These mixed mesophytic forests represent a mingling of northern deciduous forest species and typical southern broad-leaved evergreens, like magnolia. But most of this dry upland southern habitat is covered by an immense belt of pine forest. Coniferous evergreen forest stretches 1,200 miles across the coastal plain, and covers a greater area than all other forest types combined. South of Lake Pontchartrain, a thick layer of delta mud overlies the sandy soils, so south of the lake hardwood trees are the dominant forest species. North of the lake, where soils are very sandy, pines are the dominant forest species.
Angiosperms are generally better competitors than gymnosperms.
When angiosperms first evolved, they quickly replaced gymnosperms as the dominant vegetation over most of the planet. But in areas that are very dry or very cold, gymnosperms are better competitors. Gymnosperms evolved in the Permian, during a relatively cool and dry period, and are very well adapted to cold and arid conditions. Plants draw water up through their roots. Gymnosperms have hollow tubes called tracheids, while Angiosperms have larger hollow tubes called vessels.