Polar forests of the Cretaceous

[2] As a response to elevated global temperatures, the Earth's hydrologic cycle was significantly enhanced due to greater volume of moisture evaporation from the surface of the ocean.

An increase in surface area between shallow, warm epeiric seawater and the atmosphere permits higher evaporation rates and more precipitation at various latitudes, producing a more temperate global climate.

The dominant forms of vegetation at these high latitudes during the previous 100 million years were rapidly evolving and ultimately being replaced during a time known as the Cretaceous Terrestrial Revolution.

During the Cretaceous Terrestrial Revolution, conifers, cycads and ferns were selectively replaced by angiosperms and gymnosperms, becoming the main species dominating the high paleolatitudes.

In this Cretaceous greenhouse world, Arctic conifer forests were considered predominantly deciduous, while those that grew on Antarctica contained a significantly greater proportion of evergreens.

[5] In the early Cretaceous, approximately 130 million years ago, there was a major diversification of angiosperms that set in motion a large evolutionary change in high paleolatitude forest composition.

[6] This transition from conifers, cycads and ferns to predominantly angiosperms reflects an interesting evolutionary adaptation to the regional polar climate and quite possibly numerous other factors like sea-floor spreading rates, eustatic sea level and high global temperatures.

According to experimental results, tree species with long lived evergreen foliage tend to benefit the greatest in a carbon dioxide rich environment because of their longer growing season and adaptations like canopy development that allow them to thrive in the temperate polar paleolatitudes of the Cretaceous.

The most abundant and globally widespread plant taxa were the araucarioid and podocarpoid conifers, extending approximately 80° into both hemispheres and composing more than 90% of the canopy generating evergreen vegetation.

As global climate evolved, the rise of angiosperms began to put pressure on conifers at higher latitudes by growing taller and ultimately winning the battle for sunlight.

Studies on the mid-Cretaceous paleorecord conclude that forest compositions in Northern hemisphere high paleolatitudes were mainly populated by mixed evergreen and deciduous tree types.

[2] Dendrochronology of fossilized wood growth rings from high paleolatitudes suggests the presence of greenhouse-like climatic conditions on a global scale during this time period.