Perennial Species Richness Research Articles

Post-fire recovery of herbaceous species composition and diversity, and soil quality indicators one year after wildfire in a semi-arid oak woodland

Disturbance and environmental heterogeneity are factors that affect forest ecosystems under different climates. Although fire is an important disturbance agent in deciduous oak forests of western Iran, its effects on vegetation composition are still poorly understood. This study examined the short-term impact of different fire intensities on the composition and diversity of herbaceous species, together with physical, chemical and biological soil properties. In sampling a large area that had burned in 2013, we surveyed the vegetation and soil properties in quadrats established in each of 25 plots that had been selected for each of three fire intensities. Detrended correspondence analysis revealed greater similarity in species composition between low-intensity fire (LFI) and unburned (Un) areas compared to LFI versus high-intensity fire (HFI). Compared to Un, LFI increased richness of annual and perennial herbaceous species, while HFI exerted the opposite effect. Moreover, the number of indicator species was decreased with increasing fire intensity. Higher soil microbial biomass carbon (MBC) and nitrogen (MBN) and basal respiration (BR), as well as microbial quotient (qMic) were found in Un compared to burned areas; these variables averaged 1098μgg−1, 85.4μgg−1, 17.08mg CO2-Ckg−1day−1 and 1.96mgCmic/g C total, respectively. Also, Shannon indices of herbaceous species were positively related to these microbial responses. Overall, soil microbial characteristics were more sensitive indicators of fire intensity than soil physico-chemical properties. These results suggest that low intensity fires could be used effectively as a management tool to obviate the effects of intense fires in such semi-arid ecosystems, thereby reducing forest floor fuel loads while maintaining or even improving herbaceous plant richness.

Biodiversity effects and rates of spread of nonnative eucalypt woodlands in central California

Woodlands comprised of planted, nonnative trees are increasing in extent globally, while native woodlands continue to decline due to human activities. The ecological impacts of planted woodlands may include changes to the communities of understory plants and animals found among these nonnative trees relative to native woodlands, as well as invasion of adjacent habitat areas through spread beyond the originally planted areas. Eucalypts (Eucalyptus spp.) are among the most widely planted trees worldwide, and are very common in California, USA. The goals of our investigation were to compare the biological communities of nonnative eucalypt woodlands to native oak woodlands in coastal central California, and to examine whether planted eucalypt groves have increased in size over the past decades. We assessed site and habitat attributes and characterized biological communities using understory plant, ground-dwelling arthropod, amphibian, and bird communities as indicators. Degree of difference between native and nonnative woodlands depended on the indicator used. Eucalypts had significantly greater canopy height and cover, and significantly lower cover by perennial plants and species richness of arthropods than oaks. Community composition of arthropods also differed significantly between eucalypts and oaks. Eucalypts had marginally significantly deeper litter depth, lower abundance of native plants with ranges limited to western North America, and lower abundance of amphibians. In contrast to these differences, eucalypt and oak groves had very similar bird community composition, species richness, and abundance. We found no evidence of "invasional meltdown," documenting similar abundance and richness of nonnatives in eucalypt vs. oak woodlands. Our time-series analysis revealed that planted eucalypt groves increased 271% in size, on average, over six decades, invading adjacent areas. Our results inform science-based management of California woodlands, revealing that while bird communities would probably not be affected by restoration of eucalypt to oak woodlands, such a restoration project would not only stop the spread of eucalypts into adjacent habitats but would also enhance cover by western North American native plants and perennials, enhance amphibian abundance, and increase arthropod richness.

Changes in plant life‐form, pollination syndrome and breeding system at a regional scale promoted by land use intensity

AbstractAimParallel declines in plant and insect pollinator diversity under land use intensification may occur as a result of both taxonomic groups responding similarly, but independently, to habitat change or as a consequence of interdependence as insect‐pollinated plants decline due to pollinator loss. Here, we explore the relative roles of independent and interdependent declines by comparing correlations of species richness and land use intensity for different functional groups of plants.LocationAustria.MethodsGeneralized linear and generalized linear mixed models were used to analyse trends in species richness of plant functional groups sampled along a land use intensity gradient across 100 agricultural landscapes (=625 × 625 m each). Plants were classified according to their pollination syndrome, breeding system and life span. Species numbers were related to the site‐specific proportional area of semi‐natural habitats as an indicator of land use intensity.ResultsOverall, as the level of agricultural intensification increased the proportion of outcrossing plants declined and the proportion of self‐pollinating plants increased. However, while perennial plant species richness decreased under more intensive land use independently of pollination syndrome or breeding system, the richness of annuals only declined for outcrossing species requiring specialized insect pollinators but not for those pollinated by wind‐ or unspecialized insect pollinators.Main conclusionFrom these patterns we infer that land use intensification mainly drives plant species loss by excluding perennial species which suffer from the conversion of land to annually harvested crop fields. Hence, parallel declines in plant and insect richness largely result from a common response of perennials and pollinators to habitat change. Nevertheless, for annual plants with specialized pollinator requirements our data support a cascading effect of pollinator decline on species richness.

Agroforestry systems in the highlands of the Tehuacán Valley, Mexico: indigenous cultures and biodiversity conservation

In this study we analysed: (1) the biodiversity conservation capacity of Agroforestry Systems (AFS) in temperate highlands of the Tehuacan–Cuicatlan Valley, Central Mexico, (2) human cultural motives and actions for conserving such diversity and (3) problems endangering that capacity. We evaluated the richness and diversity of perennial plant species maintained in AFS through vegetation sampling of 14 agricultural plots and compared their composition with that of natural forests (14 plots of 500 m2 each). We examined the situations among communities of Nahuatl, Ixcatec and Cuicatec people, documenting through interviews the management practices of plant species and the whole system, reasons why people maintain vegetation cover within AFS, and factors influencing changes in decisions favouring agriculture intensification. In the AFS studied we recorded a total of 79 species of trees and shrubs, 86 % of them being native species and representing 43 % of all species of trees and shrubs recorded in the sampling of the natural forests the AFS derive from. People leave standing on average a total of 40 individual trees and shrubs per agricultural plot. Reasons for leave plant species standing were more frequently associated with their use as fruit trees, firewood, shade, beauty, respect to nature and other environmental benefits. Water availability for irrigation, land tenure, and dependence on agriculture and forest for peasant's subsistence were main decision factors influencing AFS variation in their composition. AFS in temperate zones are important reservoirs of biodiversity and biocultural heritage and should be keystones for conservation policies in the Tehuacan–Cuicatlan Valley.

Agrobiodiversity in an Oasis Archipelago

Oases on Mexico’s Baja California peninsula harbor farms and gardens which largely feature crops first introduced by Jesuit missionaries (1697–1768). These spring-fed agricultural landscapes are currently managed as diverse agroecosystems with original heritage food crop species as well as newer crop and livestock introductions. These isolated landscapes are relict sanctuaries for unique desert crop varieties and farming systems that may be important for in situ conservation of agrobiodiversity and crop resources. Historical records in 1774 describe 21 original perennial crop species introductions in cultivation on the peninsula just after the Jesuit expulsion. This research expands rapid-assessment surveys conducted in nine mission oasis sites on the peninsula in 2010 through in-depth surveys of Mission era and total perennial crop species richness and relative frequency in twelve Jesuit mission oases. In all, 241 large field-gardens were surveyed with eighty-nine total perennial crop species cultivated in the mission oases. Species-area and rankabundance relationships were calculated to determine patterns of inter and intra-oasis agrobiodiversity. A high persistence of Mission era species indicates that these oases serve as agrobiodiversity refugia, or protected source areas for heritage perennial crop species. The cultural and agricultural islands of the oases should be considered as an archipelago of interconnected sites for the long-term resilience of the region’s farming and food systems.

Regional signatures of plant response to drought and elevated temperature across a desert ecosystem

The performance of many desert plant species in North America may decline with the warmer and drier conditions predicted by climate change models, thereby accelerating land degradation and reducing ecosystem productivity. We paired repeat measurements of plant canopy cover with climate at multiple sites across the Chihuahuan Desert over the last century to determine which plant species and functional types may be the most sensitive to climate change. We found that the dominant perennial grass, Bouteloua eriopoda, and species richness had nonlinear responses to summer precipitation, decreasing more in dry summers than increasing with wet summers. Dominant shrub species responded differently to the seasonality of precipitation and drought, but winter precipitation best explained changes in the cover of woody vegetation in upland grasslands and may contribute to woody-plant encroachment that is widespread throughout the southwestern United States and northern Mexico. Temperature explained additional variability of changes in cover of dominant and subdominant plant species. Using a novel empirically based approach we identified "climate pivot points" that were indicative of shifts from increasing to decreasing plant cover over a range of climatic conditions. Reductions in cover of annual and several perennial plant species, in addition to declines in species richness below the long-term summer precipitation mean across plant communities, indicate a decrease in the productivity for all but the most drought-tolerant perennial grasses and shrubs in the Chihuahuan Desert. Overall, our regional synthesis of long-term data provides a robust foundation for forecasting future shifts in the composition and structure of plant assemblages in the largest North American warm desert.

On the importance of shrub encroachment by sprouters, climate, species richness and anthropic factors for ecosystem multifunctionality in semi-arid Mediterranean ecosystems.

One of the most important changes taking place in drylands worldwide is the increase of the cover and dominance of shrubs in areas formerly devoid of them (shrub encroachment). A large body of research has evaluated the causes and consequences of shrub encroachment for both ecosystem structure and functioning. However, there are virtually no studies evaluating how shrub encroachment affects the ability of ecosystems to maintain multiple functions and services simultaneously (multifunctionality). We aimed to do so by gathering data from ten ecosystem functions linked to the maintenance of primary production and nutrient cycling and storage (organic C, activity of β-glucosidase, pentoses, hexoses, total N, total available N, amino acids, proteins, available inorganic P and phosphatase activity), and summarizing them in a multifunctionality index (M). We assessed how climate, species richness, anthropic factors (distance to the nearest town, sandy and asphalted road, and human population in the nearest town at several historical periods) and encroachment by sprouting shrubs impacted both the functions in isolation and M along a regional (ca. 350 km) gradient in Mediterranean grasslands and shrublands dominated by a non-sprouting shrub. Values of M were higher in those grasslands and shrublands containing sprouting shrubs (43% and 62%, respectively). A similar response was found when analyzing the different functions in isolation, as encroachment by sprouting shrubs increased functions by 2%-80% compared to unencroached areas. Encroachment was the main driver of changes in M along the regional gradient evaluated, followed by anthropic factors and species richness. Climate had little effects on M in comparison to the other factors studied. Similar responses were observed when evaluating the functions in isolation. Overall, our results showed that M was higher at sites with higher sprouting shrub cover, longer distance to roads and higher perennial plant species richness. Our study is the first documenting that ecosystem multifunctionality in shrublands is enhanced by encroaching shrubs differing in size and leaf attributes. Our findings reinforce the idea that encroachment effects on ecosystem functioning cannot be generalized, and that are largely dependent on the traits of the encroaching shrub relative to those of the species being replaced.

Plant functional traits improve diversity‐based predictions of temporal stability of grassland productivity

SynthesisThe temporal stability of plant production is greater in communities with high than low species richness, but stability also may depend on species abundances and growth‐related traits. Annual precipitation varied by greater than a factor of three over 11 years in central Texas, USA leading to large variation in production. Stability was greatest in communities that were not dominated by few species and in which dominant species rooted shallowly, had dense leaves, or responded to the wettest year with a minimal increase in production. Stability may depend as much on species abundances and functional traits as on species richness alone.Aboveground net primary productivity (ANPP) varies in response to temporal fluctuations in weather. Temporal stability of community ANPP may be increased by increasing plant species richness, but stability often varies at a given richness level implying a dependence on abundances and functional properties of member species. We measured stability in ANPP during 11 years in field plots (Texas, USA) in which we varied the richness and relative abundances of perennial grassland species at planting. We sought to identify species abundance patterns and functional traits linked to the acquisition and processing of essential resources that could be used to improve richness‐based predictions of community stability. We postulated that community stability would correlate with abundance‐weighted indices of traits that influence plant responses to environmental variation. Annual precipitation varied by a factor of three leading to large inter‐annual variation in ANPP. Regression functions with planted and realized richness (species with > 1% of community ANPP during the final four years) explained 32% and 25% of the variance in stability, respectively. Regression models that included richness plus the fraction of community ANPP produced by the two most abundant species in combination with abundance‐weighted values of either the fraction of sampled root biomass at 20–45 cm depth, leaf dry matter content (LDMC), or response to greater‐than‐average precipitation of plants grown in monocultures explained 58–69% (planted richness) and 58–64% (realized richness) of the variance in stability. Stability was greatest in communities that were not strongly dominated by only two species and in which plants rooted shallowly, had high values of LDMC, or responded to the wettest year with a minimal increase in ANPP. Our results indicate that the temporal stability of grassland ANPP may depend as much on species abundances and functional traits linked to plant responses to precipitation variability as on species richness alone.

Manipulating livestock grazing to enhance native plant diversity and cover in native grasslands

Temperate perennial grasslands globally have been subject to extensive biodiversity loss. Identifying livestock grazing regimes that maintain and enhance the diversity and cover of native plant species in these ecosystems remains a key challenge. The responses of vegetation to different sheep grazing regimes were assessed over 3 years in grasslands of south-eastern Australia. An open communal experimental design was used to assess the effects of varying season and duration of exclusion of grazing by sheep, replicated at three locations. Manipulation of season and duration of exclusion of grazing led to few major changes in the cover of native perennial grasses or forbs, although seasonal variation was considerable. Exclusion of grazing in the spring did increase the likelihood of occurrence of grazing-sensitive native forb species but also lead to an increase in the cover of exotic annual species. However, cover of exotic annual species tended to decline with increasing duration of exclusion, while the abundance of native, grazing-sensitive forbs and the cover of perennial grasses increased. Small-scale richness of native perennial forb species increased with a 3-month period of exclusion of grazing, but declined with year-round exclusion of sheep. Total species richness also declined in response to year-round exclusion of sheep and rates of decline were correlated with the rate at which herbage mass accumulated. While strategic grazing did not result in major vegetation changes in the short term, it is suggested that some grazing exclusion may enhance the survival of infrequent species most sensitive to sheep grazing. Caution, however, should be taken when grazing regimes implemented benefit both desirable (native forbs) and undesirable (exotic annuals) species. Having a mosaic of flexible grazing management regimes across the landscape is likely to be beneficial for native plant diversity.

Biophysical Correlates with the Distribution of the Invasive Annual Red Brome (Bromus rubens) on a Mojave Desert Landscape

AbstractBecause of its ability to transform ecosystems by increasing the prevalence of fire, the invasive annual red brome is a priority exotic species for management in arid lands of the southwestern United States. By sampling red brome presence and 97 environmental (climatic, topographic, and soil) and native vegetation (e.g., perennial species richness) variables on 126 sites, we assessed biophysical correlates with red brome distribution on a 755,000-ha (1.9 million ac) Mojave Desert landscape. Brome occupied 55 of 126 (44%) 0.09-ha plots. The simplest models (i.e., those containing the fewest or most easily obtained variables) in multivariate (classification trees and nonparametric multiplicative regression) and univariate (χ2) models often portrayed red brome distribution as well, or nearly as well, as more complicated models containing more variables harder to obtain. The models varied, however, in their abilities for describing brome presence compared with absence. For example, a simple classification tree using only elevation, soil great group, parent material, and vegetation type improved estimates of brome presence for 55% of sites, absences for 87%, and overall for 73% of sites compared with a naïve model containing the observed frequency of brome in the data. Conversely, a more complicated model, including soil boron and sulfur, performed better for presences (96%) than for absences (73%; 83% overall). Results also showed variable support for two general postulates in invasive species science. Red brome distribution was not correlated with soil N, which is inconsistent with the supposition that nutrient-rich soils are more prone to invasion. Brome was correlated with native perennial species richness to support the postulate that exotic species abundance is correlated with species-rich habitats, but the correlation was weak (r= 0.38) and similar in strength to correlations with many other environmental variables. On this relatively low-elevation landscape, the areas currently most invaded by red brome include the higher elevations (> 777 m [2,549 ft]), limestone–sandstone soils, and burrobush and mixed perennial communities. Areas least inhabited by brome are the lowest elevations (< 491 m), gypsum soils, and creosotebush and saltbush communities.

The role of phylogeny in desert rodent community assembly

Recent advances in molecular genetics and phylogenetic reconstruction have the potential to transform ecology by providing new insights into the historical evolution of ecological communities. This study by Stevens and collaborators complements decades of previous research on desert rodents, by combining data from a field study and a phylogenetic tree for Mojave Desert rodents to address patterns and processes of community assembly. The number of coexisting rodent species is positively correlated, and the average phylogenetic distance among these species is negatively correlated with perennial plant species richness. As rodent species diversity increases along a gradient of increasing environmental heterogeneity, communities are composed of increasingly related species: there is a consistent pattern of phylogenetic structure from over-dispersed through random to clumped. I discuss this pattern in the light of complementary results of previous studies. This paper is noteworthy for calling attention to still unanswered questions about how the historical events of speciation, colonization, extinction, and trait evolution and their relationship to past climates and vegetation have given rise to current patterns of community organization.

Patterns of plant diversity in ironstone ranges in arid south western Australia

Patterns of plant diversity were examined across 24 ironstone ranges in arid south western Australia. The high levels of beta diversity displayed between ranges primarily resulted from high turnover of perennial species and was not influenced by the lower species richness on the more arid ranges. The variance in composition of the vegetation across the ranges was evenly distributed between the broad spatial pattern and environmental factors measuring climate gradients, local site variables and soil chemistry. In contrast broad scale spatial and climatic gradients were most important in explaining the variance in perennial species richness. Ranges along the boundary of the Arid Zone appear to have acted as refugia during the climatic cycles of the Tertiary with several hotspots of species endemism and taxa with distributions centered on these ranges. On the more arid ranges these specialist ironstone taxa are largely absent. The variation in richness of these specialists taxa was strongly influenced by patterns in soil chemistry in addition to the broad scale spatial and climate gradients. The concentration of the ironstone specialist taxa is largely coincidental with the most prospective areas for iron ore mining and this will provide considerable challenges in conserving these unique ecosystems.

Vegetation recovery in a desert landscape after wildfires: influences of community type, time since fire and contingency effects

Summary1. Theories of plant succession are poorly developed in arid lands, hindering our understanding of how long communities may take to recover after disturbances such as fire. In desert landscapes vulnerable to fire, information about vegetation recovery is important when deciding whether land managers should facilitate vegetation recovery. The deserts of the southwestern USA are increasingly subject to unprecedented fires, facilitated by fuel from exotic grasses, yet management strategies are unclear.2. We evaluated post‐fire recovery patterns of perennial plant species richness and diversity, compared the rate and direction of succession between two major community types, and explored the relationship of time since fire (TSF) and other environmental factors with vegetation recovery. We sampled perennial plant communities and environmental variables (e.g. soil N) on 32 burns, ranging from 2 to 29 years TSF and each paired with their own unburned area, within a 1·8 million ha landscape in the Mojave Desert, USA.3. Species richness, diversity and composition exhibited different post‐burn recovery patterns, and recovery rates differed between community types. Specifically, diversity in Coleogyne ramosissima communities was greater in burned than unburned areas, but diversity did not differ in Larrea tridentata communities. Species composition in Larrea communities exhibited trajectories that indicate convergence with unburned community composition after 19 years TSF. Conversely, burned and unburned Coleogyne communities lacked convergence irrespective of TSF. Environmental variables (e.g. soil texture and P) accounted for 79–83% of the variation in burned species composition, suggesting environmental characteristics in part control recovery patterns.4. Synthesis and applications. The results indicate that geographically similar vegetation types within the same landscape can have markedly different post‐disturbance successional rates and trajectories. Furthermore, the persistence of fire effects varied depending on the community measure, with fire effects on species composition more long‐lasting than the effects on species diversity. This work supports (i) the use of post‐disturbance successional analyses for helping to prioritize management where it is most needed (e.g. communities not recovering naturally) and (ii) the need to assess whether persistent, early successional desert communities meet functional management objectives.

Invasive plants and plant diversity as affected by groundwater depth and microtopography in the Great Basin

ABSTRACTWe evaluated invasive exotic weeds and plant species diversity in relation to depth to groundwater (DTW) and microtopography in areas with DTW from 0·3–4 m in Owens Valley, California. Transects dominated by common plant species of the area were read at 1‐cm intervals, and species cover was obtained at different scales: 1‐m transect portions (microsites), whole transects (68 m average length), and the whole study area. Species richness and the Shannon–Wiener diversity index were obtained in microsites. DTW and microtopographical variation (soil‐surface relative elevations) were jointly measured along the vegetation transects. Found in 34% of the sampled transects, the annual Bassia hyssopifolia was the most common exotic weed of the area. Its cover in the whole study area was only 0·9%, but it was the second most dominant species (19% cover) in microsites. B. hyssopifolia coexisted mainly with herbaceous species, typically in places with shallow groundwater (average <1·5 m) and microtopographical depressions. However, B. hyssopifolia cover was not affected by variations in DTW or relative elevation. In contrast, B. hyssopifolia cover was negatively associated with perennial cover and species richness. Species diversity (Shannon–Wiener) slightly decreased with the increase in DTW but not with changes in microtopography. In contrast, species richness clearly varied with the identity of the dominant species in microsites. Our study suggests that the variation in community‐intrinsic factors such as competition and diversity may play a greater role in the growth of invasive plants than the variation in physical factors such as groundwater and microtopography. Copyright © 2011 John Wiley & Sons, Ltd.

Response of dry grassland vegetation to fluctuations in weather conditions: a 9-year case study in Prague (Czech Republic)

AbstractThe extreme habitats of dry grasslands are suitable for investigations of the response of vegetation to local climate changes. The impact of weather variability on the dynamics of a plant community in a dry grassland was studied. Correlations were found between different functional groups of species and individual species and weather variability. During a 9-year study in five nature reserves in Prague (Czech Republic), the following responses of dry grassland vegetation to weather conditions were observed: (i) wetter conditions, especially in the winter, affected the dominance and species richness of perennial grass species and the decline of rosette plants; (ii) the year-to-year higher temperatures in the winter produced a decline in the dominance of short graminoids and creeping forbs; (iii) spring drought adversely impacted the overall abundance, especially the abundance of dicotyledonous species, and the species richness. However, these relationships may be manifested in different ways in different locations, and in some cases the vegetation of different locations may respond to weather conditions in opposite manners.

Directional climate change and potential reversal of desertification in arid and semiarid ecosystems

AbstractOur objective was to determine if long‐term increases in precipitation can maintain grasslands susceptible to desertification, and initiate a reversal of historic regime shifts on desertified shrublands. Perennial grass production and species richness in a multi‐year wet period were hypothesized to be greater than expected based on precipitation in a sequence of dry years. These responses were expected to differ for grasslands and shrublands with different dominant species and topo‐edaphic properties. Long‐term trends in desertification were documented using vegetation maps beginning in 1858, 1915, 1928, and 1998). These trends were compared with herbaceous and woody species responses to a sequence of dry (1994–2003) and wet years (2004–2008) for two grassland (uplands, playas) and three desertified shrubland types (honey mesquite, creosotebush, tarbush) in the Chihuahuan Desert. Analyses showed that both types of grasslands decreased in spatial extent since 1858 whereas areas dominated by mesquite or creosotebush increased. Production of upland grasslands in the wet period was greater than expected based on responses during the dry period whereas the relationships between species richness and precipitation was the same for both periods. Precipitation was not important to responses in playa grasslands in either period. For all ecosystem types, the production response in wet years primarily was an increase in herbaceous plants, and the most pronounced responses occurred on sandy sites (upland grasslands, mesquite shrubland). Results suggest that multiple wet years are needed to initiate a sequence of grass establishment and survival processes that can maintain upland grasslands without management inputs and lead to a state change reversal in desertified shrublands. Restoration strategies need to take advantage of opportunities provided by future climates while recognizing the importance of ecosystem type.

Long-term consequences of mechanical fuel management for the conservation of Mediterranean forest herb communities

Mechanical clearing of understory vegetation is increasingly used in Euro-Mediterranean forests to reduce fire hazard, yet its long-term consequences for biodiversity remain poorly understood. This study analysed the influence of time since understory management and management frequency, on herbaceous species richness, cover and composition, functional richness and composition, and richness and cover within functional groups (life and growth forms, dispersal strategy, clonality, and plant height), using a chronosequence of cork oak (Quercus suber) stands spanning about 70 years. Overall species richness was virtually constant over time, but the richness of species with annual life form and plasticity in height was much higher in recently and recurrently treated stands; the opposite was found for perennial (mainly hemicryptophytes and chamaephytes), tussock-forming and clonal species richness, and functional richness. Overall herbaceous cover and that of annual, semi-basal, non-clonal and plastic species (in height) were favoured by recent and recurrent fuel treatments; cover by perennial (hemicryptophytes and chamaephytes), short basal, tussock-forming, and clonal species tended to increase for >10–20 years after management, and declined with management frequency. There was a marked shift in species and functional composition associated with time since understory management and management frequency. These findings suggest that widespread fuel management at <10 year intervals may shift understory herb communities to early-successional stages, impairing the persistence of species and functional groups recovering slowly after disturbance. Fuel management needs to balance the dual goals of fire hazard reduction and biodiversity conservation, retaining undisturbed patches in landscapes otherwise managed to reduce fuel accumulation.

Comparing biodiversity between protected savanna and adjacent non-protected farmland in the southern Kalahari

In this study we investigated the effect of different land use options (wildlife versus livestock) on species richness of plants and reptiles in the protected Kgalagadi Transfrontier Park (KTP) versus adjacent non-protected farmland within the same savanna habitat type (Aoub dune veld) in the southern Kalahari, South Africa. Our results show that both plant and reptile species richness as well as plant cover and reptile abundance was significantly higher in the protected KTP than in the non-protected farmland. The higher proportion of shrub but lower proportions of perennial grass cover, herb cover, and herb species richness in the farmland can be explained by higher stocking rates and the differences in feeding behaviour between native wild ungulates (e.g. Antidorcas marsupialis, Oryx gazella) and livestock (mainly sheep). The reptile’s prey availability and microhabitats (perennial grass tussocks and rodent burrows) for thermoregulation and protection against predators were significantly lower in the farmland. To conclude, our results clearly show that long term effects of different land use options (wildlife in protected KTP versus extensive livestock production in the non-protected farmland) even within the same habitat type have led to significant changes in vegetation composition, availability of microhabitat structures and in the reptile community.

Reintroducing fire into a ponderosa pine forest with and without cattle grazing: understory vegetation response

Reestablishing historical fire regimes is a high priority for North American coniferous forests, particularly ponderosa pine (Pinus ponderosa) ecosystems. These forests are also used extensively for cattle (Bos spp.) grazing. Prescribed fires are being applied on or planned for millions of hectares of these forests to reduce fuel loads, alter forest structure, and maintain and enhance the productivity of native plant communities. However, cattle grazing is ubiquitous in ponderosa pine forests and the consequences of post-fire cattle grazing on plant communities are not well understood. We evaluated cattle grazing effects (grazing, no grazing) on upland bunchgrass and Carex geyeri dominated ponderosa pine plant communities over five growing seasons after prescribed fires (spring reburn, fall reburn, no burn). Vegetation was measured prior to a 5-year interval reburn and the subsequent exclusion of cattle, and in the second and fifth growing seasons thereafter. We found no interactions between reburning and grazing for the understory response variables. For all reburn treatments, including unburned areas, five growing seasons of cattle grazing exclusion significantly increased: (1) total vegetative cover, (2) native perennial forb cover, (3) grass stature, (4) grass flowering stem density, and (5) the cover of some shrub species and functional groups. Grazing exclusion did not strongly affect plant compositional patterns, although differences were detected. Compared to unburned areas, neither spring nor fall reburning increased perennial native species cover or richness, and reburning reduced sedge cover. Fall reburning increased cover of native colonizers, and exotic species cover and richness (largely Bromus tectorum and Cirsium vulgare), although overall exotic cover remains low (<1%). We document several potentially chronic impacts of cattle grazing in both burned and unburned areas, and show that the understory release from a long history of cattle grazing caused a greater degree of change than the initial reintroduction of fire. If a goal of ecological restoration in these forests is increased cover of native perennial plants, and the potential for increased native perennial grass reproduction, then cattle grazing exclusion, or a change in cattle management, could provide critically important options in restoration plans.

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.