Invasibility of a coastal strip in NE Spain by alien plants

Abstract

The alien plant species and the ecological factors that facilitate their invasion to a coastal strip in the Baix Camp region (Tarragona, NE Spain) were studied. A detailed inventory of the area showed that 20% of the plant species, most of them from the American Continent, were aliens, many of which were strongly invasive.At the habitat level, the relationships between the invasive behaviour and a number of autecological, ecological and habitat variables were analysed by means of logistic analyses. In the best model five variables were related to alien plant invasions: climatic affinity, disturbance of the invaded habitat, route of introduction, soil moisture during summer, and life form. To elucidate the environmental factors that could be responsible for alien plant invasions at a regional scale, the number of alien taxa and the environmental features at 13 localities of the western Mediterranean area were analysed. The warm lowlands, subjected to low annual rainfall and high population density, exhibited the greatest reception capacity for alien plants.It is concluded that various specific environmental features -high mean temperatures, the abundance of riparian systems, the existence of biotopes with favourable water balance which harbour a great richness of alien species and the high human pressure to which the enclave is subjected, combined with the ecological requirements of the alien species and certain species attributes (biotype) can interact at different scales and have caused the over-representation of alien plants.

Temporal and spatial changes in plant dune diversity in urban resorts

“…These authors reported the invasion of this tree on the South African coast. However, in the Pampean coastal region there were no clearly dominant exotic species in the sampled sites, suggesting that the stressful conditions of the studied habitats present a barrier to alien invasion (Sobrino et al 2002). These findings were in agreement with observations by Von Holle and Motzkin (2007) from coastal sand plains in the United States, who found that few invasive plants could thrive on the xeric, poor nutrient soils in the coastal region, or compete with the native species.…”

The historical role of agriculture and gardening in the introduction of alien plants in the western Mediterranean

“…At the opposite end of the scale, we find the north of Africa, where tourism is not very developed and the economy is still linked to agriculture and livestock. In this case, the percentage of alien species present that have been introduced through gardening has not varied in any considerable way (Sennen and Mauricio 1934;Valdés et al 2002). It would have been desirable to have correlated the variations in time of the socio-economic factors with the presence of exotic flora.…”

“…One case where it would have been especially interesting to study the effect of socioeconomic factors is that of North Africa. Unfortunately, the catalogue of the flora of the Eastern Rif (Sennen and Mauricio 1934) was compiled at a time when there had been a colonial war between the Spanish army and the native tribes led by Abd el-Krim for more than a decade. Apart from causing the deaths of thousands of men on both sides, the war meant that it would have been impossible to carry out any accurate population census or socio-economic study.…”

“…For example, those environments which are most susceptible to receiving and accepting exotic flora have been closely examined (Vilà and Pujadas 2001;Sobrino et al 2002;Vilà et al 2007) and the determining characteristics which most favour the introduction of alien species have been investigated (Domènech and Vilà 2006). Other studies have examined the influence of climatic change on the process of invasion by alien plants (Gritti et al 2006) and have tried to establish whether insularity is a factor which makes an area more susceptible to this invasion Vilà and Gimeno 2006).…”

Do alien plants on Mediterranean islands tend to invade different niches from native species?

“…This pathway could constitute a particularly acute threat to the colonization of sensitive rural environments. Since most release events occur adventively from inhabited areas (Sobrino et al 2002), it may also be advantageous if the escapees can survive and persist at least temporarily in urban or other ruderal habitats before successfully colonizing more widely. The requirement for such contrasting pre-adaptations may partly explain why so few species establish away from towns and cities, and the relative paucity of stresstolerators in the alien flora.…”