Forest Grassland Edge Research Articles

Indigenous forest edges increase habitat complexity and refuge opportunities for grassland butterflies

Heterogeneity at local and landscape scales can promote insect diversity and moderate insect declines that stem from global change. Determining how species respond to different landscape components provides insight into the role of heterogeneity in landscapes undergoing change. We examine how indigenous forest-grassland edges are used by butterflies. We assessed butterfly diversity and behaviour at forest edges and adjoining grassland, and tested whether these patterns are influenced by differing weather conditions between seasons. Forest edges supported a species rich butterfly assemblage. Forest specialists were more diverse at forest edges than in grassland, whereas grassland specialists and habitat generalists were as diverse at forest edges as in grassland. All butterfly groups showed more inter- and intra-specific interactions and more patrolling behaviour at forest edges, but more feeding and transient behaviour in grassland. Occurrence and behavioural patterns were not mediated by season, suggesting that the influence of forests does not change with varying environmental conditions. Nonetheless, certain species preferentially utilized forest edges in the hot and windy season, indicating that shelter provided by forest edges influences butterfly habitat use. We found no evidence that complementary nectar sources influence butterfly distribution patterns.Implications for insect conservation: The diverse butterfly assemblages and range of behaviours supported by indigenous forest edges indicate that forest patches are an important habitat component for butterflies. Conserving forest patches in these coastal grasslands may help buffer butterfly populations against global change.

Human Effects on Habitat Use of Japanese Macaques (Macaca fuscata): Importance of Forest Edges

Habitats of the Japanese macaque (Macaca fuscata) have been modified by human activities such as deforestation, conifer plantation, agriculturalization, and forest fragmentation. Such modifications likely affect habitat use of the macaques. We examined the habitat use of two macaque troops: a “forest troop” and a “cropland troop”. We focused on forest edges, which have not been previously categorized as a habitat type. Both troops frequently used deciduous broad-leaved forest in autumn and forest edges in summer. The forest troop frequently used forest-grassland edges, whereas the cropland troop frequently used forest-cropland edges. The selection index for the deciduous broad-leaved forest of the cropland troop exhibited significantly higher values than those of the forest troop in summer, autumn, and winter. Since the Japanese macaque is a forest-dweller and tends to avoid open areas, both troops may have used forests more frequently. Meanwhile, a decline in food resources in the forest due to the establishment of conifer plantations and an increase in food resources due to agriculturalization may have led to more frequent use of forest edges by the macaques. Forest edges should be treated as an independent habitat for accurate assessment of macaque habitat use.

Modification of plant communities by bison in Riding Mountain National Park

ABSTRACT Plains bison (Bison bison bison) are suspected to have played an important role in maintaining and structuring the plant communities throughout the Aspen Parkland. We examine the effects of a fenced bison herd on grassland plant communities in Riding Mountain National Park, Manitoba, Canada. We focus on the relationship between bison and woody plant encroachment along the forest-grassland ecotone, and on the effects that short- and long-term occupation by bison have on Festuca hallii grassland communities including the effects of bison reintroduction to a grassland area ungrazed by bison for 165 years. We found limited impacts of bison on the shrub community at the forest grassland edge. Bison rarely entered areas with dense, tall shrub understories, and thus bison cannot be a major factor controlling the ecotone. Shrub stem mortality due to fire may be a necessary precursor to bison effectively mitigating woody encroachment in the Aspen Parkland. We found limited short-term impacts of bison on grassland communities, with reduced sward heights but no change in composition. The long-term (>80 year) presence of bison was associated with greater species richness, reduced litter accumulation, and a distinct plant community composition compared to areas without bison impacts.

Spatial patterns of tree recruitment in a montane Hawaiian wet forest after cattle removal and pig population control

AbstractQuestionWe measured tree recruitment over approx. 17 to 18 years after cattle removal and pig population control in a Metrosideros polymorpha (Myrtaceae) montane wet forest. We analysed how tree recruitment varies in space and between species.LocationHakalau Forest National Wildlife Refuge, Island of Hawai'i.MethodsAll woody plants with diameter at breast height ≥5 cm were surveyed twice at approx. 17‐ to 18‐year intervals in 200 circular plots (15‐m radius) located in two sites. We used generalized linear mixed models to analyse how the number of recruits of wind‐ and bird‐dispersed species per plot varied between plots as a function of the number and sizes of remaining trees, grass cover, distance to the forest–grassland edge, and the identity of sites. Within plots, for each species we analysed the density distribution of recruits as a function of a neighbourhood crowding index and grass cover. Observed distributions were compared to null distributions.ResultsAbout 4,000 recruits representing seven species were inventoried. Wind‐dispersed species tended to recruit randomly, including in open, grassy areas. The number of bird‐dispersed recruits was negatively associated with grass cover and positively associated with basal area of remaining trees. Bird‐dispersed species recruited more in areas with an intermediate neighbourhood crowding index. The number of recruits was strongly correlated with the number of remaining trees for each species. One species, Cheirodendron trigynum (Araliaceae), recruited twice as much as expected given the number of remnant trees.ConclusionsThe high levels of recruitment of all species were likely due to cattle removal as well as pig population control. Competition with grasses constitutes the main limiting factor for tree recruitment following removal of ungulates. Remnant Metrosideros polymorpha likely create favourable conditions for the recruitment of bird‐dispersed species. Higher seed production and growth rates likely allowed Cheirodendron trigynum to recruit much more than the other species.

Differential seedling regeneration patterns across forest–grassland ecotones in two tropical treeline species (Polylepis spp.)

AbstractSuccessful forest expansion into grassland can be limited by seed dispersal and adverse conditions for tree seedlings in the grassland environment. In the high‐elevation Andes, human‐induced fragmentation has exacerbated the patchy distribution of Polylepis forests, threatening their unique biological communities and spurring restoration interest. Studies of Polylepis forest extent in Peru suggest that forest borders have remained stable over the past century despite decreasing anthropogenic disturbance, suggesting that tree seedling recruitment is being limited in the open grassland habitat. We studied natural seedling dispersion patterns of Polylepis sericea and Polylepis weberbaueri (Rosaceae) at forest–grassland edges across a range of environmental conditions to examine seedling recruitment and colonization of grasslands in Huascaran National Park (Peru). Using data from 2367 seedlings found in 48 forest–grassland edge plots (15 m × 15 m) at forest patches between 3900–4500 masl, we employed generalized mixed modelling to identify the significant associations of seedling densities with environmental covariates. In addition, we compared these associations to patterns of adult presence on the landscape. Seedling densities were associated with a combination of variables varying within (distance to forest edge) and among (elevation and dry season solar irradiation) plots across the landscape. For both species, seedling densities decreased with increasing distance away from the forest in a manner consistent with short‐distance seed dispersal by wind. Our results suggest that such short‐distance dispersal may slow forest expansion, but that there also appear to be substantial post‐dispersal limitations to seedling establishment in the grassland. Polylepis sericea densities decreased with elevation, while P. weberbaueri increased with elevation and decreased with solar irradiation. Associations of adult presence with elevation and solar irradiation mirrored those of seedling densities. Management of areas with forest patches dominated by these species should consider these differences in their environmental tolerances, particularly during species selection and zonation for reforestation.

Austroeupatorium inulifolium invasion alters soil seed bank in anthropogenic grassland: a case study from Sri Lanka

Austroeupatorium inulifolium is aggressively invading many land use types in the Knuckles Conservation Area (KCA) in Sri Lanka. The Cymbopogon nardus dominated grasslands, often demarcated by native forests, are the most vulnerable. The present study quantified the soil seed bank and the standing vegetation of these highly invaded grasslands. Forest-grassland edge (FGE) has been identified as the starting point for this invasion, and therefore sampling was carried out twice at different distances from the FGE towards the grassland (0, 10 and 30 m). The soil seed bank showed high seasonality with higher abundance and richness in the wet season than in the dry season. Interestingly, the dry season soil seed bank was dominated by native species (78%) while the wet season seed bank was dominated marginally by exotics (52%), with the highest contribution from Austroeupatorium . The scarcity of tree seedlings was noticed during the study. Austroeupatorium and tree seeds showed decreasing trends from the FGE towards the invasive grassland, and were evident in the seed bank as well as in the standing vegetation. Despite similar trends, the soil seed bank and the standing vegetation of invasive grasslands showed low similarity in terms of richness and abundance due to the dominance of a single species. The results suggest that Austroeupatorium invasion has the potential to alter the existing vegetation in these highly degraded grasslands and influences their succession over time.

Spatial patterns and edge effects on soil organic matter and nutrients in a forest fragment of southern Brazil

The discrimination between edge effects and spatial patterns of the availability of soil nutrients exerts a great influence on measures of forest productivity and the global carbon pool. We sampled a regular grid with infill points of topsoil in a 13-ha Atlantic forest fragment and surrounding grassland in southern Brazil, and tested the influence of the underlying spatial nutrient availability and edge effects on this pattern using Generalised Additive Models. Soil phosphorus was controlled by vegetation type. Magnesium and potassium were controlled by parent material and pedogenesis, whereas calcium and soil organic matter were influenced by both processes. The depth of edge influence was estimated at 50m inside the forest and at 25m distance from the forest edge in the grassland. These continuous estimates of forest–grassland edge effects in soil nutrient availability may play a major role in determining global ecosystem functioning, as forests and landscapes become even more fragmented.

Asymmetrical responses of forest and “beyond edge” arthropod communities across a forest–grassland ecotone

Historically, where forest habitats are deemed as the pristine landscape state, anthropogenic habitats such as managed grasslands or open spaces are often perceived to be antagonistic and of secondary conservation priority. Traditionally, studies on biodiversity responses to ecological variation, i.e. edge effect, have mostly focused on forest habitats. Yet recently there has been increased attention on communities beyond the forest edge in an effort to better understand how interactions between forests and adjacent habitats may potentially affect regional biodiversity. However, in Europe and the Mediterranean basin (a biodiversity hotspot), areas with high landscape heterogeneity and high edge density, there is a paucity of studies analysing the community responses across forest and “beyond edge” habitats across ecotones. In a protected area of central Italy, we investigated the responses of ground-dwelling arthropods [Araneae (spiders), Chilopoda (centipedes) and Carabidae (ground beetles)], which were differentiated into habitat-specific guilds (forest, edge and grassland species) across a forest–grassland ecotone. We investigated the extent to which a habitat edge influenced communities of arthropods associated with either the forest or grassland, and how far from the edge this effect penetrated into each habitat. Twelve 150 m-transects perpendicular to a forest–grassland edge were established and arthropods were sampled at nine progressive distances across the ecotone. An indicator species analysis was used to detect species significantly associated with forest, edge-belt or grassland habitats, which were assumed representative of the respective communities. Logistic models of indicator species richness and abundances were used to describe responses of grassland and forest communities across the ecological boundaries. We found that grassland and edge habitats had habitat specialists and higher species richness compared to the forest habitat. Moreover, the occurrence of grassland-specific species was influenced by the presence of an edge up to 15 m from the habitat border. In contrast forest-associated indicator species were not affected by proximity to the habitat edge, rather individuals typical of forest habitats tended to “spill over” into grassland habitats. These findings support the hypothesis that in a forest–grassland mosaic, forest species are less sensitive to an edge and influence the community beyond the forest edge and into the grassland more than the reverse, i.e. the effect was asymmetric. From these data, we estimated that a minimum grassland habitat width of 600 m is necessary for grassland species to maintain a core area that is relatively unaffected by the spillover of species from adjacent forest habitats. Incorporating the directional influences of adjacent communities on each other allows for an empirical assessment of habitat vulnerability that doesn’t a priori value the conservation of one habitat over another.

Changes in plant diversity and composition across forest edges bordered by Austroeupatorium inulifolium invaded grasslands in the Knuckles Conservation Area, Sri Lanka

Austroeupatorium inulifolium has become a ferocious invader over the years in many ecosystems in the wet zone of Sri Lanka, including the grasslands of the Knuckles Conservation Area (KCA). Two field studies were conducted to assess the impacts of Austroeupatorium invasion on the diversity and composition of the plant communities. In the first study, three habitat categories were identified: less-invaded grassland (LIG), highly-invaded grassland (HIG) and the forest-grassland edge (FGE) adjacent to HIG. In the second study, two transects were selected that run across the FGE bordered by less or highly invaded grasslands (FGE-LIG and FGE-HIG). At each community, 5 linear quadrats (12 m x 3 m) were laid parallel to the FGE at different distances away from the edge to the forest interior and the open grassland. Each quadrate was further sub-divided into 3 quadrats. Three such transects were studied for each community. In both studies, the vegetation less than 2 m in height was enumerated. The stem density and abundance of Austroeupatorium were significantly higher in HIG and FGE compared to LIG. However, the plant community at FGE was less diverse than that of HIG and LIG. Tree saplings were observed only in the HIG, suggesting its favourable conditions for their establishment. The abundance of Austroeupatorium was markedly reduced towards the forest interior, suggesting that the FGE acts as a barrier against invasion towards the forest. The tree sapling abundance decreased from the forest interior towards the open grassland but the abundance was higher in transects bordered by HIG than by LIG. This suggests a facilitative effect on the forest tree regeneration potential under the Austroeupatorium canopy. The invasion may have led to improved micro-climatic and edaphic conditions and may also have facilitated the tree seedling establishment and survival in the forest interior as far as 10 m away from the FGE. Current findings depict positive impacts of Austroeupatorium-invaded grasslands on the forest regeneration process. Therefore, it is time to explore the positive effects of exotic species, especially when they colonize highly degraded landscapes, rather than generalizing that all invasive species cause detrimental impacts on every landscape.DOI: http://dx.doi.org/10.4038/cjsbs.v42i2.6607 Ceylon Journal of Science (Bio. Sci.) 42(2): 29-43, 2013

Can Austroeupatorium inulifolium Invasion Favour Tree Species Establishment on Highly-Degraded Man-made Grasslands

It is well known that invasive species alter vegetation structure and composition, but most ofthe evidence to support this claim come from natural ecosystems. In many instances, thesestudies reported negative consequences on these natural habitats. Within last few years, thehighly degraded grasslands at the Knuckles Conservation Area (KCA) have rapidly invadedby Austroeupatorium inulifolium, a notorious invasive species. The present study was aimedat investigating the impacts of Austroeupatorium on grassland communities, and also to seeany positive role in forest expansion process towards these invasive grasslands by borderingforest remnants.A complete vegetation sampling was carried out in 3 grassland communities having differentlevels of invasion; grasslands densely-invaded with Austroeupatorium (HIG), and lessdenselyinvaded (LIG) and the forest-grassland edge (FGE). For each grassland community,nine randomly placed 4 m2 quadrates were used to enumerate the vegetation. Anothersampling was carried out using two forest-grassland edge (FGE) communities; forest remnantbordered by LIG (FGE- LIG) and forest remnant bordered by HIG (FGE- HIG). At each site,5 linear quadrates (3 m x 12 m) were placed parallel to the FGE at different distances; 0(edge), 5 and 10 m away from the edge towards the grassland and towards the forest interior.Six such transects were sampled for each FGE category.A total of 30 species have been identified belonging to 20 families in HIG while 21 species(belonged to 14 families) and 14 species (belonged to 9 families) were identified from LIGand FGE respectively. Tree saplings (4 species) were recorded only in HIG. The two edgehabitats showed somewhat different vegetation composition. Of the 182 and 430 individualsof tree saplings encountered at FGE-LIG and FGE-HIG respectively, majority of them werefound in quadrates laid inside the forest (76 and 88% respectively). Abundance and richnessof tree saplings were significantly higher at 10 m towards the forest interior bordered by HIGthan that of LIG.Present results suggested that Austroeupatorium invasion has a facilitative effect on treeseedling establishment probably through enhanced shading effect and improved edaphicconditions. The results also suggest that Austroeupatorium invasion has the potential tochange the community structure in forest-grassland edges which eventually influence thevegetation community in the forest interior, at least up to 10 m. The facilitative effect ofAustroeupatorium invasion on the forest tree establishment needs further studies to verify itslong-term effect on these grasslands.

Temporal variation in nest predation risk along habitat edges between grassland and secondary forest in Central Europe

Habitat fragmentation alters many ecological processes, including trophic cascades. For example, increased predation pressure along habitat edges has often been observed in fragmented landscapes. Here, we studied how nest predation risk varies along the transition zone between grassland and mixed forest in Central Europe. Using artificial nests, we tested the two mechanisms that are expected to underlie higher predation rates along edges: (1) the matrix effect model that supposes predator penetration from a habitat type with higher predator density to one with lower predator density and (2) the ecotonal effect model that assumes specific predator preferences for habitat edges. Although our results do not fully support either of these scenarios, our data show high temporal instability in nest predation along forest–grassland edges. Predation was higher in habitat interiors compared to edges during the first year, whereas the opposite pattern was observed during the subsequent year. In addition, dramatic between-year differences in the species composition of nest predators were observed. Therefore, we hypothesise that the effect of edges on nest predation is difficult to predict in landscapes with high predator diversity. In addition, our data indicate that a high abundance of wild boar considerably increases the risk of predation for ground-nesting birds.

Testing mechanistic explanations for mammalian predator responses to habitat edges

Increased predator activity along habitat edges (the edge effect) is often documented in the temperate zone, but earlier studies have rarely been able to explicitly test the suggested mechanisms underlining this phenomenon. In this study, we measured the distribution of mammalian predators by scent stations and their main prey (rodents) in four types of landscape elements corresponding to an edge gradient between two habitat types; grassland and forest. We found a contrasting pattern in carnivore activities between years. Whereas carnivores did not exhibit a significant occurrence along the forest–grassland edge in the first year with low prey abundance, they were more likely to be detected along habitat edges in the subsequent year with high prey abundance. Our results do not suggest that the increased activity of carnivores at habitat edges arises as a consequence of predator overflow from higher quality habitat through the edge into lower quality habitat, but showed that most predator species focus their activity specifically to the edge structure. On the other hand, our data do not provide straightforward support for the hypothesis that predator edge preferences are caused by a spatial gradient in carnivores’ main prey—rodents.

Grasslands as movement barriers for a forest-associated salamander: Migration behavior of adult and juvenile salamanders at a distinct habitat edge

The persistence of amphibian populations in fragmented landscapes requires dispersal and recolonization of habitat patches after local extinction. These processes entail individuals crossing habitat edges. Edge permeability integrates the behavior of individuals with the vegetative structure of the habitat edge and may influence the dispersal rates between habitat patches. We used drift fences, radio telemetry, and an experimental displacement to examine the movement behavior of juvenile and adult spotted salamanders ( Ambystoma maculatum) at a pond located in continuous forest and a pond located on a distinct forest–grassland edge. At the pond on the habitat edge, adult salamanders migrated to and from the forested side of the pond. Resident adults with transmitters migrated to forested habitat without approaching the habitat edge. Displaced adults with transmitters halted emigration movements when they approached the habitat edge. None of the radio-tagged adults were observed more than a few meters into the grassland. Recently metamorphosed juveniles exiting the grassland side of the pond changed their direction of movement and migrated into the forested habitat. We conclude that salamanders oriented movements with respect to features in the terrestrial habitat, detected the habitat edge, and behaviorally avoided the grassland. Exploring the permeability of habitat edges will improve our understanding of dispersal within fragmented landscapes and enhance efforts to conserve regional populations of amphibians.

Shading out species richness: edge effect of a pine plantation on the Orthoptera (Tettigoniidae and Acrididae) assemblage of an adjacent dry grassland

Edge effects are increasingly recognised as a threat to interior species, but the influence of edges on open habitats has rarely been addressed so far. We investigated the diversity pattern of the Orthoptera fauna across a habitat edge between a pine plantation and a natural steppe ecosystem. Thirty pitfall traps were positioned along a transect line from 80 m in the forest to 208 m in the grassland at 10 fixed distances from the edge. The orthopteran assemblage of the pine plantation was depauperate in species and individuals and, with a few exceptions, lacked steppe species. We found no increase in species richness at the forest–grassland edge. In the grassland, Orthoptera species numbers increased steadily with increasing distance from the forest edge. Two-phase regression analysis revealed a traceable edge effect up to about 30 m into the grassland. This effect was exclusively caused by an increase in acridid species numbers, while tettigoniid species numbers showed no clear relation to edge distance. Correlation analysis of the habitat variables suggested that this pattern is a result of irradiance and soil temperature sums. Since acridids show species-specific temperature requirements for their development, shading of the soil surface prevents a number of species from completing their life cycle. We suggest that present trends of shrub encroachment and eutrophication of dry grassland habitats in eastern Austria are serious threats for a large part of the orthopteran fauna.