If you are starting to learn about wild plants and the seasonal cycles a calender is useful.
After you have a bit of time in you quit going by calendar dates as much and start going with the seasonal signs instead. This happens because the seasons are different depending on where you are and they are not the same from one year to the next either. Spring may be early or late according to the calendar but you still go morel hunting when the basswoods are just starting to leaf out.

Making the calendar will also help you get the idea of what grows when into your mind,so that helps too.
It also helps you to plan your outings.

Edited to add: By what grows when I was thinking about nut and berry crops as well as mushrooms. You might not nail them to a day or even a certain week but you can get close enough that you know what you will look for during the Easter holidays or around Thanksgiving for example. Some of your crops have fairly long periods to gather them in as well. You might be looking at a month or two for picking some of the berry crops instead of a week or two for most of the commercial ones.


For animals you are a bit stuck with legal hunting seasons. These are directly calendar events.

If you hunted according to the animal's cycles you would likely end up out of season half of the time and be getting arrested.

I think it still helps to understand when the animals make their shifts in activities though. An early fall can start the deer moving to their yarding areas up to a month ahead of the normal time for that. A late fall may delay that move for a month.
It is the same for the shift from forage to browse feeding or for the rutting season for the deer.

With other animals you see the same sort of shifts to match the real season instead of just the calendar season. Early cold with a good crop year might force early hibernation, late crops might force animals to still be fattening up for hibernation late into the season.