Georgia is a PhD student at the University of Nevada, Reno, in the USA. She is a plant ecologist with a special interest in conservation and biogeography. Here, Georgia shares her recent work on how the trait variation of a dryland pine species responds to regional climatic gradients.
Georgia enjoying the beautiful petroglyphs at one of her field sites, Mount Irish.
Institute. The University of Nevada Reno (during her recent master’s graduation)
Academic life stage. PhD student at the University of California Santa Cruz
Major research themes. Plant Ecology, Conservation Biology, Restoration Ecology, Biogeography.
Current study system. Driving across the most mountainous and driest state in the U.S., Nevada, you will explore beautiful semi-arid woodlands that dominate the landscape up to the alpine-treeline ecotone. Singleleaf pinyon pine (Pinus monophylla) is a foundational tree species in semi-arid woodlands of the Great Basin and upper-montane environments of the Mojave Desert. Across its wide range, you will see it growing next to giant Joshua trees at the lowest elevations, all the way to establishing the understory of Ponderosa pine and White fir at higher elevations. It is the most xeric pine in the U.S., slow-growing and long-lived (>800 years), with a scrubby, rugged stature. Producing pine nuts, its legacy as the most culturally important plant for the local Indigenous people of the area, as well as a dominant food source for many animals, makes it an important species to research.
Left: Large singleleaf pinyon at the lower site in the San Bernardino Mountains, California. Right: Expanse of singleleaf pinyon pine in the Pine Nut Mountains near Carson City, Nevada.
Recent JBI paper. Vasey, G. L., Weisberg, P. J., & Urza, A. K. (2022). Intraspecific trait variation in a dryland tree species corresponds to regional climate gradients. Journal of Biogeography, 49(12), 2309-2320. DOI: https://doi.org/10.1111/jbi.14515
Motivation behind this paper. Tree species worldwide are experiencing drought-induced mortality as temperatures steadily rise. A recent drought from 2013–2015 caused eightfold dieback of singleleaf pinyon pine in the central region of the Great Basin, motivating the co-authors P.J. Weisberg and A.K. Urza to apply for funding to better understand the species’ functional limitations and adaptive capacity. Many long-lived species rely on their intraspecific trait variation to manage climate change pressures; however, knowledge of this species was limited. As a foundational tree species in dryland woodlands, large-scale mortality would dramatically alter community assembly and threaten the ecosystem. This paper aims to investigate how much functional trait variation exists within the species’ distribution, and whether it may be enough to withstand future environmental conditions.
Key methodologies. In this research, we obtained samples across singleleaf pinyon pine’s geographic range, both latitudinal and elevational, encompassing local and broad-scale gradients of climate and soil characteristics. At each of the 23 sites, six climate variables were obtained that related to important life-history trade-offs related to drought stress. We measured nine morphological traits, both reproductive and vegetative, for each tree (N = 137). These data, in conjunction with the environmental variables, evaluated (1) how trait variation was partitioned across ecological scale, and (2) the relationship between traits and broad-scale environmental gradients across its range. We also looked at interannual variability for needle size across three growth years compared to annual weather data from 2016–2018 to measure phenotypic plasticity. One of the more novel approaches to this data analysis was using two-block partial least squares analysis (2B-PLS), a newer ordination method to evaluate maximum covariance between two matrices (in this case, traits, and environmental variables). After trying other methods, I found this one to be the most visually interpretable and highly recommend it.
Upper Left: Field helper, Paul Burow, harvesting pine cones from the upper ⅔ of canopy at Mount Irish, Nevada. Lower Left: PPE to manage sticky pine cones when measuring cone length. Right: Research Technician, Erica Sutherland, helping measure cone traits.
Unexpected challenges. As a mast seeding tree species, seed production varies greatly from year to year. We were lucky that 2019 was a good year for sampling singleleaf pinyon pine. While you can clearly observe on Google Earth that the tree is located in a particular area, it’s not until you arrive 10+ hours later at your destination that you officially find out if it’s actively reproducing. Additionally, the window of time that the cones are ripe but haven’t completely opened is short. Trying to harvest enough cones before animals predate them was a race, to say the least. We managed to overcome these obstacles by putting in long days and working systematically. At the greenhouse, I also couldn’t have measured ~25,000 measurements (i.e., nine traits measured multiple times according to their sample size) without the help of two amazing research technicians. These kinds of projects aren’t possible without an enthusiastic and dedicated team!
Major results. The highest proportion of trait variation was explained at the scale of individual trees, suggesting within-population adaptive capacity is possible. However, a substantial portion of variance was also explained at regional scales related to environmental gradients (e.g., seed mass and cone-level seed number in response to aridity, and specific leaf area and needle weight in response to precipitation seasonality), suggesting that certain traits are adaptive in different environments. Additionally, for some foliar traits, our results suggest that singleleaf pinyon pine is phenotypically plastic in response to the environment. Our results inform management decisions on potential assisted migration efforts (e.g., use larger seeds from drier populations), while also suggesting that in situ variation may allow the species to persist without intervention. This paper also highlights that using mean trait values in predictive modelling is not always sufficient and that more research on individual species (particularly foundational ones) merits more attention.
Left: Sticky green pine cones before they open. Right: Compilation of morphological traits: cones, seeds, and needles.
Next steps for this research. Stay tuned for my second chapter in the queue to be published! I conducted a common garden greenhouse experiment with the seeds from each maternal tree to evaluate seedling trait response to a gradient of water availability. I also helped with the establishment of two additional common garden experiments, one using the same seeds in an outdoor site in Carson City, Nevada, and another using the surviving greenhouse seedlings at a site in the Shoshone Mountains. We hope these follow-up studies will provide a better understanding on the traits adaptive value and plasticity, with an emphasis on seedling stage establishment (a known bottleneck period).
If you could study any organism on Earth, what would it be? I’m really excited to currently be working on my PhD in coastal California (my home), studying wildflowers in grasslands. Who doesn’t love these ephemeral beauties that paint the landscape in the spring!?
Anything else to add? I’m so grateful I was advised by two amazing advisors, Peter Weisberg and Ali Urza, during my master’s research. I learned how to be a scientist: ask thoughtful questions, make informed predictions, understand the nuances of experimental design, and everything that happens thereafter from completing the study, data analysis, and writing. We were an excellent team, and I’m excited to continue collaborating! I’m also thankful to Journal of Biogeography for publishing my first paper that I’m the lead author on. If you are interested in my research and would like to learn more or collaborate, feel free to contact me by email (email@example.com).
Singleleaf pinyon pine growing alongside Joshua trees in the San Bernardino Mountains, California.