well-drained soils and make it available for plants to extract. There are also even smaller pores where the water is held so tightly that plants cannot extract it.
When all gravitational pores/voids are empty of water and it is present only in so called capillary pores/void we speak about the field water capacity — which is considered to be the best soil moisture status of the soil — enabling plants to retrieve the water they need, whilst leaving enough air for roots to breathe. If no new water is added into the soil, the soil dries as water is used by plants or evaporates. As soil dries less water is available to plants until the point of decreased availability when water remains only in the smallest capillary pores/voids. But this water is bound to soil particles so strongly that most plants are not able to extract it suffer from drought. Ultimately, all the available water is used up by plants, and the remaining water is inaccessible. Soil reaches the so-called wilting point and water is not available for the plants anymore. Plants permanently wilt and eventually die.
How Soil Characteristics Relate to Moisture The tricky thing with soil moisture however is that the same amount of water (volumetric percent of the total soil column volume) can, in different soils, represent different amount of water available for plants. How big this difference could be is defined by many soil characteristics.
The most important is the soil texture — a blend of all fine-earth soil mineral constituents (sand, silt, clay) and stones in various rates. In general, the finer the texture is (i.e. more clay, less sand) the more water is bound in the soil too tightly to be retrieved by plants. Even if the soil feels moist, plants can permanently wilt in clay soils. In contrast, those soils with coarse texture (i.e. more sand, less clay) can support plants with nearly all the water they can hold. Although the soil looks dry, plants can still effectively take the water out of it. The drawback here is that in coarse textured, sandy, soil nearly all water drains down the gravitational pores and therefore such a soil cannot support plants for very long time. That is also why medium textured soils (loam, silty loam, clay loam) are considered best for holding and providing the water for plants. Medium textured soils can effectively drain excess water, yet hold much water in capillary pores/voids for a long time, and still, only a relatively small amount of water remains unavailable for the plants.
A practical implication of this behavior of soil with different soil texture could be that one has to apply slightly different strategies to maintain soil moisture in the way that it can effectively supply plants with water. Sandy soils will require more frequent watering with smaller amount of water. It would not make any practical sense to try build-up a storage of water in these soils. All extra water added will simply drain out of the topsoil. Clay rich soils can absorb big amounts of water but a lot is bounded too strongly to the soil particles and thus not available for the plants. Therefore one should water even if the soil looks moist or wet — and if dry a lot of water must be added to recharge the topsoil so that it can support plants effectively. With loamy soils it is possible to be more relaxed with watering frequency, simply because one can build solid storage of water in such soils. Adding a bit more water than is necessary is perfectly fine with these soils because the water is effectively kept in the soil profile and it can be used later on.
Interested in learning more? Why not sign up for GROW Observatory’s next free online course – Citizen Research: From Data to Action – to discover how citizen-generated data on soils, food and a changing climate can create positive change in the world. Starts 5th November.
By Marcus Thomson, researcher, IIASA Ecosystems Services and Management Program
While living in Cairo in 2010, I witnessed first-hand the human toll of political and environmental disasters that washed over Africa at the end of the last century. Unprecedented numbers of migrants were pressing into North Africa, many pushed out of their homelands by conflict and state-failure, pulled towards safer, richer, less fragile places like Europe. Throughout Sub-Saharan Africa, climate change was driving up competition for scarce land and water, and raising pressure on farmers to maintain the quantity and quality of their crops.
It is a similar story throughout the developing world, where many farmers do without the use of expensive chemical fertilizer and pesticides, complex irrigation, or boutique seed varieties. They rely instead on traditional land management practices that developed over long periods with consistent, predictable conditions. It is difficult to predict how dryland farmers will respond to climate change; so it is challenging to plan for various social, economic, and political problems expected to develop under, or be exacerbated by, climate change. Will it spur innovation or, as has been argued for the Syrian civil war, set up conflict? A major stumbling block is that the dynamics of human social behavior are so difficult to model.
Instead of attempting to predict farmers’ responses to climate change by modelling human behavior, we can look to the responses to environmental changes of farmers from the past as analogues for many subsistence farmers of the future. Methods to fill in historical gaps, and reconstruct the prehistoric record, are valuable because they expand the set of observed cases of societal-scale responses to environmental change. For instance, some 2000 years ago, an expansive maize-growing cultural complex, the Ancestral Puebloans (APs), was well established in the arid American Southwest. By AD 1000, members of this AP complex produced unique and innovative material culture including the famed “Great Houses”, the largest built structures in the United States until the 19th century. However, between AD 1150 and 1350, there was a profound demographic transformation throughout the Southwest linked to climate change. We now know that many APs migrated elsewhere. As a PhD student at the University of California, Los Angeles, I wondered whether a shift to cooler, more variable conditions of the “Little Ice Age” (LIA, roughly AD 1300 to 1850) was linked to the production of their staple crop, maize.
I came to IIASA as a YSSP in 2016 to collaborate with crop modelers on this question, and our work has just been published in the journal Quaternary International. I brought with me high-resolution data from a state-of-the-art climate model to drive the crop simulations, and AP site information collected by archaeologists. Because AP maize was quite different from modern corn, I worked with IIASA soil scientist Juraj Balkovič to modify the crop simulator with parameters derived from heirloom varieties still grown by indigenous peoples in the Southwest. I and IIASA economic geographer Tamás Krisztin developed a statistical technique to analyze the dynamical relationship between AP site occupation and simulated yield outcomes.
We found that for the most climate-stressed high-elevation sites, abandonments were most associated with increased year-to-year yield variability; and for the least stressed low-elevation and well-watered sites, abandonment was more likely due to endogenous stressors, such as soil degradation and population pressure. Crucially, we found that across all regions, populations peaked during periods of the most stable year-to-year crop yields, even though these were also relatively warm and dry periods. In short, we found that AP maize farmers adapted well to gradually rising temperatures and drought, during the MCA, but failed to adapt to increased climate variability after ~AD 1150, during the LIA. Because increased variability is one of the near certainties for dryland farming zones under global warming, the AP experience offers a cautionary example of the limits of low-technology adaptation to climate change, a business-as-usual direction for many sub-Saharan dryland farmers.
This is a lesson from the past that policymakers might take note of.
 Kelley, C. P., Mohtadi, S., Cane, M. A., Seager, R., & Kushnir, Y. (2015). Climate change in the Fertile Crescent and implications of the recent Syrian drought. Proceedings of the National Academy of Sciences, 201421533.
 Thomson, M. J., Balkovič, J., Krisztin, T., MacDonald, G. M. (2018). Simulated crop yield for Zea mays for Fremont Ancestral Puebloan sites in Utah between 850-1499 CE based on temperature dailies from a statistically downscaled climate model. Quaternary International. https://doi.org/10.1016/j.quaint.2018.09.031
by Melina Filzinger, IIASA Science Communication Fellow
Ecosystems worldwide are changed by the influence of humans, often leading to the extinction of species, for example due to climate change or loss of natural habitat. But it doesn’t stop there: as the different species in an ecosystem feed on each other and are thereby interconnected, the loss of one species might lead to the extinction of others, which can even destabilize the whole system. “In nature, everything is connected in a complex way, so at first glance you cannot be sure what will happen if one species disappears from an ecosystem,” says IIASA postdoc Mateusz Iskrzyński.
This is why the IIASA Evolution and Ecology (EEP) and Advanced Systems Analysis (ASA) programs are employing food-web modeling to find out which properties make ecosystems particularly vulnerable to species extinction. Food webs are stylized networks that represent the feeding relationships in an ecosystem. Their nodes are given by species or groups of species, and their links indicate how biomass cycles through the system by means of eating and being eaten. “This type of network analysis has a surprising power to uncover general patterns in complex relationships,” explains Iskrzyński.
Every one of these food webs is the result of years of intense research that involves both data collection to assess the abundance of species in an area, and reconstructing the links of the network from existing knowledge about the diets of different species. The largest of the currently available webs contain about 100 nodes and 1,000 weighted links. Here, “weighted” means that each link is characterized by the biomass flow between the nodes it connects.
Usually, food webs are published and considered individually, but recently efforts have been stepped up to collect them and analyze them together. Now, the ASA and EEP programs have collected 220 food webs from all over the world in the largest database assembled so far. This involved unifying the parametrization of the data and reconstructing missing links.
The researchers use this database to find out how different ecosystems react to the ongoing human-made species loss, and which ones are most at risk. This is done by removing a single node from a food web, which corresponds to the extinction of one group of species, and modeling how the populations of the remaining species change as a result. The main question is how these changes in the food web depend on its structural properties, like its size and the degree of connectedness between the nodes.
From the preliminary results obtained so far, it seems that small and highly connected food webs are particularly vulnerable to the indirect effects of species extinction. This means that in these webs the extinction of one species is especially likely to lead to large disruptive change affecting many other organisms. “Understanding the factors that cause such high vulnerability is crucial for the sustainable management and conservation of ecosystems,” says Iskrzyński. He hopes that this research will encourage more, and more precise, empirical ecosystems studies, as reliable data is still missing from many places in the world.
As a next step, the scientists in the two programs are planning to understand which factors determine the impact that the disappearance of a particular group of organisms has. They are going to make the software they use for their simulations publicly available, together with the database they developed.
Note: This article gives the views of the author, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.
By Sandra Ortellado, 2018 Science Communication Fellow
China is the world’s biggest producer of both wild and farmed fish, yet the massive commercial fishing industry threatens thousands of years of tradition in ocean and freshwater fishing, as well as the livelihoods of coastal fishing communities.
In the past decade, some coastal ecosystems and environments have been destroyed and polluted in the process of industrialization. Millions of tons of fish are caught in Chinese territorial waters each year, such that overfishing of high value commercial species has led to a drastic decline of some native fisheries resources and species.
In response, the Chinese government released a five-year plan for protecting marine ecosystems and restoring wild capture fisheries. The plan promotes an agenda of “ecocivilization,” which emphasizes land–sea coordination, green development, and social–ecological balance.
It also calls for the introduction of additional output control measures, which directly limit the amount of fish coming out of a fishery. Existing input control measures restrict the intensity of gear used to catch fish, but they may not be sufficient to protect ecosystems.
Yi Huang, a member of this year’s YSSP cohort, has made it her goal to figure out how social ecological balance can be achieved even as fishery regulations shift towards increased input and output control.
Given the size of China’s fishing industry, large scale change requires the abstract concepts of “ecocivilization” to be translated into action, compliance, and enforcement at the local level. That means engaging with individual fishers, their communities, and their way of life, says Huang.
“If you want to control overfishing; the object of fishery management policy are fishers. So you need to understand human behavior to help you control overfishing.”
Huang’s project investigates how changes in fishery management will affect demographic, geographic, and socioeconomic trends in the Chinese fisher population. With the guidance of her supervisors, she’s also developing a bioeconomic model to analyze how output control measures like catch limits will affect ecological and socioeconomic conditions.
“I just want to figure out how to improve enforcement of this kind of policy and see if we can use it to solve the overfishing problem at the same time as giving those in the fishing industry a better life,” says Huang.
Current input control measures like licensing systems, vessel buyback programs, closed seasons, restricted areas, and fisher relocation programs are meant to discourage overfishing and transition towards more sustainable practices. Nevertheless, a decline in fishing vessels and restricted fishing seasons only resulted in an increase in total vessel engine power and large spikes in fishing activity just prior to the closed season.
According to the Chinese fishery statistical yearbook, the number of people employed in the fishing industry proliferated to 13.8 million in 2016, so in recent years the government has issued subsidies encouraging fishers not to fish in the off-season and to change vocation. Older fishers are hesitant to abandon an identity that has been passed down from generation to generation in their families. However, younger generations with access to higher education are lured by the prospect of more stable work outside of their fishing communities, which could really change the socioeconomic and demographic structure of coastal villages.
With the potential for increased output controls to incur drastic changes in coastal communities, it’s more important than ever that regulations are carefully designed with both socioeconomic and ecological factors in mind.
Huang hopes her research will help inform the process of policy development, which involves balancing the needs of both vulnerable fisheries labor and delicate ecosystems.
“When policymakers want to use output control in fishery management, maybe they will think more about the fisher or the socioeconomic aspect of the resolution,” says Huang.
“My research is at the national level, but when they design a regulation it’s at the local level, so my research can teach them how socioeconomic surveys at the local level can be used together with ecological research when they are preparing for regulations.”
Huang, who studied sociology at the Ocean University of China before starting as a PhD student in Marine Affairs at Xiamen University, has spent the past ten years researching coastal fishing communities. She has a deep fondness for the people she surveyed, who welcomed her into their homes and showed her the beauty of the environment that sustained them.
“I want to protect the ocean and the people that connect with it,” says Huang.
A sociological perspective has given Huang an eye for nuance and an appreciation for things that don’t turn out quite how you expect, as they often don’t in scientific research—especially when it attempts to explain human behavior.
For example, Huang says that although fishers may look like countryside people, they act very differently from farmers.
“The ocean has a lot more risk involved than planting on land,” explains Huang.
Because Chinese fishery regulation is currently focused almost exclusively on analyzing resources from an ecological perspective, she thinks sociology and anthropology research could add another revealing dimension to the approach.
“After doing surveys and analyzing the data, I will find maybe I’m wrong or maybe there is something more. That’s why I’m really interested in this kind of research,” says Huang.
As her research project develops, Huang says she’s grateful for the feedback of her supervisors and peers at IIASA, who both challenge and encourage her.
“Even when they have some critical comments on my research, I feel more confident that my research is meaningful, that they support me, and that they’re really interested in my research,” says Huang. “That’s what I can feel every day.”
By Anatoly Shvidenko, senior researcher in the IIASA Ecosystems Services and Management Program
The forest region known as the circumpolar boreal belt comprises almost a third of the global forest area and about a fourth of the world’s wetlands. There are substantive structural, ecological and management similarities and connections between boreal and global mountain forests of high elevation. Specific features of both boreal and high-elevation forests – or as we started calling them cool forests – include evolutionary adjustments to cold climates; dominance of coniferous species; permafrost over huge territories; vulnerability to climate anomalies and ecological disturbances; large remote and practically unmanaged territories; and lack of infrastructure over vast areas. Under climate change, these landscapes are on the one hand exposed to extreme pressures and risks and on the other, they are decisive for our efforts to reach the climate goals. These cool forests could substantially help to cool down the climate. This is why I became a Cool Forest Ambassador.
A particular threat to global climate mitigation efforts is the thawing permafrost, which contains about 1,000 billion tons of carbon as methane and hydrates in the frozen grounds of the Northern Eurasian high latitudes alone. Furthermore, a number of models predict forest deaths over large areas, loss of biodiversity, and negative impacts on social hotspots in the highly populated southern (mid-latitude) ecotone of the boreal zone.
Since the most critical climate change on the planet is expected in continental regions of the boreal and mountainous regions, these forest and wetland landscapes require specific societal, scientific, and managerial attention. The current paradigm of co-evolution of people and forests calls for a transition to adaptive and risk-resilient sustainable forest management (ASFM), which is a complicated task, both mentally and professionally.
Diversity of forests, ownership, socioeconomic conditions, forest management practices, and policies for cool forests are extensive, as are the above-mentioned associated risks. Large differences prevail in stakeholder preferences, understanding, and the valuation of ecosystem services, as well as in understanding relevant strategies of implementing ASFM. We need to advocate the investigation of socioecological drivers that define current and future states, the resilience and vulnerability of forests, as well as the stability of forests and agro-forest landscapes. Moreover, we need to consider the close connection of cool forests with the specifics of surrounding landscapes within the paradigm of the multi-functional use of forests.
About 20 countries have cool forests, but three of them comprise almost 90% of the total area: Russia 56%, Canada 27%, and the USA 6%. The starting point, preparedness, and capacity of these countries to introduce ASFM are substantially different, but the majority of them are lagging behind in terms of real progress in the proper direction. Cross-border analysis of national specifics and commonalities are needed to understand the potential and challenges of ASFM, as well as to identify problems that cannot be completely resolved by means of ASFM alone (e.g., slowdown of permafrost thaw). There is no silver bullet strategy that would allow us to reach all the goals of ASFM. The high uncertainty of climatic predictions and lack of knowledge on the behavior of boreal and high-elevation forests under new environmental conditions, require new operative information, as well as a new philosophy and management tools. In particular, new types of models are needed to present sufficient information for decision making within regional forest management systems. The IIASA Ecosystem Services and Management Program has intensively studied cool forests for the last three decades (large international projects included SIBERIA-II, Siberia-II, the Third Millennium Ecosystem Assessment etc.).
All pressing problems, hot topics, and required actions related to cool forests will be discussed at the 18th Conference of the International Boreal Forest Research Association “Cool forests at risk? The critical role of boreal and mountain ecosystems for people, bioeconomy, and climate”, taking place at IIASA from 17 to 20 September 2018. More information about this event is available on the conference website (IBFRA18.org). We invite scientists and stakeholders from policy, business, and civil society and all who are interested in the topic, to express their opinion about the most important and urgent actions that should be realized. Join me in signing-up as a Cool Forest Ambassador to bring this globally important problem to the attention of societies and governing circles globally.
Note: This article gives the views of the authors, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.
Last year, I had the fantastic opportunity to spend three months at IIASA as part of the Young Scientists Summer Program (YSSP), to collaborate with the Ecosystems Services and Management (ESM) research program. During this very enriching experience, both intellectually, socially, and culturally, I worked with Petr Havlik, David Leclère, and Christian Folberth on modeling global rangelands and pasturelands under farming and climate scenarios. I also progressed on the development of a global animal stocking rate optimizer. The overall objective of this YSSP project, and more broadly of my PhD, is to assess the role of grazing systems in a sustainable food system.
However, my trip to IIASA was not my only adventure last year. Just before moving to Vienna, I received the great news that I was selected along with 77 other women to take part in a women in science and leadership program called Homeward Bound.
What would our world look like if women and men were equally represented, respected, and valued at the leadership table? How might we manage our resources and our communities differently? How might we coordinate our response to global problems like food security and climate change?
Homeward Bound is a worldwide and world-class initiative that seeks to support and encourage women with scientific backgrounds into leadership roles, believing that diversity in leadership is key to addressing these complex and far-reaching issues. The program’s bold mission is to create a 1000-strong collective of women in science around the world over the next 10 years, with the enhanced leadership, strategic, and visibility capacity to influence policy and decision making for the benefit of the planet.
This year-long program culminated in an intensive three-week training course in Antarctica, a journey from which I have just come back. The voyage to Antarctica was incredible. We learnt intensively during this 24/7 floating conference in the midst of majestic icebergs, very cute penguins, graceful whales, and extraordinary women from various cultures and backgrounds, from PhD students to Nobel Laureates. I have returned full of hope for the planet, deeply inspired, and emotionally energized. It was a truly unforgettable experience, one that will keep me reflecting for a lifetime.
Our days in Antarctica typically followed a similar routine – half of the day was dedicated to a landing (we visited Argentinian, Chinese, US, and UK research stations) and the other half to classes and workshops. We discussed systemic gender issues and learnt about leadership styles, peer-coaching, the art of providing feedback, science communication, core personal values, or what matter to us. The list goes on! We were also encouraged to practice reflective journaling. Regularly recording activities, situations, and thoughts on paper is actually a very powerful technique for self-discovery and personal and professional growth as it helps us think in a critical and analytical way about our behaviors, values, and emotions. We also spent quite some time developing our personal and professional strategies: What is our purpose as individuals? What are our core values, aspirations, and short- and long-term goals? From that, we developed a roadmap that could be executed as soon as we stepped off the ship. While I haven’t solved all my life’s mysteries, this activity gave me strong foundations to keep growing and actively shape my own life, rather than letting society do it for me.
In the evenings, we watched our film faculty sharing their tips with us on television, including primatologist Jane Goodall, world leading marine biologist Sylvia Earle, and former Executive Secretary of the UN Framework Convention on Climate Change (UNFCC), Christiana Figueres. We also had a collective art project called “Confluence: A Journey Homeward Bound”, which was underpinned by our inner journey of reflection, growth, and transformation and our outer physical journey to Antarctica.
Both my stay at IIASA and my journey to Antarctica taught me a lot about the value of getting out of my comfort zone, exploring different leadership styles, and collaborating. I have also witnessed how visibility (visibility to ourselves, to understand who we are, and visibility to others, to let the world know we exist) helps to open up opportunities. The good news is that the beliefs we have about ourselves are just that – beliefs – and these beliefs can be changed.
My visibility to others has also increased notably in relation to my involvement in Homeward Bound and my recent award of the Queensland Women in STEM prize. This Australian annual prize, awarded by the Minister for Environment and Science, Leeanne Enoch and Acting Chief Scientist Dr Christine Williams, aims to celebrate the achievements of women who are making a difference in the fields of science, technology, engineering, and mathematics. As a result, I have been contacted by fascinating people from various fields of work, from researchers and teachers to entrepreneurs, start-ups, and industries. All these connections have broadened my approach to food security and global change and helped me shape my research vision, purpose, and values.
When we were in Antarctica, our story reached 750 million people. Why? Because, and may we never forget, the world believes in us – ‘us’ in its broadest sense: humans, scientists, women, etc. – in our skill, compassion, and capability. While we are facing alarming global social, economic, and environmental challenges, I believe that the many collaborations that embrace diversity of knowledge, skills, processes, and leadership styles that are currently emerging all around the world, will help us get closer to our development goals.