崖柏群落植物区系分析及其最优垂直结构搭配探究

崖柏(Thuja sutchuenensis Franch.)为中国特有珍稀濒危裸子植物。在多次调查的基础上,通过区系分析、聚类分析和热图分析等方法,对大巴山崖柏群落的区系特点、群落结构和搭配模式进行了研究,以明确群落区系的本质特征及伴生物种的成层结构对崖柏种群的影响。结果表明:(1)崖柏的伴生物种组成丰富,地理成分较为复杂,区系成分主要以温带成分为主;物种生活型以矮高位芽植物、地面芽植物和小高位芽植物占优势。(2)样地间聚类分析结果表明,海拔和空间地理位置是影响崖柏群落伴生植物区系组成的重要因素。(3)崖柏群落平均高度越矮越有利于崖柏种群的扩大和延续;其中,群落以灌木层、乔木下层类群为主时,崖柏种群内个体数量最多。(4)根据优势种热图结果分析,以崖柏为优势种的群落结构中,乔木层物种搭配以崖柏+多脉青冈+川陕鹅耳枥、崖柏+川柯+小叶青冈和崖柏+马尾松+高山栎最优,灌木层物种搭配以崖柏+球核荚蒾+豪猪刺、崖柏+粉背黄栌最优。(5)较为丰富的物种多样性和高大的伴生物种给崖柏种群造成较大威胁,结合崖柏群落的垂直结构构建适合崖柏种群延续和扩大的物种搭配模式对于崖柏的保护尤为重要。     

Spatial distribution and regeneration of Quercus semecarpifolia and Quercus floribunda in a subalpine forest of western Himalaya, India

Studies were conducted on population status and regeneration of Quercus semecarpifolia and Quercus floribunda in a subalpine forest of western Himalaya. Saplings of Q. semecarpifolia belonging to the 51-100 cm size class and those of Q. floribunda belonging to the 101-150 cm size class were well represented in studied subalpine forests. Comparable seedling emergence and establishment of both species, either in the habitat dominated by same or different species seems to be an adaptational strategy of these species in subalpine forests. Seedling to tree ratio for Q. semecarpifolia was higher in the stand dominated by Q. floribunda, while comparable pattern was observed for Q. floribunda in the stand dominated by Q. semecarpifolia. Establishment of higher percent of seedlings of one species in the habitats dominated by another species of Quercus appears to indicate an oligarchic nature of oaks in subalpine forests. This study describes regeneration strategies, and spatial distribution of these species in a subalpine forest of Uttarakhand.     

Structures and topographical pattern of the tree layer of Fagus engleriana-Cyclobalanopsis oxyodon community in Shennongjia area, Hubei Province, China

Shennongjia represents an area of considerable plant biodiversity, not only for China but for the whole world. The numerous species are distributed along an altitude gradient. The genus Fagus, commonly known as Beeches, constitutes one of the dominant woody species of the humid temperate forests in China. This paper deals with the community structure of a mixed, broadleaved deciduous-evergreen beech forest dominated by the Fagus engleriana and Cyclobalanopsis oxyodon, which occurs along an altitude gradient range in this area. The community consists of 46 woody species, belonging to 22 families and 27 genera. The tree layer can be divided into three sub-strata. The upper layer is composed of deciduous trees, 80.7% of which is F. engleriana. The second and third layers are dominated by the evergreen species, such as C. oxyodon and the Rhododendron hypoglaucum. These species increase from 55.9% in the second layer to 80.5% in the third, and regeneration at that rate allows us to assume that the stability of the community may be guaranteed. The micro-site heterogeneity plays an important role in maintaining species diversity in plant communities. In this research, a terrain surface of 0.96 hm² was simulated using the digital elevation model (DEM) in order to analyze the influence of the topography on plant community structures on a small scale. The slope relief aspect obtained with the DEM showed an accentuated heterogeneity. Semivariance analysis was used to measure the heterogeneity scale. The range and nugget variance of the semivariograms for slope were 285.8 and 280.5, respectively; for aspect, were 21.8 and 498, respectively. The elevated value of the nugget variance suggested that even on a small scale, the topographic variations influenced the species distribution. Twenty-four species were selected to estimate the correlation coefficient between the slope, aspect, and orientation. Then based on the correlation results using the Square Euclidean Distance cluster analysis, the 24 species were divided into four groups.     

Seed dispersal of three sympatric oak species by forest rodents in the Qinling Mountains, Central China

Forest rodents play an essential role as seed dispersal vectors through their caching behaviors. Using seeds of Quercus aliena, Q. glandulifera, and Cyclobalanopsis engleriana (Fagaceae), which are dominant, but poorly studied species, in the Qinling Mountains, Central China, we investigated seed predation and dispersal by forest rodents in 2010 and 2011. There were significant differences in rodent seed-eating and caching strategies among the three tree species. Seeds of Q. aliena and C. engleriana had hard coats, high nutrition contents (e.g., protein, fat, and starch), and long germination schedules (C. engleriana only). They were less frequently eaten in situ, but more likely to be eaten after removal or cached. Seeds of Q. glandulifera had soft coats and low nutrition contents and were more often eaten in situ and less likely to be eaten after removal or cached. Our findings indicated that forest rodents were primarily responsible for seed predation and dispersal of these three tree species in the Qinling Mountains, and seed traits, especially coat hardness, nutrition content, and germination schedule, were important factors influencing rodent eating and caching behaviors. In addition, seed dispersal process of each tree species differed significantly between the 2 years, reflecting the effect of mast seeding on the eating and caching strategies of forest rodents.     

Community structure of a species-rich temperate forest,Ogawa Forest Reserve,central Japan

Species assembly and niche differentiation were studied, and future species composition was predicted by simple Markov models, in an old-growth deciduous forest at the Ogawa Forest Reserve in central Japan. The dominant species in our 6ha study site are Quercus serrata, Fagus japonica, and F. crenata.An ordination by population parameters revealed four different combination 3 of life forms and regeneration niches. Cluster analysis based on interspecific spatial correlation revealed three groups of species. The species in cluster A, such as F. japonica, occurred at the bottom of the valley, while those in cluster B, such as Q. serrata, occurred along ridges. Species in cluster C, such as F. crenata, did not show any particular habitat preference. Clusters B and C were further divided into three smaller clusters (a-c). Both clusters Ba and Bb included shade intolerant species. Species in cluster Ba had large clump sizes (>1500 m²), reflecting regeneration following large-scale disturbances. Species in cluster Bb had smaller clump sizes (<400 m²) reflecting regeneration following local disturbances. Clusters Ca and Cb mainly included shade tolerant species and shade intolerant species, respectively. Markov models predicted that shade intolerant species, particularly those in cluster Ba, would be eliminated. Thus, species coexist by differentiation of both habitats and regeneration niche in this forest community. Some species such as Quercus serrata, however, regenerate following large-scale disturbances or human activity.     

Population persistence of a Tertiary relict tree Tetracentron sinense on the Ailao Mountains, Yunnan, China

The persistence of the Tertiary relict tree Tetracentron sinense Oliv. on the eastern slope of the Ailao Mountains, Yunnan, SW China, was here studied in terms of population structure (size, age) and regeneration patterns. T. sinense occurred in unstable habitats by stream banks, on steep slopes, on scree slopes, or on roadsides near streams in narrow valleys, all places subject to frequent natural disturbances, whereas none were found on stable gentle slopes free of major disturbances at similar altitudes. Further, no established saplings of T. sinense were found in forests having high bamboo (Yushania crassicollis Yi) coverage in their understory. The size and age structure of T. sinense were multimodal. The reproduction of the tree was either by means of abundant minute wind-dispersed seeds or by resprouts in unstable habitats. These populations depended on disturbance or gap regeneration to survive. T. sinense, along with other tree life-forms including evergreen broad-leaved species and conifers, dominated in the forest canopy layer, even reaching the emergent layer in places. Results of the study provide insight into the ecological characteristics and survival mechanisms of this East Asian paleoendemic tree species. The study will provide a scientific basis for recommendations for the conservation of this species and for other Tertiary relict plants having similar regeneration dynamics.     

Secondary succession after perturbations in a shrubland community

Shrubland responses to experimental burning, cutting and ploughing treatments were studied over 15 years in two shrubland communities dominated by Erica australis. The treatments represent the most frequent forms of anthropogenic disturbances experienced by these communities throughout their history. The response to burning and cutting treatments is similar, and the succession process is characterised as autosuccession. The highest values for herbaceous annuals and perennials were observed in the third and fourth years. Generally, herbaceous species remain present throughout the study period, while woody taxa ones increase their cover values over time. The quantity of herbaceous species present is in inverse proportion to the quantity of woody taxa. The woody species that appear immediately after treatments are sprouting species, namely Erica australis and Arctostaphylos uva-ursi. The response to ploughing is slower, reflecting the recovery mechanism (seedlings). However, after 15 years, there are no significant differences in regeneration between treatments. The first stages of this post-ploughing succession are dominated by annual species until the fourth or fifth years, after which woody species begin to dominate and herbaceous taxa decrease considerably. Woody species with high germination values are Halimium alyssoides and Halimium umbellatum. These shrubland communities have a very high resilience to such perturbations and start regenerating rapidly, reaching the original state in about 9 years. The appearance of the climax arboreal species of the area, Quercus pyrenaica, when it comes from germination, occurs 15 years after the perturbations.     

More than just drought: complexity of recruitment patterns in Mediterranean forests

Understanding community dynamics during early life stages of trees is critical for the prediction of future species composition. In Mediterranean forests drought is a major constraint for regeneration, but likely not the only factor determining the observed spatial patterns. We carried out a sowing experiment aimed at identifying main filters during seed-seedling transition. Specifically, we studied seed fate (predation, fungi infection, emergence) and subsequent seedling performance (mortality during the first summer and overall recruitment after 2 years) of four co-occurring Mediterranean tree species (Quercus ilex, Quercus faginea, Juniperus thurifera, Pinus nigra). We related these processes to the dominant species composition, microhabitat heterogeneity, herb cover and seed mass. The identity of the dominant species in the forest canopy was more important for recruitment than the forest canopy being dominated by conspecific vs. heterospecific species. The patterns we found suggest that biotic interactions such as facilitation (lower mortality under the canopies) and herb competition (during emergence of J. thurifera) are relevant during recruitment. Moreover, our results pointed to ontogenetic conflicts regarding the seed mass of Q. faginea and to density-dependent seed mortality for Q. ilex, rarely described in Mediterranean ecosystems. We propose that our study species experience population growth in forests dominated by heterospecifics where the recruitment success depends on habitat heterogeneity and on moderated biotic and abiotic stresses created by each species. Our results reveal patterns and mechanisms involved in recruitment constraints that add complexity to the well-known drought-related processes in Mediterranean ecosystems.     

Ecological and biogeographical analyses of Mediterranean forests of northern Morocco

Mediterranean forests in northern Morocco have been studied. Tree species composition and abundance were investigated in 84 forest sites, distributed throughout the sandstone formation of the Tangier region. The relative abundance of 15 tree and arborescent shrub species was related, by ordination analysis, to altitude, disturbance by fire, and soil fertility. High-elevation forests were dominated by Cedrus atlantica, Quercus pyrenaica and Pinus pinaster. Sacred forests (protected as holy burial places) had a distinct stand structure, and were considered as refuges, for maintaining biodiversity at landscape scale. The evergreen oak Quercus suber and the semideciduous Quercus canariensis co-dominated the lowland forests. The mean basal area of the studied forests was 34 m² ha^–1. The mean trunk size (dbh) for Q. suber was 24 cm and for Q. canariensis 36.5 cm; in both cases there were indications of declining regeneration at population level. A comparative biogeographical analysis with the equivalent region in southern Spain (separated by the Strait of Gibraltar; 14 km wide), indicated a possible biodiversity loss in the Moroccan forests.     

A molecular survey of ectomycorrhizal hyphae in a California Quercus–Pinus woodland

Ectomycorrhizal (ECM) hyphal communities have not been well characterized. Furthermore, there have been few studies where the ECM hyphal community is compared to fungi detected as sporocarps or ECM-colonized root tips. We investigated fungi present as hyphae in a well-studied California Quercus–Pinus woodland. Hyphal species present were compared to those found as sporocarps and ECM root tips at the same site. Hyphae were extracted from root-restrictive nylon mesh in-growth bags buried in the soil near mature Quercus douglasii, Quercus wislizeni, and Pinus sabiniana. Taxa were identified using PCR, cloning, and DNA sequencing of internal transcribed spacer and 28s rDNA. Among the 33 species detected, rhizomorph-forming ECM fungi dominated the hyphal community, especially species of Thelephoraceae and Boletales. Most fungi in soils near Quercus spp. and P. sabiniana were ECM basidiomycetes, but we detected two ECM ascomycetes and three non-mycorrhizal fungi. Many ECM species present as hyphae were also previously detected at this site as sporocarps (18%) or on ECM root tips (58%). However, the hyphal community was mostly dominated by different taxa than either the sporocarp or ECM root communities.     

Morphological and Molecular Phylogenetic Data Reveal a New Species of Primula (Primulaceae) from Hunan,China

A new species of Primulaceae, Primula undulifolia, is described from the hilly area of Hunan province in south-central China. Its morphology and distributional range suggest that it is allied to P. kwangtungensis, both adapted to subtropical climate, having contiguous distribution and similar habitat, growing on shady and moist cliffs. Petioles, scapes and pedicels of them are densely covered with rusty multicellular hairs, but the new species can be easily distinguished by its smaller flowers and narrowly oblong leaves with undulate margins. Molecular phylogenetic analysis based on four DNA markers (ITS, matK, trnL-F and rps16) confirmed the new species as an independent lineage and constitutes a main clade together with P. kwangtungensis, P. kweichouensis, P. wangii and P. hunanensis of Primula sect. Carolinella.     

A Neighborhood Analysis of the Consequences of Quercus suber Decline for Regeneration Dynamics in Mediterranean Forests

In forests, the vulnerable seedling stage is largely influenced by the canopy, which modifies the surrounding environment. Consequently, any alteration in the characteristics of the canopy, such as those promoted by forest dieback, might impact regeneration dynamics. Our work analyzes the interaction between canopy neighbors and seedlings in Mediterranean forests affected by the decline of their dominant species (Quercus suber). Our objective was to understand how the impacts of neighbor trees and shrubs on recruitment could affect future dynamics of these declining forests. Seeds of the three dominant tree species (Quercus suber, Olea europaea and Quercus canariensis) were sown in six sites during two consecutive years. Using a spatially-explicit, neighborhood approach we developed models that explained the observed spatial variation in seedling emergence, survival, growth and photochemical efficiency as a function of the size, identity, health, abundance and distribution of adult trees and shrubs in the neighborhood. We found strong neighborhood effects for all the performance estimators, particularly seedling emergence and survival. Tree neighbors positively affected emergence, independently of species identity or health. Alternatively, seedling survival was much lower in neighborhoods dominated by defoliated and dead Q. suber trees than in neighborhoods dominated by healthy trees. For the two oak species, these negative effects were consistent over the three years of the experimental seedlings. These results indicate that ongoing changes in species’ relative abundance and canopy trees’ health might alter the successional trajectories of Mediterranean oak-forests through neighbor-specific impacts on seedlings. The recruitment failure of dominant late-successional oaks in the gaps opened after Q. suber death would indirectly favor the establishment of other coexisting woody species, such as drought-tolerant shrubs. This could lead current forests to shift into open systems with lower tree cover. Adult canopy decline would therefore represent an additional factor threatening the recruitment of Quercus forests worldwide.     

Obolarina persica sp. nov., associated with dying Quercus in Iran

A new species, Obolarina persica, is described from Iran. It is widely associated with dying Quercus brantii, on which it produces charcoal-like stromata. The fungus described herein differs from the other described species, Ob. dryophila, primarily in its much larger ascospores.     

Epilithic and Cryptoendolithic Cyanobacteria of Clarens Sandstone Cliffs in the Golden Gate Highlands National Park,South Africa

A cryptoendolithic cyanobacterial community is described from Clarens sandstone in a montane ecosystem of the north-eastern Orange Free State, South Africa. The community is dominated by a species of the unicellular cyanobacterial genus Chroococcidiopsis. Chlorophyll_a content of the colonised sandstone ranged between 44.3 and 51.8mg m^?2. The establishment and species composition of an artificially created tintenstrich cyanobacterial community is documented. The possible contribution of cryptoendolithic cyanobacterial communities in the biological formation of hollows and caves in Clarens sandstone cliffs is discussed.     

长白山云冷杉林幼苗幼树空间分布格局及其更新特征

长白山云冷杉针阔混交林是我国东北主要的森林类型之一,其乔木树种幼苗幼树的结构和动态决定着未来林分的结构和生长动态。在长白山地区设置一块具有代表性的云冷杉针阔混交林幼苗幼树更新样地,统计分析幼苗幼树更新特征,绘制地径结构图、树高结构图及其空间分布图。运用点格局分析中的单变量O-ring统计方法,分析更新树种的空间分布格局;用双变量O-ring统计方法,分析更新树种种间的空间关联性。研究结果表明:(1)更新树种组成有冷杉(Abies nephrolepis)、色木槭(Acer mono)、紫椴(Tilia amurensis)、红皮云杉(Picea koraiensis)、红松(Pinus koraiensis)、蒙古栎(Quercus mongolica)、春榆(Ulmus japonica)7种,其中以冷杉、色木槭为主,更新幼苗幼树的地径近似呈倒J型分布,树高结构近似呈双峰分布;(2)所有更新树种、冷杉、色木槭在小尺度1—10 m的范围内呈聚集分布,随着尺度增加,聚集程度减弱,逐渐趋于均匀分布和随机分布,紫椴、云杉和红松在空间所有尺度上以随机分布为主;(3)更新树种之间的空间关联性在小尺度范围上正关联性比较多,较大尺度范围上负关联性比较多,随着尺度增加,空间关联性减弱。     

湘中丘陵区南酸枣阔叶林群落特征及群落更新

南酸枣阔叶林群落是湘中丘陵区的重要的森林群落类型之一,在森林演替过程中占有重要的地位。在湘中丘陵区长沙县大山冲林场的代表性群落——南酸枣阔叶林群落(The Choerospondias axillaries broad-leaved community)设立1 hm2固定样地,对其群落学特征进行调查,分析其植物多样性和更新动态。结果表明:群落中胸径≥1cm的乔木树种共有25科42属59种。乔木层中南酸枣(Choerospondias axillaries)的重要值最大(23.57),是群落中的建群种;南酸枣胸径和树高结构均呈正态分布,南酸枣幼苗(1.0cm≤DBH1.5cm)只有6株;群落中四川山矾(Symplocos setchuensis)的重要值(10.46)排第二,但胸径小于1.5 cm的幼树数量较多(占种群数量的22.0%),格药柃(Eurya muricata)、千年桐(Aleurites montana)和毛豹皮樟(Lindera coreana)的重要值分别为7.98(幼树数占种群数量的16.8%),5.39(幼树数占种群数量的11.7%),4.17(幼树数占种群数量的11.0%),这4个乔木树种的径级结构均呈倒J型分布;林分的成层结构中,上层木主要为南酸枣,下层木主要为四川山矾、格药柃、千年桐和毛豹皮樟。林下幼苗主要为常绿阔叶树种,且更新良好,并将成为下一个演替阶段的建群种。南酸枣的幼苗更新不良情况说明其在群落中的优势地位在逐年降低,而四川山矾、格药柃、千年桐、毛豹皮樟等树种的优势地位呈上升趋势,表明湘中丘陵区的南酸枣阔叶林群落正在朝常绿阔叶林的方向演替。灌木、草本层中共有植物37种,重要值前5位的种为檵木(Loropetalum chinensis)、满山红(Rhododendron mariesii)、乌饭(Vaccinium bracteatum)、栀子(Gardenia jasminoides)、映山红(Rhododendron simsii)分别为54.59、21.85、4.98、4.63、4.53,其中,檵木和满山红在灌木层中的优势地位明显。     

Growth,allometry and shade tolerance of understory saplings of four subalpine conifers in central Japan

The conifers Abies veitchii, A. mariesii, Picea jezoensis var. hondoensis, Tsuga diversifolia dominate in subalpine forests in central Japan. We expected that species differences in shade tolerance and in aboveground and belowground architecture are important for their coexistence. We examined net production and carbon allocation of understory saplings. Although the four species allocated similar amounts of biomass to roots at a given trunk height, the root-zone area of T. diversifolia was greater than that of the three other species. T. diversifolia often dominates shallow soil sites, such as ridge and rocky slopes, and, therefore, a wide spread of lateral roots would be an adaptation to such edaphic conditions. Crown width and leaf and branch mass were greatest for T. diversifolia and A. mariesii, followed in order by A. veitchii and P. jezoensis var. hondoensis. Although leaf mass of P. jezoensis var. hondoensis was lowest among the four species, species differences were not found in the net production per sapling because net production per leaf mass was greatest for P. jezoensis var. hondoensis. The leaf lifespan was longer in the order A. mariesii, T. diversifolia, P. jezoensis var. hondoensis and A. veitchii. The minimum rate of net production per leaf mass required to maintain the current sapling leaf mass (MRNP_LM) was lowest in A. mariesii and T. diversifolia, and increased in the order of A. veitchii and P. jezoensis var. hondoensis. A. mariesii and T. diversifolia may survive in shade conditions by a lower MRNP_LM than the two other species. Therefore, species differences in aboveground and belowground architecture and MRNP_LM reflected their shade tolerance and regeneration strategies, which contribute to their coexistence.     

Linking responses of native and invasive plants to hurricane disturbances: implications for coastal plant community structure

Hurricane disturbances produce significant changes in forest microclimates, creating opportunities for seedling regeneration of native and invasive plant species alike. However, there is limited information on how changes in microclimates and pre-existing forest conditions affect native and invasive plants responses to hurricane disturbances. In this manipulative study, we examined the responses of three common shrub/small stature tree species, two of which are native to the coastal region of the southeastern USA (Baccharis halimifolia and Morella cerifera) and one that is invasive (Triadica sebifera), to two key components of hurricane disturbance (canopy damage and saline storm surge). In a greenhouse, we grew seedlings of these species under a range of shade levels that mimicked pre-and post-hurricane canopy conditions for wet pine forest and mixed hardwood forest, two forest communities common in coastal areas of the southeastern USA. Seedlings were subjected to saline storm surges equivalent to full strength sea water for 3 days. Seedling responses (mortality and growth) to the treatments were monitored for 16 months. All species benefitted from higher canopy openness. Storm surge effects were short-lived and seedlings readily recovered under high light conditions. The storm surge had stronger negative effects on survival and growth of all species when coupled with high shade, suggesting storm surge has greater negative impacts on seedlings where hurricane winds cause minimal or no canopy damage. The invasive T. sebifera was by far more shade tolerant than the natives. Survival of T. sebifera seedlings under highly shaded conditions may provide it a competitive edge over native species during community reassembly following tropical storms. Differential responses of native and invasive species to hurricane disturbances will have profound consequences on community structure across coastal forest stands, and may be regulated by legacies of prior disturbances, community structure, extent of canopy damage, and species’ tolerance to specific microclimates.

     

Vegetation recovery and plant facilitation in a human-disturbed lava field in a megacity: searching tools for ecosystem restoration

Unplanned urban development threatens natural ecosystems. Assessing ecosystem recovery after anthropogenic disturbances and identifying plant species that may facilitate vegetation regeneration are critical for the conservation of biodiversity and ecosystem services in urban areas. At the periphery of Mexico City, illegal human settlements produced different levels of disturbance on natural plant communities developed on a lava field near the Ajusco mountain range. We assessed natural regeneration of plant communities 20 years after the abandonment of the settlements, in sites that received low (manual harvesting of non-timber forest products), medium (removal of aboveground vegetation), and high (removal of substrate and whole vegetation) disturbance levels. We also tested the potential facilitative role played by dominant tree and shrub species. Plant diversity and vegetation biomass decreased as disturbance level increased. Sites with high disturbance level showed poor regeneration and the lowest species similarity compared to the least disturbed sites. Six dominant species (i.e., those with the highest abundance, frequency, and/or basal area) were common to all sites. Among them, three species (the tree Buddleja cordata, and two shrubs, Ageratina glabrata and Sedum oxypetalum) were identified as potential facilitators of community regeneration, because plant density and species richness were significantly higher under their canopies than at open sites. We propose that analyzing community structural traits of the successional vegetation (such as species diversity and biomass) and identifying potential facilitator species are useful steps in assessing the recovery ability of plant communities to anthropogenic disturbances, and in designing restoration strategies.     

Altered Microbiomes in Bovine Digital Dermatitis Lesions,and the Gut as a Pathogen Reservoir

Bovine digital dermatitis (DD) is the most important infectious disease associated with lameness in cattle worldwide. Since the disease was first described in 1974, a series of Treponema species concurrent with other microbes have been identified in DD lesions, suggesting a polymicrobial etiology. However, the pathogenesis of DD and the source of the causative microbes remain unclear. Here we characterized the microbiomes of healthy skin and skin lesions in dairy cows affected with different stages of DD and investigated the gut microbiome as a potential reservoir for microbes associated with this disease. Discriminant analysis revealed that the microbiomes of healthy skin, active DD lesions (ulcerative and chronic ulcerative) and inactive DD lesions (healing and chronic proliferative) are completely distinct. Treponema denticola, Treponema maltophilum, Treponema medium, Treponema putidum, Treponema phagedenis and Treponema paraluiscuniculi were all found to be present in greater relative abundance in active DD lesions when compared with healthy skin and inactive DD lesions, and these same Treponema species were nearly ubiquitously present in rumen and fecal microbiomes. The relative abundance of Candidatus Amoebophilus asiaticus, a bacterium not previously reported in DD lesions, was increased in both active and inactive lesions when compared with healthy skin. In conclusion, our data support the concept that DD is a polymicrobial disease, with active DD lesions having a markedly distinct microbiome dominated by T. denticola, T. maltophilum, T. medium, T. putidum, T. phagedenis and T. paraluiscuniculi. Furthermore, these Treponema species are nearly ubiquitously found in rumen and fecal microbiomes, suggesting that the gut is an important reservoir of microbes involved in DD pathogenesis. Additionally, the bacterium Candidatus Amoebophilus asiaticus was highly abundant in active and inactive DD lesions.