We have made several informative findings based on these measurements. First, ponderosa pine can both increase (swell) or decrease (shrink) in circumference over time, much like a sponge can change size as it is soaked in water, allowed to dry, and then soaked again. Figure 3 shows the change in size of trees at the low-elevation site during 1992. During the growing season, trees shrank during drier times but quickly swelled following precipitation.