By Ailene Ettinger, TNC Washington Quantitative Ecologist
All photos © Tim Savas
The leaves on the trees outside my home office window have dropped, making the branches look bare and lifeless. But they are not dead. They are quiescent, one of my favorite words, meaning “in a state of dormancy.”
American beech bud, Fagus grandifolia
During this cold, dark season, the leaf buds on these apparently inactive beings are quietly counting down to the start of spring, akin to my kids counting down the days until their winter break from school.
Indeed, when spring rolls around and the dull brown twigs become swollen buds with emerging vibrant green leaf tips, my excitement rivals my children’s.
I study phenology, or the timing of seasonal biological events such as such autumn leaf death and spring budburst. The transition to spring is a particularly exciting event to witness. It’s also an incredibly complex process, involving cellular pathways and genes that are not well understood, and affected by winter temperatures, spring temperatures, and day length, among other things. The beauty apparent in observing phenology in nature and the complexity of biology underlying phenological events fascinate and ground me.
Instead of a calendar, leaf buds “keep time” with temperature; exactly how this occurs is an active area of research. It is thought that dormant buds must experience a certain amount of cold temperature, or “chilling,” followed by a certain amount of warm temperatures, or “forcing,” before budburst will occur. The specific amounts of chilling and forcing required vary across species and daylength can also play a role.
Paper birch bud, Betula papyrifera
These cues work together to determine the timing of budburst. Getting the timing right can be a matter of life and death. Trees that burst their leaf buds too early can be subjected to devastating frosts, harming forest and agricultural species alike. Phenology is important for many species and biological events. From salmon migration and insect emergence to egg-hatching and birthing, the timing of these events has critical implications not just for the individuals involved, but for interacting organisms as well. If a plant and its pollinator have mismatched timing, for example, this can lead to low reproduction for the plant and low resources for the pollinator.
I also study phenology because climate change is causing shifts in the timing of budburst, migration, and other biological events. These shifts have cascading ecosystem effects: changes to forest tree phenology, for example, affect the length of the growing season and therefore how much carbon is sequestered each year. Shifts in phenology are one of the most widespread and unambiguous effects of climate warming around the world. Yet, there is great variation in the magnitude of shifts occurring, with some species and populations shifting a lot and others very little.
This variation has shined a light on the fact that the implications of biological responses to climate change remain poorly understood. As agricultural crops from wheat to fruit trees start the growing season earlier in the spring, are they at greater risk for severe frost events? In addition, communities of interacting wild species may be rearranged depending on how they respond to climate change. In some cases, plants and animals that have shifted their timing with recent warming have benefited (showing increased growth, for instance) compared to those that have not shifted their phenology with warming.
Viburnum bud
There are many interesting scientific questions to uncover and many ways to get involved. You can support our work at The Nature Conservancy, where we are studying the drivers and consequences of phenology in diverse species, including salmon, southern resident killer whales, and wildflowers on our Yellow Island Preserve.
You can also participate in phenology monitoring yourself through community science initiatives such as MeadoWatch at Mount Rainier National Park or Nature’s Notebook, which includes phenology monitoring of a wide range of plants and animals in Washington state and beyond. I find solace and purpose in the practice of monitoring an individual tree’s phenology- does it have leaves? If not, does it have buds? How big are they? Visiting the same tree week after week and asking these questions forces me to tune into minute details of trees. This has awakened me to their beauty, and to notice the small changes happening around me, particularly valuable at a time when we’re urged to stay close to home and isolate ourselves.
And studying phenology is an act of hope. The idea that I’m contributing to a communal body of scientific knowledge, improving our understanding of climate change, while monitoring the countdown to spring, when the quiescent buds will transform to bright green leaves, gives me the hope and strength to get through the dark days of winter.
Banner photo American beech, Fagus grandifolia
