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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

In 2019, we are seeking observations of flowering and leaf color in your maples, oaks, and poplars! These observations will help us learn more about pollen activity and the timing of fall color. Of course, you are are still welcome to report on breaking leaf buds, leaves, and other phenophases as well.

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)*
bigleaf maple (Acer macrophyllum)
bigtooth maple (Acer grandidentatum)
mountain maple (Acer spicatum)
Norway maple (Acer platanoides)
Rocky Mountain maple (Acer glabrum)
silver maple (Acer saccharinum)
striped maple (Acer pensylvanicum)
sycamore maple (Acer pseudoplatanus)

laurel oak (Quercus laurifolia)*
Oregon white oak (Quercus garryana)*
northern red oak (Quercus rubra)*
Arizona white oak (Quercus arizonica)
bear oak (Quercus ilicifolia)
black oak (Quercus velutina)
blue oak (Quercus douglasii)
bur oak (Quercus macrocarpa)
California black oak (Quercus kelloggii)
California live oak (Quercus agrifolia)
chestnut oak (Quercus montana)
Emory oak (Quercus emoryi)
Gambel oak (Quercus gambelii)
huckleberry oak (Quercus vacciniifolia)
live oak (Quercus virginiana)
pin oak (Quercus palustris)
sand live oak (Quercus geminata)
shingle oak (Quercus imbricaria)
Shumard's oak (Quercus shumardii)
southern red oak (Quercus falcata)
turkey oak (Quercus laevis)
valley oak (Quercus lobata)
white oak (Quercus alba)
willow oak (Quercus phellos)

balsam poplar (Populus balsamifera)*
Eastern cottonwood (Populus deltoides)*
Fremont cottonwood (Populus fremontii)*
quaking aspen (Populus tremuloides)*
bigtooth aspen (Populus grandidentata)
blck cottonwood (Populus trichocarpa)
narrowleaf cottonwood (Populus angustifolia)

*Due to their geographic spread, these species are of special interest. 

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 leafing and fruiting as well.

Phenophase Definition


(Click to enlarge)

Flowers or flower buds One or more fresh open or unopened flowers or flower buds are visible on the plant. Include flower buds or inflorescences that are swelling or expanding, but do not include those that are tightly closed and not actively growing (dormant). Also do not include wilted or dried flowers.   Red maple flower buds, Photo: Ellen G Denny
Open flowers One or more open, fresh flowers are visible on the plant. Flowers are considered "open" when the reproductive parts (male stamens or female pistils) are visible between or within unfolded or open flower parts (petals, floral tubes or sepals). Do not include wilted or dried flowers.  Red maple open flowers, Photo: Ellen G Denny
Pollen release One or more flowers on the plant release visible pollen grains when gently shaken or blown into your palm or onto a dark surface.  Not pictured
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! 

2018 Green wave Results

This year, 1,144 observers reported data on Green Wave species at 662 sites. These observers recorded 895 onsets of breaking leaf buds and 959 onsets of colored leaves on their trees - well done!

The winter of 2018 was relatively average across much of the continental US. The biological start of spring arrived 1-2 weeks late across the Southeast, 1-3 weeks early across the mid-Atlantic, southern Appalachia and parts of the West, and 1-3 weeks late across much of the North. In parts of the country, the period of July to September was the warmest on record (

This year, red maples leafed out earlier at southern latitudes than at northern latitudes, reflecting the wave of tree green-up across the country.

Green wave timing of red maple breaking leaf buds 2018

This year, the peak in the proportion of red maples with breaking leaf buds was slightly later than last year. This could be due to the very early spring that occurred across much of the eastern US in 2017.

 Green wave red maple breaking leaf buds 2017-2018

The peak in colored leaves for red maple was also slightly later this year than last year.

Green wave red maple colored leaves 2017-18

We see this same pattern reflected in Northern red oak, with trees at northern latitudes leafing out later than those at southern latitudes. Green wave timing of northern red oak breaking leaf buds 2018


Observers reported the peak in the proportion of oak with breaking leaf buds later in 2018 than in 2017.  

Green wave northern red oak breaking leaf buds 2017-18

As for red maple, the peak in colored leaves for northern red oak was later in 2018 than in 2017.  

Green wave northern red oak colored leaves 2018

For quaking aspen, we see earlier leaf out at lower elevations, and later leaf out at higher elevations. Green wave timing of quaking aspen colored leaves

We see a similar pattern in the timing of the peak for breaking leaf buds in quaking aspen, with a later peak in 2018 than in 2017. 

Green wave quaking aspen breaking leaf buds 2017-18

For quaking aspen, the timing of the peak in colored leaves was about the same time this year as last year. 

Green wave quaking aspen colored leaves 2017-18