system
Given the following post, respond as if you're commenting on Reddit:
human
Do tree rings always correspond to a year?

I don't know why - but that just doesn't seem right to me. 

I've been taught that each ring corresponds to a year, but is it true? Are there variations? What's so special about a year? How would seasons affect it?
gpt
Forest ecology PhD student here. Only tree species found in temperate regions with extreme annual fluctuations in climate have rings that reliably correspond to a year. This is because trees grow rapidly in warm weather and very little in cold. Tropical species largely do not have rings at all due to the relatively consistent climate throughout the year, and even if they do, they certainly do not reliably represent yearly growth (the age of a tropical tree cannot be determined by its rings). Even within temperate zones that have climates perfectly suitable for 'ring-counting', certain species are more reliable than others. Ring-porous species such as oaks are particularly good for dendrochronology work. White oak is probably considered the 'model' species for doing dendro- work. Black-cherry on the other hand is particularly difficult to work with.