Can anyone tell me how botonisits determine whether flora or fawna is native to a given place?

What means do they use to determine if plants grew in a certain area thousands of years ago? I know that many settlers brought to Australia roses, geraniums, and lots of trees from their native countrires, because they were homesick and wanted a slice of home. But how do we know some of the flora and fawna didn't exist here prior to the introduction from people immigrating?
Can anyone tell me how botonisits determine whether flora or fawna is native to a given place?
There are a number of ways. Firstly there are first hand accounts, record of plant species shipped in and descriptions of existing native plants. Then you can look at the plants morphology, most exotics brought into Australia are not adapted to our climate. Then you can look at the plants adaptations, eg an Australian acacia species is different to one found in Africa, many Australian species have evolved in isolation and are endemic to the country. Lastly native species have a niche, they don't grow out of control or need special attention or artificial conditions to thrive.



It's a good question though. There are species that no one is sure about and some which become naturalised in an area to the point that they effectively become a native.

I'm sorry I can't remember the example I was thinking of. There is a species of Hibiscus in Australia which may or may not have been introduced.
Reply:they check the bbb hives to see what the honey be been feeding on .check bird droppings also why ????????then see where bees and birds are from
Reply:For plants that would grow thousands of years ago, they would use an auger to take soil samples from deep within the soil (or from wetlands) and use that to identify the plants that were around.



For the past few hundred years, they rely on journals and collections from early botanists and naturalists.