Tesa Madsen-Hepp: Plant functional traits lend predictability to idiosyncratic range shifts

In this new post, Tesa Madsen-Hepp—PhD candidate at the University of California Riverside, USA—presents her latest research ‘Plant functional traits predict heterogeneous distributional shifts in response to climate change’. She highlights the high value of the Deep Canyon Transect, discusses the response of diverse dryland plant communities to long-term climate change, and shares the challenges in intense field campaigns.

About the paper

Our paper investigates the ability of plant functional traits to predict how different plant species are responding to climate change. As temperatures warm and precipitation regimes change, plants are expected to track their optimum conditions by dispersing and establishing new populations in more favourable locations, presumably to cooler temperatures at higher elevations and latitudes. However, accumulating long-term data on the range redistributions of plants show that this isn’t necessarily the case; some species are shifting in directions opposite from what existing models predict with climate warming, such as downslope shifts or toward lower latitudes, while some species are showing delayed responses or no response. This lack of generalization is problematic because it prevents us from being able to accurately predict future ecosystem organization and the consequences of that organization, such as rates of carbon sequestration and nutrient cycling.

The Deep Canyon Transect viewed from the highest elevation sites looking toward the Coachella Valley (credit: Tesa Madsen-Hepp)

Since plant functional traits reflect adaptations to a given suite of environmental conditions, they have strong theoretical support to predict plant responses to changing climate regimes. However, few studies have found that traits are predictive of range redistributions. This is likely due to a focus on seed traits impacting dispersal and categorical functional types (like trees, grass, etc.) rather than traits influencing how plants acquire and utilize resources, such as leaf size and thickness, chlorophyll content, and water use efficiency. Furthermore, most long-term data on plant distributions are located within a single ecosystem type and are overrepresented by temperate alpine ecosystems, making the Deep Canyon Transect an extremely valuable long-term dataset in that its steep elevation gradient spans multiple ecosystem types (desert scrub, pinyon-juniper woodlands, chaparral, montane coniferous forest) within the underrepresented dryland biome. Because of this ecological diversity, it’s the perfect location to test the role of functional traits in mediating range shifts because of the extensive trait diversity and turnover across the elevation gradient. Therefore, our study stands out from past research by encompassing such a large elevation gradient, being conducted within a dryland biome, and incorporating population-specific functional traits rather than using average species values from large databases.

About the research

Our paper is important to the fields of biogeography and functional ecology because it shows that commonly measured plant functional traits can explain interspecific differences in range redistribution patterns under recent climate change. We also found range shifts at the higher end of global average rates, demonstrating that diverse dryland species are highly responsive to recent warming trends, and show that patterns of abundance tend to reflect these changes. Our paper is also important in its implications for dryland ecosystems, which tend to contain more stress-tolerant species and are generally viewed as resilient to climate change. Similar to other recent studies, we found that species with stress-tolerant traits are reaching their physiological thresholds, resulting in a rapid transformation of the dominant functional trait strategies which govern essential ecosystem functions.

View of the elevation gradient from the lower elevation transects toward the highest elevation transects (credit: Tesa Madsen-Hepp)

Though I have done a fair amount of fieldwork before, nothing could have prepared me for the challenges and rewards of re-surveying the Deep Canyon Transect. The data collection took nearly four months of full-time work with a four-person crew working ten-hour days. We needed this lengthy field season because we sampled all annual as well as perennial plants at the centimeter scale in 400-meter transects. Due to the above-average precipitation, we were met with a spectacular proliferation of annual plant diversity. The elevation gradient is also quite challenging terrain, and, unlike most historical vegetation data, the transects were often difficult to access. Between scrambling up steep canyon slopes filled with cacti spines, precarious cliffside data collection, encountering venomous snakes, nearly rolling our field truck to access some remote sites, and fracturing my foot on a boulder, it was quite an adventure. Witnessing the incredible ecological diversity and steepness of the vegetation change made the experience the most inspiring of my scientific career thus far.

Field assistants Shane McFaul and Lisa Schauer record transect data at the edge of the canyon wall (credit: Tesa Madsen-Hepp)

While our paper is a big step forward in generalizing plant responses to climate change, there are still a lot of gaps to fill before we can make more accurate predictions on a global scale. For instance, there are very few studies addressing climate change effects on dryland ecosystems compared to other biomes, and more long-term studies that are conducted in the northern versus southern hemisphere. In addition to geographic biases, plant populations establish, grow, and survive in response to other species within a community. We have yet to account for the importance of biotic interactions in mediating range shifts on any generalizable scale since plant community structure and diversity vary within and across ecosystems.

About The Author

Tesa Madsen-Hepp

I’ve always been captivated by the beauty of the natural world but wasn’t that interested in science until falling in love with plants. As a young adult struggling with my mental health, I sought out time in nature—hiking, kayaking, camping—which eventually helped me rediscover my curiosity and sense of wonder, as I began teaching myself about the local flora. After working in a series of field botany positions, I craved to learn more about ecology and biogeography. I pursued a Master’s degree, and realized just how much I wanted to stay in academia and keep doing research. As a first-generation college student, I hadn’t intended to pursue higher education; however, learning about the natural world around me kindled an insatiable appetite for scientific understanding. The realization of the complex, interdependent nature of the natural world has been and continues to be my biggest source of inspiration.

As a Ph.D. candidate at the University of California Riverside, I am interested broadly in the causes and consequences of functional trait diversity, investigating the impact of climate change on plant distributions and trying to disentangle the dynamic interplay between abiotic and biotic forces shaping plant community organization. As the disturbances of global industrialized society continue to exert pressure on ecosystems, we need to better understand the processes shaping how plant species form diverse assemblages in time and space, and how their future organization will impact ecosystem functioning.

Enjoyed the blogpost? Read the research here!

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