Scaling Aspen-FACE experimental results to century and landscape scales

The Aspen-FACE experiment generated 11 years of empirical data on the effect of CO₂ enrichment and elevated ozone on the growth of field-grown trees (maple, birch and six aspen clones) in northern Wisconsin, but it is not known how these short-term plot-level responses might play out at the landscape scale over multiple decades where competition, succession and disturbances interact with tree-level responses. In this study we used a forest landscape model (LANDIS-II) to scale these site level results to broader temporal and spatial scales. These general principles emerged from the results. (1) The productivity of taxa under future conditions is the primary determinant of short-term taxon dominance. (2) Longer-term, longevity and shade tolerance may supersede productivity as the determinant of importance, depending on the disturbance regime. This result offers hope that, even in the face of atmospheric changes, managers may have some control over future forest composition and carbon sequestration through modification of disturbance regimes. (3) Changes in the abundance of taxa were mostly gradual and none of the taxa were extirpated from the landscape, even under treatments for which they were poorly adapted. This suggests that as atmospheric conditions change, abrupt extirpations are expected to be rare. (4) Similarly, different taxa fared relatively well under different treatments. This suggests that maintaining species and genetic diversity is a prudent forest management strategy in the face of global change. (5) Accounting for spatial processes is important because seed dispersal and establishment may limit the ability of some species to colonize available habitat.