They’re both worth owning, and now there’s been a 2nd printing of The Fundamentals, so you can have a hard copy for 35$ I think. The CA study guide is around 100$ I think.
The Fundamentals is good stuff for most tree service workers, climbers, loggers, and folks that usually make their money with a chainsaw. There’s sharpening instructions and tips, learn how to make a chain without a breaker and spinner, and other saw maintenance stuff. Gets much more in depth about different cuts and hinges. Felling, bucking, limbing. The climbing stuff in it is from before single/ stationary rope technique work positioning was a thing, but there’s some single rope access and a good amount of doubled rope/ moving rope work positioning. With how rapidly climbing tools and techniques have evolved over the past 15 or 20 years, the climbing info in The Fundamentals might seem dated, but it’s still worth knowing. Lots of rigging info with pics and clear descriptions.
The ISA CA study guide is a good reference. This book has info about plant health care, diseases, risk assessment, soil and watering, selecting a tree for planting, pruning techniques, I’m sure I’m forgetting a lot. The illustrations from Brian Kotwica are great and there’s lots of them.
I do suggest both books and a few others. If I must pick one, it’d be The Fundamentals. Jerry is a great writer and has a great passion and talent for photography too. A legendary old school tree worker who’s still very open to the new school. If he hadn’t retired, I’d bet he’d be zipping around on a Rope Wrench, Rope-Walker system, and a modern saddle. Kind of a down to earth writing style, humble but very knowledgeable and capable. The photos speak volumes to his skill in working with massive conifers out in the woods. After you finish the book, you’ll almost feel like you know the man.