In recent decades, recreational activities in natural open areas have increased substantially. At the same time, stresses imposed upon these areas have increased considerably as a result of a significant reduction in their dimension. These activities strongly affect ecosystem attributes and processes.
This paper intends to review several studies that were conducted in one of the protected areas in Israel, Ramat Hanadiv Park, aiming to (a) quantify the rate of pedestrian trail development and (b) examine the impact of high and low trampling intensities on soil and vegetation properties at different trail sections (center, edge and control – a natural area adjacent to the trail).
The following properties were examined: soil compaction, bulk density, aggregate size distribution, organic matter, moisture, electrical conductivity, pH, sodium and potassium concentrations, vegetation cover, species richness, and composition.
The results indicated that: (a) the number of pedestrian trails increased slightly between the years 1944 and 1990; (b) soil properties, except for soil compaction and aggregate size, were not affected by low trampling intensity. A slight decrease in the soil measured properties was recorded at trail centers. However, under high trampling intensity, a reduction in most soil measured properties was detected on all trail sections; (c) vegetation cover, height and species richness were lower at the trail center under high and low trampling intensities. Herbaceous plant species that are common in compacted soils were found under intense trampling impacts.
The conclusions from the studies conducted at Ramat Hanadiv Park were: (a) there is a positive correlation between trampling intensities and soil and vegetation properties; (b) an increase in trampling intensity is followed by spatial degradation of soil properties beyond the trail's visible boundaries (what we referred as the “control”); and (c) most of the trails in Ramat Hanadiv Park experience low trampling intensities.
Coastal sand dunes are susceptible to invasive plants that significantly alter these endangered ecosystems. Acacia saligna is a small Australian tree that has become a significant invasive plant in Israel and in many other Mediterranean countries. The aim of this research was to study the impact of A. saligna on the indigenous vegetation of three coastal habitats (sand dunes, inter-dune depressions, and aeolianite [sandstone] ridges) in the Nizzanim Long Term Ecosystem Research Nature Reserve, Israel. Plant observations were conducted in the spring, in the following site types: (1) sites planted with A. saligna and sites invaded by A. saligna; and (2) reference sites not invaded by A. saligna. A simple index, the aggregate ecological value, was developed in order to evaluate the impact and the ecological value of each habitat and site for conservation purposes. The results indicate that planting A. saligna and invasion by A. saligna changed plant community composition, reduced psammophyte species richness, caused the disappearance of most endemic, rare, and protected species, and overall reduced the ecological value of the Nizzanim Nature Reserve.
Habitat loss and landscape fragmentation are considered factors that cause a significant decrease in biodiversity and changes in the community composition. The impact of fragmented natural patches of various sizes on plant species richness, plant composition, and soil properties were investigated in this study. The study area was located in a semiarid Mediterranean region (average annual rainfall 300 mm/ winter) and dominated by Sarcopoterium spinosum L. (SP) association. The results indicated that: (a) SP dwarf-shrubs were absent from patches of less than one hectare; (b) SP and other perennial coverage increased with patch size; however (c) herbaceous plants dominated the patches (70-100%); (d) the annual grasses Stipa capensis Thunb. and Avena sterilis L. were the dominant species and their coverage was significantly higher in the small patches; (e) species richness increased with patch size; (f) the total number of species for all the patches was almost two times higher than in the adjacent nature reserve; (g) native weeds such as Chrysanthemum coronarium L. and Centaurea hyalolepis Boiss. abounded in the patch edges; (h) the similarity between the patches and the adjacent nature reserve increased with patch size, but was less than 35%; and (i) rock fragments were almost absent from the small patches where the soil was shallower than in the large patches. In conclusion, on the patch scale, it is important to conserve larger patches. However, on the landscape scale, it is recommended to conserve the various patch sizes because of their high biodiversity.
Throughout the world, Acacia saligna is considered an invasive species that has negative impact on natural ecosystems. The aim of the present study was to quantify the rate of the biological invasion process (arrival, establishment, and spreading rates) of Acacia in Israeli Mediterranean coastal dunes, and to characterize the distribution patterns and trends within various habitats in the ecosystem. Black-and-white aerial photographs from five points in time (1965, 1974, 1982, 1990, and 1999) were analyzed using field observations, GIS (geographic information system), and remote sensing methods. The results indicate that over the 34 years studied, the area covered in Acacia grew by 166% at an annual growth rate of 2.92%. The "Arrival Stage" lasted for 20 years, and the "Establishment Stage" lasted another eight years. Since 1990, Acacia has spread over the coastal dunes (the "Spreading Stage"). Spreading was dictated primarily by optimal soil moisture regime. Acacia invaded disturbed habitats, such as sand quarries and depressions between dunes, but never shifting sand dunes.
This study investigated the effects of microhabitat characteristics on soil seed bank structure, regeneration strategies, and plant composition in a Mediterranean coastal sand dune in Israel. Three different microhabitats were selected: (a) open patches between shrubs, (b) shrub understorey, and (c) open, disturbed patches in pedestrian trails. In each microhabitat two types of sampling plots were established: (a) seedling removal and (b) control (seedlings not removed). Emerging seedlings in each microhabitat were identified, counted, and removed every two weeks. In the controls, the vegetation was sampled only once at the peak of the herbaceous growing season. At the end of the growing season in plots where seedlings were removed, the upper soil was collected and sieved before seeds set. Viable non-germinated seeds were identified and counted. An estimation of persistent seed banks was obtained for each plot. Species composition, species richness, species diversity, and aboveground biomass by species were estimated. Germination fractions among species and plant functional groups were measured.
Microhabitats differed in soil seed bank density, germination characteristics, above-ground biomass production, and species composition. The open patches between shrubs generally had the highest densities of seeds, seedlings, and mature individual herbaceous plants. Important density differences between total seedlings removed and mature vegetation may indicate strong plant mortality in all microhabitats. Annual and perennial grasses, composites, annual crucifers, and annual forbs produced transient seed banks, while legumes, umbelifers, and perennial forbs had persistent seed banks. Disturbance by public trampling in trails led to low seed and plant densities in this microhabitat. No effects of facilitation of shrubs on the annual vegetation were noted in shub understorey. Habitat heterogeneity had a strong impact on vegetation structure and regeneration strategies.