Abstract
The influence of functional diversity on ecosystem productivity has practical implications for the carbon sequestration potential of forest ecosystems. Vertical stratification may be one key aspect of functional diversity that influences stand productivity through differential resource use. Although additive basal area of canopy and emergent species has been reported in some forests, it is unclear whether this represents significant additive productivity, or mainly a reflection of the great longevity of the emergent trees. We asked if the presence of emergent Nothofagus dombeyi influences carbon sequestration in wood of the associated canopy species in an old‐growth temperate forest in south‐central Chile, the canopy species all being more shade‐tolerant than N. dombeyi . We estimated wood volume increment of all trees on four pairs of plots in old‐growth stands in Parque Nacional Puyehue, each pair consisting of one 25×25 m plot with emergent trees and another lacking emergents. Heights and diameters of all trees were measured, and increment cores were extracted to permit back‐estimation of the same variables 2 years earlier. Published data on density and carbon content of wood were then used to convert wood volume production to carbon sequestration rates. Rates of carbon sequestration in wood of the canopy species were very similar on plots with and without N. dombeyi , showing that productivity of the emergent trees was additive to that of the canopy species. As a result, the average total carbon sequestration rate of plots with emergents was nearly twice that of plots lacking emergents (2.8 versus 1.5 T C ha −1 yr −1 ). The occurrence of additive productivity highlights the importance of functional diversity and vertical stratification for forest management and carbon sequestration. Conservation of vertical stratification is desirable when complementary light‐use characteristics of the dominant species optimise carbon sequestration.