This study examined the floristic composition and age-class structure of the Taiwan spruce (Picea morrisonicola Hay.) forest in the Salihsian River watershed of Yushan National Park (elevations above 2600m). We tried to elucidate the population dynamics and regeneration process of this endemic tree species. A one-ha square sample area was selected and divided into 100 plots, each 10m×10m. For each plot, height of each tree and diameter at its breast height were measured. Based on the result of cluster analysis, the plots were divided into two patches：one mainly composed of spruce of large diameter-classes, and the other with spruce of small diameter-classes and Chinese hemlock of small and middle diameter-classes. The former patch represented the stand of mature phase, with an average height of 35m, an average diameters 40㎝, and an average age of 220 years (range 159-317years). The latter one represented the stand of building phase, with an average height of 20m, an average diameter of 18㎝, and an average age of 83 years (range 45-120 years).
Seedlings of spruce did not occur under the forests of both patches, but were found in the canopy gaps of gully erosion. The area of the gaps was estimated to be 1600 to 2500㎡. However, openings resulted from the death of single or few old trees in later successional stages showed no sign of regeneration. Since there were many gully erosions or landslides where spruce can regenerate, the forest is capable of persistence, and shows a mosaic structure of different large patches.