Geoscience Reference
In-Depth Information
are carried by the wind and surface runof into lakes, ponds, and the coastal
ocean. h e abundance, size, and nature of charcoal in sediment are used to
assess the history of wildi res in regions throughout the West. h is area of
study has received much attention, with interest fueled by the growth in
population and economic importance of these mountain areas. As we will see
in later chapters, some of these records show a disturbing pattern of recurring
large i res throughout the region.
Trees
Earlier in this chapter, we discussed how trees contain evidence of climate
histories within their trunks. In addition to bristlecone pines, many other
trees contain valuable information about past climate. Trees have unique
attributes as paleoclimate archives: they stay in one place for centuries or
even millennia, adding new growth layers, or rings, to their trunks every
year. Scientists who understand the specii c biological needs of particular
tree species and the ecological setting of the study area use trees to “measure”
ancient rainfall and temperature patterns.
Of course, no single tree contains a complete climate history. Typical tree-
ring climate chronologies require dozens of individual trees in each study site,
and typically several study sites are needed to produce an accurate regional
climate history. To avoid cutting down large numbers of trees, researchers
have devised a nondestructive method of extracting small-diameter wood
cores that causes no harm. h ese cores are obtained by drilling through the
bark from the outer edge of the trunk to the center. h e extracted cores, as
narrow as long pencils, are scanned into a computer, and the yearly growth
rings are counted and measured. h e width of the rings provides a measure
of annual weather conditions. Good years (for the West, this usually means
wet with a long growing season) produce wider rings, and poor years (drier
and cooler) produce narrower rings. During years of extreme drought, rings
may even be absent.
telling time: dating and age control
Age control is an important aspect of reconstructing past climate change.
Age determinations of sediment samples from cores or other recorders of
past environmental change are critical for placing the records into a larger
