Pere Pons

Transformation of a Rural Landscape in the Eastern Pyrenees Between 1953 and 2000

Abstract In the mid-20th century, the southern parts of the Madres and Mont Coronat massif (Eastern Pyrenees, France) were characterized by a Mediterranean landscape shaped by human activity. Long-term use of these mountains for crops, livestock, and forestry led to an increase in grassland areas at the expense of forest. However, socioeconomic transformation (abandonment of agriculture and a decrease in the rural population) in recent decades has caused profound changes in this massif. Interpretation of aerial photographs (1953, 1969, 1988, and 2000) made it possible to detect and analyze the changes produced in the study area (6787 ha) during this period. In 1953 most of the massif landscape consisted of grasslands (38%) and open forests (18%), with some areas of dense forest (15%). By 2000, dense forest cover had doubled in size (31%), and grassland had decreased considerably (by 73% of the initial area). Since 1953, the study area has become more homogeneous, with a few local exceptions. The results of this study suggest that socioeconomic factors might be the main cause of landscape transformations in this period of approximately 50 years.

Exclusive frugivory and seed dispersal of Rhamnus alaternus in the bird breeding season

We studied avian frugivory and seed dispersal in a dioecious shrub, Rhamnus alaternus, focusing on the quantitative and qualitative components of effectiveness. The study took place at three locations in the northeast of the Iberian Peninsula, and examined bird behaviour, intensity of feeding, and the consequences for seedling emergence. The coincidence between the bird breeding season and fruit ripening of R. alaternus in the absence of other ripe fruit, generates a monospecific interaction. The extant frugivorous species were mainly legitimate seed dispersers and their abundance was low. Sylvia melanocephala and S. undata were the most important at one site whereas S. atricapilla, Erithacus rubecula and Turdus merula predominated at the other two sites. Fruit handling took place directly on the branches. Bird species used microhabitats differently as first post-feeding perch, which usually was a short distance away. The low density of frugivorous birds in all localities, among others factors, resulted in satiation of the disperser community and many mature fruits unconsumed. Both adults and juveniles feed upon the plants and their foraging patterns are similar. Adults of S. melanocephala were observed to feed fruit to nestlings and consequently a second phase of dispersal potentially arises from the transport of fecal sacs. Pulp removal and passage through the digestive tract increased the probability of seedling emergence. This plant-dispersal interaction has important consequences, both positive and negative for the plant. Positively, the fruiting of R. alaternus at a time when other ripe fruits are not available avoids interspecific competition for seed dispersers. In addition, a low density of seed rain may reduce intraspecific competition. Negatively, the low density and small size of the breeding frugivorous bird community limit fruit handling and removal away from the parent plants, while the territorial behaviour of birds at that time of the year reduces the potential distances of seed dispersal.

Territory characteristics and coexistence with heterospecifics in the Dartford warbler Sylvia undata across a habitat gradient

The study of successional gradients may help to understand the relative influence of habitat structure and competition on territory characteristics. Here, we evaluate the effects of vegetation cover, conspecific and heterospecific densities, and distance to the nearest neighbor on territory size, shape, and overlap in insectivorous birds. We studied these effects along a gradient of postfire habitat regeneration in which foliage cover and densities of focal species varied several-fold. We delineate 197 territories (minimum convex polygons) of the shrub-dwelling Dartford warbler (Sylvia undata) and 255 of the syntopic Sardinian (Sylvia melanocephala), subalpine (Sylvia cantillans) and melodious (Hippolais polyglotta) warblers at three plots in NE Catalonia (Spain and France) in 1987–2005. After accounting for the effect of the number of locations used to delineate polygons, generalized linear mixed models (GLMM) showed a reduction in territory area of the Dartford warbler as conspecific density increased and distance to nearest neighbor decreased, in accordance with the contender pressure hypothesis for territory size regulation. Heterospecific density was not included in the final model of territory size and the effect of habitat structure was marginal. Territory roundness was positively correlated with its size and with conspecific density, probably in relation to energetic constraints, and negatively with heterospecific density. Territorial exclusion was almost complete among Dartford warblers, whereas interspecific territory overlap was extensive and tended to increase with heterospecific density and with structural diversity along the gradient. Our results support the hypothesis that Mediterranean warbler coexistence derives from ecological segregation and not from interspecific territoriality.

Postfire forest management and Mediterranean birds: the importance of the logging remnants

Fire is a crucial element needed to understand the biodiversity patterns of forest landscapes in most Mediterranean countries. However, little is known about the quantitative responses of bird communities to postfire forest management in this region, in which the logging of burnt trees is a common practice. Several studies have already described the negative effects of felling burnt trees on birds but none has focussed on the remaining wood remnants. We investigated this question in a large burnt area located in north-east Iberian Peninsula. The amount of logging remnants left on the ground had positive linear and negative quadratic relationships with the indices of bird abundance and bird richness. The results obtained at a species level were similar, since 36% of the most abundant species revealed the same type of relations with logging remnants, whereas none showed an opposite pattern. Thus, birds in general seem to be positively influenced by the amount of wood remnants left on the ground to a certain point, from which the relation reverses. The results of this study indicate that a moderate amount of wood remnants left on the ground may be positive for the overall bird community. We suggest that management plays a role in the recovery of the bird community after fire and, therefore, biodiversity criteria should be incorporated in the guidelines driving postfire actions.

Home range and territory of the Sardinian Warbler Sylvia melanocephala in Mediterranean shrubland

Capsule Singing territories were well separated. Aims To examine the spatial distribution of Sardinian Warbler males during the breeding period in Mediterranean shrubland and, specifically, their territories, home ranges and spatial overlaps. Methods We studied a 12-ha plot of Mediterranean shrubland in the 1997 to 1999 breeding seasons. Sardinian Warblers were captured using mist-nets, colour-ringed and their territories mapped. In 1999, seven breeding males were radiotracked in order to map home ranges. Results The Sardinian Warbler had an average of 7.3 breeding pairs/10 ha in the study plot. The mean territory size was 8779 m2 and the mean home range was 22 321 m2. A positive relationship was found between the area of the home range and singing territory. Home ranges of males born in 1998 were about half the size of those of the oldest males. Paired males who moved with a female had smaller home ranges than those that were either unpaired or whose mate was incubating. The degree of home range overlap was high with some overlap between neighbouring territories. The estimate of home range area increased by 10% when the information generated by a mapping method was added and the estimated territory area increased by 31% when data generated by radiotracking were added. Transmitters remained attached to birds for an average of 9.63 ± 3.46 days (mean ± se). Conclusions Singing territories were segregated to a considerable degree. In contrast, the wide overlaps among home ranges was best explained by the presence of food resources that the males exploit at the same time and also by the search for extra-pair copulation in nearby territories. We consider radiotracking in this species to be feasible and valid, with no evidence of negative effects on activity levels, weight or mortality.

Coping with invasive alien species: the Argentine ant and the insectivorous bird assemblage of Mediterranean oak forests

Cork oak forests invaded by the Argentine ant Linepithema humile have a lower abundance and biomass of arthropod prey for birds than uninvaded forests. We studied whether the biomass of breeding insectivorous birds was also lower in invaded areas. We explored this and other possible effects of the ant invasion on the bird community by censusing birds in transects located in four invaded and four uninvaded forest sites in Catalonia (NE Spain) for 3 years. Redundancy analysis showed only slight differences in the community composition between forests. Two insectivorous species, Luscinia megarhynchos and Fringilla coelebs, tended to be less abundant in invaded areas although two others, Phylloscopus bonelli and Sylvia melanocephala, showed the opposite trend. Overall, the differences in prey biomass between invaded and uninvaded areas did not entail a biomass shift in the guild of insectivorous birds, regardless of whether they were shrub or canopy foragers. The main role of the habitat structure in determining bird densities and food resources being non-limiting in the studied forests are two possible non-exclusive explanations for this inconsistency. At today’s levels, the Argentine ant invasion does not appear to have greatly determined the insectivorous bird assemblage of the forests evaluated.

The importance of piled wood debris on the distribution of bird-dispersed plants in burned and logged Mediterranean pine forests

Plant dispersal and colonisation are important processes in vegetation recovery after fire and, for several species, depend on the presence of frugivorous avian seed dispersers. In burned and salvage-logged Mediterranean pine forests, the occurrence of disperser birds is enhanced by the presence of wood debris piles built as erosion barriers, which become seed dispersal foci. We hypothesised that the distribution of bird-dispersed plants after fire could be determined by the presence of wood piles. We analysed the differences in species richness and overall cover of bird-dispersed plants, as well as the cover of the most common species, within piles and outside them. We also tested if micro-environmental conditions (slope orientation and pile size) might influence plant occurrence. We found more species and overall cover within piles, when located on southern and south-eastern slopes, than outside them. Moreover, taller piles showed higher values of bird-dispersed plant cover and richness. Therefore, wood piles may provide the necessary conditions for bird-dispersed plant recruitment in dry burned areas. To our knowledge, this is the first reported man-made structure that clearly benefits the recovery of bird-dispersed plants in burned areas, and suggests that piles may be a useful restoration measure when logging Mediterranean burned forests.

Pre-dispersal seed removal of fleshy fruits and Quercus coccifera (Fagaceae) acorns in a recently burned Mediterranean habitat

The seed fate in early successional habitats can determine plant composition and regeneration capacity after disturbance. Predispersalseed removal has been poorly studied in Mediterranean habitats, especially in burned and logged habitats. We assessed it for two years in pine forests with experiments excluding vertebrates from fleshy fruits (infructescences of Smilax aspera and Rubia peregrina) and acorns (branches of Quercus coccifera). We compared one unburned and one burned area (control). Acorn removal was nil in the burned area while in the unburned habitat seed removal occurred from the beginning of the experiments. It is suggested that the greater vegetation cover in the unburned area shelter rodents from predators and increased their activity. In contrast, reduced cover in the burned area and the occurrence of gnawed acorns on the ground suggest acorn removalby rodents mainly in the post-dispersive stage. Smilax aspera seed removal was slower, and total loss of fruits due to senescence higher,in the burned area. Seed removal appears to be conditioned by interannualvariations related to the activity and density of granivores and frugivores, the availability of fleshy fruits, and the maturation of fruits.In post-fire managed areas the role of granivores and frugivores in the regeneration process should be taken into account.

Anàlisi dels factors determinants en la rebrotada del bruc boal (Erica arborea L.) després de l’incendi de l’Alt Empordà del 2012

S’han analitzat els factors determinants en el proces de rebrotada del bruc boal (Erica arborea) entre quatre i nou mesos despres de l’incendi de l’Alt Emporda del 2012.Mitjancant models lineals generalitzats mixtos (GLMM) s’han analitzat quines variables (severitat del foc i altres variables biologiques) han influit en els indicadors de la rebrotada: la biomassa i el creixement dels rebrots. D’una banda, la biomassa s’ha vist influida pels efectes de l’area de la rabassa i pel nombre i l’alcada dels rebrots. De l’altra, una severitat mes gran del foc ha promogut el creixement dels rebrots en els primers quatre mesos despres de l’incendi, tot i que en els cinc mesos seguents s’ha donat l’efecte contrari. En canvi, a baixes severitats, el creixement inicial ha estat menor, incrementant-se en el segon periode. La capacitat de resposta d’una especie dominant, com el bruc, facilita la recuperacio de l’ecosistema i s’ha de tenir en compte en la gestio postincendi.