For tracking the urban trees that my program plants and manages,
usually I use GPS coordinates for each tree.
We seem to get decent maps showing all the trees so GPS should be enough, right?
You know, not necessarily. There are several location methods for
you know, your city trees and they each have pros and cons.
Some location methods also work better in certain kinds of sites.
But before we get into the specifics, let's take a few steps back.
Why is your location even important in the first place?
Um, to map the trees right?
So yeah that's part of it.
The other really important reason to carefully record a tree's location
is to be able to reliably find that tree again in the future,
to monitor for tree mortality, for changes in growth and health over time,
we need to track every individual tree. That means ensuring that future field
crews can find that right tree. Oh yeah, that's happened to me a few
times, like when I'm trying to check on several trees in front of a large
property, it's not always clear which tree is which in the records.
Exactly. So let's begin with a location
method that's pretty common in city inventories:
the address and site code method.
In this method for
every address or property parcel, trees get coded with
something like 1F to mean the first tree in front of the house.
2F to mean the second tree in front of the house.
Those two trees are for a specific address.
The number sequence begins again at the next house and the different
letters indicate which side of the property the tree is on.
So, F for the front, S for the side, R for the rear etc, etc.
Yeah I've used that method for street trees but when I go back to the trees a
few years later, the sequence gets all messed up by old
trees removed and new trees added. Yeah, that can definitely happen which is
why this location method works well enough in the short term,
but over the long term it tends to fall apart in these
changing urban landscapes. You know, another way to record location,
is the block edge distance method. The what?
Yeah, that's a location method that's well suited to gridded urban street systems.
The idea is that you measure the
distance from the sidewalk corner to each tree.
I'll give you an example. Here you have a tree at 30 feet from the curb corner
and another tree at 80 feet from the curb corner.
That sounds like it would take a long time to set up.
Oh yeah, it can take a while to set up. But the advantage is
that it's super simple to add a new tree later.
For example, on this map you could add in a new tree 60 feet from the corner.
This is unlike the address and site code method where trees getting added and
removed messes up that numerical sequencing.
Ah OK, I can see that now. So, what about those GPS coordinates?
I still like that method. You know, taking GPS coordinates can work.
But it really depends on the equipment you're using.
If you're using a tablet and marking tree locations by dropping pins on where
you see the tree's canopy on a satellite imagery,
that can work really well. It's especially well suited to street or lawn
situations where the trees aren't too dense, and you can see distinct
crowns overhead. But when the trees are dense and the
crowns overlap, it can be hard to know where to mark
each tree on the map. Sometimes when urban foresters talk
about having GPS coordinates for their trees, they might also mean
that they have addresses geocoded. That typically happens
when a tree location gets marked as the center of the parcel which is not accurate.
Sometimes field crews can also record
GPS while collecting data, but the accuracy of that will really
depend on the device. Only high-end GPS receivers have
accuracy down to a few inches. Okay, so GPS can work as a location method,
but not all ways of recording GPS
coordinates are super accurate. Yep. Now there's two more location
methods that I want to go over.
The first is affixing a tag to a tree.
This is pretty standard in rural forestry plots
used in long-term monitoring, and although urban foresters don't use it a
lot, it's a great way to keep track of your trees.
For small trees the tag should be tied around a branch.
For large trees the tags should be nailed into a trunk.
And the last location method is taking a photo of the tree.
A photo, really? How is that a location method?
Well in cities, trees along sidewalks or in lawns and in landscape parks
are usually near buildings or other built structures.
So when you take a photo of a tree, there's a building in the background that
becomes a record that future field crews can use to make
sure that they are standing in the right place.
But having reviewed all these location methods, the most important point is actually this:
Don't rely on just one. Use at least two
complementary location methods for every tree.
None of these methods are fail-safe, and using more than one method can help
ensure the future field crews can find the right tree.
Take some time to decide which of the methods is best for your project,
given the site you're working in, your field equipment, and the inventory
software systems you're already using. I see, so a little redundancy helps huh?
Um-hm. Location is the most crucial piece of information for urban tree monitoring.
If you can't find the tree, you can't record information about how it's
changing over time.
For more information on topics covered in this video
See Urban Tree monitoring field guide and resource guide
thanks for watching