Description
A comparison of the pattern of herb and shrub growth was undertaken in two similar appearing but floristically unrelated brush land areas, the Fundo Santa Laura, Chile and Echo Dell, California. Within each study site four types of areas were sampled to evaluate the change in herb-shrub relationship with disturbance. These were: Undisturbed, Semi-disturbed, Disturbed (cleared), and a First-year burn. The point-quarter and line intercept methods were used t o gather data in both sites. The results of the study and the conclusions reached were: (1) The two herbaceous vegetations appear at different times and in different relationships to the shrub overstories. In Chile the herbs and shrubs are found concurrently, the herbs growing directly beneath specific shrub canopies. The destruction of the shrubs by fire is coupled with the loss of the herbs. In California the herbaceous vegetation is homogeneously distributed within and between the canopies and the high levels of herb growth are associated with the lack of a shrubby overstory. (2) The types of herbs commonly found are different in the two systems. In Chile 75% of the major species are herbaceous perennials, in California when the herbaceous vegetation is at its peak, following fire, 75% of the species are annuals. (3) Slight amounts of disturbance altfrs the vegetation in both countries but in Chile disturbance only serves to reinforce the pattern of herb and shrub association. In California slight amounts of disturbance allow for a greater proliferation of herbs but there is no apparent change in the distribution of the herbs, they remain relatively homogeneously distributed. (4) Extreme disturbance such as clearing causes apparently similar destruction of the vegetations. In both Chile and California clearing reduced the number of shrubs and opened the area to colonization by mediterranean weeds. (5) The role of fire in the two areas is apparently different. Fire does not appear to be common in the mattoral, now or in the past, but it is common in the chaparral system. (6) The climatic stresses appear to be somewhat different in the two countries. While both Chile and California have mediterranean climates the fluctuations in temperatures and humidities appears to be less in Chile than California, the maritime influences in Chile seem to damp out climatic variations producing an overall more constant climate. The type of perennial vegetation found in central Chile provides support for this idea. The more widely fluctuating and less predictable climate in southern California is reflected in the annual type herbaceous flora. In conclusion the two systems are superficially similar but represent different climatic and ecological types, with different fire histories. Chilean mattoral appears to be a derivative of a former forest type vegetation where fire type disturbance was uncommon, while in California the chaparral appears to be a true xerophytic scrub vegetation, constantly influenced by fire.
