Mediterranean Dehesa Research Articles

Functional redundancy in carrion decomposition by temperate forest ant communities

Abstract Scavenging of small avian corpses may provide ants with a valuable source of nutrients, a possibility poorly studied. Here, we assessed whether ants are efficient carrion‐decomposers of avian corpses in Mediterranean dehesas through an exclusion experiment comparing decomposition rates among three treatments: vertebrate exclusion, vertebrate + invertebrate exclusion and control. Treatments were applied in a paired design in bird cavities and on the ground in two zones to assess functional redundancy. Ant community was characterized by pitfall traps, and key functional traits influencing ants' presence on carrion were identified by using phylogenetic comparative methods. Carrion decomposition was influenced by the exclusion treatment, being significantly faster when ants and other invertebrates were not excluded, but not by location (cavity/ground). Vertebrates were less likely to detect baits in cavities and removed more bait mass in the most transformed zone. Twelve of 25 ant species in the community were found foraging on baits. Ant communities differed between carrion location and localities. Phylogenetic analyses revealed that the proneness of ant species to forage on carrion was unrelated to morphological or social traits, but behavioural, being higher among species foraging collectively. Our results show that ants play a functionally unique role in the decomposition of small corpses in dehesas, and particularly so in trees and less transformed pastureland. Decomposition involves different species in different microhabitats, suggesting high functional redundancy across ants. Our findings provide new insights into the role of ants as scavengers and expand our understanding of the functioning of Mediterranean communities.

Physical decomposition stage and ergosterol content predict the chemical composition of downed dead wood in Mediterranean dehesas

AbstractDead wood is a key substrate of forests that plays an important role in fertility and productivity. However, dead wood is scarce in traditionally managed forests like Mediterranean dehesas. The chemical composition of downed dead wood in Quercus pyrenaica dehesas was analysed in different physical decomposition stages as a proxy of dead wood decay length. We also assessed the contribution of fungal activity, by quantifying ergosterol, to the chemical composition of deadwood. Chemical analyses included elemental composition determination, thermogravimetry and infrared spectroscopy. Our results showed that both the physical decomposition stage and ergosterol content extensively predicted the chemical composition of Q. pyrenaica dead wood decay processes under field conditions. The physical stage was a better predictor of the C/P ratio and polysaccharides proportion, while ergosterol better predicted P content and the N/P ratio. In other cases like lignin, the relation between ergosterol content and chemical composition varied depending on the physical stage. In addition, environmental local factors differentially affected chemical composition across physical decomposition stages. We conclude that the physical decomposition stage and ergosterol content complementarily contribute to estimate the temporal behaviour of the chemical composition of dead wood in Mediterranean areas. Moreover, we recommend using the FT-IR analysis to assess the nature of temporal chemical changes in downed dead wood. Finally, our study claims to consider the potential impact of local environmental factors, such as air temperature and relative humidity, on dead wood decay processes in traditionally managed forests in the current global change scenario.

Impact of climate change on pasture quality in Mediterranean dehesas subjected to different grazing histories

Background and aimsForecasted climate change and overgrazing are threatening the sustainability of dehesas, human-managed ecosystems where pastures, livestock and scattered trees coexist. Pasture quality is particularly sensitive to these global-change drivers, but there are still many gaps to broaden knowledge about the interactive effects of both factors on it. In addition, scattered trees might play a relevant role in maintaining high levels of pasture quality under future scenarios of higher aridity, but its role remains largely unexplored.MethodsWe designed a field manipulative experiment of rainfall exclusion and increased temperature aimed to evaluate the impact of forecasted climate on pasture quality under different historical grazing intensities. To test the potential buffering effect of trees, experimental plots were installed equally in two habitat types: under trees and open grassland.ResultsWarming reduced the nutrient concentration of pasture, while drought increased it. Tree canopy improved soil fertility, which translated into an increase in pasture quality. Livestock exclusion and high grazing intensity caused a decrease in pasture quality, whereas moderate grazing intensity exerted positive effects on it. Finally, warming beneath tree canopy negatively affected the P concentration of pasture, specifically in the site subjected to moderate grazing intensity.ConclusionOur findings suggest that communities subjected to moderate grazing are more sensitive to climate change from a nutritional standpoint, likely because this management type provides high levels of P to the soil. In addition, we highlight the essential role of trees in agroforestry ecosystems to maintain high values of nutritional quality of pasture.

A Farmer’s Perspective on the Relevance of Grassland-Related Innovations in Mediterranean Dehesa Systems

Grasslands are of key importance for the provision of ecosystem services (ES). Suitable management is essential to guarantee their persistence and functionality. There is a growing interest in innovations such as new technologies aimed at facilitating and improving the management of grasslands while increasing their provision of ES. The uptake of innovations by farmers is a complex process, and relevant socio-economic or technological factors that are crucial to farmers are often overlooked. This information can be useful for increasing the adoption of these innovations through the design of public policies to facilitate them. This paper analyses the relevance of the main innovations that can be applied to the management of the grasslands of Dehesa farms for the farmers and the factors that might affect this relevance. Through questionaries, we gathered information on the relevance that farmers give to the selected innovations and analysed it by cumulative link models. The results show that innovations aimed at increasing the biomass production of grasslands and resilience such as the use of seed mixtures and the use of forage drought-resistant species are considered highly relevant by Dehesa farmers. However, high-tech innovations such as GPS collars were poorly rated which could denote low applicability to the context of Dehesas or the existence of barriers hindering the adoption but also a need for further development and better information on their potential. Characteristics of the farmer and farm such as age, education level, and stocking rate seem to be related to the relevance given to some of the innovations. These results provide insightful information for the implementation and research of relevant grassland-related innovations in the context of Mediterranean Dehesa/Montado systems, as well as for the design of policies supporting them.

Cattle dung and bioturbation by dung beetles improve oak seedling establishment in Mediterranean silvopastoral ecosystems

This study aims to determine whether the application of cattle manure and associated bioturbation by dung beetles and other invertebrates can increase oak seedling establishment in the high biodiversity Mediterranean silvopastoral systems known as “dehesas”, which are comprised of scattered oaks and a grassland layer and are used for livestock rearing. A two-year study was conducted in a representative dehesa in southern Spain. Firstly, the effect of cattle dung pads on acorn consumption by livestock and wild predators was monitored, along with dung beetle abundance and plot bioturbation. Secondly, the indirect effects of bioturbation on acorn burial, acorn predation by rodents and oak seedling establishment were assessed under the condition of livestock exclusion. The results consistently demonstrate a high positive indirect effect of the presence of cattle manure on the persistence of acorns, as well as on seedling establishment, as a result of reduced predation by rodents and improved microhabitat conditions for the acorns and seedlings. These processes were mediated by bioturbation. Tunneler dung beetles, which move a great amount of soil material, were dominant in our records, which suggest their importance for passive acorn burial, without disregarding the influence of other edaphic invertebrates present. We conclude that the presence of cattle manure significantly improves oak seedling establishment in Mediterranean dehesas through the passive burial of acorns by bioturbation, which acts to protect them from predation by rodents, desiccation and other damage. Passive acorn burial by dung beetles and other invertebrates thus emerges as an important ecosystem service that has been little-studied to date. Appropriate rotational management of livestock could therefore contribute to addressing the bottleneck of oak regeneration in Mediterranean dehesas.

Can trees buffer the impact of climate change on pasture production and digestibility of Mediterranean dehesas?

Sustainability and functioning of silvopastoral ecosystems are being threatened by the forecasted warmer and drier environments in the Mediterranean region. Scattered trees of these ecosystems could potentially mitigate the impact of climate change on herbaceous plant community but this issue has not yet tested experimentally. We carried out a field manipulative experiment of increased temperature (+2–3 °C) using Open Top Chambers and rainfall reduction (30%) through rain-exclusion shelters to evaluate how net primary productivity and digestibility respond to climate change over three consecutive years, and to test whether scattered trees could buffer the effects of higher aridity in Mediterranean dehesas. First, we observed that herbaceous communities located beneath tree canopy were less productive (351 g/m2) than in open grassland (493 g/m2) but had a higher digestibility (44% and 41%, respectively), likely promoted by tree shade and the higher soil fertility of this habitat. Second, both habitats responded similarly to climate change in terms of net primary productivity, with a 33% increase under warming and a 13% decrease under reduced rainfall. In contrast, biomass digestibility decreased under increased temperatures (−7.5%), since warming enhanced the fiber and lignin content and decreased the crude protein content of aerial biomass. This warming-induced effect on biomass digestibility only occurred in open grasslands, suggesting a buffering role of trees in mitigating the impact of climate change. Third, warming did not only affect these ecosystem processes in a direct way but also indirectly via changes in plant functional composition. Our findings suggest that climate change will alter both the quantity and quality of pasture production, with expected warmer conditions increasing net primary productivity but at the expense of reducing digestibility. This negative effect of warming on digestibility might be mitigated by scattered trees, highlighting the importance of implementing strategies and suitable management to control tree density in these ecosystems.

The role of brush encroachment in Mediterranean ecosystems: a review

Abstract Encroachment of woody plants into grasslands and subsequent brush management are among the most prominent changes occurring in arid and semiarid ecosystems over the past century. The reduced number of farms, the abandonment of marginal land and the decline of traditional farming practices have led to encroachment of the woody and shrubby components into grasslands. This phenomenon, specifically in the Mediterranean region, which is followed by a reduction in herbage production, biodiversity and increased fire risk, is generally considered an undesirable process. Sarcopoterium spinosum has had great success in the eastern Mediterranean as a colonizer and dominant bush species on a wide variety of sites and climatic conditions. In the Mediterranean dehesa, the high magnitude and intensity of shrub encroachment effects on pastures and on tree production were shown to be dependent on temporal variation. Accordingly, there are attempts to transform shrublands into grassland-woodland matrices by using different techniques. The main management interventions that are commonly used include grazing, woodcutting, shrub control with herbicides or by mechanical means, amelioration of plant mineral deficits in the soil, and fire. However, the effects of these various treatments on the shrubs under diverse environmental conditions were found to be largely context-specific. As such, the most efficient option for suppressing encroachment of shrubs is combining different interventions. Appropriate management of grazing, periodic control of the shrub component, and occasional soil nutrient amelioration can lead to the development of attractive open woodland with a productive herbaceous understory that provides a wider range of ecological services.

Effects of Domestic and Wild Ungulate Management on Young Oak Size and Architecture

Scattered oaks in traditional silvopastoral systems (i.e., “dehesas”) provide important ecological services. However, livestock intensification applied to these systems over the last century has affected the architecture of young oak plants. This unsuitable rangeland management practice jeopardizes the long-term system sustainability. Here we examine the alterations in architecture of regenerating oak plants in Mediterranean dehesas under three representative management regimes: (1) traditional management with extensive sheep grazing; (2) commercially driven management with extensive cattle grazing, and (3) native deer grazing at moderate stocking rates (<0.11 livestock units × ha−1). Plant architecture was considerably altered in cattle-grazed “dehesas”, finding a 50% reduction in plant height–diameter ratios, compared to sheep-grazed dehesas where plants with higher height–diameter ratios predominated. Young oak plants, however, showed less altered architecture and less probability of damage on shoot apex (0.20-fold difference) in areas with deer grazing at moderate stocking rates. In addition, those young oak plants with multi-stemmed individual architecture were more stunted (lower values of crown height–diameter ratio) in areas with livestock grazing than wildlife areas (0.78-fold difference). Shrub presence, under all management schemes, helped to increase in plant height, except when shrubs were located under tree canopies. Conversely, plants without shrub protection showed stunted architecture with well-developed basal diameters but short stature. Appropriate sustainable practices should include cattle stocking rate reduction, traditional sheep grazing promotion, nurse shrub preservation and fencing stunted individuals along with pruning basal sprouts. Our study indicates that management may have important consequences on dehesa regeneration via alterations of plant architecture and therefore on system sustainability.

Livestock grazing abandonment reduces soil microbial activity and carbon storage in a Mediterranean Dehesa

Extensive livestock grazing is a major determinant of local biodiversity and ecosystem functioning in many regio1ns of the world. In sub-humid Mediterranean areas with long history of extensive grazing, abandonment of grazing has been linked to changes in the composition and structure of vegetation communities and decreases in soil multifunctionality, with potential cascading consequences for ecosystem services such as soil fertility and potential for soil carbon storage. Herein, we assessed the effects of livestock grazing abandonment on soil fertility and the ability of soil microbial communities to process organic matter (enzymatic activity and decomposition rate using the Tea Bag Index) in twenty-four study sites in a Quercus ilex dehesa from Central Spain. Sites were distributed across four levels of grazing (none, very low, low and moderate) and two levels of resource availability in terms of water and nutrients (upper slope and lower slope zones). Grazing abandonment and upper slope zones were associated with a lower accumulation of organic matter and availability of nutrients such as phosphorus and potassium in the soil. Grazing abandonment also had a negative effect on microbial enzyme activity, which was directly related to litter decomposition and the ability of microbial communities to stabilize soil carbon. Microbial effects were particularly marked in the lower zones, indicating the modulating role of topography on the consequences of land use changes. Environmental management policies should consider the positive ecological effects of traditional grazing in regions with long evolutionary history of grazing by domestic livestock, and how the abandonment of these practices could negatively affect soil ecosystem functions and the provision of soil-related ecosystem services.

Are sown legume-rich pastures effective allies for the profitability and sustainability of Mediterranean dehesas?

Sowing legume-rich mixtures in managed grasslands is becoming increasingly important due to the need for improvements in forage quantity and quality and the need to strengthen soil fertility and carbon fixation. These factors increase the profitability of grasslands and make them more resilient ecosystems in the face of climate change. The aim of this study was to assess the effects of sowing legume-rich pastures in Iberian dehesas, considering direct (yield, legume richness and persistence) and indirect effects (nitrogen content of soils, pasture species and trees). Differences in conditions created by scattered trees were also evaluated. The study includes a chronosequence of pastures sown from 2002 to 2015 on seven dehesa farms in western Spain. Yield increased to more than triple the first year of sowing compared to control plots, remaining nearly doubled during 8 years after sowing. Legume cover followed a similar, although less pronounced pattern, with positive effect on N content of soils, grasses and forbs. Positive trends occurred irrespective of habitat (beneath or outside the tree canopy), although trees favoured legumes coverage in the dry year while affected negatively in the wet year. These results show that sowing legume-rich pastures can be a cost-efficient way to increase the productivity and soil quality of Iberian dehesas and presumably other Mediterranean wood pastures in the face of the climate change.

Estimation of soil erosion rates in dehesas using the inflection point of holm oaks

The exposure of tree or shrub roots represents a clear indicator of soil loss in the surrounding area. Previous studies have used this type of botanical evidence to estimate soil erosion rates, preferring roots at some distance from the tree stem because the inflection point (or root collar) undergoes a vertical displacement caused by basal growth. The aim of this paper is to develop a method that combines the inflection point of holm oaks and high-resolution digital images obtained by means of a terrestrial laser scanner to estimate soil erosion rates in Mediterranean dehesas. To correct for vertical displacement, the basal growth of each tree was determined in the field, differentiating the part of the roots that had been exposed by erosion from that generated by wood growth. Two datasets obtained through different approaches were used for validating the basal growth measured in the field survey: (i) a growth study analysing stems and cores of holm oaks and (ii) field measurements of basal growth of holm oaks located in an area without soil erosion. The results obtained by each method offered similar mean values (12.7 and 8.4 cm, respectively) as compared to the values estimated in the field survey (10.2 cm). Afterwards, soil erosion rates were corrected, reducing the values on average by 40%, with a mean loss of 26.7 t ha‐1 y−1. No relationship was found between tree age and basal growth. On the other hand, soil erosion rates showed a slightly negative trend with relation to tree age, indicating an upward tendency of soil losses from the year 1640 to 2014. Finally, it was possible to define three periods with varying erosion rates: 10.4 t ha−1 y−1 (1640–1830), 19.2 t ha−1 y−1 (1831–1888) and 27.2 t ha−1 y−1 (1889–2014).

Changes in livestock footprint and tree layer coverage in Mediterranean dehesas: a six-decade study based on remote sensing

ABSTRACTThe decade of the fifties of the twentieth century triggered huge changes in land use and management in ecosystems worldwide, including the iconic Mediterranean ecosystems known as dehesas. In this study, we have quantified the changes in dehesa landscape status within a geographic area of 200,000 km2 covering mainly the Spanish dehesa range over the last 60 years. We focused on changes of two important dehesa elements: tree density and live stocking rates. Tree density and tree cover change were measured via remote sensing in 29 sample plots (16 km2 each) and selected from the plot-monitoring network of Spanish Rural Landscapes (SISPARES). Live stocking (cattle, sheep, and pig) rates data were obtained from the National Statistical Institute of Spain and were used to assess the entire study area. During the 1950–80s, tree density and cover declined significantly (by 18% and 13%, respectively). By the 1960s, sheep was predominant over cattle in all provinces; pigs had higher stocking rates than in the following decades. However, during the 1970–80s, sheep and pig stocking rate declined drastically (by 90% and 70%, respectively) in just 20 years. In contrast, cattle stocking rate increased progressively since the 1960s, reaching a 60% increment by the 2000s. At the municipality level, we observed similar trends. Our multi-scaled analysis explains the impact of social, political, and economic factors on the conservation status of the main dehesa territory within Spain. We conclude that it is necessary to ensure the effectiveness of these systems through sustainable activities to avoid negative consequences of poor management practices which threaten dehesa perpetuation.

Comparison of two methodologies used to estimate erosion rates in Mediterranean ecosystems: 137Cs and exposed tree roots

The 137Cs deposited in soil and exposed tree roots have been widely applied to estimate medium-term soil erosion rates. However, comparative studies between these methods are scarce. For this purpose, three hillsides in two Mediterranean dehesas (rangeland with disperse tree cover) were selected. Regarding the 137Cs technique, a reference site close to the study areas and with similar altitude and rainfall was selected. In order to reduce uncertainties related to the use of point soil profiles, all those collected in an area were combined to form a representative composite profile. The total inventory was 2790±50Bq/m2, and the relaxation coefficient indicated it was an undisturbed soil. The radiocaesium inventory in the study areas was 14–23% lower than in the reference area. The erosion rates for 137Cs were in the range 20.9–38.1tha−1y−1. The exposed root technique was applied to holm oak trees (age about 90years), and the erosion rates were in the range 22–34tha−1y−1. The ratio between exposed root and 137Cs techniques was 1.02±0.11 (S.D.) within the range 0.89–1.2. Both methods produced very similar results equally with respect to the mean erosion rate as well as the relative difference between the hillslope sections, i.e. displaying the same spatial variation in the study areas. As the accounting time for these two techniques is different, 50 and 90y for 137Cs and exposed roots respectively, results suggest that no change in mid-term erosion rates was implied for these areas for almost a century. The use of 137Cs and exposed roots methodology for the determination of mean erosion rates can be reproduced in other ecosystems, but a careful selection of the reference site for 137Cs is essential.

Assessing drought risk in Mediterranean Dehesa grazing lands

Extensive grazing activities in the Mediterranean area will have to confront an increasing risk of drought. This threat poses a challenge to the long-term viability of these activities that play an important role in rural development and have traditionally shaped highly valued ecosystems such as the Dehesa landscape in the Iberian Peninsula. The aim of this research is to assess the economic impact of drought on this extensive livestock farming system and evaluate the potential of adaptation strategies such as reducing the stocking rate. A dynamic and stochastic bioeconomic model is developed to account for the complex climatic, ecologic and economic relationships at play during drought.We simulate the 1999–2010 weather time series to characterize seasonal patterns and evaluate the risk caused by drought spells. We assess the consequences of drought in terms of duration, frequency and intensity, finding that economic losses increase at an increasing rate with long lasting droughts. Our findings reveal different patterns between climate and economic risk variables. The risk of a climate shock concentrates in spring and the beginning of autumn while the risk of suffering economic losses occurs with a 3–4weeks delay and lasts for a longer period of time. We integrate Monte Carlo routines in our simulation model to assess risk exposure and propose the use of Value-at-Risk to capture downside risk at different thresholds. Our simulation results show that the farmer may have to confront annual economic losses above 22.9% with a 5% probability in the current or baseline scenario. Finally, we use the model as a tool to evaluate the potential of adaptation strategies such as increasing or reducing the stocking rate. We find that the former has rather limited impact on average income as compared to the later but both show significant impacts on risk exposure, which may entail important economic consequences. In particular, we find that increasing the stocking rate by 20% decreases the probability of incurring moderate losses, from 45.0% to 40.6%. Furthermore, it also increases the probability of favourable outcomes, from 50.0% to 52.0%. However, this comes at the expense of a significant increase in the chance of experiencing severe economic impacts, from 5 to 6.9%. On the contrary, reducing the stocking rate by 20% reduces the chance of severe impacts from 5% to 3.7%, but also entails an increase in the probability of moderate losses and a significant drop in the probability of experiencing a favourable outcome.

The important role of scattered trees on the herbaceous diversity of a grazed Mediterranean dehesa

Scattered trees are considered keystone structures and play an important role in Mediterranean sylvopastoral systems. Such systems are associated with high biodiversity and provide important natural resources and ecosystem services. In this study, we measured the contribution of scattered trees and different grazing management (cattle, sheep and wildlife only) to the diversity of the grassland sward in a dehesa (open holm oak woodland) located in Central Spain. We analyzed alpha and beta diversity through measurement of species richness, Shannon-Wiener, and Whittaker indices, respectively; and the floristic composition of the herb layer using subplots within two adjacent plots (trees present vs. trees absent) under three different grazing management regimes, including wildlife only, during a year. We found a 20–30% increment in the alpha diversity of wooded plots, compared to those without trees, regardless of grazing management. All beta indices calculated showed more than 60% species turnover. Wooded plots were occupied by different herbaceous species in different heterogeneous microsites (under the canopy, in the ecotone or on open land) created by the trees. Livestock grazing modified species composition (e.g. more nitrophilous species) compared to wildlife only plots. In addition to all their other benefits, trees are important to maintaining grassland diversity in Mediterranean dehesas.

Scattered trees and livestock grazing as keystones organisms for sustainable use and conservation of Mediterranean dehesas

Mediterranean scattered oak woodlands support relatively high biological diversity, and provide important ecosystem services. However, there is still a lack of knowledge about livestock-tree-grassland relationships, knowledge necessary for effective conservation management in these systems. To address such lacuna, we measured the effects of scattered trees and grazing animals (livestock vs. wild ungulates, mostly deer) on biomass and diversity (and their relationship) of the herbaceous layer (understory) of open holm oak woodland (known as dehesa) in Central Spain, for two years. We located two 1-ha plots within three different grazing management schemes (cattle, sheep and wildlife only). Within each plot, we randomly selected four focal trees from which a subplot was established in two directions and three distances. In each subplot, we measured plant diversity and biomass, along with microclimatic variables across sites. We found rainfall variability affected herbaceous biomass and diversity in the dehesa system, and the effects were nuanced: in a dry year (<300mm annual rainfall) the presence of livestock grazing correlated with higher herbaceous biomass (14%), and in moister year (>600mm annual rainfall) the effect was enhanced, as plots under livestock grazing exhibited even higher herbaceous biomass (42%). In addition, livestock, particularly cattle, generated a more diverse community (52 speciesm−2). Microsites created by trees generated high plant diversity among herbaceous communities, where alpha diversity was higher (20%) in ecotone and inter-tree gaps than under the canopies. In addition, species turnover was higher than 50% in all cases. Biomass was higher (15%) under the canopies only under humid conditions. Legume dry matter was positively related to plant diversity. We concluded that agroforestry management practices such as promoting tree development through silvicultural techniques to create different microsites, and maintaining livestock grazing are needed to preserve these emblematic ecosystems.

Livestock vs. wild ungulate management in the conservation of Mediterranean dehesas: Implications for oak regeneration

Dehesas are traditional silvo-pastoral systems with scattered oak trees that maintain considerably high biodiversity. Over the last five decades, dehesas have undergone significant management changes, causing a reduction in oak recruitment that threatens their long-term persistence. Here we examine oak regeneration in Mediterranean dehesas of Central Spain under three distinct and representative management regimes for more than 30years: (1) traditional management of extensive sheep rearing; (2) high commercially-competitive management with extensive cattle grazing, and (3) wildlife grazing, mostly by deer. We found that cattle-grazed dehesas sustained a very low density of young oaks (0.05 young plants per 4m2), one third and one fifth of that found in sheep and wildlife areas, respectively. We also found differences in young oak densities depending on plant growth stage, revealing that saplings (late-stage regeneration), but not seedlings, were more abundant under traditional sheep management. Overall, the probability of herbivory damage was higher in areas with cattle (0.85 probability) than in areas with sheep (0.68) and wildlife (0.30). Cattle areas presented, by far, the highest intensity of herbivory, with 63% of the plants showing very high browsing levels (>70% of the biomass damaged). For all management regimes, shrubs were important microhabitat (nurse plants) for seedlings but not for saplings or oak bushes. Our results suggest that conservation practices should include promotion of traditional sheep rearing, reduction of cattle stocking rates, protection of saplings and oak bushes, rotational grazing and preservation of some shrubs. We conclude that agriculture policies that favor traditional sheep rearing and sustainable wildlife populations can promote the conservation of these valuable systems.

A state-and-transition model of Iberian dehesas based on spatial patterns

Aim of study: In this study a process based on a Geographic Information System (GIS) is proposed as a tool for analyzing the spatial structure of the Mediterranean dehesa ecosystem.Area of study: Western Peninsular Spain.Material and methods: The method allows a semi-quantitative “state and transitions” (S&amp;T) net that provides original information derived from spatial patterns that cannot be obtained by other means.Main results: This GIS analysis also supplies a spatial basis which complements the conceptual framework of vegetation series successional proposals. Moreover, the proposed method can be a useful tool for understanding landscape changes.Research highlights: Our work proposes not only a descriptive model but also a methodology based on spatial metrics and topological relationships.Keywords: geographic information systems; successional net; landscape management.Abbreviations used: S&amp;T: State and Transition; RFP: Regional Forest Plan.

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

Acorn 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.

The effect of tree cover on the biomass and diversity of the herbaceous layer in a Mediterranean dehesa

AbstractMediterranean dehesas are an archetypal example of high nature value farmland in Europe. To better understand the interactions between trees and grasslands in the conservation and management of the dehesa, we measured, over 3 years, the contribution of scattered trees to the diversity and biomass dry‐matter (DM) yield of the herb layer and the relationship between the herb layer (biomass and diversity interaction) and the trees. The study was based on 135 subplots representing four aspects and three distances from fifteen trees selected randomly in a plot within a dehesa in central Spain. The specific questions were the following: (i) To what extent do trees affect biomass of the herbaceous layer? (ii) What is the relationship between herbaceous layer biomass and species diversity under the influence of trees? and (iii) What are the effects of trees and small‐scale topography on the herbaceous diversity? Results differed between years depending on water availability. Legume and forb DM yields were highest at the edge of the tree crown and beyond the canopy. Species richness was positively related to legume DM yield, and both were higher at the bottom of the hillside, especially in dry conditions. Given the importance of tree influence on the biomass and diversity of grasslands, maintaining proper agroforestry management practices for trees and grasslands is important for conserving dehesa diversity and productivity under the conditions of high climatic and soil variability in Mediterranean dehesas.