Passive Revegetation Research Articles

Passive revegetation limited by seed availability in a salt marsh sediment addition site

Many approaches to restoring salt marsh habitats assume flora will naturally colonize the restoration site following the reinstatement of tidal hydrology that is appropriate for halophytes. However, this passive strategy can fail to meet restoration targets because of unfavorable site conditions and/or limited propagule dispersal. This study analyzes propagule availability in a restored southern California salt marsh that experienced slow passive revegetation following sediment addition to combat subsidence‐driven habitat loss. We performed a seedling emergence experiment to assess the quantity and species composition of viable halophyte seeds in the restoration site compared to nearby established salt marsh habitat. Additionally, we irrigated seed bank samples with freshwater or saltwater to test the effects of restoration site salinity conditions on seedling emergence and survival. Due to the proximity of the restoration site to seed sources, we expected to find ample seeds within its seed bank. However, only two seedlings emerged from restoration site seed bank samples (collected over 1.18 m2 of soil surface area), compared to an average of 44.33 seedlings from control site samples. Control site samples receiving saltwater irrigation had similar quantities of seedlings emerge, but seedlings in salt water had a reduced survival rate compared to seedlings in the freshwater treatment. Overall, these results suggest that passive restoration should be paired with techniques that retain seeds, such as increasing the topographic complexity of the restoration site. However, in scenarios where salinity or elevation may limit seedling recruitment, active planting should be considered to speed restoration trajectories.

Precipitation and time effects on vegetation change in Southern Arizona abandoned farmland

Farmland abandonment represents a significant issue globally, and in arid environments reclaiming ecosystems is challenging. In the Sonoran Desert, much irrigated farmland has been abandoned since 1950. Our objective was to compare changes in vegetative (canopy) cover and species over a 26-year period on abandoned farmland and unfarmed controls in southcentral Arizona (precipitation <300 mm/year). We evaluated time since abandonment and precipitation effects on these variables between 1976 and 2003 with point frame methods on eight farmland sites using stepwise multiple regression. Results suggest antecedent precipitation (AP) is more important than time since abandonment in explaining cover changes. On 26 abandoned sites, we used non-parametric ANOVA to show that vegetative cover (point frame and line intercept methods) declined by about 43% from 1977 to 2023, which was greater than on non-farmed controls. Few farmlands had cover and species composition like reference communities in 2003. Paired farmland-control sites exhibited similar vegetation in 1977 and 2003 suggesting local factors (e.g., soil chemistry, roadways) may have overwhelmed that of farming. Uninterrupted (natural) surface water flow may predict where revegetation was most successful. Our research indicates that farmland may exist in alternative states, and passive revegetation will not reestablish native Sonoran Desert communities on most abandoned farmland sites.

How long do seeds float? The potential role of hydrochory in passive revegetation management

AbstractDespite research into the dynamics of seed transport in fluvial systems, few consider how far seeds will travel, and how far from local or upstream seed sources passive regeneration can occur. We experimentally test the seed floating time of 60 plant species (50 native and 10 exotic) commonly found in riparian corridors of southeastern Australia. Around 50% of species had seeds that floated for 2 days or less, and for most species' (90%) all seeds had sunk within one week. Seeds of native species tended to sink more quickly than exotic, with 64% of native species' seeds floating for less than 2 days. In contrast, most exotic species (80%) floated for longer than 2 days, and 40% had seeds still floating after one week. This suggests that exotic species are good floaters and likely to travel long distances, making them excellent hydrochores. Finally, we applied the findings to a real case study, Wollombi Brook, NSW, Australia. We combined the findings from the seed floating experiment with low flow hydrology calculations to map the potential travel distance of seeds from known extant vegetation sources. We show that maximum seed travel distance per day could be up to 21 km. Thus, species that float for a week could potentially travel almost 150 km downstream before sinking or being deposited. We discuss how local versus upstream seed sources, and hydrochory, could be utilised in passive revegetation and weed management of riparian corridors.

To Establish a Healthy Forest: Restoration of the Forest Herb Layer on a Reclaimed Mine Site

Restoration efforts, such as invasive species removal and establishment of native flora, can be resource intensive. Therefore, understanding the effectiveness of restoration efforts can provide land managers with the confidence to pursue restoration. This study evaluated the effects of invasive species removal and compared active revegetation to passive revegetation in enhancing forest integrity on reclaimed surface coal mine land in southeastern Ohio. Surface coal mining occurred in the area from the 1940s to the 1980s, leaving a near continuous disturbance footprint of 3704.5 ha. This study occurred within 3.6 ha of the larger disturbance footprint where mining activity ceased and reclamation with tree planting occurred in the 1960s. Due to the disturbance, the site was prone to invasive species until their removal began in 2017. In spring 2019, 2 y following invasive species removal and 1 y following seeding and planting, we completed vegetation and bloom surveys across three treatments: managed forest with invasive species removed and subsequent native plantings (planted), managed forest with invasive species removed only (unplanted), and unmanaged forest (control). Our study found vegetative species diversity, vegetative species richness, and floral species richness and bloom time were enhanced for treatments in which invasive species were removed. The planted and unplanted treatments also supported understories comprising a different community composition when compared to control plots. However, no difference was found in community composition between planted and unplanted treatments despite application of active revegetation to support understory regeneration. Overall, results after 2 y support invasive species removal to improve the herbaceous layer of an understory, with more time likely needed for planted material to establish in order to distinguish between revegetation methods.

Soil Properties and Bacterial Community Dynamics in a Coal Mining Subsidence Area: Active Versus Passive Revegetation

Soil Properties and Bacterial Community Dynamics in a Coal Mining Subsidence Area: Active Versus Passive Revegetation

Plant community development in a coal mining subsidence area: active versus passive revegetation

ABSTRACT Vegetation restoration is a fundamental method of ecological reconstruction in disturbed areas, and revegetation can be achieved by passive (spontaneous succession) and active (human-induced) approaches. Plant community composition, productivity, and diversity were studied in coal mining subsidence areas after 0–15 years of restoration with active (AR) and passive (PR) revegetation approaches in a semiarid region. Moreover, plant community composition, succession, and their relationships with soil variables were analyzed. The results showed that both PR and AR contributed to the recovery of the plant community in terms of plant cover, density, biomass, and diversity, with AR accelerating the recovery of the plant comm unity to a greater extent than PR. Soil moisture and organic matter had close relationships with the plant community variables. The plant communities in PR sites had the same species composition as those in non-subsidence (NS) areas, which led to a more natural plant community in PR than AR sites. Plant community structure in AR sites was altered by the introduced shrubs, with mesophytes developing under the introduced shrubs. These changes produced a different successional trajectory in AR sites from that in NS sites; thus, environmental fluctuations may easily change AR community stability in semiarid environments.

Effects on vegetative restoration of two treatments: erosion matting and supplemental rock cover in the alpine ecosystem

Unsanctioned travel routes through alpine ecosystems can influence water drainage patterns, cause sedimentation of streams, and erode soils. These disturbed areas can take decades to revegetate. In 2012, a volunteer‐driven project restored a 854‐m section of unsanctioned road along the Continental Divide in Colorado, United States. The restored area was seeded with three native grass species and then treated by installing erosion matting or adding supplemental rock cover. Four years later, results suggest that the seeding along with the use of erosion matting or supplemental rock can enhance revegetation. Matting appeared to accumulate litter, and this effect might have contributed to enhanced moisture retention. Treated areas contained 40% of the vegetation cover found on adjacent controls, which averaged 69% vascular plant absolute cover. Recovery on both treatments was markedly higher than published estimates of passive revegetation of disturbed areas measured elsewhere suggesting seeding with added cover or protection led to substantial vegetative cover after 4 years. Two of the 3 seeded grass species, Trisetum spicatum and Poa alpina, dominated the restored plots, composing 81.7% of relative vegetation cover on matting sites and 73.4% of relative cover on rock‐supplemented areas. Presumably due to its preference for moister sites, Deschampsia cespitosa had low establishment rates. Volunteer species, that is species that appeared on their own, contributed 6.3% to the absolute vegetation cover of matting and rock sites, and species such as Minuartia biflora, Minuartia obtusiloba, Poa glauca, and Festuca brachyphylla should be considered for use in future restorations.

Assessment of revegetation of an acidic metal(loid)-polluted soils six years after the incorporation of lime with and without compost

The process of passive revegetation of chemically degraded soils through assisted remediation was assessed under field conditions 6 years after amendment application. In 2009, three treatments were applied: unamended soil (untreated), soil amended with lime, and soil amended with lime + compost. For each field plot, main soil physico-chemical characteristics were determined (pH, organic matter, moisture content at field capacity and exchangeable Cu), while plant colonist development was assessed (plant cover and aboveground biomass). The same evaluation was carried out in 2015. A single application of amendments maintains a neutral pH after 6 years. Thus, neutralization of the soil acidity was stable over time. In 2009, lime + compost was the best treatment for increasing the plant cover. Although the soil organic matter content decreases in year 6, plant cover remained stable over time in this treatment. Incorporation of both organic matter and lime was pivotal at the beginning of the revegetation process, allowing the creation of a potentially self-sustaining ecosystem. No maintenance and/or additional application of amendments was required. Aboveground biomass showed differences between years, possibly explained by changes in climate conditions between 2009 and 2015, and/or changes in nutritional conditions (soil fertility) and plant competition. Plant biodiversity in year 6 was similar for all treatments. The long-term results of plant cover show lime and specially lime + compost as promising amendments to revegetate polluted soils of the Puchuncaví Valley.

Spatial and Temporal Variation in Brackish Wetland Seedbanks: Implications for Wetland Restoration Following Phragmites Control

Chesapeake Bay tidal wetlands are experiencing a broad-scale, aggressive invasion by the non-native, clonal grass Phragmites australis. The grass is often managed with herbicides in efforts to restore native plant communities and wildlife habitat. Management efforts, however, can act as a disturbance, resulting in increased light availability, potentially fostering reinvasion from soil seedbanks. If native vegetation establishes quickly from seedbanks, the site should have greater resiliency against invasion, while disturbed sites where native plants do not rapidly establish may be rapidly colonized by P. australis. We surveyed the soil seedbank of three vegetation cover types in five Chesapeake Bay subestuaries: areas where P. australis had been removed, where P. australis was left intact, and with native, reference vegetation. We determined the total germination, the proportion of the seedbank that was attributable to invasive species, the richness, the functional diversity, and the overall composition of the seedbanks in each of the cover types (i.e., plots). After 2 years of herbicide treatment in the P. australis removal plots, vegetation cover type impacted the total germination or the proportion of invasive species in the seedbank. In contrast, we also found that seedbank functional composition in tidal brackish wetlands was not influenced by vegetation cover type in most cases. Instead, plots within a subestuary had similar seedbank functional composition across the years and were composed of diverse functional groups. Based on these findings, we conclude that plant community recovery following P. australis removal is not seed-limited, and any lack of native vegetation recruitment is likely the result of yet-to-be-determined abiotic factors. These diverse seedbanks could lead to resilient wetland communities that could resist invasions. However, due to the prevalence of undesirable species in the seedbank, passive revegetation following invasive plant removal may speed up their re-establishment. The need for active revegetation will need to be assessed on a case-by-case basis to ensure restoration goals are achieved.

Natural Plant Establishment along an Urban Stream, Onondaga Creek, New York

Abstract Urbanization results in a suite of harmful effects to streams, including removal or degradation of riparian vegetation. Many stream-restoration programs address this by adding plants, with limited quantitative knowledge about vegetation dynamics already occurring within the stream corridor. This project examined natural plant establishment along an urbanized stream channel in Syracuse, NY. It had three objectives: first, to relate plant establishment along an urban stream gradient to substrate condition; second, to quantify seeds dormant in the soil at those same sites; and third, to indicate what passive revegetation responses might occur to various treatments along a rural-to-urban gradient. Three sites were selected along such a gradient on Onondaga Creek, near Syracuse, NY. Vegetation plots were established at each site to assess plant germination and establishment under substrate conditions designed to mimic restoration interventions. We also conducted a seedbank study using soil cores colle...

Sewage sludge application for spontaneous plant restoration of a New Caledonian Ferralsol

Soils from New Caledonia typically present poor nutrient content and large quantities of heavy metals such as nickel, chromium and cobalt, resulting in slow plant development. We evaluated the impact of sewage sludge application (0–30 t dry weight (DW) ha–1) on the passive revegetation of a former pine plantation. The spontaneously regenerated plant cover was mainly represented by the dominant Pinus caribaea, a shrub (Sannantha leratii), and a grass (Costularia comosa). The density of pine seedlings was significantly higher in the moderately amended zone (1.2 and 0.2 pines m–2 for 0.5 and 30 t DW ha–1 respectively). The same tendency was observed for S. leratii, but for C. comosa, no net change was observed. With no amendment, after 5 years many species were present, although aboveground biomass (0.3 kg m–2) was low, whereas, with sludge amendment, aboveground biomass was high (5 kg m–2) but diversity low. Amendment increased pine tree heights from 0.15 to 3.92 m with increased amendment from 0 to 30 t DW ha–1. The uptake of nitrogen (N) by pine trees was also improved with sludge supply, as was the uptake of phosphorus (P). Regarding S. leratii, N and P levels were highest at the sludge dosage of 2 t DW ha–1. Carbon storage in P. caribaea biomass increased from 0.40 to 180 kg m–2 with increased amendment applied. Five years after spreading at the highest amendment levels, available soil P remained enhanced. For heavy metal uptake by pine trees, no significant effect of sewage sludge was observed. The optimal dosage to stimulate biodiversity was 0.5–2 t DW ha–1 but maximal biomass was reached at 8–30 t DW ha–1.

Monitoring land cover change of the dryland forest landscape of Central Chile (1975–2008)

Land cover and its configuration in the landscape are crucial components in the provision of biodiversity and ecosystem services. In Mediterranean regions, natural landscapes mostly covered by evergreen vegetation have been to a large extent transformed into cultural landscapes since long time ago. We investigated land cover changes in Central Chile using multi-temporal satellite imagery taken in 1975, 1985, 1999 and 2008. The major trends in this highly dynamic landscape were reduction of dryland forest and conversion of shrubland to intensive land uses such as farmland. The average net annual deforestation rate was −1.7%, and shrubland reduction occurred at an annual rate of −0.7%; agriculture, urban areas and timber plantations increased at annual rates of 1.1%, 2.7% and 3.2%, respectively, during the 1975–2008 period. Total forest and shrubland loss rates were partly offset by passive revegetation. However, most of the areas that were passively revegetated remained as shrubland and did not turn into forests due to a low capacity of forest recovery. This resulted in a progressive loss and degradation of dryland forest over the entire region. Overall, the documented land cover changes increase provisioning services such as crops, cattle, and timber that are characteristic of cultural landscapes in the area but may cause an irreversible loss of biodiversity and a depletion of other ecological services provided by forests and shrubland. The implications for conservation of this area and the need for territorial planning and adapted land-use strategies are discussed.

Integrating ecological uncertainty and farm‐scale economics when planning restoration

Summary Many ecological management problems involve assessing competing options based on the trade‐off between economic costs and short‐ and long‐term probabilities of success. In many cases the time to success is crucial, and opportunity costs may be greater than direct costs of implementation. We analyse the problem of how to choose between options when risks of failure vary systematically. Ecological uncertainty propagates through to uncertainty about economic outcomes. We used an ecological model of tree recruitment that accounted for uncertainty surrounding the effects of climate and seed fall, coupled with a farm economics model, to examine how a land manager should act when deciding between active and passive revegetation (planting seed/seedlings or relying on natural recruitment, respectively) for restoration purposes on a farm managed for livestock production. The outcome of the analysis was driven by the relative sizes of up‐front costs and opportunity costs, which were a function of potential productivity and the time until successful revegetation was achieved. Active revegetation was less costly than passive revegetation in high‐productivity situations, because there was less risk of long periods without production and the associated opportunity costs. At low productivity, passive revegetation was less costly than active revegetation. However, because the probability of a successful outcome increased over time, passive revegetation is only likely to be preferred over medium time‐frames (&gt; 5 years) and the strategy may not be chosen by risk‐averse farmers. Synthesis and applications. This analysis has implications for (i) decision‐making by individual land managers and regional planners and (ii) the design of policies for delivery of incentive schemes targeted at revegetation. Risk‐averse individual land managers are likely to select active regeneration scenarios, particularly when costs of capital works are shared with the community. For a regional planner, the analysis aids thinking about the probable balance of financial assistance schemes for attaining regional objectives: over high‐productivity areas, capital works programmes and short‐term opportunity cost incentives (&lt; 5 years) are cheaper; at low productivity, incentive schemes for medium‐ to long‐term land retirement will be cheaper. This analysis provides a starting point for devising the mix of approaches required to achieve broad‐scale revegetation targets, which would include greater investment in uncertain, long‐term strategies.

Abandonment of agricultural land: an overview of drivers and consequences.

Abstract Agricultural activities and their complex effects on nature conservation, and the services that ecosystems deliver to humans are controversial. We present an overview of land abandonment, its driving forces and its consequences for landscape, biodiversity and humans. A descriptive metaanalysis of independently published studies highlighted the fact that the abandonment of agricultural land is a phenomenon mostly driven by socio-economic factors such as immigration into areas where new economic opportunities are offered to rural people. Ecological drivers such as elevation and land mismanagement leading to soil erosion are of secondary importance. We identified the major problems related to abandonment of agricultural land and quantified their relative importance. In order of decreasing importance, they were biodiversity loss, increase of fire frequency and intensity, soil erosion and desertification, loss of cultural and/or aesthetic values, reduction of landscape diversity and reduction of water provision. The impacts of these problems were not equally relevant in all regions of the world. The abandonment of agricultural land may also benefit humans. The benefits include passive revegetation and active reforestation, water regulation, soil recovery, nutrient cycling and increased biodiversity and wilderness. In a world that is becoming less natural and more intensively exploited by humans, we suggest that (1) farmland must be viewed in a context of multi-functionality to take advantage of ecosystem goods and services, (2) at the global scale, the abandonment of agricultural land is mostly positive for humans and (3) there is a need for the implementation of policies based on the payments for environmental services that encourage human societies to reconcile agricultural use, nature conservation and ecological restoration.

Testing a Passive Revegetation Approach for Restoring Coastal Plain Depression Wetlands

Abstract Restoration of coastal plain depressions, a biologically significant and threatened wetland type of the southeastern United States, has received little systematic research. Within the context of an experimental project designed to evaluate several restoration approaches, we tested whether successful revegetation can be achieved by passive methods (recruitment from seed banks or seed dispersal) that allow for wetland “self‐design” in response to hydrologic recovery. For 16 forested depressions that historically had been drained and altered, drainage ditches were plugged to reestablish natural ponding regimes, and the successional forest was harvested to open the sites and promote establishment of emergent wetland vegetation. We sampled seed bank and vegetation composition 1 year before restoration and monitored vegetation response for 3 years after. Following forest removal and ditch plugging, the restored wetlands quickly developed a dense cover of herbaceous plant species, of which roughly half were wetland species. Seed banks were a major source of wetland species for early revegetation. However, hydrologic recovery was slowed by a prolonged drought, which allowed nonwetland plant species to establish from seed banks and dispersal or to regrow after site harvest. Some nonwetland species were later suppressed by ponded conditions in the third year, but resprouting woody plants persisted and could alter the future trajectory of revegetation. Some characteristic wetland species were largely absent in the restored sites, indicating that passive methods may not fully replicate the composition of reference systems. Passive revegetation was partially successful, but regional droughts present inherent challenges to restoring depressional wetlands whose hydrologic regimes are strongly controlled by rainfall variability.

Early development of vascular vegetation of constructed wetlands in northwest Ohio receiving agricultural waters

Constructed wetlands are currently being explored for use in reducing non-point source (NPS) pollution. The Wetland Reservoir Subirrigation System (WRSIS) project links water management in agricultural fields, constructed wetlands and water storage reservoirs to enhance crop production and reduce delivery of agrichemicals and sediments to local waterways. Three WRSIS demonstration sites have been developed on prior converted cropland in the Maumee River watershed located in northwest Ohio. Construction of the wetlands was completed in 1996 and they were then allowed to passively revegetate while receiving drainage water from adjacent fields. The primary goal of this study was to characterize the initial development of vegetation, and the availability of propagules within these wetlands. Preliminary vegetation inventories conducted in 1998 identified moderate species richness but low percentage of wetland species. A germination study completed on soils from one location showed additional viable wetland species available in the seed bank. Passive revegetation of these three constructed wetlands associated with WRSIS systems has resulted in good vegetation cover, but it is lacking the desired percentage of wetland species to date. Passive revegetation may prove to be an effective and economical method of revegetating constructed wetlands within agricultural landscapes that have suitable propagule availability.