Circulación de nutrientes en algunos ecosistemas forestales del Montseny (Barcelona)

Se comparan las pautas de circulación de nutrientes en la deposición global, la trascolación, y el desfronde de un encinar montano, un hayendo, y un abetal del Montseny. Las precipitaciones lavan mucho más nutrientes de las copas del abetal que de las del encinar y el hayedo. En el encinar se lava mucho más K+ que Ca2+, mientras que en los otros dos bosques sucede al contrario. Las cantidades de desfronde (peso seco) y en los flujos de nutrientes en el desfronde resultaron ser: encinar > hayedo > abetal. El hayedo del Montseny se diferencia de los demás hayendos europeos por sus reducidos aportes de N en el desfronde, indicando quizá una menor disponibilidad de N en este macizo meridional. En el encinar montano se midieron además la biomasa, producción, y mineralomasa aéreas. La biomasa arbórea de hojas es de 6.1 t ha- 1 , cifra superior a la encontrada normalmente en bosques caducifolios templados. Las concentraciones de nutrientes en la madera de encina son relativamente altas. Por este motivo, las mineralomasas del rodal son también elevadas, a pesar de que la biomasa es sólo moderada. Destaca la importancia de la corteza como acumuladora de Ca. Las ramas y ramitas vivas de encina podrían actuar como reserva de nutrientes que amortiguaría las fluctuaciones en la disponibilidad de elementos esenciales. Tal capacidad resultaría adaptativa ante el régimen irregular de pluviosidad de los climas mediterráneos.Individual stands of evergreen-oak (Quercus ilex), beech (Fagus sylvatica), and fir (Abies alba) in the Montseny mountains (NE Spain) are compared in terms of nutrient fluxes in bulk precipitation, throughfall, and litterfall. Precipitation washes out a greater amount of nutrients from the fir canopy than from either the evergreen-oak or beech canopies. More K+ than Ca2+ is washed out from the evergreen-oak canopy, while the reverse is true for beech and fir. Dry weight of litterfall and nutrient return in litterfall were: evergreen-oak > beech > fir. Our beech stand markedly differs from the other European beech forests because of its much lower N flux in litterfall, probably indicating a lower availability of N in this southern mountain. Above-ground plant biomass, production, and nutrient contents were measured in the evergreen- oak stand. Tree leaf biomass is 6.11 h a - 1 , a higher figure than those commonly found in temperate deciduous forests. Nutrient concentrations in evergreen-oak wood are relatively high. Therefore, plant nutrient contents (Kg ha- 1 ) are also relatively high, in spite of moderate biomass. Large amounts of Ca accumulate in the bark of this stand, developed on silicate bed-rock. Living twigs and branches of evergreen-oak could act as a store of nutrients, counteracting the fluctuations in soil nutrient availability brought about by erratic rainfall patterns. This trait should be adaptive under Mediterranean climates.Comité Conjunto Hispano-Norteamericano de Cooperación Científica y Tecnológica (COOP-370 sobre el encinar), «Servei de Parcs Naturals de la Diputació de Barcelona» (hayedo y abetal) y «Serveis de Protecció de la Natura de la Generalitat de Catalunya» (infraestructura de la zona experimental de la Castanya)

Effects of reduced and conventional tillage on weed communities: results of a long-term experiment in Southwestern Spain.

An important drawback in adopting minimum tillage (MT) and no-tillage (NT) techniques is the frequently observed weed shift promoting adapted species and achieving poorer weed control. These changes can be detected best with long-term experiments, and results might differ depending on soil characteristics and the local flora. The objectives of this work were to evaluate the effect of reduced tillage on weed seed distribution in the soil profile and to identify possible consequences on weed diversity on a long-term experiment maintained during 24 years in Seville (Spain) with three tillage systems: NT, MT and conventional tillage (CT) including moldboard plow on a vertisol. For this purpose, soil seedbanks at 0-8 cm and 8-16 cm depths were enumerated in autumn 2005 and in-field emerged plants in autumn 2005 and winter 2006. Shannon diversity index (H) and evenness (J’) were calculated for seedbank and aboveground weed communities. Total weed seed density was highest for NT and lowest for CT. Some big-seeded species, such as Chrozophora tinctorea L., showed highest seed density in CT. NT increased the relative density of Amaranthus blitoides S. Watson seeds in the seedbank and the abundance of emerged plants of Malva parviflora L., Anagallis arvensis L. and Picris echioides L. Overall, MT led to a less diverse seedbank in the 0-8 cm depth of soil than CT. The frequent drought-induced deep fractures in the expandable clay soil caused natural tillage, which probably resulted in fewer differences in weed seed and seedling densities among tillage treatments compared to what might be expected in other soil types.Uma desvantagem importante na adoção de técnicas de cultivo mínimo (MT) e plantio direto (NT) é o deslocamento de plantas daninhas frequentemente observado, promovendo espécies adaptadas e, com isso, um controle de plantas daninhas mais precário. Essas mudanças só podem ser detectadas com experimentos de longo prazo, e os resultados podem diferir, dependendo das características do solo e da flora local. Os objetivos deste trabalho foram avaliar o efeito da lavoura reduzida sobre a distribuição de sementes de plantas daninhas no perfil do solo e identificar possíveis consequências na diversidade de plantas daninhas em um experimento de longa duração mantido durante 24 anos em Sevilha (Espanha) com três sistemas de plantio: NT, MT e preparo convencional (CT), incluindo arado de aiveca em um Vertissolo. Com esse propósito, amostras de solo com 0-8 e 8-16 cm de profundidade foram coletadas no inverno de 2005 e na primavera de 2006, e as plântulas de plantas daninhas emergentes foram registradas. O índice de diversidade de Shannon (H) e a uniformidade (J’) foram calculados para comunidades de banco de sementes e plantas daninhas acima do solo. A densidade total de sementes de plantas daninhas foi maior para NT e menor para CT. Algumas espécies de sementes grandes, como Chrozophora tinctorea L., apresentaram maior densidade de sementes no CT. NT aumentou a densidade relativa de sementes de Amaranthus blitoides S. Watson no banco de sementes e a presença de plantas emergidas de Malva parviflora L., Anagallis arvensis L. e Picris echioides L. Com relação aos resultados gerais, a TM levou a um banco de sementes menos diversificado na profundidade de 0 a 8 cm do solo do que a CT. As frequentes fraturas profundas na argila expansível do solo provocam um preparo natural, originando provavelmente menos diferenças dos parâmetros analisados do que em outros tipos de solo

Biodiversidad de la flora arvense en cultivos de mandarino según el manejo del suelo en las interfilas.

En la zona citrícola circundante al delta del Ebro se inventarió, en la primavera del 2002, la flora arvense presente en 62 parcelas de mandarinos en producción. Se trata de una muestra suficientemente representativa de la superficie dedicada en esta zona a los cultivos de cítricos. En total se catalogaron 112 especies pertenecientes a 30 familias botánicas. Entre éstas, destacan las Gramíneas y las Compuestas que contribuyen, entre las dos, con un 34 % al total de especies. En este trabajo se detallan la estructura florística y funcional de las parcelas estudiadas. El número de especies presentes fue mayor en las parcelas cuyas calles o interfilas fueron segadas, respecto a las que sufrieron aplicaciones de herbicidas químicos. En cambio, el número de especies encontradas no fue significativamente distinto ni en función del marco de plantación, ni en función de la edad de los árboles, ni en función de la clase textural, ni tampoco fue distinto en las cuatro zonas geográficas delimitadas en el área de estudio

Estructura y funcionalismo de un encinar montano en el Montseny. III: contenido de sodio, potasio, calcio y magnesio en las aguas de lluvia

Volume and dissolved nutrient content (Na,K,Ca, and Mg) of incident precipitation and throughfall are under study in a montane-Mediterranean evergreen-oak (Quercus ilex L.) forest at La Castanya (Montseny, Barcelona). Amount of precipitation is measured with 4 (within) and 2 (outside the forest) polyethylene gauges with 19 cm funnels. Precipitation chemistry is monitored through 8 (within) and 2 (outside the forest) acid-washed, continuously-open polyethylene rain collectors with the funnels covered by a hood made of 2 mm plastic mesh to exclude insects and coarse debris. Rain collectors are changed by clean ones on a biweekly basis and the precipitation samples deep frozen until chemical analyses. This paper reports preliminary results from the first year of study : 24 June 1978 to 30 June 1979. As judged through the records of a nearby weather station, this year proved to be a normal one as for total rainfall, although an abnormal one as for monthly distribution of precipitations. Total incident precipitation and throughfall amounted to 969 and 617 mm, respectively. Concentrations of the four analysed cations were highly variable along the year (figs. 1-2), being generally higher in spring-summer than in autumn-winter rains both within and out side the forest. Volume-weighted mean concentrations are given in table 1, and nutrient fluxes in table 2. On the average, incident precipitation at La Castanya is relatively high in Ca (1.5 mg 1 ), medium in Na (0.7), and low in K (0.2) and Mg (0.2). Throughfall is enriched in all four elements with respect to incident precipitation: K 21 times, Mg 3 times, Ca 2.5 times, and Na 2 times.Este trabajo ha disfrutado de una Ayuda de Investigación Cooperativa Hispano-Norteamericana

Estructura y funcionalismo de un encinar montano en el Montseny. IV: producción de hojarasca

Litterfall and its concomitant mass and nutrient (Na, K, Ca and Mg) fluxes to the forest floor are studied in a montane-Mediterranean evergreen-oak (Quercos ilex L.) wood at La Castanya (Montseny, Barcelona). Litterfall is colected biweekly in 16 (only 8 during the first 6 months) conical, 0.25 m litterfall traps randomly distributed over a 0.22 ha experimental plot. Results from the first year of study (May 1978 - May 1979) are reported in this paper. Litterfall a mounted to 4.5 t ha-1 yr-1, not including in this figure the branches longer than 40 cm or thicker than 5mm. Leaves represented 3.08 t ha-1 yr-1 (68.11% of litterfall), twigs 1.05 t ha-1 yr-1 (23.22%), and fruits and inflorescences 0.14 t ha-1 yr-l (3.21%). Leaf fall exhibited a distinct seasonal maximum in late spring-early summer, but total litterfall peaked later when an autumn hailstorm and a November windstorm struck the forest. Nutrient contents of freshly-fallen evergreen-oak litter were within the range of published values for this species. Nutrient fluxes in litterfall were (kg ha-1 yr-1): Na 0.76, K 18.28, Ca 41.64 and Mg 5.43. Throughfall data from Rodá et al. (1980) allowed to compute the following nutrient fluxes in litterfall plus throughfall (kg ha-1 yr-1): Na 9.1, K 38.0, Ca 64.7 and Mg 9.3.Este trabajo ha disfrutado de una Ayuda de Investigación Cooperativa Hispano-Norteamericana

Estructura y funcionalismo de un encinar montano en el Montseny. II: biomasa arbórea

Above-ground tree biomass data are reported as first results of a study on the structure and dynamics of the tree stratum in the evergreen-oak wood at La Castanya (Montseny, Barcelona). 15 evergreen-oaks (Quercus ilex L.ssp ilex) were fallen from a spot near the experimental plot. An alometric table for the evergreen-oak is given, together with estimates of the total above-ground tree biomass for the experimental plot, partitioned in wood 0>5 cm, wood 0 < 5 cm, bark, and leaves by leave-age. Results are compared with those from evergreen-oak woods obtained by other workers.Este trabajo ha disfrutado de una Ayuda de Investigación Cooperativa Hispano-Norteamericana

Estructura y funcionalismo de un encinar montano en el Montseny. I: planteamiento del estudio y descripción del área experimental

This paper is a preliminar one on objectives of a new project in terrestrial ecology and on the characteristics of selected study area. The project is being drived by Ecology departments of Universitat de Barcelona and Universitat Autonoma de Barcelona, and is embodied in a larger one on nutrient cycles in forest ecosystems. The parameters measured and their relationships are exposed and future developments briefly discussed. The La Castanya valley is included in the Montseny nature park, a Biosphere Reserve, in a Mediterranean mountain stage with relatively humid climate but with great interanual fluctuation. The bedrock is nearly all constituted by paleozoic shales and valley-side slopes are pronounced (30%) . There is a soil catena from litosols to rankers and brown acid soils that can be lixiviated in some places. Vegetation is a green oak mountain forest (Quercetum ilicis mediterraneo-montanum) in nearly all the valley. There are, however, some grasslands and a beech forest near the summits and also a little Taxus baccata trees clump. The green oak forest is a young one, in a regeneration stage, after a very intensive explotation period (wood for fuel and coal making) interrupted some years ago, and an early farming period. In the experimental plot direct insolation is lowered by topographic position and the soil is colluvial, deep but with loose rocks at surface. Herb and shrub layer are poor, being the young Quercus ilex also dominants. The experimental plot surface is 0,22 ha, including 450 trees (more than 5 cm dbh) between 7 and 12 m high. The branch system has a lowe layer level, with a few horizontal branches, and a higher one with near vertical branches. The major axis is not clearly defined, as it divides in two or three over 2,5-4 m.Este trabajo ha disfrutado de una Ayuda de Investigación Cooperariva Hispano-Norteamericana

Fertilización en la revegetación de áreas degradadas en el pre-Pirineo catalán

Experiencias previas de revegetación de áreas degradadas en los Pirineos, demostraron la necesidad del abonado mineral. Se ha realizado una experiencia de laboratorio utilizando el material regolítico de badlands del Alto Llobregat para estudiar la influencia del tipo de nutriente y la dosis del fertilizante en las plantas utilizadas en su revegetación. Las dosis de fertilizante fueron: 1 (usual en los cultivos de la zona: 64 kg N ha-1, 120 kg P2O5 ha-1y 120 kg K2O ha-1), 0.5, 1.5 y 2. Los resultados demuestran que el fósforo es el nutriente que limita principalmente la fertilidad química de este tipo de sustrato, ya que su aporte incrementa dos veces la producción vegetal, mientras que los niveles de potasio son suficientes. Los mayores valores de producción se obtienen cuando se utilizan fertilizantes NPK y NP y especial-mente cuando la dosis es 1.5. En condiciones de campo, es la adecuada para conseguir la revegetación de los badlands