High dissimilarity within a multiyear annual record of pollen assemblages from a North American tallgrass prairie.

Julie L Commerford,Kendra K Mclauchlan,Thomas A Minckley

doi:10.1002/ece3.2259

Julie L Commerford, Kendra K Mclauchlan + Show 1 more

Open Access

https://doi.org/10.1002/ece3.2259

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Abstract

Grassland vegetation varies in composition across North America and has been historically influenced by multiple biotic and abiotic drivers, including fire, herbivory, and topography. Yet, the amount of temporal and spatial variability exhibited among grassland pollen assemblages, and the influence of these biotic and abiotic drivers on pollen assemblage composition and diversity has been relatively understudied. Here, we examine 4 years of modern pollen assemblages collected from a series of 28 traps at the Konza Prairie Long‐Term Ecological Research Area in the Flint Hills of Kansas, with the aim of evaluating the influence of these drivers, as well as quantifying the amount of spatial and temporal variability in the pollen signatures of the tallgrass prairie biome. We include all terrestrial pollen taxa in our analyses while calculating four summative metrics of pollen diversity and composition – beta‐diversity, Shannon index, nonarboreal pollen percentage, and Ambrosia:Artemisia – and find different roles of fire, herbivory, and topography variables in relation to these pollen metrics. In addition, we find significant annual differences in the means of three of these metrics, particularly the year 2013 which experienced high precipitation relative to the other 3 years of data. To quantify spatial and temporal dissimilarity among the samples over the 4‐year study, we calculate pairwise squared‐chord distances (SCD). The SCD values indicate higher compositional dissimilarity across the traps (0.38 mean) among all years than within a single trap from year to year (0.31 mean), suggesting that grassland vegetation can have different pollen signatures across finely sampled space and time, and emphasizing the need for additional long‐term annual monitoring of grassland pollen.

Highlights

Grasslands occupy 24% of Earth’s land area and contribute to global food production through row-crop agriculture and grazing or pasture lands
We provide greater insight into the factors that drive grassland pollen assemblage composition and diversity, as well as highlight the amount of variation that exists among grassland pollen assemblages across space and through time
The presence of bison manure had no influence. This suggests that bison herbivory does have an effect on grassland pollen assemblage diversity, but this signal can only be detected with quantitative herbivore abundance

Summary

Introduction

Grasslands occupy 24% of Earth’s land area and contribute to global food production through row-crop agriculture and grazing or pasture lands. Grasslands in North America are at risk because they are currently spatially restricted and regularly experience severe droughts such as the Dust Bowl of the 1930s (Cook et al 2010). The precise timing of these changes and the factors influencing those changes at various spatial scales are still unknown. Both the composition and biodiversity of grasslands over time and the role that biotic and abiotic factors have played in structuring them remain unanswered questions. A long-term perspective is essential to capture the slow processes thought to be important in North American grasslands, such as megadroughts, grazing from large herbivores, and changes in fire regimes

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