Monday, April 1, 2019
April 2019 science journal article summary
Since I've just changed jobs I asked for help in putting this summary together; Steve Wood from The Nature Conservancy kindly reviewed four of the articles below. Also, these summaries come from me (and Steve in this case) and do not reflect the views of our employers or any other organization. Any mistakes are my own.
If you know someone who wants to sign up to receive these summaries, they can do so at http://bit.ly/sciencejonFinally, for folks interested in science communications, I've been getting a lot of good ideas from the short daily emails Bob Lalasz (from Science + Story) sends. You can check out a few examples at https://medium.com/science-plus-story and if interested sign up at https://scienceplusstory.com/quick-list-opt-in/
Tack et al. 2019 identifies priority areas to focus land protection on the most important wildlife corridors used by pronghorn and greater sage grouse in the Northern Great Plains, specifically north-central Montana into southern Saskatchewan. Sage grouse in this area depend on migration, as do about half of the pronghorn population. Private lands in the area are roughly half ranches on native sagebrush, and half cropland (with public land typically primarily used for cattle grazing). Cropland expansion is the main driver of habitat loss (followed by energy development), and protected areas only cover ~5% of pathways for both species. So priorities for protection are on lands used for migration with a higher chance of cultivation. Note Figure 4 which shows the importance of unprotected public, private, and even cultivated land. Fences impede migration, but marking them with flags reduces collisions.
McGill et al. 2018 modeled greenhouse gases (GHGs) of groundwater-irrigated vs rainfed croplands in the Midwest US. Irrigated fields had higher net GHGs (27 g CO2e/m2/yr) than rainfed (a net sink, -14g CO2e/m2/yr), mainly due to higher N2O emissions and fossil fuel use to pump groundwater. However, since irrigation also increased yield the emissions per unit of crop yield were similar: 0.04 kg CO2e/ kg yield for irrigated vs -0.03 kg CO2e/ kg yield for rainfed (again a GHG sink). Finding the rainfed system to be a net GHGS sink is surprising and unusual, even if you assume that no-till farms have net C sequestration (which is unlikely). There are some other odd findings like fertilization reducing soil C. But the overall idea should be valid: irrigation will generally lead to wetter soil (w/ higher N2O emissions more than offsetting higher soil C) plus energy use to pump water.
Smith et al. 2019 is a review of the environmental impact widespread adoption of the voluntary Bonsucro standard for sugar cane could have. They find impressive potential, especially if efforts are targeted well and involve compliance with all standards and criteria. Half of global environmental potential benefits could be met with only 10% of total production area (check out figure 4 for details). However there are several challenges, including what to do with farms totally unable to meet those standards (e.g. large areas in India). This paper also models impact IF all participating farms actually met all target outcomes, and doesn't look at how companies could drive that or what would be practical with different levels of investment. Nonetheless, this shows a lot of potential especially if we can move beyond practice based frameworks to those that are outcome-based and carefully targeted. You can read a blog about this work here:
Han et al. 2018 is a meta-analysis of 68 studies of how straw incorporation affected carbon sequestration and crop yields across China. On average it sequestered 0.35 t C / ha / yr in the upper 20 cm of soil, and boosted crop yields 13%. It worked best on clay soils, high crop intensities, and in areas where soil is currently being degraded (NE China).
GUEST REVIEWS FROM STEVE WOOD:
Have questions about the four papers below? Contact Steve at stephen.wood@TNC.ORG.
Soil health has become a major are of interest, but there is uncertainty about how to measure and define it. Derner et al. 2018 tackle the question of how to define soil health for grazing lands. This is an important task because the notion of soil health emerged from row-crop agriculture, yet the way grazing lands are managed and the environmental services they provide are starkly different to row crop agriculture.
The authors argue that a soil health approach to grazing lands should re-focus grazing management on managing for ecosystem processes, rather than maximizing short-term profit. And this requires building cross-institutional capacity and training, adaptive management, and long-term monitoring. The authors argue against adoption of a single set of practices or indicators. For instance, a soil health indicator from row crop agriculture is high soil cover, but in grazing systems high amounts of bare ground can be necessary for some grassland bird species. This paper is also noteworthy for the mix of authors--everything from university professor to rancher.
The two papers by Unks et al. 2019 aim to understand the drivers of pastoralist livelihood vulnerability in one of the Northern Rangeland Trust community conservancies. They argue that the rangeland institutions in central Kenya going back to the colonial era have promoted formal land tenure, whether at the individual or community level. But, because forage production is patchy, successful grazing requires a high level of mobility to access resources in different areas at different times. This type of management is at odds with formal property regimes, as well as at odds with realities of modern life, like employment at conservancy lodges and keeping children in school. Herders now face limited mobility, which means that livestock husbandry has shifted towards browsers, like goats and camels, which do better on lands with low grass productivity. Limited mobility also has made livestock husbandry more individualistic, leading to greater inequality among households. Greater inequality leads to unequal ability to cope with future climate change.
The papers offer nuanced insight into the drivers of change and livelihood vulnerability. The narrative promoted by conservation non-profits tends to be more simplistic: poor current management--stocking rates, population growth--is the main driver of poor vegetation and livelihoods. By showing the importance of long-standing institutional, climatic, and socio-economic change, the authors imply that land-tenure-based management plans (like those promoted at NRT) will not fix the ecological or livelihood challenges. In bringing more nuance they highlight greater challenges, but they don’t offer insight into what solutions to those greater challenges might be.
Finally, Rosenzweig et al. 2018 focuses on quantifying whether it is possible to lower fertilizer and herbicide use while maintaining yields via changing crop rotations. The focus is on dryland, no-till wheat in Colorado and Nebraska. They tested three groups of cropping systems, all of which had wheat in the winter. In the summer they differed by: (1) natural fallow one out of two years; (2) a summer crop (corn, sorghum, millet, peas, or sunflowers) replacing fallow every couple of years; (3) continuous cropping with mixtures of the same crops from (2). They showed that the continuous cropping system had the highest nutrient retention, greater fungal colonization of roots (which increases nutrient retention), lowest herbicide use, lowest yield penalty, and highest profitability. Continuous cultivation had greater net revenue than basic fallow by $100 per hectare per year.
One reason I like this paper is that it challenges the idea that continuous cultivation is inherently bad and that natural fallow/regeneration is good. The paper shows that planning cropping and restoration is likely the key to ecological intensification. One limitation of this study is that because there were multiple crop combinations in each of the categories tested that it’s not possible to discern which of those combinations had the greatest effect.
Derner, J. D., Smart, A. J., Toombs, T. P., Larsen, D., McCulley, R. L., Goodwin, J., et al. (2018). Soil Health as a Transformational Change Agent for US Grazing Lands Management. Rangeland Ecology & Management, 71(4), 403–408. http://doi.org/10.1016/j.rama.2018.03.007
Han, X., Xu, C., Dungait, J. A. J., Bol, R., Wang, X., Wu, W., & Meng, F. (2018). Straw incorporation increases crop yield and soil organic carbon sequestration but varies under different natural conditions and farming practices in China: a system analysis. Biogeosciences, 15(7), 1933–1946. https://doi.org/10.5194/bg-15-1933-2018
McGill, B. M., Hamilton, S. K., Millar, N., & Robertson, G. P. (2018). The greenhouse gas cost of agricultural intensification with groundwater irrigation in a Midwest U.S. row cropping system. Global Change Biology, 24(12), 5948–5960. https://doi.org/10.1111/gcb.14472
Rosenzweig, S. T., Stromberger, M. E., & Schipanski, M. E. (2018). Intensified dryland crop rotations support greater grain production with fewer inputs. Agriculture, Ecosystems and Environment, 264, 63–72. http://doi.org/10.1016/j.agee.2018.05.017
Smith, W. K., Nelson, E., Johnson, J. A., Polasky, S., Milder, J. C., Gerber, J. S., … Siebert, S. (2019). Voluntary sustainability standards could significantly reduce detrimental impacts of global agriculture. Proceedings of the National Academy of Sciences, 116(6), 2130–2137. https://doi.org/10.1073/pnas.1707812116
Tack, J. D., Jakes, A. F., Jones, P. F., Smith, J. T., Newton, R. E., Martin, B. H., … Naugle, D. E. (2019). Beyond protected areas: private lands and public policy anchor intact pathways for multi-species wildlife migration. Biological Conservation, 234, 18–27. https://doi.org/10.1016/j.biocon.2019.03.017
Unks, R. R., King, E. G., German, L. A., Wachira, N. P., & Nelson, D. R. (2019). Unevenness in scale mismatches: Institutional change, pastoralist livelihoods, and herding ecology in Laikipia, Kenya. Geoforum, 99, 74–87. http://doi.org/10.1016/j.geoforum.2018.12.010
Unks, R. R., King, E. G., Nelson, D. R., Wachira, N. P., & German, L. A. (2019). Constraints, multiple stressors, and stratified adaptation: Pastoralist livelihood vulnerability in a semi-arid wildlife conservation context in Central Kenya. Global Environmental Change, 54, 124–134. http://doi.org/10.1016/j.gloenvcha.2018.11.013
p.s. If you'd like to keep track of what I write as well as what I read, I always link to both my informal blog posts and my formal publications (plus these summaries) at http://sciencejon.blogspot.com/