This study evaluates the idea that differences in reproductive phenology and traits between coexisting exotic and native species may promote exotic invasiveness. Reproductive phenology, proportions of flowers setting unripe fruits and ripe fruits (fruit set), abundance and morphology of fruits, and seed viability were compared between two invasive (Crataegus monogyna and Sorbus aucuparia) and six native woody fleshy-fruited species at three sites in temperate forests of northwestern Patagonia, Argentina. Flowering and the onset of fruit ripening occurred later in the exotic species than in most of the native species. The exotic species differed between them in some aspects of the reproductive process: C. monogyna had a higher fruit set, whereas S. aucuparia produced more flowers which offset its low values of fruit set. In both the exotic species and one simultaneously fruiting native species (Schinus patagonicus), high numbers of ripe fruits with a high proportion of viable seeds remained on the plants at a time when fruits of other native species were either scarce or absent (autumn-winter period). Compared to the fruits of S. patagonicus, those of both the exotic species are larger and fleshier. Therefore, the fruits of both the exotic species offer the dispersers, especially birds which were the most important frugivores in these studied temperate forests, a resource that would not be provided by the native plants. The success of these exotic species in Patagonian forests appears to be attributable in part to differences in their reproductive attributes such as fruit phenology and fruit traits such as size and fleshiness.
We studied the growth and photosynthetic capacity of Berberis darwinii shrub growing under different light conditions in their native area of Argentina to test if plant physiology differs from invaded area (using studies carried out in New Zealand). In its native range B. darwinii grows under different light conditions by adjusting shoot and leaf morphology and physiology. Plants of B. darwinii growing under the same light environments show similar physiology in native and invasive ranges. Therefore, intra-specific variations of the functional traits in native area do not condition successful invasiveness.
Exotic fleshy fruited plants are often dispersed by generalist frugivores into undisturbed or weakly disturbed forests. The establishment and spread of these plants in the understory may pass unnoticed until their abundance and size turns them a nuisance. Sorbus aucuparia is a fleshy fruited tree recently established in temperate forests of northwestern Patagonia. Our aim was to determine the invasion dynamics of S. aucuparia in a Nothofagus pumilio forest. We analyzed age structure, minimum age of reproduction, the time from colonization to effective recruitment (lag time), and demographic parameters to pinpoint critical stages for management. Currently, the population of S. aucuparia is increasing. Large numbers of suppressed, potentially reproductive individuals were found. Lag time was relatively short (25 years) in comparison to other invasive woody plants. The minimum reproductive age was 10 years, and all reproductive individuals were located in high light conditions. The number of trees at the reproductive stage made the most significant contribution to population growth; a 5 % reduction in this number would be enough for the population growth rate to be negatively affected. Thus, the reproductive stage is key to the control of S. aucuparia. Forest disturbance leading to increase light availability may result in higher rates of growth and reproduction among currently suppressed individuals, triggering further expansion events and increasing the number of invasion foci. Management strategies for tree species which present an inconspicuous bank of individuals in the understory, like S. aucuparia, should focus on early detection and eradication of reproductive individuals while avoiding the increase in light availability in the affected environment.
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