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Age-based population dynamics of Opuntia engelmannii, a shrubby cactus with flattened cladodes, were investigated at a Sonoran Desert site protected from grazing since 1907. Demographic statistics were determined from births and deaths on six permanent vegetation plots mapped four times between 1968 and 2001. Moderate longevity (13–56 years) and modest per capita annual survival (0.9298) were associated with fairly rapid turnover; cycles of population growth and decline were thus evident over relatively short periods. Age–frequency distribution, determined for subpopulations in two neighboring habitats in 1996 and 2003, was used to calculate residual regeneration, an index of the difference between observed cohort...
In the northern Colorado Front Range, fire suppression during the 20th century is believed to have created a high hazard of catastrophic fire in ponderosa pine (Pinus ponderosa) forests. Since the early 1990s, resource managers have increased the use of prescribed fires to re-create fire regimes and forest structures similar to those of the pre-Euro-American settlement period in order both to reduce fire hazard and to improve forest health. To improve understanding of historical fire regimes, we conducted a study of fire history along an elevational gradient from \sim1830 to 2800 m in ponderosa pine forests in the northern Front Range. Fire-scar dates were determined from 525 partial cross sections from living and...