The role of nutritional impairment in carbon-water balance of silver fir drought-induced dieback.

Rear-edge populations at the xeric distribution limit of tree species are particularly vulnerable to forest dieback triggered by drought. This is the case of silver fir (Abies alba) forests located in Southwestern Europe. While silver fir drought-induced dieback patterns have been previously explored, information on the role played by nutritional impairment is lacking despite its potential interactions with tree carbon-water balances. We performed a comparative analysis of radial growth, intrinsic water-use efficiency (iWUE), oxygen isotopes (δ18 O) and nutrient concentrations in leaves of declining (DD) and non-declining (ND) trees in silver fir in four forests in the Spanish Pyrenees. We also evaluated the relationships among dieback predisposition, intraspecific trait variation (wood density and leaf traits) and rhizosphere soil physical-chemical properties. The onset of growth decline in DD trees occurred more than two decades ago, and they subsequently showed low growth resilience against droughts. The DD trees presented consistently lower foliar concentrations of nutrients such as P, K, Cu and Ni than ND trees. The strong effects of foliar nutrient status on growth resilience indices support the key role played by mineral nutrition in tree functioning and growth before, during and after drought. In contrast, variability in wood density and leaf morphological traits, as well as soil properties, showed weak relationships with tree nutritional status and drought performance. At the low elevation, warmer sites, DD trees showed stronger climate-growth relationships and lower δ18 O than ND trees. The uncoupling between iWUE and δ18 O, together with the positive correlations between P and K leaf concentrations and δ18 O, point to deeper soil/bedrock water sources and vertical decoupling between nutrient and water uptake in DD trees. This study provides novel insights into the mechanisms driving silver fir dieback and highlights the need to incorporate tree nutrition into forest dieback studies.

Las poblaciones del límite xérico de distribución de las especies de árboles son particularmente vulnerables al decaimiento forestal inducido por sequía. Este es el caso de los bosques de abeto (Abies alba) situados en el suroeste de Europa. Si bien los patrones de decaimiento provocado por sequía del abeto se han explorado previamente, falta información sobre el papel que desempeña el deterioro nutricional a pesar de sus interacciones potenciales con los balances de agua y carbono de los árboles. En este estudio, hemos realizado un análisis comparativo del crecimiento radial, la eficiencia intrínseca del uso del agua (iWUE), los isótopos de oxígeno (δ18O) y las concentraciones de nutrientes en hojas de árboles decaídos (DD) y no decaídos (ND) en cuatro abetares de los Pirineos españoles. También evaluamos las relaciones entre la predisposición al decaimiento, la variación de rasgos intraespecíficos (densidad de la madera y rasgos de las hojas) y las propiedades físico-químicas de la rizosfera. El inicio de la disminución del crecimiento en los árboles DD ocurrió hace más de dos décadas y posteriormente mostraron una baja resiliencia de crecimiento frente a las sequías. Los árboles DD presentaron concentraciones foliares consistentemente más bajas de nutrientes como P, K, Cu y Ni que los árboles ND. Los fuertes efectos del estado de los nutrientes foliares en los índices de resiliencia del crecimiento respaldan el papel clave que desempeña la nutrición mineral en el funcionamiento y el crecimiento de los árboles antes, durante y después de la sequía. En contraste, la variabilidad en la densidad de la madera y los rasgos morfológicos de las hojas, así como las propiedades del suelo, mostraron una relación débil con el estado nutricional de los árboles y la respuesta del crecimiento a la sequía. En los sitios más cálidos y de baja elevación, los árboles DD mostraron relaciones clima-crecimiento más fuertes y un δ18 O más bajo que los árboles ND. El desacoplamiento entre iWUE y δ18 O, junto con las correlaciones positivas entre las concentraciones foliares de P y K y δ18 O, apuntan a fuentes de agua más profundas del suelo/lecho rocoso y un desacoplamiento vertical entre la absorción de nutrientes y agua en los árboles DD. Este estudio proporciona información novedosa sobre los mecanismos que impulsan el decaimiento del abeto y destaca la necesidad de incorporar la nutrición de los árboles en los estudios de muerte regresiva del bosque.

Variability in source sediment contributions by applying different statistic test for a Pyrenean catchment.

Information on sediment contribution and transport dynamics from the contributing catchments is needed to develop management plans to tackle environmental problems related with effects of fine sediment as reservoir siltation. In this respect, the fingerprinting technique is an indirect technique known to be valuable and effective for sediment source identification in river catchments. Large variability in sediment delivery was found in previous studies in the Barasona catchment (1509 km2, Central Spanish Pyrenees). Simulation results with SWAT and fingerprinting approaches identified badlands and agricultural uses as the main contributors to sediment supply in the reservoir. In this study the <63 µm sediment fraction from the surface reservoir sediments (2 cm) are investigated following the fingerprinting procedure to assess how the use of different statistical procedures affects the amounts of source contributions. Three optimum composite fingerprints were selected to discriminate between source contributions based in land uses/land covers from the same dataset by the application of (1) discriminant function analysis; and its combination (as second step) with (2) Kruskal-Wallis H-test and (3) principal components analysis. Source contribution results were different between assessed options with the greatest differences observed for option using #3, including the two step process: principal components analysis and discriminant function analysis. The characteristics of the solutions by the applied mixing model and the conceptual understanding of the catchment showed that the most reliable solution was achieved using #2, the two step process of Kruskal-Wallis H-test and discriminant function analysis. The assessment showed the importance of the statistical procedure used to define the optimum composite fingerprint for sediment fingerprinting applications.

Disentangling the Legacies of Climate and Management on Tree Growth.

Legacies of past climate conditions and historical management govern forest productivity and tree growth. Understanding how these processes interact and the timescales over which they influence tree growth is critical to assess forest vulnerability to climate change. Yet, few studies address this issue, likely because integrated long-term records of both growth and forest management are uncommon. We applied the stochastic antecedent modelling (SAM) framework to annual tree-ring widths from mixed forests to recover the ecological memory of tree growth. We quantified the effects of antecedent temperature and precipitation up to 4 years preceding the year of ring formation and integrated management effects with records of harvesting intensity from historical forest management archives. The SAM approach uncovered important time periods most influential to growth, typically the warmer and drier months or seasons, but variation among species and sites emerged. Silver fir responded primarily to past climate conditions (25-50 months prior to the year of ring formation), while European beech and Scots pine responded mostly to climate conditions during the year of ring formation and the previous year, although these responses varied among sites. Past management and climate interacted in such a way that harvesting promoted growth in young silver fir under wet and warm conditions and in old European beech under drier and cooler conditions. Our study shows that the ecological memory associated with climate legacies and historical forest management is species-specific and context-dependent, suggesting that both aspects are needed to properly evaluate forest functioning under climate change. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10021-021-00650-8.

Epidemiological patterns of bovine besnoitiosis in an endemic beef cattle herd reared under extensive conditions.

Bovine besnoitiosis is a parasitic disease caused by the protozoan Besnoitia besnoiti. Described many decades ago, recent epidemiological studies reveal its important spread within Europe in the last years. To date, many epidemiological aspects related to life cycle, routes of transmission, incidence rates and associated risk factors are lacking; hence, the establishment of appropriate disease control programmes poses an important challenge. Thus, the aim of the present study was to determine the epidemiological pattern of the disease in an endemic herd reared under extensive conditions (Spanish Pyrenees) by identifying main factors associated with infection and clinical disease dynamics. The study population consisted of 276 Brown Swiss and Pirenaica adult animals and 145 calves born and weaned at the farm during the study. Three sampling time frames were used: January 2010, September 2010 and February 2011, which allowed us to differentiate two periods designated as mountain and valley periods. The data related to animals (breed, sex and age) and herd management (animal grouping and time in housing) were recorded. The data collection methodology was mainly based on clinical examinations and defining the serological status against bovine besnoitiosis by the immunofluorescent antibody testing of blood samples. The total prevalence among adult animals was 38.34% (CI95%: 34.53-42.07), with 18.54% of seropositive animals showing clinical signs. In regard to the cumulative incidence, 34.57% of new infections were detected during the mountain period, in contrast to the 24.59% observed in the valley period. The incidence density was 0.058 and 0.061 new infections per animal-month for the mountain and valley periods, respectively. According to the seroepidemiological study, the seroconversion probability of B. besnoiti infection was directly associated with the number of seropositive cows with whom an animal had been stabled as well as the housing period duration, supporting horizontal transmission by close contact as one of the most important methods of disease spread. In addition, the risk of developing the clinical course increased with age, and the presence of clinical signs was related to higher antibody responses. Among calves (from 3.1 to 7.1 months old) sampled once at weaning, the total seroprevalence was 15.17% (CI95%: 9.36-21.04), and the chronic stage was observed in three animals, supporting the ability of B. besnoiti to infect and even cause disease in animals less than 6 months old. Finally, the risk of calf seroconversion was positively related to the serological status of the cows, suggesting postnatal transmission between dams and offspring by contact during the suckling period.

Prevalence of Besnoitia besnoiti infection in beef cattle from the Spanish Pyrenees.

Reports of recent outbreaks of bovine besnoitiosis in Europe have emphasized the need for prevalence studies to determine the importance of the disease. A previous cross-sectional study carried out in a northern province of Spain showed that seropositive cattle were beef breeds primarily located in regions where the disease is endemic (such as in the Pyrenees). The present study focused on this population. Sixty-three beef herds were selected and at least 50% of the animals in each herd were sampled (n = 3318). The herd, intra-herd and animal prevalence rates were calculated. All breeding bulls located in the same region were also sampled (n = 587), and the animal prevalence calculated. Sera were tested by ELISA. The herd prevalence rate of bovine besnoitiosis was 87.3%, and both sexes were similarly affected (approximately 50%). The results indicate that the disease is highly widespread in the Pyrenees, and that serological examination of cattle should be recommended when trading beef cattle.