Seed dispersal by cattle may cause shrub encroachment of Grewia flava on southern Kalahari rangelands

Abstract. Shrub encroachment, i.e. the increase in woody plant cover, is a major concern for livestock farming in southern Kalahari savannas. We developed a grid‐based computer model simulating the population dynamics of Grewia flava, a common, fleshy‐fruited encroaching shrub. In the absence of large herbivores, seeds of Grewia are largely deposited in the sub‐canopy of Acacia erioloba. Cattle negate this dispersal limitation by browsing on the foliage of Grewia and dispersing seeds into the grassland matrix. In this study we first show that model predictions of Grewia cover dynamics are realistic by comparing model output with shrub cover estimates obtained from a time series of aerial photographs. Subsequently, we apply a realistic range of intensity of cattle‐induced seed dispersal combined with potential precipitation and fire scenarios. Based on the simulation results we suggest that cattle may facilitate shrub encroachment of Grewia. The results show that the severity of shrub encroachment is governed by the intensity of seed dispersal. For a high seed dispersal intensity without fire (equivalent to a high stocking rate) the model predicts 56% shrub cover and 85% cell cover after 100 yr. With fire both recruitment and shrub cover are reduced, which may, under moderate intensities, prevent shrub encroachment. Climate change scenarios with two‐fold higher frequencies of drought and wet years intensified shrub encroachment rates, although long‐term mean of precipitation remained constant. As a management recommendation we suggest that shrub encroachment on rangelands may be counteracted by frequent fires and controlling cattle movements to areas with a high proportion of fruiting Grewia shrubs.     

Living in a world of fire: the population dynamics of Mulinum spinosum in Northwestern Patagonia grasslands

Questions

How do fire frequency and fire size affect the long-term population dynamics of Mulinum spinosum? Which demographic parameters contribute most to the overall effect of fire on population growth? What is the relative importance of resprouting in sustaining population increase?

Location

Grass-shrub northwestern Patagonian steppe, Argentina.

Methods

We monitored five permanent plots excluded from grazing for 6 years. We measured shrub abundance, dimensions, reproductive status, seedling emergence, and the size structure of M. spinosum, a resprouting native shrub inhabiting the northwest Patagonian steppe. Data were used to parametrize a stochastic matrix model developed to explore the influence of fire frequency and fire size on long-term population dynamics. We analyzed hypothetical scenarios that included fire frequencies ranging from one per year up to exclusion.

Results

Except for annual fires, projections show growing populations regardless of fire frequency. For fire return intervals greater than 50 years, the population becomes independent of fires, with an annual population growth rate of 5.6%. The results suggest two relevant aspects of the population dynamics of this species: M. spinosum is well adapted to the current fire frequency and its resprouting capability will allow M. spinosum to survive and persist in the community, even under frequent fires.

Conclusions

Climate change models forecast an increase in summer temperature in NW Patagonia and, consequently, an enhanced fire frequency. Fire is a driver of M. spinosum encroachment that gets worse in overgrazed grasslands. Mulinum spinosum encroachment derivate in a relative replacement of palatable grasses by shrubs changes the ecosystem functionality and reduces productivity. Controlling this process is highly difficult and we suggest a change in the land use for the areas already deteriorated.

     

An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape

Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrub–grassland site in central Oregon (USA) using a modified version of Cellular Automata Tree–Grass–Shrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics represented by the model were first evaluated using satellite-derived leaf area index and measured evapotranspiration data. Reconstructed pre-encroachment vegetation cover percentages and the National Land Cover Database (NLCD 2006) vegetation map were used to estimate parameters for encroachment factors to represent juniper encroachment in CATGraSS. Model sensitivity experiments examined the influence of each encroachment factor and their combinations on trajectories of modeled percent cover of each plant functional type and emergent spatial vegetation patterns in the modeled domain. Simulation results identified grazing as the key factor leading to juniper encroachment, by reducing shrub and grass cover and promoting the formation of juniper tree clusters. Reduced fire frequency and increased seed dispersal by grazers further amplified juniper encroachment into grassland patches between clusters of juniper trees. Each encroachment factor showed different consequences on modeled vegetation patterns. Time series of modeled plant cover and spatial patterns of plant functional types were found to be consistent with an existing conceptual model described in the literature. The proposed model provides a tool that can be used to improve our understanding of the drivers and processes of woody plant encroachment and vegetation response to global change.     

Spatial relationships between the standing vegetation and the soil seed bank in a fire-prone encroached dehesa in Central Spain

Postfire vegetation regeneration in many fire-prone ecosystems is soil seed bank dependent. Although vegetation and seed bank may be spatially structured, the role of prefire vegetation patterns and fire in determining postfire vegetation patterns is poorly known. Here, we investigated the spatial patterning of species abundance and richness in the vegetation and seed bank of a Mediterranean encroached dehesa in Central Spain. The seed bank was studied with and without a heat shock simulating a spatially homogeneous fire. Semivariograms and cross-semivariograms showed that species richness in the vegetation was aggregated in patches, mainly of herbs, with highest values corresponding to high herb cover and low tree cover. Species richness in the seed bank was also structured in patches, but the spatial pattern was weak. Seedling density of germinates in the seed bank also showed weak spatial pattern. Heating increased overall germination and species richness, and the intensity of the spatial pattern of species richness, particularly of herbaceous species. However, seed bank density patterns disappeared after heat shock because of increased germination of shrubs without spatial pattern. Our results document that the spatial structure of plant richness in the vegetation may persist after fire due to the spatial patterns of herbaceous species in the seed bank, and that postfire species richness patterns can arise independently of fire intensity patterns. However, the spatial structure of the vegetation after fire can be altered by the feedback between shrub encroachment and an eventual fire because of the ubiquitous germination of shrubs.     

Is prescribed fire a suitable management tool to reduce shrub encroachment in palm savannas?

Shrub encroachment in grasslands is a worldwide problem that has many ecological consequences, transforming previously open environments into dense forests. Disruption of natural fire regimes is one of the main causes of shrub encroachment, and the use of prescribed fire is a common strategy used to restore these ecosystems. In this study, we provide information about how a palm tree savanna under a process of shrub encroachment responds to the reintroduction of fire. We describe the effects of a first fire event on vegetation composition and structure using an experimental approach. We examine a species‐specific response to the fire. After one prescribed fire event applied to four study areas of 16 ha each, we analyzed the change in vegetation physiognomy and composition in burned and control plots for 1 year. Low‐intensity prescribed fire decreased height and cover of most shrub species and increased herbaceous vegetation cover over time. We classified shrub and herbaceous species response to fire according to the time they became present and their phenological characteristics. Our results can help stakeholders to determine if prescribed fire is helpful at reducing shrub encroachment in short term in similar ecosystems, considering how plant community responds to the reintroduction of fire after decades of fire suppression.     

Using consecutive prescribed fires to reduce shrub encroachment in grassland by increasing shrub mortality

Woody plant encroachment into open grasslands occurs worldwide and causes multiple ecological and management impacts. Prescribed fire could be used to conserve grassland habitat but often has limited efficacy because many woody plants resprout after fire and rapidly reestablish abundance. If fire‐induced mortality could be increased, prescribed fire would be a more effective management tool. In California's central coast, shrub encroachment, especially of Baccharis pilularis (coyote brush), is converting coastal prairie into shrub‐dominated communities, with a consequent loss of native herbaceous species and open grassland habitat. B. pilularis has not been successfully controlled with single prescribed fire events because the shrub resprouts and reestablishes cover within a few years. We investigated whether two consecutive annual burns would control B. pilularis by killing resprouting shrubs, without reducing native herbaceous species or encouraging invasive plants. As expected, resprouting did occur; however, 2 years after the second burn, B. pilularis cover on burned plots was only 41% of the cover on unburned plots. Mortality of B. pilularis more than doubled following the second burn, likely maintaining a reduction in B. pilularis cover for longer than a single burn would have. Three native coastal prairie perennial grasses did not appear to be adversely affected by the two burns, nor did the burns result in increased cover of invasive species. Managers wanting to restore coastal prairie following B. pilularis encroachment should consider two consecutive annual burns, especially if moderate fire intensity is achievable.     

Modelling oldfield species richness in a mountain area

Seed predation by rodents affects plant population dynamics and it mayrespond to changes in vegetation structure at forest edges. This studyinvestigates the magnitude and direction of a potential edge effect intemperatedeciduous forests, and it seeks possible explanations based on predatorabundance and vegetation structure. The study was conducted at twelve forestedges in northern Switzerland; in six sites all shrubs at the forest edge wereremoved, whereas the other sites maintained a structurally rich shrub layer. Ineach site three transects were laid out from the edge towards the forestinterior. In six plots along these transects (at 1, 3, 6, 12, 25, 50m) we studied seed removal from experimental dishes, rodentabundance in live-traps and four characteristics of the vegetation structure.For both woody seed species (Prunus avium,Viburnum lantana) predation was significantly higher nearthe forest edge in the structurally rich sites; in the other sites no suchgradient was found. Selectively accessible dishes revealed that rodents werethemain predators, whereas predation by insects or molluscs was not observed.Abundance of rodents (Apodemus flavicollis, A.sylvaticus, Clethrionomys glareolus) washighestunder dense shrubs close to the forest edge. In the structurally rich sitesthere was a clear gradient of decreasing shrub cover from the edge towards theforest interior; a weaker gradient was observed in the structurally poor sites.We conclude that high shrub cover near the forest edge is the main determinantfor edge effects in seed predation, and edges without a shrub belt show no sucheffect.     

Post-fire natural regeneration of a <Emphasis Type="Italic">Pinus pinaster</Emphasis> forest in NW Spain

The aim of this study was to analyse the regeneration of Pinus pinaster after wildfire and the possible inter and intraspecific competition during the first 3 years after fire. The study area is located in a P. pinaster stand in León province (NW Spain). Three study sites (S1, S2 and S3) were established in an area burned in 1998. In each site, three permanent plots (20 × 1 m) were marked. A total of 20 quadrats of 1 m ² were studied in each plot. The number and height of pine seedlings 1, 2 and 3 years after fire was recorded in each quadrat. The regeneration of understorey vegetation in the quadrats was analysed concurrently. The significance of linear correlations among the number and height of seedlings and understorey vegetation cover was tested by calculating Pearson correlation coefficients.Seed germination and seedling emergence took place massively during the first year after the fire and decreased through time. The height growth was constant over the 3 years at site S2, while a growth burst could be observed between years 2 and 3 at sites S1 and S2. Also, pines from site S2 reached shorter maximum heights in all years compared to pines from site S1 and S3. The understorey vegetation showed minimal regeneration during the first year but then increased greatly with time. Woody understorey cover and total vegetation cover were negatively correlated with pine seedling density in sites with a high number of seedlings (e.g. S1 and S3). When woody cover, total cover and pine seedling density were low (e.g. S2), there were no correlations. There was a positive correlation between vegetation cover and the maximum height of Pinus seedlings in all study sites.     

Analysing Betula litwinowii encroachment and reforestation in the Kazbegi region,Greater Caucasus,Georgia

Aims

The encroachment of tree and shrub species in high mountains is an increasing worldwide phenomenon, which is expected to dramatically alter high‐mountain ecosystems and their functioning. Moreover it indicates in some cases a reforestation process, which will result in important ecological and social benefits, including carbon sequestration and protection against landslides. We therefore examined the spatial extent of forest growth and shrub encroachment mainly of birch (Betula litwinowii) in the sub‐alpine belt of the Central Greater Caucasus between 1987 and 2010 and its relation to topographic site conditions.

Location

Kazbegi district, Central Greater Caucasus, Georgia.

Methods

We analysed 155 vegetation relevés sampled in 2009, 2011 and 2015, mainly derived from the Caucasus Vegetation Database, to obtain information about topographic site conditions and structure of B. litwinowii stands. B. litwinowii forest growth was assessed by digitizing the forest outlines from aerial and space‐borne imagery (1987, 2005 and 2010). To identify areas of B. litwinowii encroachment as an indicator for different encroachment stages, we modelled the tree and shrub cover using the Random Forest algorithm.

Results

We found four types of B. litwinowii stands, characterized by different tree and shrub coverage (initial Bromus variegatus–Betula litwinowii encroachment indicating the first stage of succession, Aconitum nasutum–Betula litwinowii forest, Rubus idaeus–Betula litwinowii forest and Rhododendron caucasicum–Betula litwinowii tree line scrubs). B. litwinowii forest increased 25% compared to 1987 mainly in an uphill direction. Furthermore the modelled tree and shrub cover (R² = .69) could be related to the four vegetation types.

Conclusions

Our results indicate a recent trend towards shrub encroachment and consequently reforestation in the Kazbegi region.     

Effects of fire on soil respiration,ATP content and enzyme activities in Mediterranean maquis

Question: Do low or high intensity fires affect micro‐organism activity in the upper soil layer of Mediterranean maquis? Location: 600 m from the sea in the Nature Reserve of Castel Volturno (Campania, southern Italy, 40°57’N; 13°55’E). Methods: Soil respiration was measured in situ on intact soil; enzyme activity (cellulase, xylanase, invertase, trehalase and protease) and ATP content were measured on soil samples collected under three species of maquis vegetation: Phillyrea angustifolia L., Myrtus communis L. and Cistus incanus L. Results: Soil microbial respiration showed no significant differences in CO₂ flux in treated and untreated plots, but the ATP content in the soil under C. incanus and M. communis was lower in the treated plots for most of the study period. In the soil under Ph. angustifolia, ATP content was low only for one week after fire. The reduction was more marked in the samples from ‘high fire intensity’ than from ‘low fire intensity’ plots. Soil respiration and ATP content exhibited seasonal variations linked to soil water content. Among the enzyme activity measured in the soil under the three plant covers, only invertase declined in burned plots throughout the study period, particularly in the ‘high fire intensity’ plots. Activity of the enzymes cellulase, xylanase, trehalase and protease had a different sensitivity depending on the respective shrub cover. Conclusions: Impact of fire on soil microbial activity is largely dependent on vegetation mosaic and species identity.     

Fire and regeneration: the role of seed banks in the dynamics of northern heathlands

Questions: How do species composition and abundance of soil seed bank and standing vegetation vary over the course of a post‐fire succession in northern heathlands? What is the role of seed banks – do they act as a refuge for early successional species or can they simply be seen as a spillover from the extant local vegetation? Location: Coastal Calluna heathlands, Western Norway. Methods: We analysed vegetation and seed bank along a 24‐year post‐fire chronosequence. Patterns in community composition, similarity and abundances were tested using multivariate analyses, Sørensen's index of similarity, vegetation cover (%) and seedling counts. Results: The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa, respectively, with 39 shared species, resulting in 68% similarity overall. Over 24 years, the heathland community progressed from open newly burned ground via species rich graminoid‐ and herb‐dominated vegetation to mature Calluna heath. Post‐fire succession was not reflected in the seed bank. The 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna vulgaris (49%; 12 018 seeds m^?2) and Erica tetralix (34%; 8 414 seeds m^?2). Calluna showed significantly higher germination the first 2 years following fire. Conclusions: Vegetation species richness, ranging from 23 to 46 species yr^?1, showed a unimodal pattern over the post‐fire succession. In contrast, the seed bank species richness, ranging from 21 to 31 species yr^?1, showed no trend. This suggests that the seed bank act as a refuge; providing a constant source of recruits for species that colonise newly burned areas. The traditional management regime has not depleted or destroyed the seed banks and continued management is needed to ensure sustainability of northern heathlands.     

Significato fitogeografico e fitosociologico delle cenosi a Sarcopoterium spinosum (L.) Spach di Capo S. Elia (Cagliari - Sardegna meridionale)

Abstract

Phytogeographic and phytosociological meaning of the Sarcopoterium spinosum (L.) Spach community at S. Elia Cape (Cagliari).—Sarcopoterium spinosum (L.) Spach station at S. Elia Cape, the most western station of its distributive area, sets the question whether the accompanying vegetation must be attributed to eastern or western associations. An analysis of the species shows some residual members of the Poterium spinosum and Corydothymus capitatus Lavrentiades 1969 association, but not sufficient to recognize this coenosis, which is anyhow included in the Oleo-Ceratonion. The boundary of these coenosis with the eastern area is attributed to a N-W/S-E climate gradient, set possibly in post glacial ages.     

Ant-mediated expansion of an obligate seeder species during the first years after fire

Most obligate seeder species build up a soil seed bank that is associated with massive seed germination in the year immediately after a fire. These species are also shade‐intolerant and disappear when vegetation cover closes, creating unsuitable conditions for seedling recruitment. The only way for these plants to expand their populations is when habitats suitable for seedling recruitment arise (i.e. in years immediately after a fire). However, short primary seed dispersal of obligate seeders does not allow these plants to colonise the suitable habitats, and these habitats can only be colonised by secondary seed dispersion. We hypothesised that Fumana ericoides, an obligate‐seeding small shrub, not only establishes abundantly in the first year after fire, but also expands its local range in the following years due to secondary dispersal by ants while suitable habitats are still available. We tested this hypothesis using experimental studies and a simulation model of potential population expansion in a recently burned area. Results showed that F. ericoides not only established prolifically in the year immediately after fire, but was also able to recruit new individuals and expand its population in the years following the fire, despite a low germination rate and short primary seed dispersal. Ant‐mediated seed dispersal and availability of suitable habitats were key factors in this phenomenon: ants redistributed seeds in suitable habitats while they were available, which accelerated the expansion of F. ericoides because new plants established far away from the core population.     

Physiognomie development of Pseudotsuga forests in relation to initial structure and disturbance intensity

Abstract. Physiognomic patterns may vary significantly during succession despite a tendency for larger-growth forms to gradually replace smaller ones. Development of understory structure was observed for 25 yr after harvest of Pseudotsuga forests on two sites in the western Cascade Range, Oregon. We examine the influences of disturbance intensity and initial vegetation structure on the origin, direction, and rate of physiognomic change. Broad-scale changes in vegetation structure differed between sites. On Watershed 1, herbs dominated for 11 yr, after which shrubs became co-dominant. In contrast, Watershed 3 never exhibited a distinct, transitional shrub phase - herbs dominated for 18 yr, after which trees assumed co-dominance. The pattern and rate of physiognomic succession also varied among pre-disturbance plant communities and with disturbance intensity. Differences among communities largely corresponded with initial vegetation structure, reflecting the disturbance tolerance of forest herbs and shrubs. Canopy closure occurred most rapidly in the initially depauperate, but tree-dominated Coptis community. Along the disturbance gradient, shifts from herb to shrub dominance occurred earlier on burned than on unburned sites due to rapid development of invading shrubs, whose germination and establishment were stimulated by fire. However, subsequent transitions to tree dominance showed no clear relationship with disturbance intensity. These long-term trends suggest that pre-disturbance community structure and disturbance intensity are major determinants of physiognomic succession, but that their effects may be modified by historical or stochastic factors such as limited seed availability or local fluctuations in weather.     

Regeneration of a dominant Mediterranean dwarf-shrub after fire

Abstract. The regeneration after fire of the dominant east Mediterranean dwarf-shrub Sarcopoterium spinosum was studied under various habitat and geographic conditions in northern Israel, northern Crete and the Aegean coast of Turkey. Age structures of regenerating stands were determined 3–9 yr after fire on 13 1 mx 1 m sample stands by analysis of growth rings in the taproot crown of 874 plants. S. spinosum regenerated either by massive seedling recruitment in some habitats or by resprouting from surviving meristems in others. This versatility facilitates adaptation of the species to widely different environmental conditions and is a factor in the maintenance of its dominance after fire at occupied sites. In the years after fire, the growth of younger plants within the stand at all sites was severely suppressed by the older shrubs. Consequently, the age structure of the stands was dominated by one or two older cohorts that became established soon after fire. In addition, on most habitats, older shrubs (usually older than 6 yr) were often composed of clusters of plants that suggested clonal proliferation of ramets. The strongly peaked age structure, together with the appearance of clonal regeneration on the older plants, suggests that subsequent maintenance of the stand was not dependent on recurrent seedling recruitment. This can explain the persistence of S. spinosum in stands of herbaceous vegetation despite the extreme sensitivity of the seedlings to competition under such conditions.     

Effects of re‐introducing fire to a central Florida sandhill community

Abstract. A southern ridge sandhill site in central Florida, USA, was burned in 1989, 1991, and 1995 after 63 years of fire‐suppression to simulate a pre‐settlement fire regime. Fire changed species abundance and vegetation structure but caused only minimal changes in species turnover and diversity. There was a general trend for an increase in the cover of herbs following fire but this was a statistically significant effect for only one species, Liatris tenuifolia var. tenuifolia. Aristida beyrichiana increased, litter cover and litter depth were significantly reduced, and ground lichens were eliminated in response to burning. Scrub oaks and palmettos in the ground cover and small shrub layers (height ≤ 1 m) either increased or did not respond to burning, reflecting strong post‐fire resprouting. Diversity in the ground cover and small shrub layers were not affected by fire. Scrub oaks and palmettos in the large shrub and overstorey layers (height > 1 m) were reduced in density, basal area, and longest canopy measurements in response to fire. Species diversity also decreased within these layers following fire. Some Pinus elliottii var. densa survived fire, but their density was reduced. All Pinus clausa were eliminated by fire. Periodic burning can suppress the dominance of shrubs (Quercus spp.) while increasing the cover of grasses and herbs in southern ridge sandhill vegetation.     

Attempting to restore mountain big sagebrush (Artemisia tridentata ssp. vaseyana) four years after fire

Restoration of shrubs is needed throughout the world because of altered fire regimes, anthropogenic disturbance, and overutilization. The native shrub mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle) is a restoration priority because of its value to wildlife in western North America. One of the principal threats to mountain big sagebrush is encroachment by western juniper (Juniperus occidentalis ssp. occidentalis Hook) and other conifers. Fire is frequently applied to control juniper; however, sagebrush recovery after fire can be variable. Seeding sagebrush postfire can hasten sagebrush recovery; however, seeding is not always necessary. Therefore, it may be advantageous to monitor postfire recovery to determine if seeding is needed. The effect of seeding sagebrush several years after fire is unknown. We evaluated the efficiency of seeding mountain big sagebrush four years after fire‐controlled junipers at five sites. Sagebrush cover (<0.5%) and density (<0.07 plants/m²) was low in seeded plots and did not differ from unseeded controls in the three postseeding years. We conclude that seeding sagebrush four years after fire did not accelerate sagebrush recovery. We speculate that seeded sagebrush failed to establish because of competition from herbaceous vegetation that had four years to recover after fire. Although it would be beneficial to seed sagebrush only when needed, our results suggest postponing seeding until monitoring has determined that recovery is inadequate may not be advisable. We suggest researchers investigate methods to improve predicting sagebrush recovery to allow for seeding, when needed, before the first postfire growing season.     

The age of Calluna stands moderates post‐fire regeneration rate and trends in northern Calluna heathlands

Questions: Does stand age influence the direction and rate of post‐fire successional dynamics in coastal Calluna heaths and can old degraded heath vegetation be restored through reintroduction of fire? Location: Coastal heaths in the Tarva archipelago, central Norway. Methods: We investigated revegetation dynamics after experimental fires set in young (8 years since last fire) and old (>50 years since last fire) grazed heath stands. A repeated measures design was used, with floristic data recorded in permanent plots in the post‐fire successions (n=12) over a 7‐year period. The data were analysed using multivariate ordination techniques (PCA, RDA and PRC) and mixed effects models. Results: The age of Calluna stands strongly influenced post‐fire succession, different trends due to age explained 10.4% of variation in floristic data. Young heath showed faster succession towards pre‐fire community composition than old heath, and this could partially be explained by succession‐related factors: young heath had lower cover of mosses and lichens in the pre‐burned vegetation, and lower cover of litter early in succession. Young heath had a less pronounced overall community response to fire than old heath. Vegetative regeneration of C. vulgaris was absent in both old and young heath, but Calluna still re‐established as the dominant species within 5–7 years in both young and old stands. Regeneration dynamics were also affected by habitat conditions, different trends due to habitat explained 6% of variation. Conclusions: Our study demonstrates that old stands do develop characteristic heathland vegetation and structure after fire, and while potential invasives into the system such as trees and rhizomatous species are present, they do not impair Calluna regeneration or vegetation development towards the target heathland community composition and structure. Further, as our young stands are only in their second fire rotation after restoration, we suggest that characteristic dynamics of managed heathlands can re‐establish relatively rapidly, even in severely degenerated sites (>50 years since last fire). Site‐specific factors also need to be considered. We conclude that there is restoration potential in old heaths, despite slow dynamics in the first rotation.     

Responses of mammalian carnivores to land use in arid savanna rangelands

Shrub encroachment due to heavy grazing has led to dramatic changes in arid savanna landscape structure worldwide. It is considered to be one of the most threatening forms of rangeland degradation altering plant diversity. However, possible impacts of shrub encroachment on species diversity at higher trophic levels remain poorly understood. Additionally, indirect effects, such as changes of trophic interactions, are often ignored when trying to understand changes in biodiversity patterns. In this study, conducted in the southern Kalahari, we explored how the diversity of small carnivores and their prey is affected by shrub encroachment. We analysed the relationships between abundance and diversity of small carnivores, the availability of their main prey groups (coleopterans, termites, grasshoppers, rodents) and the structural diversity of the landscape (shrub, grass and herb cover). Eight hundred track surveys were conducted to determine carnivore abundance on 20 rangeland habitats, which represented a gradient of grazing intensity. Prey availability was surveyed for each study site and related to vegetation cover.

Results show a significant impact of shrub cover on abundance and diversity of carnivores and their prey. The diversity of both, carnivores and their prey, showed a hump-shaped response to increasing shrub cover whereas relative carnivore abundance decreased. Availability of prey groups was affected differently by shrub cover increase. Diversity of carnivores was best predicted by shrub cover (R²>0.7, p<0.001) indicating the overriding role of habitat structure as compared to prey availability. We conclude that intermediate shrub cover values enrich structural diversity of savanna landscape and in consequence sustain diversity of small carnivores and their prey in arid and semiarid ecosystems.     

Post-fire regeneration strategies of Californian coastal sage shrubs

Summary Regeneration methods for coastal sage srub vegetation after fire were studied in the coastal Santa Monica Mountains of southern California. Six sites were sampled two years after a large fire of fall, 1978. The intensity of fire varied. Foliar cover and flowering incidence were recorded for individuals regenerating by resprouting or from seed. Resprouting plants contributed most to post-fire recovery, comprising 95% of the relative foliar shrub cover; 84% of resprout and 47% of seedling cover had flowered. An ANOVA of reproductive mode and fire intensity indicates that resprout total cover and individual size are significantly greater than those of seedlings, regardless of fire intensity. Among sites the average foliar cover of resprouts exceeded that of seedlings by factors ranging from 9 to 63. All coastal sage species examined resprout, although the potential vigor of resprouting appears to vary widely within genera (e.g. Encelia, Eriogonum, and Salvia) and even within species. In the second growing season following fire seedling density increased due to seeds shed by resprouted shrubs. Most of the cover on these stands of coastal sage scrub is destined to be either crown-sprouted individuals or their progeny.