Article Review: Climate Sensitivity to Short-leaf Pines

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.