Introduction
The researchers in this article propose to use college
campuses in the southeast U.S. for analyzing climatic variability in the
tree-ring width of shortleaf pines (Watkins et al 2018, 147). Because the campuses were established on
former agricultural land, shortleaf pines remain intact on them despite campus development
(ibid., 147). Shortleaf pines can be
used as climatological indicators in a process called dendroclimatology, in
which the analysis of tree-ring width is used to determine their sensitivity to
climate fluctuations. The researchers
are advocating for more evaluation of trees on campus because they are easier
to access and their proximity to other urban sites is ideal for comparative
evaluation (ibid., 149). Only one other
urban site was used in the study, but it was enough to strengthen their
position.
Literature Review
Previous studies on the climatic sensitivity of shortleaf
pines were based on tree-ring data collected in non-urban areas (ibid. 147). A number of studies have demonstrated how
trees in built-up environments experience urban disturbance (ibid. 148), but
few of them have been specifically on the shortleaf pine. The aim of this study is to introduce urban data
on the shortleaf pine to see if it is compatible with other tree species in
urban or exurban settings.
Background and
Geographical Context
The
university selected for the study was the University of North Carolina (UNCG)
in Greensboro. Holding many shortleaf
pines in Peabody Park and the commons (ibid. 149), it is an ideal site because it
is in the piedmont and has a flat topography.
It is also close to other urban sites that have shortleaf pines,
including Green Hill Cemetery. Located
approximately 1 kilometer northeast of the university, the cemetery was
selected as an urban site for comparative evaluation (ibid. 149). The site has a similar climate and soil to
the university, being home to many shortleaf pines that are dispersed inside
it.
Methods Used
One
of the research methods used by geographers to examine vegetation is called
dendrochronology. These studies involve
collecting cores and disks from trees “in order to count the annual growth
rings and reconstruct vegetation changes over the past few centuries” (Gomez and
Jones 2010, 139). The method can provide
evidence of climate changes by measuring the annual changes in tree-ring width
(ibid, 139-140). Researchers in the
study used these methods with several programs that are useful for
dendrochronology to determine statistical evidence of the climatic sensitivity of
shortleaf pines. On the UNCG campus, 19
shortleaf pine trees were sampled. First,
core extraction was used to retrieve the samples from the bases of the
trees. The sampled trees grew near
disturbed environments such as dormitories, buildings, walkways, and roads (Watkins
et al 2018, 151). 12 shortleaf pine
trees were then sampled at Green Hill Cemetery (GHC) using the same procedures. The GHC trees likely had root-structure
disturbances because they were located next to burial plots or access roads
(ibid. 151).
After
collecting the data, software programs were used to enhance it. Ring-width measurements were taken from
samples at both sites to be used in the programs. First, each core was measured using WinDENDRO,
an image analysis system specifically for tree-rings (Image Analysis, n.d.). Cross-dating was then used to evaluate the
accuracy of the annual and relative changes in tree-ring width using a program
called COFECHA (Watkins et al 2018, 151).
Finally, using the program ARSTAN, chronologies from each site were
standardized to correlate them with climate variables.
Data for several climate variables were retrieved from
the Climatic Data Center. The variables
included precipitation, temperature, and drought severity (ibid. 152). These variables were selected because they
are the most consistent at predicting the radial growth of shortleaf pines. Based on previous studies, temperature and
precipitation are the strongest indicators of radial tree-width growth (ibid. 152). Thus it was critical for the analysis of the
data to include them.
Analysis and Discussion
Analysis of the data involved using SPSS, a statistical
software program. The relationship
between chronology and monthly climate variability was determined using
Pearson’s product moment 2-sided correlations (ibid. 152). Both sites were involved in the
analysis. After similar relationships
were found at both sites, the samples were combined to be repeated using the
same analysis with the climate variables.
It was found that the two chronologies from different
urban sources followed a similar correlation and sensitivity pattern to previous
shortleaf pine studies (ibid. 157) that were away from urban settings. However, there was a difference between the
two; samples from the UNGC campus indicated a weaker relationship, while
samples from the GHC indicated a stronger one (ibid. 157). This is likely due to the cemetery having
less disturbances than the university. The
researchers found that by combining the two urban sources, a stronger
understanding of tree-ring chronology was provided- one that more closely aligns
with previous studies.
Conclusion
Dendrochronological studies on college campuses provide a
convenient and inexpensive way of researching the climate sensitivity of
exurban forests, where it is harder to retrieve data. Since the same environmental factors were
found to influence urban trees as exurban trees, it is advantageous to monitor the
annual growth patterns of trees on campus.
Climate sensitivity and urban disturbances are positive indicators for
other environmental issues like loss biodiversity and habitat. Old trees are critical to the ecology of the
southeast, because they provide a habitat for other species- especially in
urban settings, where biodiversity is scarce.
As climate change and urban expansion continue, there will be an
increasing reliance on environmental analysis in urban areas, making the
dendrochronological study of shortleaf pines on southeast campuses essential to
local ecologies.
Bibliography
Gomez,
Basil, and John Paul Jones III. Research Methods in Geography. Chichester:
Blackwell Publishing Ltd, 2010.
“Image
Analysis for Plant Science”. Regent Instruments. Accessed January 31, 2024. https://regentinstruments.com/assets/windendro_about.html
Watkins,
Keith, Thomas Patterson, and Paul Knapp. "Investigating the Climatic
Sensitivity of Shortleaf Pine on a Southeastern US College Campus." Southeastern
Geographer 58, no. 2 (Summer, 2018): 146-163.
doi:https://doi.org/10.1353/sgo.2018.0019.
