Why are deciduous forests poor in species compared to tropical rainforests?

Deciduous forests are species poor compared to tropical rainforests due to fluctuations in climate. Deciduous forests tend to exist in temperate climate belts which shift away from and towards the poles during glacial and interglacial periods, whereas the tropical climate belt tends to shrink closer towards the equator. Therefore the vegetation has undergone greater extremes of climate over millions of years thus species extinction rates are far higher in the temperate belt than in the tropical belt. If we compare number of temperate tree species in North America (NA) and Europe there are far greater NA tree species. This is because the last ice age affected Europe far more than NA. As vegetation is the basis for all food chains, if the vegetation becomes extinct then so do the species than rely on them. One other point is that climate seasonality fluctuations acts as selectional force that species have to endure and this also affects the number of species that live in deciduous forest ... more