Large-scale perturbations were addressed in the study, because the study area was a fairly large
area, PLSR data were spatially extensive and it was mentioned in the article that the
environmental change was ubiquitous.
Chemical, biological as well as physical perturbations were all addressed in the study, because
the study was to compare the forest compositional change due to American settlement with the
change predicted under 2X CO2 and 3.5X CO2, where CO2 change is essentially a chemical
perturbation. Human activity such as deforestation can be considered a physical perturbation.
Tree diseases and biological invasions which were mentioned, can be considered a biological
perturbation.
The perturbations which happened or were predicted to happen were reflected on FCTs in the
study. FCTs could be considered a part of land surface or earth’s surface. Therefore land surface
is addressed and there’s little information regarding ocean and hydrologic cycle in the article.
The study was to measure the forest compositional change from pre-settlement to present as
well as the change predicted in terms of CO2 change. So the time scales in this study are as large
as centuries.
Human-caused perturbations were specifically noted and discussed in this article, with a stress
on deforestation, fire frequency and tree diseases, the impacts on society however weren’t
specially noted.