Tristerix tetrandrus (Loranthaceae) and its host-plants in the Chilean matorral: patterns and mechanisms.

Interactions between a Chilean mistletoe, quintral (Tristerix tetrandrus, Loranthaceae) and its potential host plants were studied at a site with mediterranean type climate. The results show that the distribution of T. tetrandrus is related to the behavior of avian dispersers, which feed on its fruit, and evacuate the seeds at random in the field, but the distribution is also influenced bymicroenvironmental conditions, survival of seedlings is hampered at drier locations. The infection capacity of the seeds is increased after birds have eliminated the fruit coat.Survival of T. tetrandrus seeds differed depending on the species to which they were attached experimentally. Seeds germinated, and plants developed on Colliguaya odorifera and Kageneckia oblonga, previously reported as susceptible to infection. Survival was significantly higher on C. odorifera, although in the field it is infected less frequently than K. oblonga. In species on which no T. tetrandrus has been previously reported, resistance to infection might be ascribed to different mechanisms: in Quillaja saponaria, differentiation of cork layers apparently prevents penetration by haustoria; in Lithraea caustica haustoria enter the cortex and phloem, but no further development ensues. K. oblonga seldom bears more than one T. tetrandrus plant. Experimental inoculations showed that significantly more seeds developed into plants on K. oblonga individuals not previously infected with quintral, suggesting that they become resistant to infection.

Vegetation change in large clearings: Patterns in the Chilean matorral.

Previous studies have shown that in Chile the so called mature matorral can have the form of either a continuous matrix of shrubs (wet sites) or of multispecific clumps of shrubs (dry sites). After clearing, sites are known to be initially covered by annuals and then byBaccharis spp. orAcacia caven shrubs. Further vegetation changes are still not documented. In the first part of this contribution we show evidence indicating that the "seed rain" of plants dispersed by birds is important only around bird perches and that in general "seed shadows" of mature matorral shrubs are small. These results suggest that late recolonization of cleared areas occurs by a slow diffusion process in which the presence of perching sites for birds plays a significant role. Then we exhibit results regarding the importance of seasonal droughts and European rabbits in explaining transitions between the various types of plant cover. Here we conclude that nursing by older shrubs and not by rocks or fallen branches, is a requirement to insure the survival of seedlings belonging to mature matorral shrubs. Nurses are important regarding both summer desiccation and herbivory. These nurse effects seem to be more important at dry sites where rabbits are also more numerous, than at wet sites where conditions seem somewhat milder and vegetation change could be faster. In the last part we discuss a scheme of vegetation change that incorporates these processes and explains the relation between them, the vegetation types and the recolonization of wet and dry areas. Finally, a brief mention is made to the difference between these processes and the comparable ones in the California chaparral.