Predicting Future Threats to the Native Vegetation of Robinson Crusoe Island, Juan Fernandez Archipelago, Chile

: The Juan Fernandez Archipelago, a Chilean national park and biosphere reserve, is 700 km west of continental Chile. Invasive plant species pose major threats to the native, highly endemic vegetation, especially on Robinson Crusoe Island (Mas a Tierra), where there is a permanent settlement. We used historical and recent vegetation map data as well as recent vegetational point data to reconstruct vegetational changes on the island since the early twentieth century. In addition, we used logistic regression models with environmental variables or their surrogates (elevation, solar radiation, topographic similarity index, slope position) to estimate the potential distributions of the worst invaders. Native vegetation has been affected most severely by Acaena argentea, Aristotelia chilensis, Rubus ulmifolius, and Ugni molinae, leading to a significant decrease of endemic plants in the montane forests and native shrublands. The native forest has decreased by approximately one-third. The area affected by Aristotelia chilensis increased from 6.5% to 14% of the total island area. Ugni molinae, once rare, is now abundant (4.6%), as is Acaena (11.9%). Rubus ulmifolius, not present 80 years ago, now covers about 7% of the island's surface. The distributions of all studied species except Rubus ulmifolius are significantly (p 60%) by these plants. Based on the invasion speed of the past 80 years, this would take another 80 years if conservation measures do not succeed. Resumen: El Archipielago Juan Fernandez, un parque nacional y reserva de la biosfera chileno, esta 700 km al oeste de Chile continental. Plantas invasoras son la mayor amenaza para la vegetacion nativa, altamente endemica, especialmente en la Isla Robinson Crusoe (Mas a Tierra), donde hay un asentamiento permanente. Utilizamos datos historicos y recientes de mapas de vegetacion asi como datos puntuales recientes de vegetacion para reconstruir los cambios de vegetacion en la isla desde el inicio del siglo veinte. Adicionalmente, utilizamos modelos de regresion logistica con variables ambientales o sus sustitutos (elevacion, radiacion solar, indice de similitud topografica, pendiente) para estimar las distribuciones potenciales de los peores invasores. La vegetacion nativa ha sido afectada mas severamente por Acaena argentea, Aristotelia chilensis, Rubus ulmifolius y Ugni molinae, lo que traido una disminucion significativa de plantas endemicas en los bosques montanos y matorrales nativos. El bosque nativo ha disminuido aproximadamente en un tercio. El area afectada por Aristotelia chilensis aumento de 6.5% a 14% del total de la superficie de la isla. Ugni molinae, antes rara, ahora es abundante (4.6%), como lo es Acaena (11.9%). Rubus ulmifolius, ausente hace 80 anos, ahora cubre aproximadamente 7% de la superficie de la isla. Las distribuciones de todas las especies estudiadas excepto Rubus ulmifolius estan significativamente (p 60%) por estas plantas. En base a la velocidad de invasion en los ultimos 80 anos, esto llevaria otros 80 anos si las medidas de conservacion no son exitosas.

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