I observed a tree which I thought is a hickory, but it turned out to be a beech, and @tanker-aviator-naturalist showed me pictures of hickories. I went back there today to flag a line and saw a tree that matches the pictures, with pinnately compound leaves. I took a picture and a GPS measurement, then went to the bottom of the trunk and got another measurement (not fixed) and a picture of the trunk. The two points are 15.6 m apart horizontally, with a slope of 1/6, the root end of the trunk being lower. The first picture was only 1.4 or so meters above ground. The tree is bent way over, yet it’s still alive. Should I set the location of the observation to the location of the pinnately compound leaves, which is fixed, or the base of the trunk, which is DGPS or float?
In the same lot was an oak which Helene toppled. (It’s since been sawn and is no longer blocking the street.) The location of this observation is currently a traverse point, with the metal detector in the third picture pointing to the nail. The location of the traverse point is, of course, fixed. On the way back from flagging the line, I measured the position of the hollow left by the uprooted oak. This measurement is not fixed and is 18.4 m nearly east of the traverse point. Should the location be the traverse point, which the oak was lying on when I first saw it, or the place where it stood?
there’s no standard way of determining the coordinates of an observation in iNaturalist. unless you’re doing some sort of survey that requires this sort of precision, and you’re using tools that can reliably provide such precision, i would say that where exactly on the trees you get coordinates doesn’t really matter. if precision does matter to you, then you need to do it according to whatever set of rules you’re using. from a general iNaturalist observation perspective, the coordinates you got are fine, as they’re probably good enough for someone else to find the organism if they wanted to.
I am in fact doing a survey, but none of those trees is a lot corner. The front corners are metal pipes, and I know their positions within 20 mm or so. I surveyed a lot two years ago where several corners are described as trees, two of which (a pine and an oak) were still standing at the time of the survey. (I have pictures but haven’t uploaded them yet.) I recently surveyed a lot where one of the corners is an iron (missing but I set it) next to a “poplar”; that tree is now a research grade tuliptree. If a tree is a lot corner, and it’s leaning or fallen over, then I have to measure the position of its base.
Honestly, no one cares about that level of precision on iNat. Think about this - if someone takes a photo of a bird in the sky from a lookout, how accurate do you think their coordinates are going to be? It’s an approximation and generally people aren’t using iNat to be able to return to the exact square cm of an observation.
For iNat it doesn’t matter as most of the time the precision isn’t tight enough to actually mark individual parts of the tree.
If you’re needing to be exceptionally precise for other reasons though then there are two methods. The first is the center of the trunk, and the other is the center of the canopy.
The center of the trunk is preferred as the canopy method is based on the idea that the center of the copy is usually the center of the tree and therefore the trunk.
I’ve recently been putting together a project of plants that can be used for seed or cutting collections, and for something like that, good accuracy is key as they’re no good as a source if they can’t be found. Although as long as it’s within a few metres, it’s fine, but if it’s a 30-50m area to search, that’s a bit rough.
When I’m putting in observations, I’ve been trying to make sure I either upload in the moment, or take an accurate GPS recording at the same time, as I’ve certainly noticed the EXIF coordinates are a bit rubbish much of the time, so not particularly useful where accuracy is required.
My personal thought is that the base of the trunk would be the best point to record coordinates, as that enables it to be found easily, while if the top were to die off, and then the tree took off from a point closer to the base, the coordinates would take someone to a now defunct location.