Harvard Grad Student Looks at 12 years of Schoolyard Data

Harvard University Graduate student, Nate Edelman, was able to analyze  the data that thousands of K-12 students have contributed to the Harvard Forest Schoolyard Ecology program  over the past 12 years. 

So what is all the data showing anyhow?

Nate has created a series of graphs from the complex and large Buds, Leaves and Global Warming project dataset.  We are pleased to share these graphs with you now.

Until now, we have focussed most of our data analysis efforts on helping you, teachers, to understand our Project Ecologists' long term data as well as to represent patterns in your own site's data.  Last year, we were challenged by  The Long Term Ecological Research (LTER) network to do some synthesis of Schoolyard data over time and across sites to see if any patterns are evident.

The first six graphs here are looking at the timing  of leaf fall  for Sugar Maple (Acer Saccharinum), Red Maple (Acer Rubrum),  Black Cherry (Prunus Serotina), and Black Birch (Betula Lenta), Oak (Quercus) and Beech (Fagus) across Schoolyard Ecology field sites over 12 years.

How to interpret these graphs:

According to Nate Edelman, the blue lines on these graphs is a "smoothed Loess regression" calculated by R (Graphing program), which uses information from before and after each date to estimate the mean value for that date.  The grey area is the 95% confidence interval for that estimation.  The black dots are the calculated  means using only information from that exact day.  

Notice that the line drops towards the end of the season in these 2 figures above.  We would not expect the line to go down because more leaves would presumably fall at the end of the growing season. Please see Nate's comments followed by my comments  below to understand why the curve took this unexpected turn.  

Nate's thoughts about the drop in percent leaf fall of Oak and Beech at the end of the season:  
 I've plotted a histogram of the number of observations taken on each Julian data  and superimposed it on the leaf fall graph.What they show is that the number of observations reported dropped significantly at the end of the year, and that's when we get the unexpectedly low values.  I have an idea for how to get around this but didn't have time to test it out yet. 

Schoolyard Coordinator notes:  Please keep in mind that both species of Oak and Beech frequently retain leaves through much of the winter.  The leaves turn brown but many do not fall in the autumn when leaves from other species typically fall.  Some researchers stop monitoring leaf drop once most of the leaves have turned brown.  Our protocol asks to record oak and beech leaves as fallen after they have turned completely brown, in order to show that those leaves have stopped photosynthesizing and therefore the growing season is officially over for those leaves.  Sometimes, researchers forget to mark the leaves as "fallen" and this affects the ability to accurately graph the end of the growing season.    I'm interested to see that even Red Maple leaves fallen go down which must be due to far fewer observations at that time per Nate's notes above. 

                                               

Comparison of Schoolyard Data to  Project Ecologist, John O'Keefe's Data 

The next thing I did (above) was to take the two species we talked about, red oak and red maple, and compare them to John’s data. Qualitatively, the data for average 50 percent leaf fall and bud burst look similar, but when we look at the leaves on days, there are some fairly major discrepancies. In John’s data, there is a nice consistent separation of about 3 weeks of leaves on days between the species. However, the schoolyard data has some years in which the maple has a longer growing season than the oak, and in all cases the difference was much smaller.  
               

Below, I made the J.O.K.-style graphs and the leaf fall curves for each of the four species mentioned above, as well as black birch and black cherry

 -Nate Edelman

What is the spatial distribution of trees in the study?

Finally (Below),  I used the same species and tried to get a more geographical perspective. I combined the data by town, and made two maps for each species. One is the average number of leaves on days across the whole experimental period. The size of the dot corresponds to the number of years of data we have, and its color corresponds to the number of leaves on days.   

-Nate Edelman

          

 

 Below are map graphs of the most common 3-5 species with the larger circles showing where there are more trees of a certain species. I looked at the number of individuals of each species, and a natural cutoff seemed to be at 4 species (Red Oak, Red Maple, Sugar Maple, and Beech). I grouped all the trees by town, and plotted circles on those towns with sizes corresponding to how many trees of each species were used. I made two graphs – the first one is of unique trees, and the second is of all observations. So if a certain town had a single Red Maple, it would show as a small circle on the first graph, but if they had followed it for several years and had many records, it would be relatively larger on the second graph. I also included the total numbers next to the key. These graphs can unfortunately be a little hard to read because so many of the points overlap one another.

-Nate Edelman

The other graphs below show the change in leaves on days across the time period. I only included sites that had at least three years worth of data for this, and the color corresponds to the slope of the regression line. Positive slope (and red color) indicates an increase in growing season length. Negative slope (and blue color) indicates a decrease in growing season length. There is a big caveat here, which is that to get the growing season each year, I averaged the 50p bud burst and the 50p leaf fall for that town and took the difference. That would be fine if there was lots of data, but sometimes there were very few (or only one) trees, and they might be different trees for the bud burst date vs the leaf fall date! This is in contrast to John’s data, where we are looking at the exact same tree each season and each year.

                                                                                                       -Nate Edelman 

Stay Tuned for Multi Site Graphing Tool Next Year...

Harvard Forest Information Manager, Emery Boose, has proposed developing some cross site analysis capability using  Schoolyard Ecology Online Graphing tools.  In the meantime, give it a try using your graphing method and send us some examples!

Links for More Information on Harvard Forest Schoolyard Data Synthesis:

Dr. John O'Keefe's Phenology Graphs 2016.pdf to see graphs of 26 year dataset. 

Download Schoolyard Ecology Data from our online database to see all student generated data

Buds, Leaves, and Global Warming Schoolyard Ecology Project Information and Resources

Interactive Field Site Map to access data by school field site locations. This map will be updated this winter to include  schools who have joined our projects this year. 

A Peek at Student Learning; Graphs,and Notes from Schoolyard Students

What do Students Understand from Schoolyard Ecology?

A Collection of Samples of Student Work related to Harvard Forest Schoolyard Ecology studies

This illustrated poem was excerpted from  a  final report from a High School student in Jana Matthei's Notre Dame Academy Environmental Studies class in Hingham, MA.    

At Harvard Forest, we are very interested in getting a sense of the learning outcomes for students engaged in our Schoolyard Ecology projects.   One of the most direct ways to do this is to look at student work related to project themes.   Last year's blog of student samples related to the Vernal Pool project. This year, we have some samples related to the ever popular, Buds, Leaves and Global Warming project.  

Sample introduction, graphs, and conclusion from students at Notre Dame Academy:  

Harvard Forest Introduction:

Over a period of five weeks, my group and I observed two branches on our Red Maple tree. The common name is Red Maple, while the scientific name is Acer rubrum. The Red Maple normally begins budding during late winter-early spring. It buds earlier than most other trees during the springtime and it is one of the first to change color during the fall. Because the leaves on the Red Maple bud earlier than other trees, I predict that senescence will occur earlier than other trees. The Red Maple is one of the most widespread trees found in North America and can grow between 60-75 feet tall. The Red Maple is considered a deciduous tree and is best grown in wet areas. We examined the color change of the leaves and when they fell off of the trees, which marks the end of the growing period. My group and I were nicknamed, “The Tree Huggers” and on both branches we observed six different leaves. We calculated the percentage of leaves that were not green on Branch A and Branch B. Each week, my group and I recorded our outdoor observations about the weather, temperature, and how much of the leaves were eaten by insects. Our Honors Environmental science class is learning about phenology, which is the effect that climate is having on the trees, study of the life cycles, and how the leaves are changing due to climate.

Sample Graph from Student Report

Students formed conclusions about what their  tree phenology data were saying:  

Conclusion:

After reviewing the results of the other trees in my Honors Environmental Science class, I came to the realization that the Red Maple tree does not have the longest growing period. Based on the results in the table, I concluded that one of the Black Oak trees, one of the Black Birch trees and one of the Black Cherry trees began their growing period on the same day as the Red Maple tree.  The tree with the longest growing period is the Black Oak tree, while the tree with the shortest growing period is the Black Birch. The Shagbark Hickory has the earliest beginning of the growing period. Although the Red Maple tree is one of the trees that flowers earlier than most trees, it does not have the longest growing season. I predict that the Red Maple tree’s growing period varies depending on the climate in the fall and in the winter. I think that if there is a rainy spring, the leaves will begin to bud earlier verses when there is a dry spring. There are some modifications that I would make to the project. I think that students should upload information onto a class discussion board on the portal.  Everyone would be able to share information with one another about various tree growths, leaf fall, weather notes and observations. Next year, I think that students should find a way to use the excel document on the iPads because there were many technological difficulties with the computers.  

Another Sample Student Graph from Notre Dame Academy

See two complete student Phenology study reports at: 

Student Phenology Report Sample 1.pdf

and 

Student Phenology Report Sample 2.pdf

Samples of data analysis work done at Holyoke Catholic High School: 

Students in Lise Letellier's Holyoke Catholic High School freshman Environmental Science class first input field data onto an Excel worksheet including growing season calculations

Students then entered the growing season length  from larger table on this individual table in order to develop bar graph to the right.

After producing a variety of graphs, students formed a conclusion about what the data for their project was indicating.  

A student with severe learning challenges, formed the following conclusion from their study:

Conclusion


The purpose of this observational study is to determine if there are any patterns in the lengths 
of growing season of different types of trees and the different years of each tree. We are also trying to determine if the growing season length of the trees is getting shorter, longer, or staying the same over the years. At first it seemed that the data of this tree was very random and had no pattern but after comparing it to the data of other trees of the same species I can tell that the trees growing seasons are very slowly getting shorter and shorter every year and may continue to get shorter as the years go on. The average growing season of the tree is about 180 days long but shortens about 5 to 10 days every year. I think this will continue until the tree either stops producing leaves or will eventually die. The earliest growing season started for this tree was in 2012 where the leaves started to bud at around April 13th. The latest growing season it had ended was in 2013 where 100 percent of the leaves had fallen by November 2nd. The latest growing season had started was in 2014 starting at around April 28th and the earliest a growing season had ended was in 2015 ending at around October 25th. So far this information makes me assume that the older the tree gets, the growing seasons may be getting shorter and shorter every year.

An honors student formed this summary from their analysis of project data:   

Summary:
The purpose of these observations is to answer the questions of when the growing season starts and ends. It also answers how long the growing season is and if the length of the growing season is changing. In order to answer these questions data was collected on leaf growth and budburst in the spring and on the percent of leaves fallen and the tree color in the fall. This is the data collected for Tree 17. Tree 17 is a crabapple tree on Springfield Street.
Tree 17’s growing season started the earliest in 2012. The leaves started growing the earliest and were the longest this year. The buds were 100% open before the observations started. In 2013, the leaves started growing later and took longer to reach their maximum length. In 2014, the leaves took the longest to start growing and reached 100% budburst the latest. This shows that the growing season has been starting later for Tree 17 over the years.
In 2012, the leaves started falling the earliest. In 2013, the leaves started to fall the latest, but 100% of the leaves were fallen the soonest. Also in 2013, the tree took the longest to start changing color and took the longest to reach 100% not green. In 2014, the tree color started changing the earliest and reached 100% not green the earliest. In 2015, the leaves took the longest to all fall off. As years have progressed, it has taken longer for all of the leaves to fall off, except for 2012, which was in between 2014 and 2015.

There was only enough data to calculate a definite growing season for 2013 and 2014. For 2012, only the minimum growing season could be calculated. There was no data for spring 2015 so no growing season could be calculated for that year. The growing season for 2012 is equal or greater to 228 days. This is the longest of the calculated growing seasons. The growing season for 2013 is 208 days, and the growing season for 2014 was 205 days. 2014 had the shorted growing season of the calculated years. The growing season of Tree 17 decreased over time. There was a large decrease between 2012 and 2013 and a smaller decrease between 2013 and 2014.
Tree 17’s spring and fall data was compared to that of Tree 24. Both trees are crabapple trees. Both trees had their earliest budburst in 2012. In addition, for both trees, the year in which they took the longest to drop all of their leaves was 2015. Unlike Tree 17, Tree 24 started to lose its leaves earliest in 2013.
Tree 17’s data was also compared to that of Tree 12. Tree 12 is an exotic cherry. In all years, the leaves on Tree 24 started falling earlier and reached 100% fallen sooner than the leaves on Tree 17. In 2012, the budburst for Tree 17 started earlier than the budburst for Tree 24. Both trees had very rapid budburst in 2013 and 2014. In 2013, the budburst for both trees started and ended on the same dates and in 2014 the budburst started on the same date for both trees.

Overall, Tree 17’s data shows that the growing season has been starting later, ending later and that the overall growing season has been becoming shorter over time.

A "regular" level student make the following analysis:

Questions:
1. Yes, I can determine how long my tree’s growing season is. In 2012 the growing season started around April 23 and ended around October 28. In 2013, the growing season started around April 26 and ended around October 29. In 2014, the growing season began around May 8 and ended around October 31. In 2015, the growing season began around May 6 and ended on November 9. The growing season was about six months in 2012. In 2013, the growing season was about six months also. In 2014, the growing season was about a little less than six months. In 2015, the growing season was about six months also.
2. The leaves burst out first in 2013 around April 23. The leaves fell off first around in 2012. The leaves burst out last in 2014 around May 8. The leaves fell off last in 2015 around November 9.
3. In comparison to my data, Tree #4, which is a Hawthorn also, in 2012 had the same growing season. In 2013, they again have similar growing seasons. In 2014, there is no data for the start of the growing season, but they end around the same date. In 2015, tree #4’s growing season starts within a week of each other but there is no data of tree #4’s growing season ending.
4. In comparison to my data, Tree #1, which is an Eastern Hornbeam, the growing season in 2012 and 2013 started around the middle of April and ended around the middle of November. In 2014 and 2015 the growing season started around the end of April and the beginning of May and ended around the end of November. Their growing season is longer because it starts around the same time but ends later.

5. The tree’s growing season in the last four years have all been around six months, but each year the leaves burst later each year except for in 2013, and the leaves fell off later each year.


Results Statement:
The growing seasons of the trees on our campus were observed. The growing season of Tree 3 – Hawthorn in 2012 was about 190 days, in 2013 was about 180 days, in 2014 was about 180 days also, and for 2015, we were unable to calculate the data because we did not have the data entered for when the leaves were 50% fallen. Tree 20 – Red Maple’s growing season was about 185 days in 2012, 2013, and 2014. We were unable to determine the growing season for 2015 because the data was not entered for when the leaves reached 50% fallen.
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In order to compare the trends discussed in the  student work above, here is a graph by John O'Keefe of his own data recorded at Harvard Forest over 26 years, up through 2015:

We'd love to hear what teachers, educators, ecologists and other students have to say about what we are learning from this work, and what remains confusing or unknown.

Please provide feedback and questions about this blog entry directly or email Pamela at: psnow@fas.harvard.edu

Teacher Overview,  Directions and Rubric, along with more student work samples are available on our website. Search for these 9 documents under Buds, Leaves and Global Warming heading beginning with Letellier. 2016.http://harvardforest.fas.harvard.edu/schoolyard/lesson-plans

To find these schools on our field site map and explore their data on our online database, go to: Schoolyard Buds and Leaves Field site Map

To see the field protocol and related materials for this Schoolyard Ecology study, go to:  http://harvardforest.fas.harvard.edu/buds-leaves-global-warming

WELCOME NEW SCHOOLYARD TEACHERS!  

Thanks to our Mentor Teachers and Project Scientists

27 Teachers participated in the Harvard Forest Schoolyard Ecology Summer Institute for Teachers in August. Twenty of those are beginning Schoolyard projects for the first time.   Four of our experienced teachers served as official Mentor Teachers to support new teachers along with our 3 project Scientists, and 2 Harvard Forest education staff.

Photos by Clarisse Hart

Project Ecologist David Orwig and Mentor Teacher, Kate Bennett, introducing new Schoolyard Teachers to the Woolly Bully project

Teachers from the Hemlock Woolly Adelgid group said this about what they gained from the Summer Institute: 

• My students will be excited to participate and be responsible for a real-life scientific project (at least I hope they will be!) :) I learned a lot more about the HWA than I previously knew, and I am excited also about helping to contribute to the body of knowledge to control the pest.

• I'm in the woolly bully group and I really enjoyed the presentation on how to do the field study. I thought it was very helpful and David was very thorough in his explanation. I feel more confidant executing this project.
• Learning about the life cycle of the HWA, and how to identify at various life stages. How to read the forest and generally assess forest health/presence of HWA. (In response to question about the most valuable aspect of Summer Inst.)  

 
Project Ecologist, John O'Keefe and Mentor Teacher, Maria Blewitt showing new Schoolyard teachers how to identify trees for the Buds, Leaves, and Global Warming project.

Mentor Teacher, Lise Letellier and John O'Keefe help teachers practice labelling trees for Buds, Leaves, and Global Warming study

Teachers from the Buds, Leaves, and Global Warming group said this about what they gained from the Summer Institute: 

• Specific modeling of how to flag branches, how to use database and graphing
• Identifying the leaves and learning how to mark the trees so students can successfully begin collecting data.
• Lise (mentor teacher) was great. Having the experienced teachers talking about their experience implementing the project was super helpful.

Research Forester, Emily Silver, teaches how to lay out a plot

for the Our Changing Forests project. (left)

Mentor Teacher, Melanie McCracken, helps teachers practice laying out a plot. (below)

Teachers from the Changing Forests group said this about what they gained from Summer Institute: 

• Confidence in taking a more rigorous approach to field data collection (tree ID not just DBH measurements, site orientation); sense of connection to & importance in larger project.
• How to begin the process of choosing the plots that my students will use for this study. THe materials that have been supplied are very valuable as well.
• very helpful, and not overwhelming. Seems very doable in my class
• It was very helpful having the mentor teacher (Melanie McCracken) in the field with us, giving us suggestions for what worked with her class.

 Data Manager, Emery Boose, previews the Online Database

Teachers said this about what they gained from the Data presentation:

• Great ideas, and a great support system to implement this project right away in the classroom. I am especially excited about the graphing capabilities of the database and the tremendous resources available on the website.
• The value of long term data collection (in response to what was most valuable aspect of the Summer Institute)

What is the most valuable thing you will take away from today's workshop?

• Confidence that I can translate the protocol to success for my students
• That this is very doable in my curriculum and does not require an immense amount of background. I did expect it to be more overwhelming. Now, I'm just excited!
• Dedicated time to learn from others about how to setup and implement this study on our field site and in the classroom
• Knowing how to do the set up will be very valuable!
• Project is achievable without the necessity of lots of forestry experience. There are also many people who can support my efforts as I move through the project.
• A new science project students in our schoolyard habitat program can participate in as citizen scientists.
• Fits nicely with AP Environmental Science
• Fantastic program!!!

• • Thanks All!