Long-term impacts of goat browsing on bush-clump dynamics in a semi-arid subtropical savanna

The effects of 16 years of continuous browsing by goats in a South African savanna at stocking rates intended for bush control were compared with plots unbrowsed for the same period of time. Differences in bush-clump density, structure and species composition were recorded. Bush-clump density did not differ between browsed and unbrowsed plots. Within individual bush-clumps, browsing was shown to impact more on structure than species composition, with smaller, shorter bush-clumps, containing fewer species but much greater stem-densities. Although species presence/absence was little affected by browsing, many species showed differences in abundance, growth and location within browsed and unbrowsed bush-clumps. Species reduced in abundance in browsed plots included Cussonia spicata, Ehretia rigida, Grewia occidentalis, Jasminum angulare and Senecio linifolius. Several species showed reduced growth in browsed plots, particularly those located at bush-clump edges. The relatively unpreferred Aloe ferox was a notable exception. Although browsing had little effect on the composition of the main clump founding species, emergents or late arrivals, there were twice as many single plants in browsed plots and emergence of several species was restricted to the middle of bush-clumps. Comparison of our findings with aerial photographic evidence and other literature suggest that browsing alone is unlikely to significantly reduce scrub cover, although it can clearly control further expansion. Combinations of fire and browsing, rather than one factor alone, are considered likely to act fastest and most effectively to significantly reduce or remove scrub cover altogether.     

Grazer diversity effects in an eelgrass–epiphyte–microphytobenthos system

The dramatic loss of biodiversity and its consequences for ecosystem processes have been of considerable interest in recent ecological studies. However, the complex and interacting processes influencing diversity effects in multitrophic systems are still poorly understood. We used an experimental eelgrass system to study the effects of changing richness of three consumer species on the biomass, diversity and taxonomic composition of both epiphytic and benthic microalgal assemblages. After 1 week, consumer richness enhanced the grazing impact on epiphyte biomass relative to single consumer treatments and a positive effect of consumer richness on prey diversity was found. Moreover, strong effects of consumer species identity on taxonomic composition were found in both microalgal assemblages. However, the effects of consumer richness were not consistent over time. The consequences of high nutrient availability seemed to have masked consumer richness effects.     

Geographic locality and host identity shape fungal endophyte communities in cupressaceous trees

Understanding how fungal endophyte communities differ in abundance, diversity, taxonomic composition, and host affinity over the geographic ranges of their hosts is key to understanding the ecology and evolutionary context of endophyte–plant associations. We examined endophytes associated with healthy photosynthetic tissues of three closely related tree species in the Cupressaceae (Coniferales): two native species within their natural ranges [Juniperus virginiana in a mesic semideciduous forest, North Carolina (NC); Cupressus arizonica, under xeric conditions, Arizona (AZ)], and a non-native species planted in each site (Platycladus orientalis). Endophytes were recovered from 229 of 960 tissue segments and represented at least 35 species of Ascomycota. Isolation frequency was more than threefold greater for plants in NC than in AZ, and was 2.5 (AZ) to four (NC) times greater for non-native Platycladus than for Cupressus or Juniperus. Analyses of ITS rDNA for 109 representative isolates showed that endophyte diversity was more than twofold greater in NC than in AZ, and that endophytes recovered in AZ were more likely to be host-generalists relative to those in NC. Different endophyte genera dominated the assemblages of each host species/locality combination, but in both localities, Platycladus harboured less diverse and more cosmopolitan endophytes than did either native host. Parsimony and Bayesian analyses for four classes of Ascomycota (Dothideomycetes, Sordariomycetes, Pezizomycetes, Eurotiomycetes) based on LSU rDNA data (ca 1.2 kb) showed that well-supported clades of endophytes frequently contained representatives of a single locality or host species, underscoring the importance of both geography and host identity in shaping a given plant's endophyte community. Together, our data show that not only do the abundance, diversity, and taxonomic composition of endophyte communities differ as a function of host identity and locality, but that host affinities of those communities are variable as well.     

The distribution,abundance, and the effects of fire on mound building termites (Trinervitermes and Cubitermes spp., Isoptera: Termitidae) in northern guinea savanna West Africa

Summary Termite mound densities in typical guinea savanna, Detarium, and grassland (boval) habitats in northern guinea savanna were determined by random quadratting of 2–3 sites in each habitat (100, 10x10 m quadrats per habitat). Dominant species in guinea savanna were T. geminatus (46 mounds ha^-1) and T. oeconomus (21 mounds ha^-1), in Detarium T. geminatus (59 mounds ha^-1) and C. curtatus (45 mounds ha^-1) and in boval C. curtatus (72 mounds ha^-1) and T. geminatus (22 mounds ha^-1). Only C. curtatus densities and total densities differed significantly between sites within habitats, but all species differed significantly in abundance between habitats. The composition of each community was related to general environment but no particular environmental variable was shown to be a major determinant of termite distribution. Evidence for the limitation of termite populations was obtained from indirect evidence of competition between colonies in Detarium, and by experimental manipulation of fire regimes in the typical guinea savanna habitat. Harvester termites increased four-five fold over two years in fire-protected plots as a result of increased food supplies. Total termite densities in the fire-protected community equilibrated to the new population density (100 mounds ha^-1) after only two-three years.     

Host-preference and density of woodrose-forming mistletoes (Loranthaceae) on savanna vegetation,South Africa

In the Bushbuckridge region of South Africa host preference and density of two woodrose-forming mistletoes, Erianthemum dregei (Eckl. & Zeyh.) V. Tieghem and Pedistylis galpinii (Schinz ex Sprague) was quantified in relation to land-use (harvested or unharvested), rainfall (high > 660 or low < 660 mm year^–1) and catenal position (top or lower slope). These two mistletoes are generalist hemi-parasites of savanna trees and shrubs occurring on 25 and 17 hosts respectively, seven of which are shared. Thirty-six percent of woody plant species recorded were found to be hosts. Although Sclerocarya birrea (A. Rich.) Hochst. comprised only 4% of woody plant density in the environment, it was the principal host for both mistletoes, accounting for 71% of total E. dregei and 42% of P. galpinii infection. Mistletoe infection relative to density of Ficus stuhlmanii, Trichilia emetica and Cassine transvaalensis indicated that these were preferential hosts to S. birrea. Mistletoe host preference was negatively correlated with host wood density. Mistletoe number per tree had a weak relationship to canopy size. Mistletoes of all size classes were denser at high rainfall relative to low rainfall sites. Interestingly, the overall mistletoe size class distribution was similar between harvested and unharvested sites. The ratio of living to dead mistletoe was 2 to 1 for E. dregei and 1.5 to 1 for P. galpinii. There are sufficient dead mistletoes in unharvested and harvested areas to satisfy present market demand. Living E. dregei predominated in harvested rather than unharvested areas suggesting that current-harvesting levels had little or no negative effect on the population. In contrast, P. galpinii was denser in unharvested areas possibly owing to its higher market value and thus higher harvesting levels.     

Use of vegetation classification and plant indicators to assess grazing abandonment in Estonian coastal wetlands

Question: What are the effects of grazing abandonment on the vegetation composition of Estonian coastal wetlands? Location: Vormsi Island and Silma Nature Reserve in western Estonia, Europe. Methods: Local knowledge and field reconnaissance were used to identify current and historical management levels of wetland sites within the west Estonian study area. Nine study sites, with varying management histories, were selected comprising an area of 287 ha. A total of 198 quadrats were taken from 43 distinct vegetation patches in five of the sites. TWINSPAN analysis was used to identify community type, and a phytosociological key was constructed for character taxa. This vegetation classification was then applied within a GIS‐based context to classify all the study sites, using a ground survey technique and 1:2000 scale air photos. Results: We identified 11 different brackish coastal wetland community types. Indicator species were defined with community characteristics for the seven main vegetation types readily recognisable in the field. Coastal wet grasslands were most extensive in grazed sites, or sites that had been more intensively grazed, while abandoned sites were largely composed of Phragmites australis stands, tall grassland, and scrub. Site variations based on vegetation composition were significantly correlated with past grazing intensity. Plant community types showed significant edaphic differences, with particularly low soil moisture and high conductivity and pH for open pioneer patches compared to other vegetation types. Conclusion: Abandonment of traditionally grazed coastal grasslands threatens their characteristic biodiversity. This study found that grazing abandonment reduced the extent of coastal wetland grasslands of particular conservation value. Nevertheless, plant species of conservation interest were found across the sequence of community types described. The study shows that grazing is an important factor influencing coastal wetland plant communities but suggests that vegetation distribution is affected by environmental variables, such as topography.     

Influence of Forest Types and Effects of Forestry Activities on Species Richness and Composition of Chrysomelidae in the Central Mountainous Region of Japan

Species richness and composition of the Chrysomelidae (Coleoptera) were studied in larch (Larix kaempheri [Lamb.] Carrière) plantations, secondary forests, and primary forests. In addition, the effects of forest management practices, such as thinning and long rotation, were examined in the larch plantation. The species richness of Chrysomelidae was higher in the larch plantation than in the secondary forest or in the primary forest. Among the larch plantations, the species richness in old-aged plantations was higher than that in middle-aged plantations. The composition of the beetle assemblages in the larch plantation differed from that in the secondary forest or in the primary forest. Exosoma akkoae (Chujo), Batophila acutangula Heikertinger, and Calomicrus nobyi Chujo were caught with a bias toward the larch plantation. Longitarsus succineus (Foudras) and Sphaeroderma tarsatum Baly were caught more in the secondary forest and the primary forest, respectively. More B. acutangula and S. tarsatum were caught in stands where their host plants occurred at higher rates. Species richness of understory plants was an important factor for chrysomlid species richness, and frequency of host occurrence affected the number of individuals of leaf beetles examined. It seems that forest types and forest management practices affect host plants as well as Chrysomelidae, and that these effects on the host plants also influence chrysomelid assemblages.     

Using Piper Species Diversity to Identify Conservation Priorities in the Chocó Region of Colombia

The forests of the Chocó Region are among the most diverse in the world, however they are under imminent threat of significant degradation. This study uses species diversity and phylogenetic data in the plant genus Piper to select areas of maximum biological diversity to be considered as conservation priorities. Species distributions were obtained from herbarium collections and the literature. A molecular phylogeny based on nucleotide sequence data from the ITS region of the nuclear genome was used to estimate phylogenetic diversity indices. Three diversity indices were estimated: total species richness, number of endemic species, and phylogenetic diversity. Area selection was conducted by maximizing the total value for these indices and also by complementarity. Four regions were selected as the highest conservation priorities: the vicinity of Buenaventura, the Rio San Juan watershed (south of Quibdó), the department of Nariño, and the Rio Atrato watershed. All of them had the highest rankings for all or some of the diversity indices evaluated. Furthermore, this study shows that in the Chocó Region, Piper phylogenetic diversity increases with total number of species, but decreases with the proportion of endemics.     

Foraging and building in subterranean termites: task switchers or reserve labourers?

Task-switching between foraging and building in workers of Nasutitermes exitiosus (Termitidae), a subterranean termite, was followed using mark-recapture. Foragers were collected from wood-filled drums and marked with Nile blue (ca. 12,500 per colony), whereas builders were collected from damaged sections of mounds and marked with Neutral red (ca. 18,500 per colony). Two protocols were followed: the first marked foragers and then damaged the mound; the second reversed this order. In the first protocol few foragers switched to building, i.e. blue-marked workers in mound samples, measured either as numbers (81 ± 28) or proportion of originally marked (0.66 ± 0.20 %); whereas more than double blue-marked foragers remained foraging (222 ± 64 workers or 1.76 ± 0.44 %). In the second protocol few builders had switched to foraging, i.e. red-marked workers found in the first drum sample (82 ± 33 workers or 0.29 ± 0.09 %). Up to eight drums were sampled for foragers over about 80 days; the numbers of blue-marked workers decreased slowly (ca. 1.6 workers per day) whereas those of red-marked workers increased slowly (ca. 2.4 workers per day). These results suggest that relatively few termite workers switch directly between foraging and building. The possibility of builders being recruited from other tasks is discussed. Received 24 March 2005; revised 27 June 2005; accepted 2 July 2005.     

The effect of increased nutrient availability on vegetation dynamics in wet heathlands

A three year fertilization experiment was conducted in which nitrogen (N series: 20 g N m^–2 yr^–1), phosphorus (P series: 4 g P m^–2 yr^–1) and potassium (K series: 20 g K m^–2 yr^–1) were added to a mixed vegetation of Erica tetralix and Molinia caerulea. At the end of each growing season the percentage cover of each species was determined. At the end of the experiment percentage cover of each species was found to be positively correlated with the harvested biomass. In the unfertilized control series the cover of Erica and Molinia did not change significantly during the experiment. In all fertilized series however, especially in the P series, cover of Erica decreased significantly. The cover of Molinia increased significantly in the P series only.In the fertilized series the biomass of Erica and total biomass per plot did not change significantly compared with the control series. In the P series the biomass of Molinia increased significantly.It is suggested that with increasing phosphorus or nitrogen availability Molinia outcompetes Erica because the former invests more biomass in leaves which in turn permits more carbon to be allocated to the root system, which thereupon leads to a higher nutrient uptake.     

Edaphic limitations to growth and photosynthesis in Sierran and Great Basin vegetation

Summary Soils derived from hydrothermally altered andesite support unique communities of Sierran conifers (Pinus ponderosa Laws. and P. jeffreyi Grev. and Balf.) amongst sagebrush (Artemisia tridentata Nutt.) vegetation in the western Great Basin. Plants grown in soil derived from hydrothermally altered bedrock had lower growth rates, total biomass, and net photosynthetic rates than plants grown in soil derived from unaltered andesite of the same formation. Total dry mass was 10 to 28% lower for conifers grown in altered soil whereas dry mass of Artemisia tridentata and Bromus tectorum L. was reduced by over 90%. Results from a nutrient amendment experiment indicated that low phosphorus was the dominant limitation in altered soil, and phosphorus-deficiency affected growth primarily by limiting leaf area development rather than direct inhibition of photosynthesis. The proportionately greater reduction of biomass for Artemisia and Bromus grown in altered soil supports our hypothesis that Great Basin vegetation is excluded from altered soil by intolerance to nutrient deficiency. The Sierran conifers growing on this rock type are therefore free of competition for water with Great Basin vegetation and are able to persist in an exceptionally dry climate.     

Species richness and seasonal abundance of ectomycorrhizal fungi in plantations of<Emphasis Type="Italic"> Eucalyptus dunnii</Emphasis> and<Emphasis Type="Italic"> Pinus taeda</Emphasis> in southern Brazil

The abundance and diversity of ectomycorrhizal fungi (EMF) was assessed based on the collection of basidiocarps during 12 months comprising the spring of 1995, and the summer, autumn, and winter of 1996, in three stands of young, middle-aged, and rotation age plantations of Pinus taeda and Eucalyptus dunnii, in the state of Santa Catarina, southern Brazil. A total of 3,085 collections yielded 34 presumed EMF taxa in ten genera, including mushroom-like and sequestrate species. Fruiting patterns of EMF differed with host and season, and host specificity was apparent in some. The overall relative importance (RI) and the Shannon diversity index (H) suggested that stands of E. dunnii had a more diverse aboveground EMF community than those of P. taeda. Overall, species of Scleroderma and Laccaria were not only the most abundant but also had the highest biomass values. The results show that a small number of species of abundant biomass and a larger number of species of less-abundant biomass characterize each forest class.     

Biogeography of wild <Emphasis Type="Italic">Arachis</Emphasis> (<Emphasis Type="Italic">Leguminosae</Emphasis>):distribution and environmental characterisation

Geographic Information System (GIS) tools are applied to a comprehensive database of 3514 records of wild Arachis species to assist in the conservation and utilisation of the species by: (a) determining the distributional range of species and their abundance; (b) characterising species environments; (c) determining the geographical distribution of species richness; and (d) determining the extent to which species are associated with river basins. Distributional ranges, climatic variables and indices of endemism for each species are tabulated. A. duranensis Krapov. & W.C. Gregory, the most probable donor of the A genome to the cultivated peanut, is distributed in close proximity to both the proposed donor of the B genome, A. ipaënsis, and the closest wild relative of the cultigen, A. monticola Krapov. & Rigoni. This region in the eastern foothills of the Andes and the adjoining chaco regions of Argentina, Bolivia and Paraguay, is a key area for further exploration for wild Arachis. An area of particularly high species richness occurs in the State of Mato Grosso, close to the Gran Pantanal in southwest Brazil. Seventy-one percent of the species were found to have some degree of association with water catchment areas, although in most cases it was difficult to determine whether this was due to climatic adaptation reasons, restricted dispersal due to geocarpic habit, or the role of watercourses as a principal dispersal agent. In only two cases could climatic adaptation be eliminated as the reason for species distribution.     

The effect of seeds of exotic species transported via horse dung on vegetation along trail corridors

It has been suggested that exotic species will colonize within forests more frequently by the continual introduction of seeds through horse dung deposited along trails. Whether or not these exotic species have the ability to spread into and establish in the forest interior has been disputed. To address this, horse dung and soil samples were collected from trails during Autumn 1994 and Summer 1995 from three areas in southern Illinois, USA open to recreational horse travel. In addition, deer dung samples were collected from each of the study areas. Vegetation data were collected from each of the trail systems as well as from a trail along which horse travel was prohibited. The density of vascular plants in 0.25 m² quadrats placed at varying distances from the trail center to 5 m into the forest interior were recorded. Finally, dung samples were placed in situ along horse trails at one site to examine seedling germination in natural conditions. While 23 exotic species germinated from samples of horse dung placed out in a greenhouse, only one of these exotic species was also found in trail plots (Kummerowia striata). Similarly, while there were empirically more exotic species found along the trails allowing horse travel than there were on the trail lacking horse travel, the relative importance of those species was negligible along both trails. These results suggest that the emigration of exotic species via horse dung does not pose an immediate threat to the plant communities adjacent to trails in these forest systems. Nevertheless, the large number of exotic species in horse dung reflects the constant threat to any system from these species. Care must be taken, when allowing horseback use in areas, to anticipate invasion by exotic species from horse dung     

青藏高原两种植被类型净初级生产力与气候因素的关系及周转值分析

基于2008—2016年青海海北站9年净初级生产力及气候因子监测数据,分析了青藏高原高寒小嵩草草甸和高寒金露梅灌丛两种植被净初级生产力年际动态,并探讨了气候因子对其影响及其不同土层深度根系周转值特征。结果表明:(1)年际尺度上,小嵩草草甸地上净初级生产力表现为显著增加趋势,增幅为7.02 g m~(-2) a~(-1),而金露梅灌丛地上净初级生产力相对较为稳定;对于其地下净初级生产力和总生产力,小嵩草草甸和金露梅灌丛均表现为增加趋势(P0.05),9年间小嵩草草甸地上、地下和总净初级生产力平均值分别为(217.55±9.95)、(1882.75±161.33) g m~(-2) a~(-1)和(2100.30±163.38) g m~(-2) a~(-1),金露梅灌丛地上、地下和总净初级生产力9年间平均值分别为(256.27±11.4)、(1614.31±173.03) g m~(-2) a~(-1)和(1870.58±177.93) g m~(-2) a~(-1)。(2)不同植被类型地上净初级生产力对气候因素响应不同,金露梅灌丛地上净初级生产力主要受温度影响,而温度对小嵩草草甸地上净初级生产力无显著影响。此外,降水不是限制高寒生态系统草地地上净初级生产力主要因子,相比于降水影响,高寒生态系统地上净初级生产力更受温度调控。(3)年均温和年降水对金露梅灌丛和小嵩草草甸地下净初级生产力均无显著影响(P0.05),表明高寒生态系统,其地下生产力受外界气候条件变化影响微弱,是一个稳定的碳库。(4)两种植被类型其根系周转值均随着土壤深度的增加呈逐渐增加趋势,且高寒灌丛根系周转值明显高于高寒草甸根系周转值。研究表明,在全球气候变暖背景下将会增加金露梅灌丛地上净初级生产力,而对小嵩草草甸地上净初级生产力无显著影响。     

Herbivore responses to nutrient enrichment and landscape heterogeneity in a mangrove ecosystem

Complex gradients in forest structure across the landscape of offshore mangrove islands in Belize are associated with nutrient deficiency and flooding. While nutrient availability can affect many ecological processes, here we investigate how N and P enrichment interact with forest structure in three distinct zones (fringe, transition, dwarf) to alter patterns of herbivory as a function of folivory, loss of yield, and tissue mining. The effects of nutrient addition and zone varied by functional feeding group or specific herbivore. Folivory ranged from 0 to 0.4% leaf area damaged per month, but rates did not vary by either nutrient enrichment or zone. Leaf lifetime damage ranged from 3 to 10% of the total leaf area and was caused primarily by the omnivorous tree crab Aratus pisonii. We detected two distinct spatial scales of response by A. pisonii that were unrelated to nutrient treatment, i.e., most feeding damage occurred in the fringe zone and crabs fed primarily on the oldest leaves in the canopy. Loss of yield caused by the bud moth Ecdytolopha sp. varied by zone but not by nutrient treatment. A periderm-mining Marmara sp. responded positively to nutrient enrichment and closely mirrored the growth response by Rhizophora mangle across the tree height gradient. In contrast, a leaf-mining Marmara sp. was controlled by parasitoids and predators that killed >89% of its larvae. Thus, nutrient availability altered patterns of herbivory of some but not all mangrove herbivores. These findings support the hypothesis that landscape heterogeneity of the biotic and abiotic environment has species-specific effects on community structure and trophic interactions. Predicting how herbivores respond to nutrient over-enrichment in mangrove ecosystems also requires an assessment of habitat heterogeneity coupled with feeding strategies and species-specific behavior measured on multiple scales of response.     

Diversity measurements in shrubland communities of Galicia (NW Spain)

Diversity was studied in 10 communities, including the understory of native oak woodland, planted woodlands (pine and eucalypt), and shrublands in the strict sense (heathlands, broom shrublands, gorse shrublands).In each community, species richness, diversity, dominance and evenness were analysed. Differences were observed among communities with regard to species composition, richness in annual herbs, perennial herbs and shrubs, dominant plant families (Ericaceae, Papilionaceae) and diversification of shrub species.The possible relations between environmental stress and/or human influences on differences in diversity are discussed.