Shrubland

Climate change is increasing the frequency and extent of high-severity disturbance, with potential to alter vegetation community composition and structure in environments sensitive to tipping points between alternative states. Shrub species display a range of characteristics that promote resistance and resilience to disturbance, and which yield differential post-disturbance outcomes. We investigated differences in shrub patch size and stem density in response to variations in fire severity, vegetation community, and post-disturbance reproductive strategies in Sky Island forested ecosystems in the southwestern United States. Patterns in shrub structure reflect the effects of fire severity as well as differences among species with alternate post-fire reproductive strategies. Increased fire severity correlates with larger patch sizes and greater stem densities; these patterns are observed across multiple fire events, indicating that disturbance legacies can persist for decades. High severity fire produces the largest shrub patches, and variance in shrub patch size increases with severity. High severity fire is likely to promote expansion of shrub species on the landscape, with implications for future community structure. Resprouting species have the greatest variability in patch structure, while seeding species show a strong response to disturbance: resprouting species dominate at low disturbance severities, and obligate seeders dominate high severity areas. Differential post-fire reproductive strategies are likely to generate distinct patterns of vegetation distribution following disturbance, with implications for community composition at various scales. Shrub species demonstrate flexible responses to wildfire disturbance severity that are reflected in shrub patch dynamics at small and intermediate scales.

The relative influence of the factors acting on burn probability, namely fuel and weather, is not well understood, especially in Europe. We use a digital fire atlas (1975–2008) and apply survival analysis to individual fires (1998–2008) to describe how burn probability changes with fuel age in Portugal. The typical fire return interval and median fire-free interval vary regionally from 23 to 52 and 18 to 47 years. Increase of the hazard of burning with time is generally near-linear, denoting moderate fuel-age dependency, as in some other shrub-dominated Mediterranean environments. Analysis of complete fire intervals resulted in shorter fire return interval and higher fuel-age dependency of burn probability than findings that included censored observations. Increasingly severe weather conditions either expressed through fire size or by extreme fire danger concurrently decreased fuel-age dependency and selected older fuels. The results are discussed from the viewpoints of fire suppres...

Current climate projections predict drier and warmer conditions in the Mediterranean basin over the next century. While advanced spring growth due to warming has been described in the literature, few data are available on the effects of drought on phenology. Hence, the phenology and growth of two Mediterranean shrubs, Erica multiflora and Globularia alypum, was studied in a rainfall exclusion field experiment to simulate spring drought in a natural shrubland. We estimated the onset of growth in spring by monitoring the appearance of new stems, and the end of growth in summer by following the elongation of stems. Drought treatment caused earlier onset of the spring growing season in E. multiflora, whereas no advance was observed in G. alypum. However, growth cessation was not affected in E. multiflora. Drought reduced the growth of both shrubs, as reflected in less stem elongation. The results show that a drier climate might affect not only growth but also spring phenology of some Mediterranean species. We suggest that a reduction in the cooling effect of transpiration may have analogous effects to warming and might advance the start of growth in E. multiflora, a species whose phenology has been described as warming-sensitive. The lengthening of the growing season resulting from advanced growth did not imply higher productivity, as growth was restricted by drought.

Mediterranean ecosystems are global hotspots of biodiversity threaten by human disturbances. Growing evidence indicates that regeneration of Mediterranean forests can be halted under certain circumstances and that successional stages can become notoriously persistent. The Mediterranean sclerophyllous forest in central Chile is been largely transformed into savannas dominated by the invasive legume tree Acacia caven as result of interacting management and ecological factors. We used multi-temporal satellite imag- ery to study the transition dynamics of these major vegetation types over the last four decades (1975– 2008). Vegetation changes were related to indicators of resource availability (topography, water avail- ability, solar radiance), potential propagule availability (distance to forest remnant patches) and distur- bance regimes (grazing, fire occurrence and distance to roads and cities). During this study period, forests were mostly converted into Acacia savannas (46.1%). Aca...

We investigated the factors that influenced the distribution of the African elephant around a volcanic shield dominated by a mosaic of forest and savanna in northern Kenya. Data on elephant distribution were acquired from four female and five bull elephants, collared with satellite-linked geographical positioning system collars. Based on the eigenvalues (variances) of the correlation matrix, the six factors that contributed significantly to high total variances were distance from drinking water (24%), elevation (15%), shrubland (10%), forest (9%), distance from settlements (8%) and distance from minor roads (7%), contributing to 73% in the observed variation of the elephant distribution. The elephants were found at high forested elevations during the dry season but they moved to the lowlands characterized by shrubland during the wet season. Elevation acts as a proxy for the vegetation structure. The presence of elephants near permanent water points (13%) and seasonal rivers (11%) during the dry and wet seasons, respectively, demonstrates that water is the most important determinant of their distribution throughout the year. We conclude that the distribution of elephants in Marsabit Protected Area and its adjacent areas is influenced mainly by drinking water and vegetation structure.Nous avons étudié les facteurs qui influencent la distribution de l’éléphant africain autour d’un bouclier volcanique dominé par une mosaïque de forêt et de savane dans le nord du Kenya. Les données sur la distribution des éléphants furent acquises grâce à quatre femelles et cinq mâles équipés de colliers radio avec GPS par satellite. En se basant sur les valeurs propres (variances) de la matrice de corrélation, les six facteurs qui ont contribué significativement à de fortes variances totales étaient la distance par rapport à l’eau (24%), l’élévation (15%), la savane arbustive (10%), la forêt (9%), la distance par rapport à des installations (8%) et celle par rapport à des routes peu importantes (7%), qui contribuent donc ensemble à 73% de la variation observée dans la distribution de l’éléphant. Des éléphants se trouvaient sur de hautes élévations forestières pendant la saison sèche, mais ils se déplaçaient vers les terrains de basse altitude caractérisés par des broussailles pendant la saison des pluies. L’élévation sert de proxy à la structure de la végétation. La présence d’éléphants près des points d’eau permanents (13%) et des rivières saisonnières (11%) pendant la saison sèche et la saison des pluies respectivement montre que l’eau est le déterminant le plus important de leur distribution tout au long de l’année. Nous concluons que la distribution des éléphants dans la Marsabit Protected Area et dans les zones adjacentes est influencée principalement par la disponibilité de l’eau et la structure de la végétation.

Changes in grazing behaviour can be used as an early indicator for detecting plant community composition and structure modification. The purpose of this study was to evaluate the interrelationships between plants on offer at pasture and animal behaviour, so as to forestall desertification by applying management measures. The experimental area was a shrubland, dominated by Cistus monspeliensis, Olea europea, Phillyrea latifolia, Pistacia lentiscus and Quercus coccifera, in which a flock of 300 local goats grazed freely. The total area was divided into lightly, moderately and heavily grazed unfenced plots. Grazing behaviour data were recorded separately in each plot, in early spring, early summer, late summer and early winter. The preferred species during early spring, early summer and early winter was Phillyrea latifolia, while during late summer it was Pistacia lentiscus. The goats' average bite size, intake rate and total intake gradually decreased as the growing season progre...

Wildfires are one of the major disturbances in the dynamics of forests and shrublands. However, little is known about their effects on insect communities that contribute to faunal biodiversity and play key roles in the ecosystem's dynamics. An intense and widespread fire occurred in 1999 in the Nahuel Huapi National Park in the Andean forest in northern Patagonia, Argentina. This fire affected adjacent, but different, habitat types. After the fire, beetle abundance, species richness and assemblage composition were ...

The value of Traditional Ecological Knowledge (TEK) for informing resource management has long been recognized; however, its incorporation into ecosystem services (ES) assessments remains uncommon. Often “top-down” approaches are utilized, depending on “expert knowledge”, that are not relevant to local resource users. Here we propose an approach for combining participatory methods with remote sensing to provide a more holistic understanding of ES change. Participatory mapping in focus group discussions identified TEK regarding what ES were present, where, and their value to communities. TEK was then integrated with satellite imagery to extrapolate to the landscape-scale. We demonstrate our method for Nyangatom communities in the Lower Omo Valley, Ethiopia, showing for the first time the ES impacts of regional environmental change, including the Gibe III dam, for communities in the Omo River basin. Results confirmed the collapse of flood-retreat cultivation associated with the loss o...

Regional variation in nitrogen (N) deposition increases plant productivity and decreases species diversity, but landscape- or local -scale influences on N deposition are less well-known. Using ion-exchange resin, we measured variation of N deposition and soil N availability within Elk Island National Park in the ecotone between grassland and boreal forest in western Canada. The park receives regionally high amounts of atmospheric N deposition (22 kg ha−1 yr−1). N deposition was on average higher ton clay-rich luvisols than on brunisols, and areas burned 1–15 years previously received more atmospheric N than unburned sites. We suggest that the effects of previous fires and soil type on deposition rate act through differences in canopy structure. The magnitude of these effects varied with the presence of ungulate grazers (bison, moose, elk) and vegetation type (forest, shrubland, grassland). Available soil N (ammonium and nitrate) was higher in burned than unburned sites in the absenc...

ABSTRACT The effects of climate change on plant reproductive performance affects the sequence of different plant reproductive stages from flowering to seed production and viability, as well as the network of relationships between them. These effects are expected to respond to different components of climate change, such as temperature and water availability, and may be sensitive to differences in species phenology. We used long-term experimental drought and warming treatments to study the effect of climate change on flower production, fruit and seed-set, seed size and seed germination rate (proportion of germinating seeds) in three Mediterranean shrubs coexisting in a coastal shrubland. Larger plants produced significantly more flowers in all three species, and higher fruit-set in Dorycnium pentaphyllum. Flower production was reduced in drought and warming treatments in the spring-flowering species D. pentaphyllum and Helianthemum syriacum, but not in the autumn–winter species Erica multiflora, which increased flowering in the warming treatment. However, the drought treatment eventually resulted in a decreased seed-set in E. multiflora. Structural equation modelling revealed strong correlations between the sequential reproductive stages. Specifically, flower density in inflorescences determined seed-set in H. syriacum, and seed size and germination rate in E. multiflora. Nevertheless, the relevance of relationships between reproductive traits changed between climatic treatments: in D. pentaphyllum a direct relationship between plant size and seed size only arised in the drought treatment, while in H. syriacum climate treatments resulted in a stronger relationship between the number of flowers and seed-set. This experimental study shows the ability of changing climatic variables to determine the reproductive sequential process of woody species. We show that several parameters of the reproductive performance of some Mediterranean species are affected by drought and warming treatments simulating climate change, highlighting the importance of changes in both water availability and temperature, and the sequential relationship between reproductive stages. Phenological patterns also contribute to species’ differential responses to climatic change, due to the relationship of these patterns with resource availability, environmental conditions and plant–pollinator interactions.