Observing Trees
I see a fair number of tree observations that are a single image, sometimes little more than a tree in silhouette. These are often impossible to identify. From my own experience, which is still on-going, I'll offer these suggestions for making better tree observations.
All of the following can be helpful in identifying a tree. As many of these as possible should go into an observation:
entire tree, or best approximation thereof
detail of leaf/leaflets, including needles for conifers
buds, bud scars, leaf scars
flowers and/or fruit/cones/pods, including any fallen to ground
bark
Don't forget scale. How big is the thing in your photograph?
Obviously, there have some seasonally dependent items here. But that's good; go back to that tree, watch it through the year. Mature trees may hold a lot of these things above eye-level, so scout the ground below.
In New York City, where I live, many of the trees we come across on the street, and in yards, parks, and cemeteries, are planted specimens raised by the horticulture industry. This means that, for iNaturalist purposes, they are captive/cultivated or "casual" observations.
There is an existing street tree map https://tree-map.nycgovparks.org. It isn't error-free; when it first came out I noticed that the two common hackberries I can see from my window were classified as hawthorns. (There's a way to submit corrections.)
So the actual urban tree may not be worth an iNaturalist observation as such -- good luck on the trademarked varieties sold by the industry! -- but because the tree is habitat it's worth noting what kind of tree it is and pairing it with your observations of what's living on the tree. Trees are home to algae, fungi, lichens, mosses, and liverworts. Invertebrates are all over them, from the obvious pollinators to the ants crawling up and down them all day long. And that ticking sound in the fall? A katydid!.
Don't forget the reptiles, birds, mammals....
Look for galls; nests/drays; webs; leaf damage from herbivores and diseases; pupae; ambush predators; eggs laid on leaves; beetle excavations and frass. E.O. Wilson has said you could spend an entire lifetime of exploration around a single large tree.
Lately, I've been observing the types of trees Yellow-bellied Sapsuckers drill into for sap.
