On vegetation recovery, goats and giant tortoises on Pinta Island, Galápagos, Ecuador

Published source details Hamann O. (1993) On vegetation recovery, goats and giant tortoises on Pinta Island, Galápagos, Ecuador. Biodiversity and Conservation, 2, 138-151.
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Summary

The flora of the uninhabited island of Pinta in the Galápagos is extremely rich compared to other small islands in the archipelago. In the 1950s goats Capra hircus were introduced and multiplied rapidly, soon having a very detrimental impact on the vegetation. Data on vegetational changes on Pinta from 1970 to 1988, show that feral goats had opened up the forest and shrubland with some plants being severely effected e.g. the endemic Scalesia baurii ssp. hopkinsii (Asteraceae) and Opuntia galapageia var. galapageia (Cactaceae) were close to extinction. In the early 1970s the Galápagos National Park Service (GNPS) initiated a goat eradication campaign; in 1990 the last goats were removed, with an estimated 40,000 killed. During eradication, the responses of the vegetation were monitored.

Study area: Pinta in the northern Galápagos archipelago (Ecuador) covers about 59 km² and reaches an altitude of 650 m. Of the 180 higher plants known from Pinta, 59 are endemic to, Galápagos, 117 are indigenous, and only four are considered weeds (early accidental introductions). Of the 176 native taxa, at least 19 are considered rare on an archipelago scale.

Goat eradication: Goats introduced around 1959 or perhaps 5 years earlier, were preventing regeneration of vegetation and leading to the near-collapse and extinction of several plant species. It was foreseen that unless goats were eradicated or at least controlled, the plant communities would suffer perhaps irreversible changes within a short time. The GNPS therefore initiated a goat eradication campaign in the early 1970’s which continued until 1990, when finally all goats had been removed. In total, the park wardens shot about 40,000 goats during the 20 year period.

Vegetation monitoring: Following earlier studies, in 1988 an expedition was made to Pinta in order to monitor vegetation changes in response to eradaction of almost all goats. In 1988 goats were no longer present in the vegetated parts on Pinta where permanent 10 x 10 m quadrats (established in 1966) were located.

Data show that goats had a serious detrimental impact on native plants, the endemic Scalesia and Opuntia, and the native Bursera graveolens (Burseraceae) where particularly badly affected, with stands of Scalesia and Opuntia close to a complete collapse; Bursera appeared more resilient, surviving longer without new recruitment. After goat removal, all three species recovered, and recovery of vegetation in general as the goats were reduced in numbers, was rapid. Regeneration patterns were different, reflecting species life history traits including longevity, growth form, seed germination and seedling establishment patterns.

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