Recovery of terrestrial and marine communities in a New Zealand fiord after large-scale disturbances.

Bernard Brosnan
January 1999

Abstract

The steep fiord landscape of New Zealand is prone to landslides. These result in large scars in both terrestrial and marine communities where the substratum has been scraped clean of most living organisms.

Species diversity and richness indices of terrestrial vegetation and marine epibenthic communities were obtained from three such scars of different age. Species composition and successional development of the vegetation were compared to mature forest communities, and to different landslide scars. Univariate and multivariate analyses were used to quantify similarity/difference between sites.

Results from botanical observations showed that species diversity and richness indices of the landslide scars were higher than those of the mature forest community, even after 60 years of development. The terrestrial vegetation showed a plateau in successional development whereby scars of 34 and 60 years were similar in measues of richness and diversity. Marine epibenthic communities showd no significant differences in diversity, species richness or species composition between disturbed and undisturbed sites.

Recovery of the terrestrial scar was initiated from the landslide boundaries where pioneer species encroached onto the scar, in turn producing favourable conditions for higher order plants. The period of this progression appeared to be short (30 years). This was thought to be facilitated by landslide debris that had collected in cracks and crevices, as well as by islands of vegetation situate in the middle of the scar that had been protected from the landslide by the slope topography. Recovery of the marine scar was attributed to recruitment of larvae from outside the affected area. This recovery appeared to be rapid so that development of a mature community was largely completed before this study was initiated.

Findings suggest that recovery of a terrestrial scar to a mature forest would take in excess of 60 years to be completed but that recovery of many components of marine epibenthic systems occurs in less than 2 years. Landslides appear to be a major structuring factor in terrestrial communities where such major catastrophes occur infrequently. However, in marine epibenthic communities landslides appear to be a relatively minor structuring factor where other types of large-scale disturbances occur frequently.