Composition Of Aboveground Vegetation Research Articles

Plant species richness in intensively managed temperate wet grasslands: current state and the importance of edge habitats

AbstractThis study investigates within-site variation in the diversity and composition of aboveground vegetation and seed bank in intensively managed wet grasslands of north-western Germany, comparing field edges, field margins and field interiors. We tested the hypothesis that unfertilized buffer strips at field edges function as refugia of characteristic species even in grasslands that are managed intensively for silage production. In 55 grassland sites on each marsh and moor soils, respectively, we conducted vegetation surveys, seed bank analyses and soil chemical measurements in field edge, margin and interior plots, and searched for the factors causing within-site variation in vegetation composition. The total species pool was small at the 110 sites, i.e. 148 species in the aboveground vegetation and 107 species in the seed bank, demonstrating severe impoverishment. The α-diversity decreased from 23 species (median) per 200 m2 at the edge to 15 species in the interior, with 38 species occurring only at field edges. The number of species with conservation value was very low in aboveground vegetation and seed bank and was only slightly higher at the edge than in the interior. Soil P availability was ca. 30% lower at the unfertilized edges than in the interior. We conclude that unfertilized buffer strips at grassland edges may help reducing nutrient leaching from high-input grassland systems, but they have mostly lost their refugial function for phytodiversity after decades of intensive management. Restoration efforts with seed or green hay transfer from richer source habitats are needed to promote biodiversity in field-edge buffer strips.

Phytolith-reconstructed Holocene vegetation dynamics from a subalpine peat deposit in the mid-subtropical zone of China

With the improvements in our knowledge of the phytolith morphology of different Poaceae subfamilies and even different species, phytolith records in paleosols provide valuable information on past vegetation in situ, especially for herbaceous plants. Nevertheless, the reliability of phytolith records for the reconstruction of forest vegetation needs to be further verified, and it needs to be assessed before they can be used in palaeoecological contexts. In this study we analyzed the topsoil phytolith assemblages of 39 sampling sites and established a modern soil phytolith reference dataset for five plant communities in the mid-subtropical zone of China. We then used the phytolith reference dataset to analyze a stratigraphic sequence of fossil phytolith assemblages from the same region. The results show that the topsoil phytolith assemblages and phytolith indices (Ic and Iph) vary substantially among different plant communities, and that there is a good correlation with the aboveground vegetation composition. This shows that modern soil phytoliths are reliable analogues for reconstructing the paleovegetation. The results of a paleovegetation reconstruction based on the modern phytolith reference dataset show that the SWGT region has experienced substantial vegetation changes during the Holocene—from evergreen and deciduous broadleaved mixed forest to evergreen broadleaved forest, and finally to evergreen broadleaved forest with occasional shrub and herbaceous communities. The phytolith-based Holocene vegetation types are consistent with those reconstructed by a pollen record from the same stratigraphic profile. Moreover, the phytolith reconstruction also records changes in the understory herbaceous plants and C3/C4 grasses, which supplements the results of the pollen-based paleovegetation reconstruction. Overall, our results confirm the reliability of phytolith analysis for interpreting the entire vegetation landscape and forest composition in the mid-subtropical zone of China. They also provide a new perspective for the application of phytoliths to the study of forest dynamics in this region.

Endozoochorous Seed Dispersal by Yak and Tibetan Sheep on Alpine Meadow and Shrubland

The presence of seeds in livestock dung can alter the composition of aboveground vegetation. However, there have been few studies of the composition of the dung seed bank of Tibetan livestock on different vegetation types on the Qinghai-Tibet Plateau. The aims of this study were to identify the differences of endozoochorous seed dispersal in dung type and vegetation type and determine the relationships between the dung seed bank and aboveground vegetation in meadow and shrubland. We conducted experiments to assess the density and plant diversity of the seed bank of yak and sheep dung in meadow and shrubland. The dung seed density in Tibetan sheep dung from meadow sites was the highest (239.3 ± 13.8 seeds kg−1), and the number of species in yak dung from meadow sites was the highest. Among seasons, the livestock dung seed density was highest in November and the lowest in April. The species richness of the dung seed bank was higher in meadows than shrubland and higher in yak dung than that in Tibetan sheep dung only for shrubland. The dispersal of dung seeds has a greater impact on vegetation changes in meadows than shrubland, and the dispersal of seed in yak dung has a greater effect on vegetation changes than does dispersal in Tibetan sheep dung in shrubland. There were more monocotyledons in yak dung of shrubland (42%), whereas there were more dicotyledons in Tibetan sheep dung of meadow (45%). This suggests that yak and Tibetan sheep are complementing each other in their seed dispersal potential. Therefore, we recommend grazing more Tibetan sheep in the meadow and more yak in the shrubland on the Qinghai-Tibet Plateau.

The feasibility of using soil seed bank for natural regeneration of degraded sandy grasslands

Desertification in degraded grasslands is manifested through the development of bare sandy patches, which eventually lead to habitat fragmentation. The ability of these bare sandy patches to regenerate naturally through in-situ soil seed banks is not well understood. To fill this knowledge gap, we randomly selected 24 bare sandy patches with areas ranging from 19 to 898 m2 in a desertified grassland of the Horqin sandy land, Northern China to determine whether soil seed bank can be used for natural regeneration of bare sandy patches. Species composition and density of soil seed bank as well as aboveground vegetation composition, abundance and coverage were investigated. We then determined their relationships with in-situ habitat characteristics. Our observations showed that the studied area had low soil seed bank density and species richness, as well as depauperate soil seed bank communities. Consequently, local soil seed bank was not able to provide sufficient seed source for natural regeneration. This was indicated by the relationships between aboveground vegetation, soil seed bank and the in-situ habitat characteristics. For bare patches with an area between 300 m2 and 900 m2, increase the soil seed bank density and species richness should be the main restoration measures. For bare patches with a small area of less than 50 m2, restoration of vegetation density should be the main measure. Our data highlighted that different extents of desertification, indicated by different bare patches, are requiring distinct restoration measures.

Edge effects on the realised soil seed bank along microclimatic gradients in temperate European forests

Despite the crucial role of the seed bank in forest conservation and dynamics, the effects of forest edge microclimate and climate warming on germination responses from the forest seed bank are still almost unknown. Here, we investigated edge effects on the realised seed bank and seedling community in two types of European temperate deciduous forest, one in the Oceanic and one in the Mediterranean climatic region. Responses in terms of seedling density, diversity, species composition and functional type of the seed bank at the forest edge and interior were examined along latitudinal, elevational and stand structural gradients by means of soil translocation experiments. Moreover, we translocated soil samples from high to low elevation forests in the two regions, thus performing a warming simulation. Density, species diversity and mortality of the seedlings varied with region and elevation. Seedling density also differed between forest edge and interior position, while seedling cover mainly depended on forest structure. Both the edge and interior forest seed bank contained a high proportion of generalist species. In Belgium, a more homogeneous seed bank was found at the forest edge and interior, while in Italy compositional and ecological differences were larger: at the forest edge, more light and less moisture demanding seedling communities developed, with a higher proportion of generalists compared to the interior. In both regions, the upland-to-lowland translocation experiment revealed effects of warming on forest seed banks with thermophilization of the realised communities. Moreover, edge conditions shifted the seedling composition towards more light-demanding communities. The establishment of more light and warm-adapted species from the seed bank could in the long term alter the aboveground vegetation composition, with communities becoming progressively richer in light-demanding generalists and poorer in forest specialists.

Soil Seed Banks, Alternative Stable State Theory, and Ecosystem Resilience

Abstract In restoration ecology, the transition from desired to degraded state is based solely on the composition of the aboveground plant community, whereas belowground propagules are often neglected. We developed a conceptual framework integrating seed bank dynamics into alternative stable state theory, highlighting the important relationship between aboveground and belowground composition. This integration emphasizes the role of resilience in systems that appear to have shifted to an “undesirable” state. Belowground propagules, especially soil seed and bud banks, provide buffering capacity and may serve as valuable indicators of potential resistance to state transition based on the degree of similarity between belowground and aboveground vegetation composition. Ecosystem states may have multiple components that differ in their rate of change, as well as in their capacity to promote resilience. We recommend that the application of alternative stable state theory from a management perspective should incorporate components of both above- and belowground vegetation.

Resistance of the soil microbial community to land-surface disturbances of high-intensity winter grazing and wildfire

Common land-surface disturbances in rangelands with potential to influence the resistance and resilience of the ecosystem include livestock grazing and fire. The impact of these land-use disturbances on the soil microbial community is important to understand because the soil microbial community provides and supports many ecosystem services. Conventional management of land-surface disturbances have led to a decrease in the ecosystem services provided by rangelands. To combat this decrease, alternative land-surface disturbance regimes are being investigated. Therefore, this study assessed the impact of alternative land-surface disturbances (high-intensity winter-grazing and a wildfire, compared to a widely used conventional summer-long continuous grazing on the soil microbial community measured by changes in total soil microbial biomass, soil microbial functional groups, and soil microbial diversity. The soil microbial community was evaluated at beginning of the growing season and peak growing season for two years following the treatments. Prior to the treatments, the pastures had a long history of summer-long continuous grazing. Our results indicate that the soil microbial community is resistant to land-surface disturbance treatments (high-intensity winter-grazing and wildfire) although the response of soil microbial community was influenced by the composition of aboveground vegetation. Overall, neither wildfire nor high-intensity winter-grazing caused significant impacts on the soil microbial community.

Seed banks trigger ecological resilience in subalpine meadows abandoned after arable farming on the Tibetan Plateau.

Although long-term agricultural activity frequently decreases biodiversity, it remains unclear whether such biodiversity losses are readily reversible. There is no doubt that the important ecological function of seed bank is ecological memory, but few researchers have explored the role of seed banks in grassland ecosystem resilience and threshold theory. We used a space-for-time subrogation method, i.e., a natural meadow (never farmed but used for moderate gazing) and meadows farmed for 30yr and then abandoned for 1, 10, and 20yr, to determine if the biodiversity/ecosystem of subalpine meadows could be reversed to the natural vegetation state and to investigate the role of soil seed banks in grassland ecosystem restoration and resilience. After 20yr of natural regeneration, aboveground vegetation composition and properties had recovered to the natural meadow state, suggesting that critical thresholds were not crossed. Seed bank composition and structure exhibited almost no change after agricultural disturbance for decades. The persistent seed bank had the highest contribution to vegetation regeneration in the 1-yr abandoned field, which had the highest seed density. Similarity between the seed bank and aboveground vegetation and seed density decreased with years since abandonment. Since the seed bank still reflected the desired state, the system had inherent resilience and had not have crossed the transition threshold. Thus, high-diversity persistent seed banks are an important indicator of high resilience of this ecosystem. High similarity between the seed bank and vegetation in early-abandoned fields may indicate that ecological resilience is triggered and be a warning signal that interventions are needed to avoid a state transition. In applying alternative stable state theory to ecological restoration, much attention should be given to the soil seed bank.

Direct and indirect effects of long-term fertilization on the stability of the persistent seed bank

If and how eutrophication influences the persistent soil seed bank is poorly understood. Here, we hypothesized that eutrophication alters the composition of the persistent seed bank indirectly through changes in the soil characteristics and aboveground plant community and productivity. We also hypothesized that changes in the persistent seed bank will consequently impact the aboveground vegetative composition. We tested these hypotheses using data from a 9-year nitrogen and phosphorus fertilization experiment in an alpine meadow ecosystem on the eastern Qinghai-Tibet plateau. We found that long-term nitrogen and phosphorus fertilization indirectly impacted the composition of the persistent seed bank through changes in soil pH, aboveground vegetation composition and annual net primary productivity (ANPP). Changes in the composition of the persistent seed bank, however, were relatively minor in comparison to changes in aboveground vegetation composition. Finally, changes in the persistent seed bank did not feedback on aboveground vegetation composition. Our findings demonstrate the importance of soil pH, ANPP and vegetation composition in regulating the persistent seed bank under eutrophication. Our results also highlight the relative stability of the persistent seed bank to long-term eutrophication and their important contribution to the sustainability of grassland ecosystems.

Assessment of Topsoil Salvage and Seed Augmentation in the Restoration of Coastal Sage Scrub on Santa Catalina Island, California

The Catalina Island Conservancy manages over 22,000 acres of coastal (California) sage scrub (CSS) habitat off the coast of Southern California, including much of the infrastructure, roads, and recreation associated with habitat disturbance. Restoration trials were initiated to establish best management practices for roadside and disturbed site revegetation under local site conditions. Site treatments compared excavated native subsoil and surface soil (±20 cm) reapplication practices with and without seed augmentation. Evaluation of native and nonnative germinants indicated that salvaged surface soil alone may not be sufficient to restore native cover. Seeding improved native cover and reduced establishment of nonnative species on unirrigated sites. Evaluation of water potential of seedlings indicated that high-frequency irrigation may favor establishment of nonnative annual grasses. Most compelling for land managers is the indication that CSS habitats may contain a significant nonnative seed bank in spite of the composition of aboveground vegetation, such that disturbance may facilitate habitat-type conversion without seed augmentation or weed control.

Nutrient cycling in a tropical montane rainforest under a supply-limited weathering regime traced by elemental mass balances and Mg stable isotopes

Forest ecosystem nutrition and rock weathering are intimately linked through the supply of mineral nutrients and recycling (re-utilisation of nutrients released from plant litter during mineralisation). Here, we report on novel applications of Mg stable isotopes in combination with mass balance calculations to quantify nutrient supply (from bedrock, atmospheric wet and dry deposition) and recycling in a tropical ecosystem, characterised by a supply-limited weathering regime in the Central Highlands of Sri Lanka. We measured Mg stable isotopes, radiogenic Sr isotope ratios, and element concentrations in the different compartments of the Earth's Critical Zone (bedrock, saprolite, soil, soil pore water, stream water and vegetation) as tracers for element mass fluxes and pathways. We find that in the clay-rich saprolite Mg isotopes are fractionated towards isotopically heavy Mg during secondary mineral formation. Soil pore water and stream water are the complementary isotopically light reservoirs. The Mg isotope composition of above-ground vegetation is on average identical to soil pore water. Based on these observations we suggest that a tight near-surface mineral nutrient loop between plants and soil sustains the tropical forest ecosystem. This loop is disconnected from the rock weathering nutrient source in the saprolite beneath soil. External atmospheric wet and dry inputs (mainly Mg and Ca) strongly contribute to the plant-available nutrient budget that the nutrient depleted regolith does not supply. These findings, based on Mg stable isotopes, agree with independently-obtained information on bio-element (P, K, Ca, Mg, Si) recycling. This nutrient supply setting contrasts with that reported for the Southern Sierra Nevada (USA), where a kinetically limited weathering regime prevails. Our study illustrates the application of new flux estimators based on elemental and metal stable isotope measurements across a range of climate and weathering regimes.

The influence of fire history on soil nutrients and vegetation cover in mixed-severity fire regime forests of the eastern Olympic Peninsula, Washington, USA

The rain shadow forests of the Olympic Peninsula exemplify a mixed-severity fire regime class in the midst of a highly productive landscape where spatial heterogeneity of fire severity may have significant implications for below and aboveground post-fire recovery. The purpose of this study was to quantify the impacts of wildfire on forest soil carbon (C) and nitrogen (N) pools and assess the relationship of pyrogenic carbon (PyC) to soil processes in this mixed-severity ecosystem. We established a 112-year fire chronosequence with nine similar forest stands ranging in time since lastfire (TSF) from 3 to 115 years prior to site establishment. At each site, we measured understory vegetation cover, overstory composition, physical and chemical attributes of surface mineral soils to a depth of 10 cm, and forest floor organic matter. Additionally, non-ionic resin lysimeters were buried over the winter and spring (7–8 months) at the interface of organic and mineral soil to collect O-horizon leached DOC that would potentially contact PyC particles on the forest floor. Nitrogen transformations were also monitored in laboratory soil incubations for a subset of sites. The TSF gradient was significantly correlated with PyC mass in the O-horizon (r = −0.4), O-horizon C (r = 0.4), total phenol content in both O-horizon (r = 0.4) and mineral soils (r = 0.2), and potentially mineralizable N (PMN) (r = 0.4). Recent fire sites contained higher mineral soil total N and inorganic available N, but were not correlated with TSF. Total DOC that accumulated on the non-ionic resins averaged 1.14 (SE ± 0.54) g DOC m−2 year−1 and increased with TSF (r = 0.52; p < 0.0001). Over time, soils appeared to shift toward a more phenolic-rich organic and surface mineral soil, a higher PMN index, denser moss cover, and higher cover of Mahonia nervosa and Rosa gymnocarpa. Multivariate, non-parametric analysis of soil and vegetation factors showed a significant relationship with the TSF gradient between sites (p < 0.001), but not within sites. Soil characteristics were found to be less sensitive to wildfire disturbances than aboveground vegetation composition.

Restoration Implications of Land Management Legacy on Aboveground and Seed Bank Composition of North American Grasslands

Abstract A variety of nonprairie landscapes, including pastures, crop fields, and unmanaged seral ground, are being restored to native prairie on a yearly basis. Seldom is the seed bank associated with these nonprairie lands taken into account in the restoration process. We examine the seed bank potential of nonprairie lands and the relationship between aboveground vegetation and seed bank composition at the largest grassland restoration east of the Mississippi River, the Midewin National Tallgrass Prairie (U.S.A.), by surveying six land management histories: remnant prairie, restored prairie, new pasture, active pasture, old field, and crop field. Both aboveground vegetation and seed bank composition varied with land management history. However, species composition of aboveground vegetation differed significantly from the species composition of the seed bank irrespective of land management history. Aboveground vegetation carried a higher proportion of the seed bank flora than vice versa. In contrast to s...

Nutrient mineralisation and microbial functional diversity in a restored bog approach natural conditions 10 years post restoration

Peatland restoration has been implemented on sites exploited for horticultural peat for over a decade in Eastern Canada. However, little is known about nutrient dynamics and microbial processes in this region. Belowground nitrogen (N) and phosphorus (P) transformations and carbon utilisation by microorganisms were examined in a harvested peatland 10 years after restoration measures were implemented to assess whether restoration is returning the peatland to a state that falls within the natural range of variation found in a neighbouring bog. N mineralisation rates were almost 10-fold higher in the surface (0–10 cm) compared to the subsurface (10–20 cm) layers for all sites and were highly variable within sites. P pools were small (<0.02 μg g−1 dry peat) and mineralisation rates of P were low in all sections. In the surface layer, the net mineralisation and ammonification rates appeared to be highest in unrestored sites but lowest in restored sites. In contrast, the capacity of microorganisms in using different carbon (C) sources, also described as microbial functional diversity, was highest at restored sites but lowest at unrestored sites. The preferable C sources varied between sites and were significantly correlated with aboveground vegetation composition. Our study suggests that microbial activity and nutrient transformations differ between natural and unrestored harvested peatlands. Our results indicate that the presence of vegetation regrowth in the unrestored area of a peatland alters belowground processes by stimulating microbial activity and increasing the uptake of nutrients, leading to smaller pools of inorganic N available in the peat. When restoration has been carried out, microbial activity is even higher than in natural conditions, possibly leading to high immobilization of N, and net mineralisation rates are very low. This research indicates that while belowground processes have shifted from unrestored conditions following restoration, they do not appear to be fully re-established to a degree similar to natural conditions 10 years post-restoration.

Characteristics of soil seed bank in plantation forest in the rocky mountain region of Beijing, China

We investigated characteristics (scales and composition) of soil seed banks at eight study sites in the rocky mountain region of Beijing by seed identification and germination monitoring. We also surveyed the vegetation communities at the eight study sites to explore the role of soil seed banks in vegetation restoration. The storage capacity of soil seed banks at the eight sites ranked from 766.26 to 2461.92 seeds·m−2. A total of 23 plant species were found in soil seed banks, of which 63–80% of seeds were herbs in various soil layers and 60% of seeds were located in the soil layer at 0–5 cm depth. Biodiversity indices indicated clear differences in species diversity of soil seed banks among different plant communities. The species composition of aboveground vegetation showed low similarity with that based on soil seed banks. In the aboveground plant community, the afforestation tree species showed high importance values. The plant species originating from soil seed banks represented natural regeneration, which also showed relatively high importance values. This study suggests that in the rocky mountain region of Beijing the soil seed banks played a key role in the transformation from pure plantation forest to near-natural forest, promoting natural ecological processes, and the role of the seed banks in vegetation restoration was important to the improvement of ecological restoration methods.

Does aboveground vegetation composition resemble soil seed bank during succession in specialized vegetation on gypsum soil?

AbstractThis paper evaluates the aboveground vegetation in relation to the soil seed bank throughout a 60‐year succession process following agricultural abandonment in a semi‐arid Mediterranean gypsum habitat. There is little information regarding the relationship between these two community components in the context of succession on semi‐arid gypsum soils. Aboveground vegetation and the corresponding seed bank of gypsum plant communities were sampled through a chronosequence of 24 abandoned fields. Generalized linear models were used to model seed species richness and density, redundancy analyses to model the effect of time since abandonment and the effect of soil physicochemical parameters on seed bank species composition, and Mantel tests to analyze resemblance between above‐ and belowground species composition. In this last case, the effect of time since abandonment was controlled using a partial Mantel test. Mantel correlograms using time intervals instead of distances were used to describe the resemblance of above‐ to belowground species occurrence in different aged fields. No significant variability in seed species richness, seed density, or species composition due to time since abandonment was found. Differences in seed species composition were mainly due to small spatial scale predictors such as slope and soil calcium content. High correlations between species composition in the soil seed bank and the aboveground vegetation were detected during succession. The lack of a significant trend in aboveground species replacement over time was also reflected in seed bank composition. We concluded that the rapid establishment of strict gypsophyte species relied mainly on the long‐term persistence of these species in the seed bank.

The effect of successional stage and salinity on the vertical distribution of seeds in salt marsh soils

Seed bank density and similarity between above-ground vegetation and seed bank with depth were compared between two adjacent salt marshes that differ in age. In addition, the effect of salinity on the variation in seed bank density and similarity between above-ground vegetation and seed bank with depth was compared between euhaline against mesohaline conditions in three salt marshes. Ten plots of 2 m×2 m were situated in a new salt marsh (existing since 2002) and 80 plots in three old salt marshes. Soil samples were collected at three different depths (0–5, 5–10, 10–15 cm) in spring 2006. Soil seed bank was investigated in germination experiments under greenhouse conditions. Germination experiments lasted 6 months and all seedlings were identified and removed after identification. Above-ground vegetation composition was determined during the growing season in all plots. Viable seed density was calculated for each plot and for the three different depths; the similarity between seed bank and floristic composition of the above-ground vegetation was calculated. A general linear model was used to investigate the effect of soil depth, salinity and age of the salt marsh on density and similarity between seed bank and above-ground vegetation. The results showed that seed density decreased with depth in all salt marshes, irrespective of their age and soil salinity. Seed density and similarity between seed bank and above-ground vegetation were higher in the new salt marsh than in the old one in the same study area. This is because in young as well as in old successional stages, the seed bank was mostly composed of new colonizers, while most perennial species were absent from the soil seed bank, although they were dominant in the standing vegetation of the old salt marsh. The characteristics of the seed bank of a mesohaline salt marsh were found not to be fundamentally different from that of both euhaline salt marshes.