Forest ecologists often evaluate how well the species composition of saplings in the understory matches that of the canopy: absence of juveniles suggests that a tree species is suffering population decline. Here we offer a theoretical and empirical test of this assertion using data from a 50-ha census plot in Panama. Theory indicates that higher rates of population change, lambda, lead to more steeply declining size distributions (more juveniles relative to adults). But other parameters also affect the size distribution: lower growth rate of juveniles and lower survival at any size produce more steeply declining size distributions as well. Empirical evaluation of 216 tree populations showed that juvenile growth was the strongest predictor of size distribution, in the direction predicted by theory. Size distribution did correlate with population growth, but weakly and only in understory species, not canopy species. Size distribution did not correlate with the growth rate of larger individuals nor with survival. Results suggest that static in formation on the size distribution is not a good predictor of future population trends, while demographic information is. Fast-growing species will have fewer juveniles in the understory than slow growing species, even when population growth is equal.

The use of standardised classifications, or operational definitions, is essential if different researchers are to measure and compare similar entities. In the marine realm, algal 'turfs' are increasingly reported to be globally expanding at the expense of kelps and canopy-forming algae. However, ecological research about the underlying drivers of this shift is limited by a vague and inconsistent definition of what exactly a turf is. In order to stimulate more effective descriptions of 'turfs' and facilitate communication of research outcomes and comparisons across studies, we reviewed the use of the term turf in ecological studies of temperate coasts and coral reefs and (1) identified the main types and distribution of algal assemblages known as 'turfs', (2) examined the descriptions of turfs so that we may recognise some general characteristics, including those contingent on environmental conditions; and (3) offered character descriptions that could improve communication and comparisons. These descriptors centre on reporting information on the morphology, height, density of thalli, the amount of sediment trapped in turfs and a description of the area covered by turfs, including their patchiness and persistence. Our review recognised these as common attributes that could be usefully described across a wide range of circumstances and provide insights into the ecology of turfs and their interactions with other assemblages in a community. The use of common descriptors would provide the term 'turf' with greater scientific value.

Sporophyte recrultment, holclfast growth and mortality of giant kelp Macrocyst~spynfera were measured seasonally on permanent transects at 3 sltes [protected Intermediate and exposed) along a wave exposure gradient on the Monterey Peninsula, c e n t~a l Cal~fornia (USA) between 1988 and 1991 The constant presence of cold, nutnent-nch water and the relative absence of o t h e~ kelps and large grazers allowed the dynanucs of M pynfera populations to be examined under conditions in which wave exposure was highly vanable and ~nfluences of other abiotlc and biotic factors were minimized Recovery of M pynfera populations fiom decreased adult density (presumably due to stormlnduced mortality, adult density was negatively correlated with storm activity) was a 2-stage process requiring the establishment of luvenile populations and condit~ons suitable for ]uvenile growth to adult size Sporophyte recrultment was negatively correlated with M pynfera canopy cover, and thus appeared to be related to irradiance Recruitment was low and continuous under a temporally stable M pyrifera canopy at the protected slte At the intermediate and exposed sites, canopy cover was more variable, canopy loss was greater, and durdt~ons of low canopy cover were longer than at the protected site resulting in episodic sporophyte recruitment These distinct patterns in sporophyte lecruitment resulted In continuous luvenile populations at the protected site and intermittent luvenlle populations at the intermediate and exposed sites Growth of luveniles to adult size required additional irrad~ance probably d u e to gleater light requirements for luvenlle growth than for sporophyte recrultment We observed that luveniles grew to adult slze when canopy cover was low and adults were below a threshold denslty estimated at -10 plants 100 m 2 , but ~uveniles also occasionally grew to adult size following periods of low canopy cover only Ep~sodic sporophyte recruitment at the intermediate and exposed sites resulted in decreased coincidence of the 2 recovery stages, adult dens~ties were often decreased below threshold piior to the establishment of luvenile populations Recovery time, that required by populations to return to densities above threshold was equal to the time lag between occurrence of the 2 recovery stages and was therefore greatest at the more exposed sites Compansons between central and southern Cal~tornia M pyl~fera populat~ons suggest that by altering recovery time variable frequency and magnitude of storm disturbance may result in different periodlclties of adult population cycles K E Y WORDS. Glant kelp. Macrocyst~spyr~fera . Wave exposure. Demography. Recruitment. Recovery

La composición y abundancia de algas marinas, invertebrados epibénticos y peces se estimó en marzo y octubre de 2003, mientras que los invertebrados endobiontes de los rodolitos (criptofauna) fueron cuantificados en marzo de 2003. De todos los organismos, los rodolitos y S. horridum tuvieron las mayores coberturas en los 0.5 km 2 de fondos de cantos rodados y arena estudiados, de 2 a 8 m de profundidad. Se muestreó un total de 29 especies de algas, 40 taxones de invertebrados bénticos y 33 especies de peces. Como resultado de la pérdida y el reemplazo de taxones, las diversidades de microalgas y peces fueron similares en ambos muestreos, mientras que la de invertebrados disminuyó sin ocurrir reemplazo de marzo a octubre. La cobertura de rodolitos fue similar en ambos muestreos. La cobertura y densidad de S. horridum fue altamente estacional, y la flora no rodolítica varió de abundancia de S. horridum (35% de cobertura) en marzo a abundantes tapetes de algas rojas en octubre (22% de cobertura). Los invertebrados epibénticos más abundantes en marzo fueron el erizo Arbacia incisa, los tunicados y los poliquetos; sin embargo, para octubre, el primero ya no estaba presente. Haemulon maculicauda y Calamus brachysomus fueron los peces más abundantes en ambos muestreos, pero se observaron grandes variaciones temporales especialmente en especies de peces que forman cardúmenes. La densidad de rodolitos en marzo fue de 24 ind m-2 , con numerosos individuos >8 cm de diámetro. Quince rodolitos de varias clases de talla contuvieron 114 taxones criptofaunales, con un promedio de 40 taxones/individuo para los rodolitos más grandes. Estos resultados muestran la importancia de los hábitats de rodolitos para la diversidad, las grandes variaciones temporales en algunas comunidades y la excepcional diversidad de esta comunidad subtropical.