Alicia J. Hoffmann

Shrub clumps of the Chilean matorral vegetation: structure and possible maintenance mechanisms

SummaryPrevious studies have claimed that the Chilean matorral is more open than the Califonia chaparral, and have attributed this dissimilarity largely to the role of man in Chile. In this paper we show that in general the Chilean matorral has a structure better described as shrub clumps that merge to form a continuous vegetation matrix only in very mesic habitats, where it is comparable to the Califonia chaparral. We also present evidence that these clumps have been present for at least the last 26 years and that even without human disturbance they are likely to maintain themselves. Evidence for the latter pertains to seed dispersal, seed germination and establishment, seedling survival, and the diameter size structure of shrub clumps. Finally, we propose that differences between the California chaparral and Chilean matorral are more profound than previously thought and are due not only to different degrees of human disturbance, but also to the presence of periodical natural fires in California and not in Chile, and to different shrub recruitment patterns and mammalian herbivore activity in the two areas.

Vegetation change in large clearings: Patterns in the Chilean matorral

SummaryPrevious 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.

Interactions in the patterns of vegetative growth and reproduction in woody dioecious plants

SummaryInteractions between vegetative growth and reproduction were evaluated in Peumus boldus, Lithraea caustica and Laretia acaulis, three woody dioecious species in central Chile. Phenological observations were made periodically on marked branches of male and female plants, and biomass allocation (dry weight) to vegetative and reproductive tissues was measured. The magnitude of flowering was evaluated in groups of plants in three successive seasons. The patterns of activities are species- and sex-dependent, and cycles of 2–4 years have been established. Branches that produce flowers either do not grow or grow less than branches without flowers, and males and females have differential resource allocation: male branches attain higher biomass values. Groups of plants show seasonal behavior that suggest synchrony in their reproductive activities.

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

SummaryInteractions 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.

Banks of microscopic forms and survival to darkness of propagules and microscopic stages of macroalgae

Estudios previos han encontrado que el numero de especies formando un banco de formas microscopicas en pozas de mareas de Chile central incluyo solo la mitad del numero de especies presentes en la vegetacion macroscopica en las cercanias de las pozas intermareales. Una primera condicion para sobrevivir en estos bancos radica en la capacidad de las formas microscopicas para tolerar oscuridad total o baja iluminacion por periodos prolongados. Para evaluar dicha capacidad, los propagulos de 17 especies de algas verdes, pardas y rojas, presentes y ausentes del banco de formas microscopicas fueron incubadas a distintas combinaciones de intensidad luminosa y fotoperiodo. Propagulos del 47 % de las especies evaluadas (ocho especies) germinaron en oscuridad mientras que los propagulos de las otras nueve especies requirieron valores muy bajos de intensidad luminosa (2-10 µmol m-2 s-1) para germinar. En una mayoria de las especies, las formas microscopicas mostraron una mayor tolerancia a la oscuridad que los propagulos. Algunos sobrevivieron en la oscuridad por sobre un ano y una especie (Gelidium lingulatum) pudo sobrevivir en oscuridad absoluta por 500 dias. La habilidad para sobrevivir en oscuridad total no se relaciona con presencia de la especie en los bancos de formas microscopicas, con grupos filogeneticos o con historias de vida especificas, con tamano de propagulo, morfologia de la forma microscopica o estatus sucesional (especies fugitivas versus sucesionales tardias). Por lo tanto, tolerancia a la oscuridad aparece como un patron comun a propagulos y formas microscopicas de una mayoria de algas bentonicas. Los patrones de crecimiento exhibidos por las formas microscopicas de Lessonia nigrescens, Chaetomorpha firma y Glossophora kunthii sugiere que el efecto de altas intensidades luminosas sobre estos reclutas podria determinar los limites superiores de distribucion vertical de estas especies

Morphology and Histology of Trevoa trinervis (Rhamnaceae), a Drougth Deciduous Shrub from the Chilean matorral

Summary The ramification system and the histological structures of Trevoa trinervis, a shrub from the Chilean matorral, are studied. The axilar bud system of the principal branches is constituted by a summer bud that originates a thorn-shoot in the first year, and a winter bud. This remains dormant, to sprout rapidly as soon as the soil humidity increases during the following winter. The winter bud originates a small branch, bearing most of the leaves; its growth is completed by the development of a terminal inflorescence. When humidity decreases, both the branches and the leaves dry and drop. The leaves present a mesophytic structure. Several of the characters described are interpreted as adaptations to drought.

Daylength and light responses in growth and fertility of Glossophora kunthii (Phaeophyta, Dictyotales) from Pacific South America

Excised ligulae of Glossophora kunthii (C. Ag.) J. Ag. were cultured in photoperiods of 4–24 h and photon fluence rates of 10–75 μmol.m−2.s−1. Daylength interacted with irradiance on the growth of the ligulae. Maximal growth of primary ligulae occurred in long‐day regimens with high irradiances suggesting an effect of irradiance on photosynthesis and growth. In contrast, growth of secondary ligulae was greatest in short‐day regimes. Differences were significant at the highest irradiance tested. Differentiation of tetrasporangia on the ligulae is a short‐day photoperiodic response. Daylengths of 8.5 h or less induced a sharp increase in numbers of fertile ligulae and tetrasporangia attaining maturity. Interruptions of the dark period decreased the development of tetrasporangia; the number of interruptions had a cumulative inhibitory effect. Differentiation of reproductive structures was influenced by interactions of photoperiod and irradiance. Maximum numbers of tetrasporangia were formed at short‐day regimes and low irradiances; differentiation was completely inhibited at long‐day conditions and high irradiance.