Biological nitrogen fixation (BNF) is a key process for ecosystem development on new substrates. On young volcanic substrates, the near absence of nitrogen (N) and the presence of available phosphorus (P) in the soil should stimulate the activity of diazotrophic, N-fixing, bacteria. Our main hypothesis is that ecosystem N gain through BNF is tightly coupled to the development of progressive and maximum phases of ecosystem succession, as element contents build up.
Vegetation succession on 4 recent (1852-1942) montane lava Rows on Mauna Loa, Hawaii, was remeasured 22 years after the first measurement in 1967. Colonisation patterns of vascular plant species were observed on a new lava flow (1984) which overwhelmed part of the earlier studied 1852 flow. An influx of adventive species, positively correlated with flow age, was noted at the remeasured sites; most were herbs and grasses that do not appear to interfere with the succession to Metrosideros- dominated forest.
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.
Exclosure plots established in three separate areas of kanuka (Kunzea ericoides var. ericoides) forest on south Kaipara spit in 1983 to assess the impact of introduced fallow deer (Dama dama) were remeasured in 1993. Kanuka shared canopy dominance with mapou (Myrsine australis), houpara (Pseudopanax lessonii) and mahoe (Melicytus ramiflorus ssp. ramiflorus) in relatively old forest in Lookout Bush, Woodhill, and dominated exclusively in two younger stands at South Head; Coprosma rhamnoides dominated understories throughout.