Comparison of historical and contemporary forest structure and composition on permanent plots in Southwestern ponderosa pine forests

ABSTRACT. We compared historical (1909–1913) and contemporary (1997–1999) forest struc-ture and composition on 15 permanent plots in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests of Arizona and New Mexico. We used the same sampling methods as in the early 1900s and compared stand density, diameter distributions, species composition, and broad age classes from the two periods. Stand density (trees 9.14 cm dbh) significantly (P 0.001) increased on plots from an average of 77.4 trees per plot (s 49.9) at plot establishment in 1909–1913 to 519.1 trees per plot (s 252.3) at remeasurement in 1997–1999. Basal area significantly (P 0.001) increased from 8.0 m2 per plot (s 3.5) to 28.5 m2 per plot (s 10.1). Contemporary tree diameter distribution shifted toward smaller size classes as demonstrated by a significant (P 0.001) decrease in quadratic mean diameter from 38.5 cm (s 7.5) in 1909–1913 to 28.6 cm (s 7.1) in 1997–1999. Broad age classes yielded an average of 61.5 (s 49.5) residual live trees classified as “blackjack ” ponderosa pine (P. ponderosa150 years) and 13.3 (s 11.9) “yellow pine ” (P. ponderosa 150 years) in 1909–1913. In 1997–1999, 416 live trees (s 229.6) were “blackjack ” and 57.2 (s 28.5) trees on average were “yellow pine.” Twelve of the 15 plots were not invaded by other tree species (remained pure ponderosa pin