Foc, pluges i resposta hidrològica del sòl a les muntanyes d'Alacant

El foc afecta el sòl mitjançant l'increment de la temperatura i la deposició de cendres, però també per la pèrdua de vegetació i horitzons orgànics, modificant la incidència de la pluja sobre la superfície. El risc de degradació postincendi està controlat, entre altres factors, pel clima, la vegetació prèvia i el tipus de sòl. Les localitats d'estudi es situaren en zones de transició entre climes semiàrid i subhumit. Se seguí la dinàmica temporal de l'escolament superficial i de la producció de sediments mitjançant simulació de pluja. En ambient semiàrid, la capacitat d'infiltració no es modificà tot just després de l'incendi. Tant en ambient semiàrid com subhumit, s'observà una pèrdua de la capacitat d'infiltració comparant els períodes previ i posterior a l'acció de la pluja sobre el sòl cremat. La resposta de la vegetació va ser un factor fonamental en el control de la degradació del sòl posterior al foc.Fuego, lluvias y respuesta hidrológica del suelo en las montañas alicantinas. El fuego afecta al suelo a través del incremento de la temperatura y la deposición de cenizas, pero también por la pérdida de vegetación y horizontes orgánicos, modificándose la incidencia de la lluvia sobre la superficie. El riesgo de degradación post-incendio está controlado, entre otros factores, por el clima, la vegetación previa y el tipo de suelo. Las localidades de estudio se situaron en zonas de transición entre climas semiárido y subhúmedo. Se estudió la dinámica temporal de las producciones de escorrentía y sedimentos mediante simulaciones de lluvia. En ambiente semiárido, la capacidad de infiltración no se vio modificada directamente por el fuego. Se observó una pérdida general de capacidad de infiltración comparando los periodos previo y posterior a la acción de las lluvias sobre el suelo quemado. La respuesta de la vegetación fue un factor fundamental en el control de la degradación del suelo posterior al fuego.Forest fires, rainstorms and soil hydrological response in the Alicante rangelands (SE Iberian Peninsula). Forest fires directly affect the soil surface through the increment of temperature and the deposition of ashes. Fires also result in the reduction or elimination of aboveground biomass and organic layers, thereby modifying the impact of raindrops on the soil surface. The post-fire degradation risk is controlled by diverse factors, e.g. climate, pre-fire vegetation and soil characteristics. Study sites were located in transitional areas between semiarid and subhumid climates. We assessed the temporal dynamics of runoff and sediment yield using a rainfall simulator. Under semiarid climate, the infiltration capacity was not directly modified by the fire. Both under semiarid and under subhumid climates, an increase in runoff and sediment production was observed by comparing the post-fire results obtained prior to and after than the rainy season. Plant response was one of the main factors controlling the post-fire soil degradation risk

THE SUBANTARCTIC TIERRA DEL FUEGO: NOTHOFAGUS FORESTS OF DISTRIBUTION, STRUCTURE AND PRODUCTION

Evergreen Nothofagus betuloides and deciduous N. pumilio form the main forest types in Tierra del Fuego. These forests were sampled along two altitudinal gradients to study their structure and dynamics and assess the causes of their distribution. The distribution pattems of the two species of Nothofagus seem to respond to different climates and soils. The dornÍnant soil processes are hydromorphy in the evergreen forest and podzolization in the deciduous one. N. betuloides is an evergreen resilient to short-term environmental fluctuations, due to its ability to retain nutrients. Leaves on the tree may last up to 7 years, with an average density of 17 mg cm,2 . In contrast, the leaves of N. pumilio are shed in autumn and reach only 8 mg cm,2 . In both types of forests the following features can be outlined. Old-growth forest stands develop in the middle and lower slopes. The distribution of diameter sizes of the trees usually shows a pronounced bimodality. Recruitment is discontinuous as shown by the spatial pattem of tree sizes, and regeneration is vegetative in the upper slopes. Leaf area indices range between 2.3 and 2.8 m 2 m,2 for the deciduous forest and from 2.5 to 4.5 m 2 m,2 for the evergreen forest. It appears that tree standing biomass ranges between 6.0 and 1 3.6 kg e m'2 in the deciduous forest, and between 10.5 and 1 5.6 Kg e m,2 in the evergreen forest. Production varies from 148.0 to 372.1 g e m ,2 yr , 1 , and from 204.6 to 346.4 g e m ,2 yr,l , respecti vely. In relation to boreal forests, biomass can be considered high, but production is medium to low. The relation of wood production to leaf biomass shows that N. betuloides be ha ves similar to coniferous forests and N. pumilio as hardwood forests. There is much accumulation of organic matter on the forest floor, especially coarse wood debris, reflecting the stage of development of these forests and the unfavourable conditions for litter decomposition

Analysis of soil carbon in Spanish agricultural soils: relevant aspects in relation to the organic farming reconversion in the Mediterranean area

Los niveles de carbono orgánico en suelos agrícolas son especialmente relevantes en los modelos de gestión que se basan en la reserva orgánica de nutrientes. La disminución de materia orgánica que ocurre en los suelos roturados puede en algunos casos determinar la degradación del suelo. Este hecho puede ser especialmente relevante en condiciones climáticas límite (secas y semiáridas). A partir del análisis de una base de datos de suelos españoles se discute la distribución del C en el horizonte superficial de suelo según el clima y según el uso. Para cada área climática, mediante comparación entre suelos forestales y agrícolas se observa que los suelos de clima semiárido presentan una mayor resistencia a la pérdida de C y una menor resiliencia que los suelos de climas más húmedos. Este hecho nos hace pensar que los suelos semiáridos pueden estar cerca de los umbrales de degradación y que por lo tanto su gestión debería evitar les pérdidas de materia orgánica.Organic carbon levels in agricultural soils are specially relevant in the management models based on the organic reserve of the soil. Losses of soil organic matter that occur associated to tillage practices can enhance, in some cases, soil degradation. This fact may be specially relevant in dry and semiarid climates. By analysing a soil data base of the Spanish forest and agricultural soils we discuss the distribution of C in the soil surface horizon across climates and land uses. In each climatic area, by comparing forest with agricultural soils we found that soils in semiarid climate show greater resistance to soil C losses and lower resilience than soils of wetter climates. This fact suggest that semiarid soils can be at or near soil degradation thresholds and thus its management should avoid any losses of soil organic matter.Este trabajo ha sido posible gracias a un convenio establecido entre la Dirección General de Evaluación Ambiental del Ministerio de Medio Ambiente y la Universidad de Barcelona

Different techniques for afforestation with Quercus ilex ssp. ballota (Desf.) Samp. in degraded lands (Comunidad Valenciana)

El agua es un recurso limitante para el establecimiento y el desarrollo posterior de brinzales en ambientes mediterráneos. Una alternativa a la irrigación de repoblaciones es el empleo de técnicas dirigidas a incrementar la disponibilidad hídrica de los brinzales o reducir las pérdidas evaporativas. Entre estas técnicas se encuentran la enmienda con geles hidrofílicos o la modificación del microambiente físico del plantón utilizando tubos protectores. En 1997 establecimos tres parcelas experimentales en las que aplicamos hidrogeles, tubos protectores, siembra directa de bellotas y bellotas pregerminadas. Los brinzales de una savia presentaron en enero de 2003 una supervivencia superior al 60% con independencia del tratamiento. La pregerminación de la bellota y el uso de tubo protector incrementó la supervivencia de las plantas. Así, seis años después de la plantación la combinación de ambos tratamientos ofreció un 42% de supervivencia del total de bellotas introducidas. La altura de los brinzales aumentó significativamente con el protector. Al cabo de seis años estos brinzales superaban los 35 cm de altura, un 55 % superior a la de los brinzales no protegidos. También fue significativo el aumento en altura de las bellotas con tubo protector.Water is a limiting resource for seedlings establishment in Mediterranean ecosystems. Techniques that increase water availability as hidrophylic gels (PAM's) and treeshelters represent an alternative to irrigation, wich is costly and usually unfeasible. Most Quercus species have a pivot root that grows deeply in the soil. Nursery cultivation in forest containers cause root prunning wich may hamper species strategy to colonise deep soil horizons. In 1997 we established three experimental plots in wich we tested the following treatments: PAM’s amendment, treeshelters, seeded acorns, pregerminated acorns and one year old seedlings. One year old seedlings showed a 60% survival in January 2003, independently of the treatments. Pregerminated acorns showed 42% survival. Treeshelters on 1 year old seedlings showed a 60% survival. In this treatment, stem height was also promoted, reaching 35 cm six years after planting time, i.e. approximately 55% more than unprotected 1 year old seedlings. Treeshelters also favoured the growth of pregerminated acorns

On the distinctive features of Mediterranean soils

En aquest article es revisen els components de la fertilitat dels sòls mediterranis i es discuteixen les seves característiques generals, així com la suposada oligotrofia que sovint se'ls ha atribuït. La tipologia d 'aquests sòls i els cicles del N i P presenten alguns trets comuns que vénen de tenninats per trobar-se en un règim de clima mediterrani, tanmateix existeixen diferències remarcables que es relacionen, sobretot, amb el tipus de roca mare i que expliquen les diferències sovint atribuïdes als sòls de les cinc regions mediterrànies. La matèria orgànica i el cicle del nitrogen són especialment actius en els sòls mediterranis, la qual cosa es relaciona amb temperatures característicament altes. El contingut de Pi la seva disponibilitat presenten una elevada variabilitat originada pels diferents tipus de substrat litològic i grau de meteorització. Els incendis sempre comporten pèrdues netes de nutrients per al sistema i la seva recuperació pot requerir períodes llargs de temps. Tanmateix, immediatament després de l 'incendi, acostuma a haver-hi un increment temporal de nutrients disponibles que pennet una regeneració eficient de la vegetació durant un període curt de temps. En àreas fràgils de la Conca Mediterrània, sovint prèviament modificades antròpicament, el foc pot desencadenar una forta degradació dels sòls.Soil fertility components in Mediterranean soils are reviewed to discuss their possible com mon general features and the oligotrophy often attributed to these soils. Mediterranean soils typology and N and P cycling show some similar overall trends owing to the common climatic characteristics, but also considerable differences especially related to the parent bedrock. Differences often attributed to the soils from the five Mediterranean regions of the world can be mostly explained from the above mentioned factors. Soil organic matter and nitrogen cycling are especially active in the Mediterranean soils, in relation to the relatively high characteristic temperatures. P content and availability show considerable variation owing to differences in parent material and degree of soil weathering. Wildfires always produce nutrient losses to the ecosystem that could require long periods of time to recover. However, the enhanced fertility commonly produced just after the fire allows an efficient short-term regeneration of the vegetation. The human impacts on the ecosystems such as fires and cultivation/abandonment, that have been especially relevant in the Mediterranean Basin for centuries, can introduce strong soil degradation in fragile areas

Post-fire Regeneration Traits of Understorey Shrub Species Modulate Successional Responses to High Severity Fire in Mediterranean Pine Forests

Recurrent fires can impede the spontaneous recruitment capacity of pine forests. Empirical studies have suggested that this can lead to a prolonged replacement of pine forest by shrubland, especially if shrub species are pyrophytic. Model-based studies, however, have suggested that post-fire succession of pine forest under current climatic conditions will eventually tend towards the dominance of oaks under high fire severity and recurrence. These previous modelling studies did not address the role of the various post-fire regeneration traits of the understory shrub species. Considering the dichotomy of obligate seeder vs. resprouter species, either obligate or facultative resprouter, we hypothesized that when the shrubs present are post-fire seeders, the oaks steadily occupy the forest, whereas resprouter shrub species might compete with oaks and delay or arrest post-fire succession. To test this hypothesis, we developed a dynamic, cellular automaton model for simulating post-fire successional transitions in pine forests, including shrubs, pines and oaks, and stochastic fires of regular frequency. Our results showed a strong tendency towards oak dominance as final model state and a very reduced role of fire recurrence in this final state, with low yearly acorn input delaying oak dominance. Most relevantly, and in line with our hypothesis, the trend towards oak dominance depended markedly on the two types of shrub species, being delayed by resprouter species, which extended the shrub-dominated succession stage for several centuries. Our simulation results supported the view that the type of understorey species should be a key consideration in post-fire restoration strategies aiming to enhance fire resilience.This research has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under the grant agreement no. 283068 (CASCADE project). Thanks are due to FCT/MCTES for the financial support to CESAM (UIDP/50017/2020+UIDB/50017/2020), through national funds and the post-doctoral research contract of Jacob Keizer (FCT-IF/01465/2015), and to the Spanish Ministry of Science and Innovation for financial support (CGL2017-89804-R) of the work of Susana Bautista. The work of Paula Maia was partially supported by the project SuSPiRe (PTDC/ASP-SIL/30983/2017) funded by FCT, through COMPETE2020—Programa Operacional Competitividade e Internacionalização (POCI)