ECR feature: Grasslands and functional traits with Emma Jardine

Emma Jardine is currently an environmental land management scientist at DEFRA. She is interested in the use of functional traits to understand how plants respond to the environment. Her recently published work in the Journal of Biogeogrphy considers the relationship between functional traits in grass species and environmental variables at a macroecological scale. Emma shares how the rich collection of plant specimens in Kew Royal Botanical Garden’s herbarium made her research possible.

(left) Emma Jardine, finding some time to visit the Great Plains and Rocky Mountains on a trip to think about grassland ecosystems and how they respond to drought at a DroughtNet data synthesis meeting, Fort Collins, Colorado. (middle) Herbarium specimen of Digitaria eriantha Steud. collected in 1927 in South Africa which is part of the collection at the Royal Botanical Gardens Kew. (right) One of the many rooms which form the herbarium at Kew botanical Gardens. The collection houses approximately 7 million herbarium specimens in total which have been collected from around the world over the past 170 years.

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Institute. The featured research was conducted at the University of Sheffield.

Current role. Former postdoc now working on the environmental land management team at DEFRA.

Major research themes. Using functional traits to explain plant response to environment.

Current study system. I use grasslands as a study system to explore trait environment relationships. Grassy biomes are perfect for macro-ecological research as they cover between 20-40% of the terrestrial globe, have evolved to tolerate a wide variety of climatic conditions and soil regimes and have fewer dominant species than for example tropical forests. Grasslands play an important role in carbon sequestration, silica cycling and food security. These are important ecosystems but are threatened by land-use and climate change.

Recent paper in Journal of Biogeography. Jardine, Emma & Thomas, Gavin & Forrestel, Elisabeth & Lehmann, Caroline & Osborne, Colin. (2020). The global distribution of grass functional traits within grassy biomes. Journal of Biogeography, 47(3):553–565. 10.1111/jbi.13764.

Motivation of this paper. A central goal of ecology is to find rules to describe patterns in nature and how these patterns arise. The identification of patterns that determine vegetation dynamics at the global scale has the potential to improve our understanding of how ecosystems will respond to global change.  Studies of global change often divide plants into functional types to make predictions without requiring detailed knowledge of species, with grasses being grouped by photosynthetic type (C3/C4). However, this approach ignores functional variation within these groups. We therefore wanted to know if relationships between functional traits and resource availability that are well known at community scale, could be applied over global scales.

Key methodologies. One problem that needs to be overcome when working at macro scale is sampling large numbers of globally distributed species. Trait databases are often biased towards woody taxa, so this makes accessing a large set of grass species grown in their natural environment across a global distribution very challenging.  It would be a dream come true to travel to all the savannas, steppes, prairies and pampas of the world to assemble such a dataset. Unfortunately, this was beyond the timescale and budget of this research project. I instead developed methods for measuring functional traits from herbarium specimens and went on a worldwide tour of grassy biomes from within the herbarium at the Royal Botanical Gardens, Kew. I was amazed at the scale of the collection and there I found hundreds of specimens collected by intrepid explorers from surprisingly remote parts of the globe.

Unexpected challenges. Functional traits are usually measured from fresh material, so the first part of the project was to develop methods for taking measurements from dried material. Grasses can be notoriously tricky to identify, but one of the great things about using the herbarium (as opposed to field collection for this piece of research) was that the expert taxonomists at Kew had already done this job for me. One of the daunting aspects of this work was the number of specimens required to obtain a globally representative sample. Several weeks were spent just searching through the many thousands of specimens in the cupboards at Kew for the globally dominant species I was interested in, before any measurements for the final dataset could begin.

Major contributions. We conducted a comparative analysis of functional traits, climate and soil fertility for almost one third of the globally dominant grass species from all continents including representatives from all major grass phylogenetic clades. Global scale studies of trait environment relationships commonly span broad taxa whereas ours was specific to grasses. Previous studies have also not accounted for the influence of phylogeny on observed patterns. We found that relationship between traits and environment are weak. This is because trait variation is greater within than between different vegetation types. We also discovered a strong phylogenetic signal in all of the leaf traits measured. We therefore concluded that evolutionary history provides a stronger explanation of trait distribution than contemporary environment.

What is the next step? We found it interesting that traits varied more within than between different vegetation types and this result led naturally to research focused on processes that vary over smaller scales than climate, for example fire and herbivory. In collaboration with other colleagues we have been using this dataset to contribute to work investigating how globally fire filters functional traits. We have also been looking at the relationship between traits, fire and mammals across Africa. Through this we hope to gain more of an understanding of the processes that are responsible for structuring grassy ecosystems, which will in turn, provide information on how to conserve them.

If you could study any organism on Earth, what would it be and why? Grasses of course! I’m fascinated by Savanna ecosystems as they are prone to so many disturbances, for example  fire, drought and herbivory. I’m particularly interested in the effects of herbivory on vegetation dynamics. As the only continent with an extant megafauna African savanna are the ideal system for studying this and provide the perfect excuse to research both plants and animals.

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