How to save urban trees from extreme heat

September 29, 2023 10:28 PM

We need urban trees more than ever: here's how to save them from extreme heat
posted by chariot pulled by cassowaries (10 comments total)

Water?
posted by sammyo at 1:43 AM on September 30, 2023 [1 favorite]

Ultimately, yes. There is discussion of approaches, like rain gardens, and also monitoring, but it comes down to — do the trees have enough water?
posted by GenjiandProust at 3:00 AM on September 30, 2023 [1 favorite]

Tree bags, or other labor saving watering techniques, are likely nownecessities when they were once envisioned as labor saving conveniences
posted by eustatic at 6:28 AM on September 30, 2023 [2 favorites]

Also, at least on the states, we need to get rid of imperial English lawns, and grow more scrub trees.

I don't know how it is in Australia, but in the states, lawns are the petroleum guzzling microclimate that make everything so hot and dry in the first place.

I've been a big advocate for willows in my area. Landscapers see them as 'unmanageable", but they can be easily trimmed, and grow to kill the lawn. It s a matter of aesthetics and training landscapers to the existing design principles. There are a couple of worker certification programs that already train on these principles, not everyone needs to be a full blown arborist

( although wouldn't that be the ideal world, where landscapers are paid enough to achieve peak professional training on the regular?)

They can grow to shade height in 6 months. Absolutely life saving In the summer.

Elderberries are similar. I ve seen abandoned lots that were habitable parks in 10 months because the elderberries grew to shade out the more aggressive grasses and vines. They give fruit for birds. Some Choctaw people think they are sacred, but land managers just see them as "trash trees" because they are not in the plan, and very hard on their lawnmowers.

Even city residents intuitively grow invasive Tallow near me.

Kind of terrible for the ecosystem, since the trees poison other plants from growing and few animals, or none, eat the seeds.

But I can't blame residents, really, the things grow to shade height in months, so even renters can grow shade trees during short term occupation of a rental. They make the lawns tolerable.

So the problem is the lawns, not the invasive trees.

So many tree decisions are made on weird colonial aesthetics that need to be thrown out if we want to survive and grow shade.
posted by eustatic at 6:50 AM on September 30, 2023 [11 favorites]

Take a look at these trees from the article. They're in an island a few feet wide in the middle of the street.

Here is a picture of a tree's critical root zone. From that link, here is the formula: Tree diameter in inches X 2, then convert to feet = CRZ diameter. Say the diameter of those trees is a mere 4 inches (these are trees that can grow up to 3m/10ft in diameter, but some people are willing to limit full-size trees to tiny pots). Their critical root zone is 8 feet in diameter. Eight feet!

Street trees are planted for their ability to tolerate intolerable conditions, but when I look at street trees trapped between impermeable surfaces, I just feel so bad for them. Streets take up a huge amount of urban space. Trees need that space. We need more urban trees, but planting trees in a space that is too small for them is in my opinion cruel.

Anyway, so there's more than one major issue here. There's climate change, that would be the extreme heat discussed in the article. And then there's the infrastructure that is designed to support motor vehicles (which are contributing to climate change).

The standard infrastructure advice would probably be "stop using asphalt, it's time for more permeable pavement for streets and car parks/parking lots". But in my opinion, it's also time to let more trees take back the streets (in a planned degrowth sort of way so that people can still get around walking and wheeling and whatnot).
posted by aniola at 8:11 AM on September 30, 2023 [8 favorites]

eustatic: Now I kinda wish we'd looked into getting a new willow for the front yard last year instead of a maple. Doesn't help that there's a weeping cherry on our corner that looks absolutely gorgeous for a couple of weeks every Spring.

We're going to pick up some plants soon for the the shaded areas in the backyard. That was the same patch we let grow wild for much of the summer. Ideally, I would eventually replace our entire lawn with non-grass plants... unless they're tall grasses (we already have a few of those).
posted by May Kasahara at 10:08 AM on September 30, 2023 [1 favorite]

An important topic! One key thing the article doesn't mention is a lot of invasive weeds (i.e. vines) can kill trees. In a lot of cities/states you can become a certified Weed Warrior, which gives you legal authority to lead crews of people removing invasive from city/state parks. It's a great way to help if you're interested.
posted by coffeecat at 12:15 PM on September 30, 2023 [1 favorite]

trees can help save themselves from extreme heat (if we stop with the gratuitous destruction for timber, monocrops, animals for meat/dairy, mining, roads, etc). related:
https://news.ycombinator.com/item?id=37715499
posted by aniola at 5:57 PM on September 30, 2023

Here in Vancouver BC, we have tree bags.
posted by porpoise at 11:36 PM on September 30, 2023 [1 favorite]

Thanks for posting chariot! This is where Sustainable Drainage SuDS comes to the fore - basically redirecting surface flow to tree either to use the tree to pump stormwater water to the sky - or to irrigate the tree - see a lot of this in Melbourne .au, and Los Angeles. Best if water supply is passive / from the tree's locale rather than relying on indifferent contractors and water supply not failing .... A lot of this kind of thinking around Elysian Valley Los Angeles, [google link], well worth a day wandering through here.

Getting the species right; like there are summer-deciduous trees in many regions of the planet, high-and-low water-requiring forms and cultivars of many species.

Siting trees so they get a little shade during the day, and so they're away from / protected from hot vents, hot infrastructure points. And yes, siting them in low points, dishes, swales...

Investing in arborists to maintain trees with a minimal branch state ie enough structure to ensure the tree provides shade, and can grow, but not so much 'motor' that it gets too thirsty.

There's a park in West Sydney - can't find link - where they take all the dry weather runoff from the surrounding district, run it through their parks and grounds, and return what clean water is left back to the city - much as Santa Monica's SMURFF does in a far more compactly [image from my visit there], with plants, bacteria and machines, anout 900,000 litres a day - really, really worth visiting SMURFF if you're into urban landscapes, planning, geography...
posted by unearthed at 12:40 AM on October 1, 2023 [2 favorites]