Nature’s Notebook

Connecting People with Nature to Benefit Our Changing Planet

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Green wave

Project Overview

sugar mapleWe invite you to join us in tracking the “green wave”—the flush of green that accompanies leaf-out–-over the course of the spring season, as well as the spread of seasonal color across the country in the autumn.

Observations of these trees are of extra importance because they can help decision-makers develop forecast models and early warning systems for use in forest management and public health administration via pollen forecasting. In fact, researchers are already using data that have been reported for these species to validate models that predict how changes in climate will impact phenology of trees, and also to learn that deciduous trees may leaf out weeks earlier under climate warming. See what we learned from this campaign last year

Join us for this special campaign! Make it easy on yourself...choose that tree that you see every day - either the one in your yard or the one you pass each day. Observations from just one tree can help fill critical data gaps!

How to Participate...

1. Select one (or more) individual maple, oak, or poplar trees to track from the list below. 

boxelder (Acer negundo)
red maple (Acer rubrum)
sugar maple (Acer saccharum)
vine maple (Acer circinatum)

laurel oak (Quercus laurifolia)
Oregon white oak (Quercus garryana)
northern red oak (Quercus rubra)

balsam poplar (Populus balsamifera)
Eastern cottonwood (Populus deltoides)
Fremont cottonwood (Populus fremontii)
quaking aspen (Populus tremuloides)

Don't have one of the target species at your site? Your observations are still valuable! select from our list of many other maple, oak, or poplar species for which we have protocols.

2. Join Nature's Notebook. If you haven't already, create a Nature's Notebook account. See our specifics of observing if you need more details on getting started.

3. Sign up to receive our Green Wave campaign messaging (in the right sidebar of this page - you may need to scroll back up to see it). You will receive messages approximately every 4-6 weeks during the growing season, providing early results, encouragement, observation tips, interesting links, and campaign-specific opportunities. Don't miss out!

4. Take observations. We invite you to track leaf out in your trees ideally 2-4 times a week, in the spring and autumn. We are especially interested in the following phenophases, though you are welcome to report on flowering and fruiting as well.

Phenophase Definition


(Click to enlarge)

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 (petiole) or leaf base.
Leaves One or more live, unfolded leaves are visible on the plant. A leaf is considered "unfolded" once its entire length has emerged from the breaking bud so that the leaf stalk (petiole) or leaf base 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. Do not include new leaves that continue to emerge at the ends of elongating stems throughout the growing season.
Colored leaves One or more leaves (including any that have recently fallen from the plant) have turned to their late-season colors. Do not include fully dried or dead leaves that remain on the plant.
Falling leaves One or more leaves are falling or have recently fallen from the plant.

 5. Report your observations. As you collect data during the season, log in to your Nature's Notebook account and enter the observation data you recorded. You can also use our smartphone apps to submit your observations! 

2017 Green wave Results

We have had a steady increase in the number of observers reporting on Green wave species over the last five years. Since 2013, the number of observers participating has more than doubled!

Number of Green wave observers reporting

The winter of 2017 was the second warmest winter on record across the continental US. In many parts of the country, the biological start of spring arrived 3-4 weeks earlier than average. Fall also was late in arriving in 2017. In parts of the country, the period of August to October was the warmest on record (

The Activity Curve below shows the difference between 2016 and 2017 in the proportion of northern red oak trees with "yes" reports for breaking leaf buds in the Northeast US. The peak in the number of trees with breaking leaf buds occurred several weeks earlier in 2017 than in 2016. 

Northern red oak breaking leaf buds 2016-17


Colored leaves in northern red oak in the Northeast peaked at about the same time this year as last year. This might reflect the similarly warm fall temperatures that the Northeast experienced last year. 

Northern red oak colored leaves 2016-17

On the other side of the country in the Southwest, the peak in breaking leaf buds in quaking aspen trees was several weeks earlier in 2017 than in 2016. 

Quaking aspen breaking leaf buds 2016-17

Quaking aspen put on their colored leaves at about the same time in 2017 as in 2016, which had similarly warm summer and fall temperatures. 

Quaking aspen colored leaves 2016-17