Saturday, April 1, 2017

April Journal Article Summary

This review is extra-large since I spent an unusual amount of time on planes reading these articles and awkwardly typing up notes with my arms in the T-rex position while wedged between other passengers. Feeling like you don't want to spend time reading all this science when it's so lovely outside? I've included blog links for three of the papers below so that you can read a bit more without having to wade through the full text.

Do you like being surprised, and finding out that things that "everybody knows" aren't necessarily true? If so, check out the abstracts for each of the 28 chapters in an upcoming book called Effective Conservation Science: Data Not Dogma (I have them in the same Box folder as the articles) which should be out this fall. Six of the chapters feature TNC authors (including myself), not counting the many ex-TNC staff and current TNC partners. The theme for the whole book is stories of ideas widely accepted as true being discovered to be flawed, and how we respond to this challenging new information. Let me know if you'd like a copy of my chapter.

There has been some debate about the upcoming March for Science, and whether scientists engaging in advocacy (whether generally in support of science and data, or specifically advocating for policies) could harm our credibility and increase polarization. Here is one data point from Kotcher et al finding that advocacy does NOT harm that credibility. They asked about 1,200 people to read a biography of a fictional scientist, then read one of six statements which had been tailored along a continuum of just presenting facts to a strong policy recommendation, then to rate his credibility (and several other variables). The degree of advocacy did not impact how trusted the scientist was (except when he made a recommendation to build more nuclear power plants), implying that advocacy scientists does not necessarily mean they will not be seen as credible. So if you are so inclined, march for science bolstered by data that you're unlikely to make things worse (as some have worried about). There is a blog on this paper here:

A new paper by TNC's Marissa Ahlering and Joe Fargione looks at the impact of preserving vs. converting rangelands (grasslands primarily used for grazing cattle, and relatively unmanaged compared to pasture which can be irrigated & fertilized). They found that at a site level in addition to obvious habitat benefits of rangelands that there are also carbon benefits; even accounting for the emissions from the cattle being grazed the rangelands still on net offer GHG benefits compared to converting the rangelands to crop. This is a great way to bolster the case for protecting rangelands that are providing good habitat. Note that it is NOT saying that all beef production is a GHG sink. Clearing forests for pasture would still entail heavy GHG emissions, and they also didn't look at the full life cycle of the cattle (in other words, the rangelands were a carbon sink, but after they finish grazing the cattle go to feedlots where there are additional emissions from enteric methane / manure / feed production). So the total GHG impact of beef vs. other crops is still complicated, but this is an important contribution to make a stronger case for protecting existing rangelands. Check out Marissa’s blog on the paper if you don't want to read the whole thing:

There are several ways in which climate change may reinforce itself via positive feedback (e.g., melting ice reducing how much sunlight is reflected, leading to more warming), and Bradford et al 2016 argue that accelerated loss of soil carbon resulting from global warming is only supported by limited evidence. They point out that there are few observations of soil C stocks decreasing due to warming and the rapid shift in how soil science characterizes soil C stability and turnover. They lay out several ideas for how future research can increase our ability to understand and model soil C changes due to climate change.

Soti et al 2016 looks at how different cover crops affect mycorrhizae (symbiotic soil fungi which crops like peppers and corn depend on) and soil quality on organic farms in the Lower Rio Grande Valley in Texas. They found cover crops boosted mycorrhizal spores, soil organic matter, and several nutrients. Different cover crops had different effects, with no clear winner or loser across all metrics. If applying this look carefully at Table 2 as the text doesn't always make clear which cover crops performed better than the control plot.

Teasdale et al 2007 compared soil quality and crop yield of organic farming and 3 variations of no-till (which used herbicide and conventional fertilizer). Essentially they found that the organic system (and even the "living mulch" no-till system with reduced herbicide and fertilizer use) suffered yield losses from weeds that got worse over time, even though soil carbon and N were significantly higher in the organic system. Interestingly, the fields that had the highest yields used conventional no-till practices on soils with a 9-year history of either organic or "living mulch" production; these fields had accrued soil benefits but were effectively controlling weeds with herbicide that reduced competition. I love that this study both shows the yield benefits of soil health, but also shows that those benefits can be counteracted by other factors (insufficient weed control).

Navarrete et al 2016 is complicated but potentially important: they look at how conversion in the Colombian Amazon impacts soil carbon, and found that it can either decrease or increase depending on management (although the paper isn't well controlled, there are several confounding variables and they make stocking density binary rather than continuous). Lots of caveats here to the potential increase (forest biomass is still lost), so this is more about how we can perhaps limit the GHG impact of pasture (not saying conversion to pasture can be good for GHGs). Essentially they found pastures averaging ~3 head per ha lost 20% of soil C in 20 years, while pastures with ~0.1 head/ha gained 40%. This is worth reading for people working in the region, as the mechanisms driving the different soil outcomes look to me like they could be modified to get higher intensity grazing with significantly less soil C losses. Even if not, on net the higher intensity grazing would still represent a net GHG benefit if it leads to less conversion.

Kopittke et al 2016 is a rough global summary of how soil C (plus N,P, & S) change (per unit of soil mass) over the long term with conversion of natural land cover (e.g. forests, grasslands, etc.) to either cropland or pasture. The findings aren't surprising (there's more loss when converting to crop than to pasture) but it's still useful to have the comparison with the caveat that the median sampling depth was only 20 cm (mean 26 cm). This limits the utility of their estimates in how changing cropping (conventional vs no-till vs organic amendment) impacted soil C.

Hijbeek et al 2016 is a metaanalysis showing that organic inputs (e.g. straw, manue) in most cases does not boost crop yield significantly if nutrients are not a limiting factor. Some exceptions: roots / tubers, wet climates, sandy soils, and potentially very dry climates show yield benefits from organic inputs. They also note how high the variance is, concluding that organic inputs or SOM alone are not sufficient to predict yields.

Finally, this is more of an editorial than a journal article, but this piece by Jess Davies in Nature calls for businesses to engage more around soils (largely absent from corporate sustainability goals and reporting), in partnership with scientists. There are lots of puns and zinger quotes about dirt too:

Levis et al 2017 presents evidence that forests have been managed by native people in the Amazon for a very long time. Specifically, domesticated tree species are quite a bit more common near to archaeological sites and rivers (argued to be a good proxy for the location of pre-Colombian settlements) in most of the Amazon. It thus challenges the notion of the Amazon as a "virgin" forest that hasn't been impacted by humans until recently. There's a blog about this here if you want to know more but don't want to read the paper:

Ceccato 2005 is about using remote sensing to detect desert locust outbreaks early enough to prevent them from growing into a full scale plague. However, the more broadly applicable and interesting aspect of this paper is the fact that NDVI (a commonly used index of "greenness" often used as a proxy for vegetation) can be the same for bare ground and sparse vegetation (see Figure 2). In this paper they added a shortwave infrared band, but in other papers the author has transformed the RGB color index into HSV, as soils and sparse vegetation typically have a different hue (brown-red-black vs green).

Olsen et al 2015 is a paper using remote sensing (MODIS) to estimate grassland biomass under three different grazing treatments (ungrazed, controlled / rotational, and uncontrolled / continuous). They found that metrics based on NDVI correlated fairly well with end of season standing biomass overall, BUT the best metric was still unable to distinguish real biomass differences between treatments. The biomass of the ungrazed plots was almost double that of the grazed ones, but the NDVI only varied by a few %. This shows the current limits of using remote sensing to detect relati

Mango et al 2017 is an analysis of how conservation ag (reduced tillage, crop rotations, and cover crops) impacted food security (measured via food consumption score, which reflects both quantity and quality) of 1600 smallholder farmers in southern Africa. They found that while it slightly improved food security in Mozambique (with a marginally statistically significant effect of p=0.09), it had no significant effect in Malawi or Zimbabwe. The authors best guess is that in Mozambique conservation ag is often promoted along with other BMPs like improved seeds and timely weeding (which is especially critical when using conservation ag). Interestingly, in both Malawi and Mozambique both groups of farmers (using conservation ag or not) were in the "acceptable" range of food consumption. This paper shows the challenge in assuming that conservation ag will necessarily lead to positive human outcomes without careful design.

Horowitz et al 2016 is an analysis of reactive nitrogen (any N other than N2) flows in Central California, using multiple metrics (e.g. mass flows, damages, and abatement costs) to investigate how to reduce damages at the lowest costs. Surprisingly, while agriculture is the dominant source of nitrogen, the authors find that reducing NOx from cars and trucks would be the most cost-effective solution. This is a result of the human health impacts of poor air quality having much higher dollar values associated with them, as well as it being relatively easier to abate those emissions. The thing I find most interesting in this paper is thinking about how changing your metric (e.g. damages, abatement costs, ROIs, etc) can shift your focus; using this multiple metrics approach you could consider the multiple axes to determine which solutions are preferable.

You're probably aware that a key part of the pitch for water funds is how changing land use affects water quality. McDonald et al 2016 is a nice TNC-led analysis quantitatively showing how much water quality in urban watersheds has been degraded by human activity (e.g., conversion of natural areas to urban and agricultural), and how that has impacted the costs of treating water for human consumption (they found 29% of large cities have had water treatment costs significantly increased [~50%] by watershed degradation).

DiMuro et al 2014 is a paper by Dow staff comparing a "gray vs green" infrastructure decision for water treatment, specifically looking at a wetland Dow constructed in 1995 (instead of building a conventional reactor). The authors conclude that over the life of the project the wetland will save ~$125 million in 2012 dollars (and accounting for interest, tax, insurance, depreciation, and other factors they put the net present value at $282 million), making it a "big win" for both Dow and the environment (as there were several co-benefits). They conclude with some of the trade-offs between green vs gray solutions like this, and how companies can approach these decisions.

Curtis and Slocum 2016 lays out a framework for improving the design of green certification of resorts using behavioral economics, given that current certification efforts have not been successful in achieving substantial reductions in food waste. I found the last two pages particularly useful, where the author make suggestions on how companies can influence their employees and customers in support of their sustainability goals.


p.s. as a reminder, you can search all of the science articles written by TNC staff (that we know of) here  

Ahlering M, Fargione J, Parton W. Potential carbon dioxide emission reductions from avoided grassland conversion in the northern Great Plains. Ecosphere. 2016;7: e01625. doi:10.1002/ecs2.1625

Bradford MA, Wieder WR, Bonan GB, Fierer, N. Raymond PA, Crowther TW. Managing uncertainty in soil carbon feedbacks to climate change. Nat Clim Chang. Nature Publishing Group; 2016;6: 751–758. doi:10.1038/nclimate3071

Ceccato P. Operational Early Warning System Using Spot- Vegetation and Terra-Modis To Predict Desert Locust Outbreaks. Proc 2nd Int Veg User Conf. 2005; 33–41. 

Curtis KR, Slocu SL. The Role of Sustainability Certification Programs in Reducing Food Waste in Tourism. In: Journal of Developments in Sustainable Agriculture [Internet]. 2016 pp. 1–7. Available:

Davies J. The business case for soil. Nature. 2017;543: 309–311. Available:

Dimuro JL, Guertin FM, Helling RK, Perkins JL, Romer S. A financial and environmental analysis of constructed wetlands for industrial wastewater treatment. J Ind Ecol. 2014;18: 631–640. doi:10.1111/jiec.12129

Hijbeek R, van Ittersum MK, ten Berge HFM, Gort G, Spiegel H, Whitmore AP. Do organic inputs matter – a meta-analysis of additional yield effects for arable crops in Europe. Plant Soil. Plant and Soil; 2016; doi:10.1007/s11104-016-3031-x

Horowitz AI, Moomaw WR, Liptzin D, Gramig BM, Reeling C. A multiple metrics approach to prioritizing strategies for measuring and managing reactive nitrogen in the San Joaquin Valley of California. Environ Res Lett. IOP Publishing; 11: 1–10. doi:10.1088/1748-9326/11/6/064011

Kopittke PM, Dalal RC, Finn D, Menzies NW. Global changes in soil stocks of carbon, nitrogen, phosphorus, and sulfur as influenced by long-term agricultural production. Glob Chang Biol. 2016; doi:10.1111/gcb.13513

Kotcher JE, Myers TA, Vraga EK, Stenhouse N, Maibach EW. Does Engagement in Advocacy Hurt the Credibility of Scientists? Results from a Randomized National Survey Experiment. Environ Commun. Taylor & Francis; 2017;0: 1–15. doi:10.1080/17524032.2016.1275736

Levis C, Costa FRC, Bongers F, Peña-Claros M, Clement CR, Junqueira AB, et al. Persistent effects of pre-Columbian plant domestication on Amazonian forest composition. Science (80- ). 2017;355: 925–931. doi:10.1126/science.aal0157

Mango N, Siziba S, Makate C. The impact of adoption of conservation agriculture on smallholder farmers’ food security in semi-arid zones of southern Africa. Agric Food Secur. BioMed Central; 2017;6: 32. doi:10.1186/s40066-017-0109-5

McDonald RI, Weber KF, Padowski J, Boucher T, Shemie D. Estimating watershed degradation over the last century and its impact on water-treatment costs for the world’s large cities. Proc Natl Acad Sci. 2016; 201605354. doi:10.1073/pnas.1605354113

Navarrete D, Sitch S, Aragão LEOC, Pedroni L. Conversion from forests to pastures in the Colombian Amazon leads to differences in dead wood dynamics depending on land management practices. Glob Chang Biol. 2016;22: 3503–3517. doi:10.1111/gcb.13266

Olsen JL, Miehe S, Ceccato P, Fensholt R. Does EO NDVI seasonal metrics capture variations in species composition and biomass due to grazing in semi-arid grassland savannas? Biogeosciences. 2015;12: 4407–4419. doi:10.5194/bg-12-4407-2015

Soti PG, Rugg S, Racelis A. Potential of Cover Crops in Promoting Mycorrhizal Diversity and Soil Quality in Organic Farms. J Agric Sci. 2016;8: 42. doi:10.5539/jas.v8n8p42

Teasdale JR, Coffman CB, Mangum RW. Potential long-term benefits of no-tillage and organic cropping systems for grain production and soil improvement. Agron J. 2007;99: 1297–1305. doi:10.2134/agronj2006.0362

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