Another advantage of tree rings is that they are clearly demarked in annual increments, as opposed to other proxy methods such as boreholes.
Along with the advantages of dendroclimatology are some limitations: confounding factors, geographic coverage, annular resolution, and collection difficulties.
[citation needed] There are multiple climate and non-climate factors as well as nonlinear effects that impact tree ring width.
In theory, collection of samples from nearby limiting stands of different types (e.g. upper and lower treelines on the same mountain) should allow mathematical solution for multiple climate factors[citation needed].
Non-climate factors include soil, tree age, fire, tree-to-tree competition, genetic differences, logging or other human disturbance, herbivore impact (particularly sheep grazing), pest outbreaks, disease, and CO2 concentration.
[citation needed] In general, climatologists assume a linear dependence of ring width on the variable of interest (e.g. moisture).
For instance, at the upper treeline, where the tree is "cold limited", it's unlikely that nonlinear effects of high temperature ("inverted quadratic") will have a numerically significant impact on ring width over the course of a growing season.
[citation needed] Botanical studies can help to estimate the impact of confounding variables and in some cases guide corrections for them.
[citation needed] While the rendering and analysis of data from thermometer records largely suggest a substantial warming trend, tree rings from these particular sites do not display a corresponding change in their maximum latewood density or, in some cases, their width.
In perhumid tropical regions, Australia and southern Africa, trees generally grow all year round and don't show clear annual rings.
In some forest areas, the tree growth is too much influenced by multiple factors (no "limiting stand") to allow clear climate reconstruction[example needed].
This problem can be dealt with by more complex modeling (a "lag" term in the regression) or by reducing the skill estimates of chronologies.
Generally, tree rings are collected using a hand-held borer device, that requires skill to get a good sample.
This tradeoff is made more difficult, because sample collection (in the field) and analysis (in the lab) may be separated significantly in time and space.
Measuring radiocarbon concentrations in tree rings has proven to be useful in recreating past sunspot activity, with data now extending back over 11,000 years.