Scalesia
From Galapedia
| Scalesia in Galapagos | |
 Scalesia incisa | |
| Species: | Scalesia incisa |
|---|---|
| Common names: | Scalesia |
| Habitat: | Lava Flows of San Cristóbal |
Scalesia trees & shrubs
The giant daisy trees of Galapagos are the plant equivalent of Darwin's finches. They are members of the sunflower family and are descended from a single ancestor which reached Galapagos in the distant past. Invasion by introduced plants, as well as agricultural activities, have pushed some species close to extinction. Scientists at the Charles Darwin Research Station (CDRS) are now trying to restore and preserve these populations.
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Unique to Galapagos
There are 15 currently recognized species plus five subspecies of Scalesia; most species are shrubs but four commonly grow into trees. All are endemic to Galapagos. They are an excellent example of adaptive radiation, the development of new species to fit different vegetation zones and islands. There is great diversity between species:
- Species vary in size, from less than one meter to over 10 meters in height.
- Leaves vary in size and shape between species and are usually hairy. Leaves cluster at ends of twigs.
- The flowers are carried in white, daisy-like heads of 15 (Scalesia cordata) to 300 (S. villosa) small flowers.
- Some species grow mainly in the arid zone while others, especially the larger trees, are adapted to the humid zone.
The tree species S. pedunculata grows in the moist highland Scalesia forests and can reach over 10 m in height. S. pedunculata is found on San Cristobal, Floreana, Santiago, and Santa Cruz Islands, with the largest remaining stand located on Santa Cruz, in and around the two sunken craters called Los Gemelos.
The two variants of S. atractyloides are among the rarest Scalesia and were both once feared extinct, until rediscovered by Galapagos National Park and CDRS staff in the 1990s. They are small trees with narrow hairy leaves, and grow in the arid and transitional zones, only on Santiago Island.
Vulnerability
Scalesia pedunculata is regarded as Endangered. Its unique forests have been reduced to small remnants by the creation of the agricultural zones on Santa Cruz, Floreana, and San Cristobal and by large herds of goats, pigs and donkeys on Santiago. Scalesia species are also readily out competed by a variety of introduced plants on the inhabited islands.
Species known to have an impact include:
- Trees: Cuban cedar (Cedrela odorata), guava (Psidium guajava), sauco (Cestrum auriculatum), and Red Quinine (Cinchona pubescens).
- Shrubs: blackberry (Rubus niveus)
- Vines: passionfruit Passiflora edulis.
- Herbaceous species, including some grasses
S. atractyloides var. atractyloides (found only in western Santiago) and S.atractyloides var. darwinii (restricted to eastern-central Santiago) were both registered as Critically Endangered until recently. These shrubs are eaten by goats and other invasive herbivores on Santiago Island. However, with the eradication of goats on Santiago they are expected to recover quickly.
CDRS research activities
The eradication of goats, donkeys and pigs from Santiago is good news for Scalesia atractyloides and S. pedunculata on that island. One extinct population of S. atractyloides may now be restored with plants cultivated at Copenhagen Botanical Garden from seed collected just before the last plants in the wild died.
In 2005 CDF began a project to restore the S. pedunculata forest at Los Gemelos. Without intervention, Cuban cedar and red quinine are expected to come to dominate these forests, as they out-compete Scalesia. Twenty-five hectares were selected for intensive control of invasive plant species. This project represents the first systematic attempt to manage the problem at this specific site and to document the effects of control on both introduced and native plants.
A number of other the Scalesia species are highly endangered and feature in CDF conservation and restoration projects. S. affinis on Santa Cruz was reduced to just 13 plants. Cross-pollination experiments to produce more viable seed are under way, to try to grow more plants. Fencing is also planned, to protect existing plants from goats, donkeys and damage by people. Other projects include monitoring and conservation of Scalesia species on San Cristobal and Isabela Islands.
