No-analogue vegetation and climate are linked in future projections. From a planning and management standpoint we are concerned about the ecological consequences of novelty during 21st century, and we are challenged to understand which novel communities will be stable in the future, and which will remain in a state of transition.
To understand the nature of transitional novelty in the past, we pair paleoclimate records against the pollen archive within the Neotoma Paleoecological Database. We identify four alternate ecological states relating to landscape and site-level dissimilarity: Ecological Novelty, Transient Refugia, Community Persistence, Community Migration and we apply a similar framework to climate data. We use this framework to understand the interrelationship between climatic and ecological novelty and the persistence of novel communities during the Holocene. In addition we examine vegetation commnuuity change from direct observation (Public Land Survey and Forest Inventory and Analysis) to show the extent and nature of novel forests in the Upper Midwest, resulting from land use conversion in the 19th and 20th centuries.
Results/Conclusions
Novel communities appear throughout the Holocene, accounting for >10% of all community transitions, and rising to 50% of all transitions during the late-Glacial/Holocene and in the last 500 years. Modern novelty is not related to climatic novelty, while late-Glacial/Holocene novelty is. Rates of novelty in the pollen record are higher than rates of climatic novelty throughout the Holocene, which suggests an ongoing process of community reorganization, even in the absence of widespread climate change. In addition, the persistence of novel communities shifts during the Holocene, with higher periods of persistence (community stability following a the deveopment of a novel community) during the mid-Holocene than at any other time. Understanding community change in the pollen records as a bivariate site-based and landscape-level process provides greater insight into the broad-scale processes structuring communities during the Holocene and the long term persistence and ecological outcomes of novel ecosystems.
Novel communities (relative to 1800s baselines) now account for >25% of the forested region in the Upper Midwest, while pollen indicates that assemblage novelty is greater than 50% of all reported pollen assemblages. We show that this high level of novelty has implications not only for modern community ecology, but also for our interpretations of the past.