Susana Bautista

POSITIVE, NEGATIVE, AND NET EFFECTS IN GRASS–SHRUB INTERACTIONS IN MEDITERRANEAN SEMIARID GRASSLANDS

Current theoretical models and field evidence suggest that facilitation and interference act simultaneously in the field, but there is little information on their joint dynamics under varying abiotic conditions. We evaluated spatial and temporal variations in the positive, negative, and net effects of the tussock grass Stipa tenacissima on the shrub Pistacia lentiscus in Mediterranean semiarid grasslands. We performed a field experiment in which positive (microclimatic amelioration and water inputs from runoff) and negative (belowground competition) effects were experimentally manipulated under contrasting levels of stress. The environment provided by S. tenacissima (tussock treatment) improved the survival and physiological status of planted P. lentiscus seedlings. The elimination of shade and competition from S. tenacissima significantly decreased and increased, respectively, seedling performance as compared to the tussock treatment. We found evidence that microclimatic amelioration is the main positive...

Pines and oaks in the restoration of Mediterranean landscapes of Spain: New perspectives for an old practice — a review

Pines have been extensively used for land restoration in the Mediterranean basin and in other parts of the world, since the late 19th century. The theoretical basis supporting pine utilisation was its stress-tolerant and pioneer features, and their attributed role of facilitating the development of late-successional hardwoods in the long-term. In the present work, the use of pines and hardwoods in forest restoration is discussed in the frame of the current disturbance regime and social demands for Mediterranean forests. Large pine plantations have recently disappeared because of their sensitivity to fire (e.g., Pinus nigra) or because of the short fire-intervals (e.g., Pinus halepensis). Combined pine and oak plantations are proposed for degraded land restoration on the basis of the complementary features of both groups of species. Seeding and containerised seedling plantation, soil amendments and plantation techniques to reduce transplant shock are evaluated for reforestation under water-stressing conditions, on the basis of several experiments performed in eastern Spain. Both P. halepensis and Quercus ilex are tested.

POTENTIAL FOR USING FACILITATION BY GRASSES TO ESTABLISH SHRUBS ON A SEMIARID DEGRADED STEPPE

In arid and semiarid environments, isolated vegetative patches establish islands of fertility in which facilitation is a dominant interaction between plant species. These patches may provide favorable microsites for revegetation with desirable species in areas where traditional revegetation procedures fail. Alpha grass (Stipa tenacissima) steppes are widely distributed within the semiarid areas of southern Europe and northern Africa and represent a degraded stage of climax vegetation. In this study, we analyzed the effects of S. tenacissima tussocks on the survival, growth, and ecophysiological features of experimentally planted seedlings of Medicago arborea, Quercus coccifera, and Pistacia lentiscus in three sites in a semiarid region in southeastern Spain. Our main objective was to test whether S. tenacissima was able to facilitate shrub establishment in semiarid degraded steppes. Soils under S. tenacissima tussocks had higher organic matter content and water availability than those from open areas. Sti...

Small-scale Environmental Heterogeneity and Spatiotemporal Dynamics of Seedling Establishment in a Semiarid Degraded Ecosystem

In semiarid environments, surface soil properties play a major role in ecosystem dynamics, through their influence on processes such as runoff, infiltration, seed germination, and seedling establishment. Surface soil properties usually show a high degree of spatial heterogeneity in semiarid areas, but direct tests to evaluate the consequences of this heterogeneity on seedling establishment are limited. Using a combination of spatial analysis by distance indices (SADIE) and principal components analysis (PCA) we quantified the spatiotemporal patterns of seedling survival of a Mediterranean native shrub (Pistacia lentiscus) during the first 3 years after planting on a semiarid degraded site in southeastern Spain. We used a variation partitioning method to identify environmental variables associated with seedling survival patterns. Three years after planting, only 36% of the seedlings survived. During the first summer, one-third of the seedlings died, with secondary major mortality in the 3rd summer after planting. The spatial pattern of survival became strongly clumped by the end of the first summer, with clearly defined patches (areas of high survival) and gaps (areas of low survival). The intensity of this pattern increased after subsequent high-mortality periods. Of the 14 variables, the ones most strongly coupled to seedling survival were bare soil cover, sand content, and soil compaction. These findings contribute to our understanding of the linkages between the spatial heterogeneity of abiotic factors and the response of plant populations in semiarid degraded ecosystems and can be used to optimize restoration practices in these areas.

Analysis of the mycorrhizal potential in the rhizosphere of representative plant species from desertification-threatened Mediterranean shrublands

An evaluation of the mycorrhizal status of desertification-threatened ecosystems has been recommended as a first step in rehabilitation/restoration approaches based on revegetation strategies using arbuscular mycorrhizal (AM) technology. Representative desertified semiarid areas were selected from southeast Spain where the vegetation is dominated by grasses, with Stipa tenacissima usually present, and with some patches of the shrubs Pistacia lentiscus, Rhamnus lycioides, Olea europaea subsp. sylvestris and Retama sphaerocarpa. The objective of this study was to evaluate the mycorrhizal potential in these soils, the contribution of the different species established to the mycorrhizal potential of the soils and to assess the main mycorrhizal propagules involved. There were more AM fungal propagules in the rhizospheres of all the shrub species studied compared with adjacent fallow soils, suggesting that AM propagules can be considered as a functional component of the resource islands developing around plant roots. R. sphaerocarpa and O. europaea had a higher capacity to enhance the development of mycorrhizal propagules in their rhizospheres than R. lycioides and P. lentiscus. Correlation analyses showed that the number of spores of the most representative AM fungal species, i.e. Glomus constrictum, and the total length of extraradical AM mycelium are the propagule sources which were best correlated with the mycorrhizal potential in terms of the number of “infective” AM propagules in the rhizosphere of the target plant species. The contribution of AM symbiosis to the potentiality of S. tenacissima as nurse plant was site dependent. Diversity of AM fungi present in the test area is rather low, indicating the high degree of degradation of the ecosystem. At most, only four AM fungal spore morphoecotypes were consistently detected in the rhizosphere of the target plant species.

Infiltration, penetration resistance and microphytic crust composition in contrasted microsites within a Mediterranean semi-arid steppe

In semi-arid areas with sparse vegetation cover, runoff generated in the open areas is crucial for the maintenance of vegetated patches. Microphytic crusts play a major role in this redistribution of water, thus influencing ecosystem functioning and dynamics. We investigated the effects of alpha grass (Stipa tenacissima L.) on the composition of the microphytic crusts, surface soil compaction, and infiltration in a semi-arid steppe of SE Spain. The microphytic crust composition differed between the upslope of S. tenacissima tussocks (tussock microsites) and the inter-tussock areas with sparse vascular plant cover (open microsites), with more moss cover in the tussock microsite, and more cyanobacteria and lichens in the open microsite. The surface soil compaction was higher in the open microsite. Variables related with infiltration showed a clear microsite effect, with higher infiltration rate and less time required by first drop to percolate in the tussock microsite. Partial correlation analysis showed a significant negative relationship between the cyanobacteria cover and the infiltration rate, and both the cyanobacteria cover and the percentage of bare soil showed a significant positive relationship with the time required for first drop to percolate. Our results reinforce the idea that open microsites act as sources of water for S. tenacissima tussocks. This study helps to understand the interactions between microphytic crusts and vascular plants in semi-arid environments.

Mulching treatment for postfire soil conservation in a semiarid ecosystem

Fire may generate soil degradation and accelerate erosion processes, depending among other factors, on the regeneration capacity of the ecosystem. Conservation measures will be beneficial in those fragile systems where a high degradation hazard is estimated. Mulching treatment was evaluated in order to establish its efficiency in protecting soil and preventing runoff generation in a semiarid area affected by a wildfire. Straw mulch was applied at 200 g m‐2 in three replicated plots. Paired mulched and control plots were established in a three block experimental design. Runoff, sediment yield, plant cover, and dynamics of soil physical properties were measured in these plots over a 2‐year period. Most of the plant regeneration after the fire resulted from resprouting of the dry grassland species, dominated by Brachypodium retusum. Total plant cover was only 50% two years after passage of the fire. Runoff and sediment yield were significantly greater from control plots. Soil loss from control plots was abou...

Does Pinus halepensis facilitate the establishment of shrubs in Mediterranean semi-arid afforestations?

Aleppo pine (Pinus halepensis) dominates forest ecosystems in dry and semi-arid areas of the Mediterranean Basin. In addition to its natural distribution, this species has been used extensively in afforestation projects during this century. The improvement in soil fertility and microclimate provided by the P. halepensis canopy is known to facilitate the establishment of perennial grasses, but little is known about the interactions of this species with woody species in natural stands and afforestations under semi-arid climate. In this study, we analyze the effects of the P. halepensis canopy on the survival and ecophysiological features of experimentally planted seedlings of several Mediterranean shrub and tree species in two semi-arid afforestations of SE Spain. Soils under P. halepensis (pine microsite) showed small differences in nutrient content relative to those outside the canopy (open microsite). Radiation reaching pine microsites was four times lower than in open microsites. Soil moisture did not show significant differences between both microsites during most of the year. One year after planting, survival of the introduced seedlings was significantly higher in the open microsites than in the pine microsites. Predawn and midday water potentials and chlorophyll fluorescence of seedlings measured before the summer did not show any microsite effect. Our results suggest that the changes in understorey microclimate associated with P. halepensis are not sufficient to facilitate the establishment of shrubs under semi-arid conditions.

Monitoring post-wildfire vegetation response with remotely sensed time-series data in Spain, USA and Israel

Due to the challenges faced by resource managers in maintaining post-fire ecosystem health, there is a need for methods to assess the ecological consequences of disturbances. This research examines an approach for assessing changes in post-fire vegetation dynamics for sites in Spain, Israel and the USA that burned in 1998, 1999 and 2002 respectively. Moderate Resolution Imaging Spectroradiometer satellite Normalized Difference Vegetation Index (NDVI) time-series data (2000-07) are used for all sites to characterise and track the seasonal and spatial changes in vegetation response. Post-fire trends and metrics for burned areas are evaluated and compared with unburned reference sites to account for the influence of local environmental conditions. Time-series data interpretation provides insights into climatic influences on the post-fire vegetation. Although only two sites show increases in post-fire vegetation, all sites show declines in heterogeneity across the site. The evaluation of land surface phenological metrics, including the start and end of the season, the base and peak NDVI, and the integrated seasonal NDVI, show promising results, indicating trends in some measures of post-fire phenology. Results indicate that this monitoring approach, based on readily available satellite-based time-series vegetation data, provides a valuable tool for assessing post-fire vegetation response.

Effects of land use and eventual fire on soil erodibility in dry Mediterranean conditions

The Mediterranean countries of Europe have suffered deep land-use transformations during this century and the expansion of wildfires after generalized land abandonment in the marginal uplands. Differences in soil properties due to land use may lead to different responses of the ecosystem in case of fire. We analyze how soil erodibility in a cropland and oldfields of different age after abandonment (bushland, shrubland and pine forest) would be affected by wildfire. Soil samples taken in each land use were analyzed to characterize soil erodibility. From fuel load measures, the range of temperatures to be attained in case of a fire were estimated for the topsoil. From these temperatures and from the information available in the literature, we predicted the changes in soil properties produced by the fire and estimated soil erodibility for the burned lands. Changes in soil erodibility were slight in the field crop with low fuel load, and increased according to biomass and forest floor accumulation. As the initial soil erodibility was inversely related to fuel load, the fire would increase the values of soil erodibility of the different land uses up to close to those of the field crop. In addition, the fire would produce very similar soil erodibility values for the different land uses, and therefore a homogenizing post-fire soil response in the landscape.