How it is studied
Field observations record when a plant reaches a defined stage, such as the start of flowering. An atmospheric series records pollen transported to the sampler. These sources are related, but their spatial scale and timing can differ.
An example to interpret it
Example: a local plant has not flowered, yet the sampler detects its pollen group. Before rejecting the count, consider transport from another area and check whether identification is precise enough to assign it to that species.
What to check
Temperature can shift dates, but chilling requirements, water and species characteristics also matter. A date observed at one location does not apply to an entire region.