Karen D. Holl

Landscape Restoration: Moving from Generalities to Methodologies

Abstract Large-scale, landscape-level restoration actions are widely implemented but receive little attention from academic ecologists. We review the methods used to assess the role of these processes in past studies, and suggest ways to use past and ongoing restoration activities to increase our understanding of large-scale processes and improve restoration projects. To make better use of past restoration, we recommend the use of a number of alternative analytical approaches that have become widely applied in conservation biology and wildlife management but have yet to be adopted in restoration ecology.

Effects of above- and below-ground competition of shrubs and grass on Calophyllum brasiliense (Camb.) seedling growth in abandoned tropical pasture

Early-successional vegetation is often a major factor that limits recovery of tropical forest in abandoned pastures by outcompeting seedlings of forest trees. The goal of this study was to compare the effects of above- and below-ground competition of pasture grasses and shrubs on the growth of tree seedlings in abandoned tropical pasture in Costa Rica. Seedlings of Calophyllum brasiliense were planted in areas of dense pasture grass and below shrub patches. In each vegetation type seedlings were subjected to one of four treatments: control, root trenching, above-ground clearing, or trenching and clearing. Seedling height was measured and above- and below-ground biomass was harvested after one year. Seedling height and biomass were higher for seedlings grown under grass than under shrubs. Above-ground clearing had a strong positive effect on seedling height and all biomass measurements (stem, leaves, tap root, and fine roots). Trenching had a significant effect on height and all biomass measurements except tap root mass; however, trenching had a weaker effect on plant growth than above-ground clearing. Root:shoot ratios were significantly affected by trenching. These results suggest that both pasture grasses and early-colonizing shrubs may slow succession of forest in abandoned pasture. Moreover, the results highlight the importance of reducing above-ground competition to improve the success of reforestation efforts.

Abundance of introduced species at home predicts abundance away in herbaceous communities

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.

Species abundance at home predicts abundance away in grasslands

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.

The effect of coal surface mine reclamation on diurnal lepidopteran conservation

Diurnal lepidopteran and vegetational communities were surveyed on 18 reclaimed coal surface-mined sites and five reference, hardwood sites in south-western Virginia. Comparison of lepidopteran communities using detrended correspondence analysis suggested that lepidopteran community composition on later-successional reclaimed sites was approaching that of the surrounding hardwoods. Diurnal moth species richness and abundance increased with time since reclamation, whereas butterfly species richness and abundance decreased. Diurnal moth communities were better indicators of vegetational community composition and species richness than were butterfly communities. While most lepidopteran species commonly found in the hardwoods were recorded in later-successional reclaimed sites, a number of less common species were not observed in them. Therefore, the success of mine reclamation in restoring the full complement of lepidopteran species native to hardwood forest in this region is debatable and further consideration must be given to the long-term effects of current mine reclamation practices.

Tropical forest recovery and restoration

R a week goes by without a news report sounding the alarm of the continued destruction of tropical forests and the concomitant loss of biodiversity and ecosystem services, such as water retention, erosion control and carbon storage. Much of tropical deforestation, particularly in Latin America, is a result of land clearing for pasture and other agricultural uses1. Increasingly, these lands are being abandoned because of decreasing productivity and changing economic incentives2,3. Little is known, however, about whether tropical forest will ever fully recover on abandoned crop fields and pastures4. A recent conference in San Juan, Puerto Rico (23–30 May), organized by the International Institute of Tropical Forestry (Ariel Lugo and John Parrotta), the Society for Ecological Restoration (Don Falk) and the University of Puerto Rico (Mitch Aide and Jess Zimmerman) brought together scientists, conservationists and wildlife area managers to discuss the potential for tropical forest restoration in the new millennium. As most research on tropical forest recovery and restoration has been conducted over the past five to ten years, the meeting was one of the first opportunities for a critical mass of scientists to assess what is known about tropical forest recovery and restoration in degraded lands and where future research efforts should be focused.

Tropical dry-forest regeneration from root suckers in Central Brazil

Seed dispersal, predation, desiccation and seedling survival are strong bottlenecks that impede tropical forest recovery on abandoned agricultural lands (reviewed in Holl 2002). The ability to resprout after disturbances overcomes these barriers, as those individuals bypass the seed stage and have more vigorous shoots than seedlings (Bond & Midgley 2001, Kammesheidt 1999, Kennard et al . 2002). Resprouting is a particularly important recovery mechanism in tropical dry forests (reviewed in Vieira & Scariot 2006). There are a number of reasons why resprouting may be more important in dry forests than in rain forests, including slower decay rates of trunk bases (Ewel 1980), or adaptation of plants to drought (Bond & Midgley 2001, Sampaio et al . 1993).

HAWAIIAN HONEYCREEPER HOME RANGE SIZE VARIES WITH HABITAT: IMPLICATIONS FOR NATIVE ACACIA KOA FORESTRY

Reforesting degraded landscapes with native, high-value timber trees may contribute to biodiversity protection while also increasing the economic value of the land. Ideally, reforested areas should have the habitat characteristics to support viable populations of native fauna. We investigated habitat use by Akiapolaau (Hemignathus munroi), an endangered Hawaiian honeycreeper, in three habitat types: a relatively intact old-growth forest, an old-growth forest with a long history of grazing, and a native Acacia koa plantation. We quantified habitat characteristics, calculated foraging preferences, mapped home ranges, measured territoriality, and determined reproductive success at all sites. We found that Akiapolaau were highly selective foragers, foraging primarily on A. koa despite its relative scarcity in the environment, and then secondarily on several subcanopy species. Home range size was significantly smaller at the intact old-growth site and the A. koa plantation, the two sites with the greater cover...

Seed dispersal limitations shift over time in tropical forest restoration

Past studies have shown that tropical forest regeneration on degraded farmlands is initially limited by lack of seed dispersal, but few studies have tracked changes in abundance and composition of seed rain past the first few years after land abandonment. We measured seed rain for 12 months in 10 6-9-year-old restoration sites and five mature, reference forests in southern Costa Rica in order to learn (1) if seed rain limitation persists past the first few years of regeneration; (2) how restoration treatments influence seed community structure and composition; and (3) whether seed rain limitation is contingent on landscape context. Each restoration site contained three 0.25-ha treatment plots: (1) a naturally regenerating control, (2) tree islands, and (3) a mixed-species tree plantation. Sites spanned a deforestation gradient with 9-89% forest area within 500 m around the treatment plots. Contrary to previous studies, we found that tree seeds were abundant and ubiquitous across all treatment plots (585.1 ± 142.0 seeds · m(-2) · yr(-1) [mean ± SE]), indicating that lack of seed rain ceased to limit forest regeneration within the first decade of recovery. Pioneer trees and shrubs comprised the vast majority of seeds, but compositional differences between restoration sites and reference forests were driven by rarer, large-seeded species. Large, animal-dispersed tree seeds were more abundant in tree islands (4.6 ± 2.9 seeds · m(-2) · yr(-1)) and plantations (5.8 ± 3.0 seeds · m(-2) · yr(-1)) than control plots (0.2 ± 0.1 seeds · m(-2) · yr(-1)), contributing to greater tree species richness in actively restored plots. Planted tree species accounted for < 1% of seeds. We found little evidence for landscape forest cover effects on seed rain, consistent with previous studies. We conclude that seed rain limitation shifted from an initial, complete lack of tree seeds to a specific limitation on large-seeded, mature forest species over the first decade. Although total seed abundance was equal among restoration treatments, tree plantations and tree islands continued to diversify seed rain communities compared to naturally regenerating controls. Compositional differences between regenerating plots and mature forests suggest that large-seeded tree species are appropriate candidates for enrichment planting.

The effect of rabbit herbivory on reforestation of abandoned pasture in southern Costa Rica

Abstract Previous research indicates that a number of factors may limit forest seedling growth in abandoned tropical pastures; however, mammalian seedling herbivory has not been previously reported as a major factor inhibiting tropical pasture restoration. Seedlings of four native tree species were planted in abandoned pasture in southern Costa Rica to test their suitability for reforestation. Overall, the stems of 64% of the seedlings were cut by rabbits and only 26% of the seedlings survived 2 years after planting. Those seedlings that were able to survive and resprout after cutting by rabbits showed much lower growth rates than uncut seedlings. This study suggests that mammalian herbivory may be a more important factor in tropical reforestation than previously assumed. Experimental tests over larger spatial and temporal scales are needed to ascertain the degree to which it limits reforestation efforts.