Tag Archives: green infrastructure

growing the urban forest

This abstract in Restoration Ecology contains an interesting result: planting shrubs along with urban trees helps the trees. You might think the opposite, due to competition, but I have heard this before. One theory I’ve heard is that shrubs help establish beneficial fungi in the soil that pave the way for healthy trees. It shouldn’t be too surprising, when this is exactly the succession that will occur in an abandoned field over time, given enough rainfall and not too much fire.

Compost also helps trees, which might be surprising to some professional engineers but not to any amateur gardener (luckily, some of us are both!). Still, in urban stormwater management we engineers are often encouraged to plant trees and other vegetation, but to minimize organic matter because the same nutrients that trees need can become water pollutants if they find their way downstream. It’s a delicate balance. Civil, “environmental”, and geotechnical engineers aren’t good at finding it because it is not part of our typical training. We need the agriculture, forestry, and soil science types to help us with this.

Forests are vital components of the urban landscape because they provide ecosystem services such as carbon sequestration, storm-water mitigation, and air-quality improvement. To enhance these services, cities are investing in programs to create urban forests. A major unknown, however, is whether planted trees will grow into the mature, closed-canopied forest on which ecosystem service provision depends. We assessed the influence of biotic and abiotic land management on planted tree performance as part of urban forest restoration in New York City, U.S.A. Biotic treatments were designed to improve tree growth, with the expectation that higher tree species composition (six vs. two) and greater stand complexity (with shrubs vs. without) would facilitate tree performance. Similarly, the abiotic treatment (compost amendment vs. without) was expected to increase tree performance by improving soil conditions. Growth and survival was measured for approximately 1,300 native saplings across three growing seasons. The biotic and abiotic treatments significantly improved tree performance, where shrub presence increased tree height for five of the six tree species, and compost increased basal area and stem volume of all species. Species-specific responses, however, highlighted the difficulty of achieving rapid growth with limited mortality. Pioneer species had the highest growth in stem volume over 3 years (up to 3,500%), but also the highest mortality (up to 40%). Mid-successional species had lower mortality (<16%), but also the slowest growth in volume (approximately 500% in volume). Our results suggest that there will be trade-offs between optimizing tree growth versus survival when implementing urban tree planting initiatives.

green roofs

Everybody kind of likes the idea of green roofs, but water professionals are not always 100% confident we understand them well enough to promise they will meet water quality and flooding regulations. But the studies are gradually trickling in. Here is a new one from Ecological Engineering:

Increasing recognition is being given to the adoption of green roofs in urban areas to enhance the local ecosystem. Green roofs may bring several benefits to urban areas including flood mitigation. However, empirical evidence from full-scale roofs, especially those that have been operational for more than several years is limited. This study investigates the hydrologic performance of a full-scale extensive green roof in Leeds, UK. Monitoring of the green roof took place over a 20 month period (between 30th June 2012 and 9th February 2014). The results indicate that the green roof can effectively retain and detain rainfall from the precipitation events included in the analysis. Retention was found to correspond significantly with rainfall depth, duration, intensity and prior dry weather period. Significant differences in retention values between the summer and winter seasons were also noted. Regression analysis failed to provide an accurate model to predict green roof retention as demonstrated by a validation exercise. Further monitoring of the green roof may reveal stronger relationships between rainfall characteristics and green roof retention.

Beyond questions on performance, there is a kind of chicken and egg problem where they are not used much (in the U.S., at least) because they are expensive and they are expensive because they are not used much. That is true of many emerging technologies. Of course, this “emerging” technology has been used in Europe for centuries, not to mention it is also popular with hobbits.

March 2015 in Review

Better late than never – here’s my month in review post.

Negative stories:

  • The drought in California and the U.S. Southwest is the worst ever, including one that wiped out an earlier civilization in the same spot. At least it is being taken seriously and some policies are being put in place. Meanwhile Sao Paulo, Brazil is emerging as a cautionary tale of what happens when the political and professional leadership in a major urban area fail to take drought seriously. Some people are predicting that water shortages could spark serious social unrest in developing countries.
  • More evidence is emerging that published science skeptical of the mainstream climate consensus may have been influenced by fossil fuel industry propaganda, reminiscent of tobacco industry propaganda of the past. (By the way, tobacco industry propaganda is not a thing of the past – the industry is still up to its old tricks in developing countries that don’t stop it.)
  • El Nino has returned. Some are suggesting this is one mechanism whereby heat that has been absorbed by the ocean in recent decades could be re-released to the atmosphere. I don’t know enough to say whether this is a mainstream opinion or not.
  • Homework appears to be useless.
  • A Wall Street Journal op-ed predicts the imminent collapse of the Chinese government.
  • Farm animals, particularly pigs, are being given huge doses of antibiotics in developing countries. Beyond the risk of antibiotic resistance, it is a sign of the increasing intensification and industrialization of agriculture that is necessary as demand continues to rise.

Positive stories:

  • The concept of critical natural capital bridges the gap between strong and weak sustainability.
  • If we want to design ecosystems or just do some wildlife-friendly gardening, there is plenty of information on plants, butterflies, and pollinators out there. There is also an emerging literature on spatial habitat fragmentation and how it can be purposely designed and controlled for maximum benefit.
  • Innovation in synthetic drugs is quickly outpacing the ability of regulatory agencies to adapt. (I struggled whether to put this in the negative or positive column. Drugs certainly cause suffering and social problems. But that is true of legal tobacco and alcohol, and prescription drugs, as well as illegal drugs. The policy frameworks countries have used to deal with illegal drugs in the past half century or so, most conspicuously the U.S. “war” on drugs, have led to more harm than good, and it is a good thing that governments are starting to acknowledge this and consider new policies for the changing times.)
  • Deutsche Bank has joined the chorus predicting the coming dominance of solar power over fossil fuels.
  • There are more Uber cars than traditional taxis operating in New York City.
  • Global maternal mortality is down 40% since 1995.
  • “Germ-line engineering is much further along than anyone imagined.” This means basically editing the DNA of egg and sperm cells at will. I put this in the positive column because it can mean huge health advances. Obviously there are risks and ethical concerns too.
  • Somebody has invented an automated indoor compost bin that finicky urbanites might actually consider using.

urban tree canopy targets

This open article in PLOS ONE mentions tree canopy targets in several cities.

Increasing UTC [urban tree canopy] has become a widespread goal, often incorporated into municipal sustainability plans. It has been proposed as a way to mitigate impacts from human-dominated systems on the immediate (e.g. shade and cooling) and global (e.g. carbon capture) environment. Sacramento Tree Foundation has pledged to plant five million trees by the year 2025, an effort that would double the region’s tree canopy cover. Philadelphia has established a goal of increasing tree canopy cover to 30% by the year 2025 (www.phila.gov/green/trees). New York City, Baltimore, and Los Angeles have also announced extensive tree planting initiatives (www.milliontreesnyc.org, www.baltimorecity.gov, www.milliontreesla.org). In addition to regional efforts, there are national and global efforts to bring more awareness to the benefits of UTC cover (Urban Environmental Accord 2005, www.sfenvironment.org/downloads/library/​accords.pdf; http://www.plant-for-the-planet-billiont​reecampaign.org/Partners/VariousPartners​/TreePlanting.aspx). One of the implications of embedding tree canopy goals in sustainability plans is that environmental justice is frequently included as an objective of the plans, and sometimes explicitly linked to UTC. For example, Philadelphia’s 2009 GreenWorks Plan includes goals of increasing tree canopy cover in all neighborhoods highlighting the desire for the equitable distribution of UTC cover (www.phila.gov/green/greenworks/2009-gree​nworks-report.html).

Incidentally, I lived on a beautiful tree-lined block in Philadelphia until a year ago, when the city cut them all down to replace a major sewer line. I suppose it couldn’t be helped, and they are promising to replant.

Here are a bunch of other articles I’ve stumbled across lately on urban tree benefits:

The last is slightly negative. There are people who don’t like trees. Most of their beliefs are erroneous, but some are based on nuggets of fact. Some species of trees will invade sewer lines, particularly if they are starved of water and nutrients because they are under sealed pavement. And trees do kill a small, but nonzero, number of people each year. I believe the tree haters are a tiny but highly vocal minority. It’s not worth spending any effort trying to reason with them. The best thing to do is put a tree everywhere but in front of their house. Maybe they will see how nice it is and eventually come around. If they don’t, well, you still have more trees than you had before.

February 2015 in Review

This blog got 173 hits in February! Pretty cool, considering I really just meant it as a place to collect my own scattered thoughts and refer back to them later. If 173 out of the 6 billion people out there like it, I am flattered. Okay, I understand there may have been a few repeat visitors. Also, judging from the most popular posts, there is one thing I mention occasionally that people really like: robots!

Negative trends and predictions:

  • Fresh Air had an interview with Elizabeth Kolbert, author of The Sixth Extinction. The idea here is that what humans are doing to other species is equivalent in scope to events that have killed off most life on Earth in the past.
  • The drought in the western U.S. continues to grind on.
  • There are some depressing new books out there about all the bad things that could happen to the world, from nuclear terrorism to pandemics. Also a “financial black hole”, a “major breakdown of the Internet”, “the underpopulation bomb”, the “death of death”, and more!
  • Government fragmentation explains at least part of suburban sprawl and urban decline in U.S. states, with Pennsylvania among the worst.

Positive trends and predictions:

  • Libraries are starting to go high-tech using warehouse robot technology.
  • I had a rambling post on technologies to watch: carbon fiber, the internet of things, self-driving cars and trucks, biotechnology for everything from carbon sequestration to cancer treatment to agriculture, and of course more automation, robots, and artificial intelligence. And yes, Clark W. Griswold’s cereal varnish is a real thing!
  • U.S. utility solar capacity is slowly ramping up.
  • A new study suggests a sudden, catastrophic climate tipping point may not be too likely.
  • Robots can independently develop new drugs.
  • According to Google, self-driving taxis are only 2-5 years away.
  • Complex ecosystems can be designed.
  • Compost toilets may save the world…if we can get over the ick factor and the sawdust problem.
  • There are lots of cheap new options for the aspiring high-tech handymen (and women and children) among us. Even better news, we may have reached the point where if you build a robot with your kid in the basement, and he then tells other kids about it, he might not get beat up on the playground.
  • New York City has some good examples of green stormwater infrastructure integrated in sidewalk and street design.

One thing that strikes me is that we keep hearing about biotechnology, but we haven’t seen big, obvious impacts in most of our daily lives yet. I suspect biotechnology is like computers and robots in the 70s, 80s, and 90s – slow but steady progress was being made in the background, the pressure was building, and then the wave suddenly broke onto the commercial and public consciousness. I suspect biotechnology is the next big wave that is going to break.

birds, bees, bugs, plants

On the green infrastructure front, there are lots of resources out there on what plants support what kinds of wildlife.

“Bugs” have a PR problem as a group, but they have their charismatic members – bees, butterflies, and dragonflies to name a few. If you support these, you will probably support others by accident. There is plenty of information out there, for example:

The Xerces Society for Invertebrate Conservation has a ton of free publications on plants, pollinators, and design; including bee-friendly plant lists for all regions of the United States and several other countries.

The Lady Bird Johnson Wildflower Center has a ton of free native plant information, including recommended mixes to attract various types of wildlife in all U.S. states and Canadian provinces.

Finally, the Natural Resources Conservation Service (part of the U.S. Department of Agriculture) has free fact sheets on about a thousand plants.

A lot of good can be done for wildlife and humanity on small scraps of land, and even more good could be done if we gave serious thought to how all those scraps of land fit together and connect to larger parks and preserves. So let’s get out and plant something this spring, even if it’s small. Or if you have a scrap of land but you don’t feel like planting anything, find a frustrated armchair gardener who doesn’t have their own scrap and let them plant something on yours.

designing ecosystem complexity

This article in Ecological Engineering is about measuring and purposely designing complexity into ecosystems to support biodiversity. I like this idea – certainly grass and trees are a step up from concrete in cities, but there might be some relatively simple design choices that could improve conditions for both wildlife and people without adding effort or cost. We actually expend enormous amounts of time, effort, and money maintaining our grass and trees, whereas natural ecosystems manage to maintain themselves while being more beautiful, diverse, and productive. The first step is to understand the systems better, the second would be to understand what variables we can manipulate, then the third and most difficult step is always translating that new understanding to actions on the ground and getting people to actually take them.

Simplification of natural habitats has become a major conservation challenge and there is a growing consensus that incorporating and enhancing habitat complexity is likely to be critical for future restoration efforts. Habitat complexity is often ascribed an important role in controlling species diversity, however, despite numerous empirical studies the exact mechanism(s) driving this association remains unclear. The lack of progress in untangling the relationship between complexity and diversity is partly attributable to the considerable ambiguity in the use of the term ‘complexity’. Here, we offer a new framework for conceptualizing ecological complexity, an essential prerequisite for the development of analytical methods for creating and comparing habitat complexity. Our framework distinguishes between two fundamental forms of complexity: information-based complexity and systems-based complexity. Most complexity–diversity studies are concerned with informational complexity which can be measured in the field through a variety of metrics (e.g. fractal dimensions, rugosity, etc.), but these metrics cannot be used to re-construct three-dimensional complex habitats. Drawing on our operational definition of informational complexity, it is possible to design habitats with different degrees of physical complexity. We argue that the ability to determine or modify the variables of complexity precisely has the potential to open up new lines of research in diversity theory and contribute to restoration and reconciliation by enabling environmental managers to rebuild complexity in anthropogenically-simplified habitats.