1. Aspen Age Effect on winter Hardiness
By Hannah Reyes
Winter Ecology- Spring 2017
Mountain Research Station, CU Boulder

2. Aspen’s Winter Photosynthetic Acclimations
Aspen are cold tolerant deciduous trees that have adapted ways to survive Colorado winters
Aspen are able to photosynthesize during the winter using chlorophyll-containing living bark tissues called chlorenchymes
By recycling carbon chlorenchymes are able to continue photosynthesis in the absence of leaves
Aspen bark provides up to 15% of the total photosynthetic surface (Schaedle et al ).
touch on carbon balancing more

3. Does the age of Aspen affect their winter hardiness?
Guido Aschan (2001) found that younger tree twigs have higher chlorophyll content since they are able to metabolize more efficiently with thinner bark.
The older trees get, the more gray their bark becomes.
Pearson and Lawrence (1958) found trees with darker green bark are more winter hardy due to higher amounts of chloroplasts.
Some Aspen with higher bark chlorophyll content are more resistant to fungal infections and mature faster (Kharouk et al. 1995)

4. Hypothesis Does the age of trees affect their chlorophyll content?
If the null hypothesis holds true there should be a p-value greater than 0.05 which would indicate that there is a high enough amount of uncertainty to support the null. However, if our alternate hypothesis is true, our chi-squared test should give us a very small p-value indicating that there is little uncertainty that the variable are unassociated.
Testing in the field the chlorophyll content of young and old trees and statistically inputting data allows to understand whether or not there’s a difference in the chlorophyll content of different age dependent trees.
The higher the chlorophyll content the more winter hardy the trees should be because of photosynthetic rates, and protection from various infections.
Expectations are a difference in chlorophyll content between young and old trees, more specifically younger trees having more chlorophyll than older trees.

5. Design I used 25x25 meter plots of land with old and young trees
Aspen were categorized as young by whether or not they exceeded 2 meters
Using a random number generator, I selected x,y coordinates and selected young and old trees nearest to the point
Photos were all equally taken
I selected for high visibility by taking photos of the bark when the sun was it’s brightest
I used a greyscape to compare
I categorized the bark 1-4
For my data, I decided to find three 25x25 meter plots of land with an abundance of old and young aspen
Aspen were categorized as young by whether or not they exceeded 2 meters
Using a random number generator, I selected an x and y coordinate and selected young and old trees nearest to the point to randomize my project
Photos were taken at the same angle which was ~320 degrees northwest.
I selected for high visibility by taking photos of the bark when the sun was it’s brightest
For reference I used a greyscape to compare
I categorized the bark 1-4 with 4 having the highest intensity
Some sources of error could potentially have been the accuracy of my rating scale

6. Methods Bar plot used to visually interpret data
I used the statistical test chi squared to determine if there was a significant association between my two variables- old and young.
This test helps us refute the null hypothesis by showing a significant relationship between our predictor and response variables.
Run an ANOVA to compare difference of means between ages and their average tree bark intensity

7. Results
bar graph and p-value

8. Results Chi-squared Test ANOVA
With a p-value of it’s clear that there is a significant correlation between age and intensity of tree bark color which can refute the null hypothesis that there is no difference between tree age.
ANOVA
Running an ANOVA I also got a very low p-value( 4.86e-5) indicating that there is a significant difference in the means of the two categories bark intensity

9. Discussion
With the aspect of aspen’s chlorophyll content, it’s clear that my data and analysis supports the hypothesis that younger trees have higher chlorophyll content than older trees
The chlorophyll from the inner bark allow the tree to continue growing and have enough energy during the winter
Reasons for the higher chlorophyll content are because smaller trees have less surface area which is needed to be exposed to sunlight.
This could support the idea that younger trees are more winter hardy than older ones since it aids in the ability to photosynthesize in the winter due to lack of leaves.
Further research for winter hardiness should look at variables besides photosynthetic ability (i.e. water usage or storage, etc.)

10. Summary
In summary there is a correlation between tree age and chlorophyll content
Younger trees have darker bark indicating that there is more photosynthesis happening
Reasons are tree bark surface area and their ability to metabolize the sunlight given.
summarize main points

11. Acknowledgements
MRS, Professor Kittel, and everyone who helped me code

12. Citations
Kharouk, V.I.; Middleton, E.M.; Spencer, S.L.; Rock, B.N.; Williams, D.L.; Apps, M.J.; Price, D.T.; and Wisniewski, J., "Aspen bark photosynthesis and its significance to remote sensing and carbon budget estimates in the boreal ecosystem" (1995). Aspen Bibliography. Paper
Aschan, G., Wittmann, C. & Pfanz, H. Trees (2001) 15: 431. doi: /s
Pearson, L.C.. Lawrence, D.B Photosynthesis in Aspen Bark. American Journal of Botany 45(5):