Research
New Zealand's mysterious divaricate plants
About 10% of New Zealand's woody flora has a divaricate habit, including many shrubs and juveniles of some tree species. Since Diel's climatic hypothesis in the late 19th century, ecologists have hotly debated the origins and significance of this growth habit. A survey across 1152 sites throughout NZ showed that divaricates made their largest contributions to tree/shrub assemblages in the rain shadow of the Southern Alps, on sites with cold winters, low solar radiation and significant vapour pressure deficits, where potential evapotranspiration exceeds precipitation by >130 mm. The distribution of divaricate plants suggests they cope with frosty, droughty environments better than most other elements of New Zealand's arborescent flora. This may reflect selection for both (1) physiological resistance to frost and drought and (2) deterrence of herbivores, as climatic constraints on plant growth rates probably leave seedlings exposed for longer to ground-dwelling browsers.
Source: Lusk, C.H., McGlone, M.S., Overton, J.McC. (2016) Climate predicts the proportion of divaricate plant species in New Zealand arborescent assemblages. J. Biogeog. 43: 1881-1892.
Rainforest study sites and study species in Australia and New Zealand
The photos below are mostly of saplings and large seedlings of the study species. Notice that the tropical and subtropical species mostly have large and/or compound leaves, whereas temperate species mostly have small, simple leaves. Ecologists are still trying to work out what these gradients in leaf size and form are all about.
Cape Tribulation, QLD
|
|
View from the canopy crane |
Endiandra microneura (Lauraceae) |
|
|
Myristica globosa ssp muelleri (Myristicaceae) |
Cleistanthus myrianthus (Euphorbiaceae) |
|
|
Dysoxylum papuanum (Meliaceae) |
Elaeocarpus angustifolius (Elaeocarpaceae) |
|
|
Palaquium galactoxylon (Sapotaceae) |
Polyscias australiana (Araliaceae) |
Danbulla NP, QLD
|
|
Aleurites rockinghamensis (Euphorbiaceae) |
Argyrodendron peralatum (Malvaceae) |
|
|
Cryptocarya mackinnoniana (Lauraceae) |
Litsea leefeana (Lauraceae) |
|
|
Melicope jonesii (Rutaceae) |
Polyscias australiana (Araliaceae) |
Bulburin NP, QLD
|
|
Brachychiton acerifolius (Malvaceae) |
Cinnamomum oliveri (Lauraceae) |
|
|
Forest interior |
Homalanthus novoguinensis (Euphorbiaceae) |
|
|
Mischarytera lautereriana (Sapindaceae) |
Mischocarpus pyriformis (Sapindaceae) |
|
Podocarpus elatus (Podocarpaceae) |
Rocky Creek Dam, NSW
|
|
Castanospermum australe (Fabaceae) |
Flindersia schottiana (Rutaceae) |
|
|
Polyscias murrayi (Araliaceae) |
Sarcopteryx stipata (Sapindaceae) |
|
Diploglottis australis (Sapindaceae) |
Nightcap Range, NSW
|
|
Callicoma serratifolia (Cunoniaceae) |
Elaeocarpus reticulatus (Elaeocarpaceae) |
|
Schizomeria ovata (Cunoniaceae) |
Pt. Lookout, NSW
|
|
Forest interior |
Barrengarry, NSW
|
|
Acmena smithii (Myrtaceae) |
Ceratopetalum apetalum (Cunoniaceae) |
|
|
Doryphora sassafras (Atherospermataceae) |
Pittosporum undulatum (Pittosporaceae) |
|
|
Ceratopetalum with vines |
Forest interior |
Okataina, NZ
|
|
Dacrydium cupressinum (Podocarpaceae) |
Knightia excelsa (Proteaceae) |
|
|
Laurelia novaezelandiae (Atherospermataceae) |
Litsea calicaris (Lauraceae) |
|
Forest margin |
Mangaehuehu, NZ
|
|
Hoheria populnea (Malvaceae) |
Nestegis cunninghamii (Oleaceae) |
|
|
Nothofagus menziesii (Nothofagaceae) |
Prumnopitys taxifolia (Podocarpaceae) |
|
Forest margin |
Arve Rd, TAS
|
|
Anopterus glandulosus (Escalloniaceae) |
Nothofagus cunninghamii (Nothofagaceae) |
|
Phyllocladus aspleniifolius (Podocarpaceae) |