Category Archives: Peer Reviewed Article Review

connectivity and corridors

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From Conservation Biology, here’s an article on connectivity and movement corridor models for wildlife:

Habitat corridors are important tools for maintaining connectivity in increasingly fragmented landscapes, but generally they have been considered in single-species approaches. Corridors intended to facilitate the movement of multiple species could increase persistence of entire communities, but at the likely cost of being less efficient for any given species than a corridor intended specifically for that species. There have been few tests of the trade-offs between single- and multispecies corridor approaches. We assessed single-species and multispecies habitat corridors for 5 threatened mammal species in tropical forests of Borneo. We generated maps of the cost of movement across the landscape for each species based on the species’ local abundance as estimated through hierarchical modeling of camera-trap data with biophysical and anthropogenic covariates. Elevation influenced local abundance of banded civets (Hemigalus derbyanus) and sun bears (Helarctos malayanus). Increased road density was associated with lower local abundance of Sunda clouded leopards (Neofelis diardi) and higher local abundance of sambar deer (Rusa unicolor). Pig-tailed macaque (Macaca nemestrina) local abundance was lower in recently logged areas. An all-species-combined connectivity scenario with least-cost paths and 1 km buffers generated total movement costs that were 27% and 23% higher for banded civets and clouded leopards, respectively, than the connectivity scenarios for those species individually. A carnivore multispecies connectivity scenario, however, increased movement cost by 2% for banded civets and clouded leopards. Likewise, an herbivore multispecies scenario provided more effective connectivity than the all-species-combined scenario for sambar and macaques. We suggest that multispecies habitat connectivity plans be tailored to groups of ecologically similar, disturbance-sensitive species to maximize their effectiveness.

informal economies

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I’m somewhat interested in the idea of informal economies. According to this paper from the National Bureau of Economic Research, economists tend to think they’re bad – either a cause of poverty and slow development, or a symptom of it:

We establish five facts about the informal economy in developing countries. First, it is huge, reaching about half of the total in the poorest countries. Second, it has extremely low productivity compared to the formal economy: informal firms are typically small, inefficient, and run by poorly educated entrepreneurs. Third, although avoidance of taxes and regulations is an important reason for informality, the productivity of informal firms is too low for them to thrive in the formal sector. Lowering registration costs neither brings many informal firms into the formal sector, nor unleashes economic growth. Fourth, the informal economy is largely disconnected from the formal economy. Informal firms rarely transition to formality, and continue their existence, often for years or even decades, without much growth or improvement. Fifth, as countries grow and develop, the informal economy eventually shrinks, and the formal economy comes to dominate economic life. These five facts are most consistent with dual models of informality and economic development.

I’ve never bought into the idea that informal economies are 100% bad. I’ve been very lucky to spend some time in central Thailand, right on the edge between a rural and urban area, and to experience a mix of the informal and formal economies. It makes perfect sense that higher-tech sectors like mining, manufacturing, banking, and so forth are run by efficient, formal, corporations. But lower-tech service sectors provide a chance for “poorly educated entrepreneurs” (a pretty condescending term, actually) to provide everyday goods and services to each other at low cost and practically no overhead. Why is it “efficient” to pay $10 for a tasteless corporate meal at the mall, with most of that money going to pay rent to a real estate corporation and its army of lawyers, accountants, human resourcers, and insurance agents, plus the gas and wasted time to get there, vs. $2 for a tastier meal from a neighborhood entrepreneur? When you stop and chat with your neighbor, that’s culture and social capital, not “inefficiency”. And when something bad happens, you and the neighbor are going to lean on each other for help, not the lawyers and accountants working for the faceless corporation that runs the mall.

green roofs

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Green roofs are still pretty expensive and not all that common, at least in North America. But here’s a study in Ecological Engineering where they turned out to work better than people thought in Hong Kong, a humid subtropical area.

Urbanization replaces permeable surfaces with relatively impervious ones to intensify mass and temporal response of stormwater runoff. Under heavy rainfalls, urban runoff could impose tremendous stress on the drainage systems, contributing to combined sewer overflow and flooding. Green roof offers an on-site source-reduction sustainable stormwater management measure that mimics pre-development hydrologic functions. It can retain and detain stormwater as well as delay and suppress peak discharge. However, previous studies were conducted mainly outside the tropics. Since green-roof hydrologic performance can be notably influenced by local meteorological conditions, dedicated investigation in the tropics are necessary. Moreover, substrate depth has long been regarded as an influential factor in green-roof stormwater retention, but recent findings have implicated that such relationship may be more complex. This study (1) evaluates green roof stormwater mitigation performance and potentials in humid-subtropical Hong Kong; and (2) investigates systematically the effect of substrate depth and addition of rockwool, a high water-retention growth medium, on quantitative performance. Using multiple 1.1-m2 raised green-roof platforms placed on an urban rooftop, the effect of four substrate-depth treatments on stormwater mitigation performance was examined over a 10-month study period. The results show that, while the retention under Hong Kong’s frequent and heavy rainfall regime seems to be less effective, remarkable peak reduction and peak delay were evidently expressed even when the green-roof systems have reached full moisture-storage capacity. No statistical significance was found between treatments, despite the slightly higher mean performance of the 80-mm soil substrate. Satisfactory peak performance of the 40-mm soil substrate implies that a thin substrate can provide effective peak mitigation, especially if building loads are of concern. Extensive green roof remains as a promising alternative mitigation strategy to urban stormwater management in Hong Kong with potential application to other tropical areas.

Part of me doesn’t like using an inorganic material like rockwool. But if somebody comes up with a simple, cheap material that we can practically just staple or spray on to roofs in urban areas, it could be a quick way to restore a lot of hydrologic function – retention, evaporation, peak flow reduction, and cooling – in urban areas. It could be a transitional step on our way to restoring both hydrologic and ecological functions together – ideally we would want to capture that water and use it to grow something of use to either people or wildlife or both. But we are far from ideal today, so I’m all for some smaller steps in the right direction.

 

functional urban streams

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If you want a functional urban aquatic ecosystem, you don’t get it just through half-hearted management measures in the area draining to the stream. You have to get in there and make a functional ecosystem, and then you might be able to protect and sustain it by managing the watershed better. The article in Restoration Ecology looks at a range of numbers from the literature that make the case pretty well:

Urban development is a leading cause of stream impairment that reduces biodiversity and negatively affects ecosystem processes and habitat. Out-of-stream restoration practices, such as stormwater ponds, created wetlands, and restored riparian vegetation, are increasingly implemented as management strategies to mitigate impacts. However, uncertainty exists regarding how effectively they improve downstream ecosystems because monitoring is uncommon and results are typically reported on a case-by-case basis. We conducted a meta-analysis of literature and used response ratios to quantify how downstream ecosystems change in response to watershed development and to out-of-stream restoration. Biodiversity in unrestored urban streams was 47% less than that in reference streams, and ecological communities, habitat, and rates of nutrient cycling were negatively affected as well. Mean measures of ecosystem attributes in restored streams were significantly greater than, and 156% of, those in unrestored urban streams. Measures of biodiversity in restored streams were 132% of those in unrestored urban streams, and indices of biotic condition, community structure, and nutrient cycling significantly improved. However, ecosystem attributes and biodiversity at restored sites were significantly less than, and only 60% and 45% of, those in reference streams, respectively. Out-of-stream management practices improved ecological conditions in urban streams but still failed to restore reference stream conditions. Despite statistically significant improvements, assessing restoration success remains difficult due to few comparisons to reference sites or to clearly defined targets. These findings can inform future monitoring, management, and development strategies and highlight the need for preventative actions in a watershed context.

So let’s focus more on function and worry less about structure in our urban ecosystems. Let’s not settle for making them less bad. Let’s make them good!

restoring the American Chestnut

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I like this abstract in Restoration Ecology on the most efficient way to reseed the American Chestnut to eastern forests.

Efforts are underway to return the American chestnut (Castanea dentata) to eastern forests of North America following its decline due to the introduction of the chestnut blight (Cryphonectria parasitica). Approaches include developing blight-resistant chestnut lines through breeding programs and via genetic engineering. Reestablishment of resistant chestnut to eastern forests would produce one of the most extensive ecological restoration transformations ever attempted. However, this undertaking is costly and optimization of reintroduction methods is needed. We used the computer program NEWGARDEN to model whether some patterns of founder placement (regular vs. random spacing at differing densities) produce more rapidly expanding populations across a range of gene dispersal distance conditions (via both offspring and pollen). For a simulated introduction project employing 169 founders, placing founders randomly in a square of side 0.85 km produced higher rates of predicted population growth compared with larger or smaller squares under near gene dispersal conditions; this side distance was 1.0 km under far gene dispersal conditions. After 100 population bouts of mating and under near gene dispersal conditions, the trial with founder placement producing the greatest population expansion rate exhibited a 314% increase in census size compared with the founder pattern yielding the slowest expansion. Neither loss of alleles nor inbreeding or subdivision was significantly increased under the founder placement patterns yielding the most descendants. Exploring different numerical and geometrical founding scenarios using NEWGARDEN can provide first estimates of founding patterns or stand manipulations that will return the most descendants produced per founder planted in restoration projects.

So it is possible to give an ecosystem a helping hand. Maybe we can use similar principles not just to restore species and ecosystems that used to exist, but to create truly functional ecosystems in rural, suburban, and urban areas and the transitions between them.

the urban carbon cycle

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This article from Landscape and Urban Planning looks at carbon emissions and carbon sequestration in Beijing:

During the study period, carbon sequestration only offset 2.4% of carbon emission, indicating a serious imbalance of the city’s carbon metabolism. The city’s core built-up area expanded along eight axes, and its form fluctuated between simpler and more complex. From a small-scale perspective, the spatial pattern mainly showed expansion and aggregation of patches with high carbon emission and shrinkage and fragmentation of patches with high carbon sequestration.

I think this sort of study is useful as we think about what it would mean for cities to be truly sustainable either within their own boundaries or in the context of the larger landscape. 2.4% doesn’t sound like much, but if that is the answer with no system-level planning or management, could it be boosted to 5% or 10% with a more systematic approach to green infrastructure? The rest of the landscape (farms, protected forests, grasslands, and wetlands, and bodies of water) would do its share. Finally, technology would have to make up the remaining gap, if we really want to one day get to carbon neutral or even begin to role back the damage we have done to the atmosphere and oceans.