Stomatal patchiness in Mediterranean evergreen sclerophylls

Midday depression of net photosynthesis and transpiration in the Mediterranean sclerophylls Arbutus unedo L. and Quercus suber L. occurs with a depression of mesophyll photosynthetic activity as indicated by calculated carboxylation efficiency (CE) and constant diurnal calculated leaf intercellular partial pressure of CO₂ (C_i). This work examines the hypothesis that this midday depression can be explained by the distribution of patches of either wide-open or closed stomata on the leaf surface, independent of a coupling mechanism between stomata and mesophyll that results in a midday depression of photosynthetic activity of the mesophyll. Pressure infiltration of four liquids differing in their surface tension was used as a method to show the occurrence of stomatal patchiness and to determine the status of stomatal aperture within the patches. Liquids were selected such that the threshold leaf conductance necessary for infiltration through the stomatal pores covered the expected diurnal range of calculated leaf conductance (g) for these species. Infiltration experiments were carried out with leaves of potted plants under simulated Mediterranean summer conditions in a growth chamber. For all four liquids, leaves of both species were found to be fully infiltratable in the morning and in the late afternoon while during the periods leading up to and away from midday the leaves showed a pronounced patchy distribution of infiltratable and non-infiltratable areas. Similar linear relationships between the amount of liquid infiltrated and g (measured by porometry prior to detachment and infiltration) for all liquids clearly revealed the existence of pneumatically isolated patches containing only wide-open or closed stomata. The good correspondence between the midday depression of CE, calculated under the assumption of no stomatal patchiness, and the diurnal changes in non-infiltratable leaf area strongly indicates that the apparent reduction in mesophyll activity results from assuming no stomatal patchiness. It is suggested that simultaneous responses of stomata and mesophyll activity reported for other species may also be attributed to the occurrence of stomatal patchiness. In Quercus coccifera L., where the lack of constant diurnal calculated C_i and major depression of measured CE at noontime indicates different stomatal behavior, non-linear and dissimilar relationships between g and the infiltratable quantities of the four liquids were found. This indicates a wide distribution of stomatal aperture on the leaf surface rather than only wide-open or closed stomata.Dedicated to Professor Otto L. Lange on the occasion of his 65th birthday     

Response of broadleaved evergreen Mediterranean forest vegetation to fire disturbance during the Holocene: insights from the peri-Adriatic region

Aim To test whether fire contributed to the expansion and compositional change of evergreen forests in the Mediterranean region during the Holocene. Location The peri‐Adriatic region, encompassing the Italian peninsula, Sicily and the western and southern Balkans between latitudes 46° and 37° N. Methods New high‐resolution pollen and microscopic charcoal data from Lago dell’Accesa (Tuscany, Italy) were used to estimate the response of the evergreen oak, Quercus ilex L., to fire during its expansion phase at 8500 cal. yr bp . The data were compared with the pollen and charcoal series from other Mediterranean sites (Lago di Massaciuccoli in Tuscany, Malo Jezero in Croatia, Biviere di Gela in Sicily) and analysed using numerical techniques (redundancy analysis, detrended canonical correspondence analysis) to identify long‐term fire–vegetation linkages and the degree of compositional change. Results Microscopic charcoal and pollen of evergreen oaks were negatively correlated during the period of quasi‐natural fire regime (Mesolithic, 10,000–8000 cal. yr bp ). In addition, there was no such positive correlation during periods when the fire regime was potentially more influenced by people (Neolithic–Bronze Age, 8000–3000 cal. yr bp ). Compared with inland sites, coastal sites that are currently located at a distinct ecotone showed more compositional change. Main conclusions The analyses suggest that climatic change, without an additional effect of fire regimes, favoured the expansion and compositional change of evergreen forests across the peri‐Adriatic region. Strikingly different patterns occurred along a north–south gradient. In the north (Tuscany and Croatia, meso‐Mediterranean belt), Q. ilex replaced deciduous forests when conditions became drier; in the south (Sicily, thermo‐Mediterranean belt) the species replaced maquis or steppe vegetation when climatic conditions became moister. We conclude that the projected increase in fire activity may lead to the loss of most of the remaining relict forests of Q. ilex in southern Europe.     

Allozyme characterisation of four Mediterranean evergreen oak species

Polymorphism at 11 enzyme loci was used to compare the four evergreen oak species of the Mediterranean Basin and to establish their taxonomical relationships. As a comparison, two evergreen oak species from Tibet, located in the primary distribution area of evergreen oaks, were analysed at the same loci. Cladistic analyses led to the separation of a cluster of four species, namely the three Mediterranean Q. ilex, Q. coccifera and Q. alnifolia and the Tibetan Q. aquifolioides. The other Tibetan species, Q. semicarpifolia, and Q. suber, from the Western Mediterranean Basin, were very distinct genetically from the four other species. These results were not consistent with previous taxonomical treatment, based on morphology alone, which classified Q. ilex and Q. coccifera in “ilex group” (=subgenus Sclerophyllodrys O. Schwartz), and the other four species in “cerris group” (subgenus Cerris, according to Schwartz). Allozyme variation has thus provided useful information to clarify the taxonomy of evergreen oaks.     

Successional trends in standing dead biomass in Mediterranean basin species

Question: Landscape models of fire occurrence in ecosystems assume that the time since the last fire determines vegetation flammability by enabling the accumulation of dead biomass. In this study we ask if Mediterranean basin shrublands respond to these models or, on the contrary, if initial successional stages in these ecosystems could be more flammable than later stages. Location: Mediterranean shrubland in the Valencia region, eastern Spain. Methods: Using different stages of vegetation development (5, 9, 14 and 26 years since the last fire), we first study the structural comiosition of the above‐ground biomass in 375 individuals of nine woody species. Then, we measure how the standing dead biomass varies during succession, taking into account the surface cover of each species and the quantity of total dead biomass accumulated in different successional stages (3, 9, 14 and 26 years since the last fire). Results: The largest amount of standing dead biomass at the plant community level is observed in the middle stages of the succession. Early successional species, such as Cistus spp., Ulex parviflorus and Pinus halepensis, have a higher percentage of standing dead biomass at earlier stages in the succession than species typical of later successional stages, e.g. Juniperus oxycedrus, Quercus coccifera and Quercus ilex. Conclusions: The results suggest that monotonic increase in fire hazard with increasing stand age is not necessarily the rule in Mediterranean basin shrublands, since early successional species may accumulate large amounts of standing dead biomass and thus promote fire at early successional stages.     

常绿阔叶林下石生藓类对森林植被发育的影响

为探讨石生藓类在森林植被稳定性、完整性维持中的作用,分析了浙江龙王山常绿阔叶林5种异质性生境缀块中石生藓藓丛维管植物的分布格局．结果表明,藓丛维管植物组成及分布受藓丛生长态势、蓄土持水能力及生境干扰程度等众多因子的综合影响．缀块1、5原生生境保持较好,藓丛平均厚度、干重、最大持水量、蓄土量以及土壤自然吸湿率等显著高于遭受不同程度干扰的缀块2、3、4,如藓丛平均厚度排序为缀块5(2．2cm)>缀块1(2．0cm)>缀块2(1．5cm)>缀块3(1．1cm)>缀块4(0．9cm),藓丛维管植物种数排序为缀块5(16)>缀块1(14)>缀块3(9)>缀块2(8)>缀块4(7),藓丛维管植物盖度排序为缀块3(30．0％)>缀块1(28．5％)>缀块5(26．5％)>缀块2(17．0％)>缀块4(4．5％)．认为在森林被发育过程中,林下石生藓类具有涵养水分、蓄积土壤、截留枯落物、富积养分、溶蚀岩面及成土等功能,对改良林下岩面生境条件具有重要作用．有利于森林维管植物更新,对森林植被范围拓展及各类干扰地植被恢复与保持具有积极意义．     

Effects of grazing on geophytes in Mediterranean vegetation

Abstract. The response of geophyte species diversity and frequency of individual geophyte species to cattle grazing was measured at 68 site pairs along fences separating ungrazed from grazed grassland and woodland on different geological formations in northern Israel. Over all site pairs, geophyte species density per 4 m² was significantly greater in grazed (2.37) than in protected (1.96) sites of the same site pair. There was considerable variation between site pairs in the magnitude and in the direction of the grazing effect. Part of this variation could be explained by differences in site altitude and in geological formation. The positive effect of grazing on geophyte diversity was lower in sites with low productivity. Of 22 geophyte taxa for which sufficient data were available, nine indicated greater frequency in grazed sites compared to only two in ungrazed sites. In 11 other taxa the response was not consistent. A positive response to grazing was most common in geophytes with narrow leaves of the Iridaceae, Liliaceae and allied families. Conservation of the entire geophyte flora in Mediterranean vegetation requires livestock grazing at moderate to high intensities in parts of the area of each community, and light or no grazing in other parts.     

常绿阔叶林植被动态研究进展

常绿阔叶林是亚热带地区的地带性植被,是亚热带陆地生态系统的重要组成部分,几十年来,中国的植物学家、生态学家对常绿阔叶林的区系成分、物种组成、外貌和结构、动态以及作为生态系统成员的功能等方面进行了大量的研究,积累了丰富的资料,取得了大量的研究成果,同时也在四川缙云山、浙江天童山、广东省鼎湖山和黑石顶、云南哀牢山、福建武夷山逐步形成了中国各具区域特色的常绿阔叶林研究基地,为常绿阔叶林的研究作出了突出的贡献。在常绿阔叶林的演替方面,研究内容从研究常绿阔叶林群落演替的过程、群落组成变化、结构动态及模型逐步向生态系统物质循环和能量流动发展,但对常绿阔叶林主要优势种动态、生理生态和群落演替机理等方面深入不够。在常绿阔叶林的更新动态研究方面,不但进行了通过研究种子雨和种子库的动态、种子的萌发、幼树生长的时空动态研究群落的更新,而且还通过研究林窗的形成、特征及其在森林动态中的作用来研究群落的更新,还进一步通过对常绿阔叶林主要树种更新植株的生理生态特性的研究来解释群落更新的原因。在常绿阔叶林退化和恢复重建研究方面,研究了常绿阔叶林各种退化生态系统的特征和恢复过程等,并将已有的理论和技术应用于退化生态系统的恢复和重建。即是以前人研究的成果为基础,从群落的演替、更新、退化和恢复等方面对我国多年来常绿阔叶林植被动态的研究作一总结。根据国内外的研究趋势提出了常绿阔叶林的动态方面急需开展3s技术在常绿阔叶林上的应用研究、常绿阔叶林的退化的生理生态机制、常绿阔叶林起源与系统发育、常绿阔叶的林保护与恢复生态学、常绿阔叶林重要物种的生理生态学和种群生物学、常绿阔叶林生态服务功能与区域可持续发展模式以及常绿阔叶林生态系统对全球变化的作用与响应机制等方面的研究。     

Post-fire bryophyte dynamics in Mediterranean vegetation

Abstract. Bryophyte dynamics after fire in the Mediterranean macchia of Southern Italy was studied both by diachronic and synchronic approaches. Changes of bryophyte cover and species composition were found in relation to both age and fire intensity. During the first 2 yr after fire, bryophytes dominated the plots which had experienced the highest fire intensity while herbs were dominant in plots affected by lighter fires. Pioneer species, such as Funaria hygrometrica, Barbula convoluta and Bryum dunense, characterized recent intense fires, whereas Bryum torquescens, B. radiculosum and B. ruderale were dominant after less intense burning. Pleurochaete squarrosa, Tortula ruraliformis and Tortella flavovirens dominated intermediate successional stages. Pleurocarpous mosses were dominant only in the older closed stands. Different patterns of regeneration strategies were described: spores dominated early stages of intense fire, while vegetative propagules characterized later successional stages and less severely burned areas. Although bryophytes usually have a low abundance in Mediterranean vegetation, their role in post-fire vegetation dynamics may be locally enhanced according to burning conditions.     

Increasing drought decreases phosphorus availability in an evergreen Mediterranean forest

Mediterranean ecosystems are water-limited and frequently also nutrient-limited. We aimed to investigate the effects of increasing drought, as predicted by GCM and eco-physiological models for the next decades, on the P cycle and P plant availability in a Mediterranean forest. We conducted a field experiment in a mature evergreen oak forest, establishing four drought-treatment plots and four control plots (150 m² each). After three years, the runoff and rainfall exclusion reduced an overall 22% the soil moisture, and the runoff exclusion alone reduced it 10%. The reduction of 22% in soil moisture produced a decrease of 40% of the accumulated aboveground plant P content, above all because there was a smaller increase in aerial biomass. The plant leaf P content increased by 100 ± 40 mg m⁻² in the control plots, whereas it decreased by 40 ± 40 mg m⁻² in the drought plots. The soil Po-NaHCO₃ (organic labile-P fraction) increased by 25% in consonance with the increase in litterfall, while the inorganic labile-P fraction decreased in relation to the organic labile-P fraction up to 48%, indicating a decrease in microbial activity. Thus, after just three years of slight drought, a clear trend towards an accumulation of P in the soil and towards a decrease of P in the stand biomass was observed. The P accumulation in the soil in the drought plots was mainly in forms that were not directly available to plants. These indirect effects of drought including the decrease in plant P availability, may become a serious constraint for plant growth and therefore may have a serious effect on ecosystem performance.     

Restoration of alpine spoil heaps: Successional rates predict vegetation recovery in 50 years

Human disturbances in the alpine region can have long-lasting ecosystem effects because biological recovery in harsh environments proceeds slowly. As a by-product of the exploitation of hydroelectricity, surplus masses from tunnel excavations are deposited as spoil heaps in the alpine landscape. The typical management goal for such spoil heaps is that their species composition converges towards that of their undisturbed surroundings. At present we lack knowledge of the rate as well as the direction of these successions. We examined the species composition of five alpine spoil heaps in western Norway at two points in time, after 6-16, and 24-34 years of succession, with regard to vegetation cover, species richness, species composition and soil conditions. We also compared the vegetation of spoil heaps with that of their surroundings. After ca. 30 years, bryophyte and lichen cover and species richness were similar to those of their surroundings, while cover of vascular plants and species richness recovered more slowly. The vegetation development of spoil heaps appears safe-site limited rather than dispersal limited. Topsoil development was slow, but some accumulation of organic matter was observed. The species composition followed a successional trajectory in direction of the vegetation of the surroundings. Estimated linear successional rates indicate that 35-48 years are needed from construction of spoil heaps till a species composition more or less similar to their surroundings has been reached. However, these estimates are likely to be over-optimistic because successional rates tend to decrease with time. Based on our results we propose three changes to the current spoil-heap construction practice that will improve their restoration: (1) to increase surface unevenness, by which the number of safe sites will increase and germination and establishment success will be enhanced; (2) to increase substrate variability, by adding more of fine-grained materials more species will establish in shorter time; and (3) to use seed from local sources or to let the spoil heaps regenerate naturally.     

Modelling the drought impact on monoterpene fluxes from an evergreen Mediterranean forest canopy

In many ecosystems drought cycles are common during the growing season but their impact on volatile monoterpene emissions is unclear. Therefore, we aimed to develop and evaluate a process-based modelling approach to explore the explanatory power of likely mechanisms. The biochemically based isoprene and monoterpene emission model SIM-BIM2 has been modified and linked to a canopy model and a soil water balance model. Simulations are carried out for Quercus ilex forest sites and results are compared to measured soil water, photosynthesis, terpene-synthase activity, and monoterpene emission rates. Finally, the coupled model system is used to estimate the annual drought impact on photosynthesis and emission. The combined and adjusted vegetation model was able to simulate photosynthesis and monoterpene emission under dry and irrigated conditions with an R ² of 0.74 and 0.52, respectively. We estimated an annual reduction of monoterpene emission of 67% for the extended and severe drought period in 2006 in the investigated Mediterranean ecosystem. It is concluded that process-based ecosystem models can provide a useful tool to investigate the involved mechanisms and to quantify the importance of specific environmental constraints.     

Contrasted Successional Trajectories in a Mediterranean Wetland Due to Geomorphic- and Human-Induced Perturbations

Ecosystems - Wetland ecosystems in water-limited environments locally boost biotic interactions, habitat diversity, and species concentrations, but little knowledge exists on their long-term...     

Evolutionary trends in Mediterranean flora and vegetation

Summary The vegetation of the Mediterranean Basin was originally composed of evergreen forests; during the Pleistocene deciduous forests expanded, chiefly in the mountains. In historical time the forest belt was strongly reduced by human activity and substituted by anthropogenous vegetation types (macchia, garigue, weed-communities). The frequency of polyploids in the present vegetation types support this interpretation. Reciprocal relationships between the vegetational system and social system are discussed and a terminology is proposed. During ancient times and the middle ages a reciprocal control of vegetation and human activity was possible (cyclic system), stabilizing the vegetation in a steady state; the technological impact modified these conditions in a linear sense, and now the vegetation is menaced by irreversible changes.Contribution to the Symposium on Plant species and plant communities, held at Nijmegen, 11–12 November 1976, on the occasion of the 60th birthday of Professor Victor Westhoff.     

Fast growth involves high dependence on stored resources in seedlings of Mediterranean evergreen trees

Background and Aims Extreme climatic events such as severe droughts are expected to increase with climate change and to limit grassland perennity. The present study aimed to characterize the adaptive responses by which temperate herbaceous grassland species resist, survive and recover from a severe drought and to explore the relationships between plant resource use and drought resistance strategies.Methods Monocultures of six native perennial species from upland grasslands and one Mediterranean drought-resistant cultivar were compared under semi-controlled and non-limiting rooting depth conditions. Above- and below-ground traits were measured under irrigation in spring and during drought in summer (50 d of withholding water) in order to characterize resource use and drought resistance strategies. Plants were then rehydrated and assessed for survival (after 15 d) and recovery (after 1 year).Key Results Dehydration avoidance through water uptake was associated with species that had deep roots (>1·2 m) and high root mass (>4 kg m⁻³). Cell membrane stability ensuring dehydration tolerance of roots and meristems was positively correlated with fructan content and negatively correlated with sucrose content. Species that survived and recovered best combined high resource acquisition in spring (leaf elongation rate >9 mm d⁻¹ and rooting depth >1·2 m) with both high dehydration avoidance and tolerance strategies.Conclusions Most of the native forage species, dominant in upland grassland, were able to survive and recover from extreme drought, but with various time lags. Overall the results suggest that the wide range of interspecific functional strategies for coping with drought may enhance the resilience of upland grassland plant communities under extreme drought events.     

Late Quaternary planktonic foraminiferal biostratrigraphy,Strait of Sicily,Mediterranean Sea

The development of a detailed planktonic foraminiferal biostratigraphy for the Late Quaternary (latest 180,000 years) has allowed the dating and correlation of sediments from the Strait of Sicily. Principal component analysis of the assemblages has extracted a climatic history similar to that based upon oxygen isotopic oscillations. Intercore correlations are supported by tephrochronology and sapropel layer stratigraphy. Identification of Termination IA and IB in several high sedimentation rate cores indicates that the Mediterranean Sea experienced a two-stage warming during the last deglaciation. Cores collected between water depths of 200 and 600 m contain an erosional hiatus near their tops, reflecting an increase in the Levantine Intermediate Water flow sometime since 25,000 years B.P. and as recently as 7000 years B.P., during deposition of the youngest sapropel layer. A distinct and unusual planktonic foraminiferal succession is associated with sapropel layers. This begins in a protosapropel layer immediately beneath a sapropel horizon and continues upwards to the immediately overlying oxidized layer.     

Relationship between net photosynthesis and leaf respiration in Mediterranean evergreen species

The relationship between net photosynthetic (P _N) and leaf respiration (R) rates of Quercus ilex, Phillyrea latifolia, Myrtus communis, Arbutus unedo, and Cistus incanus was monitored in the period February 2006 to February 2007. The species investigated had low R and P _N during winter, increasing from March to May, when mean air temperature reached 19.2 °C. During the favourable period, C. incanus and A. unedo had a higher mean P _N (16.4±2.4 μmol m⁻² s⁻¹) than P. latifolia, Q. ilex, and M. communis (10.0±1.3 μmol m⁻² s⁻¹). The highest R (1.89±0.30 μmol m⁻² s⁻¹, mean of the species), associated to a significant P _N decrease (62 % of the maximum, mean value of the species), was measured in July (mean R/P _N ratio 0.447±0.091). Q₁₀, indicating the respiration sensitivity to short-term temperature increase, was in the range 1.49 to 2.21. Global change might modify R/P _N determining differences in dry matter accumulation among the species, and Q. ilex and P. latifolia might be the most favoured species by their ability to maintain sufficiently higher P _N and lower R during stress periods.     

Revision of the central Mediterranean xerothermic cliff vegetation

Questions

What are the syntaxonomic and synchorological patterns of the xerothermic chasmophytic vegetation in the central part of the Mediterranean Basin? What are the diagnostic species of the high‐rank syntaxa of Asplenietalia glandulosi, Onosmetalia frutescentis and Centaureo dalmaticae‐Campanuletalia pyramidalis?

Location

Mediterranean coastal and subcoastal areas of southern France, Italy, Malta, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania and of mainland Greece.

Methods

The data set of 1,261 published relevés was analysed using hierarchical clustering (Flexible Beta method), involving a series of data transformations. Indicator species analysis was used to select the best dendrogram solution and identify diagnostic taxa of the main clusters. The dendrogram was interpreted from a syntaxonomic point of view, using nomenclatural type relevés as a basis. The NMDS ordination was performed in order to visualize the floristic relationships among associations and high‐rank syntaxa. MRPP was used to test for differences among alliances.

Results

The classification revealed four main clusters of relevés representing the chasmophytic vegetation of southern France, Sardinia and the northwestern part of Italy (Asplenienalia glandulosi/Asplenietalia glandulosi), the southwestern part of Italy and Malta (Tinguarrenalia siculae/Asplenietalia glandulosi), the Adriatic Basin area (Centaureo dalmaticae‐Campanuletalia pyramidalis) and the southern Balkans (Onosmetalia frutescentis). The NMDS ordination confirmed the overall pattern, while MRPP showed significant differences among the alliances of the above‐mentioned orders and suborders. The lists of diagnostic taxa of the high‐rank syntaxa were revised according to a supra‐national perspective.

Conclusions

The new syntaxonomic scheme provides a comprehensive overview of the chasmophytic vegetation of the central part of the Mediterranean Basin. This scheme mostly matches the recently published EuroVegChecklist, but also exhibits important novelties concerning the syntaxonomic position of some alliances (Dianthion rupicolae, Centaureion pentadactyli, Arenarion bertolonii and Caro‐Aurinion), and the floristic and chorological relationships among high‐rank syntaxa, with new revised sets of diagnostic taxa. This revision might be useful for further small‐scale phytosociological studies.