Avinoam Danin

EFFECT OF ROADSIDE BIAS ON THE ACCURACY OF PREDICTIVE MAPS PRODUCED BY BIOCLIMATIC MODELS

Sampling bias is a common phenomenon in records of plant and animal distribution. Yet, models based on such records usually ignore the potential implications of bias in data collection on the accuracy of model predictions. This study was designed to investigate the effect of roadside bias, one of the most common sources of bias in biodiversity databases, on the accuracy of predictive maps produced by bioclimatic models. Using data on the distribution of 129 species of woody plants in Israel, we tested the following hypotheses: (1) that data collected on woody plant distribution in Israel suffer from roadside bias, (2) that such bias affects the accuracy of model predictions, (3) that the road network of Israel is biased with respect to climatic conditions, and (4) that the impact of roadside bias on model predictions depends on the magnitude of climatic bias in the geographic distribution of the road network. As expected, the frequency of plant observations near roads was consistently greater than that ex...

A SYSTEMATIC ANALYSIS OF FACTORS AFFECTING THE PERFORMANCE OF CLIMATIC ENVELOPE MODELS

Effective application of species distribution models requires some knowledge concerning the accuracy of model predictions. Yet very few studies have attempted to systematically analyze factors affecting the predictive power of distribution models. This study fills this gap for Climatic Envelope Models, which have been applied extensively for a variety of conservation and management purposes. We hypothesized that model predic- tions are influenced by properties of the data (both quantity and quality) and distribution properties of the modeled species. Hypotheses concerning the effects of both types of factors were tested by analyzing distribution patterns of 192 species of woody plants in Israel. Analyses were based on Monte Carlo simulations and standard statistical tests. The total number of observations had a strong positive effect on model performance; but on average, 50-75 observations were sufficient to obtain the maximal accuracy. Climatic bias (the degree of sampling bias with respect to climatic conditions) had a significant negative effect on predictive accuracy. Climatic completeness (the degree to which the climatic range occupied by the species is covered by the observations) had a negative effect on model performance-a result contradicting our original hypothesis. Among the species properties, commonness had a positive effect while niche width had a negative one. Niche position with respect to rainfall and temperature was also important in determining the accuracy of model predictions. The overall results are discussed with respect to trade-offs between commission and omission errors and the potential implications of scale dependency.

The distribution of Raunkiaer life forms in Israel in relation to the environment

The distribution of Raunkiaer life forms along rainfall and temperature gradients was determined for the floras of 27 geomorphological districts in Israel. Phane- rophytes and chamaephytes are relatively strongly repre- sented in districts with very low rainfall, decrease up to 150 mm and 400 mm of mean annual rainfall respective- ly, and remain more or less constant at higher rainfall figures. Hemicryptophytes and geophytes increase along the rainfall gradient. Therophytes show an optimum between 200 and 500 mm of rainfall. The distribution of life forms is less clearly correlated with mean annual temperature, though hemicryptophytes and geophytes show a negative correlation with mean annual temperatu- re and with mean annual minimal temperature.

Isotopic values of plants in relation to water availability in the Eastern Mediterranean region

Plant C and N isotope values often correlate with rainfall on global and regional scales. This study examines the relationship between plant isotopic values and rainfall in the Eastern Mediterranean region. The results indicate significant correlations between both C and N isotope values and rainfall in C3 plant communities. This significant relationship is maintained when plant communities are divided by plant life forms. Furthermore, a seasonal increase in C isotope values is observed during the dry season while N isotope values remain stable across the wet and dry seasons. Finally, the isotopic pattern in plants originating from desert environments differs from those from Mediterranean environments because some desert plants obtain most of their water from secondary sources, namely water channeled by local topographic features rather than direct rainfall. From these results it can be concluded that water availability is the primary factor controlling C and N isotope variability in plant communities in the Eastern Mediterranean.

Plant Species Diversity and Plant Succession in a Sandy Area in the Northern Negev

Abstract Plant species diversity was measured in a sandy area, 15 km south of Beer Sheva, with a mean annual rainfall of ca. 150 mm, and mean annual temperature ca. 20 °C. Species diversity and production of phytomass was found to increase with and stability, owing to the increase of available water with increasing amounts of silt and clay in more stable sands. Supply of nutrients and the influence of a crust of blue-green algae and mosses may also play a role.

The effect of microphytes on the spectral reflectance of vegetation in semiarid regions

The normalized difference vegetation index (NDVI), which is derived from satellite sensor images, is widely used as a measure of vegetation and ecosystem dynamics, change in land use, desertification, and climatic change processes on a regional or global scale. Surprisingly, in semiarid regions, relatively high values of NDVI were measured in landscapes where little, if any, photosynthetic activity of higher plants exists. We tested the hypothesis that the high NDVI values may be caused by the photosynthetic activity of microphytes (lower plants), consisting of mosses, lichens, algae, and cyanobacteria, which cover most of the rock and soil surfaces in semiarid regions. We found that the spectral reflectance curves of lower plants can be similar to those of the higher ones and their derived NDVI values can be as high as 0.30 units. We conclude that, in semiarid environments, the reflectance of lower plant communities may lead to misinterpretation of the vegetation dynamics and overestimation of ecosystem productivity.

Spatial variations in vegetation as related to the soil moisture regime over an arid limestone hillside, northern Negev, Israel

SummaryA detailed study of the distribution of plant communities was conducted in an experimental site, located in the arid northern Negev of Israel, where the spatial variation in rainfall, runoff and soil moisture regime are currently being studied. Phytogeographical methods of analysis usually used for studies on a regional scale were applied for a small area extending over 11,325 m2 of a north-facing hillside. Data obtained indicate that the best water regime and a high diversity of plant species are characteristic of a massive limestone rock unit; whereas worse water regimes characterize densely jointed and thinly bedded limestones. Over slopes, developed in a uniform lithology, whose lower part is composed of a colluvial mantle, a gradual downslope worsening of the soil moisture regime is recorded within the colluvium. These changes are well expressed in the distribution of the plant communities and their phytogeographical affinities along the slopes.

Deterioration of limestone walls in Jerusalem and marble monuments in Rome caused by cyanobacteria and cyanophilous lichens

Abstract Hard limestone walls in Jerusalem and marble monuments in Rome were studied. An attempt was made to classify the principal biodeterioration processes in walls facing the prevailing wind and those which were protected from it. In Jerusalem, those that face the prevailing rain-bearing wind become populated by cyanobacteria and cyanophilous lichens. Within c. 100 years white walls are turned to grey or black colour by these organisms. Rain detaches rock particles from the vicinity of the microorganisms at a rate of 1 mm in 200 years. Dark patches on marble monuments in Rome indicate the presence of cyanobacteria. Such biological activity promotes detachment of particles by rain and accelerates weathering leading to pit formation. The estimated rate of pitting is 1 mm per 40 years in the Forum Traianum. To prevent the biodeterioration of limestone and marble monuments the habitats and ecological demands of the various microorganisms must be considered.

Revision of the plant geographical territories of Israel and Sinai

The phytogeographical territories of Israel and Sinai are revised using a large mass of species distribution data. With the help of chorotype frequencies for 25 km2 individual squares in Israel, territories were defined on the basis of the first two most frequent chorotypes. The similarity of boundaries in the resulting phytogeographical map with a physiognomic map suggests that the latter may be used in preliminary stages of the preparation of plant geographical maps.

Desert rocks as plant refugia in the Near East

The outcrops of smooth-faced rocks in Near Eastern deserts function as refugia for plants that do not fit the present local climate. They have survived in the area from periods when the continuous extensions of the moister climate enabled their penetration from the Mediterranean zone. The largest Mediterranean enclave in Near Eastern deserts and steppes is the sandstone and limestone outcrops at the upper escarpments of the southwestern Jordanian plateau, between At Tafila and Ras en Naqb, including the famous Petra and Wadi Dana. Hundreds of Mediterranean relict species and dozens of endemic species coexist with steppe and desert species in the crevices of these rocks. In this article I discuss the ecology, phytogeography, and distribution of this special habitat in Jordan, the Sinai, and Israel; and I compare the influence on past and present floras of climatic oscillations during the Pleistocene and Holocene in the Near East and Africa.RésuméL’affleurement des roches á surface lisse fonctionne dans les déserts du Proche-Orient comme refuge pour les plantes nonadaptées au climat local actuel. Elles ont survécu dans ces régions depuis des périodes quand les extensions contigües de climat humide ont rendu possible leur pénétration á partir de la zone méditerranéenne. La plus vaste enclave méditerranéenne dans les déserts et steppes du Proche-Orient est l’affleurement de grès et calcaires dans les talus supérieurs du plateau jordanien sudoccidental, entre At Tafila et Ras en Naqb, y compris les célèbres Petra et Wadi Dana. Des centaines d’espèces relictes et des douzaines endémiques coexistent dans les fentes de ces rochers avec les espèces de la steppe et du désert. Dans cet article je discute l’écologie, la phytogéographie, et la distribution de cet habitat spécial en Jordanie, dans le Sinaï, et en Israël; et je compare l’influence sur les flores passées et actuelles des oscillations du climat pendant le Pléistocène et le Holocène au Proche-Orient et en Afrique.