Abstract
Pyrus calleryana Decne. (Callery pear), a native of eastern Asia, has recently emerged as an important woody invader in much of the eastern U.S. Little is known about its ecology in its new range. Its shade tolerance may be an important indicator of areas it is likely to invade. In this study, allometric equations were first developed to predict aboveground biomass components, including wood, branches, bark, leaves, and fruit, from diameter at stump height (dsh; 25 cm), by destructively harvesting 13 trees, ranging from 0.1 to 19.3 cm dsh. Then, a total of 23 wild-grown stands in the northern Kentucky/southwestern Ohio region were surveyed, with diameters of all woody stems sampled. Pyrus calleryana density, basal area, aboveground biomass, stand density index, size distribution inequality, and importance value were calculated for each site. Two-factor Weibull distributions were fit to diameter distributions. Allometric equations provided good fits for total aboveground biomass as well as individual components. Aboveground biomass levels fell below mean levels of native forest stands found in the US. Stand density indices yielded values typical of shade-intolerant or midtolerant species. Stands with smaller trees generally had steeply declining monotonic diameter distributions, while stands with larger, trees trended toward positively-skewed monotonic distributions. These findings are consistent with a species that is either shade-intolerant or midtolerant. Thus, while this species is expected to invade open or disturbed areas, it is not expected to be an important invader under forest canopies. However, its extended deciduous habit is one shared by other understory woody invaders, and so this may allow it to survive under forest canopies.
Management Implications
Callery pear, which has been used in landscape plantings for decades, is now being recognized as important woody invader in much of the eastern U.S. However, little is known now about its impact on native forest stands. Here, we developed allometric equations to predict aboveground biomass components, including wood, branches, bark, leaves, and fruit, as well as total aboveground biomass, from diameter at stump height (dsh; 25 cm) measurements; dsh often works better than dbh (diameter at breast height; 1.37 m) with this species because pear stems often fork below breast height. However, there is a strong relationship between dsh and dbh, so these allometric equations can used with dbh measurements. Most biomass equations were log-log regressions, and they were corrected for bias using the UMVU estimator. However, this estimator does not give a ready-to-use equation; the original data must be used along with collected data in an R routine. Thus, we also report equations corrected with the smearing estimate, which, while not as good as the UMVU estimator, performs better than most commonly used estimators. The allometric equations will allow managers to estimate biomass of stands dominated by Callery pear. Diameter distributions from 23 wild-grown stands in the northern Kentucky/southwestern Ohio region were fit to two-factor Weibull distributions, which indicated a species that is either shade-intolerant or midtolerant, which was also indicated by relatively low stand density indices. For managers, this suggests that control efforts for Callery pear should focus on disturbed or open areas, as our results suggest that it will not become an important invader in closed-canopy forests.
Functional identity regulates aboveground biomass better than trait diversity along abiotic conditions in global forest metacommunities
