摘要：I replicated and analyzed six photographs taken in A.D. 1870 near the subalpine forest-alpine tundra ecotone in the northern Uinta Mountains to quantify changes in the distribution of vegetation. Three dramatic differences were noted. First, the historical photographs document a treeline 60 to 180 m (mean of ∼100 m) lower than at present, with greater depression on west-facing slopes. Given the modern lapse rate for mean July temperature (6.9°C km −1 ), this difference corresponds to a temperature depression in A.D. 1870 of 0.4 to 1.2°C (mean of 0.7°C). Second, timberline forests in A.D. 1870 were significantly ( P < 0.01) less dense, with tree densities approximately half those measured in the modern photographs. Third, the area of floodplain meadows decreased ∼75% from A.D. 1870 to the present. Because the original photographs were taken within a few decades of the end of the Little Ice Age, ca. A.D. 1850, I assumed that differences in vegetation distribution documented in the repeat photographs represent the biotic response to climate warming over the past ∼130 yr. This analysis provides an independent estimate of the magnitude of growing season temperature depression during the Little Ice Age.
