Like the rest of my tribe I use tree-like abstractions while computering: binary trees, balanced trees, red-black trees, etc. We call these data structures "trees" because they have roots, branches, and leaves. They are useful for parsing language, organizing things to be searched, and failing job interviews. I don't want to talk about that kind of tree.
After I moved to California I became a hiker, camper, and backpacker. There's a lot of outside here, and much of it is among the best outside anywhere. I go outside to see cool sights and feel good feelings, but some quirk of mind compels me to turn everything into a science fair project. When I was younger this manifested as bird-watching. Then, throughout my 20s I turned most of my outdoor excursions into bird-seeking trips. I saw Trogon elegans in the Chiricahua mountains, the nene in Volcanoes National Park. Birding is fun when you're younger if you can overcome the shame of doing something so nerdy. It's like collecting Pokemon, and you get to buy cool shit like binoculars and spotting scopes and field guides (clearly I do not experience nerd shame).
After my kids grew up I began to spend more and more time in the mountains of California. While I have a preternatural ability to sit still and do nothing for hours, the systematizer in me wanted a project to justify my wandering. Though I still liked birding, I'd lost my enthusiasm for carrying around optics and keeping a life-list. Then I got inspired after a friend gifted me a copy of Allan Schoenherr's great A Natural History of California.
I would learn trees. All of them.
So I started a personal project to observe every native tree species in California in their proper habitat (ie, no nurseries or botanical gardens). California has a lot of native tree species, somewhere between 225 and 300 depending on what people consider to be a tree and how seriously you take certain subspecies. We have the tallest (Coastal Redwood), biggest (Sequoia), and oldest (Bristlecone) trees in the world. The celebrity trees are not hard to find, since we build National Parks around them, but we also have 20-ish oak species, 20-30 willow species, maybe 15 pine species. Did you know that poison oak can reach tree size? As with birds, the interesting trees are the ones that require a bit of exploration and study. For example, there is the Cuyamaca Cypress, localized around King Creek in eastern San Diego county. They were already rare when a significant fraction of them were burned in the 2003 wildfires. To find them now you have to do some research, travel to a place that's not in a trail guide (or on a trail), maybe get a bit wet.
Trees also have advantages over birds. They are less mobile, usually much larger than birds, they go through different stages which makes them interesting to revisit. I no longer think of trees as being stationary or inanimate, but they don't require any special equipment to observe. Trees also have the arboreal equivalent of personality, both at the species level and the individual. I love how the live oak splits and twists and tapers from a single massive base into a vast green space-filling fractal. I love how the bark of the Jeffrey pine smells like butterscotch. One of my favorite individual trees (yes, I have favorites) is a huge Incense Cedar on the western slope of Mt. San Jacinto, who is a total drama queen. There's an Engelmann Oak in Noble Canyon whose trunk wrapped around a big chunk of granite as it grew. I swear it's an Ent.
I'm about half way through my tree list now, but the easy finds are mostly gone. The remaining species require distant travel, mildly extralegal incursions into non-public land, hikes that are off-trail or through streambeds, and maybe the assistance of a botanist who can explain why two willow trees that look identical are, in fact, not the same species. That's cool. Finishing the list is not my primary goal, but rather figuring out the best ways to seek them. Plus, I like the learning process. Trees have lore, they have history, they are embedded in the traditions of many cultures, people write (good and bad) poems about them. You can view them as living organisms, massive hydrodynamic systems, records of history, physical structures, ecosystems.
I'm not a biologist and I have no illusions that I'm contributing to the knowledge of any related field. For me the Tree Project is a way to filter down all the possibilities of the universe into a manageable list of things that I can do and want to do. I've never liked it when people say "it's about the journey not the destination" (I assume these people have never flown coach), but tree-seeking is at least half about the journey. One day in late spring a few years ago, I found myself 11,000 feet up in the White Mountains sitting in the Patriarch Grove among 4000 year old trees, looking out at the eastern Sierra. It was still and clear and as quiet as our world gets. That was a good day. Pretty good journey, pretty good destination.
Some resources for anyone who wants to become a fellow tree-seeker:
Also iNaturalist, Open Street Maps, overpass turbo, and various plant-identifying apps (PictureThis, PlantNet).