Vegetation and soil recovery on shallow landslide scars in tertiary hill country, east Cape region, New Zealand

Primary successions involving teatree (Kunzea ericoides var. ericoides with some Leptospermum scoparium) were studied on shallow landslide scars on soft sedimentary (mudstone) hill country under extensive pastoral use in the East Cape (Tairawhiti) region, using a 5-72 yr chronosequence established from sequential aerial photography and the age of the oldest teatrees on scars. Dynamics of primary even-aged teatree stands are similar to those in secondary successions on reverting pasture described previously from the region. Height growth rates and basal area indicate that the productivity of teatree stands on landslide scars is similar to that on intact regolith. Although seventy five vascular species were recorded, one-third of them adventive, only five species—all native—were consistently present. Classification and ordination revealed four distinct stages in the evolution of ground layer communities, the first three with < 50 % plant cover (establishment and persistence of adventive grasses and herbs for 15 years; exclusion by shading of species other than Hypochoeris radiata and mosses from 15—30 years; establishment of Microlaena stipoides, Uncinia spp., and ferns from 30—50 years) and the fourth with > 50 % plant cover (principally M. stipoides, from 50 years), reflecting the dynamics—dominated by intraspecific competition—of the teatree stands. Apart from Leucopogon fasciculatus, other early successional canopy species were rare and later successional canopy species typical of primary forest in the region were absent. Despite the presence of seed sources of later successional canopy species in nearby remnants of primary forest and the persistence of their dispersers, continued removal of mostly palatable potential successors by grazing will stall their progression to tall forest. Mean soil depth increased logarithmically with age, from an average of 20 cm at age 10 yr to 58 cm at age 70 yr, a rate substantially faster than on sandstone elsewhere in the country.