1 The facilitative and inhibitory effects of a nitrogen-fixing shrub, Carmi
chaelia odorata, during primary succession were studied using both field me
asurements in a New Zealand temperate montane valley, and manipulative glas
shouse experiments on seedlings of the three dominant tree species, Griseli
nia littoralis, Metrosideros umbellata and Weinmannia racemosa.
2 During a stand development chronosequence of < 100 years in which Carmich
aelia colonized, dominated and senesced, there was significant development
of soil organic horizons and a large build-up of soil nitrogen, especially
in the organic horizon. Soil organic matter and nitrogen levels across the
sequence were strongly correlated with the main DCA axis of vascular plant
species composition, along which there was change in dominance from herbace
ous to woody species. Vegetation increased in height and light levels decli
ned with stand development.
3 Similar responses to shade that mimicked that in mature Carmichaelia stan
ds suggested that inhibitory effects were likely to be uniform across the t
hree tree species.
4 Nitrogen, either added via Carmichaelia litter or in solution, enhanced s
hoot biomass and foliar nitrogen concentrations of all three tree species.
Growth in soils of increasing development increased foliar nitrogen concent
rations for Griselinia and Weinmannia, but not Metrosideros.
5 Overall, Metrosideros was the least responsive to potential facilitative
effects of Carmichaelia, and Griselinia exhibited the highest degree of pla
sticity of response. Future forest composition and spatial patterning of sp
ecies in mixed stands here, as elsewhere, is likely to result from differen
tial facilitative responses during early primary succession.