Effects of overstorey canopy, plant-plant interactions and soil properties on Mediterranean maritime pine seedling dynamics     

Encarna Rodríguez-García  Felipe Bravo  Thomas A. Spies 《Forest Ecology and Management》2011,262(2):244-251

Seedling emergence, survival and early growth of the Mediterranean conifer P. pinaster were studied under closed canopy and open canopy (gaps) cover conditions in a Mediterranean forest of central Spain during two consecutive years (March 2008 to January 2010). Our main objective was to understand how overstorey structure, shrubs and soil properties influence recruitment in this species. Natural emergence and seedling survival were significantly better under closed canopy cover than under open canopy during the two consecutive years of the study; survival increased as radiation decreased. Proximity to shrubs under closed canopy cover was associated with lower mortality rates as well as a positive and apparently transitive effect on early growth. Amelioration of microclimatic conditions is hypothesized as the primary facilitation agent of those observed. Younger seedlings established during the spring of 2008 experienced higher mortality rates than older seedlings established before 2008, and soil properties affected seedling survival significantly. Water stress during summer appeared to be the main cause of seedling mortality in both years. Our study suggests that seedlings of shade-intolerant species may require overstorey cover to establish successfully, and that positive plant-plant interactions in forest communities may be more important than expected in the milder conditions provided by overstorey canopy cover.  相似文献   

Empirical evaluation of confidence and prediction intervals for spatial models of forest structure in Jalisco,Mexico     

Robin M.Reich  C.Aguirre-Bravo  Vanessa A.Bravo  Martin Mendoza Briseo 《林业研究》2011,22(2):159-166

In recent years there has been an increasing interest in developing spatial statistical models for data sets that are seemingly spatially independent.This lack of spatial structure makes it difficult,if not impossible to use optimal predictors such as ordinary kriging for modeling the spatial variability in the data.In many instances,the data still contain a wealth of information that could be used to gain flexibility and precision in estimation.In this paper we propose using a combination of regression analysis to describe the large-scale spatial variability in a set of survey data and a tree-based stratification design to enhance the estimation process of the small-scale spatial variability.With this approach,sample units(i.e.,pixel of a satellite image) are classified with respect to predictions of error attributes into homogeneous classes,and the classes are then used as strata in the stratified analysis.Independent variables used as a basis of stratification included terrain data and satellite imagery.A decision rule was used to identify a tree size that minimized the error in estimating the variance of the mean response and prediction uncertainties at new spatial locations.This approach was applied to a set of n=937 forested plots from a state-wide inventory conducted in 2006 in the Mexican State of Jalisco.The final models accounted for 62% to 82% of the variability observed in canopy closure(%),basal area(m2·ha-1),cubic volumes(m3·ha-1) and biomass(t·ha-1) on the sample plots.The spatial models provided unbiased estimates and when averaged over all sample units in the population,estimates of forest structure were very close to those obtained using classical estimates based on the sampling strategy used in the state-wide inventory.The spatial models also provided unbiased estimates of model variances leading to confidence and prediction coverage rates close to the 0.95 nominal rate.  相似文献   

Conservation of otter (Lutra lutra) in a Mediterranean area: the importance of habitat quality and temporal variation in water availability     

Jos Prenda  Pedro Lpez‐Nieves  Rafael Bravo 《水产资源保护:海洋与淡水生态系统》2001,11(5):343-355

1. This study analyses quantitatively the association between habitat characteristics and annual variation in water availability on otter (Lutra lutra L.) distribution in a large Mediterranean area (13 717 km²) in southern Spain. 2. There was a strong positive correlation between habitat quality, estimated after the two first components of a principal component analysis of a matrix of habitat variables×sites, and an index of otter presence/absence, otter presence being most commonly associated with unpolluted and undisturbed sites surrounded by woodland. 3. After univariate analysis, the main freshwater habitat features were statistically different between sites with otters and sites lacking them. In general, otters occurred in medium‐sized fluvial habitats, with high bankside vegetation cover, unpolluted, with low or very low human disturbance and surrounded by forests or dehesas (Mediterranean‐like savannah). 4. Water availability, inferred from the water balance, strongly influenced otter distribution and the type of water body used the most. As water availability increased so did the otter distribution range and during these periods they tended to colonize low‐order streams. During periods of water shortage, otters were usually found in high‐order streams and reservoirs, the only sites that kept water. 5. This work shows that otter distribution in Mediterranean areas is strongly influenced by two factors — man‐induced habitat degradation and natural variability in water availability. The addition of the second factor to the first one introduces additional risks to the survival of otter populations in Mediterranean areas compared with more northerly and humid areas. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Effect of electrical stunning at slaughter on the carcass, flesh and eating quality of farmed sea bass (Dicentrarchus labrax)     

Toby G Knowles  Steve N Brown  Paul D Warriss  Jeff Lines  Ambrose Tinarwo  re Bravo  Hélia Carvalho  & Amparo Gonçalves 《Aquaculture Research》2007,38(16):1732-1741

Food quality aspects of farmed sea bass (Dicentrarchus labrax) were compared following two methods of slaughter: the normal commercial method of killing, by immersion in an ice slurry, or by first electrically stunning the fish, before immersion in an ice slurry. Quality was assessed for up to 10 days of storage on ice after slaughter. No differences were found between the slaughter methods in terms of an overall sensory evaluation of cooked fillets, or in terms of overall carcass quality: overall appearance, internal and external haemorrhage, fin damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. Using objective measurements of colour, no differences between fish from either treatment were found in terms of external colour or colour of the fillets. A chemical analysis of flesh nucleotide breakdown products as well as the freshness indicator K_i value did not differentiate the two treatments nor did the industry standard freshness scoring technique (QIM, quality index method), over 10 days of storage on ice. Flesh pH was marginally lower in electrically stunned fish at 4 h post mortem (6.42 cf 6.56) but by 24 h, pH in fish from both treatments had decreased to a similar level (6.22). Humane electrical stunning of sea bass at slaughter neither measurably improved nor decreased product quality for between 1 and 10 days of storage on ice. Electrical stunning accelerated the pattern of onset and resolution of rigor mortis. If electrical stunning were to be widely adopted, re‐education of buyers would be necessary as rigor mortis is currently used by buyers as a proxy measure of fish freshness.  相似文献   

Understanding the impact of climate change on the oceanic circulation in the Chilean island ecoregions     

Boris Dewitte  Carlos Conejero  Marcel Ramos  Luis Bravo  Véronique Garçon  Carolina Parada  Javier Sellanes  Ariadna Mecho  Praxedes Muñoz  Carlos F. Gaymer 《水产资源保护:海洋与淡水生态系统》2021,31(2):232-252

1. The largest changes in the circulation of the South-eastern Pacific resulting from global warming are associated with the southward shift and intensification of the anticyclone and with coastal surface warming. Coastal upwelling is projected to be increase off central Chile, due to an increase in equatorward winds, although increased oceanic stratification and associated enhanced nearshore turbulence will yield an onshore deepening/flattening of the thermocline.
2. The overall increase in south-easterly trade winds of the South-eastern Pacific in a warmer climate are likely to increase the connectivity pattern between Juan Fernandez and Desventuradas islands, and along the Sala y Gomez ridge, through increasing wind-driven mean ocean currents.
3. Deoxygenation associated with the warmer temperatures and changes in ventilation are likely to modify marine habitat and the respiratory barriers of species in the seamounts located in the vicinity of the limits of the minimum oxygen zone.
4. In the South-eastern Pacific, the prevailing 2D understanding of the responses of marine life to climate change needs to be expanded to 3D approaches, integrating the vertical habitat compression of marine organisms as a result of ocean warming and deoxygenation, as climate velocities for temperature and oxygen have contrasting vertical and horizontal patterns.
5. There is a need for regional biogeochemical-coupled modelling studies dedicated to the Chilean islands in order to provide an integrated view of the impact of anthropogenic stressors (e.g. deoxygenation, increased stratification, and climate shift) at the scale required for addressing socio-ecological interactions.
6. A refined understanding of the large-scale biogeography and spatial dynamics of marine populations through experimentation with high-resolution regional ocean models is a prerequisite for scaling-up regional management planning and optimizing the conservation of interconnected marine ecosystems across large scales.

  相似文献   

Ingestion of Brachionus plicatilis and Artemia salina nauplii by mud crab Scylla serrata larvae     

Juliana C Baylon  Ma Eugenie A Bravo  & Nancy C Maningo 《Aquaculture Research》2004,35(1):62-70

Two feeding experiments were conducted to determine if Brachionus plicatilis and Artemia salina nauplii were ingested by mud crab Scylla serrata larvae. In the first experiment, larvae were fed with increasing densities of Artemia nauplii with or without Brachionus to determine consumption with increasing densities of Artemia and with increasing zoeal stage. This experiment also aimed to determine if the presence of Brachionus as an alternative prey influenced the intake of Artemia by the crab larvae. There was generally an increase in intake with increasing densities of Artemia and increased consumption of Artemia as the larvae grew. Consumption of Brachionus was consistently high in all zoeal stages. There was a significant reduction in the intake of Brachionus with increasing consumption of Artemia in the early zoeal stages (Z1, Z2, Z3), but at later stages (Z4, Z5) the intake of Artemia was no longer affected by the presence of Brachionus. In the second experiment, daily ingestion within instar of zoeal stages and megalopa were compared. There was an increased consumption of Artemia nauplii on the day before molting and increased ingestion of Brachionus on the day after larvae had molted, except at Z3. Megalopae exhibited a decline in Artemia nauplii intake on the days before metamorphosis to crablet.  相似文献   

The Effect of Chronic High Groundwater Nitrate Loading on Riparian Forest Growth and Plant–Soil Processes     

Dianne Bravo  Alan R. Hill 《Water, air, and soil pollution》2012,223(1):73-84

The effect of chronic high groundwater nitrate loading on riparian forests is poorly understood. The growth patterns of northern white cedar (Thuja occidentalis) and related plant–soil processes were examined at four riparian sites in southern Ontario, Canada which have similar vegetation, soils, and hydrology but have differed in adjacent land use for >60 years. Fertilized cropland at two riparian sites produced groundwater-fed surface flows with high mean NO₃–N concentrations of 9 and 31 mg l⁻¹, whereas mean concentrations were <0.5 mg l⁻¹ at two control sites down slope from forest. Tree-ring analysis at the two nitrate-rich sites indicated a positive growth trend in 1980–2004 and an absence of a positive growth trend in the 1945–1970 period that preceded high rates of synthetic nitrogen fertilizer use on cropland. However, a significant increase in growth also occurred in 1980–2004 at the two control riparian sites suggesting that high groundwater nitrate inputs did not influence tree growth. Cedar foliar and litter N content did not differ significantly between the high nitrate and control sites. Litter decomposition rates measured by the litterbag technique at a nitrate-enriched and control site were similar. Litter from a high nitrate and a control site produced a similar rate of potential denitrification in lab incubations of riparian surface peat. This study indicates that prolonged nitrate inputs in groundwater did not increase nitrogen uptake and growth of white cedar or stimulate decomposition and denitrification as a result of changes in the quality of plant material. In the absence of anthropogenic nitrate inputs, riparian wetland soils are typically high in ammonium and low in nitrate, and as a consequence, white cedar may have a limited ability to utilize nitrate.  相似文献   

Thinning has a positive effect on growth dynamics and growth–climate relationships in Aleppo pine (Pinus halepensis) trees of different crown classes     

Jorge Olivar  Stella Bogino  Cyrille Rathgeber  Vivien Bonnesoeur  Felipe Bravo 《Annals of Forest Science》2014,71(3):395-404

? Context

Modification of stand density by thinning may buffer the response of tree growth and vigor to changes in climate by enhancing soil water availability.

? Aims

We tested the impact of thinning intensity on cambial growth of Aleppo pine (Pinus halepensis L.) under semi-arid, Mediterranean conditions.

? Methods

A multiple thinning experiment was established on an Aleppo pine plantation in Spain. We analysed the stem growth dynamics of two different crown classes under four different thinning intensities (15 %, 30 %, and 45 % removal of the basal area) for 2 years, based on biweekly band dendrometer recordings. Local relative extractable soil water was derived from the use of a water balance model Biljou© (available at https://appgeodb.nancy.inra.fr/biljou/) and used as an explanatory variable.

? Results

Radial growth was mainly controlled by soil water availability during the growing season, and differed by crown class. The growth rates of dominant trees were significantly higher than the growth rates of suppressed trees. Removal of 30 % and 45 % of the initial basal area produced a growth release in both dominant and suppressed trees that did not occur under less intense thinning treatments.

? Conclusions

Soil water availability was the main driver of radial growth during the growing season. Forest management confirmed its value for ameliorating the effects of water limitations on individual tree growth. These results may help managers understand how altering stand density will differentially affect diameter growth responses of Aleppo pine to short-term climatic fluctuations, promoting forests that are resilient to future climatic conditions.  相似文献   

An Evaluation of the Influence of Stock Origin and Out-migration History on the Disease Susceptibility and Survival of Juvenile Chinook Salmon     

Joseph P. Dietrich  Deborah A. Boylen  Donald E. Thompson  Erik J. Loboschefsky  Claudia F. Bravo  Dina K. Spangenberg 《Journal of aquatic animal health》2013,25(1):35-47

Abstract

Various methods have been developed to mitigate the adverse effects of the Federal Columbia River Power System on juvenile Pacific salmon out-migrating through the Columbia River basin. In this study, we found that hatchery-reared spring Chinook salmon Oncorhynchus tshawytscha in the river are in varying degrees of health, which may affect delayed mortality and the assessment of the effectiveness of management actions to recover listed stocks (e.g., barging fish downstream versus leaving fish in the river). A laboratory disease challenge with Listonella anguillarum was completed on fish from Rapid River Hatchery and Dworshak National Fish Hatchery (NFH) with different out-migration histories: (1) transported by barge, (2) removed from the river before barging, or (3) left to travel in-river. Barged fish from Rapid River Hatchery experienced less mortality than fish from Dworshak NFH. No statistical differences were found between the hatcheries with fish that had in-river out-migration histories. We suggest that the stressors and low survival associated with out-migration through the hydropower system eliminated any differences that could have been present. However, 18–25% of the fish that were barged or collected before barging died in the laboratory before the disease challenge, compared with less than 2% of those that traveled in-river. Owing to disproportionate prechallenge mortality, the disease-challenged populations may have been biased; thus, they were also considered together with the prechallenge mortalities. The synthesis of prechallenge and disease-challenged mortalities and health characteristics evaluated during out-migration indicated that the benefit of barging was not consistent between the hatcheries. This finding agrees with adult survival and delayed mortality estimates for the individual hatcheries determined from adult returns. The results suggest that the health status of fish and their history before entering the hydropower system (hatchery of origin and out-migration path) are critical variables affecting the conclusions drawn from studies that evaluate mitigation strategies.

Received November 18, 2009; accepted January 6, 2011  相似文献   

Serotypes and anti-microbial susceptibility of Plesiomonas shigelloides isolates from humans, animals and aquatic environments in different countries     

González-Rey C  Svenson SB  Bravo L  Siitonen A  Pasquale V  Dumontet S  Ciznar I  Krovacek K 《Comparative immunology, microbiology and infectious diseases》2004,27(2):129-139

A total of 73 strains of Plesiomonas shigelloides isolated from humans (24 strains) animals (21 strains) and aquatic environment (28 strains) were determined for their O:H serotype and susceptibility to 18 anti-microbial substances and to the vibriostatic agent O/129. Of all strains, 86.3% were typeable by the O and 94.5% by the H anti-sera used. The serotype distribution was heterogeneous within a country and between the countries. Of the 57 different serotypes identified, O11:H2 (2 strains), O22:H3 (4 strains), O35:HH11 (2 strains), O52:H3 (2 strains) and O90:H6 (2 strains) were found among isolates from humans and animals (mainly in cats) in Finland and Cuba, and O23:H1a1b (3 strains) among isolates from environmental sources in Slovak Republic and Italy. Most (93-100%) of all strains were susceptible to all anti-microbials tested but resistant (92-96%) to the broad-spectrum penicillins (ampicillin, mezlocillin). No correlation between anti-microbial resistance patterns and serotypes was found.  相似文献