Fifty Years of Change in Forest Understory Composition. I. Changes in Species Richness and the Species - Area Relationship

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To examine how forest understory communities are responding to changes in environmental conditions, we revisited 59 northern hardwood stands in northern Wisconsin in Summer, 2000 that John Curtis and associates first sampled about 50 years ago. We hypothesized that sites may be losing species and that these patterns of loss may be related both to species characteristics (e.g., stature, mode of dispersal, etc.) and to variable site conditions (e.g., initial diversity, logging disturbance, etc.). In this phase, we tested whether: 1) species richness among sites is correlated over time; 2) whether more diverse sites are more likely to lose species; and 3) whether z, the exponent in the species-area relationship, decreased during this interval. Species richness in 2000 at 5 m2, 20 m2, and 120 m2, are positively correlated with species richness at each site 50 years ago (p=0.006, 0.003, and 0.001, respectively), but the only significant predictor variable is aggregate (not local) richness 50 years ago. This result suggests that site conditions and/or history are important in maintaining understory diversity. More diverse sites are more likely to lose species, as expected under various models. The exponent, z, relating species number to area has also decreased from 0.544 to 0.493. This decline suggests that biotic simplification may be occurring in these understory communities.


Presented at the 86th Ecological Society of America Annual Meeting, Monona Terrace, Madison, WI.

Presentation Number 59: Conservation Ecology: Terrestrial Biodiversity.

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