Backyard Phenology: Observing the Seasonal Pulse of Nature

By Amey Bailey and Sarah Thorne
April 17, 2020

Introduction

What story can spring bud burst tell? Do trees leaf out at the same time every year? Do all tree species leaf out at the same time? Is tree location important to the timing of leaf out? Can the timing of spring leaf out be used as an indicator of climate change?

These are all good questions that can be answered by the study of phenology: the timing of seasonal changes in nature. Phenology is the scientific study of transition from one seasonal phase to another as controlled by background weather conditions and habitat condition.

Can you think of examples of phenology? The timing of spring leaf out on deciduous trees and leaf drop in the fall, salamander egg-laying in vernal pools, and arrival of migratory birds to their nesting grounds are all examples of phenology.

At the Hubbard Brook Experimental Forest in Woodstock, NH, researchers have been studying phenology at several locations since 1989. The original idea was to determine the date every spring when leaves had fully expanded in order to estimate when photosynthesis began. By pairing spring measurements with fall leaf drop, researchers could calculate the growing season. The Hubbard Brook phenology dataset can also be used to consider whether warmer and earlier spring conditions as a result of climate change are causing the forest to leaf out early and extending the growing season. The data actually support this!

Phenology research is also relevant to other aspects of ecology. Bird researchers use phenology results to estimate when insects and caterpillars will have food and substrate for their annual cycles. Insects emerge around the time leaves emerge. Once insects come out in the spring, birds arriving to their nesting grounds have food to eat. If these events happen out of synchrony, the system can become off balance. The following video describes bird research at Hubbard Brook and mentions the tenuous balance of the timing of insect and leaf emergence and food availability for nesting birds.

Why is phenology important in your life? Farmers and gardeners use their knowledge of phenology to better time when they plant and harvest crops. Wildlife observers and scientists use phenology to understand population fluctuations and food web impacts of climate change.

How to become a phenology observer of the trees in your yard

1) Identify at least 2 trees in your yard that have easy access to buds for observation. Ideally, try to find 2 of the same kind of tree so that you can track any variation in individuals. If you can’t find 2 of the same kind of tree, different types will do. If you can’t identify the tree, make the observations anyway. When the leaves are out, it will be easy to determine the species. Use one of the websites listed below to help identify your trees, or ask someone for help. Tag your trees with an old cloth or a piece of string so you don’t forget which trees are your study trees.

Tree identification websites:

2) Begin observing right away! Follow the directions on the data sheet below to keep track of your observations. The definitions for the phases are explained in the next section (“How to fill in your data sheet”). Observe your trees daily if possible.

3) When the leaves are fully elongated, email your data sheet to your teacher or to: amey.bailey@usda.gov for further data analysis instructions.

If you want more information on national phenology networks or would like to participate in phenology citizen science projects, check out these websites:

Budburst, a project of the Chicago Botanic Garden
National Phenology Network

For further information about Hubbard Brook science or assistance with backyard phenology contact: educator@hubbardbrookfoundation.org

Enjoy being outside and asking questions like a scientist! Have fun.

How to fill in your data sheet

First, fill in these three identifying features:

Date: Fill in today’s date (the date you’re making the observation)

Tree species: Record the species of tree you are observing, if you can. This will always be the same.

Tree number: You are observing 2 trees. If both of your trees are the same species, label them tree 1 and tree 2 either in your mind or mark them in a creative way you come up with that will help you remember observation order.

Next, Write yes (y) or no (n) to the following descriptions.These definitions are based on National Phenology Network and Hubbard Brook Experimental Forest phenology methods:

Breaking leaf buds: One or more breaking leaf buds are visible on the plant. A leaf bud is considered “breaking” once a green leaf tip is visible at the end of the bud, but before the first leaf from the bud has unfolded to expose the leaf stalk.

First leaves: First leaf from the bud has unfolded to expose the leaf. A leaf is considered “unfolded” once its entire length has emerged from a breaking bud so that the leaf stalk is visible at its point of attachment to the stem. Do not include fully dried or dead leaves.

Increasing leaf size: A majority of leaves on the plant have not yet reached their full size and are still growing larger. Leaves often look delicate and pale green and expanding.

Full leaf elongation: Leaves have reached full size or turned a darker green color or tougher texture of mature leaves. Tree appears in summer condition, leaves fully expanded, little sky visible through the leaves.

First flowers: One or more fresh unopened flowers or flower buds are visible on the tree.

Open flowers: One or more open, fresh flowers are visible on the tree. Flowers are considered “open” when the reproductive parts (male stamens or female pistils) are visible within open petals.

First seeds: One or more seeds are visible on the tree.

Ripe seeds: One or more ripe seeds are visible on the tree.

Seed drop: One or more mature seeds have dropped since your last visit.

If you simply can’t decide yes or no, you can put a “?” Add some notes to explain what you were seeing that made choosing hard.