Mediterranean Shrub Communities Research Articles

Better soon than never: climate change induces strong phenological reassembly in the flowering of a Mediterranean shrub community

Abstract Background and Aims Flowering is a key process in the life cycle of a plant. Climate change is shifting flowering phenologies in the Northern Hemisphere, but studies with long data series at the community level are scarce, especially those considering the consequences of phenological changes for emerging ecological interactions. In the Mediterranean region, the effects of climate change are stronger than the global average and there is an urgent need to understand how biodiversity will be affected in this area. Methods In this study, we investigated how the entire flowering phenology of a community comprising 51 perennial species from the south of the Iberian Peninsula changed from the decade of the 1980s to the 2020s. Furthermore, we have analysed the consequences of these changes for flowering order and co-flowering patterns. Key Results We have found that the flowering phenology of the community has advanced by ~20 days, which is coherent with the increasing temperatures related to climate change. Individual species have generally advanced their entire flowering phenology (start and end) and increased their flowering duration. The early flowering has resulted in a re-organization of the flowering order of the community and generated new co-flowering assemblages of species, with a slight trend towards an increase of shared flowering time among species. Conclusions The advanced flowering phenology and changes in flowering duration reported here were of unprecedented magnitude, showcasing the extreme effects of climate change on Mediterranean ecosystems. Furthermore, the effects were not similar among species, which could be attributed to differences in sensitivities of environmental cues for flowering. One consequence of these changes in flowering times is ecological mismatches, indicated by changes in the flowering order and co-flowering between decades. This new scenario might lead to new competitive or facilitative interactions and to the loss or gain of pollinators.

Pathways to global-change effects on biodiversity: new opportunities for dynamically forecasting demography and species interactions.

In structured populations, persistence under environmental change may be particularly threatened when abiotic factors simultaneously negatively affect survival and reproduction of several life cycle stages, as opposed to a single stage. Such effects can then be exacerbated when species interactions generate reciprocal feedbacks between the demographic rates of the different species. Despite the importance of such demographic feedbacks, forecasts that account for them are limited as individual-based data on interacting species are perceived to be essential for such mechanistic forecasting-but are rarely available. Here, we first review the current shortcomings in assessing demographic feedbacks in population and community dynamics. We then present an overview of advances in statistical tools that provide an opportunity to leverage population-level data on abundances of multiple species to infer stage-specific demography. Lastly, we showcase a state-of-the-art Bayesian method to infer and project stage-specific survival and reproduction for several interacting species in a Mediterranean shrub community. This case study shows that climate change threatens populations most strongly by changing the interaction effects of conspecific and heterospecific neighbours on both juvenile and adult survival. Thus, the repurposing of multi-species abundance data for mechanistic forecasting can substantially improve our understanding of emerging threats on biodiversity.

Land use/land cover change as a major driver of current landscape flammability in Eastern Mediterranean region: A case study in Southwestern Turkey

Land use/land cover (LULC) change has been one of the main drivers of landscape changes in the Mediterranean region where there has been an increase in the forested lands. LULC change in the region has not only changed forest stand structure and composition but also resulted in increase in the available combustible fuels. There have been few studies on fuel accumulation in relation to LULC, however, no study explaining quantitatively the relationship between LULC change and canopy fuel load in the Mediterranean region. The objective of this study is to evaluate the effects of LULC changes on overall crown fire hazard through examining stand structure, composition, and canopy fuel loads in Eastern Mediterranean forests for 35 years. Forest stand type maps generated from the stereo interpretation of aerial photographs and field survey data were used for the analyses. The results of the study showed significant changes in LULC during the period of 1977-2012. There was a 16.6 % decrease in agricultural areas, 144.5 % increase in settlement areas and 6.8 % increase in pine forests. As for the structural and compositional changes in forested lands, open pine stands that included Mediterranean shrub communities decreased (77.2 %); nonetheless, closed pure pine stands increased (49.9 %), resulting in an increase in the total canopy fuel load in pine stands (86.4 %). Results indicated that landscapes tended to become more homogeneous, fully closed pine stands, resulting in an increase in the continuity and the buildup of fuels available for combustion.

Contrasting patterns in leaf traits of Mediterranean shrub communities along an elevation gradient: measurements matter

We assessed the changes in community-weighted mean (CWM) and variability of specific leaf area (SLA) and leaf area (LA) of different Mediterranean shrub communities along an elevation gradient in the island of Sardinia (Italy). Furthermore, we explored the relative contribution of species turnover and intraspecific variation to shifts in CWM values along the gradient. Forty sampling units (5 × 5 m) were selected in a probabilistic way along a 1300 m elevation gradient which crossed four thermotypes (thermometric belts). Leaf traits were measured in each sampling unit. ANOVA and a trend test for monotonic changes in variance were used to assess, respectively, CWM differences and variability in both the leaf traits across thermotypes. Variance decomposition of CWM values was used to identify the role of inter- and intraspecific variation. SLA and LA responded differently along the studied gradient in terms of abundance-weighted mean values and variability: CWM of SLA showed the lowest values in the driest thermotype, while LA in the more humid one; SLA variability showed a significant increasing trend with increased water availability, while LA variability did not show any pattern. The contribution of intraspecific trait variation was significant for both the leaf traits, but higher for SLA, where negative covariation between inter- and intraspecific variation was detected. We highlight the importance of simultaneously considering measurements of both leaf traits to understand the functional response of communities in Mediterranean environments. Moreover, neglecting intraspecific variation in leaf traits, even along steep gradients with relevant species compositional changes, can result in the underestimation of the amount of trait variation in response to environmental changes.

Effects of rain shortage on carbon allocation, pools and fluxes in a Mediterranean shrub ecosystem – a 13C labelling field study

Hydrological cycle is expected to become the primary cause of ecosystem's degradation in near future under changing climate. Rain manipulation experiments under field conditions provide accurate picture on the responses of biotic processes to changed water availability for plants. A field experiment, mimicking expected changes in rain patterns, was established in a Mediterranean shrub community at Porto Conte, Italy, in 2001. In November 2011 Cistus monspeliensis, one of the dominating shrub species in the Mediterranean basin, was 13C labelled on plots subjected to extended rain shortage period and on control non manipulated plots. Carbon (C) allocation was traced by 13C dynamics in shoots, shoot-respired CO2, roots, microbial biomass, K2SO4-extractable C and CO2 respired from soil.Most of the recovered 13C (60%) was respired by shoots within 2weeks in control plots. In rain shortage treatment, 13C remained incorporated in aboveground plant parts. Residence time of 13C in leaves was longer under the rain shortage because less 13C was lost by shoot respiration and because 13C was re-allocated to leaves from woody tissues. The belowground C sink was weak (3–4% of recovered 13C) and independent on rain manipulation. Extended rain shortage promoted C exudation into rhizosphere soil in expense of roots. Together with lowered photosynthesis, this “save” economy of new C metabolites reduces the growing season under rain shortage resulting in decrease of shrub cover and C losses from the system on the long-term.

Does long-term warming affect C and N allocation in a Mediterranean shrubland ecosystem? Evidence from a 13C and 15N labeling field study

In the Mediterranean basin the effects of climate warming on ecosystem functioning will strongly depend on the warming intensity directly but also on its effects on evapotranspiration and nutrient cycling. Climate manipulation experiments under field conditions are a source of unique empirical evidence regarding climate-related modifications of biotic processes.A field night-time warming experiment, simulating the predicted near-future increase in ambient temperatures (+0.3 up to 1°C), was established in a Mediterranean shrub community located in Porto Conte (Italy) in 2001. After 11 years of continuous treatment, we labeled the dominant shrub Cistus monspeliensis with 13CO2 and studied the dynamics of the label allocation between aboveground and belowground pools and fluxes in warmed and ambient plots within 2 weeks of the chasing period. The interactions between C and N metabolism were assessed by parallel labeling of soil with K15NO3.Most of the assimilated 13C was respired by Cistus shoots (28–51%) within two weeks. Cistus under warming respired more 13C label and tended to allocate less 13C to leaves, branches and roots. The higher C and N content in microbial biomass in warming plots, combined with the higher N content in plant tissues and soil, evidenced a greater N mobilization in soil and a better nutrient status of the plants as compared to the ambient treatment. Acceleration of N cycling is probably responsible for higher respiratory C losses, but combined with the reduction in the number of frost days, should also positively affect plant photosynthetic performance.We conclude that, although Cistus plants are already growing in conditions close to their thermal optimum, long-term warming will positively affect the performance of this species, mainly by reducing the nutrient constraints. This positive effect will highly depend on the frequency and amount of rain events and their interactions with soil N content.

How soil and elevation shape local plant biodiversity in a Mediterranean hotspot

Elucidating how evolutionary and ecological factors drive the assemblage of communities in biodiversity hotspots remains an important challenge. This currently impedes our ability to predict the responses of communities to the ongoing global changes in these major world’s biodiversity reservoirs. Here, we focus on the Sierra Nevada mountain range, a core region of the Baetic-Rifan biodiversity hotspot in the western Mediterranean, and explore the relative importance of soil properties and elevation in shaping phylogenetic and functional diversity of shrub communities. We recorded the total number of each species in community transects across elevation gradients and contrasting soil conditions, and measured some ecologically relevant functional traits (specific leaf area, leaf carbon:nitrogen ratio, plant height and blooming duration). Phylogenetic distances among species were inferred from a genus-level time-calibrated molecular phylogeny. Elevation was the main factor predicting phylogenetic and functional alpha diversity of plant communities. Species in high-elevation communities were phylogenetically distant but functionally similar, being relatively smaller and having relatively short blooming durations, whilst species in low-elevation communities showed the opposite pattern. Beta diversity in SLA and leaf C:N ratio based on species incidences were positively correlated with a soil pH and micronutrient gradient. Specifically, communities that develop on soils of high pH and low micronutrient concentrations showed low SLA values and high leaf C:N ratios, whilst communities on soils of lower pH and high micronutrient concentrations showed the opposite pattern. We conclude that soil properties and elevation simultaneously shape the structure of Mediterranean shrub communities by differentially acting on the different dimensions of the species niches. Elevation seems to filter plant height and phenology-related traits whereas nutrient-related functional traits are more related to soil properties. Our study illustrates the primary role of environmental heterogeneity for the maintenance of diversity in Mediterranean mountain ecosystems.

The effects of deer exclusion on the development of a Mediterranean plant community affected by a wildfire

Despite the resilience of Mediterranean ecosystems to fire, the ecological restoration of burned plant communities can be hindered by ungulate herbivores, particularly in areas with high population densities. This study compares the postfire development of a shrub community with and without deer, after a wildfire occurred in 2003 in a protected area in Central Portugal. We monitored 12 fenced and 12 unfenced plots 2, 3, 4, and 8 years after fire. Within each plot, we established a linear transect and measured the monospecific canopy projections (plant patches). Five plant community indicators (patch number, average patch length, average patch height, patch cover, and patch phytovolume per square meter) were obtained. The diameter and height of individuals of the most abundant shrub species (Cistus salvifolius,Erica scoparia,Myrtus communis,Pistacia lentiscus,Rubus ulmifolius, andUlex jussiaei) were also measured. These measurements were used as response variables in generalized linear mixed models in order to assess the effects of time‐after‐fire and fencing, on the development of the plant community. Patch height and phytovolume had a significantly higher growth in fenced plots. At the species level,C. salvifolius,M. communis,R. ulmifolius, andU. jussiaeishowed a higher growth across time both in height and in diameter, in the absence of herbivory. This work shows that deer exclusion needs to be considered when aiming at the postfire restoration of Mediterranean shrub communities.

Estimation of above-ground biomass in shrubland ecosystems of southern Spain

Although forest biomass estimates are vital for estimating carbon fluxes, the database for estimating the biomass or carbon pool in Mediterranean shrub ecosystems is lacking. This paper reports the above-ground phytomass estimates obtained for shrub ecosystems in Southern Spain. The phytomass values obtained were 1143 g m–2 for heath, 447 g m–2 for rock rose thicket-heath, 788 g m–2 for rock rose thicket and 1404 g m–2 for gorse thicket formations; the corresponding values for bushes were 695 g m–2 for mancha phytomass and 1966 g m–2 for Pistacia lentiscus formations. The photosynthetic-to-total phytomass ratio ranged from 0.156 for mancha highbush to 0.213 in rock rose thickets, with a mean value of 0.187 for the study ecosystems as a whole. The estimates of sequestered carbon differed between the shrub-type ecosystems in the interval between 2.23 t ha–1 for Cistus ladanifer to 9.83 t ha–1 for Pistacia lentiscus. A better understanding of biomass in Mediterranean shrub communities will provide useful information on the growth pattern of these species, biomass mapping, remote sensing and regional estimations of primary productivity in these areas.

Assessment of vegetation regeneration after fire through multitemporal analysis of AVIRIS images in the Santa Monica Mountains

Spectral mixture analysis (SMA) from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) was used to understand regeneration patterns after fire in two semiarid shrub communities of the Santa Monica Mountains, California: northern mixed chaparral and coastal sage scrub. Two fires were analyzed: the Malibu Topanga fire (3 November 1993) and the Calabasas fire (21 October 1996). SMA was compared to the results of the Normalized Difference Vegetation Index (NDVI) to assess vegetation recovery. An unburned control plot (within the past 20 years), having similar environmental features, was used to generate two relative fire regeneration indices, Regeneration Index (RI) and Normalized Regeneration Index (NRI). Indices were calculated using the Green Vegetation (GV) endmember and the NDVI. These indices were determined to be largely independent of AVIRIS radiometric calibration uncertainty, minor errors in the atmospheric correction, topographic distortions, and differences in the phenological state of the vegetation because of interannual or seasonal differences. The temporal evolution of the two fires were combined to produce a longer observation period and used to fit a logarithmic regression model for each Mediterranean shrub community. The NRI developed from the GV endmember (NRI GV) produced the closest estimate for the time of recovery in both communities based on recovery times in the literature. The use of NDVI worked very well for recovery in the northern mixed chaparral, but was less successful in the coastal sage scrub, mainly because of extensive herbaceous cover during the first years of the regeneration process. Endmembers generated from hyperspectral images were more accurate because they are tuned to capture the greenness of the shrub type of vegetation. Use of matching plots having similar environmental features, but which were burned in different years were demonstrated to improve estimates of the recovery within each community.

Nectary structure of Labiatae in relation to their nectar secretion and characteristics in a Mediterranean shrub community ? Does flowering time matter?

We studied the interrelation between nectary structure (13 parameters), nectar characteristics (yield, chemical composition), and flower size of 11 Labiatae species in a Mediterranean shrub community near Athens, Greece. We also explored whether the above attributes are affected by the Mediterranean summer drought constraints. Our findings show that among all nectary parameters studied, nectary size and stomatal opening are the most important in (positively) shaping nectar secretion, nectary size being the most meaningful. Nectary structure is correlated to quantity of the nectar secreted, not its quality. Wide flowers bear wide nectaries with large stomatal openings, whereas deep flowers are not related to any nectary size. Corolla size (both length and width) and nectary stomatal opening decrease with flowering time. This applies also to nectary size, nectar volume and sugar content of the perennials (9 species). All above cases of time dependence show that there is a constraint effect of Mediterranean climate on floral and nectary structure, reflected also as a decrease in nectar secretion. Nectary structure in Labiatae is largely shaped by both phylogenetic and climate constraints. On the other hand, although nectar is largely influenced by nectary structure, it is to a large extent ecologically biased, implying that, in addition to phylogeny, there are many other ecological parameters interfering in its secretion such as time within the season, life history, and light requirements.

Neighbour effects on Erica multiflora (Ericaceae) reproductive performance after clipping

The effect of interspecific competition on resprouting and reproductive success and the relationship between above-ground vegetative biomass variability and reproductive biomass variability were analysed during resprouting after clipping. For this purpose, a field experiment was performed by removing neighbours around individuals of Erica multiflora in a Mediterranean shrub community. Removal of neighbours increased the number of sprouts and the above-ground vegetative biomass of target plants. However, it did not decrease plant size variability. Neighbours decreased the likelihood of fruiting and the biomass of fruits. In target plants that had set fruits a simple allometric relationship between above-ground vegetative biomass and the biomass of fruits explained 42% of the variation in fruit biomass. The probability to set fruits at a given plant size was smaller in plants with neighbours than without neighbours. Presence of neighbours also increased the variability of fruit biomass within the population, because 50% of target plants with neighbours did not set fruits. This failure to set fruits may be related to shading, the small size of plants with neighbours, as well as a delay in development.

Bird Species Impoverishment, Niche Expansion, and Density Inflation in Mediterranean Island Habitats

The causes and consequences of three classical features of insular faunas, namely species depauperization, increased population density, and increased niche breadth, were investigated by comparing bird communities in relation to habitat characteristics along ecological successions in southern France and the island of Corsica. Each succession comprised six habitats, which were selected on the basis of vegetation structure. There were nearly as many bird species in Corsica as on the mainland in the entire successional sequence, but fewer species in the late successional forested stages and more species in shrubby stages on the island, because of the shift of many typically forest—dwelling species into matorrals (evergreen Mediterranean shrub communities). Species utilized more habitats and subdivided them less in Corsica than on the mainland. The Corsican forest bird community was composed of a few small—sized resident species with very high populations. Thus insular faunas are very different in early and late stages of succession. These results differ in several respects from those of many earlier mainland—island comparisons, and emphasize the need for comparing a series of habitats between the island and the mainland, rather than a single habitat, as has generally been the case. These differences in species allocation to habitats between the island and the mainland are better explained by two non—mutually exclusive hypotheses than by a release in interspecific competition. The first is the so—called "habitat appropriateness" hypothesis, which predicts that the more closely a habitat resembles that which is optimal for a species on the mainland, the more species will compensate for the population densities of absent competitors. This is the case for the bird communities of the Corsican forests, which exhibit the main features of an insular syndrome, i.e., species impoverishment, high population densities, and intraspecific spillover. It is suggested that given an equitable climate and a stable level of resources, survival on the island is higher than on the mainland, dispersal is restricted, and populations expand into shrubby habitats as a result of spillover from optimal habitats. This explanation is further supported by the second hypothesis, named the "defense hypothesis" (Stamps and Buechner 1985), which stipulates that a stable allocation of resources all the year around in the benign insular environment results in a decrease in the vigor of territorial defense, a decrease in territory size, and an increase in territory overlap, which in turn allows for more individuals to coexist in the same amount of space. Long—term comparative studies on the population biology of tits of the genus Parus have shown that, compared to their mainland counterparts, Corsican populations of tits exhibit social structures supporting this hypothesis. Finally, a clear distinction between communities of early and late stages of succession is discussed in the light of history and speciation patterns in the Mediterranean area. The historical approach helps to explain the convergence of bird community composition on the mainland and the island at late successional stages.

Changes in mediterranean shrub communities with Cytisus purgans and Genista scorpius

Shrub communities are important in the mediterranean landscape and linked very much with human activities. The permaneney and the spreading of these communities are related to biological characteristics of the dominant species which control the patterns of changes in structure, richness, ‘types of life forms, and ability of colonization by trees. In this paper, changes in communities are analysed and compared for Cytisus purgans and Genista scorpius (both Papilionaceae). For both communities the schemes of origin and spreading are rather the same: overgrazing and fire play a prominent role. Changes in structure show different stages emphasized by the types of distribution of the chlorophyll containing stratum. There is a direct relation between changes in structure and changes in species richness and life form spectrum: richness decreases generally from the second or third year after fire. According to the dryness of the stand therophytes may or may not be important in the youngest stands. The colonization of the shrub communities by trees is dependent on several conditions, either on the shrub community itself, or on the plant-matrix surrounding the shrub community patch and also on animals; man, too, plays an important role. In conclusion we think that the above-mentioned changes in shrub communities fit the ‘inhibition’ model proposed by Connell & Slatyer (1977); but, more generally it seems that the plant successions observed in our regions follow both, this model and the ‘facilitation’ and ‘tolerance’ models of the same authors. Linked with this fact, it seems that the successions show generally fluctuating values of richness as is suggested by Whittaker (1975). We think that plant succession must be well analyzed at different levels of organization and include the study of the influences man and animals may have.