Using Field and Laboratory Observations to Examine the Impact of a PAN Event on
Sugar Maples in New Hampshire
Michael Handwork, Martha Carlson, and Dr. Barrett N. Rock
2. Variations in Chlorophyll Concentrations
Abstract
A hypothesized peroxyacetyl nitrate (PAN) event occurred on May 26, 2010. As a result, a number of
sugar maples (Acer saccharum) were partially or completely defoliated on Bald Mountain in West Campton,
NH. A MultiSpec image was generated from June 2, 2010 Landsat data that identified the damaged
vegetation as well as other regions in New Hampshire that exhibited the same stress signature. The purpose
of this study was to design methods that could identify post-event damage, and assess the current health of the
Bald Mountain sugar maples. The study revealed anomalous twig morphology on trees that were partially
and totally damaged in 2010. These trees had shorter annual growth units in 2010, anomalous branching
patterns, missing buds, and buds that were present but not open. Light absorbance curves were completed
with the spectrophotometer and chlorophyll concentrations are still being calculated for analysis. Leaves
collected in 2013 from the partially and totally damaged trees were thinner than leaves collected from trees
that were not damaged in 2010 due to a thinner spongy layer and a disorganized palisade layer. Also, the
twigs from the partially and totally defoliated trees showed evidence of anomalous 2010 growth rings.
Figure 1: Absorbance Curves for 5 Sugar Maples
Field – No Damage
856 – Partial Damage & A856 – No Damage
Anomalous Twig Morphology
Photo A – No Damage
Photo B – Partial Damage
Photo C – Total Damage
2012
2012
2011
2011
2010
2010
2009
Figure 2: Peak Absorbance for Leaf Pigments
Figure 2 shows the leaves from the totally damaged
trees (856A & 856B) have the highest levels of light
absorbance. Leaves from one undamaged tree (Field)
had the next highest levels. Leaves from the other
undamaged tree (A856) and the partially damaged tree
(856) had the lowest absorbance levels. Concentrations
of each pigment are still being calculated and analyzed
to fully understand the significance of the data.
Figure 7 is a cross section of a twig from a tree that was not damaged (A856) in the 2010 event. This twig
displays normal annual growth rings. The smaller 2013 growth year is a result of collecting the sample on July
12, 2013. Figure 8 is a cross section of a twig from a tree that was totally defoliated (856A) in May 2010.
There is evidence of multiple false growth rings in the 2010 growth ring indicating that the tree experienced
significant stress in the 2010 growth year.
Discussion
Figure 3: 2013 Leaf Cross Section from
Undamaged Sugar Maple (530x)
Figure 4: 2013 Leaf Cross Section from Totally
Damaged Tree (530X)
UE
Sugar maples on Bald Mountain that were partially or totally defoliated from the 2010 PAN exhibited a
higher frequency of anomalous twig morphology than the maples that were not defoliated. Most of the anomalous
growth occurred in the 2010 growth year which provides historical evidence of the defoliation event. The
chlorophyll concentrations of leaves collected in 2013 is still under investigation. Leaves collected from partially
and totally damaged trees were thinner, which may be an indication that the trees are still recovering from the
stress of the PAN event. Finally, anomalous growth was evident in the 2010 growth rings of the totally damaged
trees. Multiple false growth rings were present indicating a response to significant stress in 2010.
UE
PL
PL
SL
SL
LE
LE
Figure 3 is a SEM image of a leaf cross section collected in 2013 from a maple that was undamaged (A856)
in 2010. Figure 4 is a SEM image of a leaf cross section collected in 2013 from a totally damaged maple
(856A). UE = Upper Epidermis, PL = Palisade Layer, SL = Spongy Layers, LE = Lower Epidermis
Results
2013
2009
3. Anomalous Leaf Anatomy
• Branches were collected with a pole pruner on July 12, 2013 from five different sugar maples on Bald
Mountain in West Campton, NH. Samples were collected from two control trees (Field & A856) that were
not defoliated from the May 2010 event. Branches were also collected from one tree (856) that was
partially defoliated and two trees that were totally defoliated (856A & 856B) in May 2010. Samples of
leaves and twigs were placed in ziplock bags, transported in a cooler, and then stored in a refrigerator.
• Five twigs were analyzed for anomalous morphology from each of the five study trees using a dissecting
scope and 10x hand lens. Characteristic features were also photographed.
• Chlorophyll extraction protocols suggested by Carlson produced enough material to run two replicates for
each of the five trees. Light absorbance was measured using a HP UV Vis Spectrophotometer provided by
the UNH Leitzel Center.
• A Scanning Electron Microscope (SEM) was used to analyze annual growth rings in twigs and leaf cross
sections of leaves collected on July 12, 2013. The twigs and leaves were analyzed from A856, 856, and
856A to compare trees that experienced no defoliation, partial defoliation, and total defoliation from the
PAN event. Fresh leaves were analyzed (wet) and then dried in an oven and sampled again (dry).
Figure 8: Total Damage (36.2x)
2013
Figure 1 displays the spectrophotometer
absorbance curves for the five maples in
the study. The four vertical lines indicate
the peak absorbance for the four pigments
analyzed. Carotenoids are located at 470
nm, anthocyanins at 520 nm, chlorophyll b
at 649 nm, and chlorophyll a at 664 nm.
856A – Total Damage
A defoliation event took place on May 26, 2010 on Bald Mountain in West Campton, NH. Martha
Carlson observed a number of sugar maples that were partially or totally defoliated on May 27, 2010.
Extensive analysis of spectral reflectance data, atmospheric chemistry, leaf anatomy, and meteorological
conditions by Carlson supports the hypothesis of a PAN event as the atmospheric pollutant that caused the
defoliation. Carlson developed a supervised classification from June 2, 2010 Landsat to map the regional
extent of the damage (Carlson et al. 2013). This study focused on identifying evidence of damage to the sugar
maples three years after the PAN event and begin to ground-truth the stress signature identified by Carlson
from the Landsat data.
1.
Figure 7: No Damage (40x)
856 B – Total Damage
Background
Methods
4. SEM Analysis of Growth Rings
Figure 5: Wet Leaf Average Thickness
Figure 6: Dry Leaf Average Thickness
Conclusion
Based on the results to date, the evidence indicates that there is post-event damage from the defoliation
event that occurred on May 26, 2010 to the sugar maples located on Bald Mountain in West Campton, NH. The
field and laboratory observations showed anomalies in the twig morphology, leaf anatomy, and growth rings on
trees that were impacted by the 2010 event. Additional analysis is needed to explore the anomalous leaf anatomy
and possible variations in chlorophyll concentrations to further document the post-event damage.
This summer research experience has provided valuable insight into the process of science. I have had
many opportunities to experience the highs and lows of working through the research process. I have realized
how much time is needed to complete each step properly to ensure the evidence is accurate. The experience has
also highlighted the collaborative nature of scientific research and the need for frequent discussion and
questioning. I look forward to working with my colleagues to incorporate this experience into our high school
science curriculum.
Future Work
Photo A is a control sample (Field) showing normal twig morphology for 2009-2013 growth. Photo B is
from a partially damaged sugar maple (856) from the 2010 PAN event. Photo C shows a twig from a totally
damaged maple (856A). Photos B and C show anomalous growth for 2010.
The two control samples had normal twig morphology except for occasional missing buds, missing first
internodes, and presence of adventitious buds. The partially and totally damaged trees showed a higher
frequency of missing buds, missing first internodes, and a higher number of buds present but not open.
These trees also had examples of anomalous annual growth and branching that occurred at the 2010 growth
year. These anomalies consisted of the following:
• 12 possible buds evident on 4 internodes (856-3)
• 1 cm of growth for 2010; 5-6 leaf scars as well as rings around the twig; possibly 5-6 short
internodes; slight bend in twig (856A-1)
• 2010 and 2011 bud collars side by side with 1-2 mm of growth for 2010 (856A-5)
• Multiple branching at apical bud; three twigs and evidence of a fourth (856A-2)
• 1 internode and 2 leaf scars; bud collar with few rings; minimal growth (856B-4, 856B-2 & 856B-5)
• Ground-truth additional locations in NH that have been identified (11,000 acres) as areas impacted by the PAN
event to confirm the accuracy of the stress signature indicated in Carlson’s paper.
• Develop additional analytical field measurements to document the effects of the PAN event and the annual
recovery of different tree species.
• Design curriculum to be incorporated into high school biology courses in NH and pilot the curriculum at
Winnacunnet High School in Hampton, NH.
Figures 5 and 6 display the average leaf thickness with +1 and -1 standard deviations represented by the
black bars. Both wet and dry samples were taken from the same leaf.
SEM measurements were taken from the upper epidermis to the lower epidermis to determine leaf
thickness. Six locations on each leaf were randomly selected for the measurements. The average leaf
thickness from a tree that did not experience damage was 95.1 µm and 92.8 µm for wet and dry leaves
respectively. A leaf from a partially damaged tree had an average thickness of 60.2 µm for wet and 75 µm
for the dry sample. A leaf from a totally damaged tree had an average thickness of 42.3 µm for wet and 47.1
µm for the dry sample. SEM cross sections of leaves from 2010 damaged trees showed that the decreased
thickness was a result of a disorganized palisade layer and a thinner spongy layer. This anomalous leaf
anatomy may be an indication that the partially and totally damaged trees from 2010 may still be recovering
from the stress of the PAN event.
Literature Cited
Carlson, M., Rock, B. N., and Talbot, R. W.
(2013). Documenting A Defoliation of Maples,
May 26, 2010. (Manuscript in prep).
Carlson, M. Chlorophyll Extraction Protocol (in
prep)
Acknowledgements
• This research was funded through the NSF NH
EPSCoR Program #1101245
• I would like to thank Dr. Barrett N. Rock and Martha
Carlson for their support and guidance on this
research experience.
• We would like to thank Hank Parker for allowing
access to the Bald Mountain sugar maples.