Tag Archives: trees

a million trees in New York

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New York City has managed to get a million new trees in the ground. Planting a bunch of trees seems like a no-brainer to many of us who are familiar with the logic and evidence in favor of green infrastructure. But this can still be hard for cities. There is a vocal minority of citizens who hate trees. They’re a minority, but did I mention they’re vocal? Then, trees are not a huge expense in the big picture of all the things cities have to pay for, like police, courts, prisons and pensions for example, but their planting and especially maintenance sometimes falls to city departments who are under-funded in good times and the first to get hit by budget cuts in bad times.

New York seems to have gotten past these challenges with strong planning, strong leadership to actually implement the plan, and partnering with a non-profit entity which could really focus on this one mission.

A collaboration between New York City’s parks department and conservation nonprofit New York Restoration Project (NYRP), the initiative just succeeded in planting 1 million new trees in the city this decade. The final tree was planted last month, two years ahead of schedule. While cities like Los Angeles, Boston and Denver have all set the same goal, New York is the first to meet it.

Beyond 220,000 new street trees, MillionTreesNYC planted in parks, on public and private property, and in all five boroughs, increasing the city’s urban canopy by 20 percent.

While the city planted 70 percent of the trees in parks and on streets, NYRP was tasked with getting the remainder into public and private spaces, including hospitals, libraries, churches, public housing developments and private yards.

I do have to point out that “a million trees planted” almost certainly does not mean a net gain of a million trees. While the program was being implemented, some trees must have died of “natural” causes (air pollution, heat stress, poor soil, lack of water). Some also must have been removed for legitimate reasons in the course of construction and infrastructure projects, and if my personal experience in Philadelphia is any guide, not all of those got replanted (the vocal minority of citizens having something to do with this). But all this is exactly why focusing on tree canopy is exactly the right way to look at it. By setting a tree canopy goal and periodically measuring where you are relative to it, you should know if you are replacing the trees lost to attrition at the right rate to keep your overall canopy from dropping.

emerald ash borer targets human arteries

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The emerald ash borer is supposed to kill trees, not people. But this study found that heart attack risk for women went up 25% when all the trees were killed by this pest. Lessons learned – (1) contact with nature lowers stress in an urban environment, (2) people grieve for lost trees. So cities should plant trees and take care of them. Just not all the same kind of trees, which is a basic principle of resilience. Sure, cities have limited money to spend, but there is a public health case to be made for spending some of it on trees.

growing the urban forest

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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.

urban tree canopy targets

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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.

green infrastructure, happiness, and the ginkgo-stinkgo tree

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Do trees make people happy? Well yes, I think most people subjectively just have a sense this is true. But for the cynics out there, there is also hard scientific evidence. People have tried all sorts of economic approaches – correlations with real estate markets and willingness-to-pay surveys – for example, to try to estimate the value people place on trees. (Can you measure happiness in dollars? The average man on the street might say no, but the average economist might say it’s the best of many imperfect options for measuring value.) Medical researchers have tried having people walk around cities with brain scanners on their heads. This is a new one to me though – correlating tree coverage with antidepressant prescriptions. And the correlation is there.

Growing evidence suggests an association between access to urban greenspace and mental health and wellbeing. Street trees may be an important facet of everyday exposure to nature in urban environments, but there is little evidence regarding their role in influencing population mental health. In this brief report, we raise the issue of street trees in the nature-health nexus, and use secondary data sources to examine the association between the density of street trees (trees/km street) in London boroughs and rates of antidepressant prescribing. After adjustment for potential confounders, and allowing for unmeasured area-effects using Bayesian mixed effects models, we find an inverse association, with a decrease of 1.18 prescriptions per thousand population per unit increase in trees per km of street (95% credible interval 0.00, 2.45). This study suggests that street trees may be a positive urban asset to decrease the risk of negative mental health outcomes.

And in other urban tree news, you can collect ginkgo berries, take out the nuts, roast them and eat them. The only problem being that they stink to high heaven and are mildly poisonous. Ginkgos are very interesting trees though, sort of an ancient cross between trees and ferns if you believe this article.

Believed to be truly indigenous to only a single province in China , this 270 million year old species belongs to an ancient lineage of species that have since disappeared for one reason or another over the past few millennia, making Ginkgo biloba (known as a ‘living fossil’) the sole extant representative of what was once a vast and diverse group of organisms. In fact, the ginkgo tree is so unlike any other living plant species that this tree has it’s own genus, family, order, class and division. To put this into terms that may be easier to conceptualize: the only thing that ginkgo trees have in common with other plants is they are also plants. This means that pretty much everything about their genetic make-up, physiology, general behavior, reproductive strategies (including their mobile sperm; a trait particular to ferns, cycads and algae) and even their ability to photosynthesize is anywhere between slightly-off to fundamentally different from any other living plant. Oh, and you can eat it’s seeds…

It’s a bit of a messy operation collecting the seeds which are often produced profusely by female trees and lie unmolested by fungi, insects or most pests of any kind save for some adventurous squirrels which occasionally eat the seeds. I find some rubber or latex gloves and a plastic bag are your best bet for collecting the seeds in addition to some grubby clothes that you don’t mind smelling cheesy for a little while. The scent from the fruit tends to linger when it gets on fabric or clothing and so you might want to try extra hard to remember not to wear anything that you are particularly fond of when engaging in the participatory act of ginkgo seed collecting.

I think it’s cool that some people do this, but I personally am not going to take up this hobby right now.

trees!

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Here’s a long document from the “Trees and Design Action Group” in the UK about everything to do with planting trees in the city. Of particular use to me are some good references on dealing with underground utilities, species selection, and just lots and lots of great pictures. Even some nice stats on the odds of being killed by a tree compared to car accidents and cancer (the odds are very low, but not zero).  Trees really can be done a lot better than most American cities do them.