Rock Outcrop Vegetation Research Articles

Seed functional ecology in Brazilian rock outcrop vegetation: an integrative synthesis.

Rock outcrop vegetation is distributed worldwide and hosts a diverse and unique flora that evolved under harsh environmental conditions. Unfortunately, seed ecology in such ecosystems has received little attention, especially regarding seed traits, germination responses to abiotic factors and the potential role of phylogenetic relatedness on such features Here, we provide the first quantitative and phylogenetically-informed synthesis of the seed functional ecology of Brazilian rock outcrop vegetation, with a particular focus on quartzitic and ironstone campo rupestre. Using a database of functional trait data, we calculated the phylogenetic signal of seven seed traits for 371 taxa and tested whether they varied among growth forms, geographic distribution, and microhabitats. We also conducted meta-analyses that included 4,252 germination records for 102 taxa to assess the effects of light, temperature, and fire-related cues on the germination of campo rupestre species and explored how the aforementioned ecological groups and seed traits modulate germination responses. All traits and germination responses showed a moderate-to-strong phylogenetic signal. Campo rupestre species responded positively to light and had maximum germination between 20-25 ºC. The effect of temperatures beyond this range was moderated by growth form, species geographic distribution, and microhabitat. Seeds exposed to heat shocks above 80 °C lost viability, but smoke accelerated germination. We found a moderating effect of seed mass for in responses to light and heat shocks, with larger, dormant seeds tolerating heat better but less sensitive to light. Species from xeric habitats evolved phenological strategies to synchronise germination during periods of increased soil water availability. Phylogenetic relatedness plays a major role in shaping seed ecology of Brazilian rock outcrop vegetation. Nevertheless, seed traits and germination responses varied significantly between growth forms, species geographic distribution and microhabitats, providing support to the regeneration niche hypothesis and the role of functional traits in shaping germination in these ecosystems.

Rock n' Seeds: A database of seed functional traits and germination experiments from Brazilian rock outcrop vegetation.

Advancing functional ecology depends fundamentally on the availability of data on reproductive traits, including those from tropical plants, which have been historically underrepresented in global trait databases. Although some valuable databases have been created recently, they are mainly restricted to temperate areas and vegetative traits such as leaf and wood traits. Here, we present Rock n' Seeds, a database of seed functional traits and germination experiments from Brazilian rock outcrop vegetation, recognized as outstanding centers of diversity and endemism. Data were compiled through a systematic literature search, resulting in 103 publications from which seed functional traits were extracted. The database includes information on 16 functional traits for 383 taxa from 148 genera, 50 families, and 25 orders. These 16 traits include two dispersal, six production, four morphological, two biophysical, and two germination traits-the major axes of the seed ecological spectrum. The database also provides raw data for 48 germination experiments, for a total of 10,187 records for 281 taxa. Germination experiments in the database assessed the effect of a wide range of abiotic and biotic factors on germination and different dormancy-breaking treatments. Notably, 8255 of these records include daily germination counts. This input will facilitate synthesizing germination data and using this database for a myriad of ecological questions. Given the variety of seed traits and the extensive germination information made available by this database, we expect it to be a valuable resource advancing comparative functional ecology and guiding seed-based restoration and biodiversity conservation in tropical megadiverse ecosystems. There are no copyright restrictions on the data; please cite this paper when using the current data in publications; also the authors would appreciate notification of how the data are used in publications.

Importance of Local Studies of Vascular Plant Communities in Conservation and Management: A Case Study in Susticacán, Zacatecas, Mexico

Some parts of the globe have a deficient vegetation coverage survey causing localized plant community qualities generalized from larger scales, hindering their particular configuration. This process is emphasized in megadiverse countries such as Mexico by transformation and loss of land cover. This can be reflected in the municipality of Susticacán, Zacatecas, settled in a mountainous, scarcely explored area, the Sierra de los Cardos. This study aimed to characterize its plant communities, produce a fine-scale map and compare them to other descriptions. Oak forests, pine forests, grasslands, nopaleras, chaparral, and rock outcrop vegetation were detected through satellite image analysis, sampled, statistically evaluated, and their descriptions supported by the literature. The first two presented a high diversity and endemism, despite a small surface. The chaparral occupied the largest area, and its structure and composition suggest its secondary vegetation in expansion. The presence of exotic–invasive species and human activities threaten the native flora. This study is the first to provide detailed information on the plant communities in Susticacán and is a model for the study of local-scale regions. It highlights the importance of describing and mapping them as a contribution to delineate conservation and management efforts.

Zoomingin on quartzitic outcrops: micro-habitat influences on flora and vegetation

Abstract Rock outcrop vegetation is recognized worldwide by its singular and biodiverse flora. Campo Rupestre forms hyperdiverse mosaics in rocky environments across a wide latitudinal and altitudinal gradient, with high species turnover at macro- and micro-scales. The surrounding biomes, climate, and geological formations are the main drivers of species turnover on a macro-scale while micro-habitat seems to be the main one determining the peculiarities of the Campo Rupestre on a micro-scale. In a quartzitic Campo Rupestre area we evaluate how the outcrop micro-habitats influence floristic composition and functional traits. The study area is located in the municipality of Ouro Preto, Minas Gerais state, southeastern Brazil. Two main outcrop habitats were considered: top surfaces, with bare rock, shallow depressions and ephemeral ponds; and lateral surfaces, with clefts and crevices. We recorded the vascular species, their respective life-forms (according to Raunkiaer’s system) as well as their coverage in 18 plots. We identified 71 species in 31 families. The floristic spectra and species composition were similar between top and lateral surfaces. There was no significant difference among the vegetational spectra. However, hemicryptophytes were slightly dominant on top, while on the sides chamaephytes were the dominant life-form. Understanding plant adaptations to these environments provides insights into the mechanisms underlying geomorphological heterogeneity in plant communities.

Phylogenetic structure is determined by patch size in rock outcrop vegetation on an inselberg in the northern Amazon region

ABSTRACT Although inselbergs from around the world are iconic ecosystems, little is known on the underlying mechanisms of community assembly, especially in their characteristic patchy outcrop vegetation. Environmental constraints are expected to cause phylogenetic clustering when ecological niches are conserved within evolutionary lineages. We tested whether vegetation patches from rock outcrops of the Piedra La Tortuga Natural Monument, in the northern Amazon region, are phylogenetically clustered, indicating that environmental filtering is the dominant driver of community assemblage therein. We classified all patches according to their size as very small (< 1 m2), small (1-4 m2), medium-sized (4-8 m2), and large patches (8-15 m2). From each class, we randomly selected 10 patches, totalizing 40 patches covering 226 m2. All individuals found in the 40 isolated patches were identified to the species level. We also correlated measurements of phylogenetic community structure with patch size. We found that species from patches are restricted to the clades monocots, fabids, malvids, and lamiids. We conclude that vegetation in this rock outcrop is phylogenetically clustered. Furthermore, we found that phylogenetic turnover between pairs of patches increases with patch size, which is consistent with a scenario of higher environmental stress in smaller patches. Further research is necessary to identify nurse species in inselberg vegetation, which is pivotal for conservation and restoration of this particular ecosystem.

An Ecological Assessment of the Panama Lagoon Complex, Eastern Province, Sri Lanka

The Panama lagoon is located in, Ampara District, on the Eastern coast of Sri Lanka. This relatively small brackish water lagoon spans over an area of less than 1.5 km2, but encompasses variety of habitat types ranging from natural and semi-natural habitats to modified habitats by humans, thus performing an important ecological role. Biogeographically, Panama lagoon area falls under floristic regions I and II i.e. Coastal and Marine Belt and Dry and Arid Lowlands. It further belongs to the bioclimatic region B: Dry Zone. Field investigations carried out during the period of August to December, 2015 identified 11 major natural and man-made habitat types, including terrestrial, aquatic and semi-aquatic systems. Natural terrestrial habitats included scrublands, dry mixed evergreen forests, rock outcrop vegetation, and sand dunes. Anthropogenic terrestrial habitats were predominantly represented by chena/crop cultivations and home gardens. Natural wetland habitats included sea shore vegetation, salt marsh, mangrove and lagoon, while paddy fields represented anthropogenic wetland habitats. The plant species recorded included 41 trees, 47 shrubs, 92 herbs, 25 climbers including lianas and epiphytes. Recorded flowering plants included 160 native species (77%) with 2 endemic species (1%). Due to the high human influences on the environment, numerous alien species were found in the terrestrial habitats of the lagoon. There were 43 introduced species (exotics) (20.6%) recorded. Introduced species included 3 invasive alien species and 27 naturalized exotics. Seven (3.36%) nationally threatened plant species were recorded from the area. It includes 4 Nationally Endangered (EN) and 3 Nationally Vulnerable (VU) species. The study site also has 19 Nationally Near-Threatened (NT) species. Rapid faunal assessment undertaken to cover all habitat types in and around the lagoon recorded a total of 242 faunal species. This included 23 mammals, 128 birds, 25 reptiles, 7 amphibians, 35 butterfly species and 23 dragonfly species. Out of the total 242 faunal species recorded, 214 were native to the country (88.4%) while 7 species are listed as endemic (2.9%). There were 14 nationally threatened faunal species recorded in the study area which included 4 mammals, 6 birds, and 4 insect species (butterflies and dragonflies). A considerable area of the lagoon complex has been already subjected to human influences such as agriculture and residential developments, causing substantial threats to lagoon ecological resources. As Panama lagoon is a rich repository of native biodiversity, and an important habitat for migrant birds, it is imperative that the entire system is sustainably managed to achieve a balance between conservation and utilization. Keywords: Panama lagoon, Biodiversity, Dry zone, Floral diversity, Faunal diversity

The role of outcrops in the diversity of Patagonian vegetation: Relicts of glacial palaeofloras?

Outcrops around the world enhance biodiversity as they provide heterogeneous environments and varied habitats for species with different requirements than those living in the surroundings, and in this way they increase alpha and beta diversity. We studied the floristic composition of the vegetation of rock outcrops in northwestern Patagonia, Argentina, and compared them to the surrounding matrix of shrubland and steppe. For this we sampled 50 outcrops and 50 matrix plots close to them, identified all the species present, and analyzed their floristic composition with Detrended Correspondence Analysis (DCA). We also analyzed the floras of the north and south faces of the outcrops. The resulting ordinations were related to geographic gradients of the region. The proportions of alien to native species, different life forms, and phylogenetic groups of the outcrop floras were compared to the matrix with G-tests. Our results showed similar dominant families, life form proportions and percentage of alien species in the outcrops and the surrounding matrix. However, species composition of the outcrops was markedly different. North Patagonian outcrops present several taxa not found in the matrix, especially in their southern, less insolated walls. The previously recorded distribution of most of these exclusive species is found in colder areas further south. Thus, we hypothesize that outcrops could be acting as relicts of cold-adapted glacial paleofloras that were probably more extended during glacial times and retreated south after the last glacial maximum.

Life history and morphological variation in intraspecific seeder and resprouter populations of two species from rock outcrop vegetation in north-east New South Wales

The processes underlying differentiation of seeder and resprouter life histories were explored by studying changes in life history and morphological traits in intraspecific seeder and resprouter populations of the grass Entolasia stricta and shrub Keraudrenia hillii var. hillii from adjoining rock pavement and fringing woodland habitats. Population traits were sampled in the field and studied under controlled conditions in a randomised experimental design with two levels of population/habitat (seeder/rock outcrop and resprouter/woodland) and two levels of fertiliser (low and high). Life history traits reflecting rate of growth, relative allocation of resources to reproductive and vegetative growth and timing of events, as well as a selection of simple morphological traits were recorded. Generalised linear model analysis showed that population had a strong, significant effect on the majority of traits examined, particularly those relating to reproductive output. Many traits were also significantly responsive to nutrient, or induced plasticity, and significant interaction terms were very few. The two species exhibited parallel intraspecific changes in life history between habitats and traits recorded under experimental conditions were similar to those observed in the field. The populations from pavement shrubland produced a more compact shoot system, faster early shoot growth (E. stricta), more numerous flowers and more numerous and lighter seeds. In fringing woodland, both species produced a larger shoot system, slower early shoot growth and fewer and larger seeds. Significant intraspecific differences in population traits and correlation of population with habitat type indicated that the intraspecific seeder-resprouter populations of both species were ecotypes selected by habitat factors, most likely associated with the edaphic environment rather than fire regime variables.

Rock outcrop vegetation in Brazil: a brief overview

This paper overviews the special issue of the Brazilian Journal of Botany dedicated to Rock outcrop vegetation in Brazil. The main topics covered by this issue are phytogeography and vegetation ecology, plant life on shallow soils, plant reproduction and auto-ecology, morpho-physiology and plant adaptation, and finally conservation and global change. This collection of studies, in addition to other recent publications on Brazilian rocky outcrop vegetation, show that measurements of most of the relevant ecological and evolutionary parameters are under way and that scientific attention is now given to most Brazilian regions. However, there are still several gaps to be bridged: 1) inselbergs and high mountains in the Amazon and the Brazilian northeast, in particular, are still largely unknown to science; 2) long-term studies are almost totally unavailable, which hinders global change monitoring and assessment; 3) national and international networking are urgently needed to speed up scientific production about such habitats.

Calcareous Rock Outcrop Vegetation of Eastern North America (Exclusive of the Nashville Basin), with Particular Reference to Use of the Term “Cedar Glades”

The term “cedar glades” has been applied to several different types of plant communities that occur on rocky calcareous soils in eastern North America. A previous paper by the first two authors reviewed in considerable detail the use of this term with regard to type of vegetation on rocky limestone soils in the Nashville (Central) Basin of Tennessee. The present paper reviews use of “cedar glades” as a descriptive term for vegetation in other physiographic regions of eastern North America. In the Nashville Basin, and in some other physiographic regions, the term has been applied to true open cedar glades (“glades”) plus the surrounding redcedar/redcedar-hardwood forest, or (more recently) to the natural rocky treeless openings only. However, outside the Nashville Basin, it has also been used to describe several other disparate vegetation types, such as xeric limestone prairies (limestone glades, prairie barrens), redcedar-little bluestem savanna, dense redcedar forest, redcedar-hardwood forest, and even an open stand of redcedar-pine-sweetgum with warm-season perennial prairie grasses in the understory. In the Great Lakes region of North America and in the Baltic region of Europe, some alvars are similar to cedar glades sensu stricto of southeastern United States. Since many of the rocky calcareous openings in eastern North America can be classified as either cedar glades or xeric limestone prairies, a suite of abiotic, biotic, and anthropogenic-related factors is presented for use in distinguishing between these two vegetation types.

A new species ofIlex(Aquifoliaceae) from Espinhaço Range, Bahia, Brazil

A new species, Ilex mucugensis Groppo sp. nov. (Aquifoliaceae), is described and illustrated. The species is known only from ‘campos rupestres’ (vegetation of rock outcrops at high altitude) in the vicinity of Mucuge, Bahia State, Brazil, in the mountains of the Espinhaco Range. Comments on affinities, geographical distribution and phenology of the new species are also provided. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 153–156.

Vegetation of the rock outcrops and screes in the forest-steppe and steppe belts of the Altai and Western Sayan Mts., southern Siberia

A new concept of classification of petrophytic vegetation, i. e. plant communities on rock outcrops and screes, is proposed for the steppe and forest-steppe belts of the southern Siberian mountains, using the Braun-Blanquet approach and original releves from the Altai and Western Sayan Mts. In these areas with arid continental climate, the species composition of petrophytic vegetation seems to be less differentiated from the other habitats than is usual in Europe or the Far East. The main habitats of petrophytic vegetation include rock crevices, shallow soils on weathered rock outcrops, disturbed screes with herbaceous vegetation, and shrubberies in less disturbed places. In the proposed classification petrophytic vegetation is divided into three phytosociological classes. The vegetation of moderately dry rock crevices is included in the Eurasian class Asplenietea trichomanis (Br.-Bl. in Meier et Br.-Bl. 1934) Oberdorfer 1977 and the alliance Selaginellion sanguinolentae Hilbig 2000. Vegetation of disturbed or strongly drought-stressed rock outcrops and screes is included in the class of central Asian steppes, Cleistogenetea squarrosae Mirkin et al. ex Korotkov et al. 1991. Within this class, vegetation with predominance of succulent plants is assigned to the alliance Sedion hybridi all. nova and xeric rock-crevice vegetation to the alliance Eritrichio pectinati- Selaginellion sanguinolentae all. nova. A distinct type of central Asian petrophytic vegetation is assigned to the class Artemisio santolinifoliae-Berberidetea sibiricae cl. nova, which includes xeric shrubberies on mobile screes and rock outcrops of different lithology. Seven associations, three subassociations and four communities without syntaxonomic rank are documented in an ordered species-by-releve table and briefly described with respect to their phytosociological affinities and ecology. The DCA ordination of the releves was used to demonstrate patterns of floristic differentiation of the higher vegetation units in the Altai and Western Sayan.

Epiphytic orchids on arborescent Velloziaceae and Cyperaceae: Extremes of phorophyte specialisation

Vascular epiphytes are widespread throughout the tropics where they are usually not restricted to particular phorophytes. In contrast to this the trunks of arborescent Cyperaceae and Velloziaceae are regularly colonised by vascular epiphytes with certain orchids showing a remarkably high degree of phorophyte specificity. Arborescent, desiccation‐tolerant Cyperaceae (e.g. Afrotrilepis) and Velloziaceae (e.g. Vellozia, Xerophyta) form characteristic elements of rock outcrop vegetation in the Neotropics and Paleotropics where they frequently occur with mat‐forming species. Their woody‐fibrous stems mainly consist of persistent leaf bases and adventitious roots which possess a velamen radicum. In tropical Africa several species of Polystachya occur in mats and on stems of Cyperaceae (e.g. P. microbambusa on Afrotrilepis pilosa) and Velloziaceae (e.g. P. johnstonii on Xerophyta splendens). In Brazil a higher number of orchid species (e.g. Constantia cipoensis, Pseudolaelia vellozicola, Sophronites brevipedunculata) are largely restricted to the stems of Velloziaceae growing on rock outcrops. Moreover, in Brazil a number of non‐phorophyte specific orchids (e.g. Epidendrum saxatile, Prosthechea vespa) grow on the trunks of Velloziaceae. Orchids restricted to the stems of Cyperaceae and Velloziaceae were derived from non‐phorophyte specific, epiphytic/lithophytic ancestors and originated independently in South America and Africa. The exact nature of the relationship between arborescent Cyperaceae and Velloziaceae and epiphytic orchids growing exclusively on their trunks is not yet clear. In a number of areas both the highly host specific orchids and the arborescent Cyperaceae/Velloziaceae are seriously threatened by human lit fires and commercial collection.

The physical environment and major vegetation types of Sekhukhuneland, South Africa

A detailed account is given of the broad vegetation types of the Sekhukhuneland Centre of Plant Endemism. Phytosociological data from 415 sample plots were subjected to phytosociological classification using TWINSPAN. The resulting classification was further refined with table-sorting procedures based on the floristic-sociological approach to classification of vegetation. The analysis revealed six major vegetation types, interpreted as the Acacia tortilis - Dichrostachys cinerea Northern Dry Mixed Bushveld, the Kirkia wilmsii - Terminalia prunioides Closed Mountain Bushveld, the Combretum hereroense - Grewia vernicosa Open Mountain Bushveld, the Hippobromus pauciflorus - Rhoicissus tridentata Rock Outcrop Vegetation, the Themeda triandra - Senecio microglossus Cool Moist Grasslands and the Fuirena pubescens - Schoenoplectus corymbosus Wetland Vegetation. Each major vegetation type is described and its diagnostic species highlighted. The occurrence of rare and threatened plant species in each vegetation type is indicated.

Ilex prostrata (Aquifoliaceae): A New Species from Minas Gerais, Brazil

A new species of Aquifoliaceae, Ilex prostrata, from Minas Gerais State, Brazil, is described and illustrated. The species is known so far only from the "campos rupestres" (vegetation of rock outcrops at high altitude) from the Serra do CipO, a southern portion of the Espinhaco Range in the State of Minas Gerais, Brazil.

High‐elevation rock outcrop vegetation of the Southern Appalachian Mountains

Abstract. Species composition patterns and vegetation‐environment relationships were quantified for high‐elevation rock outcrops of the Southern Appalachian Mountains, an infrequent and insular habitat in a forested landscape. Outcrops occur over a wide geographic range encompassing extensive variation in both geology and climate. Geographic‐scale factors interact with site‐scale factors to produce variation in vegetation among outcrops. Similarly, site‐scale factors interact with micro‐scale factors to produce variation in vegetation within outcrops. To provide a quantitatively‐based classification of outcrop vegetation we used a TWINSPAN analysis of 154 100‐m2 plots. We recognized nine communities that primarily correspond to different combinations of elevation, bedrock type, geography, and moisture. Within outcrops of a single bedrock type, vegetation composition of 100‐m2 plots was consistently correlated with elevation and solar radiation, but relationships to soil nutrients varied with bedrock type. Both site‐scale (100 m2) factors (e.g. elevation, slope, aspect, and bedrock type) and plot‐scale (1‐m2) microsite factors (e.g. soil depth, vegetation height, soil nutrients) were strongly correlated with species composition at the 1‐m2 level. Environment can be used to predict composition more effectively for 100‐m2 plots on a single bedrock type than either across bedrock types or at a 1‐m2 scale. Composition‐environment relationships resemble those described for outcrop systems from other regions with pronounced topographic relief more than they do those described for the nearby but flatter and lower‐elevation outcrops of the Southeastern Piedmont. There is strong spatial autocorrelation in this community, perhaps owing to dispersal limitation. Consequently, a comprehensive conservation strategy must include reservation of both a range of geologic types and a range of geographic locations.

Vegetation of rock outcrops in Guinea: granite inselbergs, sandstone table mountains and ferricretes — remarks on species numbers and endemism

Summary A survey of characteristic plant communities and species occurring on granite inselbergs, sandstone outcrops, and ferricretes in Guinea is given. Examples of species restricted to these insular biota are Pitcairnia feliciana (Bromeliaceae) and rodracoides squamosus (Cyperaceae) . Rock outcrops harbour characteristic habitat types: cryptogamic crusts on rocks, drainage channels, crevices, rock pools, shallow depressions, Afrotrilepis pilosa -mats, ephemeral and wet flush vegetation. Sandstone outcrops of the Fouta Djalon are rich in species and endemics probably due to combined effects of vertical differentiation, large area, long-term climatic stability and isolation. Granite inselbergs and ferricretes have no local endemics and a lower number of species. Floristic homogeneity of granite inselbergs indicates the importance of deterministic processes for controlling diversity. The vegetation of Guinean inselbergs was compared with similar localities in other parts of tropical Africa. Species diversity of inselbergs in Guinean rain forests is higher than on inselbergs in Ivorian rain forests due to higher numbers of growing sites (e.g. rocky slopes of mountain ranges) available for typical inselberg species. Principally, species richness of rock outcrops is positively correlated with the existence of otherwise suitable resources. Supposedly the most diverse inselberg vegetation of tropical Africa is found in Tanzania, Malawi, Mozambique, Zambia, Zimbabwe and Angola.

The ecology of granite outcrops at Wilson's Promontory, Victoria

AbstractRock outcrops on spurs and summits on Wilson's Promontory tend to be more prevalent on hot dry slopes than cool moist ones. In this comparatively moist climate, the rock outcrop vegetation can be grouped into high altitude, low altitude and coastal types. The surrounding rock‐heath is characterized below 400–500 m by Kunzea ambigua and above this altitude by Callistemon pallidus. Moss aprons of Campylopus bicolor on rock faces are often held in place by roots of surrounding shrubs on slopes up to 20°. Bryophyte and lichen communities vary with altitude, and annuals and geophytes are common. Fire may result in retrogression if forests and shrub zones are destroyed and humic top soil burnt or eroded away. Fossil root‐grooves occur in granite on the summit of Mt Latrobe and are the legacy of a cloud forest of Nothofagus cunninghamii. The rock‐heath species are more drought resistant than the‘climax’tree species and may develop very low water potentials. The rate of succession may be correlated with the highly variable rate of decay of each individual block of granite.The soils of the early successional stages are veneers of humic sands enriched with hill‐wash, whilst the soils of the forest stages vary from duplex podzols to gradational podzolic soils of much greater moisture storage. Woody plant establishment is mostly initiated along rock joints: the rock surfaces and boulders so by‐passed are colonized by more mesic species. Many zonations appear to be static since advances are cancelled by retreats.The rate of succession on bare granite is controlled by local climate, altitude, slope, fire and macro‐and micro‐jointing patterns. In general, the early stages bear strong similarities over a relatively wide range of climate. The so‐called climaxes which have developed represent a continuum in response to the complex environments found on Wilson's Promontory.

The Cedar Glades of Middle Tennessee

In the eastern United States there are perhaps not more than a dozen well-marked types of rock-outcrop vegetation, if we leave out of consideration precipitous cliffs. Rocks are common enough in most states, but where the individual outcrops are not more than a few feet wide-as in the case of glacial boulders-they are likely to be overshadowed by surrounding trees, and also to have too few crevices to support any vegetation but mosses and lichens. Or if in grass-land or open forests any vegetation that might tend to establish itself on them is likely to be destroyed in a year or two by fire sweeping through the grass.' And, in order for a given type of rock to support any vegetation peculiar to it, the outcrops must not only be of substantial width, but also be scattered over a considerable area. For if a rock different from anything else in the world should have an area of only an acre or so, any peculiar species that might tend to develop on it would be likely to be exterminated by vicissitudes of weather, erosion, or herbivorous animals long before it could become fixed as a distinct form. But if a peculiar type of rock (or soil) is scattered over several hundred square miles, then any species confined to it, if destroyed in one spot may persist in others and re-establish itself through natural agencies. One of the most interesting types of flat rock vegetation is that of the cedar glades of Middle Tennessee. These have been visited by a few botanists, but nearly all of them were interested in flora rather than vegetation To this day no adequate description of a cedar glade seems to have ever been attempted, and apparently no one has ever thought it worth while to publish a photograph of such a place. What little descriptive matter is available is more in geological than in botanical literature. Dr. J. M. Safford, who was state geologist of Tennessee from i854 to 1860 and i871 to I899, published several interesting notes on the subject, the most accessible of which are probably those in the American Journal of Science (62: 354, 357. i851 4) and the Tenth Census of the United States (5: 400-401, 459, 46i. i884). Additional details by other non-botanical writers can be found in some of the government soil surveys of Middle Tennessee counties, and on pages 13-i6 of Bulletin 22 (i919) of the present Tennessee