Temporal signatures and harmonic analysis of natural and anthropogenic disturbances of forested landscapes: a case study in the Yellowstone region

Abstract

Diversity patterns observed for a given landscape are dependent on the spatial and temporal scales of the investigation. In this research the temporal response was investigated within the undisturbed mature forests of the Yellowstone region, the 1988 fire burns and the harvested forest tracks in Targhee National Forest. The satellite data set employed for this analysis was the 1989 to 2001 weekly NOAA AVHRR NDVI composite. Harmonic analysis was used to express the cyclical NDVI curve as a sum of a series of cosine waves and an additive term. Two research questions were addressed: 1) Can interannual and seasonal patterns for the various disturbed and undisturbed forested landscapes be discerned? 2) How do the interannual and seasonal patterns vary for undisturbed, naturally disburdened and human impacted forest landscapes? The changes in amplitude, phase and variance for the most explanatory harmonic term were compared between the two disturbance types and the undisturbed forests. The findings show that interannual and seasonal patterns differ with disturbance type and both differ from undisturbed forests. Mature forests are the most difficult to predict for interannual and seasonal patterns, predictability is easiest for young, post disturbance areas. Finally, the results show that natural forests are temporally