Figure S1 Vegetation profiles of line transects of low and medium high undisturbed native scrub above Playa Norte, Socorro (27 January 1996): (a) species-rich low scrub at 80 m elevation (8 m length); (b) complex medium scrub on terrace at 120 m elevation (8 m length); (c) overview of dominant species along a slope gradient of 80 m uphill from the beach near Playa Norte. Figure S2 Vegetation profiles (length 20 m each) of undisturbed native forest habitats on Socorro (27 January 1996): (a) Fig forest (Ficus cotonifolia) near Playa Norte at 10 m elevation above sea level (20 m); (b) evergreen forest in montane climate zone, NW of Cerro Evermann, 800 m above sea level (20 m). Figure S3 Vegetation profiles (length 8 m each) of undisturbed native dwarf forest and tall scrub (30 January 1996): (a) open evergreen forest rich in epiphytes and dense brush, SE of Cerro Evermann, 840 m above sea level; (b) bracken-rich tall scrub on lava rocks above trailhead at end of road, southern slope, 550 m above sea level. Figure S4 Vegetation profiles from the sheep-degraded southern half of Socorro Island (30 January 1996): (a) mixed forest at 400 m elevation on the south plateau, dominated by the fig Ficus cotonifolia (20 m length); (b) weedy field (formerly a forest) at 400 m elevation on the south plateau (8 m length); (c) low Croton masonii?dominated and mostly sheep-free scrub near Bahia Braulia in the extreme south of the island, 50 m above sea level (8 m length). Figure S5 Sheep exclosure on Socorro. View of the grazed landscape with prickly pear (Opuntia sp.) patch (26 August 1991). Figure S6 Detail of sheep exclosure (26 August 1991). Figure S7 View of sheep exclosure on 1 December 1992. The vegetation behind and near the fence is much higher than in the surrounding landscape. Figure S8 Typical feral sheep (Ovis aries) on Socorro Island (28 January 1996). Figure S9 A roadside transects at c. 400 m elevation above sea level on Socorro Island. Co-author G. A. Levin in the background. Table S1 Plant list of sheep exclosure on Socorro Island. Table S2 Vegetation transects: density and frequency data.

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