No-analog ecological communities since the last glacial maximum inferred from fossil pollen records for North America

• Author / Creator

  Sang, Zihaohan

• Given that efforts to reduce greenhouse gas emissions appear to fall short, we need to develop adaptation strategies to mitigate anthropogenic climate change impacts, which may include predicting and managing no-analog ecological communities, for example by selecting suitable species assemblages for ecological restoration projects or in reforestation. To develop analytical tools for the future, this study looks at the past to test if no-analog communities can be detected in the North American fossil pollen record, if they were associated with no-analog climate conditions, and if they can be predicted with species distribution models. The working hypothesis is that no-analog communities that are not associated with no-analog climates, but result from differential migration rates will be the most difficult to predict using species distribution modelling (SDM).

  This study contributes a systematic analysis of 51,427 dated pollen community records from 1,384 sites from the Neotoma Paleoecology Database with climate hindcasts for 21000, 16000, 14000, 11000, 6000 years before present from the CCM1 general circulation model. The analysis relies on a multivariate regression tree approach that delineates pollen communities but constrains the clustering of similar pollen records by using climate variables as partitioning criteria. Modern pollen records are also used to train a species distribution model and create hindcasts up the last glacial maximum to test if past no-analog communities can accurately be predicted.

  The analysis revealed three pollen communities that were widespread during the last glaciations or during deglaciation but that have no equivalence in today’s pollen record. The most distinct no-analog community was a birch parkland ecosystem with exceptionally high frequencies of Betula, Poaceae, Cyperaceae and forb pollen. This ecosystem also occupied no-analog climate space that was similar to today’s arctic tundra with high seasonality and relatively dry conditions, but had a stronger maritime influence leading to higher temperatures during the warmest and wettest quarter of the year.

  The second, widespread no-analog community was a previously described spruce woodland with spruce having a dominant frequency, but also included a large diversity of broadleaf species that today do not co-occur in spruce-dominated ecosystems. This community occurred between 14000 and 11000 years before present south of the Great Lakes region. A third potential no-analog community was a montane steppe ecosystem in the Rocky Mountains with lower frequencies of tree pollen and higher frequencies of pollen from grasses and forbs than modern equivalents. This ecosystem was associated with drier conditions than today but overlapped with the current mountain ecosystem both in pollen frequency and climate space.

  While species distribution models could hindcast birch presence in novel climate space, they failed to predict the uniquely high frequencies of birch in the observed birch-parkland community. Similarly, the uniquely high frequencies of spruce in spruce woodlands between 14000 to 11000 years before present was not correctly predicted. In both cases, violation of assumptions of species distribution models, in the first case climate equivalence, in the second case lack of consideration of habitat factors other than climate appear to prevent accurate predictions of community composition in the past, and by inference also for the future.

• Subjects / Keywords

  • ice age
  • palaeoecology
  • pollen
  • climate change
  • Species distribution model

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-jmvx-cc74

• License

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