Unplanted Sites Research Articles

Tree restoration and ecosystem carbon storage in an acid and metal impacted landscape: Chronosequence and resampling approaches

Tree restoration on degraded land has been identified as an effective and affordable capture carbon strategy but it is unclear if carbon sequestration rates are comparable to rates on non-industrially impacted silvicultural forests. To this end, we resampled a jack pine (Pinus banksiana) and red pine (P. resinosa) chronosequence 16 years after the initial measurement to quantify carbon pools following ca. 40 years of regreening on an acid and metal impacted landscape. Measured carbon pools were then compared to those reported in an unpublished study to determine how carbon sequestration rates have changed over time and if repeated sampling at the stand level validates temporal trends estimated by the chronosequence. Total ecosystem carbon (TEC) within the stands ranged from 55 to 136 Mg ha−1 with a regional mean of 90.2 ± 9.6 Mg ha−1. On average, tree and soil organic pools (SOC) were the two largest carbon pools, representing 47% and 42% of TEC, respectively. Compared with unplanted sites, tree restoration resulted in a significant increase in the mean TEC among all sites of 54.4 ± 10.2 Mg ha−1 with a corresponding sequestration rate of 1.7 ± 0.3 Mg ha−1 yr−1. The chronosequence approach was only able to consistently detect a change in the tree carbon pool. In contrast, repeated sampling at the stand level identified changes in carbon sequestration rates within SOC, LFH and shrub carbon pools and showed that the chronosequence tree carbon sequestration rate was underestimated by a factor of 2.3. Chronosequence studies assume study sites have similar landscape history and environmental conditions, which may not be reasonable in highly degraded landscapes where past events (e.g., pollution, erosion, restoration) influence multiple landscape characteristics (e.g., local hydrology and topography). We conclude that tree restoration on impacted landscapes can sequester carbon at a rate comparable to silvicultural plantations in a similar climatic region and that reforestation of industrially damaged landscapes could be part of an effective carbon capture strategy.

English

Restoration activities at the time of stand initiation can have lasting effects on subsequent recovery of stand structure and function. Here we compared several metrics, with an emphasis on soils, of structure and function in forest stands that had been planted with pine or remained unplanted, and had undergone primary succession over 48 years on mine spoils. These were also compared to reference sites in the adjacent forest, to test the hypothesis that the development of forest functional processes will differ between planted and unplanted sites. Areas planted to pine had a lower basal area, and lower soil and microbial respiration rates than did unplanted areas. Basal area of unplanted sites was comparable or higher than that of reference sites, suggesting that the natural succession of hardwood may lead to better long-term recovery than planting of pine. Differences in root biomass, along with corresponding differences in soil respiration, suggest that below-ground biomass production recovers more slowly than does above-ground productivity. Mined sites had a greater stock of phosphorus than did reference sites. The greater presence of earthworms on mined sites may speed up nutrient cycling, as indicated by faster cellulose decomposition. Additional keywords: carbon, mining, nitrogen, phosphorus, Pinus

In Situ and Microcosm Investigations into the Phytoremediation of Hydrocarbon-Contaminated Lagoon Sediments Using Phragmites australis

AbstractA phytoremediation study was undertaken at a disused fire training runoff lagoon at an ecologically sensitive area in England. The sediments in the semisaline lagoon were highly contaminated with over 145,000 mg/kg dry weight diesel range organics (DRO). Initial microcosm studies indicated that Phragmites australis and Typha latifolia were able to grow in this sediment, and P. australis was subsequently used for test planting in the lagoon. In situ DRO and microbial populations were investigated over a 15-month period. Results were difficult to interpret due to highly variable DRO concentrations in the sediment and varying water levels. Overall DRO concentrations fell but with no significant differences between planted and unplanted sites. DRO and bacterial numbers were related to moisture content. Hot weather, combined with low water levels, gave the lowest DRO levels. Destructive testing of the microcosms after 3 years also showed no difference in DRO between planted and control; however, eleva...

Successional Models as Guides for Restoration of Riparian Forest Understory

We compare two successional models as guides for restoring native riparian understory species along a 160‐km stretch of the Sacramento River in California. In 2001 and 2007, we surveyed cover, frequency, and richness of native and exotic understory species in 15 sites planted (1989–1996) with overstory species to determine whether native understory species colonized naturally (passive relay floristics model). In 2007, we surveyed 20 additional sites (planted 1997–2003) in 14 of which understory species were planted (initial floristics model) to evaluate whether planting accelerated community recovery. We surveyed 10 remnant forests as references for successional trajectories. Mean cover and frequency of natives changed little over time in sites where they were not planted initially; increases in native cover in a few sites were primarily due to a single common species (Galium aparine). Species composition shifted from light‐demanding to shade‐adapted species, both exotic and native, in response to a doubling of overstory cover. Sites with high intensity understory plantings had greater cover and frequency of native understory species than unplanted sites, but were still low relative to reference forests. Light‐demanding natives (e.g., Artemisia douglasiana, Rubus ursinus, and grasses) established in sites where they were planted; however, a shade‐adapted species (Carex barbarae) did not survive well. Our research indicates that the passive relay floristics and the initial floristic composition approaches serve to restore a few common native understory species, but that planting species as site conditions become appropriate (active relay floristics model) will be needed to restore entire native understory communities.

Long‐term effects of revegetation on soil hydrological processes in vegetation‐stabilized desert ecosystems

AbstractPlanting of sand‐binding vegetation in the Shapotou region on the southeastern edge of the Tengger Desert began in 1956. The revegetation programme successfully stabilized formerly mobile dunes in northern China, permitting the operation of the Baotou‐Lanzhou railway. Long‐term monitoring has shown that the revegetation programme produced various ecological changes, including the formation of biological soil crusts (BSCs). To gain insight into the role of BSCs in both past ecological change and current ecological evolution at the revegetation sites, we used field measurements and HYDRUS‐1D model simulations to investigate the effects of BSCs on soil hydrological processes at revegetated sites planted in 1956 and 1964 and at an unplanted mobile dune site. The results demonstrate that the formation of BSCs has altered patterns of soil water storage, increasing the moisture content near the surface (0–5 cm) while decreasing the moisture content in deeper layers (5–120 cm). Soil evaporation at BSC sites is elevated relative to unplanted sites during periods when canopy coverage is low. Rainfall infiltration was not affected by BSCs during the very dry period that was studied (30 April to 30 September 2005); during periods with higher rainfall intensity, differences in infiltration may be expected due to runoff at BSC sites. The simulated changes in soil moisture storage and hydrological processes are consistent with ongoing plant community succession at the revegetated sites, from deep‐rooted shrubs to more shallow‐rooted herbaceous species. Copyright © 2009 John Wiley & Sons, Ltd.

The early effects of afforestation on biodiversity of grasslands in Ireland

The target rate of afforestation in Ireland over the next 30 years is 20,000 ha per year, which would result in an increase of the forest cover from the current 10% to 17%. In order to promote sustainable forest management practices, it is essential to know the composition and conservation value of habitats where afforestation is planned and the effects of subsequent planting upon biodiversity. The objectives of this study were to investigate changes in vegetation composition and diversity of grasslands 5 years after afforestation with Sitka spruce (Picea sitchensis) and determine the primary ecological and management factors responsible for these changes. Species cover, environmental and management data were collected from 16 afforested and unplanted improved and wet grassland site pairs in Ireland. Our results indicate that 5 years after tree planting, there were significant changes in richness, composition, and abundance of species. Competitive and vigorous grasses were more abundant in planted than in unplanted sites, as were generalist species found in both open and wooded habitats, while small-stature shade-sensitive species were less abundant. Vascular plant species richness and Shannon’s diversity index were higher in unplanted wet grassland, than in the planted sites. Bryophyte species richness was higher in planted improved grassland than in unplanted sites. The differences were primarily the result of the exclusion of grazing, ground preparation, changes in nutrient management and drainage for afforestation. Drainage ditches provided a temporary habitat for less competitive species, but the overall effect of drainage was to reduce the diversity of species dependent on wet conditions. Variance partitioning showed differences in the relative influences of environmental and management variables on biodiversity in the two habitats, probably due to the greater pre-afforestation grazing pressure and fertilisation levels in improved grasslands. The differences in biodiversity between planted and unplanted grasslands indicate that afforestation represents a threat to semi-natural habitats where distinctive and highly localised plant communities could potentially occur.

Soil seed bank analysis of planted and naturally revegetating thermally-disturbed riparian wetland forests

Accelerating the reestablishment of a mature, biotic community following a disturbance is a common goal of restoration ecology. In this study, we describe the relative successional status of a recently disturbed riparian seed bank when compared with less recently disturbed and undisturbed systems, and the short-term effects of restoration on seed bank development within the recently disturbed system. The study location, the U.S. Department of Energy's Savannah River Site in South Carolina, provides a unique opportunity to investigate the development of wetland seed banks following a severe disturbance, in this case the release of elevated temperature and flow effluent from nuclear reactor operations. To assess the recovery of wetland seed banks over time, we compared seed banks of naturally recovering riparian corridor and swamp delta sites of two different ages since disturbance (nine years and 30 years) with undisturbed forested corridor and swamp sites. To assess the potential effects of restoration efforts (site preparation and planting of seedlings) on seed bank development, we compared seed banks of naturally recovering (unplanted) and planted riparian corridor and swamp delta sites in the more recently disturbed system. We expected total germinants and species richness to be highest in the recently disturbed sites and decline as wetland systems matured. Within recently disturbed sites, we expected planted sites to have higher abundance and richness than unplanted sites. We also expected a greater abundance of woody species in the undisturbed forested sites. The number of germinants differed among the sites, ranging from 748 individuals per m 2 in the undisturbed swamp area to 10,322 individuals per m 2 in the recently disturbed planted swamp delta. When corridor and delta sites within a stream system were combined, the mean number of germinants was greater in the recently disturbed system, intermediate in the 30-year (mid-successional) system, and lowest in the undisturbed system. Seed banks from the recently disturbed and mid-successional sites were more similar in composition than they were to the undisturbed systems. Across all stream systems, riparian corridors had greater mean species richness than swamp deltas, though differences in seed bank abundances were not significant. Sedges and rushes were the predominant life forms in the recently disturbed and mid-successional sites, while undisturbed sites had a greater proportion of herbs and woody seedlings. In addition, there were more germinants from planted sites than from unplanted sites. The dominance by early successional species at recently disturbed planted sites may be an unintended consequence of site preparation treatments, and such potential effects should be recognized and weighed during the development of restoration plans.

The initial effects of afforestation on the ground-dwelling spider fauna of Irish peatlands and grasslands

Across Europe, the majority of afforestation is carried out on former agricultural land. Given this current planting trend it is important to assess the impact that afforestation will have on the flora and fauna of habitats typically used for afforestation. The study aim was to investigate the initial effects of afforestation (5 years after planting) on the ground-dwelling spider fauna within three habitats (peatlands, improved grasslands and wet grasslands) in Ireland. A paired sampling approach was used where 24 pairs of unplanted and planted sites (eight within each habitat type) were matched for habitat, vegetation type, soil properties, and geographical location. The planted sites were comprised of 5-year-old stands of Sitka spruce ( Picea sitchensis). Within each habitat pitfall traps were established in areas of vegetation cover representative of the site as a whole, as well as in supplementary features which may also contribute to the biodiversity of a site, for instance in hedgerows, wet flushes, and the edges of ditches or streams. During the study 33,157 spiders were collected in 189 species and 18 families. Forty species sampled were associated with open habitats whereas 15 species were associated with forested habitats, 54 species were associated with wet habitats whereas two species were associated with dry habitats. Across the habitats fewer wet-associated species and fewer rare species were supported after afforestation. In particular areas of wet flush in the peatlands supported a unique and diverse spider fauna which was lost after afforestation. In contrast, the planted improved grasslands were more species rich, and supported a greater number of spider species associated with low vegetation than comparable unplanted sites. The hedgerow spider fauna did not differ notably in assemblage composition between the unplanted and planted sites. This study suggests that even in the early stages of the forest cycle (first 5 years) there is a change in the spider fauna, with the rare or specialist species being replaced by habitat generalists or species associated with forested habitats. It is also suggested that peatlands are particularly sensitive to afforestation, indicating that in terms of biodiversity loss, this habitat is the least suitable for afforestation.

Ecological Restoration of Native Forest at Aratiatia, North Island, New Zealand

AbstractSuccessional pathways in native forest, planted 15–33 years ago on reconstructed surfaces to restore aesthetic values destroyed by hydro‐electric dam construction at Aratiatia, central North Island, New Zealand, were compared with those on similar surfaces left unplanted. Only native species were planted. Classification identified three canopy communities and several ground layer communities with significant inter‐stratum relationships: Pittosporum tenuifolium‐Sophora tetraptera short forest with ground layers dominated by litter; P. tenuifolium‐Kunzea ericoides short forest over adventive grasses on planted sites; and adventive Cytisus scoparius shrubland over grasses on unplanted sites. Planted communities mirror young secondary forests on intact substrates in the district, but have lower density and similar or higher basal area than such forests elsewhere. Established seedlings of seven planted canopy trees, mostly early successional bird‐dispersed species, are reasonably widespread in floristically rich Pittosporum‐Sophora forest. Seedlings of only two species are widespread in floristically poor Pittosporum‐Kunzea forest, and none on unplanted sites. This first large‐scale attempt at ecological restoration in New Zealand, by mass planting of new surfaces with early successional native woody species, has created aesthetically‐pleasing stands of indigenous forest on sites which would otherwise remain in relatively stable adventive shrubland communities for the foreseeable future. Only continued monitoring will show whether further management is necessary and whether natural processes are operating at a level sufficient to ensure that artificially initiated successions will continue along more or less natural pathways.

The effects of conifer forest design and management on abundance and diversity of rove beetles (Coleoptera: Staphylinidae): implications for conservation

The effects of coniferous afforestation on rove beetles (Coleoptera, Staphylinidae) was investigated in Kielder Forest in 1988 by pitfall and turf sampling in plantations of various age and in unplanted sites. Tree planting decreased habitat availability for most beetles, but provided new habitat for forest species. The greatest abundance, species richness and diversity occurred in non-afforested sites. Site ordination demonstrated an upland group on acid soils and a lowland group on mineral soils, with wet and dry components; species ordination was similar. A central forest group was due to both forest species and original species being maintained. Similarly, classification separated closed-canopy forest sites with little ground vegetation from the remainder. Afforestation had increased habitat diversity by adding trees, rides and roads to the original habitats, but diversity per unit area had decreased. Forest managers should aim to increase staphylinid diversity ‘by design’, particularly by varying tree species and age class so as to develop greater biological and structural diversity. Habitat diversity could further beenhanced by conserving representative areas of former land use, such as farm fields, river banks and open moorland; active management might be necessary to sustain these. Staphylinid species are favoured by forest edge habitats, so would gain from the integration of small habitat units within plantations, resulting in a beneficial ‘knock-on’ effect by being food for birds and small mammals.