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Influence of Elevation, Land Use, and Landscape Context on Patterns of Alien Plant Invasions along Roadsides in Protected Areas of South-Central Chile AN´IBAL PAUCHARD∗ AND PAUL B. ALABACK School of Forestry, University of Montana, Missoula, MT 59812, U.S.A. Abstract: Alien plant species are a growing concern in protected areas, yet little information is available on the role of roads as corridors for alien species and the effects of elevation, land use, and landscape context in these invasions. These concerns are of particular interest in temperate zones of South America, where protected areas have high concentrations of endemic species. We studied roadside alien plant communities and forest-road edges in Villarrica and Huerquehue national parks in the Andean portion of south-central Chile. We sampled alien species and their abundance along 21 km of roads inside parks and 22 km outside parks, using 500-m roadside transects. We also sampled plant species and recorded their abundance in 15 transects located perpendicular to forest-road edges in four forest types. Of the 66 alien species encountered along roadsides, 61 were present outside parks and 39 inside parks. Elevation and alien species richness along roadsides were significantly and negatively correlated (R2 =−0.56, p < 0.001). Elevation, land use, and their interaction explained 74% of the variation in alien species richness along roadsides (p < 0.001). Transects located in pasture or disturbed secondary forests had significantly more alien species. We found no significant edge effect on native and alien species richness in any forest type. Few alien species have percolated into forest interiors. Native and alien diversity in edge plots were not related. Almost half the alien species belonged to three families and 85% were native to Eurasia. Our results suggest that alien species are moving into parks along road corridors and that elevation and land use of the matrix influence these invasion processes. Our findings corroborate the importance of early detection and control of invasive species in protected areas and highlight the importance of considering surrounding matrix land use in developing conservation strategies for reserves. Key Words: Araucaria, exotic species, forest edges, Nothofagus, protected areas, reserves, roads, southern Chile Influencia de la Altitud, Uso de Suelo y Contexto del Paisaje sobre Invasiones de Plantas Ex´oticas Resumen: Las invasiones de especies de plantas exoticas´ son una preocupacion´ creciente en areas´ prote- gidas, sin embargo se dispone de escasa informacion´ sobre el papel de los caminos como corredores para especies exoticas´ y los efectos de la altitud, uso de suelo y contexto del paisaje en estas invasiones. Estas preocu- paciones son de inter´es especial en las zonas templadas de Sudam´erica, donde las areas´ protegidas presentan altas concentraciones de especies end´emicas. Estudiamos las comunidades de plantas exoticas´ en bordes de caminos y en bordes de caminos dentro de bosques en los parques nacionales de Villarrica y Huerquehue en la porcion´ andina del centro-sur de Chile. Muestreamos especies exoticas´ y su abundancia a lo largo de 21 km de caminos dentro de los parques y 22 km fuera de los parques, utilizando transectos de 500 m. Tambi´en muestreamos especies de plantas y registramos su abundancia a lo largo de 15 transectos localizados perpendic- ularmente a los bordes de los caminos dentro de bosques en cuatro tipos de bosque. De las 66 especies de plantas ∗Current address: Faculdad de Ciencias Forestales, Universidad de Conception,´ Casilla 160-C, Conception,´ Chile, email [email protected] Paper submitted July 20, 2002; revised manuscript accepted May 1, 2003. 238 Conservation Biology, Pages 238–248 Volume 18, No. 1, February 2004 Pauchard & Alaback Alien Plant Invasions along Roadsides 239 exoticas´ encontradas en los bordes de los caminos, 61 estuvieron presentes afuera de los parques y 39 dentro de los parques. La altitud y riqueza de especies exoticas´ en los bordes de caminos estuvieron significativa y negati- vamente correlacionados (R2 =−0.56, p < 0.001). La altitud, uso de suelo y su interaccion´ explicaron 74% de la variacion´ en la riqueza de especies exoticas´ en los bordes de camino (p < 0.001). Los transectos localizados en pastizales o bosques secundarios perturbados tuvieron un numero´ significativamente mayor de especies exoticas.´ No encontramos efecto de borde significativo sobre la riqueza de especies nativas y exoticas´ en ningun´ tipo de bosque. Pocas especies exoticas´ se han propagado al interior de los bosques. La diversidad nativa y exotica´ de parcelas en los bordes no estuvo relacionada. Casi la mitad de las especies exoticas´ pertenec´ıaa tres familias y 85% fueron nativas de Europa. Nuestros resultados sugieren que las especies exoticas´ se estan´ moviendo hacia los parques a lo largo de corredores – caminos y que la altitud y el uso del suelo en la matriz influyen en estos procesos de invasion.´ Nuestros hallazgos corroboran la importancia de la deteccion´ temprana y del control de especies invasoras en areas´ protegidas y resaltan la importancia de considerar el uso del suelo en la matriz en el desarrollo de estrategias de conservacion´ para reservas. Palabras Clave: Araucaria, ´areas protegidas, bordes de bosque, caminos, Notophagus, reservas, species exoticas,´ sur de Chile Introduction areas because they often connect weed populations in the matrix with the interior of protected areas (Landres et al. Alien plants (sensu Richardson et al. 2000) are recognized 1998). Additionally, roadsides are useful for studying the as a potential threat to the conservation of protected areas influence of climatic factors and dispersal characteristics (e.g., MacDonald et al. 1989; Lonsdale 1999; Mack et al. on alien species because the roads themselves provide a 2000). These plant invasions may ultimately decrease the consistent disturbance environment across a wide eleva- capacity of protected areas to conserve biodiversity be- tional gradient (Tyser & Worley 1992; Wilson et al. 1992; cause of detrimental effects on native species and ecosys- Milton & Dean 1998; Spellerberg 1998; D’Antonio et al. tem processes (Mack et al. 2000) and the difficulty in con- 2001). trolling them in natural environments (MacDonald et al. South-central Chile is of particular interest for studies 1989). of alien plant species because it contains a highly en- Land use, disturbance, and climate are driving factors demic and diverse flora that could be especially sensi- of alien plant invasion (Lonsdale 1999; Hobbs 2000). In tive to invasion and has been little studied (Armesto et al. temperate ecosystems, most alien species are invasive 1998, 2001; Arroyo et al. 2000). Chile has approximately in human-disturbed landscapes at low elevations (Hobbs 690 naturalized alien species (15% of total flora), 381 of 2000). However, high-elevation, relatively undisturbed which occur in its humid seasonal rainforest (Arroyo et al. environments where most protected areas occur (Noss & 2000). Protected areas in this region are located mostly at Cooperrider 1994) can also be susceptible to invasion by high elevations and therefore do not appear to be signif- alien plants (DeFerrari & Naiman 1994; Heckman 1999; icantly threatened by alien plant invasions (Arroyo et al. Stohlgren et al. 1999; Pauchard et al. 2003). 2000; Pauchard & Alaback 2002). Because of increasing Roads represent the primary pathway for the intro- human disturbance and dispersal, however, alien species duction of alien plant species into protected areas, espe- are moving from agricultural landscapes into natural en- cially for generalist species with short life cycles and high vironments. At the same time, increasing international reproductive rates (Spellerberg 1998; Parendes & Jones trade is leading to greater rates of introductions to this 2000; Trombulak & Frissell 2000). Fortunately, most alien biogeographically isolated temperate forest (Arroyo et al. species growing along roadsides are incapable of coloniz- 2000). ing less disturbed natural environments. Roadsides, how- To better understand the susceptibility to invasion of ever, still may serve as starting points from which some protected areas, it is necessary to understand the role of species spread from the edges to the interiors of pris- elevation, land use, and the spatial arrangement of land tine or naturally disturbed environments (Murcia 1995; use (landscape context) in patterns of distribution of alien Cadenasso & Pickett 2001). Roadsides may also act as species (D’Antonio et al. 2001). It is also important to as- reservoirs of alien plant propagules that can be liberated sess the degree of percolation of alien species into undis- in disturbance events (Parendes & Jones 2000). turbed environments (Cadenasso & Pickett 2001). We Because of their role in plant invasions, roads are im- evaluated the influence of elevation, land use, and land- portant places to examine patterns of distribution of alien scape context on the abundance and distribution of alien species and their potential for invasion into interior habi- species along roadsides in two representative protected tats (Trombulak & Frissell 2000). Roads are particularly areas in south-central Chile and their adjacent matrices. important vectors of alien plant invasions into protected We also explored the distribution and abundance of Conservation Biology Volume 18, No. 1, February 2004 240 Alien Plant Invasions along Roadsides Pauchard & Alaback

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