Ecological Society of America 2021

Transcript for “It’s the greening of the trees that really gets to me”: Revisiting Phenological Mismatch

1. Welcome! I’m Caitlin McDonough MacKenzie. I’m a Visiting Assistant Professor at Colby College. I’m so honored to be a part of this symposium, representing the 2020 Mercer Award. Thank you to the symposium organizers, to our nominators, and to the ESA. This talk is focused on the research behind our Mercer paper, which brings me back to my time as a graduate student at Boston University and my lab’s fieldwork in Concord, MA. While I’m now at Colby in Maine, over the past year I’ve actually been teaching remotely from a closet in our apartment in Boston, so I’ve spent a surprising amount of time wandering around the old field sites.

2. I wrote and recorded this talk from the lands of the Pawtucket and Massachuset people. This beautiful map is from Lisa Brooks’ book The Common Pot: the Recovery of Native Space in the Northeast.

3. Many of us spent the last 15 months largely at home. Early on in the pandemic, some media outlets drew parallels between staying at home and Henry David Thoreau’s 19th century stay at Walden Pond. I found this to be a disingenuous comparison between a man who deliberately chose to live in the woods (and was notoriously bad at social distancing while he did so) and our collective experience in a pandemic.

4. But, in the pockets of time between existential dread, suddenly homeschooling, and transitioning to online teaching, my family did notice the backyard wildlife and neighborhood trees, I wandered along local trails instead of bagging far-flung peaks, and we observed small things in nature with heightened regularity. I bet many of you did too.

5. In these small practices, we did have a Thoreau-like 2020. Thoreau recorded seasonal changes at a local spatial scale, and his observations provide a foundation for modern phenology research.

6. Phenology is the timing of seasonal biological events

7. Advancing spring phenology is a visible, highly documented, and well-studied ecological impact of anthropogenic climate change. We see this clearly in datasets that incorporate Thoreau’s observations of flowering — in warmer springs wildflowers bloom earlier.

8. This general pattern of earlier phenology in response to warming temperatures is highly documented — We see it in Camille Parmesan’s early meta-analysis of spring phenology observational studies where nearly every species shows a shift towards earlier spring timing…

9. We see it in Lizzie Wolkovich’s meta-analysis comparing observational and experimental plant phenology studies, and we see it again, in Katie Stuble’s follow up meta-analysis of experimental warming studies.

10. Within this general pattern, we note variation in the phenology of populations, species, and functional groups. Here, Species-level variation is illustrated by the thermal units (or warm spring days) Caroline Polgar’s woody plants accrue before leaf out in Thoreau’s Concord.

11. We see variation in the sensitivity of phenological responses: some species shift earlier in warmer springs with dramatically negative slopes, while others display flatter trends.

12. These variations in phenological sensitivity may disrupt the timing of ecological interactions, causing phenological mismatch as interacting species shift their phenological events at different rates in response to environmental change.

13. Most research on phenological mismatch has focused on consumer-resource interactions. Since a theme of this talk has become meta-analyses by awesome women in ecology, Heather Kharouba put together a great paper on phenological mismatch trends across 54 pairs of interacting species engaged in herbivory, predation, and pollination, with a sprinkling of bird-bird competition. I was certainly not aware of any examples of plant-plant mismatch when I started thinking about trees, shade, and understory wildflowers.

14. Our paper explored an overshadowed mismatch in the non-trophic interaction between canopy trees and understory wildflowers. Richard Primack and I used records dating back to Henry David Thoreau to show that leaf out and flowering phenology in Concord, MA are shifting earlier in warmer years. However, the shift in leaf out is more dramatic: trees show a higher phenological sensitivity than understory wildflowers.

15. The title for this talk is a line from Ada Limon’s poem ‘Instructions on Not Giving Up’. I love all of the phenology shout outs, and I too love the greening of the trees each spring. But from the perspective of an understory wildflower, the greening of the trees is an ending, not a beginning.

16. The greening of the trees dramatically alters the light environment in the understory. Shrubs and herbs that were basking in the high light before tree leaf out, are suddenly shaded.

17. Understory species in temperate deciduous forests depend on the high light environment before tree leaf out for a significant chunk of their annual carbon gain. Mason Heberling, Susan Kalisz, and Jason Fridley documented this drop in daily carbon gain at canopy closure for eight understory wildflowers in Pittsburgh.

18. Together, we used the Pittsburgh data to model how wildflower carbon gain likely changed through time as the window of high light availability before leaf out shrank in Concord, MA from Thoreau’s time to today.

19. So what did we find? Here the x-axis is Change in spring temperature at the top, which corresponds to a change in the length of spring on the bottom. The zeroes on this axis are set to 2016. In warmer springs, leaf out shifts earlier, and the window of high light availability shrinks.

20. In Thoreau’s Concord in the 1850s, understory wildflowers had about an extra week of high light, which translated into about 7% higher annual carbon gain than today. Under future climate change scenarios, the high light window could shrink by another 6-12 days, leading to nearly 20% lower annual carbon gains for wildflowers.

21. I loved working on this project with a great team of scientists — and we were so honored to be recognized by the 2020 Mercer Award.

22. Looking back on the paper, I think it lives up to the hype for a few reasons: First, we documented phenological mismatch in a non-trophic, plant-plant interaction. Most mismatch research had focused on consumer-resource trophic interactions.

23. Second, after Richard and I documented the phenological mismatch in Concord, we reached out to Mason, Susan, and Jason to estimate the impact of this mismatch on carbon budgets. Linking mismatch to ecosystem impact is what Karen Beard calls “The Missing Angle.” For example, Beard asks what are the broader consequences of the well-known mismatches like caribou and the lichen at their calving grounds? How do mismatches ripple out across a whole ecosystem?

24. Finally, (and I know this a very hidden highlight since few folks read the supporting information), I am very proud of Table S3. One of our reviewers, Ally Phillimore (he signed his review), wrote “This paper relies on an unusually high number of assumptions and only a few of these are mentioned and rather too briefly. I don't see any of these as greatly undermining the paper, but I would like to see them out in the open and examined with a bit more thought, especially with respect to what the consequences of assumptions might be for biases.” He recommended a table outlining the assumptions. The practice of creating this table forced us to really clarify how we organized our model and where the potential weaknesses (and Future Research Directions) lay. For me, this was a powerful revising experience: it strengthened the paper, and deepened our understanding of how our research fit into the field.

25. So, fast forward to 2021, what have we learned about shade, understory wildflowers, and historical ecological records? According to “Web of Science”, our paper has been cited 27 times. Here is a word cloud of all the titles of papers that cite our study. As an early career researcher, I haven’t spent a lot of time contemplating what happens to a paper after publication — I’m just trying to get my work published! But this symposium is an opportunity to revisit my phenological mismatch research and trace its path and citations in the field of ecology; a chance to slow down, notice the budburst of an idea, and attend to my place in the scientific community.

26. Among the 27 citing papers, there are 8 review papers, six papers written by at least one member of our author team, and one paper about the phenology of goose poop!

27. We ended our paper with the thought: “Phenological mismatches between overstorey trees and understorey wildflower species may be a widespread phenomenon that will affect the future of temperate deciduous forests under climate change.” So, digging into these 27 papers, I was really curious to see if there is evidence that it is a widespread phenomenon.

28. So far, we don’t know if Concord’s mismatch is a local anomaly or a part of a widespread pattern. None of the 27 papers test this in a new location, though Mark Vellend has started monitoring Red Trillium and Trout Lily phenology relative to canopy green up with near-remote sensing in Quebec.

29. Benjamin Lee explored the shade-phenology dynamics of tree seedlings. He found that the seedlings of sugar maple and red oak display more sensitive leaf out phenology than canopy trees — this allows them to escape the fate of our understory wildflowers and boosts their spring carbon gain.

30. I want to re-highlight these two papers from earlier in this talk — I went into these pdfs looking for a citation of myself, but the whole of each work has now influenced my thinking about phenology and phenological mismatch. I see this is a kind of antidote to extractive reading; somehow my navel-gazing turned into a deeper read, a kind of conversation between our research areas. (and I certainly would not have this perspective without reading Max Liboiron’s Exchanging!)

31. Finally, I want to share two personal photos. The first is from the Saturday after we submitted our manuscript to Ecology Letters. The second is from Spring 2020 when the Mercer Award was announced. I spent some of my parental leave working on the revisions for our paper — which is itself a privilege — we need universal parental leave for students, postdocs, everyone! This I’m-so-excited-to-use-my-brain-and-talk-with-adults work was buffered by naps, lazy afternoons walking with a stroller, and support from my colleagues and family. Working on revisions for other papers in 2020 was not that.

32. COVID hit academic parents, and especially mothers, very hard. Winning the Mercer in 2020 is a reflection on my work before the pandemic. I don’t know what my career will look like after this disruption to my research.

33. I feel like an understory plant who has lost the high light window of early spring, my energy stores are depleted.

34. I’m so thankful that people who are smarter and have more seniority than I do have brainstormed and published recommendations for funding agencies, institutions, and departments to recruit, retain, and support academic parents, especially moms and parents from historically excluded groups in science.

35. To close, let’s return to Thoreau. Thoreau once wrote in his journal, “The question is not what you look at, but what you see.” His daily observations in a small town outside Boston are the foundation for our work, we can trace phenological shifts over long time series, because Thoreau saw value in noticing and recording small things in nature with heightened regularity. A century and a half later, Richard Primack looked at Thoreau’s notes and saw data. About a decade later, I looked at Richard and Thoreau’s combined data sets and saw phenological mismatch.

36. Thank you to my wonderful coauthors, to my labmates in the Primack lab who generously shared their data and Concord-based knowledge, and to my postdoc advisor who supported my work on this side project with my old lab, and to my family — especially my husband, who has carried well over half the childcare and housework burden this year while also keeping close tabs on when the local chocolate factory is releasing small batch, artisanal Choco-Tacos. Thank you, Mike!