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Condes S.,Technical University of Madrid | Del Rio M.,Sistemas de Gestion | Del Rio M.,Sustainable Forest Management Research Institute | Sterba H.,University of Natural Resources and Life Sciences, Vienna
Forest Ecology and Management | Year: 2013

Despite the increasing relevance of mixed stands due to their potential benefits; little information is available with regard to the effect of mixtures on yield in forest systems. Hence, it is necessary to study inter-specific relationships, and the resulting yield in mixed stands, which may vary with stand development, site or stand density, etc. In Spain, the province of Navarra is considered one of the biodiversity reservoirs; however, mixed forests occupy only a small area, probably as a consequence of management plans, in which there is an excessive focus on the productivity aspect, favoring the presence of pure stands of the most marketable species. The aim of this paper is to study how growth efficiencies of beech (Fagus sylvatica) and pine (Pinus sylvestris) are modified by the admixture of the other species and to determine whether stand density modifies interspecific relationships and to what extent. Two models were fitted from Spanish National Forest Inventory data, for P. sylvestris and F. sylvatica respectively, which relate the growth efficiency of the species, i.e. the volume increment of the species divided by the species proportion by area, with dominant height, quadratic mean diameter, stocking degree, and the species proportions by area of each species. Growth efficiency of pine increased with the admixture of beech, decreasing this positive effect when stocking degree increased. However, the positive effect of pine admixture on beech growth was greater at higher stocking degrees. Growth efficiency of beech was also dependent on stand dominant height, resulting in a net negative mixing effect when stand dominant heights and stocking degrees were simultaneously low. There is a relatively large range of species proportions and stocking degrees which results in transgressive overyielding: higher volume increments in mixed stands than that of the most productive pure pine stands. We concluded that stocking degree is a key factor in between-species interactions, being the effects of mixing not always greater at higher stand densities, but it depends on species composition. © 2012 Elsevier B.V. Source

Rodriguez-Garcia E.,University of Valladolid | Gratzer G.,Sustainable Forest Management Research Institute | Bravo F.,University of Natural Resources and Life Sciences, Vienna
Annals of Forest Science | Year: 2011

Background: How environmental factors affect forest regeneration is relevant for systems that depend partially or fully on natural regeneration. Methods:P. pinaster post-disturbance regeneration and its relationship to environmental factors was studied in five P. pinaster forest populations of central Spain. We expected that: 1) different harvesting methods or wildfire would promote natural regeneration in all populations, but with local and regional variations,or 2) alternatively, different site-dependent stand factors would affect natural regeneration, although generalized climate effects would be seen. Analysis of variance and multivariate analysis were used to test differences, to classify ecological variations, and to search for the most important factors affecting regeneration. Results:The results suggest that the recovery of P. pinaster forest in burnt stands, and stand replacement in harvested stands, can be achieved soon after disturbance if climatic conditions and other local-site factors (e.g., soil and overstory structure in harvested stands, cone bank in burnt stands) make the stand suitable for natural regeneration. Heterogeneous regeneration can be expected in all cases. The time of precipitation strongly influenced seedling density and successive regeneration development stages. Conclusion: Edaphic properties, combined with water availability from precipitation, can seriously limit the natural establishment of P. pinaster in xeric systems or during years of intense drought. Although many factors contribute to high variability, natural regeneration has been very effective (successful) in P. pinaster forests, which contributes to the generalization that natural regeneration is a viable forestry option in many forest types. © INRA and Springer Science+Business Media B.V. 2011. Source

Canestrari D.,University of Valladolid | Marcos J.M.,University of Valladolid | Baglione V.,University of Valladolid | Baglione V.,Sustainable Forest Management Research Institute
Journal of Evolutionary Biology | Year: 2011

Life history theory predicts that mothers should trade off current and future reproductive attempts to maximize lifetime fitness. When breeding conditions are favourable, mothers may either increase investment in the eggs to improve the quality of the offspring or save resources for future reproduction as the good raising environment is likely to compensate for a 'bad start'. In cooperatively breeding birds, the presence of helpers improves breeding conditions so that mothers may vary the number, size and quality of the eggs in response to the composition of the group. Here, we show that in cooperatively breeding carrion crows Corvus corone corone, where nonbreeding males are more philopatric and more helpful at the nest than females, breeding females decreased egg size as the number of subordinate males in the group increased. However, despite the smaller investment in egg size, fledglings' weight increased in groups with more male subordinates, improving post-fledging survival and indicating that helpers fully compensated for the initial 'bad start'. These results highlight a 'hidden effect' of helpers that bears profound implications for understanding the ultimate function of helping. © 2011 The Authors. Journal of Evolutionary Biology © 2011 European Society For Evolutionary Biology. Source

Canestrari D.,University of Oviedo | Vila M.,University of La Coruna | Marcos J.M.,University of Valladolid | Baglione V.,University of Valladolid | Baglione V.,Sustainable Forest Management Research Institute
Behavioral Ecology and Sociobiology | Year: 2012

In cooperatively breeding species, parents should bias offspring sex ratio towards the philopatric sex to obtain new helpers (helper repayment hypothesis). However, philopatric offspring might increase within-group competition for resources (local resource competition hypothesis), diluting the benefits of helper acquisition. Furthermore, benefits of offspring sex bias on parents' fitness may depend on different costs of production and/or different breeding opportunities of sons and daughters. Because of these counteracting factors, strategies of offspring sex allocation in cooperative species are often difficult to investigate. In carrion crows Corvus corone corone in northern Spain, sons are more philopatric and more helpful at the nest than daughters, which disperse earlier and have higher chances to find a breeding vacancy. Consistent with the helper repayment hypothesis, we found that crows fledged more sons in groups short of subordinate males than in groups with sufficient helper contingent, where daughters were preferred. Crow females also proved able to bias primary sex ratio, allocating offspring sex along the hatching sequence in a way that provided the highest fledging probability to sons in the first breeding attempt and to daughters in the following ones. The higher cost of producing male offspring may explain this pattern, with breeding females shifting to the cheapest sex (female) as a response to the costs generated by previous reproductive attempts. Our results suggest complex adjustments of offspring sex ratio that allowed crows to maximize the value of daughters and sons. © 2012 Springer-Verlag. Source

Canestrari D.,University of Granada | Vera R.,University of Valladolid | Chiarati E.,University of Valladolid | Marcos J.M.,University of Valladolid | And 3 more authors.
Behavioral Ecology | Year: 2010

False feeding, where individuals refrain from delivering a food item to a begging dependent young, has been described in several cooperative bird and mammal species, but its function is still unclear. False feeding has been suggested to represent either a deceptive tactic of helpers aimed at showing off provisioning behavior to the rest of the group without paying the costs or a normal provisioning behavior of caregivers mediated by the trade-off between the hunger of the young and caregivers' own conditions. Here, we employed an experimental approach to test whether false feeding in cooperatively breeding carrion crows responds plastically to variations of chicks' and caregivers' needs. In 4 different treatments, we manipulated the hunger of the brood and the conditions of group members by 1) experimentally feeding the chicks, 2) food-supplementing group members during the breeding season or 3) throughout the whole year, and 4) clipping 2 primary feathers from each wing of some individuals to increase the costs of flight. Breeders increased false feeding when the brood was food supplemented (treatment 1) and after their wings were clipped (treatment 4), whereas helpers did not change their false-feeding behavior in response to these treatments. Conversely, helpers decreased false feeding when food was supplemented year-round (treatment 3), whereas fed breeders did not show any significant difference compared with controls. These results indicate that a trade-off between chicks' needs (current reproduction) and caregivers' conditions (future reproduction) modulates the occurrence of false feeding, determining different responses in different group members. Source

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