Conversion of even-aged conifer monocultures into structurally complex, mixed-species forests is a key objective in contemporary silviculture, particularly in water-limited environments where ecosystem resilience is increasingly challenged by climate change. However, empirical guidance for implementing such transitions remains limited. We investigated how overstory thinning, expressed as a continuous gradient of leaf area index (LAI), influences resource availability, regeneration, and sapling growth of pine (Pinus halepensis) and oak (Quercus calliprinos) in mature semiarid P. halepensis monocultures. Thinning strongly increased understory light and herbaceous biomass, and moderately enhanced shallow-soil moisture, particularly during the dry season. Regeneration responses were species-specific and reflected contrasting ecological strategies. Pine recruitment increased with decreasing LAI, whereas oak recruitment was positively associated with higher LAI and declined under open conditions. Sapling growth of both species increased with decreasing LAI, with a higher aboveground growth rate in pine. Consequently, pine regeneration index (density & times; size) was substantially higher under lowest LAI. Our results demonstrate a tradeoff between conditions favoring oak establishment (high LAI) and pine recruitment and growth (low LAI), highlighting the importance of stage-specific management. We identify critical LAI thresholds for guiding conversion: LAI >= 2.5 promotes oak recruitment, whereas LAI <= 1.5 enhances pine regeneration and growth of both species. These findings support a sequential thinning approach, in which canopy cover is initially maintained to facilitate oak establishment and subsequently reduced to promote mixed stand development. The use of LAI as a continuous and operational metric provides a practical framework for managing forest conversion in water-limited ecosystems.

Climate change is profoundly affecting ecosystems globally, increasing the frequency and severity of droughts. The eastern Mediterranean, characterized by high climatic variability and water scarcity, faces critical challenges to biodiversity and ecosystem functionality. This study leverages over two decades of rainfall manipulation experiments at the Matta LTER site in Israel to investigate how Mediterranean ecosystems respond to chronic and extreme drought conditions and altered rainfall patterns.Experimental treatments included 30% and 66% reductions in annual precipitation, coupled with variations in rainfall distribution, simulated through rainout shelters. Results revealed that the ecosystem demonstrated resistant to moderate drought, with minimal changes in biomass and species diversity under a 30% rainfall reduction. However, extreme drought conditions (66% reduction) significantly impacted aboveground biomass and altered species composition, suggesting the presence of ecological thresholds. The study highlights the importance of soil moisture dynamics, drought-resistant plant traits, and seed bank contributions in maintaining ecosystem functionality under stress.The findings underline the critical need for long-term monitoring and advanced methodologies, including AI-driven modeling, to identify tipping points and predict ecosystem responses under future climate scenarios. These insights provide valuable guidance for adaptive management strategies to enhance the resilience and sustainability of Mediterranean ecosystems amid accelerating climate change.

1. Climate change increases aridity in many drylands worldwide, which has significant consequences for ecosystem functioning and may reduce carbon sequestration. However, responses of major carbon cycle processes in drylands, including primary production and decomposition, to increasing aridity remain poorly understood. 2. In this study, we assessed the quantitative effects of precipitation and the underlying impacts of functional traits on above-ground net primary production (ANPP) and plant litter decomposition in herbaceous Mediterranean plant communities. A dataset encompassing a wide range of precipitation (similar to 50-1000mm) was generated by selecting four field sites along a natural precipitation gradient and applying rainfall manipulations over several years. 3. Across the entire dataset, ANPP and decomposition decreased non-linearly with declining precipitation, showing steeper reductions at low compared to high precipitation levels. Notably, above similar to 400mm, the two processes followed a similar pattern, but below this threshold, ANPP dropped more rapidly, while decomposition decreased less and remained relatively high. 4. Plant functional traits associated with low growth rates exacerbated the reduction of ANPP at the drier sites, whereas higher litter quality at these sites compared with the wetter sites enabled relatively high rates of litter decomposition. The latter findings were confirmed by a litter transplantation study, where litter from the arid site decomposed faster at all sites compared to litter from the wetter sites. In addition, dryland decay mechanisms, such as photodegradation and microbial degradation enabled by non-rainfall water sources, might have mitigated some of the dryness-related decrease in decomposition. 5. Increasing climate change-induced aridity in drylands may drive long-term shifts in herbaceous vegetation composition towards smaller, less productive species that produce more labile litter. This trend is expected to accelerate the decline in production more than the decline in decomposition, likely reducing carbon sequestration.

The soil seed bank is a major component of plant communities. However, long-term analyses of the dynamics of the seed bank and the ensuing vegetation are rare. Here, we studied the dynamics in plant communities with high dominance of annuals in Mediterranean, semiarid, and arid ecosystems for nine consecutive years. For annuals, we hypothesized that the density of the seed bank would be more stable than the density of the standing her-baceous vegetation. Moreover, we predicted that differences in temporal variability between the seed bank and the vegetation would increase with aridity, where year-to-year rainfall variability is higher. We found that the temporal variability at the population level (assessed as the standard deviation of the loge-transformed density) of the nine dominant annuals in each site did not differ between the seed bank and the ensuing vegetation in any of the sites. For the total density of annuals, patterns depended on aridity. In the Mediterranean site, the temporal variability was similar in the seed bank and the vegetation (0.40 vs. 0.40). Still, in the semiarid and arid sites, variability in the seed bank was lower than in the vegetation (0.49 vs. 1.01 and 0.63 vs. 1.38, respectively). This difference between the population-level patterns and the total density of annuals can be related to the lower population synchrony in their seed bank. In contrast, for the herbaceous perennials (all species combined), the seed bank variability was higher than in the vegetation. Overall, our results highlight the role of the seed bank in buffering the annual vegetation density with increasing climatic uncertainty typical in aridity gradients. This role is crucial under the increasing uncertainty imposed by climatic change in the region.

&lt;p&gt;Ecosystems in many regions worldwide are projected to experience increasingly dry conditions caused by warming, often associated with lower rain amounts. These trends are expected to result in a reduction in carbon stocks, as carbon sequestration declines with increasing aridity. However, it is unclear how some of the main processes controlling carbon sequestration add up to the decrease in carbon sequestration. Here, we investigated aboveground net primary production (ANPP) and litter decomposition in ephemeral herbaceous Mediterranean plant communities as affected by various degrees of aridity. The experimental design included four sites along a steep aridity gradient between dry-subhumid and hyperarid regions, and rainfall manipulations of -30% and +30% of ambient rain amounts.&lt;/p&gt;&lt;p&gt;Results showed a progressively steeper decline in the carbon-related fluxes with increasing aridity. However, this decline was more pronounced for ANPP than for decomposition, a result supported by lower values for plant growth traits and higher values for litter decay traits at the drier compared with the wetter sites. Litter decomposition rate was more affected by litter quality and than by climate, as supported by a long-term transplantation study. Furthermore, litter quality increased with aridity and consequently litter from the most arid site decomposed faster than litter from the other sites.&lt;/p&gt;&lt;p&gt;The combined outcome of reduced carbon input by less production and relatively quick decay of newly acquired biomass carbon was reflected by a steep decline in soil organic carbon (SOC) stock over most of the precipitation gradient. However, SOC at the most arid site was higher than expected from the combination of production and decomposition, potentially indicating efficient soil organic matter formation and stabilization.&lt;/p&gt;

Aims Primary biomass production is a fundamental process for ecosystem functioning. Yet, little is known on the mechanisms driving temporal stability of biomass production in annual plant communities, particularly when subjected to highly variable environments and undergoing temporal changes in species composition. We aimed to disentangle the relative importance of biomass production, species diversity, dominance and asynchrony of species fluctuations as drivers of biomass stability in mediterranean and semi-arid annual plant communities. Location Mediterranean (31 degrees 42 ' N; 35 degrees 03 ' E) and semi-arid (31 degrees 23 ' N; 34 degrees 54 ' E) sites, Israel. Methods Above-ground biomass and species abundance were monitored in 15 plots of 250 m(2) per site during eight consecutive years. Relationships between stability drivers and community stability were studied at the regional (between sites) and local (within sites) spatial scales. Results Community biomass stability (mean biomass/SD) increased from the semi-arid to the mediterranean site concomitantly with higher biomass production, richness, and evenness. Differences in stability between sites were due to opposite effects of site conditions on the mean and SD of community biomass, leading to higher stability in the mediterranean site. Within sites, species asynchrony was the key driver of stability at the local spatial scale. Richness and biomass production affected stability indirectly through asynchrony, but in different ways at each site. At the mediterranean site, these factors had indirect negative effects on stability by reducing asynchrony, but did not rescind a positive effect of asynchrony on community stability. At the semi-arid site, biomass production had indirect positive effects on stability through asynchrony, while richness had no effect on asynchrony and stability. Stability was not driven by species evenness in either site. Conclusions Our study provides new insights into the complex control of biomass stability in the dynamics of mediterranean and semi-arid annual plant communities, with different mechanisms driving stability across the regional vs local spatial scales.

Ecological theory predicts that the soil seed bank stabilises the composition of annual plant communities in the face of environmental variability. However, long-term data on the community dynamics in the seed bank and the standing vegetation are needed to test this prediction. We tested the hypothesis that the composition of the seed bank undergoes lower temporal variability than the standing vegetation in a nine-year study in Mediterranean, semi-arid, and arid ecosystems. The composition of the seed bank was estimated by collecting soil cores from the studied sites on an annual basis. Seedling emergence under optimal watering conditions was measured in each soil core for three consecutive years, to account for seed dormancy. In all sites, the composition of the seed bank differed from the vegetation throughout the years. Small-seeded and dormant-seeded species had a higher frequency in the seed bank than in the standing vegetation. In contrast, functional group membership (grasses vs. forbs) did not explain differences in species frequency between the seed bank and the vegetation after controlling for differences between grasses and forbs in seed mass and seed dormancy. Contrary to predictions, the magnitude of year-to-year variability (the mean compositional dissimilarity between consecutive years) was not lower in the seed bank than in the vegetation in all sites. However, long-term compositional trends in the seed bank were weaker than in the vegetation in the Mediterranean and semi-arid sites. In the arid site where year-to-year variability was highest, no long-term trends were observed. Overall, the effect of the seed bank on the temporal variability of the vegetation in annual communities depends on site conditions and time scale. While the year-to-year variability of the seed bank is similar to the vegetation, the soil seed bank can buffer long-term trends.

Mediterranean forest ecosystems are of high conservation value and therefore increasingly managed to restore and promote their natural biodiversity and complexity. The present study aimed to assess plant species diversity of East-Mediterranean conifer forests as affected by overstory cover manipulation at multiple spatial scales. Understanding this interaction in water-limited forest ecosystems is particularly challenging as overstory-understory relations involve both water and light constrains. The experiment was conducted in a mature (40y) planted Pinus halepensis forest in the Jerusalem Mountains of Israel. Understory plant community structure was monitored for five years in sixteen experimental plots (0.5 ha) representing a range of overstory cover levels (leaf area index-LAI = 0-4 m(2)m(-2)) created by tree thinning. Light and water availability in the forest understory were monitored using fisheye camera (irradiance), predawn leaf water potential (PLWP) of dominant species and soil water content (SWC) measurements. Plant diversity was measured at increasing spatial scales (grain sizes, 0.01-400 m(2)), using hierarchical nested sampling. Irradiance and SWC increased with decreasing LAI while PLWP was not affected. Stand-level understory richness (alpha diversity) increased linearly with decreasing LAI, indicating a consistent, positive resource availability-diversity relationship. The results pointed towards strong dependency of species richness on light availability as compared to its dependency on water availability that was less definite. Understory species composition varied across LAI levels (beta diversity at the forest level) indicating species turnover, mainly between annual herbs benefiting from reduced overstory cover vs. woody species benefiting from higher cover. The relationships between overstory cover and understory richness and composition were rank-invariant across grain sizes. These relationships were stronger at the larger (10, 100, 400 m(2)) compared to the smaller (0.01, 0.1, 1 m(2)) grain sizes. The 10-m(2) grain-size, corresponding to the crown projection area of individual trees, showed the strongest relationship. Observed patterns of overstory cover-understory richness suggest that resource availability, rather than spatial resource heterogeneity, was the main factor shaping understory diversity. Furthermore, grain-size effects on this relationship support "environmental filtering" rather than "resource density" as the main mechanism through which reduced overstory cover promoted understory diversity. 'Synthesis and applications': Our findings demonstrate the importance of overstory cover as a key factor determining plant diversity in water-limited East-Mediterranean forests. We highlight the important role of spatial heterogeneity of overstory cover at both the stand (intra-plot) and forest (inter-plot) scales and support dynamic variable thinning as a management strategy to enhance forest biodiversity and complexity.

Aims Management of silvo-pastoral systems in planted and natural forests in semi-arid Mediterranean regions often employs seasonal night corrals for animal protection. This management system changes the spatial distribution of animal excreta, resulting in a net transfer of soil mineral resources and their accumulation in the corrals. After abandonment, corrals are colonized by ruderal species, becoming focal sources for their spread in the forest. We aimed to implement a rational management of seasonal sheep corrals based on a better understanding of the vegetation processes occurring in abandoned corrals, in order to alleviate their negative impact in the forest. Methods Relationships between temporal changes in the vegetation, the soil seed-bank and levels of soil nutrients were studied in a chronosequence of abandoned sheep corrals and compared with nearby reference plots in planted Eucalyptus forests grazed by sheep in the semi-arid North-Western Negev, Israel. The region has a bi-seasonal Mediterranean climate, with high dominance of annual species in the grazing range. Important Findings Abandoned sheep corrals were colonized by seeds of ruderals originating in older abandoned corrals. Subsequent successional changes occur at a slow rate, driven by the depletion of soil resources in the abandoned corrals, and were still in progress 20 years after abandonment. Ruderals were gradually replaced, first by taller grasses and followed by short grasses, but most forbs and particularly geophytes did not recover during this period. Recovery of the original herbaceous vegetation in the corrals was through seed dispersal from the surrounding vegetation, not from the original soil seed-bank remaining in the corrals after abandonment. Ruderal species in the grazed, planted forests behave as patch-tracking metapopulations. Their persistency depends on constant creation of new corrals compensating for the gradually dwindling populations in older abandoned corrals, and on the availability of dispersal vectors.

Aims Research in the last decades supports the idea that certain species, namely 'nurse species', can enhance ecosystem function and species diversity in their vicinity through amelioration of the abiotic environment. However, few studies have explored whether nurse plants can promote functional diversity at the microhabitat level. Here, we evaluated the hypothesis that nurse plants can increase functional diversity in the beneficiary annual plant assemblage at the microhabitat level. Location Sayeret Shaked Park, the Negev desert (Israel). Results The nurse species examined, two shrubs and one large annual, had a negligible or even negative influence on annual above-ground biomass production. Nonetheless, they increased functional diversity in terms of specific leaf area (SLA), maximum plant height (MPH), seed weight (SW), and reproductive ratio (RR) at the microhabitat level. Conclusions These findings reinforce the idea that, even if there is not a typical nurse syndrome related to enhanced plant performance, nurse plants might induce a portfolio effect on annual plant assemblages by promoting functional diversity in key functional traits associated to plant survival and reproduction under a set of different microhabitat conditions.

Food selection by foragers is sensitive to the availability of resources, which may vary along geographical gradients. Hence, selectivity of food types by foragers is expected to track these resource gradients. Here we addressed this hypothesis and asked if foraging decisions of seed‐eating ants differ along a geographic gradient of habitat productivity. The study was carried out for two years at five sites along a natural climatic gradient, ranging from arid to Mediterranean, where plant productivity varies six‐fold across a short geographic distance of 250 km. We found that in ant colonies of the genus Messor, collective foraging decisions differed along the gradient. Specifically, at the high‐productivity sites, a stronger association was found between plant seed availability and selectivity, suggesting that colonies respond more accurately to within‐patch variation in food amounts. In contrast, colonies in low‐productivity sites foraged in patches with higher concentration of seeds, suggesting that they respond more accurately to among‐patch variation in food amounts. Moreover, at the high‐productivity sites, colonies were more discriminating in their choice of food and preferred bigger seeds, while in the low‐productivity sites, where smaller seeds were relatively more abundant, food collection depended mostly on seed availability. An experiment with artificial seed patches performed along the same climatic gradient, revealed no difference in food selectivity across sites when food type and availability were similar, and a general preference for bigger over medium‐sized seeds. Overall, our findings suggest that resource availability is an important factor explaining food choice along a climatic gradient and imply that in low‐productivity regions small‐seeded species incur high predation pressure, whereas in high‐productivity regions, large‐seeded species suffer higher predation. This could have important consequences for plant species composition, particularly at the face of climate change, which could dramatically alter the foraging decisions of granivores.

Changes in rainfall amounts and patterns have been observed and are expected to continue in the near future with potentially significant ecological and societal consequences. Modelling vegetation responses to changes in rainfall is thus crucial to project water and carbon cycles in the future. In this study, we present the results of a new model-data intercomparison project, where we tested the ability of 10 terrestrial biosphere models to reproduce the observed sensitivity of ecosystem productivity to rainfall changes at 10 sites across the globe, in nine of which, rainfall exclusion and/or irrigation experiments had been performed. The key results are as follows: (a) Inter-model variation is generally large and model agreement varies with timescales. In severely water-limited sites, models only agree on the interannual variability of evapotranspiration and to a smaller extent on gross primary productivity. In more mesic sites, model agreement for both water and carbon fluxes is typically higher on fine (daily-monthly) timescales and reduces on longer (seasonal-annual) scales. (b) Models on average overestimate the relationship between ecosystem productivity and mean rainfall amounts across sites (in space) and have a low capacity in reproducing the temporal (interannual) sensitivity of vegetation productivity to annual rainfall at a given site, even though observation uncertainty is comparable to inter-model variability. (c) Most models reproduced the sign of the observed patterns in productivity changes in rainfall manipulation experiments but had a low capacity in reproducing the observed magnitude of productivity changes. Models better reproduced the observed productivity responses due to rainfall exclusion than addition. (d) All models attribute ecosystem productivity changes to the intensity of vegetation stress and peak leaf area, whereas the impact of the change in growing season length is negligible. The relative contribution of the peak leaf area and vegetation stress intensity was highly variable among models.

The western part of the distribution range is inhabited by the slender plants with small panicles and narrow leaves that are commonly classified as Sorghum halepense. The more robust specimens that inhabit the eastern part of the range are usually recognized as S. miliaceum. Since both taxa cross readily with one another, and hybrids among them are as fertile as their parents, they are considered to belong to one biological species, S. halepense. Different ecotypes of this species had been introduced as weeds to all subtropical and warm temperate regions of the world. Due to its wide distribution and hybridization with different varieties of grain sorghum, a spectrum of flowering responses is to be expected in S. halepense. However, information on the environmental control of flowering in this formidable weed is very scanty. Earlier flowering in northern latitudes is probably an adaptation to avoid autumn frost damage during the reproductive development.

Traditional sheep grazing in natural and planted forests in the Mediterranean basin is based on night penning in seasonal corrals, where excreta accumulate instead of being returned to the grazed range. Lack of planning and unawareness of the long-term effect of abandoned corrals is negatively affecting the landscape and grazing value of the forests. We studied the dynamics of soil nutrients in a chronosequence of abandoned sheep corrals in planted Eucalyptus forests in two semi-arid sites in Israel. Dung decomposition was a slow process lasting 5–10 years. Soluble-N, P and K in the soil beneath the dung layer decreased gradually. Yet, 15–20 years after corral abandonment K and P were still 2 to 3 times higher than in the surrounding range, while soluble-N decreased within 10–15 years. Biomass production in the abandoned corrals was 2–3 times higher than in the grazed range up to 20 years after abandonment. Corrals act as sinks of soil nutrients that are lost to the grazed range. We propose that a balance between nutrient inputs (i.e. atmospheric deposition, N-fixation) and outputs (i.e. grazing and night penning) is reached in the grazed range at a low level of soil nutrients, which may constrain vegetation productivity.

Different photoperiodic responses have been reported for flowering in Cynodon Dactylon. Low-temperaure pretreatments are required for flowering initiation, or are able to advance flowering. Seed production usually is very sparse and the plants spread mainly by stolons and rhizomes. The glumes are narrow and membranous, slightly unequal, and shorter than the floret. The lemma is firm, laterally compressed, with a fringe of hairs on its keel, the narrow palea as long as the lemma. Low light intensity strongly inhibits growth and flowering in Bermuda grass. Plants growing under high light intensity flowered even when subjected to high night temperature, while those growing under lower light intensities flowered only at 12°Celsius night temperatures.

Goat herding is an important tool in the ecologically sound management of Mediterranean shrublands and woodlands, although effective levels of woody biomass removal by the goats is neither guaranteed nor easy to predict. Preliminary observations indicated that one reason for this may be poor understanding of plant-herbivore interactions that operate intraspecifically at the local spatial scale. We asked, whether goats show intraspecific preferences among neighboring plants when foraging a small local population of Pistacia lentiscus, a dominant tall shrub. First, we characterized and quantified the profile of stored and emitted volatile organic compounds (VOCs) and the PEG-binding capacity of tannins (a proxy for protein binding capacity) in the foliage of P. lentiscus shrubs, sampled within an area of 0.9 ha. We then tested goat preference between pairs of these shrubs that differed in chemical composition. Almost all sampled P. lentiscus shrubs were allocated to one of two distinct VOC chemotypes: one dominated by germacrene D and limonene (designated chemotype L) and the other by germacrene D and α-pinene (chemotype P). In contrast, continuous moderate variability was found in the binding capacity of tannins in the foliage. Goats showed preference for shrubs of chemotype L over those of chemotype P, and their preference was negatively correlated with the binding capacity of tannins. Possible influences of VOCs on goat preference that may explain the observed patterns are discussed in the light of possible context-dependent interpretation of plant VOC signals by large mammalian herbivores.

Grazing has become an effective and accepted tool for managing open areas for different uses other than meat production, such as minimizing fire risk and increasing species diversity. Although woodlands in Israel are utilized for cattle grazing, the effect of grazing on woody vegetation has not been assessed quantitatively. The aim of this study was to characterize the effect of biotic and management factors, especially animal density, on the structure, composition and regeneration of woody vegetation. The study was conducted in the Western Galilee of Israel. A woodland plot of 211 ha was divided into four subplots, with two replications of two grazing intensities. Changes in the woody vegetation were monitored in 56 transects of 20 m length each, sampled at the onset of the study and after four annual grazing cycles. Woody plants up to height 2.1 meter growing along each transect were documented. From these records we derived indices to characterizing vegetation structure, woody biomass removal, species richness and woodland regeneration. It is shown that the extent of grazing effect depends mainly on cattle density, as well as on the type and state of the vegetation. The woody vegetation cover was reduced under the two grazing intensities, but grazing did not affect species richness and sapling abundance. Therefore, it was concluded that the use of cattle is an important tool for sustainable management of Mediterranean woodlands.