Comparison of two monodominant species in New Caledonia: floristic diversity and ecological strategies of Arillastrum gummiferum (Myrtaceae) and Nothofagus aequilateralis (Nothofagaceae) rainforests

Mechanisms leading to monodominance in rainforests are still commonly discussed within the framework of forest succession. Here, we focused on the comparison of two monodominant species, Arillastrum gummiferum (Myrtaceae) and Nothofagus aequilateralis (Nothofagaceae), to try to better understand the underlying ecological mechanisms. Those two species are known to dominate the upper canopy of some rainforests on ultramafic substrates in New Caledonia. We investigated the structure, diversity and composition of Arillastrum-dominated plots and compared them with adjacent Nothofagus-dominated and mixed rainforest plots. We found that the dominance of Arillastrum was more pronounced in terms of basal area, whereas for Nothofagus the dominance was mainly in terms of stem density. Species richness and diversities in the two dominated forests were not lower than those observed in mixed rainforests, suggesting that monodominance would not lead to a limitation of diversity. Finally, our observations were consistent with a transient dominance for the two species. We suggest that resistance of Arillastrum to some wildfire regimes would allow the species to survive and regenerate, whereas Nothofagus may have a supportive strategy towards their seedlings through mycorrhizal networks. Both competitive advantages would contribute to the maintenance of monodominance.