Un nuevo xenófito del género Baccharis L. (Asteraceae) para el centro de la Península Ibérica

Se indica la presencia de Baccharis pilularis DC. subsp. consanguinea (DC.) C.B. Wolf como posible nueva planta invasora en la península Ibérica.

Baccharis pilularis (coyote brush).

A datasheet on Baccharis pilularis covering, as an economically important tree, its taxonomy, importance, silviculture, distribution, biology and ecology, uses, products and pests.

Nest Site Selection and Nest Success in a Song Sparrow Population: The Significance of Spatial Variation

I tested the hypothesis that individual Song Sparrows (Melospiza melodia) choose nesting microhabitat that reduces their risk of nest predation, using two years of data (n = 196 nests) from two adjacent sites in California coastal scrub, one grazed and one ungrazed. Nesting habitat was compared between nest patches and random locations, and between successful and unsuccessful nests. In both sites, nest patch habitat differed significantly in structure and plant species composition from habitat available within territories. However, of six habitat characteristics associated with nest patch choice, only two were related to nest success, and that relationship differed between the two study sites. Only in the grazed site was the amount of coyote bush (Baccharis pilularis) in the nest patch positively associated with both nest site selection and nest success. In contrast, coyote bush was unrelated to nest site choice and had a nonlinear relationship with nest success in the ungrazed site, such that nests surrounded by intermediate amounts of coyote bush had the lowest probability of success. In the grazed site, nests surrounded by intermediate amounts of rushes (Juncus spp.) were also less successful. Nests built in larger, discrete patches of vegetation were more successful in the ungrazed site, but not in the grazed site. Although the sites differed greatly in the amount of preferred nest microhabitat available, there was no difference between the sites in the overall rate of nest success (23–32%). I suggest that spatial variation in the relationship between nest habitat and nest outcome may favor flexible nest-site preferences in this population. Selección de Sitios de Nidificación y Éxito de los Nidos en una Población de Melospiza melodia: La Importancia de la Variación Espacial Resumen. Evalué la hipótesis que dice que los individuos de Melospiza melodia eligen nidificar en microhábitats que reducen el riesgo de depredación de los nidos. Utilicé datos de dos años (n = 196 nidos) provenientes de dos sitios adyacentes, uno pastoreado y otro sin pastoreo, ubicados en matorral costero de California. El hábitat de nidificación fue comparado entre parches con nidos y localidades aleatorias, y entre nidos exitosos y no exitosos. En ambos sitios el hábitat de los parches con nidos fue significativamente diferente en la estructura y composición de especies de plantas comparado con el hábitat disponible dentro de los territorios. Sin embargo, de seis características de hábitat asociadas con la elección del parche de nidificación, sólo dos estuvieron relacionadas con el éxito de los nidos, y esta relación difirió entre los sitios estudiados. Sólo en los sitios con pastoreo hubo una asociación positiva entre la cantidad de matas de Baccharis pilularis en los parches y la selección de sitios para nidificar y el éxito de los nidos. En contraste, B. pilularis no se relacionó con la selección del lugar de nidificación en sitios no pastoreados, y tuvo una relación no lineal con el éxito reproductivo, de modo que los nidos rodeados por cantidades intermedias de B. pilularis presentaron la menor probabilidad de éxito. En los sitios pastoreados, los nidos rodeados por cantidades intermedias de Juncus spp. también fueron los menos exitosos. En sitios sin pastoreo, los nidos construidos en parches de vegetación grandes y discretos fueron los más exitosos, pero esto no ocurrió en sitios pastoreados. Aunque los sitios fueron sumamente distintos en relación a la cantidad disponible de microhábitat preferido para nidificar, no presentaron diferencias en la tasa general de éxito de los nidos (23–32%). Sugiero que la variación espacial en la relación entre el hábitat y el éxito de los nidos puede favorecer la flexibilidad en la preferencia de sitios de nidificación en esta población.

Responses of Landscape Groundcovers to Minimum Irrigation

Four irrigation regimes based on percentages of real-time reference evapotranspiration (ET0) were applied to six widely used species of landscape groundcovers (Baccharis pilularis ‘Twin Peaks’, Drosanthemum hispidum, Vinca major, Gazania rigens v. leucolaena ‘Yellow Cascade’, Potentilla tabernaemontanii, and Hedera helix ‘Needlepoint’) during a 17-month period in Irvine, CA. Irrigation treatments (50%, 40%, 30% and 20% of ET0) were applied when accumulated real-time ET0 × treatment percentage reached 4.0 cm (1.6 in). Although the response to irrigation treatment was species dependent, Baccharis, Drosanthemum, and Hedera maintained at least minimally acceptable visual quality with applied water equal to 20% ET0, while Vinca required a minimum of 30% ET0. Acceptable visual quality of Gazania and Potentilla were not maintained at any treatment. Visual quality of Potentilla was better at ET0 greater than or equal to 30% ET0, but visual quality of Gazania was not improved with more water.

PERFORMANCE OF SIX GROUNDCOVER SPECIES UNDER MINIMUM IRRIGATION

The performance of six landscape groundcover species was evaluated in a field experiment with irrigation treatments of 50%, 40%, 30%, and 20% of real-time ET0. Analysis of seasonal plant performance ratings indicated that for Baccharis pilularis `Twin Peaks', Drosanthemum hispidum, and Hedera helix `Needle point' there were no season-long increases in plant appearance when irrigated more than 20% ET0. Vinca major, Gazania hybrid, and Potentilla tabernaemontanii exhibited no significant improvement in appearance when irrigated above 30% ET0. A marked decline in performance was apparent in Gazania and Potentilla at all treatments during the study period, however, suggesting that their long-term minimum irrigation needs exceed 50% ET0. In a follow-up study, five of the above species and Osteospermum fruticosum received 30% ET0 at irrigation schedules of three times/week, once/week, once/2 weeks, and once/4 weeks. Potentilla was not sustained in acceptable condition at any treatment, while there were no season-long differences in performance within the other species due to irrigation frequency.

Influence of Irrigation Scheduling on Groundcover Performance

The performance of six landscape groundcover species was evaluated when irrigated at 30% of ET0 at irrigation schedules of three times per week, once per week, once every 2 weeks, and once every 4 weeks. Potentilla tabernaemontani could not be sustained under any of the treatments. For the other species (Baccharis pilularis, Drosanthemum hispidum, Vinca major, Osteospermum fruticosum, and Hedera helix) there were no season-long differences in a species' performance or density due to irrigation frequency, but there were significant differences among species across irrigation treatments. Drosanthemum and Osteospermum provided good overall appearance and density consistently through the season. Baccharis maintained acceptable performance most of the irrigation season, while Vinca and Hedera became unacceptable in appearance in mid-season. Soil moisture content differed among species, but was not consistently different between irrigation treatments.