Ecosystem water use efficiency and the urgent need for climate action

The pressures of global change on ecosystems now and in the future may surpass the ability of certain plant species and functional groups to adapt. Doing this research caused me to see from a new lens how critical it is for us to take action on the climate crisis now.
Published in Earth & Environment
Ecosystem water use efficiency and the urgent need for climate action
Like

Personal story: why did I get involved in climate research & activism?

I never imagined, growing up exploring the hills of sagebrush, manzanita, sycamore and oak trees of Southern CA, the changes that were happening there. Over the span of several years, I witnessed extreme drought conditions and saw multiple family friends lose their homes from wildfires. These experiences brought into clear focus the threats that climate change posed to the people and ecosystems I cared about.

At 12 years old, I knew I wanted to understand how ecosystems can be resilient to drought and, simultaneously, how we as humans can help protect these ecosystems whose well-being is inextricably tied to our own.

I became an Earth scientist to investigate the dynamic interactions between ecosystem health and the Earth’s climate. I also embarked on a parallel, yet interconnected, path of climate activism, joining numerous organizations working to actualize climate friendly policies locally, nationally and internationally. The research I’m sharing with you here is a part of my life-long exploration of ecosystem resilience in the context of a rapidly changing climate. Though the findings are based on work I do for my day job as a scientist at NASA-JPL with the ECOSTRESS mission, the opinions stated below are my own.

Exploring the chaparral in Southern California. Photo credit: Rachel Weinberg

Key research takeaways

Motivation

Droughts are increasing in frequency, intensity and duration due to human-caused global warming. We expect that plants that use water more efficiently will be better adapted to these changes than plants that use water inefficiently. Ecosystems with a wide range of plants with different water use efficiencies may also be more resilient to these changes because those plants are already suited to a variety of climate conditions.

The research that I’m sharing with you here uses data from a new NASA satellite instrument—the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS)—to measure water use efficiency in plants all over the world. We define ecosystem water use efficiency as the amount of carbon uptake (i.e., plant photosynthesis) per unit water lost (i.e., plant transpiration and soil evaporation).

Enhanced spatial resolution from ECOSTRESS

ECOSTRESS provides the highest spatial resolution estimates of plant water use available at global scales. We found that this fine resolution allows us to observe local scale variability in water use efficiency that we otherwise would not be possible to detect. For instance, ECOSTRESS observes fine scale differences between the high efficiency of intact forest and low efficiency values in adjacent cattle pasture (Figure 1).

Figure 1. ECOSTRESS enables new insight into variation in ecosystem Water Use Efficiency (WUE; amount of carbon uptake per unit water lost) at fine resolutions across landscapes and globally. (A) An example ECOSTRESS overpass from August 2019 in southwestern Amazonia differentiates daily WUE due to both natural and anthropogenic features: 1) mature forest, 2) wetlands, 3) cassiterite (tin) mining activity, and 4) converted pasture with forest buffers. The missing parts of the image are due to clouds and swath boundaries. (B) A closer look at the converted pasture (4 in panel A) demonstrates the effects of wholesale deforestation on WUE.
Figure 1. ECOSTRESS enables new insight into variation in ecosystem Water Use Efficiency (WUE; amount of carbon uptake per unit water lost) at fine resolutions across landscapes and globally. (A) An example ECOSTRESS overpass from August 2019 in southwestern Amazonia differentiates daily WUE due to both natural and anthropogenic features: 1) mature forest, 2) wetlands, 3) cassiterite (tin) mining activity, and 4) converted pasture with forest buffers. The missing parts of the image are due to clouds and swath boundaries. (B) A closer look at converted pasture (4 in panel A) demonstrates the effects of deforestation on WUE.
Re-printed from the original paper published in Nature Plants. Full citation: Cooley, S. S., Fisher, J. B., & Goldsmith, G. R. (2022). Convergence in water use efficiency within plant functional types across contrasting climates. Nature Plants, 8(4), 341-345. Access via: https://www.nature.com/articles/s41477-022-01131-z or SharedIt Link: https://rdcu.be/cPRTF

Summary of main results

This fine spatial resolution also allowed us to compare how water use efficiency varies within and among different groups of plants with distinct characteristics that span numerous climate types. We refer to these plant groups as “plant functional types”, which include grassland, cropland, wetland, savanna, woody savanna, deciduous needleleaf, deciduous broadleaf, evergreen broadleaf and evergreen needleleaf forest.

Surprisingly, we found that over half of the plant functional types we studied have a consistent water use efficiency regardless of where they grow in the world from hot and wet to dry and cold regions. These plant types include: grassland, wetland, savanna, deciduous broadleaf and deciduous needleleaf forest. The results indicate that it is the type of plants, rather than the climate in which they are growing, that mainly dictates the water use efficiency.

Plant water use efficiency: Nature or Nurture?

Many studies on human development pose the question of whether “nature or nurture” more strongly influence developmental characteristics. Our study asks a similar question for plants.

Evidence for “nurture” driving water use efficiency would arise if we found a narrow, consistent and distinct range of values in each of the regions that we studied, since each of these regions have different historic and current climate conditions. Environmental conditions–including climate—select against unfavorable phenotypes among groups of plants. Over time, favorable and heritable traits become more common. We expected to observe adaptations that optimize the tradeoff of carbon uptake versus water lost in the climate where plant communities evolved. A single study region has a common climate history.  As a result, efficiency could be more consistent (i.e., exhibit less variability) in a single study region than among plant functional types.

On the other hand, if plant physiology drove ecosystem water use efficiency, we would see similarities for all plants of the same type, regardless of the climate where they grew. This would be evidence that “nature” (i.e., plant physiology as represented by the plant types in this study) is the main driver of the ecosystem function.

When we began this study, we believed nurture (i.e., climate) was more important for driving WUE. But we were wrong. Our findings suggest that plant functional type dictates water-use efficiency more than climate conditions. In other words, “nature” rather than “nurture” seems to drive our results.

Research implications

Implications for climate adaptation & biodiversity

Many plants living in arid ecosystems—such as the California chaparral—have traits to help withstand drought. These drought adaptations allow plants to possess high WUE. Even with these drought tolerant traits, increasing drought intensity may go beyond what many of these plants can tolerate, as I observed first hand in southern CA. Irreversible ecosystem state shifts and desertification can arise as a result. For instance, the chaparral ecosystems could shift to open shrubland with less abundant woody vegetation, lower carbon sequestration potential and lower biodiversity. 

Now let’s think about plant types that do not have adaptations to cope with prolonged water stress. These generally correspond to plants with low WUE. When drought intensity and/or frequency increases for these plant types, there is less of a buffer for their survival. Our study helps to identify which plant types and geographic regions have high vulnerability, revealing that plant type matters more than historic climate conditions in understanding WUE. 

Urgent need for climate mitigation and adaptation

The pressures of global change on ecosystems now and in the future may surpass the ability of certain plant species and functional groups to adapt. Doing this research caused me to see from a new lens how critical it is for us to take action on the climate crisis now. What we choose to do in the next decade with respect to curbing global emissions has cascading implications for the well-being of many generations to come.

I realized that one of the biggest things we, as scientists and as citizens, can contribute to this upcoming century is to be willing to move beyond “business as usual” by taking action on climate change in ways we have never done before.

In writing about my personal experiences, I wanted to do just that. In going beyond the “science as usual” of simply publishing a peer-reviewed paper, I hope to reach a larger audience with the broader message that I gained through engaging in research. Writing this in my personal capacity as a concerned citizen, this piece serves as a reminder of all the ways we can become a part of the solution. My wish is that in reading this post, you will choose to join me in this and inspire others to do the same.

Call to action for readers

I think everyone has a story to tell that is similar to mine, where climate change has already impacted people and ecosystems in their lives in major ways. My invitation to you is to reflect on ways you can translate frustration or hopelessness into action that you can take in your life.

Here are a few ways you can take action now: 

  • Start by simply sharing your climate story with others
  • Contribute time and money to organizations that are part of the solution
  • Vote for the climate
  • Change your diet
  • Transition to a less car-dependent lifestyle (e.g., public transit on trains, subways, buses, biking, walking, skateboarding, boogie boarding? … whichever mode best suits you!)
  • Buy less stuff
  • Ask your institution to divest from fossil fuel
  • Pressure governments at every level to take action on the climate emergency

Are you willing to take action in at least one of these areas by the end of this month?

The health of future generations and future plant communities lies in our hands. In taking action on the climate now, we can determine whether we continue down a path of “business as usual” or whether we avoid additional catastrophic extinctions and shift to a sustainable, decarbonized economy. I invite you to leave a comment on this blog post to share with this community about the action you choose to take.

 

 

Please sign in or register for FREE

If you are a registered user on Research Communities by Springer Nature, please sign in