Document: LAW-3-67-10

Colonization dynamics and impacts of a nitrogen-fixing shrub in post-volcanic primary succession in New Zealand.

WALKER, L.R.* ¹, B.D.CLARKSON ², W.SILVESTER ² and B.R.CLARKSON ³

University of Nevada, Las Vegas, NV 89154, USA ¹
University of Waikato, Hamilton, New Zealand ²
Landcare Research, Hamilton, New Zealand ³

Abstract:
We examined the colonization dynamics and successional impacts of a thicket-forming actinorhizal shrub, Coriaria arborea, on primary succession on Mt. Tarawera, a volcano that last erupted in 1886 on the North Island of New Zealand. Seed production was high but seeds did not remain viable for >6mo. Germination was inhibited by nitrogen fertilization in indoor experiments and by the nitrogen-rich soils under Coriaria shrubs in the field but promoted by wind protection provided naturally by shrubs or by artificial barriers. Transplanted Coriaria seedlings only survived if nodulated with Frankia and Coriaria soils slowed Coriaria seedling growth and did not improve seedling survival. Therefore, establishment of Coriaria seedlings is found mostly in protected habitats where adult Coriaria are absent, suggesting that Coriaria thickets are not self-replacing. Coriaria thickets increased soil fertility by increasing leaf litter depth (3-fold over a pre-Coriaria stage dominated by herbs), SOM (40-fold), TKN (20-fold), P (2-fold), CEC (4-fold), Ca (8-fold), K (3-fold), and Mg (5-fold). These soil changes resulted in 3-6 fold increases in growth, seedling height, leaf number, and biomass of potted Griselinia, a later successional tree on Mt. Tarawera. Where frost prevents Coriaria establishment, succession is dominated by mosses and Dracophyllum shrubs that are adapted to low nutrient levels. We suggest Coriaria on Mt. Tarawera provides a classic example of a nitrogen-fixer facilitating primary succession.

Keywords: primary succession, nitrogen-fixation, New Zealand, volcanoes

This abstract is being presented at: 10:30 AM in session:
PLANT DEMOGRAPHY