Dendroclimatology of Bristlecone Pine

Juston on a bcp

 

 

 

The immediate topographic situation of individual trees (at a scale of 10s of meters) influences the response of their tree-ring-forming mechanisms to climate variability. Rather than seeking to minimize such effects, as is currently normal practice, we are using the topographic situations of the trees to recover the effects of differing aspects of climate along elevational gradients of bristlecone pine. The multi-millennial network of well-replicated chronologies from bristlecone and other pines in the semi-arid southwestern quadrant of the conterminous United States is a major, but inadequately understood, scientific resource.

Its use has been hampered by the mixed temperature and moisture influences on trees in this region found at elevations between 2800 and 3600 meters a.s.l., where the longest chronologies of paleoclimatic interest are found.

We are using two recent advances in dendroclimatology to help rectify this situation. These are:

  • The analysis of the topographic modification of tree-ring response to climate variability (the effect mentioned in the first sentence above) along elevation transects, including Holocene subfossil samples from above modern tree limit, and
  • Process-based modeling of the formation of tree rings. This approach is being applied to tree-ring data from living and precisely dated relict wood below and above the present limit of tree growth in eastern California, Nevada, and the Four-Corners States.

Each of the elements of the approach (topographic analysis using modern geospatial tools, dendrochronological elevation transects, process-based modeling of tree-rings) already exists, but the combination of them is novel and yielding new insights. The problem we are addressing is a difficult one that has challenged dendrochronologists for at least three decades.

  • What are the respective influences of various climate variables and other aspects of the atmospheric environment on the growth of these very old trees?
  • What implications might the answer to this question have for the use of these tree-ring records as natural archives of climate information?

There is a pressing and immediate need for high quality paleoclimate records capable of revealing aspects of climate variability on timescales from interannual to millennial. Undergraduates from WWU are currently assisting in this work which is funded by the National Science Foundation.

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