Abundance Of Herbaceous Plants Research Articles

The Study of Transformed Herbaceous Vegetation in the Area Flooded Due to Coal Mine Workings

Abstract The spontaneous vegetation in permanent flooding zone around technogenic water bodies arising on former pastures due to underground coal mining in the Western Donbass basin (steppe zone of Ukraine) was studied in 2018–2019. Occurrence and abundance of herbaceous plants were taken into account in 36 vegetation plots over a total area of 0.8 km2 in different habitats: dry, wet and flooded. In total, 83 plant species belonging to 31 families and 66 genera were identified, among which perennials dominated. Strong negative Pearson’s correlation was found between the amount and abundance of plant species and soil characteristics across the studied habitats, where the joint action of all edaphic factors determined the mosaic appearance of transformed vegetation. The spontaneous vegetation of the least disturbed xero-mesophilic habitats was most similar to (semi)natural grasslands, while the vegetation of hygrophilic habitats had a complete mismatch. Surrounding grasslands were not the most important diasporas’ source for spontaneous succession in the disturbed zone, and many species were supposed to come from the more remote areas. Recovery of target vegetation did not occur for 25 years of permanent subsidence and flooding due to radical transformation of landscape and soil and appearance of completely inappropriate habitats. At the same time, the unusual species composition of spontaneous vegetation and significant number of rare and endangered plants indicate the formation of valuable biotopes in the subsidence and flooding zone.

Long-term natural dynamics of an alpine lichen heath in the Teberda State Biosphere Reserve, northwestern Caucasus

The alpine vegetation of Europe and the Caucasus has experienced substantial changes due to climate warming and reduced grazing. Exposed ridge communities, such as alpine heaths, are presumed to be less vulnerable to such processes. Herein, we analyze long-term dynamics (over 37 years) of an alpine lichen heath in the Teberda State Biosphere Reserve, Karachaevo-Cherkessian Republic, Russia. We counted the shoots of all vascular plants present on permanent plots. Autocorrelated linear regressions, a non-metric multidimensional scaling ordination, and a fourth-corner analysis were applied to characterize the relationships between shoot numbers, climate variables (temperatures and precipitation), functional traits, and species strategies. Nine species, including dominant Festuca ovina L. and Antennaria dioica (L.) Gaertn., increased their abundances, whereas Carex spp. were observed to decrease. The overall dynamics were mainly driven by increasing mean temperatures during the growing season (July and August). None of the changes observed in the selected traits were correlated with increasing or decreasing numbers of species; however, some traits (plant height, specific root length, specific leaf area, and leaf carbon content) were potentially associated with climate variables. The observed dynamics suggested an overall increase in the abundance of herbaceous plants. Generally, our results support “greening” effects in tundra and alpine biomes.

Beyond forests in the Amazon: biogeography and floristic relationships of the Amazonian savannas

AbstractOpen habitats such as grasslands occupy < 5% of the Amazon and are currently grouped under the broad term Amazonian savanna, covering an area of c. 267 000 km2, mostly in Brazil and Bolivia. These habitats are found isolated within an extensive rainforest matrix, having a distinct flora from the latter. The lower Amazon River is home to several patches of savanna that occupy both south and north banks of the river, in Santarém, Alenquer and Monte Alegre. Although having an abundance of herbaceous plants, most studies on these open areas focus only on tree species, ignoring the relevant non-woody component of the vegetation. Our objectives were to provide new surveys of seed plants for two Amazonian savanna sites and to take the opportunity to revisit the biogeographical links between Amazonian savanna, Amazonian canga vegetation and the central Brazilian cerrado (CBC) and caatinga, analysing woody and herbaceous plants. We created a floristic database that includes sites of Amazonian savannas, including campinarana, coastal scrub (restinga), CBC and Amazonian campos rupestres (on canga or other substrate). We compared those sites using multivariate analyses to find out the degree of floristic resemblance between sites. We prepared a new list of 406 species of seed plants [336 in Parque Estadual de Monte Alegre (PEMA) and 117 in Serra do Itauajuri (SI)], including 23 new records for the state of Pará and some putative new species for science. The Amazonian savannas form three loosely arranged groups, whereas the Amazonian canga formed a cohesive assemblage. Both groups were contrasted against cerrado and caatinga sites and had a distinctive flora from both. Sites from north-western Pará (Alter do Chão, PEMA and SI) were grouped with their northern counterparts in Roraima. An improved representation of the flora of these sites is provided, with more insight into the relationship between the Amazonian savanna sites and other vegetation types. It is worrying that recent changes of the Brazilian legislation place open environments, such as PEMA, in the path of vulnerability to disturbance and destruction.

Leaf‐cutting ants negatively impact the regeneration of the Caatinga dry forest across abandoned pastures

AbstractThe mechanisms affecting forest regeneration in human‐modified landscapes are attracting increasing attention as tropical forests have been recognized as key habitats for biodiversity conservation, provision of ecosystem services, and human well‐being. Here we investigate the effect of the leaf‐cutting ants (LCA) Atta opaciceps on regenerating plant assemblages in Caatinga dry forest. Our study encompassed 15 Atta opaciceps colonies located in landscape patches with a gradient of forest cover from 8.7% to 87.8%, where we monitored regenerating individuals (seedlings and saplings of woody and herbaceous plants) in different habitats (nests, foraging areas, and control areas) over one year. We recorded 2,977 regenerating plant individuals, distributed among 55 species from 23 families. Herbaceous plants represented 82.1% and 58.2% of the total number of individuals and species, respectively. Species richness of both the whole and herbaceous plant assemblages increased along the forest cover gradient, but without difference between the habitats. Total plant abundance was highest in control areas followed by foraging areas and nests and this pattern held for both woody and herbaceous plants. Although forest cover did not influence the abundance of herbaceous plants and the whole plant assemblage, it positively affects woody plant abundance across control areas. Forest cover and habitat changed species composition of both the entire regenerating and the herbaceous assemblages. These results together indicate that LCA negatively impact regenerating plant assemblages, particularly in those sites with increased forest cover. As LCA proliferate in human‐modified landscapes, they may prevent plant regeneration of disturbed areas.

Gatekeepers to the effects of climate warming? Niche construction restricts plant community changes along a temperature gradient

Organisms that modify the environment (niche constructors) are likely candidates to mediate the effects of climate warming. Here we assess tundra plant community changes along a temperature gradient and how these are modified in the presence of the common allelopathic dwarf shrub Empetrum nigrum and the large herbivore Rangifer tarandus.We developed a structural equation model based on data from a field-based study of 1450 tundra plant communities across Northern Fennoscandia, covering a temperature gradient of 3.5 °C, contrasting Rangifer densities, a range of Empetrum abundances in addition to gradients in topography and bedrock.We found temperature to be a significant positive predictor of Empetrum, herbaceous and woody plant abundances. However, the effect of temperature as predictor for herbaceous plant abundance was significantly reduced in communities with Empetrum present. For woody plant abundance Empetrum was a stronger predictor than temperature. In comparison, we found Rangifer density to have marginal or no effect on either herbaceous or woody plant abundance. These findings were not modified by either topography or bedrock.Results from this study indicate that herbaceous plant responses to climate warming are currently reduced in communities where Empetrum is present, whereas the abundance of Empetrum and other woody plants is promoted. Results also indicate that any future Empetrum encroachment is likely to drive tundra communities towards slower process rates and lower biodiversity. As such our results substantiate the importance of understanding the dynamics of niche constructor species and include them in predictive models of climate change.

Facilitation between woody and herbaceous plants that associate with arbuscular mycorrhizal fungi in temperate European forests.

In late‐successional environments, low in available nutrient such as the forest understory, herbaceous plant individuals depend strongly on their mycorrhizal associates for survival. We tested whether in temperate European forests arbuscular mycorrhizal (AM) woody plants might facilitate the establishment of AM herbaceous plants in agreement with the mycorrhizal mediation hypothesis. We used a dataset spanning over 400 vegetation plots in the Weser‐Elbe region (northwest Germany). Mycorrhizal status information was obtained from published resources, and Ellenberg indicator values were used to infer environmental data. We carried out tests for both relative richness and relative abundance of herbaceous plants. We found that the subset of herbaceous individuals that associated with AM profited when there was a high cover of AM woody plants. These relationships were retained when we accounted for environmental filtering effects using path analysis. Our findings build on the existing literature highlighting the prominent role of mycorrhiza as a coexistence mechanism in plant communities. From a nature conservation point of view, it may be possible to promote functional diversity in the forest understory through introducing AM woody trees in stands when absent.

Dune-scale distribution pattern of herbaceous plants and their relationship with environmental factors in a saline–alkali desert in Central Asia

Sand dunes are the main landforms in modern deserts worldwide. As an important type of desert vegetation, herbaceous plants have long been acknowledged for their important ecological functions. We focus on the dune-scale distribution pattern of herbaceous plants and their relationship with the environment. During the early summer of 2010, the herbaceous plant density, coverage, aboveground biomass and eighteen environmental factors were surveyed from 214 plots (5m×5m) across two linear sand dunes (220m×110m) located in the Gurbantunggut Desert, China, a typical saline–alkali desert in Central Asia. Data were analyzed using univariate, ordination, and geostatistical techniques. Three vegetation variables represent a significant clumped distribution (P<0.01) across the entire study site. Obvious differences were observed among different slope positions/transects, with the lowest values observed at the summit. Geostatistics indicated that all of the variables showed a moderate spatial dependence and obvious zonal distribution along the sand dunes. The ranges (lag distance) of density (32.2m) and coverage (33.5m) were close to the average width (31.4m) of the transects. The biomass range (74.1m) was almost equal to the average width (75m) of the sand dunes. Pearson's correlation analysis and nonmetric multidimensional scaling analysis consistently demonstrated that the distributions of herbs on sand dunes were dominantly influenced by sand dune topography (slope position, convexity, and relative height), soil nutrients (total nitrogen and phosphorus) and deep-rooted shrubbery (Ephedra distachya). Compared to large, mobile and steep sand dunes, low, fixed and gentle sand dunes contribute to herbaceous plant abundance and distribution as well as the stability maintenance of the whole desert ecosystem.

Wildfire, clearcutting, and vole populations: Balancing forest crop protection and biodiversity

Early successional forest habitats that develop after wildfire may provide ideal conditions for population build-ups and subsequent fluctuations by Microtus voles. Regeneration of burned-over forest land may be hindered by consumption of planted trees by voles. A high abundance of voles, occurring in the second growing season after a wildfire, may result in serious feeding damage to seedlings leading to major plantation failures. A wildfire occurred near Golden, British Columbia, Canada in the spring of 2011 and may have initiated the successional conditions to generate a vole population outbreak with consequent feeding damage to tree seedlings. We tested the hypotheses (H) that (H1) abundance of herbaceous plants (grasses and forbs) will be greater, and (H2) abundance of voles and incidence of feeding damage to tree seedlings will be higher, in burned than unburned (control) sites. Microtus voles and other forest-floor small mammals were live-trapped for four years (2011–2014) in replicated sites of a wildfire (burned plantation), control (unburned) plantation, and a new control clearcut. Abundance of total herbs and grasses, incidence of feeding damage, and mortality to tree seedlings by voles were measured in all sites. Mean abundance of total herbs and grasses were similar among treatments during the post-wildfire period. Mean annual peak numbers of Microtus in clearcut sites ranged from 18 to 30 per index-line. Annual peak numbers in the burned and control plantation sites ranged from 5 to 8 voles per index-line and were essentially stable at these numbers. Vole populations in the control and burned plantation sites were dominated by the meadow vole (Microtus pennsylvanicus Ord), and those in the clearcut sites by the long-tailed vole (Microtus longicaudus Merriam). Mean mortality of trees was significantly higher in the control clearcut sites at 30% compared with 13% in the burned plantation sites. These results did not support either H1 or H2. Wildfire, at least in this case, did not generate high populations of voles and significant damage to tree seedlings. Mean abundance of total small mammals was similar in burned and control plantation sites, but less than in clearcut sites. Populations of the deer mouse (Peromyscus maniculatus Wagner) increased after wildfire and those of the southern red-backed vole (Myodes gapperi Vigors) declined. Populations of the northwestern chipmunk (Neotamias amoenus J.A. Allen) and Sorex spp. did not show a clear preference for any of the treatments. Disturbance by clearcutting or wildfire seemed to reduce species richness and diversity, but all eight species of small mammals were present in each of the treatments.

New enzyme boosts profits, cuts chemical use at ethanol plants

Sand dunes are the main landforms in modern deserts worldwide. As an important type of desert vegetation, herbaceous plants have long been acknowledged for their important ecological functions. We focus on the dune-scale distribution pattern of herbaceous plants and their relationship with the environment. During the early summer of 2010, the herbaceous plant density, coverage, aboveground biomass and eighteen environmental factors were surveyed from 214 plots (5 m × 5 m) across two linear sand dunes (220 m × 110 m) located in the Gurbantunggut Desert, China, a typical saline–alkali desert in Central Asia. Data were analyzed using univariate, ordination, and geostatistical techniques. Three vegetation variables represent a significant clumped distribution (P < 0.01) across the entire study site. Obvious differences were observed among different slope positions/transects, with the lowest values observed at the summit. Geostatistics indicated that all of the variables showed a moderate spatial dependence and obvious zonal distribution along the sand dunes. The ranges (lag distance) of density (32.2 m) and coverage (33.5 m) were close to the average width (31.4 m) of the transects. The biomass range (74.1 m) was almost equal to the average width (75 m) of the sand dunes. Pearson's correlation analysis and nonmetric multidimensional scaling analysis consistently demonstrated that the distributions of herbs on sand dunes were dominantly influenced by sand dune topography (slope position, convexity, and relative height), soil nutrients (total nitrogen and phosphorus) and deep-rooted shrubbery (Ephedra distachya). Compared to large, mobile and steep sand dunes, low, fixed and gentle sand dunes contribute to herbaceous plant abundance and distribution as well as the stability maintenance of the whole desert ecosystem.

Pollen-inferred late Holocene agricultural developments in the vicinity of Woljeong-ri, southwestern Korea

The pollen record from Woljeong-ri in southwestern Korea reveals a vegetation history with high temporal resolution over the period from ca. 1950 BC to AD 310. The pollen profile is divided into four phases: zone 1 (ca. 1950–1220 BC), zone 2a (ca. 1220 BC–AD 200), zone 2b (ca. AD 200–290) and zone 2c (ca. AD 290–310). The abundance of Quercus (Lepidobalanus) and Carpinus, and the paucity of Artemisia, Cyperaceae and Poaceae in the initial stage suggest the dominance of deciduous broadleaved forest with little evidence of human interference. The reduction of deciduous broadleaved trees, particularly of Quercus and Alnus, and the abundance of herbaceous plants and cultivated Poaceae indicate increasing anthropogenic disturbance in the surrounding vegetation after ca. 1220 BC, which is probably attributable to agricultural expansion and the construction of rice paddy fields. This change temporally corresponds to the transition from the Neolithic to the Bronze Age across the region. The dominance of cultivated Poaceae continues in the subsequent period, and its amount increases markedly after ca. AD 200, along with the increase of Pinus. This implies that rice agriculture and anthropogenic disturbance on vegetation may have intensified at least a century earlier than the presumed emergence of state-level societies. The decline in rice agriculture, which is possibly related to the advent of drier climatic conditions, is suggested in the current pollen record after ca. AD 290.

Pile burning creates a fifty-year legacy of openings in regenerating lodgepole pine forests in Colorado

Pile burning is a common means of disposing the woody residues of logging and for post-harvest site preparation operations, in spite of the practice’s potential negative effects. To examine the long-term implications of this practice we established a 50-year sequence of pile burns within recovering clear cuts in lodgepole pine forests. We compared tree, shrub and herbaceous plant abundance and documented indicators of soil degradation in openings where logging residue was piled and burned as part of post-harvest site preparation and the adjacent forests regenerating after clear cutting. We found that pile burning creates persistent 10–15m diameter openings with lower tree densities (<500treesha−1; stems >2.54cm diameter at 1.4m height) compared to surrounding regenerating pine stands (2000–5000treesha−1). Low tree seedling and sapling densities (stems <2.54cm diameter at 1.4m height) in the openings (10–20% of regenerating forest), suggest they will remain poorly-stocked into the future. We observed evidence of high severity burning, including layers of soil charcoal and hardened red soil across the time series, but no sign that water infiltration, compaction or other indicators of soil degradation were consistent barriers to plant recolonization. Forb and graminoid cover, for example, was higher in the burn scar openings compared to regenerating forests. Pile burn openings are formed by the loss of pine seed during burning and short-term soil changes, but it is uncertain what factors maintain the openings during subsequent decades. As conducted for site preparation, the herbaceous plant-dominated openings are not extensive (<5% cover within clear cut units), and we found few invasive, non-native plants and no indication that soil conditions were sufficiently altered to explain 50years of poor tree regeneration. Nevertheless, persistence of the openings and recent increases in the number and size of piles from fuels and bark beetle salvage treatments has prompted resource managers to consider options for utilization and on-site retention of harvest residue.

The response of Mediterranean herbaceous community to soil disturbance by native wild boars

Native wild boar (Sus scrofa lybicus) populations in Israel increased in the last decades, and their rooting activity presents an apparent severe disturbance that may affect herbaceous plant communities. We studied the extent of wild boar rooting and its effect on herbaceous vegetation in an east Mediterranean garrigue. We compared the effects of rooting soil disturbance (RSD) between summer, winter, and RSD-free control plots on herbaceous plants. RSD affected four percent of the area covered by herbaceous vegetation in winter and spring, and only 2 % in summer. Summer RSD increased herbaceous species diversity in the following spring by decreasing the abundance of the dominant species, but it did not affect total herbaceous biomass. Winter RSD lowered herbaceous biomass but did not affect herbaceous plant abundance or diversity. We conclude that Mediterranean herbaceous plant community appears to be resilient to RSD, causing only minor changes in species composition and small decrease of their biomass. The contrast between the relatively large extent of wild boars RSD, and its limited impact on the herbaceous plant community, can be attributed to the long mutual evolutionary history of wild boars and these vegetation communities.

The role of holm oak edges in the control of disturbance and conservation of plant diversity in fire-prone landscapes

Holm oak (Quercus rotundifolia) woodlands have been able to persist in fire-prone landscapes in northern Portugal where they seem to play a relevant role in community and landscape level patterns and processes, namely in the control of disturbance events and in the maintenance of biodiversity. In this research we tested the following hypotheses: (i) holm oak woodlands affect fire behavior, mainly by disrupting and delaying fire spread; (ii) disruption and delaying of fire spread is due to fire extinction at the edge of woodlands; and (iii) plant diversity is favored by frequent low-intensity fires as a result of the control of fire spread by holm oak woodland edges. We sampled herbaceous, shrub and tree structure and herbaceous plant composition across edges of holm oak woodlands with known recent contact with fire. Using BehavePlus we converted structural data into fuel models and simulated fire behavior for the locations sampled along the exterior–interior gradient of the woodlands. Our results indicate that holm oak woodlands play a relevant role in the control of fire spread and in the maintenance of plant diversity. We found differences in simulated maximum rate of fire spread (ROS) and fireline intensity (FLI) between outside and inside woodlands as well as a 100% probability of fire extinction when fuel moisture was >12% and wind speed at 10m aboveground was <40kmh−1, supporting the self-extinction hypothesis. We found also that richness and abundance of herbaceous plants varied between the interior and exterior of the woodland, with higher values outside the woodland, and that plant composition along the interior–exterior gradient had distinct patterns. These variables and the pattern of plant distribution were also significantly affected by time since last fire event. We conclude that holm oak woodlands affect fire behavior by interrupting fire spread at the edge zone and that fire-created edges affect herbaceous plant species richness, abundance and distribution by maintaining habitat diversity, which increased plant diversity at patch and landscape levels. Based on our results and other evidence, we developed a conceptual model of the dynamics of fire, landscape structure, and plant diversity in fire-prone landscapes where holm oak patches persist.

Forecasting vole population outbreaks in forest plantations: The rise and fall of a major mammalian pest

Voles of the genera Microtus and Myodes feed on tree seedlings planted on cutover forest land in temperate and boreal forests of North America and Eurasia. This damage may have serious economic implications as well as limit regeneration of appropriate tree species in certain forest ecosystems. Prediction of vole population outbreaks and feeding damage to forest plantations, across even a limited geographic range, has yet to be achieved in North America. Thus, a major objective was a detailed analysis of changes in population dynamics of long-tailed voles ( Microtus longicaudus), and to test three hypotheses (H) that vole populations would: (H 1) rise and fall in accordance with the abundance of herbaceous plants (grasses and forbs) during early vegetative succession after forest harvesting, (H 2) be positively associated with grass-seeded sites; and (H 3) incidence of feeding damage to seedlings would be positively associated with vole abundance. Voles were live-trapped for 6 years (2004–2009) from the time of harvesting on intensive sites, as well as surveyed over a range of extensive sites. Population numbers were related to habitat characteristics and tree damage in young forest plantations near Golden, British Columbia, Canada. Populations of long-tailed voles were low in the first two years after harvest with mean numbers <5–15/ha. Annual peaks of 49–84 voles/ha were recorded in 2006. In the fourth year (2007) after harvesting, numbers of voles declined on two of three sites, deepened in 2008 and reached extirpation in 2009. On the extensive sites, vole numbers increased 4.6–5.3 times from 1–2 to 3–6 years post-harvest before declining thereafter. Crown volume index of grasses and herbs, volume and abundance of downed wood, total species richness of vascular plants, and structural diversity of herbs were important habitat variables. Vole numbers were higher on those sites seeded with pasture grasses and forbs. There was a significant positive relationship of tree mortality and abundance of voles ( Microtus) across a relatively wide geographic area. This study is the first relatively long-term analysis of changes in population dynamics of the long-tailed vole and the predictions of H 1 and H 2 seemed to be supported. The positive relationship (H 3) of the incidence of overwinter damage to trees and vole abundance is the first such analysis for forest plantations, on harvested sites, in North America. At 3–4 years post-clearcut harvesting is a critical time for population buildups of voles and subsequent damage to plantation trees. Seeded grass species clearly create optimum habitat conditions for voles, generating population densities up to 30–50 voles/ha, which is in the range of a “high” damage risk to seedlings. Risk ratings (voles/ha) for feeding damage to trees were low (<7), moderate (7–34), high (35–88), and very high (>88).

Hydraulic lift in a Neotropical savanna: Experimental manipulation and model simulations

The objective of this study was to assess the magnitude of hydraulic lift in Brazilian savannas (Cerrado) and to test the hypothesis that hydraulic lift by herbaceous plants contributes substantially to slowing the decline of water potential and water storage in the upper soil layers during the dry season. To this effect, field observations of soil water content and water potentials, an experimental manipulation, and model simulations, were used. Savannas of central Brazil exhibit consistent changes in tree density along shallow topographic gradients, from open savannas with relatively few trees in the lower portions of the topographic gradients to woodlands with a relatively high density of trees in the upper portions of the gradient. Herbaceous plant abundance follows the opposite trend. The diel recovery of soil water storage was higher in sites with more abundant herbaceous vegetation. Experimental removal of the above ground portion of herbaceous plants in a site with low tree density, during the dry season, substantially enhanced diel recovery of water potentials in the upper soil layers, consistent with the release of hydraulically lifted water from their shallow roots. In a site with high tree density, the release of hydraulically lifted water by woody plants contributed only 2% to the partial daily recovery of soil water storage, whereas the herbaceous layer contributed the remaining 98%. Non saturated water flow in the same savanna type contributed 8% to the partial daily recovery of soil water potential at the beginning of the dry season, decreasing to near 0% after 20 days of drought. During a 70-day rainless period the soil water potential dropped to −2.0 MPa near the soil surface. The simulation model predicted that without hydraulic lift, water potential in the upper soil layers in relatively dense savannas would have dropped to −3.8 MPa. The maximum contribution of hydraulic lift to the upper 100 cm of soil was 0.7 mm day−1 near the middle of the dry season. During the peak of the dry season, hydraulic lift can replace 23% of the ecosystem evapotranspiration in a site with high tree density and consequently greatly influences the water economy and other ecosystem processes in the Cerrado.

REGIONAL EXTENT OF AN ECOSYSTEM ENGINEER: EARTHWORM INVASION IN NORTHERN HARDWOOD FORESTS

The invasion of exotic earthworms into northern temperate and boreal forests previously devoid of earthworms is an important driver of ecosystem change. Earthworm invasion can cause significant changes in soil structure and communities, nutrient cycles, and the diversity and abundance of herbaceous plants. However, the regional extent and patterns of this invasion are poorly known. We conducted a regional survey in the Chippewa and Chequamegon National Forests, in Minnesota and Wisconsin, U.S.A., respectively, to measure the extent and patterns of earthworm invasion and their relationship to potential earthworm introduction sites. We sampled earthworms, soils, and vegetation in 20 mature, sugar maple-dominated forest stands in each national forest and analyzed the relationship between the presence of five earthworm taxonomic groups, habitat variables, and distance to the nearest potential introduction site. Earthworm invasion was extensive but incomplete in the two national forests. Four of the six earthworm taxonomic groups occurred in 55-95% of transects; however 20% of all transects were invaded by only one taxonomic group that has relatively minor ecological effects. Earthworm taxonomic groups exhibited a similar sequence of invasion found in other studies: Dendrobaena > Aporrectodea = Lumbricus juveniles > L. rubellus > L. terrestris. Distance to the nearest road was the best predictor of earthworm invasion in Wisconsin while distance to the nearest cabin was the best predictor in Minnesota. These data allow us to make preliminary assessments of landscape patterns of earthworm invasion. As an example, we estimate that 82% of upland mesic hardwood stands in the Wisconsin region are likely invaded by most taxonomic groups while only 3% are unlikely to be invaded at present. Distance to roads and cabins provides a coarse-scale predictor of earthworm invasion to focus stand-level assessments that will help forest managers better understand current and potential forest conditions and identify uninvaded areas that could serve as important refugia for plant species threatened by earthworm invasion.

Tree regeneration and microclimate in a liana and bamboo-dominated semideciduous Atlantic Forest

We assessed the effect of native bamboo and lianas on microclimate, tree regeneration and forest structure in a semi-deciduous Atlantic Forest subjected to selective timber extraction during the last century. We hypothetized that bamboo and liana cutting would increase incoming solar radiation in the understory promoting establishment and survival of pioneer and light-requiring canopy tree species. A manipulative experiment consisting of bamboo and liana cutting was performed in a native forest stand in northeastern Argentina. In three permanent 1-ha plots bamboo and lianas were cut and allowed to decompose in situ, while other three plots were used as a control treatment. We measured solar radiation reaching the understory, soil water availability and air temperature in both bamboo and liana cutting and control plots. Tree sapling abundance and richness, stand basal area, bamboo density, and cover of lianas, herbs, shrubs, fallen trees and branches were also determined. We performed multivariate analyses to relate tree sapling abundance and richness with biotic and abiotic factors. Bamboo and liana cutting increased by 100% the solar radiation reaching the understory. The fraction of solar radiation transmitted at 0.7 m height above ground in control and treated plots was 0.1 and 0.2, respectively. Minimum soil matric potentials after a severe dry spell were less than −2 MPa. Soil water availability was higher under closed-canopy in the treated plots because liana transpiration was prevented by cutting. Although bamboo and liana cutting increased incoming solar radiation, tree seedling and sapling abundance of pioneer and light-demanding species was not improved by the treatment. Instead, an increased abundance of herbaceous plants was observed in gaps and open canopy areas (i.e., sites with amounts of herb cover greater than 75% represented the 11 and 2% of the total number of sites in treated and control plots, respectively). Sapling survival and growth rates, on the other hand, appeared to be promoted by bamboo and liana cutting. Bamboo inhibited tree sapling abundance and richness in gaps, whereas tree basal area had a positive effect. In the semideciduous Atlantic Forest, native bamboos modify gap phase regeneration, and may affect canopy cover and forest composition in the long term. Post-logging management techniques are needed for sustainable timber production in these forest stands.

CHANGES IN HARDWOOD FOREST UNDERSTORY PLANT COMMUNITIES IN RESPONSE TO EUROPEAN EARTHWORM INVASIONS

European earthworms are colonizing earthworm-free northern hardwood forests across North America. Leading edges of earthworm invasion provide an opportunity to investigate the response of understory plant communities to earthworm invasion and whether the species composition of the earthworm community influences that response. Four sugar maple-dominated forest sites with active earthworm invasions were identified in the Chippewa National Forest in north central Minnesota, USA. In each site, we established a 30 x 150 m sample grid that spanned a visible leading edge of earthworm invasion and sampled earthworm populations and understory vegetation over four years. Across leading edges of earthworm invasion, increasing total earthworm biomass was associated with decreasing diversity and abundance of herbaceous plants in two of four study sites, and the abundance and density of tree seedlings decreased in three of four study sites. Sample points with the most diverse earthworm species assemblage, independent of biomass, had the lowest plant diversity. Changes in understory plant community composition were most affected by increasing biomass of the earthworm species Lumbricus rubellus. Where L. rubellus was absent there was a diverse community of native herbaceous plants, but where L. rubellus biomass reached its maximum, the herbaceous-plant community was dominated by Carex pensylvanica and Arisaema triphyllum and, in some cases, was completely absent. Evidence from these forest sites suggests that earthworm invasion can lead to dramatic changes in the understory community and that the nature of these changes is influenced by the species composition of the invading earthworm community.

Scale-Dependent Influence of Topography-Based Hydrologic Features on Patterns of Woody Plant Encroachment in Savanna Landscapes

Rainfall in drylands is erratic. Topographic features of landscapes can dampen or amplify temporal variability by spatially influencing patterns of water loss and accumulation. The extent to which portions of a landscape may differentially capture or retain scarce water and nutrient resources is an important determinant of vegetation patterns, particularly with respect to the distribution of woody plants. We therefore hypothesized that historic changes in woody cover on landscapes experiencing similar climate and disturbance regimes would vary with catena-to-catena (hillslope-to-hillslope) variation in topography-based hydrologic features. We tested this hypothesis by comparing topographic wetness index (TWI) values on replicate landscapes where woody plant abundance has increased over the past 100 yr. These landscapes are characterized by savanna parklands on coarse-textured upland portions of catenas that grade (1–3% slopes) into closed-canopy woodlands on fine-textured (lowland) portions of catenas. TWI values for woody and herbaceous communities were comparable within uplands, suggesting factors unrelated to surface/subsurface hydrology determine patterns of woody cover in these catena locations. TWI values for upland savanna parklands were significantly lower than those of closed-canopy woodlands occupying catena footslopes. Furthermore, uplands adjoining historically static woodland boundaries had lower TWI values than those where woodland boundaries had moved upslope 2.1 m yr � 1 from 1976 to 1995. Results suggest runoff–runon relationships influence patterns of woody plant cover and change at the catena scale and may override constraints imposed by soil texture. As a result, changes in woody cover potentially accompanying changes in disturbance regimes, climate or atmospheric chemistry are likely to be constrained by topoedaphic settings. Models of vegetation dynamics may therefore need to explicitly account for rainfall–topography–soil texture relationships and associated scale-dependent mechanisms to accurately predict rates and patterns of change in woody and herbaceous plant abundance.

Effects of Western Balsam Bark Beetle on Spruce-Fir Forests of North-Central Wyoming

Abstract Western balsam bark beetle, Dryocoetes confusus (Coleoptera: Scolytidae), has caused widespread mortality of subalpine fir (Abies lasiocarpa) in western North America throughout the past decade. The objectives of this study were to document the effects of this mortality, relate mortality to pre-existing stand conditions, and investigate the role of storm-damaged fir in beetle population dynamics in north-central Wyoming. Transect cruise lines and pairs of infested and uninfested plots were installed to detect changes in the forest overstory and understory and to determine associations between stand conditions and beetle-caused fir mortality. On average, beetles killed more than 70 trees/ac over the last several years. This mortality resulted in significant decreases in: subalpine fir basal area, trees per acre, stand density index, and the percentage of subalpine fir stems in the overstory. Small, but significant increases were detected in the understory; herbaceous plant abundance increased in the infested plots compared with the noninfested plots. Moreover, significant positive linear relationships were found between the amount of fir mortality and the percentage of subalpine fir trees in a stand, subalpine fir basal area, and subalpine fir stand density index. In addition, a significant positive linear relationship was found between the percentage of wind-caused downed fir logs in an area and the percentage of logs utilized by western balsam bark beetle. The blowdown events that occurred in the mid-1990s in combination with a high percentage of fir component has provided ideal conditions for continued beetle expansion. West. J. Appl. For. 18(4):259–266.