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. The larger diameter angiosperm vessels are not especially well adapted to dry conditions. Water movement up from the roots to the leaves relies on an unbroken column of water, pulled up in part by capillary action. If that tube of water is broken, a process called cavitation, then it is very difficult for angiosperms to form a new unbroken column of water. Gymnosperms, on the other hand, do not cavitate as easily as angiosperms, and reform the rising water column more quickly when it does break.