No abstract

& Introduction In order to predict the biomass of aerial components of maritime pine stands (Pinus pinaster Ait.), generalized allometric equations were developed using data collected from the southern and northern margins of its geographical area. & Methods The data comprised biomass values divided into foliage, branch, stem and minor components collected from 26 trees in Tunisia and 152 trees in France. Some trees were taken from plots receiving fertilisation and irrigation. The equation W=aD b , where W is the biomass, D the stem diameter and a and b are fitted parameters, explained 98% of the variations in the total aerial biomass. The addition of tree age reduced significantly the residual sum of squares for the foliage component. This model explains 79% of the variations in foliage biomass observed. & Results To a lesser extent, the age variable also improved the stem and branch models that explain 98% and 71% of the observed sum of squares, respectively. Site variables such as the stocking density, stand basal area, fertilisation or annual precipitation did not reduce the residual sum of squares, suggesting that their putative effects are conveyed through tree growth rate.

In Tunisia, the Aleppo pine seed has a great importance, since in the last decades human consumption has risen considerable. Thus its regeneration and seed production capacities are important factors to take into account to reach the necessities of the country. To study the production of cones and seeds of Aleppo pine, Tunisia's native Aleppo pine forests were surveyed in summer 2006, using 79 plots (40 × 25 m: 1,000 m²) spread over four bioclimatic zones. Stand and tree characteristics, crown dimensions and cone/seed variables were measured from an average tree of each plot (i.e. a total of 79 trees). Recorded data were submitted to simple and multiple regression analyses for explaining the variability in crown volume and crown surface, cone number and seed yield per average tree. Results showed a negative correlation between the stand density, crown characteristics and number of cones and seeds harvested from the average tree. For crown volume and surface, age, stand density, tree height, diameter at breast height, crown diameter and crown height were important explanatory variables under multiple regression analyses. For cone number per tree, only the age, stand density and total height were the most determinant variables. Matures cone number per tree and cone mass per tree were the most informative parameters for the total seed yields per tree. Finally, forest managers should know that crown size affects cone and seed crop of the Aleppo pine individual tree grown in Tunisia, but has no effects on seed number per cone and seed mass per cone.Key words: Aleppo pine; crown dimensions; cone number; seed yields; bioclimatic zones; Tunisia. ResumenVariables de parcela, árbol y copa que afectan la producción de piñas y piñones en bosques de pino carrasco de Túnez En Túnez, la producción de piñones del pino carrasco tiene una gran importancia, ya que en las últimas décadas su consumo ha aumentado de forma considerable. Por ello, su regeneración y capacidad de producción de piñas/piñones en un factor a tener en cuenta en Túnez. En verano del 2006 se eligieron 79 parcelas de 1.000 m² (40 × 25 m) situadas en cuatro zonas bioclimáticas representativas de Túnez para el estudio de la capacidad de producción de piñas/piñones del pino carrasco. Teniendo en cuenta todos los árboles de las parcelas, se identificó el árbol promedio, del que posteriormente se medirían variables de árbol, dimensión de copa y producción de piñas/piñones. Los resultados demuestran una correlación negativa entre la densidad de la parcela, características de la copa y el número de piñas/piñones recolectados por cada árbol promedio. Para la descripción del volumen y superficie de copa, las variables más importantes fueron edad, densidad de parcela, altura y diámetro del árbol, y altura y diámetro de la copa. Las variables edad, densidad de parcela y altura del árbol fueron las más significativas para la determinación de nú-mero de piñas por árbol. Para el cálculo del total de piñones por árbol, las variables más informativas fueron el nú-mero ...

The thuya (Tetraclinis articulata (Vahl.) Mast.) forests are one of the most important ecosystems in semiarid environments in north-western Africa, providing important economic profit and social services to local populations. However, lack of tools aiding sustainable management of these forests is detected. In the present work models for the main tree attributes as total height, crown diameter, height to crown base and stem form are developed for the species, using data from a net of plots installed in JbelLattrech region, in the NE Tunisia. Presented models allow characterizing the actual state and timber production of forests by using variables measured in typical forest inventories and conform a preliminary step for the future development of dynamic growth models.Key words: thuya; stem curve; semiarid environments; tree-level models. ResumenHacia el manejo sostenible de los bosques de araar (Tetraclinis articulata (Vahl.) Mast.) en Túnez: modelos para las principales variables de árbolLos bosques de araar (Tetraclinis articulata (Vahl.) Mast.) constituyen uno de los ecosistemas más importantes de los ambientes semiáridos del noroeste de África, siendo además fuente de importantes beneficios económicos y servicios sociales a las poblaciones rurales. Pese a este interés, hasta el momento no se han desarrollado herramientas que faciliten la gesitón sostenible de estas masas forestales. En el presente trabajo se presentan modelos para los principales atributos de árbol individual: altura total, diámetro de copa, altura hasta la base de la copa y ecuación de perfil, desarrollados para la especie a partir de datos obtenidos en una red de parcelas permanentes instalada en la región de JbelLattrech, en el NE de Túnez. Los modelos presentados permiten caracterizar el estado y producción maderera actual de los bosques de thuya a partir de las variables medidas habitualmente en los inventarios forestales para la gestión, y constituyen además un paso preliminar para el desarrollo futuro de modelos dinámicos de crecimiento para la especie. Palabras

Abstract. Farmland is a major land cover type in Europe and Africa and provides habitat for numerous species. The severe decline in farmland biodiversity of the last decades has been attributed to changes in farming practices, and organic and low-input farming are assumed to mitigate detrimental effects of agricultural intensification on biodiversity. Since the farm enterprise is the primary unit of agricultural decision making, management-related effects at the field scale need to be assessed at the farm level. Therefore, in this study, data were collected on habitat characteristics, vascular plant, earthworm, spider, and bee communities and on the corresponding agricultural management in 237 farms in 13 European and two African regions. In 15 environmental and agricultural homogeneous regions, 6-20 farms with the same farm type (e.g., arable crops, grassland, or specific permanent crops) were selected. If available, an equal number of organic and non-organic farms were randomly selected. Alternatively, farms were sampled along a gradient of management intensity. For all selected farms, the entire farmed area was mapped, which resulted in total in the mapping of 11 338 units attributed to 194 standardized habitat types, provided together with additional descriptors. On each farm, one site per available habitat type was randomly selected for species diversity investigations. Species were sampled on 2115 sites and identified to the species level by expert taxonomists. Species lists and abundance estimates are provided for each site and sampling date (one date for plants and earthworms, three dates for spiders and bees). In addition, farmers provided information about their management practices in face-to-face interviews following a standardized questionnaire. Farm management indicators for each farm are available (e.g., nitrogen input, pesticide applications, or energy input). Analyses revealed a positive effect of unproductive areas and a negative effect of intensive management on biodiversity. Communities of the four taxonomic groups strongly differed in their response to habitat characteristics, agricultural management, and regional circumstances. The data has potential for further insights into interactions of farmland biodiversity and agricultural management at site, farm, and regional scale.