Pecan trees dont leaf out until they are certain all chance of a freeze are over for the year.
Other signs could be migrating bird returning or leaving, nesting. Whatever blooming, appearance of insects appearing, animals mating or having young. Changing Nature data can come from observations on iNaturalist. Baselines from current agriculture planting calendars cross referenced with "normal" timing of nature events. According to geographical regions/coordinates.
Pecan trees dont leaf out until they are certain all chance of a freeze are over for the year. Other signs could be migrating bird returning or leaving, nesting. Whatever blooming, appearance of insects appearing, animals mating or having young. Changing Nature data can come from observations on iNaturalist. Baselines from current agriculture planting calendars cross referenced with "normal" timing of nature events. According to geographical regions/coordinates.