Showing papers in "Restoration Ecology in 2003"
TL;DR: In this article, the authors assessed nine buffer zone schemes in North Island, New Zealand that had been fenced and planted (age range from 2 to 24 years) and compared them with unbuffered control reaches upstream or nearby.
Abstract: River and stream rehabilitation projects are increasing in number, but the success or failure of these projects has rarely been evaluated, and the extent to which buffers can restore riparian and stream function and species composition is not well understood. In New Zealand the widespread conversion of forest to agricultural land has caused degradation of streams and riparian ecosystems. We assessed nine riparian buffer zone schemes in North Island, New Zealand that had been fenced and planted (age range from 2 to 24 years) and compared them with unbuffered control reaches upstream or nearby. Macroinvertebrate community composition was our prime indicator of water and habitat quality and ecological functioning, but we also assessed a range of physical and water quality variables within the stream and in the riparian zone. Generally, streams within buffer zones showed rapid improvements in visual water clarity and channel stability, but nutrient and fecal contamination responses were variable. Significant changes in macroinvertebrate communities toward “clean water” or native forest communities did not occur at most of the study sites. Improvement in invertebrate communities appeared to be most strongly linked to decreases in water temperature, suggesting that restoration of in-stream communities would only be achieved after canopy closure, with long buffer lengths, and protection of headwater tributaries. Expectations of riparian restoration efforts should be tempered by (1) time scales and (2) spatial arrangement of planted reaches, either within a catchment or with consideration of their proximity to source areas of recolonists.
207 citations
TL;DR: In this paper, the authors focus on the western United States and look at the question of fire regimes, the single human impact which could have altered the environment at a broad, landscape scale.
Abstract: For nearly two centuries, the creation myth for the United States imagined European settlers arriving on the shores of a vast, uncharted wilderness. Over the last two decades, however, a contrary vision has emerged, one which sees the country's roots not in a state of "pristine" nature but rather in a "human-modified landscape" over which native peoples exerted vast control. Fire, Native Peoples, and the Natural Landscape seeks a middle ground between those conflicting paradigms, offering a critical, research-based assessment of the role of Native Americans in modifying the landscapes of pre-European America. Contributors focus on the western United States and look at the question of fire regimes, the single human impact which could have altered the environment at a broad, landscape scale, and which could have been important in almost any part of the West. Each of the seven chapters is written by a different author about a different subregion of the West, evaluating the question of whether the fire regimes extant at the time of European contact were the product of natural factors or whether ignitions by Native Americans fundamentally changed those regimes. An Introductory essay offers context for the regional chapters, and a concluding section compares results from the various regions and highlights patterns both common to the West as a whole and distinctive for various parts of the western states. The final section also relates the findings to policy questions concerning the management of natural areas, particularly on federal lands, and of the "naturalness" of the pre-European western landscape.
184 citations
TL;DR: If restoration is to be successful as compensatory mitigation, restoration success standards must be expanded to include arthropod communities, which are less diverse and have altered guild structure.
Abstract: Ecological restoration enjoys widespread use as a technique to mitigate for environmental damage. Success of a restoration project often is evaluated on the basis of plant cover only. Recovery of a native arthropod fauna is also important to achieve conservation goals. I sampled arthropod communities by pitfall trapping in undisturbed, disturbed, and restored coastal sage scrub habitats in southern California. I evaluated arthropod community composition, diversity, and abundance using summary statistics, cluster analysis, and detrended correspondence analysis (DCA) and investigated influence of vegetation on arthropod communities with multiple regression analysis. Arthropod diversity at undisturbed and disturbed sites was greater than at sites that were 5 and 15 years following restoration ( p � 0.05). Number of arthropod species was not significantly different among undisturbed, disturbed, and restored sites, and two restoration sites had significantly more individuals than other sites. Vegetation at disturbed and undisturbed sites differed significantly; older restorations did not differ significantly from undisturbed sites in diversity, percent cover, or structural complexity. In multiple regression models, arthropod species richness and diversity was negatively related to vegetation height but positively related to structural complexity at intermediate heights. Exotic arthropod species were negatively associated with overall arthropod diversity, with abundance of the earwig Forficula auricularia best predicting diversity at comparison (not restored) sites ( r 2 � 0.29), and abundance of the spider Dysdera crocata and the ant Linepithema humile predicting diversity at all sites combined ( r 2 � 0.48). Native scavengers were less abundant at restored sites than all other sites and, with a notable exception, native predators were less abundant as well. DCA of all species separated restored sites from all other sites on the first axis, which was highly correlated with arthropod diversity and exotic arthropod species abundance. Lower taxonomic levels showed similar but weaker patterns, with example families not discriminating between site histories. Vegetation characteristics did not differ significantly between the newly restored site and disturbed sites, or between mature restoration sites and undisturbed sites. In contrast, arthropod communities at all restored sites were, as a group, significantly different from both disturbed and undisturbed sites. As found in other studies of other restoration sites, arthropod communities are less diverse and have altered guild structure. If restoration is to be successful as compensatory mitigation, restoration success standards must be expanded to include arthropods.
176 citations
TL;DR: In this paper, the authors analyzed and compared vegetation on both spontaneously revegetated and technically reclaimed spoil heaps of different ages in one of the largest active brown coal mining districts in Europe.
Abstract: Vegetation samples from either spontaneously revegetated or technically reclaimed spoil heaps of different ages in one of the largest active brown coal mining districts in Europe were analyzed and compared. The spoil heaps are located in the northwestern part of the Czech Republic and represent ages between 0 and 45 years. Ordination analysis (detrended correspondence analysis) showed that vegetation on technically reclaimed spoil heaps developed in a different way than that on spontaneously revegetated ones. The latter exhibited much higher species diversity in the oldest stages with the number of species doubled that of technically reclaimed sites. The oldest stages were also more advanced along an expected successional gradient as indicated by the ordination. Accelerating the vegetation development by technical reclamation was only of temporal character, whereas spontaneous succession proceeded further over the longer time scale. Spontaneous succession is advocated as an inexpensive and easy alternative to technical reclamation, because it leads to a more natural and rich vegetation cover. Unfortunately, technical reclamation is still the only approach considered in the present reclamation activities for this region.
156 citations
TL;DR: It is suggested that although the rates of faunal recolonization will vary, with time most or all mammal, bird, reptile, and ant species should inhabit rehabilitated bauxite mines.
Abstract: Fauna serve a key role in many forest ecological processes. Despite this, few studies have considered long-term faunal recolonization after mining and rehabilitation of forest ecosystems. In the jarrah forest of southwestern Australia, permanent fauna monitoring sites have been established in bauxite mined areas rehabilitated in 1990 and in a range of representative unmined forest control sites. At each site mammals, birds, reptiles, and ants were surveyed in 1992, 1995, and 1998. The aims of the monitoring were to develop a better understanding of faunal recolonization trends, to produce recommendations for promoting fauna return, and to consider which techniques and fauna groups are best suited for monitoring recolonization. The results showed that successional trends varied between fauna groups. Generalist foraging mammals recolonized rapidly, whereas small predators took longer. Feral mice were initially abundant and then declined. Birds gradually recolonized, and after 8 years bird communities were very similar to those in unmined forest sites. Reptile species took longer, and after 8 years numbers of species remained lower than in unmined forests. Species richness and diversity of ants in 8-year-old rehabilitation were comparable with those of unmined forest in some rehabilitated sites but were lower in others. The composition of ant communities was still different from that of unmined sites. Ant species that only use disturbed forest declined rapidly in abundance as rehabilitation aged. The results suggest that although the rates of faunal recolonization will vary, with time most or all mammal, bird, reptile, and ant species should inhabit rehabilitated bauxite mines. The densities of many are likely to be similar to those in unmined forest, but for others it is too early to know whether this will be the case. Techniques for promoting fauna return are discussed. This study demonstrates that no single fauna group is suitable for use as an overall “indicator” of faunal recolonization; different fauna species and groups reflect different aspects of faunal succession.
152 citations
TL;DR: In this article, the authors compared the floristic composition and structure of restoration areas of eucalypt woodland with untreated pasture (control) and remnant vegetation (reference) in western Sydney.
Abstract: We compared the floristic composition and structure of restoration areas of eucalypt woodland with untreated pasture (control) and remnant vegetation (reference) in western Sydney. The restored areas comprised over 1,000 ha of abandoned pasture, which had been treated to reduce weeds and planted with seedlings of 26 native plant species raised from seed obtained locally from remnant vegetation. Plantings were carried out 0–9 years ago. Floristic composition was measured in quadrats using frequency scores and cover abundance. As far as possible treatments and restoration ages were replicated across sites. Ordination and analyses of similarity failed to distinguish the composition of restored vegetation from that of untreated pasture, which were both significantly different from that of remnant vegetation. There was a weak compositional trend with age of restored vegetation, but this was not in the direction of increasing resemblance to remnant vegetation. There was some evidence for convergence in structural features of restored with remnant vegetation, but this was at least partly attributed to plant growth. Subject to constraints imposed by the sampling design, environmental factors, and spatial variation were discounted as explanations for the results. The results therefore suggest either failure of restoration treatments or a restoration trajectory that is too slow to detect within 10 years of establishment. Our conclusions agree with those of similar studies in other ecosystems and support: (1) the need to monitor restoration projects against ecological criteria with rigorous sampling designs and analytical methods, (2) further development of restoration methods, and (3) regulatory approaches that seek to prevent damage to ecosystems rather than those predicated on replacing losses with reconstructed ecosystems.
144 citations
TL;DR: The restoration gene pool concept provides a place for cultivars of native species and noninvasive introduced plant material when use of native-site material is not feasible.
Abstract: Restoration practitioners have long been faced with a dichotomous choice of native versus introduced plant material confounded by a general lack of consensus concerning what constitutes being native The “restoration gene pool” concept assigns plant materials to one of four restoration gene pools (primary to quaternary) in order of declining genetic correspondence to the target population Adaptation is decoupled from genetic identity because they often do not correspond, particularly if ecosystem function of the disturbed site has been altered Because use of plant material with highest genetic identity, that is, the primary restoration gene pool, may not be ultimately successful, material of higher order pools may be substituted This decision can be made individually for each plant species in the restored plant community in the scientific context that ecosystem management demands The restoration gene pool concept provides a place for cultivars of native species and noninvasive introduced plant material when use of native-site material is not feasible The use of metapopulation polycrosses or composites and multiple-origin polycrosses or composites is encouraged as appropriate The restoration gene pool concept can be implemented as a hierarchical decision-support tool within the larger context of planning seedings
125 citations
TL;DR: In this article, the authors added bird perches to six Puerto Rican landslides with three types of surfaces (bare, climbing fern, grass) in an effort to facilitate inputs of forest seeds through bird dispersal and to accelerate plant succession.
Abstract: Landslides result in the loss of vertical vegetative structure, soil nutrients, and the soil seed bank. These losses impede timely recovery of tropical forest communities. In this study we added bird perches to six Puerto Rican landslides with three types of surfaces (bare, climbing fern, grass) in an effort to facilitate inputs of forest seeds through bird dispersal and to accelerate plant succession. Numbers of bird-dispersed forest seeds were significantly higher in plots beneath introduced perches than in control plots. Perches did not increase forest seedling densities compared with control plots. Seven different species of birds were observed on introduced perches. Because 99% of the seed inputs to controls and perch plots in the six landslides were wind-dispersed seeds (mostly graminoids), perches can improve landslide restoration if woody plants establish and shade out the dominant graminoid and climbing fern ground cover. Although increasing seed inputs from forest species is a critical step in accelerating revegetation of landslides, we suggest that supplemental restoration techniques be applied in addition to bird perches to promote forest recovery.
122 citations
TL;DR: In this investigation fragments of Acropora pulchra were used in a semiprotected nursery in southern Taiwan to test the possible effects of different factors on the generation of new branches and the initial skeletal extension rates of transplants.
Abstract: Coral reef degradation has been widely reported for the past 20 years. Because the recovery rate is usually low, various methods of restoration have been explored in different regions of the world. Among the effective and commonly used methods to restore coral communities is the transplantation of coral colonies or fragments. In this investigation fragments of Acropora pulchra were used in a semiprotected nursery in southern Taiwan between 1996 and 1998 to test, in situ, the possible effects of different factors on the generation of new branches and the initial skeletal extension rates of transplants. The variables under study here were the origin and length of the fragments, their new orientation, presence of tissue injury, and position in the fragment. All these factors were found to make a difference in either one or both aspects of coral growth (i.e., branching frequency and skeletal extension rate). These two factors clearly determine the success rate of a small fragment developing into a large colony that has a much higher probability to survive and grow on its own. It is now obvious that the efficiency of coral generation through fragment culture can be enhanced if the variables examined here are taken into consideration. Once coral colonies are formed, they can be fragmented again to generate more corals or can be transplanted to a suitable site.
121 citations
TL;DR: The effects of prescribed fire on the morphology, abundance, and phenology of nine abundant forb (herbaceous dicot) species used selectively by Centrocercus urophasianus (Sage Grouse) were examined.
Abstract: Historic fire return intervals in Artemesia tridentata (big sagebrush) ecosystems have been altered by livestock grazing, fire suppression, and other land management techniques resulting in ecological changes in these areas. Increases in abundance of woody vegetation may be causing declines in native herbaceous understory species. We examined the effects of prescribed fire on the morphology, abundance, and phenology of nine abundant forb (herbaceous dicot) species used selectively by Centrocercus urophasianus (Sage Grouse). In September 1997 prescribed fire was applied to four of eight randomly assigned 400-ha A.t. wyomingensis (Wyoming big sagebrush) study plots at Hart Mountain National Antelope Refuge, Oregon. Livestock had not grazed experimental plots since 1991. Burning caused morphological changes such as significantly greater numbers of racemes and flowers per raceme in Astragalus malachus (shaggy milkvetch-Legumoideae) (9 in burn vs. 6 in control; 23 in burn vs. 21 in control, respectively). Also, prescribed burning caused greater numbers of flowers in Phlox gracilis (microsteris-Polemoniaceae) (57 vs. 13), greater numbers of umbels and umbelletts in Lomatium nevadense (Nevada desert parsley-Umbellifereae) (4 vs. 2 and 59 vs. 31, respectively), greater numbers of flower heads in Crepis modocensis (Modoc hawksbeard-Compositae) (32 vs. 21), and greater number of flowers/cm3 in Phlox longifolia (longleaf phlox-Polemoniaceae) (0.11 vs. 0.06). Crown volume of Crepis modocensis (7,085 vs. 4,179 cm3) and Astragalus malachus (2,854 vs. 1,761 cm3) plants was greater in burned plots than control plots. However, burning resulted in a smaller crown area of Antennaria dimorpha (low pussytoes-Compositae) (20 vs. 37 cm2). Phenology and time of flowering were also affected by fire. The period of active growth for each species was extended later into the summer in burned plots ( p < 0.01). In addition, Crepis modocensis and Lomatium nevadense flowered 12 to 14 days earlier in burned plots. Fire had no effect on frequency, density, and relative abundance of seven of the nine studied species. Fire reduced the frequency and relative abundance of A. dimorpha and Phlox longifolia and reduced the density of A. dimorpha.
118 citations
TL;DR: Results suggest that sensitivity to drought preconditioning may be related to drought tolerance or avoidance strategy of each species, and Drought-related strategies should be considered to optimize management scale preconditionsing.
Abstract: Arid and semiarid ecosystems in the Mediterranean are under high risk of desertification. Revegetation with native well-adapted evergreen shrubs is desirable, but techniques for successful establishment of these species are not fully developed. Transplant shock is a key hurdle to plantation success. The application of a drought-preconditioning treatment during the last months of nursery culture is a potential technique for reducing transplant shock. This technique has been widely applied in boreal habitats and humid temperate areas. Three representative Mediterranean species (Pistacia lentiscus, Quercus coccifera, and Juniperus oxycedrus seedlings) were exposed to classic drought-preconditioning treatment consisting of reductions in the watering regime. The effects of preconditioning on seedling quality were assessed by cell water relationships (pressure-volume curves), minimal transpiration, leaf capacitance, chlorophyll fluorescence, and gas exchange. Moreover, seedlings were exposed to transplant shock (intense drought period) during which water potential (predawn and midday) and maximal photochemical efficiency were evaluated to establish seedling performance. Results showed that preconditioning did not affect cell water relationships and minimal transpiration in any of the three species. Preconditioned seedlings of P. lentiscus maintained higher water content during desiccating conditions as a consequence of an increase in leaf water content at full turgor. These changes allowed plants to maintain higher net CO 2 assimilation rates and an elevated photosystem II status, facilitating an increase in drought survival. Preconditioning improved the performance of Q. coccifera and J. oxycedrus seedlings, but these two species were much less responsive than P. lentiscus seedlings. Finally, results suggest that sensitivity to drought preconditioning may be related to drought tolerance or avoidance strategy of each species. Drought-related strategies should be considered to optimize management scale preconditioning.
TL;DR: In this article, the authors compared three different vegetation sampling techniques to determine the accuracy associated with each method when used to determine species composition and cover in restored Pacific coast wetlands dominated by Salicornia virginica (perennial pickleweed).
Abstract: Efficient and accurate vegetation sampling techniques are essential for the assessment of wetland restoration success. Remotely acquired data, used extensively in many locations, have not been widely used to monitor restored wetlands. We compared three different vegetation sampling techniques to determine the accuracy associated with each method when used to determine species composition and cover in restored Pacific coast wetlands dominated by Salicornia virginica (perennial pickleweed). Two ground-based techniques, using quadrat and line intercept sampling, and a remote sensing technique, using low altitude, high resolution, color and color infrared photographs, were applied to estimate cover in three small restoration sites. The remote technique provided an accurate and efficient means of sampling vegetation cover, but individual species could not be identified, precluding estimates of species density and distribution. Aerial photography was determined to be an effective tool for vegetation monitoring of simple (i.e., single-species) habitat types or when species identities are not important (e.g., when vegetation is developing on a new restoration site). The efficiency associated with these vegetation sampling techniques was dependent on the scale of the assessment, with aerial photography more efficient than ground-based sampling methods for assessing large areas. However, the inability of aerial photography to identify individual species, especially mixed-species stands common in southern California salt marshes, limits its usefulness for monitoring restoration success. A combination of aerial photography and ground-based methods may be the most effective means of monitoring the success of large wetland restoration projects.
TL;DR: This paper investigated effects of fire frequency, seasonal timing, and plant community on patchiness and intensity of prescribed fires in subtropical savannas in the Long Pine Key region of Everglades National Park, Florida (U.S.A.).
Abstract: We investigated effects of fire frequency, seasonal timing, and plant community on patchiness and intensity of prescribed fires in subtropical savannas in the Long Pine Key region of Everglades National Park, Florida (U.S.A.). We measured patchiness and intensity in different plant communities along elevation gradients in “fire blocks.” These blocks were prescribed burned at varying times during the lightning season and at different frequencies between 1995 and 2000. Fire frequency, seasonal timing, and plant community all influenced the patchiness and intensity of prescribed fires. Fires were less patchy and more intense, probably because of drier conditions and pyrogenic fuels, in higher elevation plant communities (e.g., high pine savannas) than in lower elevation communities (e.g., long-hydroperiod prairies). In all plant communities fires became increasingly patchy and less intense as the wet season progressed and moisture accumulated in fuels. Frequent prescribed fire resulted in increased patchiness but a wider range of intensities; higher intensities appeared to result from regrowth of more flammable vegetation. Our study suggests that frequent early lightning season prescribed fires produce a wider range of post-fire conditions than less frequent late lightning season prescribed fires. Our study also suggests that natural early lightning season fires readily carried through pine savannas and short-hydroperiod prairies, but lower elevation long-hydroperiod prairies functioned as firebreaks. Natural fires probably crossed these firebreaks only during drier years, potentially producing large landscape-level fires. Knowledge of how patchily and intensely fires burn across a savanna landscape should be useful for developing landscape-level fire management.
TL;DR: In this article, the authors investigated the role of nebkhas of a leguminous shrub, Retama raetam (white broom), in the restoration of arid and semi-arid environments.
Abstract: Natural accumulation of wind-borne sediments within or around the canopies of plants plays an important role in the ecological and evolutionary dynamics of many coastal and desert ecosystems. The formation of such phytogenic mounds (nebkhas) creates patches that can strongly influence the spatial distribution of plant and soil resources. In land restoration of arid and semiarid environments it is important to study the potential role of such biological patchiness that may provide sites for coexistence of species with different life and growth forms. Our main objective was to test whether the nebkhas of a leguminous shrub, Retama raetam (white broom), promote restoration of herbaceous vegetation and soil in the degraded rangelands of northern Sinai. Vegetation and microclimatic and edaphic characteristics within the nebkhas, as well as within internebkha spaces, were compared for ungrazed and grazed sites. Abundance and richness of herbaceous plants were positively related to nebkha area, which explained more of the variance of abundance and richness in the grazed site than in the ungrazed one. Protection from grazing, especially on nebkhas, was associated with an increase in abundance and richness of herbaceous plants, improved soil microclimate, and increased soil fine particles and nutrient concentrations. The results suggest that management (in casu protection from grazing) of nebkhas of woody perennial shrubs changes rangeland conditions and improves the resource regulatory processes. Furthermore, nebkhas of unpalatable plants have the potential to preserve plant diversity in overgrazed plant communities, because they are effective in capturing and retaining water, soil materials, and propagules within and from nearby areas, resources that would otherwise be lost.
TL;DR: Herbicides suppress but do not eliminate introduced grasses, so the interaction of herbicide with two additional controls: heavy clipping (to simulate grazing) and competition from native species was explored.
Abstract: Introduced perennial grasses are one of the greatest constraints to prairie restoration. Herbicides suppress but do not eliminate introduced grasses, so we explored the interaction of herbicide with two additional controls: heavy clipping (to simulate grazing) and competition from native species. A 50-year-old stand of the introduced perennial grass Agropyron cristatum (crested wheatgrass) in the northern Great Plains was seeded with native grasses and treated with herbicide annually for 7 years in a factorial experiment. Clipping was applied as a subplot treatment in the final 3 years. Both herbicide and clipping significantly reduced the cover of A. cristatum, but clipping produced an immediate and consistent decrease, whereas herbicide control varied among years. The cover of A. cristatum decreased significantly with increasing cover of a seeded native grass, Bouteloua gracilis (blue grama), suggesting that both top-down (i.e., grazing) and bottom-up (i.e., resource competition) strategies can contribute to A. cristatum control. No treatment had any effect on the seed bank of A. cristatum. Even in the most effective control treatments, A. cristatum persisted at low amounts (approximately 5% cover) throughout the experiment. The cover of B. gracilis increased significantly with seed addition and herbicide, and, after 7 years, was similar to that in undisturbed prairie. The total cover of native species increased significantly with clipping and herbicide, and species richness was significantly higher in plots receiving herbicide. Clipping season had no effect on any variable. In summary, no method extirpated A. cristatum, but clipping reduced its cover by 90% and doubled the cover of native species. Extirpation might not be a realistic goal, but relatively simple management allowed coexistence of native species.
TL;DR: The results suggest that all three factors— seasonal drought, belowground competition, and low soil nutrients—can significantly impair seedling growth on a degraded hillside site in Hong Kong but that their relative importance differs among species.
Abstract: The effects of seasonal drought, belowground competition, and low soil fertility on the survival and growth over 2 years of four native tree species planted on a degraded hillside grassland in Hong Kong were studied in a field transplant experiment using three-way analysis of variance. The tree species were Schima superba (Theaceae), Castanopsis fissa (Fagaceae), Schefflera octophylla (Araliaceae), and Sapium discolor (Euphorbiaceae), and the treatments were dry season irrigation, herbicide, and fertilizer. Each species responded differently to the treatments. Sapium had a very low survival rate as a result of wind damage at the exposed study site. All three treatments significantly reduced the survival rate of Castanopsis seedlings, whereas herbicide reduced it for Sapium but increased it for Schefflera . The significant effects on seedling growth were all positive, except for a strong negative effect of herbicide on Castanopsis growth. Overall, the results suggest that all three factors— seasonal drought, belowground competition, and low soil nutrients—can significantly impair seedling growth on a degraded hillside site in Hong Kong but that their relative importance differs among species. The growth benefits of the three treatments were largest and most consistent for Schima , which as a mature forest dominant would be expected to be particularly sensitive to the environmental conditions on degraded open sites. This study highlights the fact that more systematic planting trials are needed to identify suitable native tree species for cost-effective reforestation on degraded hillsides in Hong Kong and South China.
TL;DR: Although percentage similarities between dung beetle assemblages of approximately 12-year woodland and natural forests were comparable with those between each natural forest stand, decline in similarity in older woodland stands suggests that lasting convergence in dung beetles species abundance will only be attained once the Acacia woodland is replaced by secondary natural forest.
Abstract: In Maputaland, South Africa vegetative and microclimatic changes on mined dunes drive the composition of the dung beetle fauna toward convergence with that in natural dune forest on unmined dunes. We assessed the pattern of these changes using a 23-year vegetational chronosequence on mined dunes, which passes from grassland (approximately 1 year) to open Acacia shrubland thicket to Acacia karroo dominated woodland (approximately 9 years). Across this sequence, which represents successional stages in the restoration of dune forest, there was a sequential trend toward convergence in dung beetle species composition in both the entire species complement and, particularly, in shade specialist species. However, species abundance patterns showed a trend toward convergence only in early chronosequence Acacia woodland, followed by a decline in similarity between dung beetle assemblages of older Acacia woodland and unmined natural forest. This trend toward divergence was common both to the entire species complement, which includes widespread taxa, and to species endemic to Maputaland or the east coast. These trends in similarity and dissimilarity between dung beetle assemblages closely parallel the greater physiognomic and microclimatic similarity between early Acacia woodland and natural forest and the relative dissimilarity of older Acacia woodland. In conclusion, although percentage similarities between dung beetle assemblages of approximately 12-year woodland and natural forests were comparable with those between each natural forest stand, decline in similarity in older woodland stands suggests that lasting convergence in dung beetle species abundance will only be attained once the Acacia woodland is replaced by secondary natural forest.
TL;DR: Four tentative guidelines are concluded to manage at the species level, not the community level, to increase facilitation for seedlings, reduce competition for saplings, and be adaptable and creative with new strategies when manipulations fail.
Abstract: One of the greatest challenges for ecologists this century will be restoring forests on degraded tropical lands. This restoration will require understanding complex processes that shape successional pathways, including interactions between trees and other plants. Shrub species often quickly invade disturbed tropical lands, yet little is known about whether they facilitate or inhibit subsequent tree recruitment and growth. We examined how shrubs and other vegetation (e.g., vines, grasses, herbs) affect tree recruitment, survival, and growth during the first 6 years of forest succession in Kibale National Park, Uganda. The study was undertaken in two recently logged exotic softwood plantations. We studied the successional trajectories in two recently logged areas that varied in their initial densities of trees and shrubs. Analyses suggested tree seedling presence and density were not strongly related to shrub density or height during succession. Tree sapling presence and density were positively significantly related to shrub density and height. We found little response in the tree community to experimental shrub removal, and although removal of all nontree vegetation temporarily enhanced tree growth, the effect disappeared after 2 years. Some early-successional trees benefited from reduced competition, whereas some mid-successional trees benefited from the presence of other vegetation. Some specific tree species responded strongly to vegetation removal. We interpret our findings in light of designing manipulations promoting forest restoration for biodiversity conservation and conclude with four tentative guidelines: (1) manage at the species level, not the community level; (2) increase facilitation for seedlings, reduce competition for saplings; (3) be cautious of assumptions about plant interactions; and (4) be adaptable and creative with new strategies when manipulations fail.
TL;DR: The use of large seagrass plugs may be appropriate for transplantation in high-energy wave environments and analysis of variance indicated a significant two-way interaction between treatment and plug size.
Abstract: The effect of increasing planting unit size and stabilizing sediment was examined for two seagrass planting methods at Carnac Island, Western Australia in 1993. The staple method (sprigs) was used to transplant Amphibolis griffithii (J. M. Black) den Hartog and the plug method was used to transplant A. griffithii and Posidonia sinuosa Cambridge and Kuo. Transplant size was varied by increasing the number of rhizomes incorporated into a staple and increasing the diameter of plugs. Planting units were transplanted into bare sand, back into the original donor seagrass bed, or into a meadow of Heterozostera tasmanica, which is an important colonizing species. Sprigs of A. griffithii were extracted from a monospecific meadow; tied into bundles of 1, 2, 5, and 10 rhizomes; and planted into unvegetated areas. Half the units were surrounded by plastic mesh and the remainder were unmeshed. All treatments were lost within 99 days after transplanting, and although larger bundles survived better than smaller ones, no significant differences could be attributed to the effects of mesh or sprig size. Plugs of P. sinuosa and A. griffithii were extracted from monospecific meadows using polyvinyl chloride pipe of three diameters, 5, 10, and 15 cm, and planted into unvegetated areas nearby. Half the units were surrounded by plastic mesh and the remainder were unmeshed. Posidonia sinuosa plugs were also placed within a meadow of H. tasmanica (Martens ex Aschers.) den Hartog. Only 60% of A. griffithii plug sizes survived 350 days after transplanting back into the donor bed; however, survival of transplants at unvegetated areas varied considerably, and analysis of variance indicated a significant two-way interaction between treatment and plug size. Transplants survived better when meshed (90% survived) and survival improved with increasing plug size. Posidonia sinuosa transplants survived poorly (no plugs survived beyond 220 days in bare or meshed treatments) regardless of size. Survival of 10- and 15-cm plugs was markedly better than the 5-cm plugs in vegetated areas, including the H. tasmanica meadow. The use of large seagrass plugs may be appropriate for transplantation in high-energy wave environments.
TL;DR: It is pointed out that establishment of late successional species can be promoted by creating vegetative cover from the start of the restoration effort, as differences in establishment characteristics between early andLate successional grassland species might provide an explanation for the failure of many late successions to colonize grasslands on ex-arable land.
Abstract: Many grassland restoration projects on former arable land face problems because early successional grassland species establish vigorously and persistently but late successional grassland species fail to establish. Differences in establishment characteristics of early and late successional species might provide an explanation for the failure of many late successional species to colonize grasslands on ex-arable land. I examined whether early and late successional species had different establishment rates in the initial years of a grassland succession, whether a specific establishment stage (seedling emergence, mortality or growth) could be identified as the key process controlling establishment, and what management would enhance the establishment of late successional grassland species. Seeds of three early and three late successional species were sown separately in ex-arable plots with bare soil, 1-year-old vegetation, and 2-year-old vegetation. Emergence, mortality, and seedling growth were monitored for 1 year. Early successional species established successfully in the bare soil plots but failed to establish in plots with 1- and 2-year-old vegetation. Late successional species showed either lower establishment rates in the younger succession stages or decreased establishment with succession that nevertheless resulted in significant establishment in the oldest plots. Seedling emergence proved to be the key factor determining the establishment pattern of early and late successional species. In absolute numbers, emergence of late successional species was, however, similar or higher than that of early successional species, even in the earliest succession stage. The poor establishment of late successional species on former arable land could therefore not be explained solely by differences in establishment characteristics between early and late successional grassland species. Competitive processes between early and late successional species later in the life cycle probably play an important role. The results do point out that establishment of late successional species can be promoted by creating vegetative cover from the start of the restoration effort.
TL;DR: Surprisingly, the emergence of Agropyron from the seed bank was not decreased by 4 years of herbicide treatment, possibly because herbicide may release Agropron from intraspecific competition and allow increased seed production to compensate for decreased plant abundance.
Abstract: Prairie restoration at the northern edge of the Great Plains can be frustrated by previously established nonnative perennial grasses. We compared the emergence of a widely introduced grass, Agropyron cristatum , and a common native grass, Bouteloua gracilis , in a 4-year-old field experiment in which the Agropyron -dominated vegetation had either been left intact or treated annually with herbicide. This was done at two levels of water supply, reflecting conditions expected in wet and dry years, to examine the effects of among-year variability in precipitation. Water addition significantly increased the emergence of both surface-sown and buried (1 cm deep) seeds. Herbicide treatment of neighbors did not increase the emergence of experimentally added seeds. Emergence was much greater for buried (80%) than surface-sown seeds (20%). Significantly more Bouteloua than Agropyron germinated from experimentally buried seeds. Whereas only a single seedling of Bouteloua emerged from the existing seed bank, the mean density of Agropyron seedlings emerging from the seed bank was 930/m 2 (range, 0 to 6,455/m 2 ). Surprisingly, the emergence of Agropyron from the seed bank was not decreased by 4 years of herbicide treatment, possibly because herbicide may release Agropyron from intraspecific competition and allow increased seed production to compensate for decreased plant abundance. In summary, we found few differences between Agropyron and Bouteloua in spring and summer emergence at high or low water availability. The persistence of Agropyron stands despite repeated herbicide application may be partly due to increased seed production.
TL;DR: In the short term no high species richness is to be expected in isolated stands, but the importance of long-distance seed dispersal should not be underestimated, and more attention should be directed toward the genetic traits and viability of founding populations in isolated stand.
Abstract: The reduction and fragmentation of forest habitats is expected to have profound effects on plant species diversity as a consequence of the decreased area and increased isolation of the remnant patches. To stop the ongoing process of forest fragmentation, much attention has been given recently to the restoration of forest habitat. The present study investigates restoration possibilities of recently established patches with respect to their geographical isolation. Because seed dispersal events over 100 m are considered to be of long distance, a threshold value of 100 m between recent and old woodland was chosen to define isolation. Total species richness, individual patch species richness, frequency distributions in species occurrences, and patch occupancy patterns of individual species were significantly different among isolated and nonisolated stands. In the short term no high species richness is to be expected in isolated stands. Establishing new forests adjacent to existing woodland ensures higher survival probabilities of existing populations. In the long term, however, the importance of long-distance seed dispersal should not be underestimated because most species showed occasional long-distance seed dispersal. A clear distinction should be made between populations colonizing adjacent patches and patches isolated from old woodland. The colonization of isolated stands may have important effects on the dynamics and diversity of forest networks, and more attention should be directed toward the genetic traits and viability of founding populations in isolated stands.
TL;DR: In this article, the authors evaluated vegetation characteristics of 5- to 7-year-old operational restorations in the Lower Cache River Watershed in southernmost Illinois, U.S.A.
Abstract: Interest in restoring native ecosystems is resulting in conversion of marginal agricultural lands to bottomland hardwood-dominated forests in the midwestern and midsouthern United States. Growing stock for these efforts typically consists of planted oak (Quercus spp.) and volunteer vegetation. Reports of mixed reforestation success and the lack of post-establishment tree growth data prompted this evaluation of vegetation characteristics of 5- to 7-year-old operational restorations in the Lower Cache River Watershed in southernmost Illinois, U.S.A. Fraxinus pennsylvanica (green ash), Acer negundo (box-elder), and Liquidambar styraciflua (sweetgum) together comprised 77% of all tree stems observed. Full stocking of overstory tree species can be expected to produce a closed canopy stand within 160 m of a forested edge, due primarily to the abundance of rapidly growing volunteer-origin trees. Planted oaks contributed minimally to total tree stocking but were present in sufficient numbers to eventually improve wildlife habitat, and therefore satisfied restoration objectives. Oak height was 23% greater when in the presence of a non-oak tree species. Herbaceous cover was dominated by Solidago gigantea (late goldenrod) and Juncus spp. (rushes). Solidago gigantea was associated with poor growth and low density of non-oak stems, whereas Juncus dudleyi (Dudley's rush) was associated with taller non-oak stems. These results suggest that the presence of volunteer-origin trees is crucial for the creation of full stand stocking that will result in rapid development of a closed canopy forest. Improved success of future reforestation efforts will require more intensive methods to establish adequate stocking beyond 160 m of a forest edge. Methods described here could be adapted for agricultural field to forest restorations in other regions to predict critical distances from volunteer seed sources within which supplemental planting would be unnecessary to meet tree stocking objectives.
TL;DR: This experiment proves the potential utility of cattle dung application for the restoration of species richness in abandoned pastures, although supplementary steps are necessary, including further sowing and/or shrub cutting in subsequent years.
Abstract: Endozoochory has proven to be a highly effective mechanism in the dispersal of viable seeds in Mediterranean grasslands. We studied the effect of cattle dung application on species richness, particularly on the reintroduction of species lost after abandonment. Sown and control plots were monitored for 3 years after dung sowing. We found a significant increase in small-scale richness, which may be attributed to the treatment, with the inclusion of species detected in the dung and in the grazed pasture. The differences in richness and floristic composition diminished over time. This experiment proves the potential utility of this treatment for the restoration of species richness in abandoned pastures, although supplementary steps are necessary, including further sowing and/or shrub cutting in subsequent years.
TL;DR: In this paper, the authors investigated the role of microbial biomass in soil nutrient dynamics during the aggradation phase (vegetation recovery) of abandoned shifting cultivation systems, and determined the soil properties and microbial C and N in jhum (slash-and-burn) cultivation systems at different altitudes and 1-, 7-, and 16-year old fallow agricultural lands at lower and higher altitudes in the northeastern Indian hills.
Abstract: To characterize the altitudinal and successional trends in microbial biomass and to understand their role in soil nutrient dynamics during the aggradation phase (vegetation recovery) of abandoned shifting cultivation systems, we determined the soil properties and microbial C and N in jhum (slash-and-burn) cultivation systems at different altitudes and 1-, 7-, and 16-year-old fallow agricultural lands at lower and higher altitudes in the northeastern Indian hills. Density of ground vegetation was lower in the undisturbed forest than in the jhum fallows. In general, 1-year jhum fallow had greater herbaceous vegetation both at lower and higher altitudes. Although woody plants were observed in 7- and 16-year-old jhum fallows, their density was highest in the forest. Soil moisture, organic C, and total N also increased gradually with increasing altitude and progressive secondary succession. Soil pH showed a negative correlation with altitude (as also confounded by soil type) and fallow age. Both microbial C and N had a close correlation with altitude and fallow age. Contribution of microbial C to soil organic C was 2.0-2.6% and microbial N to total N 1.4-2.2% in jhum fields, 2.4-4.3% and 1.2-2.1%, respectively, in jhum fallows, and 2.5-2.9% and 1.6-1.9% in the forests. Microbial C and N showed a negative correlation with herbaceous plant density. Microbial biomass in the jhum fallows and forest stands had a positive relationship with woody vegetation. Along an altitudinal and/or successional gradient, microbial C and N were positively correlated with water-holding capacity, soil moisture, organic C, and total N and negatively correlated with soil pH. Microbial C and N were positively correlated with each other. Therefore, the study suggests that the altitudinal and successional dynamics of microbial C and N are linked to, among other properties, soil organic matter and total nitrogen contents in the soil during community development after land abandonment from shifting cultivation.
TL;DR: It is indicated that the ability of seagrasses to influence sediment would appear to vary with the prevailing hydrodynamic regime and that a reappraisal of the notion that allseagrass communities trap sediment is necessary is necessary.
Abstract: The wave-exposed nature of much of the southwestern Australian coastline considerably reduces the protective influence of seagrasses, and sediment movement appears to be relatively unaffected by their presence. Present seagrass restoration efforts focus on the deployment of large mechanically transplanted "sods" of seagrass as a means of combating the negative effects of water motion on transplant survival. The aim of this study was to investigate the combined role of wave energy and transplant spacing on sediment movement and transplant survival to provide guidance for seagrass transplantation in areas of high wave energy. One hundred sixty sods (0.25 m 2) of seagrass were mechanically extracted from a mixed meadow consisting of Amphibolis griffithii (Cymodoceaceae) and Posidonia coriacea (Posidoniaceae) and planted in a high wave energy site with the treatments configured as three replicates of 16 sods placed in 4 x 4-meter squares at distances of 0.5, 1.0, and 2.0 meters apart. An additional 16 single sods were planted randomly throughout the site. Monitoring was conducted at two monthly intervals and consisted of counting the number of sods surviving and measuring the shoot density of seagrass species within each surviving sod. Sediment height was monitored using a series of sediment plates and an electronic sediment level sensor. Sod spacing had no significant effect upon transplant survival, which remained above 90% for 4 months after transplantation and then declined with the onset of winter (June to August). After 14 months individual sod survival was between 9% and 40%. Initial shoot densities were 200 to 500 shoots/m 2 and declined to less than 50 shoots/m 2. Sediment fluctuations up to 35 cm were noted, occasionally taking place over a matter of hours, and storms during winter caused significantly increased sediment movement. This probably curtailed rhizome extension and prevented the expansion of the transplants. This study indicates that the ability of seagrasses to influence sediment would appear to vary with the prevailing hydrodynamic regime and that a reappraisal of the notion that all seagrass communities trap sediment is necessary.
TL;DR: In this paper, the authors installed 20 point-intercept transects (50-m long), 8 belt tranchs (10 � 50 m), 10 adapted Daubenmire tranects (four 0.5 � 2-m plots), and 4 modified-Whittaker plots (20 � 50m with smaller nested plots) in treatment and control units to measure understory herbaceous response in a forest restoration experiment that tested different treatments.
Abstract: Although there is no one correct technique for sampling vegetation, the sampling design chosen may greatly influence the conclusions researchers can draw from restoration treatments. Considerations when designing vegetation sampling protocol include determining what sampling attributes to measure, the size and shape of the sampling plot, the number of replicates and their location within the study area, and the frequency of sampling. We installed 20 point-intercept transects (50-m long), 8 belt transects (10 � 50 m), 10 adapted Daubenmire transects (four 0.5 � 2-m plots), and 4 modified-Whittaker plots (20 � 50 m with smaller nested plots) in treatment and control units to measure understory herbaceous response in a forest restoration experiment that tested different treatments. Pointintercept transects on average recorded at least twice as much plant cover as did adapted Daubenmire transects and modified-Whittaker plots taken at the same location for all control and treatment units. Point-intercept transects and adapted Daubenmire plots on average captured fewer rare and exotic species in the control and treatment units in comparison with the belt transects and modified-Whittaker plots. Modified-Whittaker plots captured the highest species richness in all units. Early successional understory response to restoration treatments was likely masked by the response of the herbaceous community to yearly climatic variation (dry vs. wet years). Species richness and abundance were higher in wet years than dry years for all control and treatment units. Our results illustrate that sampling techniques can greatly influence perceptions of understory plant trajectories and therefore the interpretation of whether restoration goals have been achieved. In addition, our results suggest that restoration monitoring needs to be conducted for a sufficient length of time so that restoration treatment responses can be detected.
TL;DR: This work evaluated two potential cover crops, Echinochloa crusgalli (barnyardgrass) and Polygonum lapathifolium (nodding smartweed), for suppressing P. arundinacea invasion in restored prairie pot-holes by reducing resource availability and found these trends were not sensitive to initial sowing density or elevation above water level.
Abstract: Rapid establishment by aggressive plants such as Phalaris arundinacea (reed canarygrass) often interferes with sedge meadow establishment in restored prairie pothole wetlands in the mid-continental United States. Introducing a cover crop during community establishment might suppress P. arundinacea invasion in restored prairie pot-holes by reducing resource availability. We evaluated two potential cover crops, Echinochloa crusgalli (barnyardgrass) and Polygonum lapathifolium (nodding smartweed), for suppressing P. arundinacea invasion in an experimental wetland using replacement series competition experiments. Further, we assessed the effects of E. crusgalli and P. lapathifolium on sedge meadow establishment by sowing Carex hystericina, a common wetland sedge, as a third species at a constant density in the replacement experiments, Echinochloa crusgalli, compared with no cover crop, reduced P. arundinacea biomass by more than 1,000 g/m 2 (65%) after two growing seasons. Polygonum lapathifolium did not affect P. arundinacea biomass. Dense E. crusgalli canopies in the first year and thick E. crusgalli thatch in the second year substantially reduced light availability for P. arundinacea establishment. Echinochloa crusgalli also reduced C. hystericina biomass by more than 1,800 g/m 2 (99%) after two growing seasons. Carex hystericina biomass was similar in plots sown with E. crusgalli to P. arundinacea monocultures. Neither E. crusgalli nor P. lapathifolium is likely to improve sedge meadow restoration success. These trends were not sensitive to initial sowing density or elevation above water level. Without methods to suppress P. arundinacea invasions, sedge meadow restorations may often fail. Thorough site preparation to remove P. arundinacea propagule sources before restoration is essential.
TL;DR: Results suggest that prescribed fire will enhance germination of Potentilla recta, but this will not always lead to increased population growth, and prescribed fire may reduce the long-term efficacy of herbicide applied to control P. recta.
Abstract: Prescribed fire is often used to restore grassland systems to presettlement conditions; however, fire also has the potential to facilitate the invasion of exotic plants. Managers of wildlands and nature reserves must decide whether and how to apply prescribed burning to the best advantage in the face of this dilemma. Herbicide is also used to control exotic plants, but interactions between fire and herbicides have not been well studied. Potentilla recta is an exotic plant invading Dancing Prairie Preserve in northwest Montana. We used a complete factorial design with all combinations of spring burn, fall burn, no burn, picloram herbicide, and no herbicide to determine the effects of fire, season of burn, and their interaction with herbicide on the recruitment and population growth of P. recta over a 5-year period. Recruitment of P. recta was higher in burn plots compared with controls the first year after the fire, but this did not lead to significant population growth in subsequent years, possibly due to drier than normal conditions that occurred most years of the study. Effect of season of burn was variable among years but was higher in fall compared with spring burn plots across all years. Herbicide effectively eliminated P. recta from sample plots for 3–5 years. By the end of the study density of P. recta was greater in herbicide plots that were burned than those that were not. Results suggest that prescribed fire will enhance germination of P. recta, but this will not always lead to increased population growth. Prescribed fire may reduce the long-term efficacy of herbicide applied to control P. recta and will be most beneficial at Dancing Prairie when conducted in the spring rather than the fall. Results of prescribed fire on exotic plant invasions in semiarid environments will be difficult to predict because they are strongly dependent on stochastic climatic events.
TL;DR: The authors examined the effect of repeated burning on French broom and associated grassland species and found that the soil seed bank of stands that were burned had fewer broom seeds than unburned areas but that repeated burning did not reduce the seed bank beyond what was observed after one fire.
Abstract: Successful control of invasive exotic plants depends to a large degree on the regeneration potential of the target exotic species and other species that might also be influenced by the removal effort. In coastal grasslands of California, exotic French broom (Genista monspessulana) forms both dense stands aboveground and abundant seed banks belowground. Land managers attempt to reduce broom cover and the seed bank through prescribed burning, but before this study, no investigators had examined the effect of repeated burning on French broom and associated grassland species. We found that the soil seed bank of stands that were burned had fewer broom seeds than unburned areas but that repeated burning did not reduce the seed bank beyond what was observed after one fire. Fire also did not have any consistent effect on the seed banks of other grassland species. We also examined the relationship between broom stand age and seed bank size but did not find a strong relationship between them. Our data suggested that the broom seed bank stays constant or declines slightly with stand age. We did, however, find that nonbroom seed numbers decreased as broom stands aged. Our results suggest that fire does reduce the size of the broom seed bank and that control of broom need not be limited to only the youngest stands.