Vegetation Recolonization Research Articles

The effect of mosses on the relocation of SOC and total N due to soil erosion and percolation in a disturbed temperate forest

Forests cover one-third of the global land and are important components of carbon and nitrogen cycling. Anthropogenic disturbances, such as forest road systems or skid trails for timber harvesting, can dramatically change the nutrient cycling in these ecosystems. Skid trails increase soil erosion and thus the displacement of soil organic carbon (SOC) and total nitrogen (Nt). Additionally, runoff transports high amounts of dissolved organic carbon (DOC), which can have a negative impact on aquatic ecosystems. One of the most important countermeasures against soil erosion is the quick recolonization of vegetation. To date, the extent to which natural vegetation succession influences the relocation of SOC and Nt, and in particular the role of mosses in this context, has not been well investigated. This study investigates the influence of natural vegetation succession and in particular of mosses on the displacement process of SOC and Nt as well as DOC caused by soil erosion. To this end, we combine the results of a field study using in-situ rainfall simulations with small-scale runoff plots in skid trails of the Schönbuch Nature Park in southwestern Germany with the results of ex-situ rainfall simulation experiments with infiltration boxes containing the substrate from the respective skid trails. The eroded sediments of skid trails were on average enriched in SOC by 16% and in Nt by 35% compared to the original soil, which lead to a decrease of the C/N ratio in sediments. As vegetation succession progressed, the displacement of SOC and Nt was reduced, confirmed by a negative correlation between the enrichment ratios of SOC (ERSOC), Nt and total vegetation cover. However, mosses tended to reduce ERSOC more than vascular plants. Additionally, mosses significantly decreased DOC concentration in surface runoff compared to bare soils, while no difference in DOC concentration in percolated water could be observed. Future research should explore the role of mosses in the storage of SOC and Nt in the soil and their impact on soil stability. Thus, utilizing mosses could potentially minimize environmental impacts from soil disturbances in forests.

Evaluating the success of vegetation restoration in rewilded salt marshes

Floodbank realignment is a common practice aimed at restoring salt marsh vegetation on previously embanked land. However, experiences indicate that it may take several years before salt marsh vegetation becomes fully established. Various challenges arising from ecogeomorphic feedback mechanisms could pose significant setbacks to vegetation recolonization. The widespread adoption of transplantation techniques for the restoration and rehabilitation of rewilded landscapes has indeed proven to be a valuable tool for accelerating plant development. In the Ria Formosa coastal lagoon (South of Portugal), a pilot plan was implemented, and two salt marsh pioneer species, Spartina maritima (syn. Sporobolus maritimus) and Sarcocornia perennis (syn. Salicornia perennis), were transplanted from a natural salt marsh to a rewilded marsh. Biodegradable 3D porous structures were installed to mimic transplant clumping, aid sedimentation, and enhance the plant's initial adjustment. Ecological, sediment, and hydrodynamic data were collected during the 12-month pilot restoration plan. The environmental profiles of the donor and restoration sites were compared to substantiate the success of the transplants in the rewilded salt marsh.Results show that although plant shoot density decreased after the transplanting, Spartina maritima acclimated well to the new environmental conditions of the restoration site, showing signs of growth and cover increase, whilst Sarcocornia perennis was not able to acclimatize and survive in the restoration site. The failure behind the Sarcocornia perennis acclimation might be related to the bed properties and topographic properties of the restoration site in the rewilded marsh. Major findings contribute to a more comprehensive understanding of how salt marsh pioneering vegetation successfully colonizes disturbed habitats, facilitated using 3D-biodegradable structures.

Phytoremediation of chloride from marine dredged sediments: A new model based on a natural vegetation recolonization

Phytoremediation is a type of bioremediation process that involves the use of plants to remove or degrade contaminants from soil, water, or air. In most of the observed phytoremediation models, plants are introduced and planted on a polluted site to take up, absorb, or transform contaminants. This study aims to explore a new mixed phytoremediation approach that involves natural recolonization of a contaminated substrate, by identifying the species growing naturally, their bioaccumulation capacity, and by modeling annual mowing cycles of their aerial parts. This approach aims to evaluate the phytoremediation potential of such a model. Both natural and human interventions are involved in this approach, which is referred to as a mixed phytoremediation process. The study focuses on chloride phytoremediation from a chloride-rich and regulated substrate that is marine dredged sediments abandoned for 12 years and recolonized for 4 years. The sediments are colonized by a Suaeda vera dominated vegetation and possess heterogeneity in lixiviate chloride and conductivity. The study found that despite Suaeda vera is the well adapted species for this environment, it is not an effective species for phytoremediation as it has low bioaccumulation and translocation rates (9.3 and 2.6 respectively), and disturbs chloride leaching below in the substrate. Other identified species, such as Salicornia sp., Suaeda maritima, and Halimione portulacoides, have better phytoaccumulation (respectively 39.8, 40.1, 34.8) and translocation rates (respectively 7.0, 4.5, 5.6) and can successfully remediate the sediment in 2–9 years. The following species have been found to bioaccumulate chloride in aboveground biomass at the following rates: Salicornia sp. (181 g/kg DW), Suaeda maritima (160 g/kg DW), Sarcocornia perennis (150 g/kg DW), Halimione portulacoides (111 g/kg DW) and Suaeda vera (40 g/kg DW).

Restoration of estuarine wetlands using thin cover placement: A pilot application in Brunswick, Georgia

This paper presents the design concepts and basis for using a thin layer cover (TLC) of sand to restore historically impacted wetlands in Georgia’s Brunswick estuary. The project site is a mix of tidal creeks, marshes, brackish estuary, and an adjacent upland area that has been affected by historical industrial operations. A pilot project to test cover placement methodology and performance in advance of future full-scale TLC implementation was completed in 2018. It involved placing 6-9 inches of material in a 2/3-acre marsh area. Two material types — sand and higher organic content fines — were tested. The contractor, Sevenson Environmental Services, identified the appropriate equipment, means, and methods to hydraulically convey and place the TLC material within the pilot area in accordance with stated performance objectives. A mat-based access road was installed to enable equipment to move the pipeline and spray nozzle for fine placement control within the pilot marsh area. The thin cover placed in the field ranged from 6-12 inches thick (versus the design thickness of 6-9 inches) to meet the minimum required thickness and account for over placement. A 30- to 45-degree spray yielded the best distribution of materials for the equipment used. Placement of sandy material was faster and more uniform than fines due to the material’s enhanced settling characteristics and ease of distribution. A modified topsoil-fines mix with a baffle plate eventually permitted optimal placement of fines within the study area while maintaining the target organic content. Turbidity in the water discharged from the pilot area was minimized by environmental controls (e.g. perimeter hay bales) installed by the contractor. The mat-based access road initially experienced some settlement due to loading on the soft sediments and marsh root mat; the road required restoration following project completion. Physical and vegetative monitoring conducted in six-month increments over a two-year period indicated strong natural recolonization of vegetation and the re-establishment of benthic species including fiddler crab. This paper presents lessons learned, design implications, and best management practices for future thin cover placement projects in estuarine settings.

Non-monotonic vegetation activity trends in the Lower Delta of the Paraná River: Masking evidence of wetland degradation?

To understand the consequences of unsustainable management practices and global change, analyzing the patterns of ecosystem functioning and land degradation is as important as quantifying the spatio-temporal patterns of land cover loss. This is particularly important for wetlands where loss and degradation are globally intensifying. In the Lower Delta of the Paraná River, Argentina, land use change has occurred in the context of cattle raising intensification, which involves water management infrastructure. However, when those changes specifically occurred and whether they permanently influenced the functional component of wetland ecosystems remain unanswered. We used a long-term (2001–2015) fused satellite-derived Normalized Difference Vegetation Index dataset to identify major shifts in vegetation activity trends using the Breaks for Additive Seasons and Trend algorithm. We assembled a set of hydro-climatic, environmental, and anthropogenic variables to study their association with the spatio-temporal patterns of vegetation activity trends. Our results show that browning-to-greening trends dominated throughout the study area. Concomitantly, the magnitude of breakpoints was mainly negative, which points towards rapid land degradation and biomass submersion or removal events. Breakpoints primarily occurred between 2007 and 2009 and were partially coincident with an extraordinary flood event and intentional fire outbreaks. Paranacito river flooding, precipitation, the synchronicity with temperature patterns, water management infrastructure and the occurrence of local land cover conversions were determining factors in the differentiation and characteristics of vegetation activity trends, shifts and breakpoints. Our results provide evidence that even though regional hydro-climatic patterns remain as main drivers of wetland vegetation dynamics, human influence and its negative effects increase in the context of adverse hydro-climatic scenarios. In this matter, we observed that the decouplement from the flood pulse promoted a post-disturbance recolonization of herbaceous vegetation. Consistently, the widespread browning-to-greening trend reversal does not necessarily relate to wetland vegetation recovery but instead, might have masked its extensive conversion to grasslands.

New palynological data from the Late Pleistocene glacial refugium of South-West Iberia: The case of Doñana

The Doñana area in southern Iberia is one of the most renowned protected areas of Europe, mostly due to the diversity and value of its wetland ecosystems. The large biogeographical significance of this territory and the outstanding availability of sedimentary archives have made this region a hotspot of paleobotanical research in the Iberian Peninsula. Specifically, the organic deposits on El Asperillo Cliff have been studied during the past few decades from the geomorphological and paleobotanical (pollen, macrofossils) points of view. However, large uncertainties remain concerning the chronology of certain sections of the exposed profile and the paleobotanical potential of this site has not been fully exploited yet. In this study, we revisited El Asperillo with the aims of completing the paleobotanical record and refining the chronology of this site. The age of the studied deposits ranges from ca. 22,000 to 30,900 cal. yr BP according to the radiocarbon dates obtained, thus embracing the particularly cold and dry Heinrich Event 2 and the Last Glacial Maximum. Our palynological results allow inferring the presence of a coastal marshland system. Additionally, the new pollen records highlight the relevance and diversity of pines (Pinus nigra-sylvestris type, P. pinaster, P. halepensis-pinea type) in the Late Pleistocene landscape of Doñana, reinforcing the native status of pines. Last but not least, the results stress the persistence of a highly diverse woody flora in Doñana during the harshest periods of the last glacial cycle, highlighting the importance of this enclave in postglacial vegetation recolonization of the Iberian Peninsula.

Quantitative pollen-based reconstruction of the vegetation diversity in response to the late-Holocene climate change near Karwar, south-west coast of India

In low latitude regions, due to impact of abrupt climate change/human interference, significant changes in vegetation, particularly the destruction of the highly fragile mangrove ecosystem has been noticed in different tropical areas of the world. In this study, a sediment core collected from the Kali Estuary has been used to determine the vegetation distribution of the Western Ghats since the late Holocene. Pollen and magnetic susceptibility data have been used as proxies to achieve objectives of the study. There has been a dramatic decrease in mangroves, evergreen (tree taxa) and deciduous forest pollens and the abundance of herbaceous/savanna type grassland pollen over the past 3.5 ka. This is supported by the significant decrease of the low-frequency magnetic susceptibility (χlf) of the core reflecting the decrease in the summer monsoon rainfall. Therefore, the post-3.5 ka time period marks the beginning of the recolonization of vegetation. Rarefied diversity pattern plots were used to evaluate abundance and evenness in the pollen data as a result of the late-Holocene climate change. A significant increase in the diversity of herbaceous/savanna grassland taxa in the post-3.5 ka sequence of the core indicates the regional expansion of the agriculture in the Kali River basin. In contrast, the reduction in the taxonomic diversity of mangroves and arboreal taxa implies less-conducive environmental conditions for their growth, with further reduction due to anthropogenic interference. The magnetic susceptibility of the core measured at one cm interval indicates the general decrease in the intensity of the summer monsoon rainfall.

Local adaptation of phenotypic stem traits distinguishes two provenance regions of silver birch in Latvia

Populations of tree species with a wide geographic range, such as silver birch ( Roth), show genetic specialization to native environments, while maintaining high phenotypical plasticity. Accordingly, assessment of local specialization is essential for adaptive management. The aim of the study was to detect geographic patterns of local adaptation of growth and stem quality based on two open-pollinated progeny trials in Latvia testing local material. Two provenance regions differing by continentality were distinguished, which also differed in genetic control of growth traits, likely originating from the post-glacial recolonization of vegetation and subsequent natural adaptation. Heritability of the traits was estimated for each of the distinguished regions, indicating differing patterns of genetic adaptation and potential for future selection. Trees from the more continental inland showed superior growth and possessed higher heritability. The coastal provenance region showed slower growth and intermediate heritability of the respective traits. Moderate to high heritability for stem quality traits was estimated irrespectively of region. Overall, better growth and higher heritability suggests that anthropogenic selection within the best inland provenances may constitute better performing and adaptable breeding population compared to the coastal one. Still, overlapping phenotypical variation and heritability of quality traits implies improved stemwood quality for plywood regardless of the provenance region. High adaptive capacity of silver birch genotypes suggests ability to cope with climatic changes, highlighting its potential for climate-smart forestry.Betula pendula

Natural rehabilitation of arsenic-rich historical tailings at the Alexander mine, Reefton, New Zealand

ABSTRACT Mine tailings resulting from orogenic gold processing commonly form arsenic (As)-enriched environments. A result of this is that they draw environmental attention in modern gold mining settings and significant effort in long-term rehabilitation. The Alexander River mine processing site in the Reefton area of Westland provides an opportunity to examine the natural rehabilitation of As-enriched tailings that have been left undisturbed for >70 years in a humid environment. These tailings comprise a ∼1 m thick package of finely laminated (mm-scale) sediments that were manually accumulated on a terrace downstream of the gold extraction plant. The tailings sediments are As-rich (up to 5000 mg/kg) due to relict arsenopyrite and As-bearing pyrite. Diagenetic Ca–Fe–arsenate (tentatively identified as yukonite) and As-bearing iron oxyhydroxide have formed during localised oxidation. There was sufficient calcite in the tailings to maintain circumneutral pH in the tailings despite sulphide oxidation. The historical tailing impoundment is now covered by grass, ferns and shrubs, with beech and rimu forest covering several metres at the margins. Leaf analyses indicate that the vegetation is absorbing only minor As. Therefore, the tailings substrate has not halted natural vegetation re-colonisation of this As-rich historical site.

Pond Excavation Reduces Coastal Wetland Carbon Dioxide Assimilation

AbstractCoastal wetlands comprise important global carbon sinks; however, anthropogenic disturbance accompanied with accelerating sea level rise threaten their continued survival. In this study, we quantified habitat disturbance to salt marshes in Barnegat Bay, New Jersey, resulting from the construction of ponds for mosquito control. Geographic object‐based image analysis of high‐resolution four‐band aerial imagery revealed that over 7,000 ponds were constructed in the marsh complex with pond densities as high as 290 ponds per km2. Physical disturbance from pond creation and sediment dispersal extended to over 17% of the bay's tidal wetlands. By tracking recolonization of vegetation, we estimated that it took 5 years for 51% vegetation recovery and 10 years for 69% recovery, with complete recover (100%) not expected for more than 50 years. This suggests that efforts to extend the lifespan of drowning coastal wetlands through sediment additions might disrupt carbon dioxide assimilation, as effects of disturbance persist. Focusing on greenhouse gas exchange, our work found that areas of marsh vegetation contribute to carbon assimilation (−42 g C · m−2 · year−1), while ponds and areas of bare peat created by pond excavation were associated with carbon emissions (44 and 125 g C · m−2 · year−1, respectively). These results suggest that the conversion of wetlands to ponds—which is a significant driver of coastal wetland loss worldwide—may convert coastal wetlands from greenhouse gas sinks to sources. Additionally, quantifying the area of vegetation within a marsh (vs. bare ground or open water) is important for quantifying their greenhouse gas mitigation function.

Changes in plant community and soil ecological indicators in response to Prosopis juliflora and Acacia mearnsii invasion and removal in two biodiversity hotspots in Southern India

Invasion of alien plant species can alter local plant diversity and ecosystem processes closely linked to soil organic carbon (SOC) and nutrient dynamics. Soil ecosystem processes such as microbial respiration and enzyme activity have been poorly explored under alien plant invasion and especially following invasive plant species removal. We studied the impact of Prosopis juliflora and Acacia mearnsii invasion and subsequent removal on local plant community composition and diversity and on soil microbial respiration and enzyme activity in two biodiversity hotspots in Southern India. Removal of Prosopis promoted recolonisation of local vegetation as indicated by a 38% and 28% increase in species richness and ground vegetation cover, respectively, compared to an unremoved site. Prosopis and Acacia removal led to a significant reduction in soil microbial biomass C (MBC), respiration, dehydrogenase and urease activity due to increased microbial respiration and N mineralisation rate. Higher metabolic quotients qCO2 in soil at Prosopis and Acacia removed sites indicate that MBC pools declined at a faster rate than SOC, resulting decreased MBC/SOC ratios compared to their respective removed sites. Natural and undisturbed ecosystems maintain more SOC through increased belowground and aboveground C input in the soil, resulting in a higher MBC content per unit SOC. Our results indicate that the interaction between above- and below-ground communities is a critical factor determining the structure and dynamics of local plant communities, especially in ecosystems affected by plant invasions.

Responses of Soil and Microbial C:N:P Stoichiometry to Vegetation Succession in a Karst Region of Southwest China

Spontaneous vegetation succession after agricultural abandonment is a general phenomenon in many areas of the world. As important indicators of nutrient status and biogeochemical cycling in ecosystems, the stoichiometry of key elements such as carbon (C), nitrogen (N) and phosphorous (P) in soil and microbial biomass, and their responses to vegetation recolonization and succession after agricultural abandonment remain poorly understood. Here, based on a space-for-time substitution approach, surface soil samples (0–15 cm) were collected from four vegetation types, e.g., tussock grassland, shrubland, secondary forest, and primary forest, which represent four successional stages across this region. All samples were examined C, N and P concentrations and their ratios in soil and microbial biomass. The results showed that soil organic C and total N content increased synchronously but total soil P did not remarkably change along a progressive vegetation succession. Consequently, soil C:P and N:P ratios increased while C:N ratio stayed almost unchanged during vegetation succession. Soil microbial biomass C (SMBC) and microbial biomass N (SMBN) concentrations elevated while SMBP did not significantly change during vegetation succession. Unlike the soil C:N:P stoichiometry, however, microbial C:N and C:P ratios were significantly or marginally significantly greater in grassland than in the other three successional stages, while microbial N:P did not significantly vary across the four successional stages. Overall, the present study demonstrated that soil and microbial stoichiometry responded differently to secondary vegetation succession in a karst region of subtropical China.

Eradication of invasive Carpobrotus sp.: effects on soil and vegetation

AbstractInvasive species management (eradication or control) can be used to promote native plant restoration. The objective of this study is to evaluate different treatments to guide the selection of future modalities for the eradication (i.e. elimination of all individuals in a population) of Carpobrotus sp. from a strict nature reserve. Two removal methods were tested: (1) living Carpobrotus removal; (2) living Carpobrotus and litter removal. To assess the effectiveness of each treatment, we studied the recolonization of native vegetation, the recolonization of Carpobrotus, and soil erosion and compared these metrics to those taken in native vegetation and in patches of intact Carpobrotus. We also tested the capacity of a 50‐cm‐wide Carpobrotus strip to retain soil. The removal of Carpobrotus together with its litter led to high rates of soil erosion. The Carpobrotus strips were found to retain the soil rather well. Removing live Carpobrotus while leaving its litter in place reduced soil erosion and led to higher native plant species recolonization. The composition of the vegetation 10 months after applying the treatments was biased in favor of native pioneer species. These are typically the first species to establish (Aetheoriza bulbosa and Arisarum vulgare resprouted, Frankenia hirsuta and Lotus cytisoides germinated, and Sonchus sp. benefited from long‐distance dispersal). Few weedy species were recorded (e.g. Sonchus asper asper). Whatever the treatment, the risk of reinvasion from the seed bank or from resprouting stems is nonnegligible, so long‐term monitoring is vital to the ultimate success of the eradication program.

UAV-derived data for mapping change on a swidden agriculture plot: preliminary results from a pilot study

ABSTRACTSwidden agriculture, or the continuing agricultural system in which clearings are cropped for shorter periods than they are fallowed, landscapes have been described as ‘difficult-to-map’ because they host a high variety of land-cover types. Consequently, satellite-borne remotely sensed data have not proven overwhelmingly successful in detecting and measuring change within these landscapes. We utilize data derived from an optical sensor carried on-board an unmanned aerial vehicles (UAVs) to measure the change on a swidden agriculture plot over a 4 month period in Guyana. UAVs were built with indigenous farmers who were trained in their operation to collect data over the swidden plot. A two-class classification was developed to quantify the change in both cultivated and naturally occurring vegetation. We found that non-vegetation surfaces rapidly decreased over the 4 months, declining from 79.42% in June to 69.69% in September. Vegetation recolonization of the swidden crop was particularly the cassava crop planted by the Makushi farmer. While our analysis was completed over a single swidden plot, our work demonstrated that UAVs could play a role in mapping swidden landscapes and change the perception that they are difficult to map. Local people involvement was critical to mapping their landscapes.

Management of the margins in cutover bogs: ecological conditions and effects of afforestation

Several studies contributed to the development of restoration techniques for open Sphagnum-dominated habitats on peat-extracted bogs. Yet, in exception to some afforestation efforts, connectivity between restored sites and surrounding landscapes has received little attention. The general goal of this study is to ameliorate management of very shallow peat fields (<30 cm) located within the margins of peat-extracted bogs. Firstly, to assist decision making in peatland management, baseline ecological conditions, peat physicochemistry and spontaneous vegetation recolonization were assessed for 18 of these fields. This first study revealed that (1) concentrations of several macro-nutrients are almost one order of magnitude lower for unrestored fields than previously characterized natural lagg habitats of the same region, and (2) there is little spontaneous colonization. In a second study, peat chemistry and soil/air microclimate were evaluated in plantations established on shallow residual peat (a 21-year-old Larix laricina plantation and an 18-year-old Picea mariana plantation) and compared to adjacent unrestored shallow bare-peat fields. This second study showed that afforested peat fields are characterized by (1) a soil enriched in nutrients, notably in N, P, and K, and (2) a more humid and cooler microclimate at the soil/air interface, with less daily humidity and temperature fluctuations. These results indicate that afforestation is an appropriate approach to start an ecological recovery. Yet, the absence of natural recolonization by herbs and mosses in the understory of afforested peat fields suggests that reintroduction of appropriate understory species should also be considered if the goal is to restore a fully functional ecosystem.

Poplar plantations along regulated rivers may resemble riparian forests after abandonment: a comparison of passive restoration approaches

Abandoning hybrid poplar plantations may be an alternative strategy for enlarging natural riparian corridors along regulated rivers where forest regeneration no longer takes place. Despite the generally high local diversity of plants in poplar plantations, their capacity to converge towards riparian forests following abandonment remains largely untested and uncertain, because maintenance‐related disturbance of plantations favors ruderal, not strictly riparian specialists. We assessed the spontaneous recolonization of vegetation in abandoned hybrid poplar plantations following two management strategies: harvesting or simple abandonment of standing trees. The floristic composition in four chronosequences of 10 active (1–15 years), 17 harvested (1–15 years), and 10 abandoned (8–20 years) hybrid poplar plantations, as well as 10 riparian sites established at gravel bars that appeared following the cessation of in‐channel gravel mining (8–25 years) along the highly regulated Garonne River (SW France) was assessed in the framework of ecological disturbance theory. Both harvested and abandoned sites still resembled active plantations more than riparian forests. When poplar resprouting was low after harvesting, sites were dominated by light‐demanding, nitrophilous herbs, sub‐shrubs, and vines showing both competitive and ruderal traits, and vegetation composition remained stable over time. Abandoned and harvested sites with high poplar resprouting developed forest communities in which competitive species that tolerate and generate shade dominated, and tree species recruitment was higher. Riparian sites hosted the highest number of indicator species, mainly wetland and exotic. Simple passive restoration strategies like abandonment of plantations can help create valuable ecosystems, although ones that diverge from riparian forests colonizing new fluvial landforms.

Effects of vegetation on runoff generation, sediment yield and soil shear strength on road-side slopes under a simulation rainfall test in the Three Gorges Reservoir Area, China

Vegetation recolonization has often been used to control roadside slope erosion, and in this paper, four restoration models – Natural Restoration, Grass, Grass & Shrub, Sodded Strip – were chosen to recolonize the plants on a newly built unpaved roadside slope in the Three Gorges Reservoir Area. After eight months growth, eight rainfall simulations (intensity of 90mmh−1 for 60min) and in-situ soil shear strength test were then carried out to identify the impacts of vegetation on roadside slope erosion and soil shear strength. The erosion on cutslopes was higher than that on fillslopes. The runoff coefficient and soil detachment rate were significantly lower on the Grass & Shrub model (4.3% and 1.99gm−2min−1, respectively) compared with the other three, which had the highest surface cover (91.4%), aboveground biomass (1.44kgm−2) and root weight density (3.94kgm−3). The runoff coefficient and soil detachment rate on roadside slopes showed a logarithmic decrease with the root weight density, root length density and aboveground biomass. The soil shear strength measured before and after the rainfall was higher on Grass & Shrub (59.29 and 53.73kPa) and decreased on Grass (46.93 and 40.48kPa), Sodded Strip (31.20 and 18.87kPa) and Natural Restoration (25.31 and 9.36kPa). Negative linear correlations were found between the soil shear strength reduction and aboveground biomass, root weight density and root length density. The variation of soil shear strength reduction was closely related to the roadside slope erosion, a positive linear correlation was found between runoff coefficient and soil shear strength reduction, and a power function was shown between soil detachment rate and soil shear strength reduction. This study demonstrated that Grass and Grass & Shrub were more suitable and highly cost-effective in controlling initial period erosion of newly built low-volume unpaved road.

The impacts of land-use changes on the recovery of saltmarshes in Portugal

Human-induced land-use changes have resulted in loss and degradation of intertidal environments worldwide. Saltmarsh ecosystem dynamics in Portugal are greatly influenced by historic uses and consequent habitat degradation. This study uses an original approach combining vegetation surveys and spatial analysis of historic maps and aerial photographs to assess the effects of land use changes on saltmarshes in two areas in the Algarve, southern Portugal. Historical maps from c. 1800 and aerial photographs from 1958 to 2010 were analyzed to map saltmarsh ecosystems and quantify land-use changes in the Alvor estuary and Arade River. Between c. 1800 and 2010 more than half of saltmarshes were lost due to dyke building and saltmarsh reclamation for agriculture. In mid-1960s, the abandonment of reclaimed agricultural areas resulted in the recolonization of saltmarsh vegetation, which developed physically separated from natural marshes. In the study area, these saltmarshes naturally evolved into two distinct typologies: (1) enclosed mixed marshes, formed by patches of brackish, freshwater and some invasive species developing due to saline intrusion in areas where dykes have not been breached; and (2) tidally-restored saltmarshes, formed in areas where dyke breaching allows incursion of tides and development of a vegetation structure similar to natural saltmarshes. In Europe, passive (without human intervention) and active (artificially planned) saltmarsh restoration are important mechanisms for voluntary or statutory re-creation of intertidal habitats. Improved understanding of the factors influencing the development of distinct saltmarsh typologies through passive ecosystem recovery can provide new insights to support decision-making concerning intertidal habitat restoration.

Trampling Impacts on Thermotolerant Vegetation of Geothermal Areas in New Zealand

Geothermal features such as geysers, mud pools, sinter terraces, fumaroles, hot springs, and steaming ground are natural attractions often visited by tourists. Visitation rates for such areas in the Taupo Volcanic Zone of New Zealand are in the order of hundreds of thousands annually. These areas are also habitat for rare and specialized plant and microbial communities that live in the steam-heated soils of unusual chemical composition. We evaluated historical and current trampling impacts of tourists on the thermotolerant vegetation of the Waimangu and Waiotapu geothermal areas near Rotorua, and compared the results to experimental trampling at a third site (Taheke) not used by tourists. Historical tourism has removed vegetation and soil from around key features, and remaining subsoil is compacted into an impervious pavement on which vegetation recolonization is unlikely in the short term. Social tracks made by tourists were present at both tourist sites often leading them onto hotter soils than constructed tracks. Vegetation height and cover were lower on and adjacent to social tracks than further from them. Thermotolerant vegetation showed extremely low resistance to experimental trampling. This confirms and extends previous research that also shows that thallophytes and woody shrubs, life forms that dominate in thermotolerant vegetation, are vulnerable to trampling damage. Preservation of these vulnerable ecosystems must ensure that tourist traffic is confined to existing tracks or boardwalks, and active restoration of impacted sites may be warranted.

Climate and vegetation changes during the Lateglacial and early–middle Holocene at Lake Ledro (southern Alps, Italy)

Abstract. Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652 m a.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early–middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitude-dependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200–7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline. We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).