Spring is just around the corner!

It’s been a really unusual winter, with almost no snow in the Northeast, and some incredibly warm temperatures. Last winter, at our research site in New Hampshire, the mean air temperature from January to mid-March was -8.5°C (17°F), and with the exception of a single day in late January, temperatures never rose above freezing during the entire first two months of the year. This year, the mean temperature over the same period was -2.9°C (27°F), and the average temperature over the last four weeks has been above freezing.

What will this do for spring phenology? It’s hard to say; the deciduous trees up north are still in a state of dormancy, but I expect it won’t be long before we start to see some buds swelling. The conifers are already starting to get a bit greener a full month earlier than normal. (Their foliage loses some of its vibrancy during the winter, as chlorophyll pigments degrade.)

One thing that I think is great about the PhenoCam network is that it enables citizen scientists to be armchair phenologists. You can travel to different corners of North America to see what the plants are doing, in near real time, all from the comfort of your living room! The green wave of spring is going to be moving north pretty quickly, and through PhenoCam you can watch it spread across the country.

It’s worth checking out what’s happening at the Duke Forest in North Carolina right now. The buds have just started to burst, and it’s pretty neat to browse through the last week’s images and see how rapidly things change from day to day.

Have fun surfing the green wave!

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Friday favorites: Michigan spring

umichbiological2c_2015_05_17_120005With all the different colors, it might look like fall. But this is a spring picture taken at the University of Michigan Biological Station in May of last year. Note the yellowish color of the new leaves as they unfold.

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Phenology from north to south

Hi again!  In my past few posts, I’ve talked about why leaf phenology is different in different places, including places further from, or closer to, urban areas, and different places within a single forest.  Continuing on this theme, today I’d like to talk about how phenology is different across latitudes.

If you live in what is called the temperate zone of the northern hemisphere, generally defined as above the Tropic of Cancer at 23.5º latitude, but below the Arctic Circle at 66.5º latitude, you are probably aware that things are warmer down south.  And, since we know that leaf phenology is largely determined by temperature, you may suspect that phenology would be different in these places.  You would be correct!

In the northern hemisphere, leaves in more southerly climates appear earlier on trees in the spring, and stay on longer in autumn.  This is illustrated in the following figure from this scientific paper:

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We see in panels (a) and (b), that in North America, vegetation green-up, an indicator of the start of spring, begins earlier in the south (blue color), while in autumn the leaves hang on longer (red color).  A similar trend is seen across Eurasia in panels (c) and (d).  You may wonder where information at such a vast spatial scale comes from, to make images such as this.  The answer is remote sensing, a technique where satellites orbit the earth at regular time intervals.  As they do this, the satellites gather images of earth’s surface, and how it changes over time, for example as leaves emerge and senesce.  An earlier blog post by Eli Melaas can tell you a little more about the fascinating practice of remote sensing.

The link between phenology and latitude is important because it allows scientists to study how different climates can affect the same kinds of plants.  This does not happen without some effort, though:  the plants that are native to a certain place are said to be adapted to their local climate.  So the temperature effects on phenology of an oak tree in Florida might be quite different from those for an oak tree in Massachusetts, due to local adaptation.

Scientists overcome this issue by making what are called common gardens.  In common gardens, plants that were originally grown in the same place are transplanted to new locations, to see how they fare in different climates.  This is more easily done with small plants, and one of the largest common garden networks consists of cloned, or genetically identical, lilacs and honeysuckles:

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With information from common garden networks like these, scientists are able to see how identical plants are affected by warmer temperatures, which are likely to represent the climate of the future.

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Friday favorites: First leaves

bartlettir_2015_05_08_120109Spring leaves start emerging at Bartlett Forest in New Hampshire.

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Launching Spring Challenge: Help Us Meet Our Goal!

Since our project started eight months ago, approximately 7,000 participants have made over 105,000 image classifications. And, although the project has come a long way, there are still many more images to be classified before our staff can begin to use those classifications to address some important research questions. For this reason, we are launching our first ever Spring Challenge today.  

For this challenge, we are asking for your help to finish classifying the remaining 9,512 images of spring. Our current rate of classification is about 2,000 classifications per week, so it would take about 4 months to finish these classification with no push. With the Spring Challenge, we hope to get all spring classifications completed in a little over a month. Once all the images from spring have been classified, our group will then be able to start generating research findings from those classifications. This is when you get to see all of your hard work really pay off!  

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Share our Spring Challenge logo! (#SpringSSchallenge)

To meet our goal, we’re going to need all the help we can get. Encourage friends and family to participate (one classification takes less than a minute!) and share information about the challenge via social media. You’ll continue to see updates posted on our project landing page, our Facebook page, and via Twitter (@SeasonSpotter). Thanks for all your continued support of our project! Click HERE to get started!

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Friday favorites: Green Alaska

snipe-lakeBoreal tundra greens up in Lake Clark National Park and Preserve in Alaska.

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Pairs of spring images

Spring is in the air. And for deciduous trees, spring means putting out new green leaves. Scientists still can’t predict with absolute accuracy the date that little green buds appear on trees, but they’ve figured out some of the things that matter: spring temperatures, amount of daily sunlight, and something called “winter chilling,” which can be defined in a number of ways. Essentially, some species may need a certain amount of coldness before they switch into put-out-leaves mode.

When we study spring green-up at the landscape or regional scale, we need to figure out how all the different trees (and other plants) contribute to overall “greenness.” It could be that the first species to put out leaves in the spring are the most important for the regional greenness signal. Or it could be an average over all species. Or it could be something more complicated.

In Season Spotter, we have a particular question for spring green-up, so we can better determine the progression of spring for sites with deciduous trees. In particular, we want to label two points: the “start of spring,” which is the day the first green leaf buds appear, and the “end of spring,” which is the day when the leaves have all fully expanded.

spring-compareTo do this, we show you two images side-by-side of the same scene. The images are taken either 1, 3, or 7 days apart and can be in either order. (In other words, the image taken first is not always on the left.) We ask you to tell us which image has “more or bigger leaves”. We are essentially asking you, “which of the two images comes second in spring?”

Why do we do this, when we know which image came first? The answer is that we want to see if people can visually see a change in leaf progression between the two days shown. If the leaves haven’t yet started to develop in either image, everyone should say that the two images have the same amount of green leaves. And if the leaves are fully developed in both images, everyone should also say that the two images have the same amount of green leaves. It is only in the in-between area when leaves are developing that people should note a difference.

We chose 7 days difference because we know you will be able to see a difference in leaf development in images taken a week apart. We chose 3 days difference because it is common for on-the-ground observers to take phenology measurements two or three times per week – or every 3 days on average. And we chose 1 day difference because we are not sure if people will be able to see minor changes on a day-to-day basis. By analyzing each of the different time lags we will be able to figure out how camera data compares to on-the-ground observations, and what time lag is most efficient for analyzing camera data.

To analyze your classifications, we will line all the days up for a site. We will look at what day everyone starts saying they see a change in leaves and what day is the last day they see changes in the leaves. That will give us the “start of spring” day and the “end of spring” day. We can compare these dates with those that we get from automated processing, from satellite data, and from on-the-ground observations. And we can start to include these dates in statistical models so we can better understand what factors matter for spring green-up at the landscape and regional scale.

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In this made-up example, each green dot is one person’s classification. If a dot is at the bottom, then that person thought the two images had leaves at the same development stage . If a dot is at the top, then that person said the leaves in one image were ahead of the leaves in the paired image. We can use the agreement among classifications for each pair to determine the first and last days of spring.

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