María José Leiva

Variability in seedling water status during drought within a Quercus ilex subsp. ballota population, and its relation to seedling morphology

Abstract Differences in morphology, growth and plant water status during drought were studied in greenhouse-grown Quercus ilex subsp. ballota seedlings produced by different mother trees occurring in a savannah-like forest (locally named dehesa) in southern Spain. There were significant differences among mother trees in the biomass of their seeds (mother tree level accounted for 62% of total variance in this trait), in the percentage of seedlings that emerged and in the time of shoot emergence. The progeny that had high emergence rates (80–90%) also had short emergence times while the opposite was true for the progeny that had low (43%) and intermediate (70%) emergence rates. Acorn biomass covaried significantly with seedling total biomass and with the biomass of different parts of the seedlings, but not with the partitioning of biomass among roots and shoots (root/shoot ratio) nor to morphological seedling traits such as shoot height, total leaf area, average leaf size, specific leaf area (SLA) and leaf number. All these traits varied significantly among the seedlings produced by different mother trees. The conductance to water vapour (glw) of the foliage of the seedlings also varied significantly among mother trees and was dependent on the root/shoot ratio as on the total leaf area of the seedlings, but not on the total seedling biomass. One of the six trees that were studied produced seedlings which had a significantly higher root/shoot ratio, smaller leaf area, smaller leaves, higher specific leaf area and shorter stems than the seedlings produced by any other tree. In addition, the former set of seedlings had significantly higher glw 15 and 30 days after drought, and higher leaf water content at the end of the experiment than the other seedlings. We discuss the value of using single seedling traits related to drought tolerance such as root/shoot ratio and leaf area in the framework of the restoration of savannah-like oak forest in the Mediterranean areas. We also discuss the functional implications of the diversity of genotypes within the oak populations in the framework of the global climate change.

Post-dispersive losses of acorns from Mediterranean savannah-like forests and shrublands

Abstract We studied post-dispersive losses of holm-oak acorns (Quercus ilex subsp. ballota) due to wild and domestic ungulates and to small mammals in two types of Mediterranean ecosystems in south-western Spain, savannah-like forests, locally named dehesa, and shrublands. Savannah-like forests which are used for sheep and cattle grazing and for acorn fattening of Iberian pig show a lack of oak regeneration. However, these ecosystems are considered as a model of sustainable resource use in all the fragile area of the Mediterranean region. During the 2 years, 1999 and 2000, we carried out a field experiment in three savannah-like forest and three shrubland sites. At each site, we added marked acorns and studied their loss from plots that were either accessible to any animal (no exclosure), protected against ungulates but accessible to small mammals (partial exclosure), or protected against big and small mammals and other vertebrates (complete exclosure). Results indicated that in the no exclosure treatment (i.e., the normal environment) acorn recovery was very low at any site (0–2.4%) without significant differences between savannah-like forests and shrublands. In the partial exclosure treatment, with small mammals having access to the plots only, acorn recovery varied from 0 to 42%. In this treatment, acorn recovery tended to be higher in the savannah-like forests (0.5–42%) when compared to the shrubland sites (0–2.5%). However, the three savannah-like forest sites, in different years, experienced >92% of acorn loss due to small mammals. In addition, many complete exclosures were disrupted, presumably by rodents, and lost 60% of the acorns. These results indicate that loss of acorns due to small mammals is very important in the two type of ecosystems, suggesting that proper management of oak self-regeneration in Mediterranean savannah-like forests should take into account the effect of small mammals, as well as livestock, especially during the seeding stage.

Effect of grazing on the population biology of Phalaris aquatica.

To examine the effect of grazing and potential interactions among grazing and biological traits of plants, we studied patch dynamics, seed production, and seedling survival in a Mediterranean population of the perennial grass Phalaris aquati ca L. in grazed and ungrazed plots in southern Spain. Grazing by cattle induced an important (70%) decrease in the abundance of plants over 4 growing seasons. In the ungrazed plots, abundance of plants remained stable. Within these plots there was some (30%) spatial replacement of plants. However, replacement was by tillering and not by genets, genetically different individuals produced from seeds. The lack of genet replacement within the ungrazed plots agrees with results on mortality of young plants that were obtained from an independent field experiment, in which 85‐95% of plants in different cohorts died within 1 to 3 growing seasons. This mortality of seedlings and young plants was concentrated in summers, especially when drought was prolonged. In contrast, seed production was apparently not a limit ing factor for plant recruitment in ungrazed plots as seed output of the perennial grass (25,312 ± 3,255 seeds m -2 ) was of the same magnitude as seed output in annual grasses that were abundant in the study site. Intensive grazing limited tiller production, patch size, and a summer drought limited recruitment of new adult individuals. These factors resulted in a low tolerance to episodes of high stocking rates from which the perennial grass was unable to recover.

Effect of artificial shelters of dead branches on acorn survival and dispersal in shrub-lacking Mediterranean dehesas

AbstractAcorn predation is a major bottleneck for oak self-regeneration in grazed Mediterranean oak savannahs (dehesas), which lack of shrub cover. Establishing artificial shelters of dead branches (SODBs) could decrease acorn predation by protecting the seeds against domestic ungulates. However, rodents are also common in dehesas and their dual role as acorn predators and dispersers could be affected by the SODBs. Two experiments were conducted to assess this role of the SODBs on acorn survival and dispersal. They were carried out in six dehesa stands with different levels of rodent activity (i.e., high and low). The results revealed a positive effect of the SODBs on the acorns safety in those stands with low level of rodent activity. Here, the SODBs acted as effective physical barriers against livestock, and the acorn survival was significantly higher (3- to 7-fold) beneath the SODBs than in the Open treatment. Conversely, in those stands with high level of rodent activity the SODBs significantly increased acorn predation by rodents (acorn survival was 1.6- to 9-fold lower beneath the SODBs than in the Open treatment). In addition, the SODBs acted as preferred sink for dispersed acorns, but these acorns were completely predated by mice. These results suggest that establishing SODBs could be a suitable and inexpensive method to improve oak regeneration in dehesas and in other disturbed ecosystems, especially whether this method is combined with other simple techniques to protect acorns against predation by rodents.

A vegetation management experiment: Goats grazing shrublands in Doñana Natural Park

We have studied the effect of goat grazing on the shrub understory of a pine forest situated in a protected area (Doñana Natural Park). Along three years we have studied the changes in phytovolume, flammability, species richness and diversity in a grazed shrubland and in a control area not grazed by the goats. We studied also food preferences of the goats and the ability of the goats to disperse the seeds of the plants they eat. Goat grazing significantly reduced shrub biomass and flammability, decreasing the risk of forest fire. Goats selected the species they eat, changing the pattern of selection throughout the year. Grazing reduced shrub diversity, but did not affected species richness. The goats can also potentially disperse the seeds of some of the species they eat, since the seeds were able to pass through the goat’s gut and germinated afterwards. Goat grazing on scrub vegetation can be used as an effective tool for the control of shrubs in protected forest areas, without losing biodiversity.