Woody Plant Recruitment Research Articles

Hailstorm damage promotes aspen invasion into grassland

Global warming is widely thought to promote the dominance of grasslands over woody vegetation, and shift the location of ecotones. In contrast, forest vegetation along the northern edge of the North American Great Plains has migrated southward over the past century into areas dominated by native grassland. Because climate change is also predicted to increase storm frequency and intensity, we quantified the impacts of an intense hailstorm on woody and herbaceous species in native grassland in the northern Great Plains of North America. The hailstorm disturbance killed or damaged mature stems of the dominant tree, aspen ( Populus tremuloides Michx.), but damaged aspen stands subsequently invaded ca. 10 m into neighbouring grassland. Damaged aspen stands also produced up to 20-fold more new stems having 67-fold higher total biomass compared with relatively undisturbed stands. Grasses and lichens suffered much higher rates of biomass removal (60%–76%) than did shrubs (6%–8%) immediately following the storm. The disturbance-mediated recruitment of clonal woody plants, and the unexpected sensitivity of grasses and lichens to this disturbance, may contribute to the counterintuitive expansion of trees into grasslands under a regime of increased storm frequency that is not predicted by simple ecosystem responses to warming.

Simulated recruitment of riparian trees and shrubs under natural and regulated flow regimes on the Wisconsin River, USA

Models that link ecological responses to hydrologic changes are important for assessing the effects of flow regulation on aquatic and riparian ecosystems. Based on the Recruitment Box Model, a graphical model used to prescribe environmental flows for cottonwood (Populus spp.) recruitment, we designed a simulation model to represent the influence of river flow dynamics on seedling recruitment of riparian pioneer woody plants. The model simulates the influence of temporal patterns of river stage on dispersal, germination, initial recruitment and over-winter survival of first-year seedlings of riparian pioneer shrubs and trees. We used the model to simulate seedling recruitment patterns for five species (Acer saccharinum, Betula nigra, Populus deltoides, Salix nigra and Salix exigua) on the Wisconsin River (Wisconsin, USA) under three flow scenarios: historic (1935–2002), simulated natural (1915–1975) and simulated regulated flows (1915–1975). Simulation results agreed well with field-observed relative differences among years (1997–2000) in seedling densities for the five focal species. Simulated successful recruitment years were highly synchronous among species, but species differed in their sensitivity to flows at different times during the growing season, consistent with among-species differences in seed dispersal timing. Comparison of simulated natural and regulated flows for 1915–1975 showed that flow regulation decreased monthly flow variability, increased late summer to winter baseflow and reduced the magnitude of spring peaks. Simulated recruitment and over-winter survival of tree seedlings of all species was enhanced under the regulated flow scenario, likely due to increased summer baseflow and reductions in peak flood magnitude. Our analyses show the utility of extending the Recruitment Box Model to include multiple species of riparian shrubs and trees, and the effects of post-colonization flows on their recruitment success. However, some key functional relationships between flow patterns and woody seedling demography (e.g. shear stress thresholds for seedling mortality) have not been adequately quantified and merit further study. Copyright © 2006 John Wiley & Sons, Ltd.

Responses of desert grassland vegetation to mesquite removal and regrowth

The purpose of this study was to determine the long-term response of understory vegetation in the desert grassland of southeastern Arizona, USA, to removal and regrowth of mesquite Prosopis juliflora (Swartz) DC. var. velutina (Wooton) Sarg. trees. The study involved 3 treatments applied to mesquite in 1966; mesquite left intact (MI), mesquite removed (MR), and mesquite removed, sprouted, and regrown (MRS). Vegetation responses to 2 litter treatments, litter intact (LI) and litter removed (LR), also were examined. Cover of understory vegetation and juvenile mesquite (< 1.5 m height) were measured in canopy and open (intercanopy) locations. Major changes between 1967 and 1991 were increased cover of juvenile mesquite, shrubs, halfshrubs, bush muhly Muhlenbergia porteri Scribn., and Lehmann lovegrass Eragrostis lehmanniana Nees., and a decline in cover of Arizona cottontop Digitaria californica (Benth.) Chase, and plains bristlegrass Setaria macrostachya H.B.K. Arizona cottontop, plains bristlegrass, and bush muhly were more abundant in canopy locations; black grama Bouteloua eriopoda Torr. and Lehmann lovegrass were more abundant in open locations. Lehmann lovegrass cover was lowest in canopy locations of the mesquite intact treatment. Combination of the mesquite removed and sprouted and litter intact treatments favored increased cover development of native perennial grasses. Litter removal enhanced cover development of Lehmann lovegrass, most likely through increased amount of red light and increased soil temperature fluctuations. Low levels of understory cover (22% average) probably facilitated recruitment of mesquite and other woody plants. Our observation that the greatest cover of Arizona cottontop, plains bristlegrass, and bush muhly occurred in the canopy location of the mesquite intact treatment suggests a potential strategy for maintaining diversity of native perennial grasses. Mature mesquite should be examined as a refuge for native species.

Recruitment limitation in secondary forests dominated by an exotic tree

AbstractQuestion: What factors limit woody plant recruitment in a mosaic landscape where former agricultural lands are dominated by the invasive tree Ligustrum lucidum (Oleaceae)?Location: Subtropical northwestern Argentina.Methods: In secondary forest patches, we measured (1) tree, shrub and liana abundance in different size classes; (2) seed rain of Ligustrum and two native trees and (3) topographic, soil and light variables. We used spatial autoregressive models to test for effects of Ligustrum dominance and environment on native plant abundance in each size class. We used multiple regression on resemblance matrices to quantify the relative importance of spatial (e.g. dispersal) and environmental effects on native species composition.Results: Native tree abundance in the smallest size class was unrelated to Ligustrum canopy dominance, while native tree abundance in larger size classes and native liana abundance were negatively correlated with Ligustrum dominance. Native species composition was both environmentally and spatially structured, suggesting that some species are dispersal limited. Seed rain was spatially correlated with conspecific basal area for one of two native species, but not for Ligustrum.Conclusions: Native tree recruitment appears to be limited primarily by sapling mortality in patches dominated by the invasive Ligustrum. Ligustrum does not appear to be dispersal limited in our study area and is likely to continue spreading. Invaded patches may persist for hundreds of years.

Responses of desert grassland vegetation to mesquite removal and regrowth

The purpose of this study was to determine the long-term response of understory vegetation in the desert grassland of southeastern Arizona, USA, to removal and regrowth of mesquite Prosopis juliflora (Swartz) DC. var. velutina (Wooton) Sarg. trees. The study involved 3 treatments applied to mesquite in 1966; mesquite left intact (MI), mesquite removed (MR), and mesquite removed, sprouted, and regrown (MRS). Vegetation responses to 2 litter treatments, litter intact (LI) and litter removed (LR), also were examined. Cover of understory vegetation and juvenile mesquite ( 1.5 m height) were measured in canopy and open (intercanopy) locations. Major changes between 1967 and 1991 were increased cover of juvenile mesquite, shrubs, halfshrubs, bush muhly Muhlenbergia porteri Scribn., and Lehmann lovegrass Eragrostis lehmanniana Nees., and a decline in cover of Arizona cottontop Digitaria californica (Benth.) Chase, and plains bristlegrass Setaria macrostachya H.B.K. Arizona cottontop, plains bristlegrass, and bush muhly were more abundant in canopy locations; black grama Bouteloua eriopoda Torr. and Lehmann lovegrass were more abundant in open locations. Lehmann lovegrass cover was lowest in canopy locations of the mesquite intact treatment. Combination of the mesquite removed and sprouted and litter intact treatments favored increased cover development of native perennial grasses. Litter removal enhanced cover development of Lehmann lovegrass, most likely through increased amount of red light and increased soil temperature fluctuations. Low levels of understory cover (22% average) probably facilitated recruitment of mesquite and other woody plants. Our observation that the greatest cover of Arizona cottontop, plains bristlegrass, and bush muhly occurred in the canopy location of the mesquite intact treatment suggests a potential strategy for maintaining diversity of native perennial grasses. Mature mesquite should be examined as a refuge for native species.

Recruitment limitation in secondary forests dominated by an exotic tree

Question: What factors limit woody plant recruitment in a mosaic landscape where former agricultural lands are dominated by the invasive tree Ligustrum lucidum (Oleaceae)? Location: Subtropical northwestern Argentina. Methods: In secondary forest patches, we measured (1) tree, shrub and liana abundance in different size classes; (2) seed rain of Ligustrum and two native trees and (3) topographic, soil and light variables. We used spatial autoregressive models to test for effects of Ligustrum dominance and environment on native plant abundance in each size class. We used multiple regression on resemblance matrices to quantify the relative importance of spatial (e.g. dispersal) and environmental effects on native species composition. Results: Native tree abundance in the smallest size class was unrelated to Ligustrum canopy dominance, while native tree abundance in larger size classes and native liana abundance were negatively correlated with Ligustrum dominance. Native species composition was both environmentally and spatially structured, suggesting that some species are dispersal limited. Seed rain was spatially correlated with conspecific basal area for one of two native species, but not for Ligustrum. Conclusions: Native tree recruitment appears to be limited primarily by sapling mortality in patches dominated by the invasive Ligustrum. Ligustrum does not appear to be dispersal limited in our study area and is likely to continue spreading. Invaded patches may persist for hundreds of years.

Experimental Techniques for Evaluating the Success of Restoration Projects

The ecological background of a restoration project is complex and difficult to betermine without experimentation. A useful context for experiments is the well-studied process of natural succession, because the factors that drive or inhibit succession are also at work during reclamation (a form of primary succession) and restoration (which often resembles secondary succession). Using experimental studies on urban wasteland reclamation, we have tested for factors that stimulate or inhibit succession during early phases of woodland development in the Northeastern United states. The emphasis has been on mutualisms (seed dispersal, pollination, and mycorrhizae) and microsite limitations in the recruitment, growth, and reproduction of woody plants. Using plantings of seeds, seedlings, and clusters of reproductively mature plants on abandoned landfills, we have observed that (1) soil microsite deficiencies lead to very poor germination (<0.1<TEX>$\%$</TEX>) and seedling survival (<0.01<TEX>$\%$</TEX>) of most native species; (2) seed dispersal by birds is a significant and reliable source of woody plant recruitment; however (3) proximity effects are strong, with most (up to 95<TEX>$\%$</TEX>) of seed rain falling in the vicinity of planted clusters that are closest to putative seed sources; and (4) remnant natural woodlands are critical components of the recruitment process. To emphasize the last point, in one case, we found that the destruction of approximately 50<TEX>$\%$</TEX> of nearby natural woodland vegetation led to a commensurate decline in seed rain. In another case, we found that the species richness of recruits was strictly limited by the species composition of nearby source plant communities, with no evidence of community enrichment by long distance dispersal over 5 years. We conclude from these results that the size and proximity of remnant natural populations are critical considerations when planning reclamation and restoration programs that rely on natural successional processes.

HOW TREE SPECIES DIFFER AS RECRUITMENT FOCI IN A TROPICAL PASTURE

In a Neotropical pasture, I predicted that two characteristics of trees, type of fruit produced and amount of shade cast, would affect recruitment and growth of woody plants underneath them. I also predicted that woody plants that persisted in active pasture would affect the species assemblages under trees after pasture abandonment. To investigate these hypotheses, I examined the assemblages of recruits under several types of trees in active pasture and also under similar trees that were fenced off (enclosed) to simulate abandoned pasture. The trees were Ficus spp. (fleshy fruits, deep shade), Pentaclethra macroloba (dry fruits, deep shade), Cecropia spp. (fleshy fruits, sparse shade), and Cordia alliodora (dry fruits, sparse shade). Recruitment into “open” pasture plots (i.e., without trees) was also examined. In active pasture, the species assemblage of woody recruits depended on the tree under which they grew. The assemblage under Ficus was dense and diverse, under Cecropia and Cordia it was moderately dense and diverse, in open pasture it was sparse and species-poor, and under Pentaclethra it was dominated by its own seedlings. These patterns were found in the enclosed pasture as well, apparently because woody plants that had survived in the active pasture continued to grow after “abandonment.” However, after enclosure, many new plants also became established, such that the enclosed pasture plots had almost twice as many woody plants and species as the active pasture plots. Growth of woody plants was most rapid under trees with the least shade (Cecropia, Cordia) and in open pasture. In contrast, growth of recruits was slower under the much shadier Ficus, and thus, in the initial stages of succession, Ficus appeared not to be as important a “recruitment focus” for woody plants. Growth of recruits under the equally shady Pentaclethra was also slow, but Pentaclethra seedlings readily established just outside the canopies of parent trees, where they grew quickly and created dense, monospecific stands. The results of this study suggest that patterns of early succession to forest after pasture abandonment will depend on the kinds of trees found in the pasture. Persistent woody recruits under trees in active pasture constitute sources of advanced regeneration that will substantially affect forest succession after pasture abandonment.

How Tree Species Differ as Recruitment Foci in a Tropical Pasture

In a Neotropical pasture, I predicted that two characteristics of trees, type of fruit produced and amount of shade cast, would affect recruitment and growth of woody plants underneath them. I also predicted that woody plants that persisted in active pasture would affect the species assemblages under trees after pasture abandonment. To investigate these hypotheses, I examined the assemblages of recruits under several types of trees in active pasture and also under similar trees that were fenced off (enclosed) to simulate abandoned pasture. The trees were Ficus spp. (fleshy fruits, deep shade), Pentaclethra macroloba (dry fruits, deep shade), Cecropia spp. (fleshy fruits, sparse shade), and Cordia alliodora (dry fruits, sparse shade). Recruitment into “open” pasture plots (i.e., without trees) was also examined. In active pasture, the species assemblage of woody recruits depended on the tree under which they grew. The assemblage under Ficus was dense and diverse, under Cecropia and Cordia it was moderately dense and diverse, in open pasture it was sparse and species-poor, and under Pentaclethra it was dominated by its own seedlings. These patterns were found in the enclosed pasture as well, apparently because woody plants that had survived in the active pasture continued to grow after “abandonment.” However, after enclosure, many new plants also became established, such that the enclosed pasture plots had almost twice as many woody plants and species as the active pasture plots. Growth of woody plants was most rapid under trees with the least shade (Cecropia, Cordia) and in open pasture. In contrast, growth of recruits was slower under the much shadier Ficus, and thus, in the initial stages of succession, Ficus appeared not to be as important a “recruitment focus” for woody plants. Growth of recruits under the equally shady Pentaclethra was also slow, but Pentaclethra seedlings readily established just outside the canopies of parent trees, where they grew quickly and created dense, monospecific stands. The results of this study suggest that patterns of early succession to forest after pasture abandonment will depend on the kinds of trees found in the pasture. Persistent woody recruits under trees in active pasture constitute sources of advanced regeneration that will substantially affect forest succession after pasture abandonment.

Demographic Characteristics of 3 Artemisia tridentata Nutt. Subspecies

Previous research suggested that woody plant recruitment may occur in pulses in semi-arid areas. The overall objective of this study was to determine if this pulse phenomena was recorded in the demographic structures of big sagebrush (Artemisia tridentata Nutt.) stands in Wyoming. In 1997, approximately 75 stem cross sections were collected from 9 stands of each of 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth-rings were used to identify year of establishment and demographic characteristics were analyzed from age-class frequencies. Mean stand ages of the 3 subspecies were different (P = 0.002), and analyses revealed that Wyoming (A. tridentata ssp. wyomingensis) and mountain big sagebrush (A. tridentata ssp. vaseyana) stand ages (32 +/- 9 and 26 +/- 9 years, respectively) were significantly older than basin big sagebrush (A. tridentata ssp. tridentata) (17 +/- 3) stands (P < 0.05). Mean recruitment intervals (years) were shorter for basin (1.6) than for Wyoming (2.3) and mountain (2.2) sagebrush (P = 0.01). The number of cohorts did not differ among the subspecies (P = 0.11), but the percent of years with recruitment was significantly higher for basin (59%) compared to Wyoming (37%) and mountain (39%) subspecies (P < 0.0001). Age-class frequency distributions of each stand and regional stand combination were assessed for dispersion across each associated period of record. Chi-square goodness-of-fit tests were performed for the negative binomial distribution. All stands (with one exception) and all 3 regional stand combinations fit the negative binomial distribution. Age-class frequency patterns indicate that recruitment is clustered or aggregated across each period of record. Recruitment in big sagebrush stands occurs in pulses throughout Wyoming. DOI:10.2458/azu_jrm_v54i2_perryman

Demographic characteristics of 3 Artemisia tridentata Nutt. subspecies

Previous research suggested that woody plant recruitment may occur in pulses in semi-arid areas. The overall objective of this study was to determine if this pulse phenomena was recorded in the demographic structures of big sagebrush (Artemisia tridentata Nutt.) stands in Wyoming. In 1997, approximately 75 stem cross sections were collected from 9 stands of each of 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth-rings were used to identify year of establishment and demographic characteristics were analyzed from age-class frequencies. Mean stand ages of the 3 subspecies were different (P = 0.002), and analyses revealed that Wyoming (A. tridentata ssp. wyomingensis) and mountain big sagebrush (A. tridentata ssp. vaseyana) stand ages (32 +/- 9 and 26 +/- 9 years, respectively) were significantly older than basin big sagebrush (A. tridentata ssp. tridentata) (17 +/- 3) stands (P &lt; 0.05). Mean recruitment intervals (years) were shorter for basin (1.6) than for Wyoming (2.3) and mountain (2.2) sagebrush (P = &lt; 0.01). The number of cohorts did not differ among the subspecies (P = 0.11), but the percent of years with recruitment was significantly higher for basin (59%) compared to Wyoming (37%) and mountain (39%) subspecies (P 0.0001). Age-class frequency distributions of each stand and regional stand combination were assessed for dispersion across each associated period of record. Chi-square goodness-of-fit tests were performed for the negative binomial distribution. All stands (with one exception) and all 3 regional stand combinations fit the negative binomial distribution. Age-class frequency patterns indicate that recruitment is clustered or aggregated across each period of record. Recruitment in big sagebrush stands occurs in pulses throughout Wyoming.

DIRECTING SPATIAL PATTERNS OF RECRUITMENT DURING AN EXPERIMENTAL URBAN WOODLAND RECLAMATION

Studies of biological invasions indicate that natural recruitment of new spe- cies can occur as a nucleation phenomenon, in which scattered colonization foci spread and coalesce. Ecological reclamation of damaged lands might make use of this potential for enhanced natural dispersal, by inoculating sites with multiple small plantings to attract animal dispersers and other mutualists from nearby remnants of natural habitat. We con- ducted an experimental test of this proposition. On a 6-ha section of an abandoned municipal landfill in the New Jersey Meadowlands, we installed 16 clusters of 21 trees and shrubs in an array of fenced plots. Clusters contained seven native species known to: (1) attract bird dispersers to introduce propagules from remnants of off-site habitat; (2) contribute propagules by virtue of high reproductive output and clonal growth; and (3) accelerate woodland succession on open, degraded habitats. Average plant size was varied, with half the plots receiving larger trees and shrubs, to test whether woody plant size would enhance any attractive function. An additional eight empty plots were studied to estimate background rates of recruitment and to test for a fencing effect. Site preparation included the addition of 90 cm of fresh substrate, including organic matter, and a cover crop of annual grasses. Recruitment of woody plants inside and sur- rounding the experimental plots was examined for five years, and results were compared on the basis of treatment and recruitment mode (avian, wind, or clonal dispersal). Woody plant recruitment into experimental plots was rapid and substantial, primarily via dispersal from natural sources. Plots with larger plants attracted significantly more recruits at the outset, but this difference diminished over time. Fall seed rain samples yielded a mean estimate of 426 seeds/M2 within plots. However, size distributions of re- cruiting woody species increasingly shifted toward larger individuals each year. Experi- mental manipulations that opened seed beds for woody plant recruitment had short-lived effects, indicating a narrow window of opportunity for establishment. Spread of the planted species themselves was generally weak, although clonal growth contributed substantially to spread on the margins of plots. Most recruitment outside experimental plots was from external sources. A strong proximity component was found for bird-dispersed recruits, which were highly clustered near planted plots, with the highest densities near source populations on the site margin. Wind-dispersed trees and shrubs, by contrast, were not associated with planted plots and were concentrated near one corner of the site. Discounting plot interiors, total recruitment density for the site after 5 yr was -800 woody stems/ha, 36% via avian dispersal, 10% via clonal spread, and the remainder via wind-borne propagules. New recruits represented 26 woody plant species, all but four from external sources, and only five common species contributed more than a few recruits. We conclude that techniques for manipulating natural seed dispersal hold promise for ecological restoration, provided that background populations are available to supply colonists.

Patterns of woody plant abundance, recruitment, mortality, and growth in a 65 year chronosequence of old-fields

We surveyed vegetation along forest margins in a 65-year chronosequence of old-fields at the Cedar Creek Natural History Area in east-central Minnesota, USA, to identify successional patterns of woody plants and to determine if these were correlated with soil nitrogen. We predicted that shrub and tree abundance, size, and distance of occurrence from the forest edge would be correlated with field age or soil nitrogen. Instead we did not find successional trends in the abundance or composition of woody species. Even in the oldest field the abundance of trees and shrubs was low and concentrated in areas close to the forest. Though trees were larger and present further from the forest edges in older fields, average tree height was less than 126 cm in all fields. Since we did not find successional trends we looked at various local factors (local seed sources, deer browsing, and forest edge aspect) and their relation to recruitment, mortality, or growth to explain variation among fields in abundance of trees or shrubs. The three most common tree species (Quercus rubra, Q. macrocarpa,and Populus tremuloides) all had a higher relative abundance of seedlings, and two (Q. rubra and Q. macrocarpa) had a higher relative abundance of large trees adjacent to forests with a high abundance of conspecific adults. Most trees taller than 20 cm were browsed by deer and were shorter in 1995 than they were in 1993. Mortality was higher for trees less than 30 cm indicating that mortality was size-dependent. Forest edge aspect did not significantly influence the abundance or demography of any species. Our results suggest that the patterns of seedling recruitment were largely determined by the proximity of seed sources and that these patterns may persist so that tree communities in old-fields resemble adjacent forests. Deer may be a significant factor in the suppression of tree populations in old-fields through repeated browsing which reduces tree growth and elevates tree mortality by prolonging the period of time trees remain susceptible to size-dependent mortality.

Early Woody Invasion Under Tree Plantations in Costa Rica: Implications for Forest Restoration

AbstractThe role of tree plantations as facilitators of tropical forest restoration in degraded lands has been explored recently, but there are few data on the effect of different tree species on invasion of the plant understory. We evaluated early patterns of understory composition in three‐year‐old native tree plantations in lowland Costa Rica using two pure‐species treatment (Jacaranda copaia and Vochysia guatemalensis) and one mixed‐species treatment (J. copaia, V. guatemalensis, Stryphnodendron microstachyum, and Calophyllum brasiliense). We also monitored woody invasion in unplanted control areas dominated by grasses. The understory of the different plantation treatments differed in light environment, woody‐plant growth and recruitment, and quantity and quality of woody regeneration. Forest tree invasion appeared to be enhanced under Vochysia, while shrubs were more abundant under the Jacaranda and mixed‐species treatments. Woody plant growth, herbaceous cover, and understory light availability were highest under Jacaranda, intermediate under mixed species, and lowest under Vochysia. Soil‐stored seeds seemed an important source for woody plant recruitment in Jacaranda and mixed species and of minimal importance under Vochysia, probably due to light suppression. It appears that competition from grasses is a major factor influencing early woody invasion in our study area. We found no woody recruitment after one year in the unplanted controls. We suggest that to promote the use of plantations as tools of forest restoration, there is a need to gather basic ecological information on how different tree species may influence patterns of plant understory colonization.

Survival, reproduction, and recruitment of woody plants after 14 years on a reforested landfill

With the advent of modern sanitary landfill closure techniques, the opportunity exists for transforming municipal landfills into urban woodlands. While costs of fullscale reforestation are generally prohibitive, a modest planting of clusters of trees and shrubs could initiate or accelerate population expansions and natural plant succession from open field to diverse forest. However, among woody species that have been screened for use on landfills, these ecological potentials have not yet been investigated. We examined a 14-yr-old landfill plantation in New Jersey, USA, established to test tolerance of 19 species of trees and shrubs to landfill environments. We measured survivorship, reproduction, and recruitment within and around the experimental installation. Half of the original 190 plants were present, although survival and growth rates varied widely among species. An additional 752 trees and shrubs had colonized the plantation and its perimeter, as well as 2955 stems of vines. However, the great majority (>95%) of woody plants that had colonized were not progeny of the planted cohort, but instead belonged to 18 invading species, mostly native, bird-dispersed, and associated with intermediate stages of secondary plant succession. Based on this evidence, we recommend that several ecological criteria be applied to choices of woody species for the restoration of municipal landfills and similar degraded sites, in order to maximize rapid and economical establishment of diverse, productive woodlands.