Rainfall‐Tuned Management Facilitates Dry Forest Recovery

Regeneration of original dry forests and shrublands in degraded arid and semiarid ecosystems can be a slow and difficult process. It has been hypothesized that restoration efforts during periods of increased water availability may potentially trigger shifts back to a high vegetation cover depending on several environmental factors that govern the response of vegetation to rainfall. Tuning restoration efforts to climate variability will likely become increasingly important under climate change conditions. The experiences evaluated here are a pioneering effort to reforest arid South American forests. We used a combination of field monitoring and remote sensing images to evaluate the long‐term effects of seeding and herbivore control in local reforestation projects tuned to the forecasted rainy El Niño Southern Oscillation (ENSO) events of 1991/1992 and 1997/1998 in North Peru and to assess the regional response of vegetation to these rainy events at a regional scale. We found that managing seed availability in combination with seedling protection from herbivores only yielded persistent higher vegetation cover when implemented on sites without calcareous layers and relatively high water availability determined by the surrounding topography. Our study shows that management tuned to forecasted rainfall events is able to trigger a long‐lasting shift toward higher vegetation cover. We provide a better insight in how environmental factors shape vegetation response to increased rainfall and discuss the implications for ecosystem resilience and restoration.     

Vegetation Recovery in Slash‐Pile Scars Following Conifer Removal in a Grassland‐Restoration Experiment

A principal challenge to restoring tree‐invaded grasslands is the removal of woody biomass. Burning of slash piles to reduce woody residues from forest restoration practices generates intense, prolonged heating, with adverse effects on soils and vegetation. In this study, we examined vegetation responses to pile burning following tree removal from conifer‐invaded grasslands of the Oregon Cascades. We quantified the longevity and magnitude of fire effects by comparing ground conditions and the cover and richness of plant species in burn‐scar centers (higher‐intensity fire) and edges (lower‐intensity fire) with adjacent unburned vegetation 7 years after treatment. We interpreted patterns of recovery through the responses of species with differing growth forms, habitat affinities, and clonality. Cover of bare ground remained elevated at the centers, but not at the edges of scars; however, much of this effect was due to gopher disturbance. Total plant cover, consisting entirely of native species, was comparable in and adjacent to scars. However, richness remained depressed at the scar centers. Cover of grass, meadow, and non‐clonal species was comparable in and adjacent to scars, but cover of forb, sedge, residual forest, and clonal species was reduced at the centers. Although scar centers had a simpler community structure (fewer but more abundant species) than the adjacent vegetation, they remained free of exotics and recovered quickly, aided by the soil‐disturbing activities of gophers and the regenerative traits of native, disturbance‐adapted species. Pile burning can be a viable and efficient approach to fuel reduction in the absence of exotics.     

Post‐fire recovery of revegetated woodland communities in south‐eastern Australia

The primary goal of restoration is to create self‐sustaining ecological communities that are resilient to periodic disturbance. Currently, little is known about how restored communities respond to disturbance events such as fire and how this response compares to remnant vegetation. Following the 2003 fires in south‐eastern Australia we examined the post‐fire response of revegetation plantings and compared this to remnant vegetation. Ten burnt and 10 unburnt (control) sites were assessed for each of three types of vegetation (direct seeding revegetation, revegetation using nursery seedlings (tubestock) and remnant woodland). Sixty sampling sites were surveyed 6 months after fire to quantify the initial survival of mid‐ and overstorey plant species in each type of vegetation. Three and 5 years after fire all sites were resurveyed to assess vegetation structure, species diversity and vigour, as well as indicators of soil function. Overall, revegetation showed high (>60%) post‐fire survival, but this varied among species depending on regeneration strategy (obligate seeder or resprouter). The native ground cover, mid‐ and overstorey in both types of plantings showed rapid recovery of vegetation structure and cover within 3 years of fire. This recovery was similar to the burnt remnant woodlands. Non‐native (exotic) ground cover initially increased after fire, but was no different in burnt and unburnt sites 5 years after fire. Fire had no effect on species richness, but burnt direct seeding sites had reduced species diversity (Simpson's Diversity Index) while diversity was higher in burnt remnant woodlands. Indices of soil function in all types of vegetation had recovered to levels found in unburnt sites 5 years after fire. These results indicate that even young revegetation (stands <10 years old) showed substantial recovery from disturbance by fire. This suggests that revegetation can provide an important basis for restoring woodland communities in the fire‐prone Australian environment.     

Hydrologic restoration in a dynamic subtropical mangrove‐to‐marsh ecotone

Extensive hydrologic modifications in coastal regions across the world have occurred to support infrastructure development, altering the function of many coastal wetlands. Wetland restoration success is dependent on the existence of hydrologic regimes that support development of appropriate soils and the growth and persistence of wetland vegetation. In Florida, United States, the Comprehensive Everglades Restoration Program (CERP) seeks to restore, protect, and preserve water resources of the greater Everglades region. Herein we describe vegetation dynamics in a mangrove‐to‐marsh ecotone within the impact area of a CERP hydrologic restoration project currently under development. Vegetation communities are also described for a similar area outside the project area. We found that vegetation shifts within the impact area occurred over a 7‐year period; cover of herbaceous species varied by location, and an 88% increase in the total number of mangrove seedlings was documented. We attribute these shifts to the existing modified hydrologic regime, which is characterized by a low volume of freshwater sheet flow compared with historical conditions (i.e. before modification), as well as increased tidal influence. We also identified a significant trend of decreasing soil surface elevation at the impact area. The CERP restoration project is designed to increase freshwater sheet flow to the impact area. Information from our study characterizing existing vegetation dynamics prior to implementation of the restoration project is required to allow documentation of long‐term project effects on plant community composition and structure within a framework of background variation, thereby allowing assessment of the project's success in restoring critical ecosystem functions.     

Importance of landscape context for post‐restoration recovery of riparian vegetation

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Environmental and socioeconomic drivers of woody vegetation recovery in a human‐modified landscape in the Rio Grande basin (Colombian Andes)

In the tropics, some agricultural lands are abandoned for economic or technical reasons, leading to the recovery of woody vegetation. Our research aimed to identify the main drivers of spontaneous recovery of vegetation in a basin located in the Colombian Andes. This was done by combining spatially explicit environmental and socioeconomic variables at landscape (e.g. distances to human settlements, to roads, and to forests and mean annual precipitation) and local scales (e.g. depth of the organic layer, soil bulk density, and canopy openness). These variables were measured in 28 temporal plots of 500 m² each, established in land cover transitions that showed the recovery of woody vegetation. The recovered woody vegetation between 1986 and 2012 exhibited a gregarious spatial pattern at the landscape scale. Ordination analysis showed distinct floristic composition among transitions and remnant forests, and species associated to each one through an indicator species analysis. Multivariate analyses revealed the relationship between the transitions and variables at both scales. Woody vegetation recovery occurred near remnant forests and far from human settlements at the landscape scale. The soil conditions (content and depth of the organic horizon and bulk density) were the main drivers at the local scale. Our findings also highlight the necessity to define different restoration approaches such as incorporation of sites where socioeconomic and environmental conditions favor the spontaneous recovery of vegetation into the existing network of protected areas in the region, and to implement active restoration projects in perturbed sites to accelerate the recovery process of Andean forests.     

Long‐term plant community trajectories suggest divergent responses of native and non‐native perennials and annuals to vegetation removal and seeding treatments

Land managers frequently apply vegetation removal and seeding treatments to restore ecosystem function following woody plant encroachment, invasive species spread, and wildfire. However, the long‐term outcome of these treatments is unclear due to a lack of widespread monitoring. We quantified how vegetation removal (via wildfire or management) with or without seeding and environmental conditions related to plant community composition change over time in 491 sites across the intermountain western United States. Most community metrics took over 10 years to reach baseline conditions posttreatment, with the slowest recovery observed for native perennial cover. Total cover was initially higher in sites with seeding after vegetation removal than sites with vegetation removal alone, but increased faster in sites with vegetation removal only. Seeding after vegetation removal was associated with rapidly increasing non‐native perennial cover and decreasing non‐native annual cover. Native perennial cover increased in vegetation removal sites irrespective of seeding and was suppressed by increasing non‐native perennial cover. Seeding was associated with higher non‐native richness across the monitoring period as well as initially higher, then declining, total and native species richness. Several cover and richness recovery metrics were positively associated with mean annual precipitation and negatively associated with mean annual temperature, whereas relationships with weather extremes depended on the lag time and season. Our results suggest that key plant groups, such as native perennials and non‐native annuals, respond to restoration treatments at divergent timescales and with different sensitivities to climate and weather variation.     

Response of blanket bog vegetation to drain‐blocking

Question: Does blocking of moorland drains increase bog vegetation on blanket peat? Location: Two sites with blocked drains and two with unblocked drains on Forsinard Flows National Nature Reserve, Sutherland, UK. Methods: Vegetation cover was recorded from 70 locations, with 12 sampling points at different distances (0.5‐14.5 m) from moorland drains in each location. Gradients in the cover of species indicative of wet and dry conditions, as well as bog recovery and degradation in relation to distance from drain, were compared from a sample of drains at two sites with blocked drains and two with unblocked drains. Results: There was evidence for drain‐blocking having a negative effect on vegetation indicative of drier conditions and bog degradation. One of the blocked sites had the lowest values of these indices near to the drain and increasing at greater distances perpendicular from the drain. The two unblocked sites, and the other blocked site, had a contrasting pattern of highest values of these indices close to the drain declining with distance. Cover of species indicative of bog recovery was greater where the drains had been blocked for the longest time. Conclusions: In some cases drain‐blocking can improve the ecological functioning of blanket bogs by increasing cover of healthy bog vegetation. Further studies into the causes of such variability in restoring vegetation through drain‐blocking are needed to aid targeting of peatland restoration projects to areas or methods most likely to be effective.     

Scaling up restoration efforts by simulating the effects of fire to circumvent prescribed burns when preparing restoration sites in South African fynbos ecosystems

The method of clearing alien species and the nature of the soil seedbank influence the quality of restoration outcomes, particularly in fire-prone ecosystems heavily invaded with fire-adapted alien species. One of the challenges encountered is reducing the likelihood of reinvasions when the invading species are equally responsive to restoration treatments. By simulating the fire effects that are required to regenerate native vegetation, the study tested whether the recovery of the native species could be initiated without conducting a prescribed ecological burn. In a case study of South African Cape Flats Sand Fynbos with a heavy invasion of Acacia saligna, the felled acacia were stacked into brush piles, with the litter raked off from the sowing areas and the collected seeds were pre-treated for germination. Despite the lack of a fire, the sowing of pre-treated seeds on raked plots led to good recovery of native vegetation over time. This was indicated by the recovery of higher density, cover and richness of native species in sown plots compared with unsown treatments. However, the recovery of native species had not approached the vegetation structure comparable to a reference site after 2 years; that is, only partial fynbos structure was recovered. The recruitment of acacia was less dense without fire, as hypothesised, and independent of treatment. However, over time, control plots had higher acacia cover than other treatments. Despite this sparse recruitment of acacia, the acacia seedbank decreased naturally to about 50% of the initial size over 2 years in control plots. Raking off litter during site preparation removed 50% of the acacia seedbank which decreased slightly thereafter. Consequently, the residual acacia seedbank was relatively similar across treatments after 2 and a half years. In conclusion, circumventing prescribed burns in heavily degraded fynbos ecosystems is a scalable restoration strategy, as recruitment of alien acacia was minimized, its seedbank declined significantly, and good native cover developed after clearing and sowing.     

Reestablishment of a Rodent Community in Restored Desert Scrub

I conducted small-mammal trapping surveys on a desert scrub restoration site in Palm Springs, California, to document concomitant recovery of the rodent community. These surveys were conducted following quantitative vegetation sampling efforts that indicated that a predefined successful restoration criterion of 15% total shrub cover had been met throughout most of the area. But shrub cover, native shrub cover, herb cover, native herb cover, total cover, and total native cover remained significantly lower in the restoration area than in undeveloped desert scrub immediately surrounding the site. Native herb species richness was also generally lower in the restoration area. Despite these vegetation differences, rodent diversity, evenness, and abundance were very similar between the restoration and natural areas (they were consistently slightly higher in the restoration area). More diverse microhabitats, proximity to water, and reduced competition with harvester ants may have contributed to this outcome. If ecosystem restoration is the goal, reestablishment of a faunal community in restored habitat, rather than surpassing a predefined percent cover of vegetation, may be a better indicator of success, because plant cover proved to be a poor predictor of mammal success.     

Exclusion of livestock grazing and wood collection in dryland savannah: an effect on long‐term vegetation succession

Sahelian savannah faces increasing pressure from human activities, leading to its degradation. The aim of this study was to investigate the possibility of restoration of dryland savannah vegetation by the elimination of disturbance factors on the ecosystem. Is degraded dryland savannah vegetation able to be restored by means of natural succession? What is the timescale for its recovery? The study took place in the Bandia Reserve, 65 km south‐east of Dakar (Senegal), a unique site with two successional stages due to the elimination of uncontrolled exploitation. The vegetation structure of 15 years (15YRS) and 5 years (5YRS) after fencing was compared with vegetation exposed to continuous livestock grazing and wood collection outside the fenced area. Calculated by redundancy analysis, a significant effect of selected areas on the cover of all species was revealed and successional stage explained more than 45% of data variability. Perennial forbs, annual forbs and perennial grasses achieved the highest cover in 5YRS, woody species in 15YRS and annual grasses in the area outside of the fenced reserve. The dominant woody species Acacia seyal, A. ataxacantha, A. nilotica subsp. adstringens and Balanites aegyptiaca reconstituted the dense formation of Acacia bushland by means of natural succession in the 15YRS area.     

Cost‐effective ecological restoration

Ecological restoration is a multibillion dollar industry critical for improving degraded habitat. However, most restoration is conducted without clearly defined success measures or analysis of costs. Outcomes are influenced by environmental conditions that vary across space and time, yet such variation is rarely considered in restoration planning. Here, we present a cost‐effectiveness analysis of terrestrial restoration methods to determine how practitioners may restore the highest native plant cover per dollar spent. We recorded costs of 120 distinct methods and described success in terms of native versus non‐native plant germination, growth, cover, and density. We assessed effectiveness using a basic, commonly used metric (% native plant cover) and developed an index of cost‐effectiveness (% native cover per dollar spent on restoration). We then evaluated success of multiple methods, given environmental variation across topography and multiple years, and found that the most successful method for restoring high native plant cover is often different from the method that results in the largest area restored per dollar expended, given fixed mitigation budgets. Based on our results, we developed decision‐making trees to guide practitioners through established phases of restoration—site preparation, seeding and planting, and maintenance. We also highlight where additional research could inform restoration practice, such as improved seasonal weather forecasts optimizing allocation of funds in time or valuation practices that include costs of specific outcomes in the collection of in lieu fees.     

A test of critical thresholds and their indicators in a desertification‐prone ecosystem: more resilience than we thought

Theoretical models predict that drylands can cross critical thresholds, but experimental manipulations to evaluate them are non‐existent. We used a long‐term (13‐year) pulse‐perturbation experiment featuring heavy grazing and shrub removal to determine if critical thresholds and their determinants can be demonstrated in Chihuahuan Desert grasslands. We asked if cover values or patch‐size metrics could predict vegetation recovery, supporting their use as early‐warning indicators. We found that season of grazing, but not the presence of competing shrubs, mediated the severity of grazing impacts on dominant grasses. Recovery occurred at the same rate irrespective of grazing history, suggesting that critical thresholds were not crossed, even at low cover levels. Grass cover, but not patch size metrics, predicted variation in recovery rates. Some transition‐prone ecosystems are surprisingly resilient; management of grazing impacts and simple cover measurements can be used to avert undesired transitions and initiate restoration.     

Weather effects on birds of different size are mediated by long‐term climate and vegetation type in endangered temperate woodlands

Species occurrence is influenced by a range of factors including habitat attributes, climate, weather, and human landscape modification. These drivers are likely to interact, but their effects are frequently quantified independently. Here, we report the results of a 13‐year study of temperate woodland birds in south‐eastern Australia to quantify how different‐sized birds respond to the interacting effects of: (a) short‐term weather (rainfall and temperature in the 12 months preceding our surveys), (b) long‐term climate (average rainfall and maximum and minimum temperatures over the period 1970–2014), and (c) broad structural forms of vegetation (old‐growth woodland, regrowth woodland, and restoration plantings). We uncovered significant interactions between bird body size, vegetation type, climate, and weather. High short‐term rainfall was associated with decreased occurrence of large birds in old‐growth and regrowth woodland, but not in restoration plantings. Conversely, small bird occurrence peaked in wet years, but this effect was most pronounced in locations with a history of high rainfall, and was actually reversed (peak occurrence in dry years) in restoration plantings in dry climates. The occurrence of small birds was depressed—and large birds elevated—in hot years, except in restoration plantings which supported few large birds under these circumstances. Our investigation suggests that different mechanisms may underpin contrasting responses of small and large birds to the interacting effects of climate, weather, and vegetation type. A diversity of vegetation cover is needed across a landscape to promote the occurrence of different‐sized bird species in agriculture‐dominated landscapes, particularly under variable weather conditions. Climate change is predicted to lead to widespread drying of our study region, and restoration plantings—especially currently climatically wet areas—may become critically important for conserving bird species, particularly small‐bodied taxa.     

Increase in nonnative understorey vegetation cover after nonnative conifer removal and passive restoration

Nonnative conifers are widespread in the southern hemisphere, where their use as plantation species has led to adverse ecosystem impacts sometimes intensified by invasion. Mechanical removal is a common strategy used to reduce or eliminate the negative impacts of nonnative conifers, and encourage native regeneration. However, a variety of factors may preclude active ecological restoration following removal. As a result, passive restoration – unassisted natural vegetation regeneration – is common following conifer removal. We asked, ‘what is the response of understorey cover to removal of nonnative conifer stands followed by passive restoration?' We sampled understorey cover in three site types: two‐ to ten‐year‐old clearcuts, native forest and current plantations. We then grouped understorey species by origin (native/nonnative) and growth form, and compared proportion and per cent cover of these groups as well as of bare ground and litter between the three site types. For clearcuts, we also analysed the effect of time since clearcut on the studied variables. We found that clearcuts had a significantly higher average proportion of nonnative understorey vegetation cover than native forest sites, where nonnative vegetation was nearly absent. The understorey of clearcut sites also averaged more overall vegetation cover and more nonnative vegetation cover (in particular nonnative shrubs and herbaceous species) than either plantation or native forest sites. Notably, 99% of nonnative shrub cover in clearcuts was the invasive nonnative species Scotch broom (Cytisus scoparius). After ten years of passive recovery since clearcutting, the proportion of understorey vegetation cover that is native has not increased and remains far below the proportion observed in native forest sites. Reduced natural regeneration capacity of the native ecosystem, presence of invasive species in the surrounding landscape and land‐use legacies from plantation forestry may inhibit native vegetation recovery and benefit opportunistic invasives, limiting the effectiveness of passive restoration in this context. Abstract in Spanish is available with online material.     

Performance of Vegetation in Reclaimed Slopes Affected by Soil Erosion

Soil erosion in reclaimed mines may affect plant colonization and performance, and may compromise restoration success; however, the magnitude of this effect has seldom been quantified. We monitored the dynamics of vegetation (seed bank density, seedling emergence, plant mortality, and seed production) during a growing season (2003–2004) in three constructed slopes with differing past erosion rates. The slopes are located in the Utrillas coalfield in Spain, which experiences a Mediterranean‐continental climate. In the most eroded slope, soil water availability was lower—especially in the interrill areas—and seedling emergence rate, plant survival, and seed production were also significantly lower than on the less eroded slopes. We found that vegetation recovery is dramatically constrained when rill erosion rate is 17 t ha^?1 yr^?1 and plant cover is 30%, but this effect disappears when plant cover is higher than 60%. Soil erosion in constructed slopes appears to inhibit natural plant colonization processes by increasing runoff water loss over the long‐term. Thus, when rill erosion networks develop, human intervention would be needed to minimize the loss of water and facilitate vegetation colonization.     

Vegetation dynamics following trampling in rich fen at Sølendet, Central Norway; a 15 year study of recovery

In Sølendet nature reserve in the upper boreal of central Norway, the effects of controlled trampling from 1977 to 1981 were observed in four rich fen localities. The vegetation recovery was monitored on permanent plots on 3–4 occasions during the period 1981–1995. During trampling the vegetation cover was reduced and bare peat increased, particularly in a wet fen expanse locality. Woody species and herbs disappeared or were considerably reduced in cover, while some graminoids (e.g. Carex spp. and Eriophorum angustifolium ) and bryophytes (e.g. Campylium stellatum and Scorpidium cossonii ), appeared to be quite tolerant. Equisetum palustre and Eriophorum angustifolium increased in cover on two tracks. Several bryophytes survived trampling, but Sphagnum warnstorfii was eradicated. Campylium stellatum and Tomentypnum nitens were able to increase after the decrease in S. warnstorfii . The recovery was dependent on which species were present at the outset and which species arrived early. Further development seemed to depend largely on the species' capacity for rapid increase in cover. Eventually, the more vulnerable dominants of the untrampled vegetation (e.g. Thalictrum alpinum, Trichophorum cespitosum and Sphagnum warnstorfii ) increased in abundance. After 15 years the tracks still contained fewer species and had less vegetation cover than the surroundings.     

Low‐cost grass restoration using erosion barriers in a degraded African rangeland

Rangeland degradation, typified by extensive bare ground and soil erosion, is a serious problem around the world. In sub‐Saharan Africa, rangeland degradation threatens the food security of millions of people who depend on livestock and the region's large mammalian wildlife diversity. We tested the ability of five simple, low‐cost erosion barriers to promote grass and forb establishment in a bare ground‐dominated rangeland in Kenya. These treatments were: (1) trenches with small berms; (2) bundles of branches; and bundles of branches with (3) elephant dung balls, (4) burlap sacking, or (5) nylon mesh sacking inside them. We also tested whether barrier performance depended on (1) supplemental seeding with the grass Cenchrus ciliaris and (2) whether a barrier was located next to existing vegetation patches versus in the open. Within months, the trench and nylon mesh barriers had accumulated 20–50% more sediment than other treatments and had greater grass and forb seedling establishment. Seeding with Cenchrus resulted in higher herbaceous cover but was not necessary for other grasses to establish. After 3 years, the trench and nylon mesh barriers had created patches of new vegetation averaging 18–63% larger than patches created by the other treatments. Barriers that were initially adjacent to existing vegetation had created new vegetation patches averaging 65% larger than those created by solitary barriers. Results suggest that all barrier types increase grass cover but that trenches—especially if placed next to existing vegetation patches—are a particularly cost‐effective way to reduce bare ground and erosion in degraded rangelands.     

Short‐term vegetation recovery after alien plant clearing along the Rondegat River,South Africa

The outcomes of ecosystem restoration projects should be periodically monitored to inform subsequent adaptive management decisions. In 2012, a project was begun to remove both invasive alien plants and fish from the Rondegat River in South Africa. Although the initial post‐intervention dynamics of aquatic fauna have been documented, the results of the simultaneous clearing of dense riparian stands of alien trees and shrubs have not been reported. We examined native riparian vegetation recovery over 3 years after alien plant clearing. We documented increased cover of native riparian shrubs, but a simultaneous increase of alien and native weedy grass cover. Secondary invasions, especially by grasses, can have strong effects on ecosystem dynamics and achieving the goals of restoration may therefore require additional active management. Our findings provide an initial baseline reference for future monitoring and adaptive management decisions.