Hawai'i tropical low shrublands

The Hawaiʻi tropical high shrublands occupy the upper slopes of four great volcanoes in the US state of Hawaii: Mauna Kea, Mauna Loa, and Hualālai on Hawaiʻi Island, and Haleakalā on Maui. Above the forest line, alpine deserts and grasslands give way downslope to subalpine shrublands, where hardy, cold- and drought-adapted plants dominate, including ʻāheahea (Chenopodium oahuense), ʻōhelo ʻai (Vaccinium reticulatum), naʻenaʻe and related Dubautia shrubs, and ʻiliahi sandalwood (Santalum haleakalae), alongside tussock grasses such as Deschampsia nubigena. This is a high-elevation subtropical highland climate marked by dry, cold conditions on the exposed summits. Its signature plant is the Hawaiian silversword, ʻāhinahina (Argyroxiphium sandwicense), part of an endemic alliance descended from a North American tarweed, while the nēnē goose and ʻuaʻu (Hawaiian petrel) are among its native fauna. The ecoregion is considered vulnerable, pressured by grazing and trampling from feral livestock and by invasive species. For mountain or rock gardeners, the native ʻōhelo (Vaccinium reticulatum), a low cranberry relative, is a notable cold-hardy ornamental from this flora.

The Northwest Hawai'i scrub ecoregion spans the remote Northwestern Hawaiian Islands, a chain of low atolls and islets in the Oceanian realm stretching roughly 1,350 to 1,600 kilometers from rocky Nihoa in the southeast to low Kure Atoll, all within the U.S. state of Hawaii. Set on the eroded remnants of ancient volcanic islands and coral sand, the vegetation is treeless tropical shrubland: banks of low, salt-tolerant shrubs and ground plants fringing lagoons, with common species including Portulaca lutea and Boerhavia repens. Conditions are harsh, with storms, flash floods, and tsunamis shaping this tropical island habitat. The ecoregion harbors several endangered endemic plants, among them the Nīhoa fan palm (Pritchardia remota), Schiedea verticillata, and Amaranthus brownii, alongside the endangered Hawaiian monk seal and endemic birds such as the Laysan duck, Laysan finch, and Nīhoa finch; collectively the islands form the largest tropical seabird rookery in the world and lie entirely within the protected Papahānaumokuākea Marine National Monument. For gardeners, the native fan palm genus Pritchardia represents the region's most horticulturally notable group, the same palms that once formed forests on Nihoa.

The Angolan mopane woodlands stretch across southwestern Angola and northern Namibia, running along the Owambo Basin and surrounding the salt flats of the Etosha Pan. As the name suggests, the ecoregion is dominated by the mopane tree (Colophospermum mopane), which grows as a single-stemmed tree up to about 10 meters tall or, where conditions are harsher, as a dense shrub, alongside associated Acacia, Combretum, and Commiphora species. The climate is dry, with rainfall concentrated in the summer and peaking in late summer. The woodlands shelter elephants, black and white rhinoceros, lion, and cheetah, as well as the near-endemic black-faced impala, and the wider region is anchored by protected areas including Namibia's Etosha National Park. Mopane here also has a direct human use, as the caterpillars of the mopane emperor moth are gathered locally as food.

The Angolan scarp savanna and woodlands form a long, narrow strip along the coast of Angola, running from the Atlantic shore up the steep west-facing escarpment that climbs roughly 1,000 meters to the country's central plateau. Vegetation shifts dramatically with elevation, grading from dry woodland and wooded grassland-where baobab, Strychnos, and Acacia welwitschii grow-up to humid mist and cloud forests whose canopy includes Khaya anthotheca, Bombax buonopozense, and Spathodea campanulata. The climate is tropical with summer rains; the coastal belt, cooled by the Benguela Current, stays humid but receives relatively little rain, while the escarpment is far wetter. Despite being poorly studied and only partly protected within reserves such as Quiçãma National Park, the region is rich in endemics, including the red-crested turaco and the grey-striped francolin, and is classified as Vulnerable. For gardeners, the showy African tulip tree (Spathodea campanulata), grown as an ornamental in warm climates worldwide, is native to these escarpment forests.

The Angolan wet miombo woodlands blanket most of the central Angolan plateau and extend north into the Democratic Republic of the Congo, sitting largely at elevations between about 1,000 and 1,500 meters. The defining habitat is miombo woodland, a moist deciduous broadleaf savanna dominated by legume trees of the family Fabaceae (subfamily Caesalpinioideae), especially the genera Brachystegia, Julbernardia, and Isoberlinia, with grassland and sandy-soil openings between the stands. The climate is tropical and notably wetter than the surrounding savanna, with rainfall strongly concentrated in the hot summer months from roughly November to March. The ecoregion is the stronghold of the giant sable antelope (Hippotragus niger variani), a critically endangered Angolan endemic protected at Cangandala National Park, and it also harbors a strict-endemic rodent, Vernay's climbing mouse. For gardeners, the signature native flora here are the canopy-forming Brachystegia and Isoberlinia legume trees that give the miombo its character.

The Arnhem Land tropical savanna covers the rugged Arnhem Land peninsula and its offshore islands, including the Tiwi Islands, Groote Eylandt, and the Wessel Islands, in Australia's Northern Territory. Eucalypt open forests dominate the landscape, led by Darwin stringybark (Eucalyptus tetrodonta) and Darwin woollybutt (Eucalyptus miniata) over a tall understory of Sorghum grasses, interspersed with monsoon rainforest patches, mangroves, and Melaleuca swamp forests. The climate is tropical and strongly monsoonal, with a summer wet season and a largely rainless dry season. Long isolation has made it exceptionally diverse: over 1,900 plant taxa have been recorded, at least 200 of them found nowhere else, and a 2017 assessment found that 36% of the ecoregion lies within protected areas such as Kakadu National Park.