Cecilia A. Pérez

Coarse woody debris biomass in successional and primary temperate forests in Chiloé Island, Chile

Coarse woody residues (snags and logs) are a massive and functionally important component of high-latitude forest ecosystems, both natural and managed. Decaying logs and snags provide habitat for many organisms and participate in biogeochemical element fluxes within the forest ecosystem. Because of their large mass and slow decay rates, they may also play a significant role in the global carbon cycle. For these reasons, it is important to understand the dynamics of coarse woody debris (CWD) during forest succession. Here, we estimated the biomass of CWD (defined as logs or snags >10 cm stem

Changes in tree species richness, stand structure and soil properties in a successional chronosequence in northern Chiloé Island, Chile

Estudiamos una cronosecuencia de bosques sucesionales en el norte de la Isla de Chiloe, con el objeto de determinar sus patrones de recuperacion luego de perturbacion antropica. Se evaluaron hipotesis referentes a las tendencias de cambio en la riqueza de especies arboreas a lo largo de la sucesion, el reemplazo de especies sombra intolerantes por especies sombra tolerantes, y el impacto de la perturbacion en las propiedades edaficas de estos fragmentos. Muestreamos nueve rodales, representados por dos bosques sucesionales tempranos (<15 anos de edad minima del rodal), tres rodales intermedios (30-60 anos), tres avanzados (129-134 anos), y un bosque antiguo (ca. 200 anos). Las edades minimas fueron estimadas a traves de muestras de incremento radial de al menos 30 arboles del dosel por rodal. Los rodales tempranos e intermedios mostraron evidencias de perturbacion por incendios moderados, con unos pocos grandes arboles vivos remanentes. En cada rodal se establecieron parcelas permanentes de 50 x 20 m para determinar densidades y areas basales de arboles, con subparcelas interiores para estimar densidades de brinzales y plantulas. Para caracterizar los procesos edaficos en los rodales se determino el pH del suelo, los contenidos totales de carbono (C) y nitrogeno (N), N disponible y densidad aparente. En contraste con la hipotesis que predice una disminucion de la riqueza de especies arboreas en rodales mas antiguos, debido a la exclusion de especies pioneras, la riqueza de especies en el dosel aumento de 3 a 13 a traves de la cronosecuencia. Esta tendencia estuvo acompanada por una mayor homogeneidad en los valores de importancia de las especies en los rodales mas antiguos. Los cambios en riqueza de especies no estaban relacionados con las densidades de cada rodal, las cuales fueron maximas en los bosques de edad intermedia. Por otro lado, el numero de especies de plantulas y brinzales no cambio con la edad del rodal. La mayoria de las especies arboreas, tanto tolerantes como intolerantes a la sombra, se encontraban presentes como plantulas en todos los rodales. Las especies sombra-tolerantes tienden a reemplazar a las especies sombra-intolerantes en los bosques de edad mas avanzada. No se observo un reemplazo completo de estos dos grupos de especies, ya que los arboles sombra-intolerantes estaban presentes en el dosel y/o en el sotobosque de los rodales antiguos. Este patron sucesional se ajusta al modelo de Composicion Floristica Inicial de Egler, en el cual diferencias interespecificas en los atributos de historia de vida darian cuenta de los principales cambios en dominancia durante la sucesion. Las propiedades del suelo fueron similares a traves de la cronosecuencia, lo que sugiere que tanto los procesos ecosistemicos como la regeneracion arborea fueron capaces de recuperarse luego de incendios de intensidad moderada. Concluimos que, debido a la breve historia de impacto humano en el area, limitada principalmente al siglo 20, y a la persistencia post-perturbacion de algunos elementos estructurales tales como detritus lenoso y grandes arboles vivos, los bosques en el norte de Chiloe se recuperan del impacto humano. En la medida en que aumente el aislamiento de los bosques remanentes, junto con la recurrencia de incendios u otras formas de impacto humano, su capacidad para recuperar su estructura y biodiversidad original deberia disminuir. Los umbrales de deforestacion y alteracion de rodales a escala del paisaje que pueden alterar las tendencias sucesionales a la escala de los fragmentos de bosque constituyen una importante pregunta abierta

Old-Growth Temperate Rainforests of South America: Conservation, Plant-Animal Interactions, and Baseline Biogeochemical Processes

A structural and compositional definition of old-growth forest is presented, which places emphasis on the lack of recurrent human impact, the presence of a shade-tolerant canopy with emergent pioneers, and a patch area that minimises edge effects. Using this definition, we provide an overview of the current conservation status, relevance of plant–animal interactions, and unique features of nutrient fluxes in old-growth forests of southern South America. Chile hosts the largest area and latitudinal extent of old-growth temperate forest remaining in the southern hemisphere, reaching 56° S in the Cape Horn Archipelago. Despite recent public and private efforts to protect remaining old-growth forests and their endemic biodiversity, they continue to decline steeply as a result of new routes of access to commercial stands, lack of protection of coastal areas, anthropogenic fire, and expansion of monoculture-based forestry toward higher latitudes and altitudes. Pollinators (insects and birds) and vertebrate frugivores (birds and an arboreal marsupial) are important mutualists of many Chilean rain forest trees, vines and epiphytes. There is evidence to suggest that some native pollinators and animal seed vectors may be highly susceptible to changes in forest structure due to loss of old-growth forest cover. Forest fragmentation and loss of keystone, animal-pollinated emergent trees due to logging and fires, have radically changed pollinator assemblages in rural landscapes, leading to reproductive dependence on European honey bees and other exotic species. Regarding other ecosystem functions, nutrient cycles in unpolluted old-growth forests of southern Chile are characterised by strong inorganic nitrogen (N) retention and large organic N leakage to forest streams. Non-symbiotic N fixation in litter and soil tends to increase in older stands. Knowledge of these “unpolluted nutrient cycles”, particularly N and P, is still meager despite its relevance to understanding the consequences of increased global disruption of element cycles by humans. Development of baseline measurements and experiments in southern Chilean old-growth temperate forests can enhance our understanding of unpolluted ecosystem functioning.

Distribution and cycling of C, N, Ca, Mg, K and P in three pristine, old-growth forests in the Cordillera de Piuchué, Chile

We assessed a number of biomass and soil parameters in order to examinerelationships among nutrient availability, forest productivity and vegetationpatterns in two old-growth forested watersheds in a pristine montane landscapeon Isla de Chiloé, Chile. We selected watersheds in both gymnosperm- andangiosperm-dominated forests and determined tree species, d.b.h. and health forall trees < 2 cm d.b.h. in plots established at 50m intervals. Soils were sampled at two depths in each plot andanalyzed for total C and N, and for exchangeable Ca, K, Mg andresin-extractableP. Allometric relationships and vegetation nutrient concentrations were used todetermine above-ground pools from the vegetation survey data. Growth rates werederived from increment core measures. Soil pools of most elements measuredappear adequate to support forest growth indefinitely. Mineralized nitrogen,which is similar in quantity to the annual demand for nitrogen from the soil isthe exception, consistent with the possibility of N limitation in two of theforest types studied. A third type, an evergreen broadleaved forest, appears torequire substantially more nitrogen than would appear to be available from netmineralization measurements. Productivity per unit of nitrogen required fromthesoil is quite high, largely as a consequence of the evergreen habit of thespecies in these forests. Compared to other temperate montane forests in theNorthern Hemisphere, nutrient pools and cycling characteristics were found tobemostly similar across forest types, in spite of considerable variation invegetation and soils.

Estación Biológica Senda Darwin: Investigación ecológica de largo plazo en la interfase ciencia-sociedad

This article discusses Senda Darwin Biological Station and the work of the scientists who study the anthropological role in ecological processes there.

NON-SYMBIOTIC NITROGEN FIXATION, NET NITROGEN MINERALIZATION AND DENITRIFICATION IN EVERGREEN FORESTS OF CHILOÉ ISLAND, CHILE: A COMPARISON WITH OTHER TEMPERATE FORESTS

Los bosques templados de Chile ofrecen un escenario unico para estudiar los ciclos biogeoquimicos debido a su condicion libre de contaminacion industrial. Comparamos tres flujos importantes del ciclo del nitrogeno (N), tales como fijacion no simbiotica, mineralizacion neta y desnitrificacion, en bosques del sur de Chile con datos de bosques templados del hemisferio norte sujetos a contaminacion. Estudiamos cinco bosques siempreverdes maduros y uno secundario en la Isla de Chiloe. La fijacion no simbiotica del nitrogeno en la hojarasca, el suelo mineral y desechos lenosos gruesos, se estimo mediante el metodo de reduccion de acetileno. La tasa neta de mineralizacion del suelo superficial se estimo con el metodo de la bolsa enterrada. La tasa de desnitrificacion se estimo mediante el ensayo de inhibicion con acetileno en muestras de suelo intactas. Los resultados muestran que en algunos bosques templados chilenos una mayor proporcion de la fijacion no simbiotica del N ocurre en la hojarasca (0,23-2,26 kg N ha-1 ano-1) y en los desechos lenosos gruesos (1,31-1,34 kg N ha-1 ano-1). En cambio, las mayores tasas de fijacion de N en los bosques templados del hemisferio norte han sido encontradas en el suelo mineral. Los bosques siempreverdes de Chiloe presentaron tasas de mineralizacion neta y desnitrificacion considerablemente menores que los bosques templados del hemisferio norte, tanto siempreverdes como deciduos. Interpretamos estos resultados como indicadores que los bosques templados del hemisferio sur poseen un control mas eficiente de la circulacion interna del N que su contra parte del hemisferio norte

Bromeliad growth and stoichiometry: responses to atmospheric nutrient supply in fog-dependent ecosystems of the hyper-arid Atacama Desert, Chile

Carbon, nitrogen, and phosphorus (C, N, P) stoichiometry influences the growth of plants and nutrient cycling within ecosystems. Indeed, elemental ratios are used as an index for functional differences between plants and their responses to natural or anthropogenic variations in nutrient supply. We investigated the variation in growth and elemental content of the rootless terrestrial bromeliad Tillandsia landbeckii, which obtains its moisture, and likely its nutrients, from coastal fogs in the Atacama Desert. We assessed (1) how fog nutrient supply influences plant growth and stoichiometry and (2) the response of plant growth and stoichiometry to variations in nutrient supply by using reciprocal transplants. We hypothesized that T. landbeckii should exhibit physiological and biochemical plastic responses commensurate with nutrient supply from atmospheric deposition. In the case of the Atacama Desert, nutrient supply from fog is variable over space and time, which suggests a relatively high variation in the growth and elemental content of atmospheric bromeliads. We found that the nutrient content of T. landbeckii showed high spatio-temporal variability, driven partially by fog nutrient deposition but also by plant growth rates. Reciprocal transplant experiments showed that transplanted individuals converged to similar nutrient content, growth rates, and leaf production of resident plants at each site, reflecting local nutrient availability. Although plant nutrient content did not exactly match the relative supply of N and P, our results suggest that atmospheric nutrient supply is a dominant driver of plant growth and stoichiometry. In fact, our results indicate that N uptake by T. landbeckii plants depends more on N supplied by fog, whereas P uptake is mainly regulated by within-plant nutrient demand for growth. Overall, these findings indicate that variation in fog nutrient supply exerts a strong control over growth and nutrient dynamics of atmospheric plants, which are ubiquitous across fog-dominated ecosystems.

Nitrogen mineralization in epiphytic soils of an old-growth Fitzroya cupressoides forest, southern Chile

ABSTRACT Epiphytic soils derive from organic matter accumulation on trunks and canopy branches of large trees. We compared chemical and physical properties, rates of net N mineralization, and bacterial biomass carbon associated with epiphytic soils and the forest floor of an old-growth, temperate forest dominated by the long-lived Fitzroya cupressoides (Cupressaceae) in Chiloé Island, southern Chile. Epiphytic soils had lower density, higher moisture content, higher total carbon and nitrogen contents, and lower pH than forest floor; however, these differences were only slight. Microbial biomass and soil C/N ratios did not differ between soil types. We estimated similar N mineralization rates in epiphytic soil and in the forest floor, but there was a significant interaction between time of the year and soil type, resulting from higher N production in epiphytic soils in some months. Microbial net N mineralization in the epiphytic layer contributed ca 6% of the internal N circulation. Fitzroya trees may access these nutrients via adventitious root uptake and leaching to the forest floor, thus exploiting an alternative path of nutrient circulation in old-growth forests.

Effects of Nitrate and Labile Carbon on Denitrification of Southern Temperate Forest Soils

The pressure for anthropogenic land use changes and logging of temperate forests in southern Chile is rapidly increasing, with its potentially high impacts on the capacity of soils to retain important limiting elements. We tested the hypotheses that logging increases the denitrification rates and nitrate and C limitation of denitrifiers activity would be higher in soils of unlogged, old-growth forests than in soils of logged forests. Potential denitrification rates were estimated by the acetylene inhibition assay in intact soil cores in laboratory short-term aerobic incubations using the following treatments: 0.7 mmol NO3-N addition, the same nitrate addition plus 23.3 mmol C-glucose, and controls (no additions) with and without 10% v/v acetylene. Forest logging did not significantly change soil nitrate content and C lability (e.g. soil C/N ratio). A nested two-factor ANOVA for repeated measures showed that denitrification was enhanced by nitrate plus labile C additions in both forests, suggesting that in both logged and unlogged forests labile C and nitrate limit denitrifiers activity. Increases were up to one order of magnitude when glucose was added to nitrate treated soils; from 373 ± 113 to 3 353 ± 451 µg N2O-N m -2 d -1 in the unlogged, oldgrowth forest and from 1 369 ± 941 to 12 192 ± 7 474 µg N2O-N m -2 d -1 in the logged forest. We conclude that, denitrification would be enhanced in logged forests in the longer term due to a greater nitrate and labile C availability of both in disturbed soils.

ACTIVIDAD RESPIRATORIA EN EL HORIZONTE ORGANICO DE SUELOS DE ECOSISTEMAS FORESTALES DEL CENTRO Y SUR DE CHILE

El mantillo del suelo (horizontes Oi y Oe) de ecosistemas boscosos es utilizado como habitat, fuente de nutrientes y energia para una gran diversidad de organismos. Ocurre, en consecuencia, un flujo de carbono (C) desde el detritus debido a la produccion de CO2 por respiracion de la biota. En este trabajo se midio y comparo la actividad respiratoria en condiciones de laboratorio de muestras de mantillo, colectadas en tres tipos de bosques del centro y sur de Chile: bosque Nordpatagonico (Nothofagus), bosque Siempreverde de Coniferas (Fitzroya) y bosque Esclerofilo (Cryptocarya). Las muestras de este ultimo se separaron en tres fracciones de tamano de particulas (>2,4; 2,4-1,2 y < 1,2 mm), con el fin de poner a prueba la hipotesis de la constancia de la tasa de respiracion por unidad de masa seca durante la descomposicion de sustratos homogeneos, derivada del modelo teorico de Agren & Bosatta, tomando en cuenta el contenido hidrico de las muestras. Las incubaciones se realizaron a 20 oC, durante un maximo de 22 dias, y el CO2 producido fue colectado en solucion alcalina y determinado por titulacion. Se construyeron curvas de produccion acumulada de C-CO2, estimando la tasa de respiracion por unidad de masa seca por la pendiente de la porcion lineal de dichas curvas. Se obtuvieron estimaciones insesgadas de las tasas mediante remuestreo sin reposicion. Las tasas de respiracion por unidad de masa seca fluctuaron entre 2,8 y 57,7 mg C-CO2 100 g-1 dia-1, siendo mayores en las muestras del bosque Nordpatagonico. En la hojarasca del bosque Esclerofilo no se observaron diferencias significativas entre las fracciones de tamano de particulas. Sin embargo, la mayor tasa respiratoria observada en la fraccion fina (11,8 mg C-CO2 100 g-1 d-1) estuvo asociada a un mayor contenido hidrico de la misma. No se encontraron diferencias significativas entre la actividad respiratoria de la hojarasca de los bosques de Coniferas y Nordpatagonico, a pesar de las diferencias en su relacion C/N. Se discuten los resultados en el contexto teorico del proceso de descomposicion de la materia organica y la dinamica del carbono en suelos de ecosistemas forestales