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  • 1
    ISSN: 1432-1939
    Keywords: Baccharis pilularis ; Episodic invasion ; Shrub stablishment ; Community change ; El Niño
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We studied the invasion of a California annual grassland by the shrub, Baccharis pilularis ssp. consanguinea (DC) C.B. Wolf. A series of aerial photographs indicated that the shrub had been present at the study site for 35–45 years but spread very little until the early 1970's. A period of slow expansion was followed by rapid outward spread of the shrub population and large increases in shrub density. Detailed demographic studies showed a period of rapid population increase from 1978 to 1983, with the highest stablishment rates in 1982–83. Establishment was strongly correlated with annual and spring rainfall amounts. An iniiall period of slow outward spread is thought to have profided foci for rapid spread during years of high rainfall.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Baccharis pilularis ; Shrub establishment ; Succession ; Coexistence ; Episodic invasion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Previous studies have shown that the shrub, Baccharis pilularis spp. consanguinea, invades annual grasslands in the San Francisco Bay region in a sporadic manner. Invasion was shown to be positively correlated with the amount of rainfall received in the spring. Here we show that, although Baccharis seeds are dispersed near the beginning of the winter rainy season, seedling root growth is extremely slow until spring. At this time, cessation of the winter rains and transpiration by the grassland annuals results in drying of the upper soil profile. We conclude that establishment of Baccharis seedlings at our study site usually fails because seedling roots cannot reach depths of permanently moist soil, below the depth of the grass roots, before this soil drought occurs. The continuation of rains into the warmer spring months provides a window of time when favorable temperatures and adequate soil moisture allow shrubs to establish.
    Type of Medium: Electronic Resource
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