Antonio Gómez-Sal

Assessing landscape values: a proposal for a multidimensional conceptual model

Abstract To evaluate a specific form of resource management, for example, the maintenance of valuable cultural landscapes, the contributions of many different viewpoints must be considered. In this paper, a model for assessing and integrating the different aspects contributing to landscape evaluation is proposed. Some results of its use in landscape assessment in the Madrid region (central Spain) are discussed. The model takes into account five assessment dimensions which are considered to be independent—the ecological, productive, economic, social and cultural evaluative systems and it recognises and assumes conflicts and trade-offs between these components. The inclusion of the production system as an independent assessment dimension is original and is justified because it is the link that connects the ecological and economic systems. Since this dimension acts most directly on the ecosystem, the production system includes the attribute of ecological or strong (in the sense of [For the Common Good, Beacon Press, Boston, 1994]) sustainability. The evaluation method places special emphasis on defining a conceptual framework, and from this defines scenarios in comparison with which particular development models (landscape planning, resources management) can be evaluated. Seven scenarios, coming from a hypothetical, traditional sustainable scenario of resources management, are defined. One of these, the sound sustainable scenario, is defended as the only one viable in the long term, particularly in developing countries. This method was employed to evaluate the agricultural and natural landscape of the Madrid region municipalities. The multivariate approach adopted was based on the selection of indicator sets for each evaluative dimension. The structure of relationships among indicators was then analysed separately for each dimension and values assigned to the municipalities according to their position on the main axes of the multivariate analyses. Each municipality was assigned to one of the seven development scenarios by means of discriminant analysis. The approach’s greatest assets are its flexibility in the selection of the indicators and the efficacy in its monitoring and comparison of the different analysed cases once a rigorous conceptual framework was established. The paper discusses the conditions for the sustainability of the human activities and provides a method for evaluating and comparing scenarios of resources management.

Stability May Decrease with Diversity in Grassland Communities: Empirical Evidence from the 1986 Cantabrian Mountains (Spain) Drought

Frank and McNaughton reported that community stability, measured by the resistance to change in species composition when perturbed by drought, increased with species diversity in grasslands of Yellowstone, USA. They also found that species diversity increased with spatial heterogeneity of the community, pattern diversity. In a similar study of grasslands in the Cantabrian Mountains, we found exactly the opposite; when affected by drought, the resistance of these communities to change in species composition decreased as diversity increased, and diversity was not related to spatial heterogeneity. The contrasted results in Yellowstone and Cantabrian grasslands match theoretical predictions derived from model systems and suggest the existence of complex relationships between diversity and community stability.

Vole mound effects and disturbance rate in a mediterranean plant community under different grazing and irrigation regimes

A factorial field experiment was used to assess the influence of soil-disturber mammals in the structure of a 9-year-old Mediterranean annual plant community subjected to different sheep grazing and irrigation regimes. We estimated the disturbance rate (mound building activity) by Mediterranean voles, their effects on vegetation and the mechanisms of these effects during a period of vole outbreak. The effects on vegetation were analysed at the levels of species, functional groups and plant community. Disturbance rate was high and voles can disturb the entire soil surface once every four or five years. The availability of certain trophic resources (perennial plants) appeared to drive vole expansion in the experimental plots and it was independent of the irrigation and grazing treatments. Mound building activities largely affected vegetation but conserved plot differences. Total vegetation cover, absolute cover of all functional groups, mean vegetation height and species richness were less on mounds than on undisturbed ground. These effects did not change the relative abundance of annuals, perennials, grasses and forbs. Only the relative abundance of small-seeded species decreased on mounds. As the proportion of these seeds was similar in both types of patches, we suggest that small-seeded species had more difficulties for germinating or emerging when they are buried during mound formation. Irrigation and sheep grazing promoted large changes in the vegetation parameters but these effects were, in general, similar on mounds and undisturbed ground. Our results show that the availability of germinable seeds may be the major limitation for mound revegetation, probably due to the scarcity of seeds existing at the depths from which soils are excavated. Our results also suggested a resource limitation on mounds. The results provide additional evidence that soil disturbances by small herbivore mammals exert relevant ecological effects on abandoned Mediterranean croplands. We discuss the ecological implications of vole mound-building activities for plant succession, plant species conservation and forage resource availability for livestock.

The role of urban greenspaces in fauna conservation: the case of the iguana Ctenosaura similis in the 'patios' of León city, Nicaragua

Private urban greenspaces, called ‘patios’ in Latin America, can act as important refuges for wildlife in scattered growing cities of the tropics. We studied the presence and abundance of the black spiny-tailed iguana (Ctenosaura similis) in patios of León city (Nicaragua). Forty patios were structurally characterized and abundances of iguanas were determined through surveys of inhabitants supported by observations of specimens and burrows. Patio area and maximum tree height were variables positively related with presence and abundance of iguanas and presence of burrows. The permeability of fences for iguana movements and the presence of preferred trees for food were also related to presence and abundance of iguanas. Stepwise selection model for abundance of iguanas included number of preferred trees, maximum tree height and permeability of fences. The presence of iguanas was only explained by maximum tree height. Our results show that the indigenous-root types of patios offer the most adequate conditions for the establishment and maintenance of iguana populations among the studied cases. In the light of these results, management practices to preserve the Ctenosaura similis populations in urban patios are suggested.

Determination of animal behavior-environment relationships by Correspondance Analysis.

The paper describes an analytical procedure to preliminarily investigate large scale animal-environment interactions. The method is based on Correspondence Analysis applied over a contingency table in which the columns are percentage categories of animal activities and the rows, states of environmental variables. Each cell entry in the table represents the number of times a row and a column have been recorded together. This means that investigation of animal-environment interactions does not require defining specific sampling stations, or subdividing the study area into environmental units; i.e. the method can be used in studies in which sampling consisted of following the animals and noting their activities and characteristics of the environment. The graphical display resulting from the analysis shows the main patterns of association between animal activities and environment, and its numerical output allows one to identify the variables that have played a major role in the display. Taking into account these variables and their associated animal activities, the method allows one to define archetypal habitat models for each animal activity. Correspondence Analysis of animal activities by environmental variable matrices may give insights about animals perception of the environment. The use of the method is illustrated by analyzing habitat preferences of free-ranging cattle during 2 different seasons on an estate in Spain. Results indicate the validity of the method as a first global analysis of the relative importance of environmental variables for the distribution of the animal activities in the landscape.

Changes in the Herbaceous Communities on the Landslide of the Casita Volcano, Nicaragua, during Early Succession

This study examined the main changes in the herbaceous communities during the first four years of succession in a large landslide on Casita Volcano, Nicaragua, located in a densely populated area that has a tropical dry climate. Our main objective was to determine the major pathways of change in community features, such as richness, biovolume, species composition, and abundances of plant traits and to verify if they varied between the different landslide areas based on abiotic heterogeneity and landscape context. Number, percent cover, mean height and traits of herbaceous species, and several abiotic factors related to fertility and geomorphological stability of substrates were sampled in 28 permanent plots. Environmental heterogeneity strongly influenced early successional changes in the herbaceous communities during the four years of the study. Biovolume increased in the unstable and infertile areas and decreased in the stable and fertile landslide areas. In most zones, species richness decreased significantly because of the expansion of a few dominant species that developed a large cover and excluded other species. Those dominant species were mainly responsible for changes in species composition and included annual forbs, e.g., Calopogonium mucunoides and Stizolobium pruriens, graminoids that have rhizomes or stolons, e.g., Hyparrhenia rufa, and perennial nitrogen-fixing forbs, e.g., Clitoria ternatea. They might be important in determining future successional patterns on the Casita Volcano landslide.

Different growth strategies in the tropical pioneer tree Trema micrantha during succession on a large landslide on Casita Volcano, Nicaragua

In this studv we examined the size-structures and allometric relationships between height and diameter over 2 y in populations of the pioneer tree Trema micrantha on a large landslide (Casita Volcano, Nicaragua). The landslide comprised three different zones (erosional, depositional and transitional) based on fertility and geomorphological stability. We attempted to analyse the development of canopy hierarchies and intraspecific competition, and the existence of different growth strategies, within the T. micrantha populations of the different landslide zones. Vegetation was surveyed in 2 8 10 x 10-m plots in which a total number of 3 07 T. micrantha individuals were recorded and tagged. In the depositional zones, size-hierarchies and one-sided competition for light were apparent and, among the short stems (0.0-2.5 m) of the understorey, plastic responses to shade consisting in a marked increase in height in relation to diameter were evident. In the erosional zones, size-hierarchies were not apparent. All stems were small and, among them, the shortest ones (0.0-1.0 m) were dead whereas the tallest (> 1.5 m) grew slowly, increasing their diameter to a greater extent than their height. Our study shows that T. micrantha individuals developed different growth strategies in the different areas of the landslide and suggests that this species allocates resources to growth and survival differently depending on environmental conditions. Trema micrantha is a highly versatile species capable of dealing not only with extremely infertile substrates and conditions of high light availability, but also with partially shaded environments such as those in secondary forests.

Understanding Mediterranean Pasture Dynamics: General Tree Cover vs. Specific Effects of Individual Trees

Abstract The study investigated the effect of general and homogeneous tree cover on grassland composition on an extensive Mediterranean rangeland with sparse oak trees in central Spain. We analyzed this effect together with other significant factors identified in this type of rangeland: topography and plowing. Data were collected in the 1984 growing season and they form part of a historical database on the characteristics of vegetation and livestock behavior; these data refer to grasslands below and away from the tree crowns of 91 individual trees, located in different topographical positions and in areas that were last plowed at different times. We used multivariate analyses to identify the main compositional trends of variation in pasture communities. The results indicate that the herbaceous community below tree crowns was more similar to that of the lowland areas than to the nearby areas away from the tree. This result supports the idea of tree cover in semiarid rangelands as a factor attenuating the effects on pastures of environmental conditions typical of high and intermediate topographical positions—generally presenting low soil moisture and fertility. Coupled with this, we also found effects of some individual trees related with the way livestock uses them as shelter and resting places. Our results indicate that the role played by dispersed trees in the management of this type of rangeland should be analyzed at two complementary spatial scales: the overall effect of tree cover as a factor acting at landscape scale and the specific effect of some individual trees acting at a more detailed scale.

Vertical distribution of below-ground biomass in intensively grazed mesic grasslands

. Previous work has shown that below-ground biomass is more concentrated in surface soil layers in intensively grazed mesic grasslands than in moderately grazed grasslands. However, since the mesic grasslands previously studied shared similar compositional traits, the question remained whether grasslands with differing species composition, and intensive defoliation, showed similar biomass distribution patterns. Eight grasslands at four sites distributed along an elevational gradient were investigated. The upper and lower zones of a slope were sampled at each site. Four of these grasslands were grazed by livestock and the other four were grazed and mown. Biomass was divided into above-ground, root crown and three root layers. Species composition varied according to management and topography. Annuals and perennial forbs had relatively more above-ground biomass at the upper part of the slopes, while perennial grasses dominated the lower parts. The above-ground biomass and root biomass at 4 — 7 cm depth attained maximum values in the lower, potentially more fertile, parts of the slopes. Crown biomass increased with altitude at the upper part of the slopes. Despite their differences in composition and structure, seven out of the eight stands showed a remarkable concentration of the below-ground biomass near the soil surface, which decreased drastically with soil depth. This pattern is similar to that observed in the intensively grazed mesic communities studied earlier. This similarity was more evident in the more mesic-like grasslands, since it increased from the upper, potentially drier parts of the slopes, to the lower parts, and, when each topographic position was considered separately, from low to high elevation.