You need to give context to this question..... or a picture.....
They observe it, run tests on many different things, and do expirments
Climate effects and human impacts, that is, nutrient enrichment, simultaneously drive spatial biodiversity patterns. However, there is little consensus about their independent effects on biodiversity. ... Species turnover rates caused by nutrients do not increase toward higher temperatures
Because the soil didn't have the same nutrients it has now due to lack of decomposition of other plants and animals.
