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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 Canopy Crane Endiandra microneura
View from the canopy crane Endiandra microneura (Lauraceae)
Myristica globosa ssp muelleri Cleistanthus myrianthus
Myristica globosa ssp muelleri (Myristicaceae) Cleistanthus myrianthus (Euphorbiaceae)
Dysoxylum papuanum Elaeocarpus angustifolius
Dysoxylum papuanum (Meliaceae) Elaeocarpus angustifolius (Elaeocarpaceae)
Palaquium galactoxylon Polyscias australiana
Palaquium galactoxylon (Sapotaceae) Polyscias australiana (Araliaceae)

Danbulla NP, QLD

Aleurites rockinghamensis Argyrodendron peralatum
Aleurites rockinghamensis (Euphorbiaceae) Argyrodendron peralatum (Malvaceae)
Cryptocarya mackinnoniana Litsea leefeana
Cryptocarya mackinnoniana (Lauraceae) Litsea leefeana (Lauraceae)
Melicope jonesii Polyscias australiana
Melicope jonesii (Rutaceae) Polyscias australiana (Araliaceae)

Bulburin NP, QLD

Brachychiton acerifolius Cinnamomum oliveri
Brachychiton acerifolius (Malvaceae) Cinnamomum oliveri (Lauraceae)
Forest interior Homalanthus novoguinensis
Forest interior Homalanthus novoguinensis (Euphorbiaceae)
Forest interior Mischocarpus pyriformis
Mischarytera lautereriana (Sapindaceae) Mischocarpus pyriformis (Sapindaceae)
Podocarpus elatus
Podocarpus elatus (Podocarpaceae)

Rocky Creek Dam, NSW

Forest interior Flindersia schottiana
Castanospermum australe (Fabaceae) Flindersia schottiana (Rutaceae)
Polyscias murrayi Sarcopteryx stipata
Polyscias murrayi (Araliaceae) Sarcopteryx stipata (Sapindaceae)
Diploglottis australis
Diploglottis australis (Sapindaceae)

Nightcap Range, NSW

Callicoma serratifolia Elaeocarpus reticulatus
Callicoma serratifolia (Cunoniaceae) Elaeocarpus reticulatus (Elaeocarpaceae)
Schizomeria ovata
Schizomeria ovata (Cunoniaceae)

Pt. Lookout, NSW

Forest interior Blank
Forest interior

Barrengarry, NSW

Acmena smithii Ceratopetalum apetalum
Acmena smithii (Myrtaceae) Ceratopetalum apetalum (Cunoniaceae)
Doryphora sassafras Pittosporum undulatum
Doryphora sassafras (Atherospermataceae) Pittosporum undulatum (Pittosporaceae)
Ceratopetalum vines Forest interior
Ceratopetalum with vines Forest interior

Okataina, NZ

Ceratopetalum vines Knightia excelsa
Dacrydium cupressinum (Podocarpaceae) Knightia excelsa (Proteaceae)
Laurelia novaezelandiae Litsea calicaris
Laurelia novaezelandiae (Atherospermataceae) Litsea calicaris (Lauraceae)
Forest margin
Forest margin

Mangaehuehu, NZ

Hoheria populnea Nestegis cunninghamii
Hoheria populnea (Malvaceae) Nestegis cunninghamii (Oleaceae)
Nothofagus menziesii Prumnopitys taxifolia
Nothofagus menziesii (Nothofagaceae) Prumnopitys taxifolia (Podocarpaceae)
Forest margin
Forest margin

Arve Rd, TAS

Anopterus glandulosus Nothofagus cunninghamii
Anopterus glandulosus (Escalloniaceae) Nothofagus cunninghamii (Nothofagaceae)
Phyllocladus aspleniifolius
Phyllocladus aspleniifolius (Podocarpaceae)
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