New goats on the island?

Novas cabras na ilha?

SHORT COMMUNICATION

New goats on the island?

Novas cabras na ilha?

Micheline Carvalho-Silva¹; Paulo R.F. Amorim; Paulo E.A.S. Câmara

Universidade de Brasília, Depto. Botânica, Asa Norte, 70910-900, Brasília, DF, Brazil

ABSTRACT

Trindade is an oceanic island located ca. 1200 km east of the Brazilian coast with only 65% of its original vegetation cover remaining. Devastation was mainly caused by the presence of goats for a long time. Since goats were eliminated in 2005 the island vegetation is going through a recovering process. However during a visit to the island in 2012 another threat to the vegetation was noted: a Leguminosae species is spreading and killing part of the endemic herbaceous vegetation of Cyperus atlanticus.

Key words: Ilha da Trindade, vegetation, Guilandina bonduc, Cyperus atlanticus.

RESUMO

Trindade, uma ilha oceânica localizada a cerca de 1200 km da costa do Brasil, possui apenas 65% da sua cobertura vegetal original. A principal causa da devastação foi a presença de cabras por um longo período de tempo na ilha. Em 2005 as cabras foram eliminadas e a vegetação voltou a se recuperar, mas uma visita à ilha em 2012 revelou um novo perigo a vegetação: a presença de uma espécie de Leguminosae que está se espalhando e matando a parte da vegetação herbácea endêmica de Cyperus atlanticus.

Palavras chave: Ilha da Trindade, vegetação, Guilandina bonduc, Cyperus atlanticus.

Trindade is a small oceanic island of volcanic origin located at ca. 1200 km east of the Brazilian coast at 20º31'30"S and 29º19'30"W. Its vegetation has been investigated since the early 1900's (Alves 1998). Currently, however, it has only about 65% of its surface covered by vegetation, being only 5% of forests (Alves 1998; Silva & Alves 2011). The main cause of the devastation observed in Trindade is due to a long-term presence of goats, which were introduced in the island by Edmund Halley in 1700 (Alves 1998; Silva & Alves 2011).

Goats are well known for overgrazing and consequently for causing plant extinction on oceanic islands (Campbell & Donlan 2005). Knowing this, the Brazilian Navy (responsible for the Island) worked on the complete eradication of the introduced goats in the last decade. The goat extermination has allowed the vegetation to slowly recover towards what is believed to be its original form (Silva & Alves 2011). However, a recent expedition to Trindade (June 2012) revealed another problem affecting the vegetation, maybe of same magnitude as the one caused by the goats. It was noted that the species Guilandina bonduc L. (Leguminosae, Caesalpinoideae) is killing the herbaceous vegetation, in particular the endemic Cyperus atlanticus Hemsl. (Cyperaceae).

Guilandina bonduc is a pantropical species, with drift seeds able to disperse and survive across the ocean (Lewis et al. 2005). According to Alves (1998), the presence of G. bonduc in the island was previously reported by Lobo in 1916 (as Caesalpinia bonducella (L.) Fleming) and by Becker in 1965.

Due to the grazing behavior of goats, the population of G. bonduc was maintained under control (Alves 1998). After goats' elimination, however, G. bonduc is spreading across the island. This species seems to have strong allelopathic effect, forming halos that are visible from miles of distance (Fig.1).

Alves et al. (2011), already reported similar phenomenon of halos caused by the killing of the native species, but it was attributed to the presence of exotic species mistakenly introduced (mostly Syzigium cumini (L.) Skeels, Myrtaceae). We have not seen any traces of halos around any of the exotic species present but only around G. bonduc.

Moreover, as a result of such species spread, individuals of Cyperus atlanticus dries, dies (Fig. 1c), and eventually only barren soil is left (Fig.1b). It seems that G. bonduc is still absent on higher altitudes, such as Morro do Desejado and adjacent areas, but quite common in the low areas. The allelopathic effect of G. bonduc on the vegetation seems to be selective not affecting island representatives of Leucaena sp. and Dioclea sp. (Fig. 1e-f) but fatal to the more sensitive endemic C. atlanticus. Voucher of all plants involved were collected and are deposited at herbarium UB (Carvalho-Silva et al. 1780, 1794).

The purpose of this paper is to report this phenomenon. At this moment studies are being carried out at the Universidade de Brasília (UnB) to determine the precise mechanism of action and which chemicals are involved. The initial results highlight that Guilandina bonduc must be removed soon enough. Otherwise, such plant species may cause damages similar to that caused by the goats.

Acknowledgments

The authors are thankful to the Brazilian Navy, Captains Otoch and Camilo, also all the crew of Frigate Constituição. We also thank Professor Christopher Fagg from University of Brasília for helping with species identification. We also thank CNPq and PROTRINDADE for providing funds.

Artigo recebido em 27/06/2012

Aceito para publicação em 30/01/2013

• Alves, R.J.V. 1998. Ilha da Trindade e Arquipélago Martin Vaz - Um ensaio geobotânico. Serviço de Documentação, Marinha do Brasil, Diretoria de Hidrografia e Navegação, Niterói. 144p.
• Alves, R.J.V.; Silva, N.G. & Aguirre-Muñoz A. 2011. Return of endemic plant populations on Trindade Island, Brazil, with comments on the fauna. In: Veitch, C. R.; Clout, M.N. & Towns, D.R. (eds.). Island invasives: eradication and management. Proceedings of the International Conference on Island Invasives. Gland, IUCN, Auckland. Pp. 259-263.
• Campbell, C. & Donlan, C.J. 2005. Feral goat eradications on islands. Conservation Biology 19:1362-1374.
• Lewis, G.P.; Schrire, B.; Mackinder, B. & Lock, M. 2005. Legumes of the world. Royal Botanic Gardens, Kew. 578p.
• Silva, N.G. & Alves, R.J.V. 2011. The eradication of feral goats and its impact on plant biodiversity - a milestone in the history of Trindade Island, Brazil. Rodriguésia 62:717-719.

Publication Dates

• Publication in this collection
  11 Nov 2013
• Date of issue
  Sept 2013

History

• Received
  27 June 2012
• Accepted
  30 Jan 2013