Grassland Matrix Research Articles

Does pine occurrence influence the macrophyte assemblage in Southern Brazil ponds?

The destruction of wetlands due to afforestation areas is a common activity in temperate and subtropical regions in Southern America. The expansion of pine (Pinus elliottii Engelm.) in the Coastal Plain of Southern Brazil is critical and its impacts on aquatic biodiversity are little known. We tested the hypotheses that: (1) pine occurrence diminishes the macrophyte richness and changes the macrophyte composition in ponds; (2) beta-diversity between natural and pine ponds is determined mainly by species nestedness (species loss). Sampling was carried out from 2007 to 2009 in five ponds in pine invasion matrix and five ponds in native grassland matrix. In natural ponds, the total richness was 87 species, followed by 51 species in pine ponds. From the total richness, 42 species were shared between natural and pine ponds. The natural ponds were richer than the pine ponds along the entire study, and the composition of macrophyte species was different between natural and pine ponds. Comparing natural ponds with each other and pine ponds with each other, the species turnover (species replacement) was determinant for beta-diversity, however, when we compared natural and pine ponds, we found that nestedness and species turnover were equivalent for beta-diversity. The increase in the nestedness mechanism indicates that the pine occurrence implies in species loss in Southern Brazil ponds. The change of hydroperiod may be one of the causes for the macrophyte species loss. The removal of pine from areas destined to conservation in Southern Brazil is urgent as well as a proper management of pine plantations in order to minimise its expansions and impacts in the aquatic biodiversity, since 90% of its wetlands have been already lost.

Cedar Infestation Impacts Avian Communities along the Niobrara River Valley, Nebraska

Habitat modification has the potential to cause changes in structure and composition of bird communities. Our goal was to determine the response of Songbird community composition to eastern red cedar (Juniperus virginiana) removal in The Nature Conservancy's Niobrara Valley Preserve, Nebraska. We used point counts to survey birds in the riparian matrix of grassland and forest habitats. More than 60 species were recorded on surveys during 2004–2005. We also use the program PRESENCE to determine the response of five species to various habitat components, including cedar density: House Wren (Troglodytes aedon), Spotted Towhee (Pipilo maculates), Ovenbird (Seiurus aurocapillus), Red‐eyed Vireo (Vireo olivaceus), and Indigo Bunting (Passerina cyanea). Species richness estimates were highest in open and mixed habitat patches. Local populations of Ovenbirds and Red‐eyed Vireos responded positively to cedar density, whereas House Wren numbers declined as cedar density increased. Cedar abundance explained the most variation in bird community similarity between survey points; species richness increased as cedar density decreased. Habitat structure and composition drove variation in community composition and population abundance at fine, local scales within the Preserve. Fine‐scale management to remove cedar from local areas should increase diversity of avian species by maintaining a matrix of habitat types. Cedar removal at any scale will affect the composition of bird communities, and we encourage a structured approach to management decisions.

Chuva de sementes de espécies lenhosas florestais em mosaicos de floresta com Araucária e campos no Sul do Brasil

Mecanismos de dispersão de diásporos e recrutamento de plântulas evitam a competição intra-específica e possibilitam a colonização de novos ambientes. Em áreas de transição entre florestas e vegetação campestre esses processos não são aleatórios, e sim associados muitas vezes a indivíduos lenhosos isolados em tais áreas de campo ou a formações arbustivas. No sul do Brasil, as Florestas com Araucária formam mosaicos com áreas campestres e observa-se o avanço da floresta sobre os campos. O estudo teve como objetivo avaliar a chuva de sementes de espécies lenhosas florestais associadas a áreas de ecótonos de Floresta com Araucária e campos e a indivíduos lenhosos isolados na matriz campestre. Os estudos foram realizados no Centro de Pesquisas e Conservação da Natureza Pró-Mata PUCRS, em São Francisco de Paula, RS, em vegetação campestre excluída de fogo e de pastejo há 16 anos, circundada por florestas. A chuva de sementes foi avaliada mensalmente por um período de oito meses com o uso de coletores que foram posicionados em ecótonos de floresta e campos com diferentes fisionomias e sob indivíduos lenhosos isolados na matriz campestre. Tais ambientes foram comparados através de análise de variância univariada e multivariada para verificar padrões de chuva de sementes. Os resultados indicaram que a dispersão de sementes em áreas campestres ocorre preferencialmente associada a indivíduos isolados de Araucaria angustifolia e a formações arbustivas de Baccharis uncinella e que tais ambientes funcionariam como extensões de condições mais semelhantes à floresta na matriz campestre.

Rock Outcrops Harbor Native Perennials in Type-Converted Coastal Scrub

Type-conversion of coastal scrub to exotic annual grassland has been extensive in certain parts of southern California, especially in drier inland locales. Field observations suggest that rock outcrops harbor native perennials associated with coastal scrub vegetation after conversion to exotic annual grassland has occurred. Surveys were conducted to test this observation. In addition, measures of fossorial mammal disturbance, soil depth, exotic annual plant abundance, and soil moisture were collected and used to infer potential mechanisms that may influence patterns of native and exotic vegetation. Results showed that larger outcrops are associated with more native perennial species than smaller outcrops, consistent with predictions based on species-area relationships. In addition, the edges of rock outcrops were shown to have greater native perennial species richness than the surrounding exotic annual grassland matrix. Higher soil moisture, lower soil depth, and less disturbance by Botta's pocket gopher (Thomomys bottae) were also found at the edge of rock outcrops compared to the surrounding grassland matrix. Furthermore, soil depth was positively correlated with pocket gopher disturbance and with exotic annual grass cover. Rock outcrops serve as refuge habitat for native coastal scrub perennials in areas where exotic annual grasses have become dominant. Rock outcrops may become increasingly important for conservation efforts if remaining coastal scrub vegetation continues to deteriorate.

The importance of nitrogen-fixation for an invader of a coastal California grassland

Whether a novel trait of an invader directly contributes to increased establishment of that invader is a relatively unstudied question in plant ecology. Nitrogen (N)-fixing shrubs comprise a significant subset of grassland invaders worldwide, which suggests the potential importance of the novel trait of N-fixation in the invasion process. We indirectly tested the importance of N-fixation in the invasion of Genista monspessulana (French broom) in a California grassland by alleviating N and phosphorus (P) limitation to the grassland matrix. Grassland productivity was co-limited by N and P; N alone did not release the resident vegetation, and did not affect Genista performance. Genista was strongly limited by P: seedlings had more nodules, greater leaf N concentration, and higher growth and survival with P additions. When N was added with P, however, growth of the resident vegetation was 50–70% greater than with N or P alone, accompanied by decreases in Genista performance. This suggests that the advantage conferred to Genista by N-fixation was dampened when the resident vegetation was released from nutrient limitation.

Polylepis woodland remnants as biodiversity islands in the Bolivian high Andes

Mountain forests deserve special attention from ecologists and conservation biologists given the ecosystem services they provide to society, and their threat under global change. In the subalpine region of the Andes, Polylepis woodlands occur as arboreal islands in a matrix of grassland and scrub. Due to overgrazing and burning, however, these woodland patches are believed to cover only 11% of their potential area in Bolivia, core area for Polylepis. We reviewed the knowledge on the species diversity for the Bolivian Polylepis woodland remnants, assessed the conservation status of the occurring species, determined their trophic niche, and related species richness with climatic variables and elevation. Based in 31 publications, we found 780 identified species occurring in Polylepis woodlands: 425 plants, 266 birds, 46 mammals, 35 butterflies and 8 reptiles. Ten of the 13 Bolivian Polylepis species, as well as 7 other plant species, 14 bird species and 4 mammal species were categorized as threatened or near threatened according to IUCN criteria. In general, plant species richness increased with increased precipitation and length of the growth season, while it decreased with increasing elevation. There was a positive relationship between bird species richness, precipitation and length of the growth season. The highest bird endemism in Polylepis woodland remnants occurred at intermediate elevations, temperatures and precipitation. Mammal species richness decreased with increasing maximum temperature. Finally, we discuss the most important knowledge gaps regarding biodiversity in Bolivian Polylepis woodland remnants.

Gap-crossing in fragmented habitats by mahogany gliders (Petaurus gracilis). Do they cross roads and powerline corridors?

The mahogany glider (Petaurus gracilis) is one of the most threatened arboreal mammals in Australia. Although its habitat is affected by fragmentation, gap-crossing behaviour of the species has not been studied. A radio-tracking survey was undertaken on six individuals (three males, three females) in a woodland patch bisected by a 35.8-m-wide highway and a 31.5-m-wide powerline corridor, in north-east Queensland. The mean home ranges of males were 20.1 ± 3.3 ha, 21.3 ± 7.9 ha and 20.9 ± 8.2 ha, as measured by the Minimum Convex Polygon, Kernel and Harmonic Mean methods respectively. The mean home ranges of females were 8.9 ± 0.5 ha, 9.0 ± 4.2 ha and 8.8 ± 2.3 ha, as measured by the Minimum Convex Polygon, Kernel and Harmonic Mean methods respectively. Two males and one female were observed crossing linear gaps. However, there was less crossing than expected, and females were less likely to cross than males. One male used a narrow strip of woodland at the opposite side of the highway as supplemental habitat for foraging. This individual also used scattered trees in a grassland matrix for foraging or denning. Another male used a wooden power pole as a launching site to cross the highway. This study emphasises the importance of protecting large trees along linear barriers in open habitat, and suggests that gliding poles may be used to facilitate gap-crossing by mahogany gliders.

Nested species subsets of amphibians and reptiles on Neotropical forest islands

AbstractNested species subsets are a common pattern of community assembly characteristic of many types of fragmented landscapes and insular systems. Here we describe nested subset patterns of amphibian and reptile occupancy on 23 forest islands in north‐eastern Bolivia. We used observed occupancy patterns to differentiate five distributional guilds: widespread species, rare species, poor colonizers, area‐sensitive species and supertramps. Amphibian occurrences were nested along a forest island isolation gradient, and when species from each of the distribution classes were removed from subsequent analyses of nestedness, we found that dispersal‐limited poor colonizers were responsible for the association between nestedness and isolation. Amphibians associated with the grassland matrix at the study site showed a nested pattern linked with area, although this pattern did not scale up to all amphibians and could not be unequivocally attributed to any of the distributional guilds we recognized. There were no strong associations between two biological characteristics, body size and relative abundance in the matrix, and the likelihood of occupancy along either forest island area or isolation gradients. The relative importance of isolation in shaping nested patterns of amphibians on these forest islands may be a result of either (1) the greater range in isolation values included in this study compared with many others; (2) the long time since isolation in this landscape, manifesting a footprint of isolation not apparent in more recently fragmented patches; (3) the relatively homogeneous grassland matrix surrounding forest islands that likely provides little refuge for animals moving among forest islands.

Mediterranean-climate oak savannas: the interplay between abiotic environment and species interactions

Abstract. Mediterranean oak savannas cover about 4 million ha in California (northwest America) and 3 million ha in Spain and Portugal (southwest Europe), and are ecologically and socio-economically important systems. Here we review literature on the interactions between the two dominant elements of savannas – the oak overstorey, the herbaceous understorey, and the surrounding grassland matrix. We focus on the main ecological factors affecting the oak understorey environment: shade, soil moisture, soil nutrients, and animal-mediated effects. We then review the main features of the herbaceous community in the oak understorey, as compared to the adjacent open grassland, in terms of species composition, biomass, diversity, and soil seed bank. We examine processes associated with oak regeneration and growth, and their relationships with the herbaceous layer and other woody plants cover. Finally, we discuss the complex facilitative and interference interactions that occur in oak-grassland systems and review models proposed to explain the dynamics and coexistence of oak trees and herbaceous plants in savannas.

Bird assemblages in fragmented agricultural landscapes: the role of small brigalow remnants and adjoining land uses

Agricultural intensification typically leads to changes in bird diversity and community composition, with fewer species and foraging guilds present in more intensively managed parts of the landscape. In this study, we compare bird communities in small (2–32 ha) brigalow (Acacia harpophylla) remnants with those in adjacent uncultivated grassland, previously cultivated grassland and current cropland, to determine the contribution of different land uses to bird diversity in the agricultural landscape. Twenty remnant brigalow patches and adjacent agricultural (‘matrix’) areas in southern inland Queensland, Australia were sampled for bird composition and habitat characteristics. The richness, abundance and diversity of birds were all significantly higher in brigalow remnants than in the adjacent matrix of cropping and grassland. Within the matrix, species richness and diversity were higher in uncultivated grasslands than in current cultivation or previously cultivated grasslands. Forty-four percent of bird species were recorded only in brigalow remnants and 78% of species were recorded in brigalow and at least one other land management category. Despite high levels of landscape fragmentation and modification, small patches of remnant brigalow vegetation provide important habitat for a unique and diverse assemblage of native birds. The less intensively managed components of the agricultural matrix also support diverse bird assemblages and thus, may be important for local and regional biodiversity conservation.

Vegetation structure and the habitat specificity of a declining North American reptile: A remnant of former landscapes

Although all species provide some spatial information about past environments, remnant populations of habitat specialists can serve as biological legacies and natural archives of historical landscapes. The endangered longleaf pine ecosystem is home to an array of imperiled fauna that specialize on the habitat. Often referred to as pine savanna, the ecosystem was characterized by longleaf pine ( Pinus palustris), but included an array of open-canopy habitats within a grassland matrix dominated by a variety of tree species. In this study, we used a coarse scale of description to quantify habitat associations of a declining reptile, the eastern diamondback rattlesnake ( Crotalus adamanteus), historically associated with pine savannas of the southeastern United States. We made cross-scale habitat comparisons and controlled for land use and geographic variability. Habitat models of within home range and microhabitat selection indicated that the species was associated with an open-canopy savanna community structure. We identified the eastern diamondback rattlesnake as a remnant of the historical southeastern savanna, which is important for species conservation and broader management of the southeastern savanna community. Given their longevity and habitat specificity, remnant eastern diamondback rattlesnake populations are biological legacies of the southeastern savanna community and act as a surrogate for the prioritization of land conservation. Thus, the species’ presence provides spatial information that can be used by conservationists to identify habitats that have high restoration potential, and also increases the probability that other species associated with pine savanna occur locally.

A comparison of trapping- and radiotelemetry-based estimates of home range of the neotropical opossum Philander frenatus

Home ranges of individuals of the gray four-eyed opossum Philander frenatus were studied by capture–mark–recapture (CMR) and radiotelemetry, within a set of eight Atlantic Forest fragments surrounded by a grassland matrix in the state of Rio de Janeiro, southeastern Brazil. Trapping sessions were carried out in all the forest fragments and in the grassland matrix. Adult individuals were fitted with radio-collar transmitters and monitored throughout the night. Locations were obtained by the “homing-in on the animal” method. Home-range sizes of the individuals with five or more captures or locations were estimated through the minimum convex polygon method. Home-range sizes estimated by radiotelemetry ranged from 0.6 to 7.4 ha ( n=8), and by CMR ranged from 0.1 to 12.1 ha ( n=17); home-range sizes estimated by radiotelemetry did not differ significantly from those based on CMR. However, comparing radiotelemetry with different CMR designs, the former estimates were larger than those based on either CMR using a single grid or CMR using two grids, but not larger than those based on multiple-grid CMR. In specific cases, animals monitored via radiotelemetry for only one or two nights showed larger home ranges than most individuals for which home ranges were estimated by CMR. Two individuals for which home-range sizes were estimated by both techniques showed larger home ranges when data from radiotelemetry were used. These data indicated that CMR can provide results comparable to radiotelemetry when multiple grids, spread across the landscape, are used, although this necessitates an intensive trapping effort. On the other hand, single- and double-grid CMR tend to underestimate home-ranges compared to radiotelemetry.

Non-native plantation forests as alternative habitat for native forest beetles in a heavily modified landscape

The once extensive native forests of New Zealand’s central North Island are heavily fragmented, and the scattered remnants are now surrounded by a matrix of exotic pastoral grasslands and Pinus radiata plantation forests. The importance of these exotic habitats for native biodiversity is poorly understood. This study examines the utilisation of exotic plantation forests by native beetles in a heavily modified landscape. The diversity of selected beetle taxa was compared at multiple distances across edge gradients between each of the six possible combinations of adjacent pastoral, plantation, clearfell and native forest land-use types. Estimated species richness (Michaelis–Menten) was greater in production habitats than native forest; however this was largely due to the absence of exotic species in native forest. Beetle relative abundance was highest in clearfell-harvested areas, mainly due to colonisation by open-habitat, disturbance-adapted species. More importantly, though, of all the non-native habitats sampled, beetle species composition in mature P. radiata was most similar to native forest. Understanding the influence of key environmental factors and stand level management is important for enhancing biodiversity values within the landscape. Native habitat proximity was the most significant environmental correlate of beetle community composition, highlighting the importance of retaining native remnants within plantation landscapes. The proportion of exotic beetles was consistently low in mature plantation stands, however it increased in pasture sites at increasing distances from native forest. These results suggest that exotic plantation forests may provide important alternative habitat for native forest beetles in landscapes with a low proportion of native forest cover.

RESOURCE SELECTION PLASTICITY AND COMMUNITY RESPONSES TO EXPERIMENTAL REDUCTION OF A CRITICAL RESOURCE

Resource selection plasticity and behavioral dominance may influence the ability of a species to respond to changes in resource availability, particularly if dominant species have highly specialized resource requirements. We examined the response of several dominant and subordinate cavity-nesting species to a reduction in the availability of an essential resource (nesting cavities) using the novel experimental approach of blocking the entrances to high-quality cavities. We monitored nest abundance on seven treatment and 13 control sites (aspen groves in a grassland matrix) in British Columbia, Canada, for two years pretreatment (2000-2001), two years during treatment (2002-2003), and two years posttreatment (cavities reopened; 2004-2005). At the community level, nest abundance declined by 50% on treatment sites following cavity blocking and returned to pretreatment levels following cavity reopening. Nest abundance of European Starlings (Sturnus vulgaris), a dominant secondary cavity-nester (SCN), declined by 89% and failed to recover posttreatment. Conversely, nest abundance of Mountain Bluebirds (Sialia currucoides; a subordinate SCN) increased following cavity blocking and remained high following reopening. Tree Swallows (Tachycineta bicolor) were unaffected by cavity blocking. We suggest that starlings, while being the dominant SCN, may be limited by availability of suitable nest sites, whereas bluebirds may be limited by starling abundance. We propose that plasticity in nest site preferences of subordinate cavity-nesters may enable them to contend with natural variation in availability of critical resources, such as nest cavities and food, in addition to coping with interspecific competition. This is the first community-level, multiyear study involving manipulation of nest site availability via experimental cavity blocking.

Spatio‐temporal variation in mortality rates of Mecodema spp. (Coleoptera: Carabidae) across a forest‐grassland edge in New Zealand

Abstract. Edge effects are a highly cited issue in conservation biology with a wealth of empirically described impacts on invertebrates, but the mechanisms underlying the responses of individual species to habitat edges have been seldom tested. One often‐raised hypothesis is that individual species vary in their ability to survive along a gradient of changing microclimatic conditions across habitat edges. I used a phylogenetically controlled, translocation experiment to investigate edge‐driven variation in adult mortality rate for two closely related species that have contrasting abundance patterns with respect to forest‐grassland edges; the habitat generalist Mecodema fulgidum Broun (Coleoptera: Carabidae) and the forest‐dwelling Mecodema rugiceps Sharp. Adult individuals of both species were live‐caught and translocated into containers at varying distances along an edge gradient extending from 1024 m inside a large forest fragment and 64 m into the surrounding grassland matrix. Experimental containers were connected to the above‐ and below‐ground environments via mesh‐covered panels, and beetle mortality over a 4‐month period in the 2006/2007 austral summer was recorded. Overall, mortality was higher for the habitat specialist M. rugiceps than for the generalist M. fulgidum. Neither species exhibited an edge‐related trend in mortality, nor were mortality rates correlated with microclimatic gradients across the edge. Weather records for the summer indicated that M. rugiceps was more sensitive than M. fulgidum to a soil moisture deficit that became more pronounced as summer progressed. Analysis of a 10‐year climate record shows that soil moisture deficits occur annually, suggesting that seasonal variation in soil moisture may contribute to the variation in the distribution and abundance of the two species.

Grazing promotes dung beetle diversity in the xeric landscape of a Mexican Biosphere Reserve

We analyze the impact of grazing on dung beetle diversity at the Barranca de Metztitlán Biosphere Reserve, a xeric ecosystem in central Mexico with a long history of use by humans. We compared the community structure, as well as the alpha and beta diversity between two cover conditions (open and closed vegetation) that represent the impact of grazing within a habitat, and between habitat types (submountainous and crassicaule scrublands). From 576 samples we collected 75,605 dung beetles belonging to 20 taxa. While mean species richness and diversity were different between habitat types, cumulative species richness was not. The effects of grazing on vegetation structure influenced the cumulative species richness and diversity of dung beetles in the submountainous scrubland, where grazing has created land mosaics of a grassland matrix with scrubland patches. This was not the case in the crassicaule scrubland where the impact of grazing is not as evident. Beta diversity significantly responds to the effects of grazing on habitat conditions. We discuss the ecological factors that may promote these responses by landscape diversity components. We also identify the species that could act as useful indicators to monitor the effect of land management on biodiversity. Our results indicate cattle farming maintains a diversified land mosaic, and these areas support more diverse dung beetle ensembles than homogeneous areas of closed, shrubby vegetation cover. Thus, controlled grazing activity could certainly favour the conservation of dung beetle biodiversity and improve ecosystem functioning by maintaining dung decomposition rates.

CLIMATIC/EDAPHIC CONTROLS ON SOIL CARBON/NITROGEN RESPONSE TO SHRUB ENCROACHMENT IN DESERT GRASSLAND

The proliferation of woody plants in grasslands over the past 100+ years can alter carbon, nitrogen, and water cycles and influence land surface-atmosphere interactions. Although the majority of organic carbon in these ecosystems resides belowground, there is no consensus on how this change in land cover has affected soil organic carbon (SOC) and total nitrogen (TN) pools. The degree to which duration of woody plant occupation, climate, and edaphic conditions have mediated SOC and TN responses to changes in life-form composition are poorly understood. We addressed these issues at a desert grassland site in Arizona, USA, where the leguminous shrub velvet mesquite (Prosopis velutina) has proliferated along an elevation/precipitation/temperature gradient and on contrasting soil morphologic surfaces. On sandy loam complexes of mid-Holocene origin, mean SOC and TN of soils in the grassland matrix increased approximately 68% and approximately 45%, respectively, with increasing elevation. Soil organic carbon pools were comparable and TN pools were approximately 23% higher in Pleistocene-aged clay loam complexes co-occurring with Holocene-aged soils at the upper elevation/climatic zone. Across the site, belowground resources associated with large Prosopis plants were 21-154% (SOC) and 18-127% (TN) higher than those in the grassy matrix. The variance in SOC and TN pools accounted for by Prosopis stem size (a rough surrogate for time of site occupation) was highest at the low- and mid-elevation sites (69-74%) and lowest at the upper elevation site (32-38%). Soil delta15N values ranged from 5.5 per thousand to 6.7 per thousand across the soil/elevation zones but were comparable in herbaceous and shrub-impacted soils and exhibited a weak relationship with Prosopis basal stem diameter (r2 < 0.1) and TN (r2 < 0.08). The SOC delta13C values decreased linearly with increasing Prosopis basal diameter, suggesting that size and isotopic composition of the SOC pool is a function of time of Prosopis site occupation. Isotopic mixture models indicate that encroachment of C3 woody plants has also promoted SOC additions from C4 plant sources, indicative of long-term herbaceous facilitation. Grassy sites in contrasting soil/elevation combinations, initially highly distinctive in their SOC pool size and delta13C, appear to be converging on similar values following approximately 100 years of woody plant proliferation.

MODEL ESTIMATION OF LAND-USE EFFECTS ON WATER LEVELS OF NORTHERN PRAIRIE WETLANDS

Wetlands of the Prairie Pothole Region exist in a matrix of grassland dominated by intensive pastoral and cultivation agriculture. Recent conservation management has emphasized the conversion of cultivated farmland and degraded pastures to intact grassland to improve upland nesting habitat. The consequences of changes in land-use cover that alter watershed processes have not been evaluated relative to their effect on the water budgets and vegetation dynamics of associated wetlands. We simulated the effect of upland agricultural practices on the water budget and vegetation of a semipermanent prairie wetland by modifying a previously published mathematical model (WETSIM). Watershed cover/land-use practices were categorized as unmanaged grassland (native grass, smooth brome), managed grassland (moderately heavily grazed, prescribed burned), cultivated crops (row crop, small grain), and alfalfa hayland. Model simulations showed that differing rates of evapotranspiration and runoff associated with different upland plant-cover categories in the surrounding catchment produced differences in wetland water budgets and linked ecological dynamics. Wetland water levels were highest and vegetation the most dynamic under the managed-grassland simulations, while water levels were the lowest and vegetation the least dynamic under the unmanaged-grassland simulations. The modeling results suggest that unmanaged grassland, often planted for waterfowl nesting, may produce the least favorable wetland conditions for birds, especially in drier regions of the Prairie Pothole Region. These results stand as hypotheses that urgently need to be verified with empirical data.

Effects of land-use intensification on soil carbon and ecosystem services in Brigalow (Acacia harpophylla) landscapes of southeast Queensland, Australia

Abstract Soil organic matter is an effective indicator of soil resource condition that reflects functional traits such as aggregation and infiltration and plays a critical role in sustaining production and ecosystem services in agricultural landscapes. Agricultural practices typically reduce soil carbon through the action of soil disturbance and mineralization. In the Brigalow (Acacia harpophylla) landscape we studied, soil carbon levels in pellic vertisols were significantly lower in the agricultural matrix of cropping and grasslands than in remnant Brigalow vegetation. There was no detectable gradient of soil carbon across Brigalow/matrix boundaries. Uncultivated grasslands showed significantly higher carbon levels than currently and previously cultivated grasslands. Regenerating grasslands showed no significant recovery of soil carbon over 15 years. Total, organic and labile soil carbon fractions were used to indicate different aspects of soil function, with the more active (labile) components reacting more sensitively to changes in land management. The carbon management index (CMI) was used to combine the active and passive components of soil carbon to provide a sensitive indicator of the rate of change of carbon dynamics in response to changes in land management at local-scales. A landscape CMI (CMIL) was developed using a combination of soil samples and GIS-derived spatial data and is proposed as a potentially useful tool for modelling soil carbon dynamics in agro-ecosystems at local and landscape scales.

Spring‐fed wetland and riparian plant communities respond differently to altered grazing intensity

Summary Spring‐fed wetlands are nested within California's oak savanna–annual grassland, which is considered a non‐equilibrium‐type system because it shows little community‐level response to changes in grazing intensity. This insensitivity to disturbance is thought to result from transient resource limitation and the annual life cycle tending to swamp the effects of defoliation. Because spring‐fed wetlands receive relatively consistent and high inputs of water and nutrients, and they are dominated by perennial herbaceous vegetation, we hypothesized that these systems would respond to a grazing intensity gradient in a predictable manner, i.e. equilibrium dynamics would prevail. We experimentally tested plant community responses of spring‐fed wetlands to two levels of grazing intensity (light and moderate) and no grazing over 10 years. Wetland vegetation was tracked at two distinct geomorphological parts of the wetland system: spring heads, where emergent water formed marshy zones, and their resultant channelized creeks. We used linear mixed effects models to estimate grazing intensity effects over time. A general result at both springs and creeks was that slope estimates of annual total herbaceous cover over time were negative under moderate grazing but positive under light grazing and grazing removal. Diversity metrics were not affected by grazing treatments at springs. At creeks, Simpson's diversity index increased over time under moderate grazing. When averaged over 10 years, species evenness and Shannon's diversity index were greater under moderate grazing at creeks. Species composition was highly variable from year to year at springs, with no separation of the first ordination axis (detrended correspondence analysis) amongst grazing treatments. In contrast, three relatively stable and distinct equilibria were evident for creeks. These results indicate that springs exhibited non‐equilibrium dynamics while their creek counterparts, separated by several metres, behaved in a more equilibrium fashion, in relative terms. Grazing removal significantly increased interannual variability in species composition at both geomorphological types, demonstrating that plant–animal interactions serve as the main control on community composition in these systems by reducing cover and promoting diversity and stability. Synthesis and applications. Grazing managers in California's oak savanna–annual grassland have little control of species composition because the annual community is entrained by the weather. Our results show that first‐order wetland–riparian communities nested within this annual grassland matrix can be manipulated via grazing intensity adjustments. However, marshy spring‐fed wetland areas are less sensitive than channelized creeks to these manipulations and grazing removal will increase variability in species composition for both geomorphological types. Grazing management decisions are usually made at the landscape level based on the matrix vegetation, but nested ecosystems may respond differentially, requiring a more nuanced approach that includes site‐specific information.