Late-successional and old-growth forests have been studied in many moist temperate regions of the world, but only recently have researchers begun to collaborate on global assessments of old-growth ecosystem structure and function.  Our research goal was to explore ecological characteristics shared by and diverging among these systems.  We tested the hypothesis that certain functions, such as a high degree of carbon storage and habitat complexity, are provided universally by old-growth forests.  The analysis combined both published biometrics and original datasets from many of the world’s major remaining old-growth formations, including the U.S. Pacific Northwest and Northeast; the Carpathian Mountains of Eastern Europe; the European Alps and Apennine Mountains; Australia; China; and Chilean Tierra Del Fuego.  Rather than pooling data across all systems, we aggregated to the global scale only the standardized relative differences between con-specific mature and old-growth forests. These were used in ANOVA and multivariate analyses to identify similarities and dissimilarities.
Results/Conclusions

Aboveground tree biomass is consistently higher (p < 0.001) in old-growth temperate coniferous forests in the U.S. Pacific Northwest (620 Mg/ha), northern hardwood-conifer forests in the U.S. Northeast (246 Mg/ha), Fagus sylvatica forests in the Ukrainian Carpathians (381 Mg/ha), and mixed broad-leaved/pine forests in northeastern China (329 Mg/ha) in comparison to mature forests (290, 165, 243, 102 Mg/ha respectively).  Mature forests have 47, 67, 64, and 31% of the aboveground carbon storage found in old-growth forests for these four regions respectively.  Coarse woody debris volumes are universally higher (p < 0.001) in old-growth forests compared to mature forests, but some systems, such as southern beech (Nothofagus spp.) forests of Tierra Del Fuego, partition a greater proportion of total carbon storage into woody debris pools.  Metrics indicative of both horizontal and vertical structural complexity show significant contrasts between mature and old-growth forests for most, but not all, of the systems examined.  For instance, vertical differentiation of the canopy in Eucalyptus regnans forests of southeastern Australia is strongly influenced by fire dynamics; Fagus sylvatica forests have sharply contrasting vertical complexity at fine scales related to unusually low light levels in closed canopy patches.  Our results suggest a universal potential for enhanced provision of late-successional ecosystem services through forest management practices that promote structural development in young to mature stands.  For instance, management for and conservation of high biomass, late-successional forests provide carbon sequestration benefits and structurally complex habitats.