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Timing of Green-Up

What is Phenology?

Why does this plant look so green in the summer? Chlorophyl is a green pigment in plant that helps the chloroplasts photosynthesize. Photosynthesis converts Carbon dioxide and water into carbohydrates(sugar) and oxygen. The green chlorophyl in plants needs light and temperatures above freezing to work. Plants in green up in the tundra when the days lengthen and warm in the spring. In the fall, when freezing temperatures arrive, the chlorophyl dies and other plant pigments such as reds, oranges, and yellows appear as fall colors until the leaves fall an die before winter. Phenology is the study of these seasonal changes in life.


  • phenology
  • chlorophyll
  • photosynthesis
  • carbohydrate
  • chloroplast
  • green-up
  • DOY
  • NDVI
  • % Greeness

Learning Objectives

The Timing of Green-Up

Each spring, as the snow melts away and the days become longer, the plants of the tundra turn from brown to green. Plants turn green when they are actively growing and making food from sunlight through photosynthesis. Many birds and animals rely on this new plant growth to feed their babies and develop enough fat to make survive through the winter. The younger green shoots of the plants are more nutritious than the tall tough leaves. The early transition from brown to green in the spring produces the best food for certain types of geese.

This is bear berry. The same plant shown in red above. During the growing season when the plant is producing food through photosynthesis, the leaves are green.[Figure2]

How do Scientist Measure Green-Up?

Method 1. Direct Observations

Scientist describe the percentage of green as a measurement of how much active growing has started in tundra plants. To collect this data a person would go outside to the same spot each day and estimate the percentage of the ground that is green each day. Digital Cameras have helped to improved the collection of this type of data by allowing a tiny computer to take one picture a day over many days and store that on a computer card with the date and time the picture was taken. Later, all of the data for one year can be compared at one time. The date at which more than 50% of the grass is green is called “Green up” The video below shows green-up taken using this method with a remote camera at Tutakoke Camp research site.The camera was set out when the snow cover melted and left until to the fall.  It recorded the tundra turning green as the plants warm up and begin to grow. The new green growth is important to young geese. Watch the video and pause the clips to find the dates for these events.

Before you start the video, make a prediction: On what day of the year does the tundra turn 100% green? 

On what date in 2014 does the tundra begin to green up?

On what date does 50% of the ground look green?

On what date does 100% of the ground look green?

Method 2. Satellite Observations

Scientist can use satellite instruments to measure the change from brown to green as the Normalize Difference Vegetation Index or NDVI. When plants are growing, the green chlorophyll reflects and scatters a type of near infrared light wave length more than plants that are brown and not growing. This allows scientists to measure and monitor plant growth by satellites that can take pictures of infrared wavelength and translate this into an NDVI number. Very low values of NDVI (0.1 and below) correspond to barren areas of rock, sand, or snow. Moderate values represent shrub and grassland (0.2 to 0.3), while high values indicate temperate and tropical rainforests (0.6 to 0.8).

Explore More about NDVI

Watch the video to learn more about NDVI and how it can affect animal patterns. You can explore the idea more by completing this activity described in the video. The handout is linked here (Student Handout Globe Lesson on NDVI).

Explore More

Both scientists and Yupik elders have observed a shift in Alaskan climate. Observations include winters that are warmer and a decrease in snowfall. Alaska has experienced the largest shift in temperature of any state in the US.

What do you think will happen to the average date of 50% green up as the climate increase in temperature?

 The more data we can collect on green-up the more we will learn. It is important to use different techniques to collect the data and make sure there is a lot of evidence that supports are understanding of nature. When multiple kinds of data support the same results, the data is accepted with less doubt than from data with just one sampling technique.  Traditional Knowledge, Citizen-Based Science and formal western science can work together to help us come up with the best understanding of how our world works.

Help us gather more data on the green up of the tundra by volunteering to place a Pheno-Cam in your village or school.  Or post your pictures to the Seasons on the Delta Phenology Blog.

You can help scientist gather evidence to support predictions about climate change by supporting a Green-up phenol cam at your school.  A small time lapse camera is set up with a clear view of the tundra to the north. The camera needs to be set up in the spring before the snow melts. Every 2 months, the camera card and batteries should be changed. The camera and the card should then be mailed back to the district office . Please contact for more details