Woody Plant Regeneration Research Articles

Woody plant diversity, structure and regeneration in the Ambo State Forest, South Gondar Zone, Northwest Ethiopia

For this study in the Ambo State Forest on woody plant diversity, structure and regeneration, 70 quadrats, each 25 m by 25 m, were selected using a systematic random sampling technique and intervals of 100 m along a transect line. For assessing seedlings and saplings, two 2 × 10 m sub quadrats were set upon opposite sides of each main quadrat. Data on species diversity, abundance, structure, basal area, density, frequency and regeneration status were collected and analyzed using standard procedures and programs. Of 58 woody plant species identified, 69 % were trees, 16 % were shrubs, 12 % were tree/shrubs and 4 % were climbers. Fabaceae was the most species-rich family comprising 17 species. The Shannon–Weiner diversity index was 2.73, and evenness was 0.67. The population structure in the cumulative diameter class frequency distribution revealed an interrupted and inverted J-shape with a very high decrease in higher diameter class. Acacia lahai (49 %) was the most important woody species with the highest importance value index. To maintain balanced structure, enhanced regeneration and protecting the forest from selective cutting are recommended.

Tree species composition, biodiversity and regeneration in response to catena shape and position in a mountain forest

ABSTRACTWe examined the variation in woody plant species composition, regeneration and biodiversity in relation to topographic heterogeneity, specifically catena shape (V and Λ) and slope position (summit, shoulder, back slope, foot slope and toe slope). All research took place at the TMU Experimental Forest Station, located in northern Iran. Two sets of replicated quadrats were established along transects that encompassed the different catena shapes and positions. We recorded the density, height, and canopy cover of all trees ≥12 cm diameter at breast height within 30 quadrats (400m2), as well as the density of all tree regenerations within 120 quadrats (4m2). In addition, three measurements of biodiversity were calculated for both mature trees and regenerations. Mature tree species composition varied greatly with catena shape and slope position, as did that of regenerating trees. Despite differences in species composition, the various measurements of biodiversity were consistent across the landscape for mature trees, whereas significant variation in evenness was detected for regenerating trees. We concluded that the broad matrix of environmental conditions occurring within this rugged mountainous area generates a variety of microhabitats, which in turn contributes to both the variation in species composition and the consistent biodiversity of these forests.

The Effects of Established Trees on Woody Regeneration during Secondary Succession in Tropical Dry Forests

AbstractUnderstanding the mechanisms controlling secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. Canopy‐forming trees in tropical forests strongly influence later stages of succession through their effect on woody plant regeneration. In dry forests, this may be complex given the seasonal interplay of water and light limitations. We reviewed observational and experimental studies to assess (1) the relative importance of positive and negative effects of established trees on regeneration; (2) the mechanisms underlying these effects; and (3) to test the ‘stress gradient hypothesis’ in successional tropical dry forests. The effects of established trees on seed dispersal, seed survival, and seed germination—either through direct changes to moisture and temperature regimes or mediated by seed dispersers and predators—are mainly positive. The balance between positive and negative effects on seedling establishment is more complex and depends on the season and leaf phenology of both trees and seedlings. Seedling survival is generally enhanced by established trees mitigating dry conditions. Established trees have counteracting effects on water and light availability that influence seedling growth. The probability of a positive effect of established trees on seedling survival decreases with increased rainfall, which supports the stress gradient hypothesis. Priorities for future research are experiments to test for facilitation and competition and their underlying mechanisms, long‐term studies evaluating how these effects change with ontogeny, and studies focusing on the species‐specificity of interactions.

Decline and Die-Back of Woody Plants in a Physiognomic and Floristically Complex Sebungwe Region and the Factors Modifying Mosaic Patch Landscapes at Sengwa Wildlife Area, Zimbabwe

An investigation of the status of woodlands at Sengwa Wildlife Research Area (SWRA) revealed factors influencing decline and die-back of woody plants at a time of low elephant densities. The vegetation condition of the study area in the elephant range area of the semi-arid area of northwest Zimbabwe was randomly assessed in 50 × 20 m permanently marked degraded and undegraded plots in a study area approximately 80 km2. Diversity of woody plants increased towards downstream. Percentage elephant damage was slight on undegraded plots and termite damage was three times greater on undegraded plots than degraded plots. Density of woody plants was high following a period of coppice regeneration. The results suggest regeneration of woody plants following a long period of elephant culls between 1960 and 1992 that altered forest structures. It is conceivable that other environmental agents may play the role of elephant damage in the presence of elephant densities < 1 individuals/ km2. Significant differences (p<0.05) in elephant densities (no/km2) were recorded in SWRA between 1958 and 1996, 1958 and 1993 suggesting that increasing elephant densities were negatively impacting on woody cover (%). Woody cover increased from 60% in 1993 to 70% in 1996 inside SWRA. SWRA vegetation may be on regeneration path if no adverse impacts are recorded from other environmental agents including termite activity, fungal attack (Fusarium oxysporum), Lantana camara L. invasions and drought. Epidemic die-back is not yet a common feature in the protected area. The results refute the postulation that elephant alone prevent woodland regeneration and recruitment into larger size classes by feeding on small trees. The findings suggest need to consider end to end cycle of each disturbance factor in order to accurately predict scale of vegetation change in savanna ecosystems.

Importancia ecológica de los mamíferos frugívoros en la dinámica de regeneración de tierras abandonadas en ambientes mediterráneos

Escribano-Ávila, G., Pías, B., Escudero, A., Virgós, E. 2015. Ecological relevance of frugivorous mammals in the regeneration dynamics of old fields in Mediterranean environments. Ecosistemas 24(3): 35-42. Doi.: 10.7818/ECOS.2015.24-3.06 Two opposite tendencies govern land use worldwide: intensification and abandonment. Land abandonment represents an opportunity for ecosystem recovery, an urgent need due to the current environmental crisis. Dispersal communities play a key role in the recovery of old fields, as they mobilize seeds that serve as the primary source for the regeneration of woody plants. Recent studies have pointed out the special relevance of frugivorous mammals for seed dispersal in degraded environments such as old fields. This is due to morphological and behavioural traits of frugivorous mammals which make this dispersal guild especially effective. Frugivorous mammals are generally bigger body-sized, use bigger home ranges and are able to perform longer dispersal distances than other frugivorous, thus dispersing a greater quantity of seeds in old fields. Once a seed arrives to an old field several stages until recruitment should be overcome (post-dispersal predation, germination, survival and growth). Seed dispersal by frugivorous mammals favors the success of dispersed seeds to be recruited due to: i. At the inter-specific level, frugivorous mammals do not present gape width limitations, thereby dispersing a wide range of fleshy fruited species. At the intra-specific level they are able to consume all fruit/seed size ranges while smaller frugivorous, like small to medium sized birds, usually select small fruits which may hamper recruitment, and ii Mammal frugivorous, specially carnivores, deposit seeds in microhabitats specially suitable for woody plants recruitment (e.g. shrubs). Overall, mammal frugivorous are key members of dispersal communities promoting regeneration dynamics in old fields thereby their ecological function should be considered from a management and restoration perspective.

Wildfire disturbance and productivity as drivers of plant species diversity across spatial scales

Wildfires influence many temperate terrestrial ecosystems worldwide. Historical environmental heterogeneity created by wildfires has been altered by human activities and will be impacted by future climate change. Our ability to predict the impact of wildfire‐created heterogeneity on biodiversity is limited because few studies have investigated variation in community composition (beta‐diversity) in response to fire. Wildfires may influence beta‐diversity through several ecological mechanisms. First, high‐severity fires may decrease beta‐diversity by homogenizing species composition when they create landscapes dominated by disturbance‐tolerant or rapidly colonizing species. In contrast, mixed‐severity fires may increase beta‐diversity by creating mosaic landscapes containing habitats that support species with differing environmental tolerances and dispersal traits. Moreover, the effects of fire severity on beta‐diversity may change depending on site conditions. Disturbance is hypothesized to increase local species richness at higher productivity and decrease local species richness at lower productivity, a process that can have important, but largely unexamined, consequences on beta‐diversity in fire‐prone ecosystems. We tested these hypotheses by comparing patterns of beta‐diversity and species richness across 162 plant communities in three sites that span a large‐scale gradient in climate and productivity in the Northern Rockies of Montana. Within each site, we used spatially explicit fire‐severity data to stratify sampling across unburned forests and forests burned with mixed‐ and high‐severity wildfires. We found that beta‐diversity (community dispersion) of forbs was higher in mixed‐severity compared to high‐severity fire, regardless of productivity. Counter to our predictions, local species richness of forbs was higher in burned landscapes compared to unburned landscapes at the low‐productivity site, but lower in burned landscapes at the high‐productivity site. This pattern may be explained by rapid regeneration of woody plants after fire in high‐productivity forests. Moreover, forbs and woody plants had disproportionately higher overall species richness in mixed‐severity fire compared to high‐severity fire, but only at the low‐productivity site. These patterns suggest that mixed‐severity fires promote higher landscape‐level biodiversity in low‐productivity sites by increasing species turnover across landscapes with a diverse mosaic of habitats. Our study illustrates the importance of understanding the mechanisms by which patterns of wildfire severity interact with environmental gradients to influence patterns of biodiversity across spatial scales.

Post-dispersal seed removal by ground-feeding rodents in tropical peatlands, Central Kalimantan, Indonesia

Forested tropical peatlands in Southeast Asia are being rapidly converted to agriculture or degraded into non-forest vegetation. Although large areas have been abandoned, there is little evidence for subsequent forest recovery. As part of a study of forest degradation and recovery, we used seed removal experiments and rodent surveys to investigate the potential role of post-dispersal seed predation in limiting the regeneration of woody plants. Two 14-day seed removal trials were done in deforested and forested peatland habitat in Central Kalimantan, Indonesia. Seeds of Nephelium lappaceum, Syzygium muelleri, Artocarpus heterophyllus (all animal-dispersed) and Combretocarpus rotundatus (wind-dispersed) were tested. Significantly more seeds (82.8%) were removed in forest than non-forest (38.1%) and Combretocarpus had the lowest removal in both habitats. Most handled seeds were eaten in situ and little caching was observed. Six species of rodents were captured in forest and five in non-forest. The most trapped taxa were three Maxomys spp. in forest (85.5% of individuals) and Rattus tiomanicus in non-forest (74.8%). Camera traps confirmed that rodents were responsible for seed removal. Seed predation in deforested areas, which have a much lower seed rain than forest, may contribute to the low density and diversity of regenerating forest.

Recovery of native plant communities in southwest Ohio afterLonicera maackiiremoval1

Abstract Lonicera maackii (Rupr.) Herder (Amur honeysuckle) is one of the most important invasive plants in the Ohio Valley. Because of its phenology and dense canopy, L. maackii can exclude native herbs and interfere with regeneration of woody plants. In 2005, in a county park in southwest Ohio, I established modified Whittaker plots in four stands with a gradient of L. maackii cover ranging from 24 yr old to 40 yr old. The L. maackii canopies were removed by herbicides in fall 2005. Plant cover was monitored from 2005 to 2013. After 8 yr, there was an increase in species richness and herbaceous cover at all sites. Herbaceous species turnover was generally greater at sites with greater initial L. maackii cover. All of the most-common herbaceous species increased or maintained their coverage; most of the species that increased were those that bloom in late spring or summer. The abundances of other invasive species also increased, including Alliaria petiolata (M. Bieb.) Cavara & Grande (garlic mustard). Ho...

Pure and Mixed Plantations of &amp;lt;i&amp;gt;Eucalyptus camaldulensis&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Cupressus lusitanica&amp;lt;/i&amp;gt;: Their Growth Interactions and Effect on Diversity and Density of Undergrowth Woody Plants in Relation to Light

Published results on the growth interactions of non-nitrogen fixing mixed plantations species, and their impact on the regeneration of woody plants are scant. This paper addresses the growth interactions of pure and mixed plantations of Eucalyptus camaldulensis and Cupressus lusitanica and their impact on the regeneration of woody plants in relation with light. Data on the regenerated woody plants, individual characteristics of the plantation species and light reaching under the canopies were collected using sample plots (n = 4) with a size of 20 m × 20 m for each plantation type. The result showed that, E. camaldulensis was suppressing the growth of C. lusitanica while its growth was favored when it was mixed with C. lusitanica (p p > 0.05). Density of plantation trees were found not having a significant relationship with diversity of species (p = 0.801). There was a significant but not direct relationship between light reached in the understory of the canopies and diversity of species in the plantations (p = 0.027). Overall, the result indicated that both the pure and the mixed plantations were favoring the recruitment of woody plants.

Climate, Deer and Hogs: Drivers of Rapid Change in a Hickory-Dominated Maritime Forest on St. Catherines Island

Maritime forests in the southeastern United States are very susceptible to climate change and have experienced dramatic reductions in extent following anthropogenic disturbances over the past two hundred years. St. Catherines Island, Georgia, an undeveloped barrier island, is home to an unusual pignut hickory (Carya glabra) maritime forest that is experiencing rapid rates of change, including a reduction in basal area from 23 m2·ha-1 in 1996 to 15 m2·ha-1 in 2014. Nine permanent forest plots and associated animal exclosures were installed across this 37 ha stand in 2012 to track forest change and seedling recruitment. From 2012 to 2014, declines in total basal area were caused by mortality of pignut hickory in the overstory and redbay (Persea borbonia) in the midstory. Pignut hickory continues to be ranked first in relative frequency, density and dominance, while Sabal palm (Sabal palmetto) is slightly increasing in relative density. In 2012, there were no woody species regenerating in any of the plots and following one year of animal exclosures, we found 478 pignut hickory seedlings ha-1; thus, deer browse and feral hog predation of nuts may be important drivers of change in this stand. The interplay among deer browse, exotic animal pressures, exotic insects and a drier climate has resulted in a very open forest with the regeneration of few woody plants. Without management of the feral hog and deer population, this unusual maritime forest, with trees as old as 250 years, may continue to decline.

Natural Regeneration and Biological Invasion by Pinus caribaea Morelet in Two Vereda Sites: Woody Vegetation Response

Veredas are regarded as humid complexes of ecological, water and scenery significance in Cerrado biome related to water table outcrop. Direct alterations in these environments can lead to species diversity reduction and also facilitate biological invasion processes. Thus our study aims to investigate the natural regeneration, the coverage of woody vegetation and the invasive species in two sites in secondary successional stage in the central part of Cerrado biome. Our study was carried out at two sites located at Minas Gerais state, Brazil. We established plots randomly throughout transects laid perpendicularly to the vereda’s drain line. We used the line intercept method to analyze the vegetation coverage. We set five 10-m width transects in each of both areas, perpendicular to the vereda’s drain line to evaluate the distribution of invasive alien species in the two areas. The richness did not vary between communities (U = 67.50; p = 0.061); on the other hand we found significant difference in density estimates (U = 36.50; p = 0.002). We found significant difference between categories for soil coverage in both sites. Grasses showed the highest coverage when compared to the other categories (K = 45.06; p < 0.001 for site 1 and K = 67.47; p < 0.001 for site 2). We observed a zonation tendency in site 1, with a higher native grass coverage at middle and backwards zones (K = 7.734, p < 0.05). We only found Pinus caribaea Morelet individuals in the invasive species survey. We recorded 46 Pinus caribaea individuals at site 1 and 116 Pinus caribaea individuals at site 2. From the latter group we found 13 individuals within the vereda and 103 in the surrounding vegetation. Both sites have a high natural woody plant regeneration potential although the presence of alien grasses in the veredas’ edge and Pinus caribaea all over the humidity gradient highlights the vulnerability of these areas to biological invasion.

Wildfire-contingent effects of fuel treatments can promote ecological resilience in seasonally dry conifer forests

Fire suppression has made many seasonally dry conifer forests more susceptible to high-severity wildfires, which cause large changes in forest structure and function. In response, management agencies are applying fuel reduction treatments to millions of acres of forest, with the goal of moderating fire behavior by reducing tree density and understory fuel loads. However, despite their wide application, we still lack basic information about the extent to which these treatments contribute to forest restoration by increasing forest resilience to recurring wildfire events. To address this question, we established 664 plots across 12 different sites in California, USA, where wildfire burned through fuel treatments, and measured a suite of forest characteristics relating to overstory structure, understory cover, and woody plant regeneration. We tested a “wildfire-contingency” hypothesis that there should be strong interactions between treatment and fire, specifically that the direction and magnitude of fuel treatment effects on forest characteristics will depend on subsequent disturbance. This interaction hypothesis had strong support, driven largely by effects on trees: without wildfire, live-tree cover was lower in treated stands than in untreated stands, but after wildfire, it was higher in treated stands than in untreated stands. Treated stands had higher soil moisture and more shrub seedlings than untreated stands without wildfire but had greater soil moisture and fewer shrub seedlings than untreated stands after wildfire. Conversely, litter depth, litter cover, and tree seedling abundance were lower in treated stands than in untreated stands without wildfire but higher in treated stands than in untreated stands after wildfire. Ordination revealed that the magnitude of ecological change attributable to wildfire is lower in treated stands than in untreated stands. We conclude that properly implemented treatments can promote resilience to both first-entry and subsequent wildfires.

Effects of gaps on regeneration of woody plants: a meta-analysis

Forest gaps, openings in the canopy caused by death of one or more trees, have a profound effect on forest regeneration and drive the forest growth cycle. It is therefore necessary to understand the effects of forest gaps on regeneration for modern forest management. In order to provide a quantitative assessment of the effects of forest gaps on regeneration of woody plants, we conducted this review of gap effects on woody plant regeneration on the basis of 527 observations from 42 individual papers, and reported the results of these data in a meta-analysis. Overall, densities of regenerated woody plants were significantly greater (359%) in forest gaps than on the closed-canopy forest floor. The regeneration density in gaps of plantation forests was significantly greater (P < 0.05) than that of natural forest because the regeneration in gaps of plantation forests was improved by both gap effects and experimental measures. Similarly, in comparison to natural gaps, regeneration was better enhanced in artificial gaps. Regeneration density exhibited a significantly positive correlation with gap size, but a negative correlation with gap age because the gap size decreased with increasing gap age. Shade tolerance of woody plants affected regeneration density in gaps and understory. Average regeneration density of shade-tolerant species exhibited a significantly positive response to gaps but densities remained lower in total than those of intermediate and shade-intolerant species. Gap effects on regeneration decreased in response to increasing temperature and precipitation because of the limiting effects of lower temperature and moisture on woody plant regeneration. In summary, forest gaps enhance woody plant regeneration, and the effects of gaps varied by forest type, gap characteristics, environmental factors and plant traits. The results of this meta-analysis are useful for better understanding the effects and roles of gaps on forest regeneration and forest management.

An efficient Agrobacterium-mediated transformation system for poplar.

Poplar is a model system for the regeneration and genetic transformation of woody plants. To shorten the time required for studies of transgenic poplar, efforts have been made to optimize transformation methods that use Agrobacterium tumefaciens. In this study, an Agrobacterium infective suspension was treated at 4 °C for at least 10 h before infecting explants. By transforming the Populus hybrid clone “Nanlin895” (Populus deltoides × P. euramericana) with Agrobacterium harboring the PBI121:CarNAC6 binary vector, we showed that the transformation efficiency was improved significantly by multiple independent factors, including an Agrobacterium infective suspension with an OD600 of 0.7, an Agrobacterium infection for 120 min, an Agrobacterium infective suspension at a pH of 5.0, an acetosyringone concentration of 200 µM, a cocultivation at 28 °C, a cocultivation for 72 h and a sucrose concentration of 30 g/L in the cocultivation medium. We also showed that preculture of wounded leaf explants for two days increased the regeneration rate. The integration of the desired gene into transgenic poplars was detected using selective medium containing kanamycin, followed by southern blot analysis. The expression of the transgene in the transgenic lines was confirmed by northern blot analysis.

Forest regeneration in gaps seven years after partial harvesting in riparian buffers of boreal mixedwood streams

Partial harvesting in boreal forest riparian buffers has been proposed as a management tool to emulate natural disturbance (END) along streams and lakes to increase shoreline habitat complexity through ensuing forest regeneration. We investigated the effect of partial harvesting in stream-side riparian buffers on regeneration of canopy species (Abies balsamea, Betula papyrifera, Picea glauca, Picea mariana and Populus tremuloides) by testing the hypothesis that juvenile trees would be more abundant, species-rich, and larger in gaps than in non-harvested buffers, and that those differences would be proportional to gap size. Our main objective was to determine what gaps sizes are conducive to promote tree and woody shrub regeneration in stream-side riparian areas of boreal mixedwood forests. We compared woody plant regeneration among harvest gaps varying in size (small, 10–20m2; medium, 21–100m2; and large, >100m2), and contrasted with regeneration under closed canopy in unharvested buffers and undisturbed reference forests. We found that woody plant communities in partial harvesting gaps were denser and more diverse than unharvested buffers. They were more so in medium to large gaps and consisted of shade-intolerant and early successional species. Favorable light and soil temperature in the large gaps appear to be responsible for this. We concluded that intentional shoreline disturbance aiming to achieve increased riparian habitat complexity and early successional forest community is possible by partial harvesting at up to 50% basal area removal. However, as END principles are increasingly applied to riparian forest management, it will be necessary to test and monitor the effectiveness and longer-term ecological responses of riparian communities to such management at catchment and landscape levels.

Effects of high-frequency understorey fires on woody plant regeneration in southeastern Amazonian forests

Anthropogenic understorey fires affect large areas of tropical forest, yet their effects on woody plant regeneration post-fire remain poorly understood. We examined the effects of repeated experimental fires on woody stem (less than 1 cm at base) mortality, recruitment, species diversity, community similarity and regeneration mode (seed versus sprout) in Mato Grosso, Brazil. From 2004 to 2010, forest plots (50 ha) were burned twice (B2) or five times (B5), and compared with an unburned control (B0). Stem density recovered within a year after the first burn (initial density: 12.4-13.2 stems m(-2)), but after 6 years, increased mortality and decreased regeneration--primarily of seedlings--led to a 63 per cent and 85 per cent reduction in stem density in B2 and B5, respectively. Seedlings and sprouts across plots in 2010 displayed remarkable community similarity owing to shared abundant species. Although the dominant surviving species were similar across plots, a major increase in sprouting occurred--almost three- and fourfold greater in B2 and B5 than in B0. In B5, 29 species disappeared and were replaced by 11 new species often present along fragmented forest edges. By 2010, the annual burn regime created substantial divergence between the seedling community and the initial adult tree community (greater than or equal to 20 cm dbh). Increased droughts and continued anthropogenic ignitions associated with frontier land uses may promote high-frequency fire regimes that may substantially alter regeneration and therefore successional processes.

Increased nitrogen cycling facilitates native forest regeneration: Potential for restoring extinct ecological processes?

Ecological processes often maintain the plant communities with which they have a long evolutionary association, and so their loss may favor invasions by nonnative species. We simulated the effects of fecal deposition and soil turnover by the extinct avian megafauna of New Zealand to test their influence on woody plant regeneration and nonnative plant invasion in a cool temperate rain forest. Hen manure increased soil available NO3-, leading to greater seedling regeneration relative to control plots. Although soil P was elevated within plots treated with hen manure, concentrations also increased within plots treated with liquid fertilizer, which did not have different seedling densities relative to controls. Simulated avian soil disturbance did not increase seedling densities, and none of the three treatments affected the proportion of woody seedlings that were nonnative. However, pretreatment variation in NO3- availability, which reflected longer-term rates of nitrogen cycling, reduced community invasibility. Our findings suggest that avian-derived nitrogen inputs increase the regeneration of native forests, raising the question of whether the functional role of extinct megaherbivores is absent in New Zealand.

Seed wasp invasions promoted by unregulated seed trade affect vegetal and animal biodiversity

Cone and seed insects are considered the most important predators of tree seeds during the pre-dispersal phase of development. Among them, exotic seed chalcids in the genus Megastigmus invaded Europe as a result of the rapidly-increasing and mostly unregulated seed trade for afforestation and ornamental plantations. Unlike their economic impact in seed orchards, until recently, little attention was paid to the ecological impact of these insects. In the present study, selected case studies of alien Megastigmus spp. were considered to assess their specific impact on the potential of natural regeneration of native woody plants and on the native entomofauna competing for seed resource. We re-analyzed data from former studies that did not focus on these ecological interactions and, here, present previously unpublished results. Seeds of Douglas-fir, true cedars, true firs and wild roses were sampled all over Europe, and the relative importance of the native and invasive chalcid species was assessed as well as their specific impact on seed yield. In most cases, the recent arrival of alien chalcids resulted in a significant decrease in the regeneration potential of the host trees. In the absence of competitors, alien chalcids occupied the entire seed niche in Douglas-fir, but their impact tended to decrease after the arrival of invasive seed bugs. In firs, alien chalcids tended to displace the native chalcids, but not in wild roses and cedars, where their damage was increasing. Different biological traits that might explain invasive success of alien chalcids are discussed. However, no general invasive patterns seem to exist.

Shrubby today but not tomorrow? Structure, composition and regeneration dynamics of direct seeded revegetation

Summary The establishment of direct seeded revegetation is well researched. However, there is little understanding of whether revegetation simplifies with age and loses many of the short‐lived understorey shrub species that provide critical resources for birds and other fauna, or regenerates sufficiently to be self‐sustaining. We sought to address this by investigating the change in structure and composition of 33 direct seeded sites established by Greening Australia between 1990 and 1996 in the Southern Tablelands of NSW. Transects were used to collect data describing the abundance and richness of woody plants in 1998 and 2008, and the abundance of woody plant regeneration in 2008. Our analysis showed the predicted number of live stems per metre declined exponentially from 5.8 stems/m (∼17 000 stems/ha) at age 1.5 years to 1.5 stems/m (∼4500 stems/ha) at age 17.5 years. Predicted woody plant species richness also declined with age, with a linear relationship. The number of species in the seed mix affected predicted woody plant species richness. However, large increases in seed mix richness produced relatively small increases in predicted species richness. Regeneration (new stems) was present at high levels (&gt;100 stems/ha); however, 82% of regeneration appeared to originate from delayed germination of sown seed rather than seed from established plants (recruitment). The predicted abundance of new stems (delayed germination and recruitment) declined with age, and for a given age increased with row width. Young stands (11.5 years), seeded with wide rows (4 m), had approximately six times the new stems of similar aged stands seeded with narrow rows (2 m). Our results indicate direct seeded stands simplify with age, becoming less dense and containing fewer species. Maintaining a diversity of shrub species in direct seeded sites may therefore require ongoing disturbances (scarifying, scalping, fire, thinning) of established sites and changes to establishment techniques for new sites. We suggest further research to establish the status of soil seed banks in direct seeded sites, testing different forms of disturbances to trigger regeneration in older revegetation sites and establishing new sites using wide rather than narrow rows and seed mixes enriched with species from genera other than Eucalyptus or Acacia.

Heavy impact on seedlings by the impala suggests a central role in woodland dynamics

Abstract:Research has increasingly established that mesoherbivores influence the regeneration of woody plants. However the relationship between mesoherbivore density and degree of impact, and the spatial component of this impact, has not been well established. Using a novel sampling design, we assessed in iMfolozi Park, South Africa, the impact of impala (Aepyceros melampus) across the full complement of woody species within the home range, evaluating its spatial component and relationship to impala density. We used four GPS collars, in separate breeding herds, and a GIS to detect zones of different density of impala in the landscape, thus defining a fine-grain browsing gradient. We assessed impact on woody recruits (≤ 0.5 m height) across this gradient by means of 1600 random 1 × 1-m quadrats. Densities of woody seedlings, and mean percentage of remaining canopy, were significantly less in areas of high impala density versus low-density areas. There was a significant correlation between increasing impala density and decreasing density of favoured woody recruits. We propose a hypothesis of impala-induced patch dynamics. It seems likely that the ubiquitous impala may create and sustain a shifting mosaic of patches, and thus function as a key determinant of landscape heterogeneity.