The role of the soil seed and seedling bank in the regeneration of diverse plant communities in the subtropical Ailao Mountains,Southwest China

We compared species composition and diversity of the soil seed and seedling banks in three secondary vegetation types (shrubland, Populus bonatii forest, Lithocarpus regrowth forest) and a primary old-growth forest in the subtropical Ailao Mountains of southwestern China to clarify the importance of seed and seedling banks for forest dynamics. The average species richness was the highest in soil samples from the shrubland (26.80 ± 1.98), and the lowest from the primary forest (9.93 ± 0.50). The density of germinable tree seeds increased from the secondary vegetation to the primary forest, and the density of shrub, forb, and graminoid seeds decreased significantly. The most abundant seedlings recorded in soil samples were light-demanding species in the shrubland and Populus bonatii forest. For ground flora, the number of shrub seedlings strongly decreased with the increase in stand age, and shade-tolerant tree seedlings tended to increase. The species similarity between the seed bank and the aboveground vegetation in all sites was low (Sørensen’s index = 0.11–0.33), however, the shrubland had higher similarity compared with the other three plant communities. In the primary forest, light-demanding woody species dominated in soil seed banks, while shade-tolerant species dominated in the overstory and the forest floor. In the primary forest, seedlings of dominant tree species were rare in the understory, and no seeds of the dominant species were found in the soil. Results indicated that the early stages of vegetation recovery should take into account the possibility of recovering soil seed bank processes. However, colonization and establishment of tree seedlings will be difficult once a primary forest is destroyed.     

东太湖水生植被及其沼泽化趋势

１９９６年东太湖水生植被调查结果表明,沉水植被、挺水植被及浮叶植被面积分别为７３．８、４５．５和６．７ｋｍ２。有９个群丛,其中微齿眼子菜（Ｐｏｔａｍｏｇｅｔｏｎｍａａｃｋｉａｎｕｓ）群丛、菰（Ｚｉｚａｎｉａｌａｔｉｆｏｌｉａ）群丛、伊乐藻微齿眼子菜（ＥｌｏｄｅａｎｕｔａｌｉＰｏｔａｍｏｇｅｔｏｎｍａａｃｋｉａｎｕｓ）群丛和芦苇（Ｐｈｒａｇｍｉｔｅｓｃｏｍｍｕｎｉｓ）群丛分布面积较大,分别占东太湖总面积的３９３９％、２８２７％、１１２０％和６４０％。与１９６０年相比,水生植被变化极为明显,突出表现为环湖水陆交错带的芦苇群丛严重退化和消失,菰群丛发展迅速并向湖心蔓延占据了东太湖总面积的２８２７％;微齿眼子菜取代了竹叶眼子菜（Ｐｏｔａｍｏｇｅｔｏｎｍａｌａｉａｎｕｓ）、黑藻（Ｈｙｄｒｉｌａｖｅｒｔｉｃｉｌａｔａ）及苦草（Ｖａｌｉｓｎｅｒｉａｎａｔａｎｓ）,成为沉水植被的优势种,占据了东太湖整个湖心区;外来种伊乐藻（Ｅｌｏｄｅａｎｕｔａｌｉ）侵入,并形成一定规模的群丛。综观该湖区水生植被演化过程,可知东太湖已经出现沼泽化趋势,应引起足够重视     

六种沉水植物的克隆生长特征

为构建种群动态模型以指导沉水植被修复工程实践, 研究采用同质园实验方法对6种常见沉水植物(竹叶眼子菜(Potamogeton wrightii)、眼子菜(P. distinctus)、光叶眼子菜(P. lucens)、穿叶眼子菜(P. perfoliatus)、扭叶眼子菜(P. intortifolius)和苦草(Vallisneria natans)的克隆生长模式进行了连续观测研究, 获取了分株形成速率、空间扩张速率、株高增加速率等种群扩张动态参数,及分株数、间隔子长度、分株高度等克隆构件特征参数。结果表明, 6种沉水植物的分株数从28d开始增长, 其中苦草的分株形成速率最高, 平均为1.09株/d, 分株形成最大速率出现在55d之后; 穿叶眼子菜和扭叶眼子菜的分株形成速率低于苦草, 但是高于竹叶眼子菜、眼子菜和光叶眼子菜, 最大速率出现在41d之后。虽然苦草的分株最多, 但是分株的株高最低, 其株高增长速率均值为0.2 cm/d。眼子菜属物种中竹叶眼子菜和眼子菜株高增长速率最高, 光叶眼子菜的株高增长速率和分株形成速率都最低。克隆系占据面积随时间的扩张速率为穿叶眼子菜(113.22 cm2/d)>扭叶眼子菜(71.70 cm2/d)>苦草(35.48 cm2/d)>竹叶眼子菜(12.09 cm2/d)>眼子菜(3.07 cm2/d)>光叶眼子菜(0.53 cm2/d)。此外, 研究还发现眼子菜属植物普遍表现出匍匐茎上“节”的形成, 而苦草则不具备这种特性, 匍匐茎“节”的形成及随之形成的不定根在眼子菜属植物空间扩张过程中具有重要的生态功能, 并在种群构建方面与苦草等其他物种发生分异。基于眼子菜属植物匍匐茎上的“节”可以形成跳跃性的分株, 在种群面积扩张方面更具优势; 而苦草形成分株的数量更多、速度更快, 在提高种群密度保障种群稳定方面更有优势。     

Ten years of vegetation dynamics in two rivulets in Lower Saxony (FRG)

The vegetation dynamics in six permanent plots in two lowland rivulets of the Federal Republic of Germany are analyzed. The year-to-year change in species cover is displayed by means of tables. In each site there are core species (both hydrophytes and helophytes) which have been able to successfully reproduce within the sampling plots over the total observation period. There are also transient hydrophytes which regularly become washed in from the upper course, and transient helophytes growing permanently into the river from the banks.A numerical analysis of the performance of the 12 most frequent and abundant hydrophytes in relation to various independent variables was carried out using canonical correspondence analysis. There is no directional temporal variation within the vegetation data set. The hydrochemical variables were almost constant within the observation period. Rainfall in summer has some influence via discharge and turbidity. Most of the variance in the data set is explained by the position of the sites along the rivers. Most of the residual variance can be explained by a binary disturbance variable. The processes observed can mostly be explained from life history characteristics of the dominant species, particularySparganium emersum, Ranunculus peltatus andPotamogeton natans. The spatial scale of the study site was relatively adequate. A smaller size would have produced noisy data (suggesting erratic change), while a greater size would have produced no change at all. The adequate temporal scale for observation is the comparison of the yearly maxima because of the seasonality of most of the species. An exact prediction of dominance and species composition of the following year is impossible.     

鄂东花马潮水生高等植物研究——Ⅱ.水生植被

花马湖位于湖北省鄂州市境内,面积约27.5km~2。湖中分布有水生高等植物82种2变种。花马湖水生植被可分为15个群丛,其中菱群丛、竹叶眼子菜群丛、金鱼藻+狐尾藻+菹草+苦草群丛较为重要。湖中水生植波呈不规则的环带状分布,并可划分为湿生、挺水、浮叶和沉水4个植被带,各带均有相应的群丛分布。     

Germinable soil seed banks of anthropogenic native grasslands and grassy forest remnants in temperate south-eastern Australia

Soil seed banks of anthropogenic native grassland and grassy forest remnants on the Gippsland Plain in south-eastern Australia were studied using the seedling emergence method. Intact examples of both ecosystems are rare, owing to extensive agricultural development. Both ecosystems are assumed to have been derived since European settlement from the same original, grassy forest ecosystem. It was hypothesised that species now restricted to grassland remnants might persist in the soil seed bank of forest remnants, and vice versa. This hypothesis was not supported. In total, 25554 seedlings of at least 155 species emerged from forest and grassland seed banks collectively. Small-seeded, annual and perennial herbs were most abundant. Forest seedbanks differed substantially in composition from grassland seedbanks, and both essentially contained a subset of the species in the vegetation. Forest seedbanks contained significantly more species and individuals of annual and perennial native dicotyledons than grassland seedbanks. Seedbanks made a major contribution to local diversity, since many species in the seed bank at each quadrat were not recorded from the vegetation, but only a minor contribution to regional diversity. Species in the seedbank that were absent from all vegetation samples were recorded at few quadrats, except Juncus species, which were widespread and abundant in the seedbank. The apparent absence from forest seed banks of species that are best represented in grassland remnants (and vice versa), suggests that there is little opportunity of recruiting grassland-restricted species in forest remnants by instigating grassland management practices.     

Germination in Baltic coastal wetland meadows: similarities and differences between vegetation and seed bank

The abundance and variety of seedlings in Baltic coastal grasslands was studied in cattle grazed and ungrazed areas in seashore and delta on the western coast of Finland. The vegetation, seed bank and environmental conditions of the same sites were also studied. Altogether 4609 seedlings were observed in 79 field plots (20 cm× 20 cm) making an average of 1458.54 seedlings/m². The majority of the seedlings were dicots (67.5%) and perennials (96.8%). Altogether 44 species and an average of 4.14 species per plot were identified as seedlings. The most abundant taxon, Carex formed 23.2% of all the seedlings observed in the field. In the delta the seedling density was two times that found at the seashore. Also, the numbers of species of seedlings per plot were significantly higher in the delta than in the seashore, but in total, more species germinated from the seashore than from the delta even though the number of plots was higher in the delta (n = 51) than in the seashore (n = 28). The numbers of species and seedlings per plot were smaller in grazed sites than in ungrazed ones similar to the pattern earlier reported concerning the mature vegetation and seed bank. The mean numbers of seedlings were the highest at lower geolittoral plots (about 20 cm elevation), where the seed bank was also densest. About 60.0% of the mature species in the plots were also detected as seedlings and 91.4% of the seedling species were found in the mature vegetation of the plots. The number of seedlings was positively correlated with the cover of mature vegetation giving support to the nurse effect theory. Seedling numbers were negatively correlated with the abundance of litter indicating that litter restricts germination because it is a mechanical barrier but also decreases the amount of light. The number of seedlings and species, both in total and per unit area, were greater in the seed bank than in the field seedling population. The seedling population was more similar to the mature vegetation than to the seed bank. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Role of Soil Seed Banks in the Rehabilitation of Degraded Hillslopes in Southern Wello,Ethiopia1

The species composition in the soil seed bank of degraded hillslopes in southern Wello, Ethiopia, was assessed using the seedling emergence method and compared with that of the standing vegetation. Surface soils were sampled at 0‐to 5‐cm depth from 49 plots of four physiognomic vegetation classes (hereafter vegetation classes): forests, shrublands, grasslands, and degraded sites. Soils were spread on sterile sand in a glasshouse and watered. Emerging seedlings were recorded for five months until no new seedlings emerged. A total of 3969 seedlings belonging to 71 species and 30 families germinated. The species composition of the seed bank was dominated by 53 herb species (75%) compared to 2 tree species which accounted for only 3 percent of the total number of species. Seedling density differed significantly among vegetation classes and ranged from 391 to 7807 seeds/m². Mean species richness also differed significantly among the vegetation classes. Forty‐two species were found to be common to the seed banks and the standing vegetation; however, correspondence between species numbers and composition of the seed banks and the standing vegetation was poor. Although most of the species that germinated in the seed banks were herbs and grasses, they can develop a vegetative cover and contribute to reduction of soil erosion. Regeneration of the tree species (some of which have seed viability up to four years) however, requires both time and the presence of mature individuals. Together with hillside closure and soil conservation measures (e.g., terracing), planting of native woody seedlings might help to expedite rehabilitation of degraded hillslopes devoid of trees and shrubs.     

Plant community changes induced by experimental climate change: Seedling and adult species composition

Experimental manipulation of climate provides a powerful tool for studying plant community dynamics with respect to current climate change. We experimentally investigated the vegetation dynamics of a Mediterranean shrubland under directional climate change by manipulating rain and temperature at stand level throughout 7 years. We focused on seedling establishment in relation to the between-year variability of drought conditions. We also compared seedling dynamics to changes in the established adult vegetation to assess the coupling between both dynamics. We used multivariate techniques (principal response curves (PRC) and redundancy analysis (RDA)) to explore changes in the whole community, and Generalized Linear Model (GLZM) to analyse the influence of drought on the abundance and survival of the most abundant species.Drought treatment induced significant changes in the species composition of the seedlings, via a differential decrease in the seedling density of most species. No species was particularly favoured in terms of seedling abundance under water-deficit conditions. Warming only explained a low percentage of the variability in seedling species composition. The emergence of seedlings in control plots – which may be considered an estimation of the between-year variability in the conditions for seedling establishment – was a better predictor of seedling emergence in experimental plots than climate manipulation treatments. The PRC analysis of the adults showed dynamics that were different from those recorded for seedlings, and it also showed that drought treatment significantly explained species composition. This result is reinforced by the change in the relative abundance of seedling and adults of the more common species in the drought and warming treatments, supporting the hypothesis that climatic directional change heightens discrepancies between recruitment and the adult performance. The RDA analysis applied to species composition at the end of the experiment failed, however, to attain any statistical significance. The warming treatment did not produce any significant shifts in adult vegetation.In conclusion, directional climate change – particularly drier conditions in Mediterranean shrublands – would result in a change in the recruitment of the plant community. This change in seedling recruitment tends to be different from the dynamics of adults, suggesting that potential adult mortality would not be compensated by actual seedling recruitment, thus enhancing shifts in community composition.     

Fire,canopy cover and seedling dynamics in Mediterranean shrubland of northeastern Spain

Abstract. Seedling establishment and survival of the main woody species of early-successional shrubland in northeastern Spain were studied from 1992 to 1995 with emphasis on the importance of vegetation cover (existence of open areas and the situation beneath the plant canopy) and microhabitat (occurrence of stones, litter and bare soil). In the absence of fire, vegetation cover (measured at a scale of 30cm × 30 cm) was not correlated with seedling emergence of most species, nor with growth and survival of seedlings up to one year old. Seedlings older than one year showed a similar pattern: their density was not significantly different in both kinds of habitats. The emergence of seedlings was mainly associated with the presence of mature plants – which can provide seeds – and with the absence of unsuitable microhabitats (large stones, deep litter and bare soil). In April 1994 a wildfire burned the study area. This enabled a study of the pattern of post-fire establishment. After the wildfire, seedling emergence of several species increased and most species produced seedlings with higher survival and growth rates than in the period before the fire. Pre-fire cover, however, did not show significant effects on post-fire seedling dynamics in most cases.     

Insect grazing and post-fire plant succession in south-west Australian woodland

This study investigates the impact of insect grazing on the establishment of plant populations from seed after bushfires in coastal plain woodland near Perth, Western Australia. Seedling germination was measured and individual seedlings were observed frequently to estimate survivorship and causes of mortality. Invasion rates of acridid grasshoppers into both small and large burnt areas were measured and palatabilities of seedlings to the most abundant grasshopper species were estimated. Escape of seedlings from insect grazing was influenced by both seedling palatability and area of burning. Grasshoppers were absent from large burnt areas for one to two years. In small burnt patches of vegetation, the patterns of grazing on seedlings were related to seedling palatabilities. These results are discussed in the light of current models of plant succession and the main conclusion is that fire is not a succession-initiating disturbance in this ecosystem because the long association with fire has allowed the evolution of specific survival and recruitment strategies.     

Estimation of Leaf Area Index and Plant Area Index of a Submerged Macrophyte Canopy Using Digital Photography

Non-destructive estimation using digital cameras is a common approach for estimating leaf area index (LAI) of terrestrial vegetation. However, no attempt has been made so far to develop non-destructive approaches to LAI estimation for aquatic vegetation. Using the submerged plant species Potamogeton malainus, the objective of this study was to determine whether the gap fraction derived from vertical photographs could be used to estimate LAI of aquatic vegetation. Our results suggested that upward-oriented photographs taken from beneath the water surface were more suitable for distinguishing vegetation from other objects than were downward-oriented photographs taken from above the water surface. Exposure settings had a substantial influence on the identification of vegetation in upward-oriented photographs. Automatic exposure performed nearly as well as the optimal trial exposure, making it a good choice for operational convenience. Similar to terrestrial vegetation, our results suggested that photographs taken for the purpose of distinguishing gap fraction in aquatic vegetation should be taken under diffuse light conditions. Significant logarithmic relationships were observed between the vertical gap fraction derived from upward-oriented photographs and plant area index (PAI) and LAI derived from destructive harvesting. The model we developed to depict the relationship between PAI and gap fraction was similar to the modified theoretical Poisson model, with coefficients of 1.82 and 1.90 for our model and the theoretical model, respectively. This suggests that vertical upward-oriented photographs taken from below the water surface are a feasible alternative to destructive harvesting for estimating PAI and LAI for the submerged aquatic plant Potamogeton malainus.     

Post-fire regeneration strategies and tree bark resistance to heating in frequently burning tropical savanna woodlands and grasslands in Ethiopia

Regeneration mechanisms of vegetation and the role of tree bark resistance to frequent fire were studied in savanna woodlands and grasslands in Gambella, Western Ethiopia. Data were collected from four sites, each with three replicate plots. The variation between sites in species composition and biomass correlated with the differences in fire intensity. Foliar cover was recorded for individual plant species regenerating by sprouting from older parts of plants that had survived fire or by seedlings; records were made during the dry season and at the beginning of the wet season. Data on bark thickness and tree diameters of 12 dominant tree species were also recorded. Both facultative and obligate sprouters significantly contributed to post‐fire recovery, comprising 98.5 % of total vegetation cover. The contribution of seedlings to cover and abundance immediately following fire was negligible, but seedling density increased in the beginning of the rainy season, 4 to 5 months after fire. The importance of the sprouting and seeding strategies varied between the different plant growth forms. The highest contribution to cover and frequency was made by the most abundant grass species, which reproduced in both ways. Facultative sprouters made up 67.3 % of the vegetation cover, out of which 54 % consisted of grasses. Broad‐leaved herbs and trees/shrubs regenerating mainly by sprouting made up 31.3 % of the vegetation cover. Adaptations to fire in tree species seemed to include the development of a thick bark, once the tree has passed seedling stages. Tree bark thickness and tree diameter at breast height were strongly correlated with the time taken for cambium to reach an assumed lethal temperature of 60°C when exposed to fire, which indicated that mature trees with thick barks might resist stronger fire better than, e.g., small or young trees and trees with thin bark. However, for a given bark thickness the cambium resistance to heat varied three‐fold among species. Hence, site differences in fire intensity seemed to influence the distribution of trees depending on their bark characteristics and resistance to fire.     

Are cloud forest tree structure and environment related in the Venezuelan Andes?

Cloud forest vegetation structure and composition were studied in the Venezuelan Andes at three sites in Mérida State. Although the sites are within 10 to 30 km of each other, climatic, geologic and topographic differences are remarkable. The main purpose of the study was to determine the relationship of specific environmental variables to forest vegetation characteristics, including basal area, tree height, density and diversity, and leaf area index (LAI). At 51 plots, all trees' diameter at breast height >10 cm were recorded and identified. Although the environment at the three sites is distinctive, the tree species composition of the most abundant species was very similar. None of the measured environment variables were significantly correlated with the measured vegetation structure variables, except LAI, which was correlated with slope orientation; LAI showed higher values at south‐facing plots. Tree height was relatively uniform, while basal area was highly variable and reached very high values. Stem densities were in the range reported elsewhere in cloud forests. Multivariate analysis using structure or composition data shows segregation of the plots by site. Principal component analyses by site indicate a minor impact of environmental factors on forest variables. At each site, a particular group of species are correlated with the ordination axes. We conclude that species pools and forest dynamics add to the complexity of the structure of the studied cloud forests.     

Invasion and persistence of bird-dispersed,subtropical thicket and forest species in fire-prone coastal fynbos

Abstract. Seedling abundance at four microsites (open fynbos, beneath emergent fynbos shrubs, beneath thicket, and beneath forest) was determined at three coastal dune landscapes, located along a gradient of increasing summer rainfall and where fire-dependent fynbos was the predominant vegetation. At all sites thicket seedlings were most common beneath emergent fynbos shrubs and under thicket clumps; seedlings of forest species were most abundant at forest microsites although some individuals were recorded beneath thicket. Very few thicket seedlings were observed in open fynbos. Birds play a keystone role in facilitating establishment of the fleshy fruit-bearing thicket flora. Seedling abundance at microsites of different thicket and forest species was generally unrelated to fruit abundance. Germination success of most species was highest under shaded conditions; soil organic content had no effect on germination. Removal of pulp and birdingestion enhanced the germination, relative to untreated controls, of two out of three species tested. A simple Markov model predicted a gradual increase in cover of the thicket and forest component and a gradual decline in fynbos under a ‘normal’ (20-yr interval) fire regime simulated over 10 cycles. Although inter-fire seedling establishment under emergent fynbos shrubs is important in the initial colonisation of fynbos by obligate resprouting thicket shrubs, these species persist and expand by vegetative recruitment after and between fires, respectively. In the prolonged absence of fire, the endemic-rich and fire-dependent fynbos flora would be replaced by species-poor forest and thicket.     

Seed dispersal in the dung of large herbivores: implications for restoration of Renosterveld shrubland old fields

Species-rich, winter-rainfall, microphyllous Renosterveld vegetation in the Western Cape Province of South Africa has largely been transformed for production of wheat and wine. Remaining fragments thus have high conservation value. Abandoned old fields adjacent to natural vegetation fragments could potentially be restored as corridors and habitat for indigenous flora and fauna. We hypothesised that indigenous antelope maintained in a matrix of natural vegetation and abandoned field could play a role in restoration of Renoserveld via seed dispersal.We collected dung of indigenous ungulates in an abandoned field at various distances from natural Renosterveld vegetation, in order to assess the potential of large herbivores to contribute to restoration of plant diversity through seed dispersal. Emerged seedlings from the collected dung represented 29 forb, 13 grass, four sedge, four geophyte and one shrub species. The most abundant emerging seedlings were lawn grass Cynodon dactylon (38%), alien pasture grasses (31%) and indigenous geophyte Romulea rosea (12%). Whereas seeds of annual forbs and grasses were dispersed, only one shrub species was dispersed at very low density. We concluded that large herbivores could retard the rate of recovery of Renosterveld vegetation because viable seeds of herbaceous plants, particularly alien annual grasses and lawn-grasses were more abundant in the dung than the shrub, geophyte or perennial tussock grass species that characterise this vegetation type.     

Tree recovery and seed dispersal by birds: Comparing forest, agroforestry and abandoned agroforestry in coastal Ecuador

We used a highly replicated study to examine vegetation characteristics between patches of intervened forest, abandoned agroforestry systems with coffee and actively managed agroforestry systems with coffee in a tropical landscape. In all habitats, plant structural characteristics, individual abundance, species richness and composition were recorded for the three plant size classes: adult trees, saplings and seedlings. Furthermore, bird species richness and composition, and seeds dispersed by birds were recorded. Tree abundance was higher in forest habitats while saplings and seedlings were more abundant in abandoned coffee sites. Although species richness of adult trees was similar in the three habitats, species richness of saplings and seedlings was much higher in forest and abandoned coffee than in managed coffee sites. However, in spite of their relatively low species richness, managed coffee sites are an important refuge for tree species common to the almost disappeared mature forest in the area. Floristic similarity for adult trees was relatively low between land use types, but clearly higher for seedlings, indicating homogenizing processes at the landscape level. More than half of the saplings and seedling were not represented by adults in the canopy layer, suggesting the importance of seed dispersal by birds between habitats. Our results show that each of the studied ecosystems plays a unique and complementary role as seed source and as habitat for tree recovery and tree diversity.     

Lizard assemblages in the Vizcaino Biosphere Reserve, Mexico

Lizard assemblages were surveyed in eight selected habitats in the Vizcaino Biosphere Reserve in Baja California Sur, Mexico. We compared the species composition and relative abundance among habitats, considering habitat characteristics, such as vegetation type, vegetation ground coverage, and soil types. Thirteen lizard species were recorded. The most abundant species in almost all habitats was Uta stansburiana, accounting for 59% of all observations. Cnemidophorus tigris was the second most abundant species, accounting for 12% of all observations. The richest habitat was the rocky lower elevations of the Sierra de San Francisco (nine species). However, the habitat with the highest diversity value was Scammon's dunes. Implications of our findings for lizard conservation in this biosphere reserve are discussed.     

The seed bank in an estonian calcareous grassland: Comparison of different successional stages

Seed bank species-composition and seed-density were determined in a successional calcareous (alvar) grassland in western Estonia. Three similar study areas were chosen to compare two different successional stages: open alvar grassland and overgrown areas with young pine forest 30 to 40 years old. In both successional stages, the centre and the edge of a relatively uniform stand were examined. Fifteen soil samples (7 cm in diameter, 5 cm deep) were taken from each of twelve sampling sites. The seedling emergence method was used to estimate seeds in the soil samples. A total of 69 species were detected in the seed bank, of which 18 did not occur in the vegetation. Eighty-nine taxa were recorded in the vegetation and of these 38 were not detected in the seed bank. Fifty-one species occurred both in the seed bank and in the vegetation. The three most abundant taxa in the seed bank wereCarex tomentosa, Linum catharticum andPlantago media, which together made up 49% of the seedlings recorded. Differences in the species compositions of seed bank samples from grassland and forest sites were negligible, although the species richness per area of the above-ground vegetation was significantly higher in the open grassland. The only species tending to be lost from forest site vegetation but still occurring in the forest soil seed bank wereArenaria serpylifolia, Cerastium fontanum andLinum catharticum. About half of all the emerged species from all samples belonged to the transient or short-term persistent seed bank. In the grassland sites there were more species which belonged to the transient seed bank than in the forest sites, where the seed bank contained more short-term persistent type seeds. The seed density was significantly higher in forest sites and lower in grassland sites, which may be explained by the better germination conditions in well-illuminated communities. On the basis of the current study it might be assumed that the soil seed banks of overgrown alvar grasslands which include young pine forests can play a certain role in grassland restoration management.     

Vegetation zonation along the desert-wetland ecosystem of Taif Highland,Saudi Arabia

Saudi Arabia has no permanent lakes or rivers but has wet meadows, which are desert wetlands temporarily formed due to the seasonal rainfall. This work investigates the environmental variables' impact on the vegetation pattern in the desert-wetland ecosystem in Taif highlands. Forty-one stands were randomly selected representing three main habitats (wet meadows, slopes, and terraces) to study their floristic features and vegetation analysis. A total of 142 species were recorded belonging to 111 genera and 45 families in the desert wetlands of Taif Province. About 64.1% were natural plants, while 25.4% were segetal weeds, 7.7% were aquatic plants, and 2.8% were plants that escaped from cultivation. Therophytes dominated over the other life forms, and mono-regional taxa were the dominant chorotype. Multivariate analysis of the recorded plants produced eight vegetation groups; four of them (A: Potamogeton nodosus-Nasturtium officinale, B: Lemna gibba-Leptochloa fusca, C: Typha domingensis- Xanthium strumarium and D: Conyza stricta- Cyperus longus) represented the wet meadows, while two (E: Acacia gerrardii- Commicarpus plumbagineus and H: Osteospermum vaillantii- Eragrostis Pilosa) for slopes and other two (F: Argemone ochroleuca-Cyperus rotundus and G: Pulicaria undulata- Solanum incanum) for the desert terraces. The vegetation zonation was clear, which started from real aquatic species in the wet meadows passing through mixed vegetation in the slopes and ended with proper xerophytic vegetation in the terraces. Conyza stricta- Cyperus longus community had the highest species diversity, while that of Potamogeton nodosus-Nasturtium officinale had the lowest. The principal component analysis indicated that HCO₃, NO₃, Mg, Cl, Ca, and pH values were the most effective soil variable. The presence of several segetal weeds suggests the alteration of the natural status of the desert-wetland ecosystem, and thus the conservation of these natural habitats becomes urgent.