Changing tree composition by life history strategy in a grassland‐forest landscape

Abstract

After rapid deforestation in the eastern United States, which generally occurred during the period of 1850–1920, forests did not return to historical composition and structure. We examined forest compositional change and then considered how historical land use and current land use may influence forests in a grassland‐forest landscape, the Missouri Plains, where frequent surface fire was the historical land use and intensive agricultural is the current land use. We compared composition, distribution, and environmental relationships during historical (1813–1860) and current (2004–2008) forest surveys. We also examined changing composition of life history strategies of (1) stress tolerators based on fire tolerance, (2) colonizers based on shade intolerance, and (3) competitors based on shade tolerance. Open forest ecosystems of fire‐tolerant oaks have been replaced by forests of fire‐sensitive species, such as ashes, hackberry, and maples that expanded from riparian firebreaks and osage‐orange and eastern redcedar that expanded from planted windbreaks and rocky firebreaks. Colonizing species increased from 7% to 32% of total composition, with assisted tree migration from planting; we expect continued expansion particularly by eastern redcedar into areas unoccupied by trees. Competitive species have increased slightly to 38% of total composition although the trajectory of current forests suggested competitors may increase to 56% of total composition by replacing oaks in forest ecosystems. Changed success of life history strategies in an agricultural landscape without fire resulted in increased composition and extent of fire‐sensitive colonizers compared to fire‐tolerant oaks. We suggest that patterns of loss of fire‐tolerant oaks and increased distribution of fire‐sensitive species reflect suppression of fire, the historical land use. In addition, we suggest that subsequent land use dictates the success of either shade‐intolerant colonizers or shade‐tolerant competitors in current forests. Forests will be composed of shade‐intolerant colonizers where land use disturbance is frequent, such as in agricultural landscapes, and forests will be composed of species with greater shade tolerance where land use disturbance is less frequent.