Recovery from clearing,cyclone and fire in rain forests of Tonga,South Pacific: Vegetation dynamics 1995–2005

Abstract In late 2001 a category 3 cyclone impacted forest plots that were established in Tonga in 1995, and additionally, one plot was accidentally burned by an escaped land‐clearing fire. Subsequent surveys provide observations of 10 years of forest dynamics in this poorly studied region, and the first reported observations of large interannual variation in juvenile (seedling and sapling) abundance in the western tropical Pacific. The severely disturbed (burned) plot was initially colonized by a non‐native early pioneer, Carica papaya L., but 3.5 years later a native pioneer, Macaranga harveyana (Muell. Arg.) Muell. Arg., was the most abundant tree species. The seedling layer included some long‐lived pioneers and shade‐tolerant species. Two mature forest plots affected only by the cyclone changed very little over a decade. Late‐successional shade‐tolerant species that dominated the overstory were also abundant as seedlings and saplings. This is in contrast with a 30‐ to 40‐year‐old, formerly cultivated, secondary forest plot that still shows no recruitment of late‐successional dominants, in spite of the proximity of remnant forest patches. This study suggests differing pathways of succession following shifting cultivation versus cyclone and fire disturbances in Tonga. Land use legacies appear to have a long‐lasting effect on community composition.     

Assessing the response of open-habitat bird species to landscape changes in Mediterranean mosaics

In Mediterranean landscapes, wildfires and land abandonment lead to major landscape modifications primarily by favouring the presence of open, shrub-like habitats. At present, we know very little of how these changes affect patterns of species occurrence at the landscape scale. In this work, we analyse the impact of these landscape changes on the occurrence patterns of eight open-habitat species by using presence/absence data collected in the Catalan Breeding Bird Atlas (NE Spain). We compared the species occurrence patterns along habitat gradients for three different landscape settings: a semi-permanent farmland–forest landscape (i.e. with variable proportions of farmland and forests) and two landscape settings which mimic those favoured by land abandonment and fire: farmland–shrubland landscapes and mosaic landscapes (i.e. variable proportions of farmland and forest coexisting with a shrubby matrix). In the forest–farmland landscape, we found a dominant negative effect of adjacent forest on species occurrence rates. This overall effect mostly disappeared in farmland–shrubland landscapes composed by two habitats with more similar vegetation structure. In mosaic landscapes, the general negative effect of forest habitats also appeared to be partially compensated by the presence of a shrubby matrix. Our results suggest that landscape gradients induced by fire and to some degree also land abandonment, mainly favouring availability of shrublands may potentially enhance the resilience of threatened open-habitat species at the landscape scale by increasing the range of potential habitats used. The analysis of species-occurrence patterns along predefined habitat gradients appears as a useful tool to predict potential species responses to land use change.     

Structural and floristic diversity of shrublands and woodlands in Northern Israel and other Mediterranean areas

Summary Between 1974 and 1978 structure and diversity of shrublands and woodlands of northern Israel were studied along climatic and human-disturbance gradients using 0.1 ha vegetation samples. Diversity increased along the moisture gradient, with highest woody and herb species richness in open Pistacia shrubland on the xeric border of the Mediterranean region, and highest equitability and lowest dominance concentration in sub-humid, moderately grazed, open oak woodlands. Semi-open disturbed shrublands were rich in herbs and had much higher structural, plant species, and animal species diversities than the closed, mature, climax maquis. Diversity showed a two-slope response to grazing with highest species numbers in heavily (but not the most severely) grazed woodlands and shrublands. These communities have some of the highest plant alpha diversities in the world; the richness of their floras (especially in annual plants) is the product of relatively rapid evolution under stress by drought, fire, grazing, and cutting.Comparative data on diversity and growth-form composition are compiled for mediterranean communities: Israeli' shrublands and woodlands, California chaparral and woodlands, Chilean matorral, South African fynbos, and Australian heath and mallee. Communities of three of these areas are of more recent (primarily Pleistocene) development and share some similarities; these threc form a sequence (California, Chile, and Old World Mediter-ranean) of increasing length of human disturbance and consequent species diversity. The southwest Australian heath or kwongan and the South African fynbos are, in contrast, derived from ancient Gondwanan heath like communities and are adapted to very old, nutrient-poor soils. The Gondwanan communities are quite different in growth-form structure and soil and nutrient relationships from communities of the three more recent mediterranean areas; the Gondwanan communities are almost lacking in annual species and are exceedingly rich in woody species. The richest temperate plant communities known — grazed Mediterranean pastures vs. fynbos and Australian heath — are in almost polar contrast in their growth-form structures and the bases of their species diversities.This study, sponsored by the U.S.-Israel Binational Science Foundation (No. 450), was carried out by Z. Naveh as principal investigator with R.H. Whittaker as American collaborator. We thank Mr. A. Mann, S. Burmil, Mrs. Chaim, and Mrs. A. Kleen for botanical field work and statistical computations, Mr. D. Feigin and S. Ben Ezrah for technical assistance, Mr. S. Asherow for identification of young plants, and the Nature Reserve Authorities, the Neve Yaar Experimental Station, the Agricultural School Kfar Hanoar Hadati, and Kibbutzim Allonim and Allone Abba for allowing us to use their land for this study. The work by R.H. Whittaker was supported by the U.S. National Science Foundation, Australian National University, and Canberra Botanic Gardens; and we thank all the collaborators in this work.Nomenclature follows Zohary et al. (1948).     

Landscape dynamics and their effect on the functional connectivity of a Mediterranean landscape in Chile

Land use and cover changes have been identified as a major factor contributing to shape landscape structure and biodiversity patterns, particulary in areas with a long history of human occupation and habitat fragmentation, such as the Mediterranean landscapes. However, the existing studies on landscape change indicators for Mediterranean areas have mostly focused in Europe, while for other Mediterranean zones, and especially for South America, there is a serious lack of knowledge concerning the impact of landscape dynamics on ecological processes. Further research on this topic is urgently needed, given the high biodiversity levels and the rapidly increasing rates of human modification in the Mediterranean landscapes of South America. For this purpose, we investigated the dynamics of a landscape in the semiarid region of the Mediterranean zone of Chile, and measured the effect of those dynamics on functional connectivity, during a period of about four decades (1975–2011). Landscape connectivity indicators were extracted from a series of Landsat images. The Equivalent Connnected Area index (ECA) was used as indicator of connectivity trends, and was evaluated for three representative distances of seed dispersal in the study area (150 m, 500 m and 1000 m). In addition, the patches that most contribute to maintain the present connectivity, and their roles as connectivity providers, were identified through a set of commensurable indicators: betweenness centrality and the fractions (intra, flux connector) of the Integral Index of Connectivity. We found that these indicators were useful to detect and summarize a number of previously unreported trends in these Mediterranean landscapes. First, population growth and economic development were compatible with an increase in functional connectivity for forest habitats, mainly because the abandonment of marginal agricultural lands and their subsequent conversion to espinals (Acacia caven) triggered vegetation succession towards secondary forests. Second, increased forest connectivity was not associated to a decrease in the characteristic heterogeneity of Mediterranean landscapes. Third, many patches of espinal, despite being commonly regarded as of poor conservation value, were crucial to promote connectivity by acting as stepping stones among other patches with higher habitat quality. The approach here presented provides a combined assessment of landscape structure, function and change that should be valuable and applicable to deliver operational indicators in dynamic landscapes in South America and other Mediterranean regions.     

Vegetation dynamics in north-western Mediterranean regions: Instability of the Mediterranean bioclimate

Abstract

Pollen and plant macrofossil records from a selection of sites in Spain, France and Italy are used to explore the origin and the development of the Mediterranean vegetation. The role of evergreen and summergreen taxa is discussed. The expansion of sclerophyllous trees during the Pleistocene interglacials is well correlated with the orbital forcing. During the Holocene, the large number of data illustrates latitudinal and longitudinal differences in vegetation dynamics. Multidisciplinary studies identify short terms climatic fluctuations. The debate is still open between those who attribute an increase of sclerophyllous forests during the late Holocene to a trend toward aridity and those who consider this dynamic as human-induced.     

Variation in the riparian landscape of the Segura River Basin,SE Spain

Abstract. The woody and shrubby riparian vegetation of the Mediterranean Region of Spain shows a progressive displacement from the Querco-Fagetea, typical of Central Europe, towards the Nerio-Tamaricetea, which has its maximum expression in North Africa. We studied the occurrence of 107 riparian plant communities on 52 locations in the Segura River Basin (SE Spain) and their presumed relation to variation in rainfall and temperature. On the basis of agglomerative clustering and Redundancy Analysis (RDA) three riparian vegetation complexes were identified and characterized by (a) Central European-related temperate communities, (b) predominantly North African riparian communities and (c) a combination of both community types, respectively. North African communities predominated in the lower stretches of the Segura Basin, probably due to the prevailing semi-arid bioclimate.     

Holocene climatic changes in the Western Mediterranean, from south-east France to south-east Spain

Holocene climatic changes along coastal regions from south-east France to south-east Spain were studied using pollen ratios. Comparing modern pollen rain, vegetation and climate along selected transects from the Atlantic Ocean to the Mediterranean, we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects. These pollen ratios and threshold values were employed to characterize the Holocene climatic changes from nine Mediterranean coastal sites. The results were compared with data from marine and continental pollen sequences distributed in the western Mediterranean basin, and with additional regional data independent of human activity: lake-level fluctuations, alpine glacier advance and retreat chronology, ¹⁴C anomaly and cooling phases in Eastern France and Central Europe. The role of anthropogenic activities and climate on the changes in vegetation is discussed. Six major changes in vegetation cover were identified. They correspond to aridification phases that occurred around 9500–9000 yr BP (10 900–9700 cal BP), 7500–7000 yr BP (8400–7600 cal BP), 4500–4000 yr BP (5300–4200 cal BP), 3700–3300 yr BP (4300–3400 cal BP), 2600–1900 yr BP (2850–1730 cal BP) and 1300–1000 yr BP (1300–750 cal BP). These arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover. Humans undoubtedly enhanced the vegetation changes, but none the less had to adapt to these new climatic conditions.     

Vegetation patterns and their dependency on site conditions in the pre-industrial landscape of north-eastern Japan

We reconstructed the vegetational landscape of the pre-industrial era (the beginning of the twentieth century) in north-eastern Japan, and estimated the distribution patterns of traditional land-uses, as suggested from the vegetation. We found significant correspondence between the spatial patterns of vegetational landscape and site attributes, and hypothesized the underlying mechanisms. The study area was classified into three vegetation types: grasslands, secondary forests and old-growth forests. It was determined that the grasslands were formed and maintained by burning; secondary forests were derived from either charcoal woods or forests recovered on abandoned grasslands; and old-growth forests had suffered the least anthropogenic disturbance. Each past vegetation type showed significant dependency on site attributes such as altitude, slope angle, slope aspect, hydrological topography and distance from the nearest human habitation. The relative importance of these site attributes varied depending on the vegetation type. Grasslands and old-growth forests, which were the most and the least disturbed sites in the study area, respectively, showed clear contrasts in their dependencies especially on the slope aspect and on elevation. These site attributes were thought to have had influences on each vegetation type by determining the inflammability of the site. Satellite photographs indicated that north-facing valleys had been relatively wet throughout the fire-prone spring season. Hence, these areas would have been free from frequent fire, and more likely to preserve old-growth forests. Ground wetness in spring was thought to be the underlying factor determining the contrasts in past vegetation and land-use patterns in the area.An erratum to this article can be found at     

Land‐use and fire history effects on post‐fire vegetation dynamics in eastern Spain

Question: Is post‐fire, medium‐term vegetation dynamics determined by land‐use or fire history prior to fire? Location: South‐facing slope in the Gallinera valley, Alicante province, eastern Spain. Methods: After mapping the land‐use and fire history of the study site using photo‐interpretation, we sampled vegetation structure on a set of plots representing the most frequent land‐use and fire history combinations on an area burned six years before sampling. We studied the effects of land‐use history, comparing the one‐fire land‐use trajectories. We analysed the effects of fire history; comparing one‐ and two‐fire plots for both previously cropped and uncropped areas. Results: Most variables were not significantly different between the earliest abandoned plots (abandoned at least 38 years before the fire) and the uncropped plots. On the most recently abandoned plots (abandoned between one and four years before the fire), the therophyte richness and the ratio of seeder: resprouter richness were significantly greatest. Different fire recurrences did not determine different post‐fire vegetation on either the uncropped or the early abandoned plots (all dominated by fire‐recruited seeder shrubs). The most recently abandoned plots had a lower resilience to fire. Conclusions: Land‐use history and recent pre‐fire land use, in particular, determined the post‐fire vegetation in the medium term. The vegetation composition converged during secondary succession among land‐use histories. Increasing fire recurrence had a small effect on mature plant communities, due to the combination of life‐history traits determining the response to fire of the dominant species.     

Indicators of landscape organization and functionality in semi-arid former agricultural lands under a passive restoration management over two periods of abandonment

Abandoned lands previously used for agricultural purposes may constitute an opportunity for understanding the variables involved in the restoration of native ecosystems over time. In this study, we assessed the functional status of an abandoned farmland currently used for conservation, using a methodology based on indicators of landscape organization and soil surface. We analyzed changes in plant cover, patch and interpatches structure and several soil surface properties during two periods of land abandonment (less and more than 40 years). Using this methodology, we characterize the potential of the ecosystem to capture and transfer resources, and the state of functional properties such as infiltration capacity, soil stability and nutrient cycling.We detected a significant development of the shrub layer and an increase of the number, type and area occupied by vegetated patches in old fields. The contribution of vegetated patches to the recovery of stability, infiltration and nutrient functions was significant at the local scale. Nonetheless, when analyzing the landscape as a whole only the nutrient cycling index was significantly higher in old fields. The lack of improvement of the stability and infiltration in old fields can lead to further degradation and indicates that even though vegetation cover may have improved over time in old fields, the current cover might not be enough to prevent further degradation by erosion. Our results reinforce the importance of using functionality indexes in future studies focused on adequate restoration measures to protect the function of desert ecosystems, especially when aimed for biodiversity conservation. Hence, the use of monitoring systems based on organization and function indicators is a useful tool to represent the current state and potential recovery of previously disturbed ecosystems, provided that the time scale is taken into account.     

Phenology of Mediterranean woody plants from NE Spain: Synchrony,seasonality, and relationships among phenophases

Plant phenological studies in the Mediterranean have traditionally focused on the limits that summer drought exerts over plant seasonal behaviour. However, Mediterranean areas also occur across extensive regions under cooler climates. Here, we analyse phenological data of Mediterranean woody species from winter-cold sites to address the following questions: what is the most limiting period of the year for phenological development? How, and how synchronously, do different phenophases adjust to the bimodal limitation of summer drought and winter cold? How ample is the suit of phenological strategies that are successful for Mediterranean phanaerophytes from cool areas?     

A comparative study of Cistus ladanifer shrublands in Extremadura (CW Spain) on the basis of woody species composition and cover

The ecological structure and diversity of woody species in the Cistus ladanifer shrubland (jaral), one of the most widespread Mediterranean scrub systems in the western half of the Iberian Peninsula, was studied in Extremadura (CW Spain). 57 points were sampled for presence/absence and abundance (line interception) of woody species. Several diversity indices were calculated to elucidate the role of both C. ladanifer and bare soil in the jaral structure. The sites were classified by agglomerative hierarchical clustering and ordinated by Principal Component Analysis (PCA). Most of the examined scrubs have diversity within the range 1–3, evenness above 0.5 and species richness between 1 and 12. Clustering and PCA distinguished three groups of scrubs: A, those with a certain Atlantic influence and highest values of diversity and total cover, in which Lavandula stoechas subsp. luisieri, Erica umbellata and Halimium ocymoides are frequent; B, the most continental scrubs, growing on moderately acid soils with Cistus salvifolius and C. crispus, and, C, those as continental as group B but on more acid soils, characterized by Genista hirsuta. Differential species between groups basically coincide with those used in phytosociological classifications. Diversity data, together with affinity and PCA analyses, emphasize that the ecological structure of Mediterranean shrublands is strongly influenced by humidity and the annual temperature range.     

Effects of decadal experimental drought and climate extremes on vegetation growth in Mediterranean forests and shrublands

Increased drought combined with extreme episodes of heatwaves is triggering severe impacts on vegetation growth, particularly for plant communities in arid and semiarid ecosystems. Although there is an abundance of short‐term field drought experiments in natural ecosystems, remaining knowledge gaps limit the understanding and prediction of vegetation growth to ongoing and future climate scenarios. Here, we assessed the impacts of long‐term (1999–2016) experimental drought (ca. ?30% rainfall) on the vegetation growth of a Mediterranean high (H) and low (L)‐canopy forests and an early‐successional shrubland, as indicated by above‐ground biomass increment (ABI) and standing density, respectively. We found habitat context (impact of historical climate change, soil depth and successional status) of the study sites significantly affected the magnitude of climate impacts; there were synergistic effects of experimental drought and meteorological drought (Standardised Precipitation–Evapotranspiration Index, SPEI) as well as extreme dry years on vegetation growth. Long‐term experimental drought decreased the ABI for the two forest canopy types and the standing density for the shrubland. Water availabilities in winter–spring (SPEIs) were positively correlated with the ABI and standing density. Moreover, experimental drought decreased the vegetation growth in extreme dry years for the shrubland. We propose that future work not only study the vegetation dynamics with physiological, phenological and demographical changes in long‐term processes and across climate gradients, but also should explore the changes of multiple functions simultaneously (e.g. multifunctionality) under long‐term processes and extremes. This type of analysis of long‐term data is essential to understand and predict biodiversity loss, composition shifts, declines in ecosystem function and carbon budgets at temporal and spatial scales, to enable policy makers to design and implement strategies for the maintenance of sustainable ecosystem function under future climate change scenarios.     

天山北麓典型地段植被对景观格局和动态的指示意义

景观是由气候、地貌、水文、土壤、植被等组分构成的综合体。这些组分之间相互影响、相互作用,其中植被对其它组分的反映最为敏感。研究了天山中段北坡从中山开始,向下经准噶尔盆地南缘壤质和黏土荒漠,到古尔班通古特沙漠南缘的范围内,以典型温带荒漠植被为主的天然植被格局及其与环境梯度的关系,并以此为基础探讨了干旱区荒漠植被对于景观格局及相应的景观过程的指示意义。结果表明,土壤质地对研究区植被类型有显著的影响,白梭梭-梭梭群落、梭梭群落、琵琶柴群落对细粒物质的偏好依次增大,对粗粒物质含量则有相反的规律;研究区壤质和黏土荒漠中的白梭梭-梭梭群落可以作为景观中土壤沙化过程的指示体。在对土壤含盐量的适应性方面,琵琶柴群落高于梭梭群落,分布在总盐含量更高的生境中,柽柳群落则对土壤盐分没有明显的偏好;盐生矮半灌木群落可以作为土壤盐渍化过程的指示体。在对土壤水分与地下水位的适应性方面,柽柳群落表现出较明显的对高的土壤含水率的偏好,可以指示景观中具有优良生境的斑块。荒漠化过程是干旱区重要的景观生态过程,主要表现为土壤沙化和土壤盐渍化,而这两个过程都有非常明显的植被表征,因此,在以荒漠化动态为目标的干旱区景观动态分析中,可以通过植被的演化来推断景观格局的动态变化,进而推断荒漠化动态。     

Nitrogen immobilization in leaf litter at two Mediterranean ecosystems of SW Spain

Nitrogen immobilization in relation to the dynamics of lignin and tannins in nine different types of leaf litter was investigated during a 2-yr study at two Mediterranean ecosystems of SW Spain. Net nitrogen immobilization for all the species was higher in a forest than in the more nutrient-poor soil of a shrubland. Absolute amount of lignin increased in both ecosystems in the first 2–4 months whereas tannin rapidly decreased in the same time period. Increases in lignin were significantly correlated to losses of tannins during decomposition. Initial tannin content was the best predictor of the maximum amount of immobilized nitrogen in litter in both ecosystems. Mechanisms that could explain the immobilization of nitrogen in litter are discussed.     

2001—2015年天山北坡植被覆盖动态变化研究

利用天山北坡2001—2015年植被生长比较旺盛月份(6—9月)的MODIS NDVI产品数据,结合像元二分法进行植被覆盖度提取,并对其空间分布特征、随时间及地形的动态变化和面积加权重心进行分析。研究表明:(1)天山北坡6—9月多年平均植被覆盖度介于0.4—0.5,以低、中低植被覆盖度为主,各等级植被覆盖度大致呈西北-东南向相间分布;(2)2001—2015年间,植被覆盖度有逐渐上升的趋势;植被覆盖改善区域(54.42%)大于退化区域(45.58%),西部较东部改善更为明显;植被覆盖度变异类型以弱变异和中等变异为主,植被覆盖度变化类型以稳定型为主;(3)天山北坡区域植被覆盖度变化受海拔高度影响明显:随着海拔高度的上升,较低植被覆盖度比例呈现先上升后下降再次上升趋势,较高植被覆盖度则与之相反;海拔3880 m以上低植被覆盖度占绝对优势,较高的植被覆盖度占比逐渐下降直至几乎绝迹;(4)各等级植被覆盖度面积加权重心集中在沙湾县、石河子市、玛纳斯县及呼图壁县;并呈现由集中到相对分散的趋势。     

林草交错区植被动态变化及其影响因子——以中国东北大兴安岭为例

东北大兴安岭林草交错区对气候变化和人类活动高度敏感是我国重要的生态脆弱区,研究表征生态环境变化的植被指数时空变化及驱动因子是制定政策、改善生态环境的理论基础。基于此,利用遥感区域分析和地面实证分析对大兴安岭林草交错区的植被变化趋势及影响因子进行分析,并通过重要性指标定量阐述环境因子和人类活动因子影响的相对重要性。结果表明：1982-2015年的植被呈退化趋势（-0.02/10a）,最低温度、平均温度和最高温度均呈增温趋势分别为0.13℃/10a、0.16℃/10a和0.20℃/10a,而年平均降水量呈下降趋势（-16.3 mm/10a）。植被NDVI随云量的增加而降低（R=-0.21）,并且显著负相关占总面积的24.98%。NDVI随最低温度、平均温度和最高温度的增加而增加（R_TMN=0.01、R_TMN=0.02和R_TMN=0.04）。潜在蒸散对NDVI的影响存在差异,降水量在200-400 mm NDVI与潜在蒸散显著负相关（占总面积18.60%）,400 mm以上显著正相关且占总面积16.01%。降水量与NDVI正相关（R=0.03）,其中显著正相关占总面积的19.55%,显著负相关仅占总面积的5.31%。降水量是陈巴尔虎旗、新巴尔虎左旗以及鄂温克族自治区西部植被（草地）的主导影响因子,云分量是东部林地的主导影响因子。此外,实证分析结果表明人类活动因子（家畜密度和开垦面积）对NDVI的解释率高于温度和降水,并且人类活动的平均重要性指标（VIP_{人类活动因子}=2.48）高于气候因子（VIP_气候因子=0.80）,气候因子中的降水解释率和重要性均高于温度。因此,气候变暖背景下,东北林草交错区气候呈变暖变干旱趋势,而人类活动因子对植被的影响作用不容忽视,合理调控农牧业是改善林草交错区植被生态系统稳定可持续的重要途径。     

The role of the seed bank,seed rain and the timing of disturbance in gap regeneration

Abstract. Question: Does the degree and timing of disturbance contribute significantly to the pattern and process of regeneration in plant communities as a consequence of the availability and number of species of propagules present? Location: Acid grassland at 230 m a.s.l., eastern Scotland, UK. Methods : Plots were surface disturbed or had their soil profile inverted at monthly intervals at 12 dates during a year. Seed bank and seed rain were assessed at each treatment time. The effect of disturbance intensity and timing on the regenerating vegetation was assessed. Results: Removing the seed bank significantly slowed regeneration, as it contributed 43 % of developing cover after one year where it was present. At an individual seed level, seed in the seed rain had a much higher likelihood of contributing to the regenerating vegetation than a seed in the seed bank. Some species showed a reliance on the seed bank for regeneration, and hence there was a significant difference in the vegetation that developed between plots with the seed bank intact and those where it was removed. Winter disturbed plots (little seed rain) had slower rates of re‐vegetation than summer disturbed plots. Timing had little effect on species composition, though a significantly higher cover of perennial forb species developed on the winter disturbed plots. Conclusion: Removing the contribution of the seed bank had a greater effect on the composition of regenerating vegetation than the effect of seasonal variation on the seed rain.