Category Archives: Peer Reviewed Article Review

urban vegetation design for heat

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When you see completely mangled English in a paper that has supposedly passed peer review, you have to wonder about the quality of the peer review. Nonetheless, I was interested in the results of this study that looked at trees, shrubs, and lawn to see which had the most effect on urban heat.

Numerical simulation of the impact of different vegetation species on the outdoor thermal environment

For air temperature at 1.5 m and thermal comfort and safety (PET and WBGT), the sequence is trees> lawn> shrubs, but for surface temperature, the sequence is lawn> shrubs> trees

I’m always interested in the idea of designing urban areas to maximize hydrologic function, ecological function, and human comfort simultaneously. There is so much that could be done, and so much closed-mindedness and poor communication among the various professions and disciplines that could be doing it.

I’ve always assumed trees are the gold standard, because you get both the evapotranspiration function and the shading function, whereas with lawn and shrubs you only get the former. Also, you only need a small area of soil to plant the tree (although often more than we allow in urban areas), and then its leaves can cover a large area of concrete or asphalt, which would otherwise be generating a lot of heat and polluted runoff. Also, grass provides very little ecological function (unless you let it grow taller and/or take a lenient approach to what some of your neighbors choose to define as “weeds”, which can be socially unacceptable), where trees and bushes provide ecological function. Bushes take up a lot of space, either in a sidewalk context or a small urban yard – paradoxically, once trees mature a little bit they take up less space because there is space under them. On the other hand, I’ve argued with purists that if people really want lawn in urban areas, it is a lot better than concrete in terms of hydrology, heat, and aesthetics. Although if you’re in a water-stressed area, that adds another factor to the hydrology equation that those of us in wetter areas have the luxury of not worrying about too much.

no coffee grounds in compost?

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This article is a bit disturbing, because I have been composting coffee grounds for years with seemingly good results. Then again, I wasn’t doing an actual controlled experiment.

Applying spent coffee grounds directly to urban agriculture soils greatly reduces plant growth

There are frequent anecdotal recommendations for the use of locally produced spent coffee grounds in urban agriculture and gardens, either through direct soil application or after composting with other urban organic wastes. This study investigates the scientific basis for direct application of spent coffee grounds (SCG) and the influence of different: i) plant pH and nitrogen preferences, ii) soil types, and iii) application rates. We specifically consider impacts upon plant growth, soil hydrology and nitrogen transformation processes.

We grew five horticultural plants (broccoli, leek, radish, viola and sunflower) in sandy, sandy clay loam and loam soils, with and without SCG and fertilizer amendments. The same horticultural plants were grown in the field with 0, 2.5, 5, 10 and 25% SCG amendment rates. Plant biomass growth was related to soil pH, soil moisture, nitrogen concentration and net mineralization, as was weed growth after harvesting.

All horticultural plants grew poorly in response to SCG, regardless of soil type and fertiliser addition. Increasing SCG amendment significantly increased soil water holding capacity, but also decreased horticultural plant growth and subsequent weed growth. There was evidence of nitrate immobilization with SCG amendment. Growth suppression was not explained by soil pH change, or nitrogen availability, so is more likely due to phytotoxic effects.

Fresh SCG should not be used as a soil amendment in ‘closed loop’ urban food production systems without consideration of potential growth suppression. Further research is required to determine the optimal composting conditions for SCG and blends with other organic wastes.

I’m not a very scientific composter. I just throw stuff together in an old recycling bin, then when it fills up I move it to another bin, and then a third (despite a few raised eyebrows from neighbors, I rescued all these bins on my old street after they were abandoned for at least a week, and filled with litter and dog crap). At that point it’s usually a nice crumbly organic mix that I can use. I don’t follow any of the rules. I don’t mix green and brown items in the right proportions, I let it get wet and dry according to the rain, I compost perennial weeds, and my pile almost certainly doesn’t get hot enough. I probably wouldn’t give the stuff away because there are weeds in there, but I don’t worry about putting it back on my garden, which is where the weeds came from. If they want to keep pulling carbon dioxide out of the air and turning it into organic matter for me, I am fine with that. I would rather be outside pulling weeds than doing almost anything inside.

1 billion dogs

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I never thought to even wonder how many dogs there are in the world. But according to this article, about a billion. I don’t know if that is morally right or wrong. I like dogs. They are generally benign, kind-hearted creatures, and you could certainly make an argument that the world would not be as good a place without them. But they certainly have an ecological footprint. The article contrasts dogs and wolves, which have been systematically eradicated in many cases. So while dogs are neat creatures in many ways there are probably many wild creatures that might exist out there if they did not. Now we could examine this same moral conundrum with respect to a certain species of intelligent hairless ape…

“hybrid” infrastructure

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I like a couple things in this abstract from the journal Cities.

One is a definition of hybrid infrastructure as “infrastructure systems that are integrated within buildings and landscapes that also provide non-infrastructure uses”. In other words, you are trying to kill two birds with one stone. This should be efficient and cost-effective compared to killing two birds with two stones, but the reason it often doesn’t happen (at least in the U.S. cities I am familiar with) is that there are typically two entities responsible for killing one bird each, and if their stone happens to kill the other bird they will ignore that and not count it as a benefit. Each agency calculates the cost as one stone, while the actual cost to society was two stones. (The only problem with this analogy, obviously, is that we are talking about ecological benefits and killing birds would actually be bad.)

The second thing I like is that the question asked is about the “maximum ecological performance potential of buildings and landscapes”. This is a nice question to ask – not just how can one type of infrastructure perform one function cost-effectively, but how can it fit into the landscape and perform many functions at the same time. If those two agencies (or in real life, 10 or 20 agencies) were all asking this question together, maybe you could achieve much better outcomes in cities.

value of trees

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There have been a lot of studies on the value of urban trees. Well, here’s another. This one is notable for giving a canopy target at which value is maximized (30% at the property level, 38% at the county level).

The implicit value of tree cover in the U.S.: A meta-analysis of hedonic property value studies

Trees in residential neighborhoods and communities provide benefits for homeowners that are capitalized into residential property values. In this paper, we collected data from hedonic property value studies and merged these data with ancillary spatial data describing forest and socio-economic characteristics surrounding each study area to conduct a meta-analysis of the impact of tree canopy cover on the value of residential properties. The meta-analysis suggests that property-level tree cover of about 30% and county-level tree cover of about 38% maximize the implicit price of tree cover in property values. Currently, tree cover in the original study areas was about 14%, on average, around or near study properties. The empirical results, therefore suggest under investment of tree cover on private property from the perspective of individual property owners and from a societal perspective. The findings also have implications for community forest programs regarding planting trees and protection of mature trees to address potential changes in tree abundance, species diversity and stand age due to development and climate change.

green space and mental health

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Here’s a new study on green space and health, based on the large-scale nurses’s study. One interesting finding is that mental health explains around 30% of the total benefit.

Exposure to Greenness and Mortality in a Nationwide Prospective Cohort Study of Women

In models adjusted for mortality risk factors (age, race/ethnicity, smoking, and individual- and area-level socioeconomic status), women living in the highest quintile of cumulative average greenness (accounting for changes in residence during follow-up) in the 250m area around their home had a 12% lower rate of all-cause non-accidental mortality (95% CI 0.82, 0.94) compared to those in the lowest quintile. Results were consistent for the 1,250m area, although the relationship was slightly attenuated. These associations were strongest for respiratory and cancer mortality. Findings from a mediation analysis suggest that the association between greenness and mortality may be at least partly mediated by physical activity, particulate matter less than 2.5 micrometers, social engagement, and depression.

scenario analysis

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Maybe this is not of interest to everyone, but I am always looking for new ways to analyze and communicate the results of alternatives and scenarios.

The diversity of socio-economic pathways and CO2 emissions scenarios: Insights from the investigation of a scenarios database

The new scenario framework developed by the climate change research community rests on the fundamental logic that a diversity of socio-economic pathways can lead to the same radiative forcing, and therefore that a given level of radiative forcing can have very different socio-economic impacts. We propose a methodology that implements a “scenario discovery” cluster analysis and systematically identifies diverse groups of scenarios that share common outcomes among a database of socio-economic scenarios. We demonstrate the methodology with two examples using the Shared Socio-economic Pathways framework. We find that high emissions scenarios can be associated with either high or low per capita GDP growth, and that high productivity growth and catch-up are not necessarily associated with high per capita GDP and high emissions.

infectious disease

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The Royal Society says that the annual number of disease outbreaks and types of diseases causing them have both increased since 1980, although the fraction of the population affected has actually decreased. I assume this last trend has to do with population growth. I am not sure this should be comforting. If there are more outbreaks and more different types, it seems like there would be more potential for something really bad to emerge and then get out of control. But this article isn’t really about that, it’s just a presentation of the data.

Our analyses indicate that the total number of outbreaks and richness of causal diseases have each increased globally since 1980 (figure 1a). Bacteria and viruses represented 70% of the 215 diseases in our dataset and caused 88% of outbreaks over time. Sixty-five per cent of diseases in our dataset were zoonoses that collectively caused 56% of outbreaks (compared to 44% of outbreaks caused by human-specific diseases). Non-vector transmitted pathogens were more common (74% of diseases) and caused more outbreaks (87%) than vector transmitted pathogens (table 1). Salmonellosis caused the most outbreaks of any disease in the dataset (855 outbreaks reported since 1980). However, viral gastroenteritis (typically caused by norovirus) was responsible for the greatest number of recorded cases: more than 15 million globally since 1980.

It’s interesting how we tend to be less afraid of diseases that are more common and more afraid of ones that are less common, even though a given person would be more likely to suffer from a common disease. Of course, this analysis doesn’t take into account the severity of the disease and suffering caused, which should certainly be a factor in what kinds of controls and research we invest our efforts and money in.

ecosystem disservices

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This paper proposes the idea of “ecosystem disservices” to address criticisms scientists have made of the ecosystem services concept.

Limitations of the Ecosystem Services versus Disservices Dichotomy

Ongoing debate over the ecosystem services (ES) concept highlights a range of contrasting views and misconceptions. Schröter et al. (2014) summarise seven recurring arguments against the ES concept, which broadly relate to ethical concerns, translation across the science—policy interface, and how the concept’s normative aims and optimistic assumptions affect ES as a scientific approach. In particular, recent criticism has focused on how the concept is unable to address ecological complexity due to the limitations of the economic stock–flow model that ES is based on (Norgaard 2010). Acknowledging ecosystem disservices (EDS) (i.e. outcomes of ecosystem functions that negatively affect human communities) has been suggested as a way to account for this ecological complexity (McCauley 2006; Lyytimäki 2015). The impact of EDS on communities (i.e. the ‘cost’ of the action) can be measured financially, or through changes in individual or social well-being. McCauley (2006) and Lyytimäki (2015) list EDS examples like pest damage to crops, or trees removing water from watersheds.

Integration of ecological-biological thresholds in conservation decision making

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Here’s another attempt to link ecological and economic systems:

Integration of ecological-biological thresholds in conservation decision making

In the Anthropocene, coupled human and natural systems (CHANS) dominate and only a few natural systems remain without drastic human influence. Conservation criteria, such as many of those proposed by conservation biologists and ecologists with reference to areas of minimal human impact, are not relevant to much of the biosphere. On the other hand, conservation criteria delineated within economics are problematic with respect to their ability to arrive at operational indicators of well-being that can be applied in practice over multi-generational time spans. CHANS are subject to the process of economic development which, under current management structures, tends to afflict natural systems and transgress planetary boundaries. Hence, designing and applying conservation criteria applicable in real world systems where human and natural systems need to interact and sustainably coexist is essential. By both recognizing the criticality of satisfying basic needs as well as the great uncertainty over the needs and preferences of future generations, the current paper seeks to incorporate strict conservation criteria into economic evaluation. Specifically, these criteria require the conservation of environmental conditions such that the opportunity for intergenerational welfare optimization is maintained. In this direction, we propose the integration of ecological-biological thresholds into decision-making and use as an example the planetary boundaries approach. As such, both conservation biologists and economists must be involved in defining operational ecological-biological thresholds which can be incorporated into economic thinking and reflect the objectives of conservation, sustainability and intergenerational welfare optimization. As a result, we delineate the axioms of an operational framework of sustainability and hence set the basis for an interdisciplinary research agenda.