Exploring Phenology through Observation, Experimentation, and a Common Garden

Dr. Dan Flynn is a researcher in the Wolkovich lab at Arnold Arboretum in Boston. The Wolkovich lab is examining the phenology of woody tree and shrub species across a range spanning from Quebec, Canada to Massachusetts. In this interview, Dan discusses multiple approaches to the study of phenology and how these approaches will provide scientists with a greater understanding of species’ responses to environmental conditions.

How did you become interested in examining phenology?

I had been doing research in community ecology, interactions between species and how communities assemble. What are the rules that determine how species can coexist with one another? What happens when communities get disassembled because of extinction? This idea of community assembly and disassembly is something that I’ve worked on a lot. In the past, my research was in alpine grasslands in western China. We were tracking the phenology of different grassland plants under different experiments. We had experimental warming in the field at 3000m of elevation in Tibet and very strong responses for the different species there. That’s what got me interested in these phenological approaches, integrating between observation and experiment using phenology as the key focus.

What is the focus of your current research?

Climate change and phenology are the central themes. Some questions that we ask in the lab are: What are the patterns? Which species are able to take advantage of warmer temperatures earlier in the spring? Who are the winners and losers? Also, within species, how do different populations respond at the northern and southern edges of their range?

How does your lab gather phenology data?

We think about three levels of scientific research. Observational is the most natural. We’re observing actual individuals in the field, exposed to all sort of environmental conditions. Then, there’s this growth chamber experiment where we’re forcing spring and that’s definitely not very natural. We have hundreds and hundreds of glass flasks with distilled water and cuttings [from target species] placed in the water. We’re growing them in chambers with different day length and temperature. That is really useful because we can control everything. We can put cuttings from the same individual under different environmental conditions. We couldn’t do that in the field. An approach that’s intermediate, between those two (observational and experimental), is the common garden. It’s sort of an old school approach, but really useful for this kind of large scale adaptation to environmental change question. We take seed material from individuals in the field that were exposed to different environments for a long time, like Canada vs. Massachusetts. Then, we grow those seeds under one common environment here at the Arboretum. This removes the environmental differences that the offspring are experiencing, so the [observed differences in phenology] between the offspring are due to what [traits] they got from their parents. Those are the three phases of the research that we’re working on here. We’re interested in really integrating across these different approaches.

Why are multiple approaches so useful?

The basis for all phenology research is observation, but experiments are also very important because we want to be able to focus our efforts on one particular set of drivers. We need experiments that control for the environmental factors. We get a lot of control in growth chambers to just change temperature or just change day length, but we lose that naturalistic application. To understand the driving mechanism, we’re merging that observational approach with experiments. We’re going in the field. We’re taking clippings of plants and we’re bringing them back to the lab. On these same plants that we’re doing [field] observations, we’re also doing experiments in growth chambers.

 What phenophases are you looking at?

We’re really interested in spring. We can take dormant twigs and control how much winter they get, when they get spring and what kind of spring they get. We’re looking at both the early flower out and the early leaf out phases. In this experiment, since we’re working with cuttings, we’re not able to look at the later phenophases, but this study is integrated with field observations. [Observing the later phenophases] is something that we’re going to be doing with those individuals in the field.

How does phenology affect an organism’s role in an ecosystem?

Phenology is not just reflecting the performance of these plants in the climate conditions, but it’s also determining their fitness. In biology, fitness has a really concrete definition. For trees, their fitness, over the lifetime of the tree, is how many acorns or other seeds are produced and how well their offspring survive. We’re focusing on that balance between the different strategies, conservative vs. opportunistic. Under what circumstances and for what species are these different strategies advantageous? If you have an opportunistic strategy, you might be willing to put out leaves really, really early in the spring, even if the day length is still short. The light cues are saying late February or early march, but temperatures happen to be warm due to a warm spell that year or a long term trend of climate warming. This kind of opportunistic strategy would give an individual a head start to grow taller and shade out its neighbors. It would be a better competitor for resources. If that plant can actually produce more offspring that survive better, it would be an indication that there’s an adaptive benefit to being opportunistic. The cost of this opportunistic strategy is [risk]. An individual can put out its leaves really early, but, if a cold snap comes, all those little leaves that were so tender are now frozen under a sheet of ice. It’s much more conservative to follow the day length regardless of the temperature fluctuations. The shaping of ecosystems occurs over the long term, over generations, as populations of plants with different strategies expand or shrink.

How is citizen science important to phenology research?

Citizen science is one of the best ways for people to get involved in science because all you have to do is look out in your backyard. It has a really important role in providing the basis for great observational datasets, like the phenology network is putting together [for which Signs of the Seasons is a contributor].

To learn more about research in the Wolkovich lab and view photos,
follow the lab blog Temporal Ecology: A Snail’s Eye View of the Wolkovich lab.