Multi-scale comparisons of cliff vegetation in Colorado

We developed a nested vegetation sampling protocol to sample the plant diversity on south-facing cliffs and cliff bases in Jefferson County, Colorado. The multi-scale plots included three nested spatial scales, 1 m², 20 m², and 40 m². We compared plant species richness and species diversity among large cliffs, medium cliffs, small cliffs, and non-cliff sites using Hill's diversity numbers (N ₀, N ₁, and N ₂) for the 1-m² quadrats. Species richness (N ₀) was calculated for the 20-m² and 40-m² plots. Our results indicate that plant species diversity on the cliff faces did not increase with increasing cliff area. This pattern was consistent at all three sampling scales. A model selection was run to determine if plant species diversity values on the cliff faces were associated with cliff variables. None of the cliff variables measured were good predictors of diversity at the 1-m² scale. However, at the 20-m² scale, canyon differences and a positive relationship with increasing cliff surface roughness explained 70% of the variability in species richness. Although most plant species sampled on the cliff faces were also found in the base plots, 13 species were sampled only on the cliff faces. Additionally, dry south facing cliffs support a mix of xeric and mesic plants indicating that cliffs may provide unique microenvironments for plant establishment. This revised version was published online in August 2006 with corrections to the Cover Date.     

The phytosociology of British sea-cliff vegetation with special reference to the ecophysiology of some maritime cliff plants

The major factors thought to control the distribution of associations on the sea cliffs in Britain are discussed in relation to the zonation of cliff vegetation, and some experiments to investigate the effects of these factors are described.The seeds of the maritime cliff species are able to germinate in higher salinities than those of closely related inland species.Relative growth rates of maritime cliff species indicate stimulation at low salinities over non-saline conditions, and less reduction in growth at higher salinities than those of closely related inland species.Increasing salinity reduces both photosynthesis and dark respiration in Lavatera arborea. Mesophyll and stomatal resistances are increased while transpiration is reduced.The distribution of ions within Lavatera arborea grown at different salinities indicates differential accumulation between young leaves, old leaves and roots.Nomenclature follows Clapham, Tutin & Warburg (1962).     

The role of seed rain in determining the assembly of a cliff community

Abstract. Cliff-face communities of the Niagara Escarpment in Ontario, Canada, are dominated by long-lived Thuja occidentalis and a consistent assemblage of other plants. Our objective was to determine whether seed rain plays a role in determining why these species are dominant. Seed rain was collected from the cliff face and from the surrounding plateau-and talus communities at two sites over a 2-yr period in order to compare these three adjacent, but different communities. Multivariate Discriminant Analysis first separated the two sites: primarily due to the importance of Betula papyrifera at one site. The three community types were also separated, although there was still substantial overlap. There was a predictable array of species associated with each community although the seed rain on the cliff faces differed slightly. When characterized by univariate ANOVAs, seed rain in the cliff faces and plateaus had a lower species richness and lower total seed density than the talus sites. Seeds of two of the 11 species analysed individually showed an influence of habitat type on their number. Seed morphology did not influence patterns of seed rain. Finally, there was no correlation between the seed rain and above-ground vegetation in any of the communities. We conclude that the seed rain patterns that exist do not act to filter the plants that form the mature vegetation of cliffs.     

Changes between 1927 and 2004 and effect of rock climbing on occurrence of Saxifraga paniculata and Draba aizoides, two glacial relicts on limestone cliffs of the Swabian Jura, southern Germany

A number of glacial relicts can be found on limestone cliffs of the Swabian Jura in southern Germany. In general, they are rare and endangered, particular on cliffs where rock climbing is allowed. Two glacial relicts, Saxifraga paniculata Mill. and Draba aizoides L., were quantitatively surveyed on 28 cliffs in 2004 to investigate their occurrence compared to former surveys and to analyse the effect of rock climbing on species abundance. Number of cushions per cliff and number of rosettes per cushion were counted, smallest and largest diameter of cushions and rosettes, as well as aspect and inclination were also measured. S. paniculata was found on 75% and D. aizoides on 30% of the cliffs. Up to 150 S. paniculata and 370 D. aizoides cushions were noted per cliff, in total there were 696 S. paniculata and 705 D. aizoides cushions. In cliff areas where rock climbing takes place, S. paniculata was only located in relatively uninfluenced parts of the cliffs. In contrast, D. aizoides was found with at a significantly higher frequency on climbed cliffs, and surprisingly, also at the foot of the cliffs, which means that climbing activities even increased numbers of D. aizoides. Rosettes might have been cut of by trampling and climbing and fell to positions where they established new cushions at the base of the cliff. Compared to earlier studies in 1927 and 1966, a higher number of cliffs containing both glacial relicts were found. It can be assumed that not all cliffs had been surveyed in the past and that cliffs were not surveyed as completely as possible. The former locations were confirmed except for one cliff where D. aizoides did not exist anymore. From the cliffs studied, D. aizoides and S. paniculata do not seem to be directly in danger of disappearance in the near future. Nevertheless, rock climbing or visits of hikers on certain cliffs can be a threat, in particular to S. paniculata. This study provides the groundwork for future quantitative monitoring of these two glacial relicts.     

Factors affecting breeding habitat selection in a cliff-nesting peregrine Falco peregrinus population

We studied factors affecting breeding habitat selection in a population of cliff-nesting peregrines Falco peregrinus across multiple spatial levels (cliff site, cliff context and land-use of the surrounding landscape), over a 2,100 km² study area in the Alps (Italy and Switzerland). We detected 30 breeding pairs (density: 1.43 territorial pairs/100 km²), whose territories were uniformly distributed over the study area. We compared 15 habitat features characterising occupied cliffs and 30 randomly selected unoccupied cliffs by means of stepwise forward logistic regression and hierarchical partitioning. The logistic regression analysis showed that occupied cliffs were longer (horizontal length), steeper, and had a greater extension of urban areas in the surrounding landscape compared to non-occupied cliffs. The model had a discrimination ability of 0.95. Hierarchical partitioning indicated that the logistic regression model was appropriate. Neither the distance of cliffs to the nearest site occupied by a potential competitor and predator, the eagle owl Bubo bubo, which occurred at a low density (0.67 pairs/100 km²), nor the distance to the nearest site occupied by peregrines had any effect on the cliff suitability model. Therefore, habitat selection in cliff-nesting peregrines was mainly influenced by cliff site features and surrounding landscape characteristics, whereas the proximity to conspecifics and to an intraguild predator had no apparent effects on peregrine settlement in our study population.     

Breeding density,habitat selection and reproductive rates of the Peregrine Falcon Falco peregrinus in Álava (northern Spain)

A population of 33–35 pairs of Peregrine Falcon in álava (north Spain) was studied with the aim of assessing the habitat attributes that influence breeding density, habitat selection and breeding success. A strong relationship was found between density of the species in each UTM (Universal Transverse Mercator) square of 10 × 10 km and cliff availability. Habitat selection was analysed by comparing 15 variables in 33 occupied and 25 unoccupied cliffs located at least 2 km from the nearest Peregrine pair. Significant differences were found in five variables: cliff dominance, distance to the nearest Golden Eagle Aquila chrysaetos nesting cliff, steepness and altitude (all showing larger values in occupied cliffs), and cliff orientation, with occupied cliffs facing preferably south and east. Orientation, dominance and distance to the nearest Golden Eagle pair, and the distance to the nearest Eagle Owl Bubo bubo nesting cliff, were included in a discriminant analysis which classified 82.76% of the cliffs correctly. The productivity of the studied population was 1.44 young/territorial pair (n = 45), and no consistent relationship was found between breeding success and habitat variables.     

Full light and soil drought constrain plant growth in Mediterranean cliffs: the case of Primula palinuri Petagna

In any biogeographical region, cliffs shelter a larger number of relict species than do the surrounding areas. To develop effective conservation strategies, experimental studies are needed. We focused on Mediterranean coastal cliffs and on Primula palinuri Petagna, an endangered narrow-endemic plant, included in the IUCN Red List and chosen as a key species. The hypothesis was that light intensity and soil water availability could affect survival and growth of juvenile plants. To avoid the bias of other cliff environmental factors and to overcome problems of cliff site inaccessibility, we performed an ex-situ experiment. The effect of two light regimes and two soil water availability conditions on survival and morpho-functional traits were analysed. Plants grown under reduced light intensity and wet soil showed no reduction in survival and performed very well in terms of growth and storage accumulation. By contrast, full light and dry soil proved to be detrimental conditions. Overall results suggested that cliff environmental conditions play an important role in conservation of narrow-endemic species. The decreasing trend of the already severely fragmented populations of P. palinuri and the ongoing increasing aridity is likely to contribute to a further reduction of the already narrow distribution this cliff relict species.     

Environmental factors affecting patterns of distribution and co‐occurrence of two competing raptor species

Habitat selection is a complex process, that is affected by several factors, including habitat characteristics, environmental conditions, and both intra‐ and interspecific interactions. We analysed habitat preferences of two top avian predators, Peregrine Falcon Falco peregrinus, a medium‐sized diurnal raptor, and Eagle Owl Bubo bubo, a large nocturnal raptor. These two species are known to compete for preferred nest‐sites, and proximity to cliffs with Eagle Owls may reduce Peregrine breeding output through predation of young Falcons. We investigated the environmental factors affecting occurrence and coexistence of the two species and the potential role of habitat suitability in favouring co‐occurrence in 3519 km² of the central pre‐Alps of Italy, where the two species breed on cliffs and sometimes co‐occur on the same cliff. Peregrines settled on long, steep and favourably orientated cliffs in woodland landscapes close to urban areas. Eagle Owls settled on topographically similar cliffs, but in lower rainfall areas compared with cliffs occupied by Peregrines and cliffs unoccupied by either species. Sites where the two species co‐occurred were characterized by more horizontally extended cliffs compared with sites of exclusive occurrence of each species. An analysis of relative habitat suitability revealed that sites where the two species co‐occurred had the highest predicted probability of occupancy for both species, suggesting that those sites should be regarded as high‐quality sites. Breeding productivity of Eagle Owls was negatively affected by the co‐occurrence of Peregrines, whereas the effect of Eagle Owl proximity on Peregrine productivity varied according to cliff suitability for the Peregrines. Habitat selection had fitness consequences for Eagle Owls because breeding productivity increased with cliff length. Environmental conditions, particularly climatic factors, could allow the widespread coexistence of these competing raptors at the landscape scale, whereas at the local scale co‐occurrence could take place only on larger cliffs. These were preferred sites for both species, presumably because breeding at such sites offsets the costs of settling close to the competitor species.     

Leaf demography and leaf traits of temperate-deciduous and tropical evergreen-broadleaved trees in a Mexican montane cloud forest

The spatial variation in epilithic lichen community structure was investigated as part of a larger study of the vegetation and ecology of the tall limestone cliffs within the Niagara Escarpment Biosphere Reserve in southern Ontario, Canada. The cover of all lichen taxa was visually estimated for a total of 199 samples taken from the top, middle, or bottom of the cliff face at five sites. Twelve environmental variables were also measured. Twenty-seven lichen taxa were identified on the samples. Multivariate ordinations of species composition (DCA, CCA, PCCA) revealed variation in community structure on multiple scales, but no groupings of sites that would have suggested the presence of several distinct species assemblages. A gradient in species composition from north to south, most clearly reflected in the decreasing cover of foliose and fruticose species, may reflect a gradient in human disturbance. There was also intermediate-scale patchiness in species composition in a horizontal plane across cliffs, but despite earlier claims made in the literature, no evidence of vertical zonation of the lichens on cliffs was found. Species composition also responded to small-scale factors possibly related to exposure, light, or moisture. Unlike community composition, the total cover of all lichens was homogeneous over large spatial scales and varied only on a small scale, illustrating that scale as well as resolution of a study may influence the ecological patterns seen. More than half of the species found on the Niagara Escarpment are rare on rock substrates elsewhere in southern Ontario, and two are new for North America (Candelariella heidelbergensis (Nyl.) Poelt and Lecanora perpruinosa Fröberg). The result that cliffs support a distinct flora containing many rare species suggests that they are a reservoir for biodiversity not just for vascular plants, but also for lichens.     

Plant species coexistence in cliff habitats

An ecological analysis of the ledge and crevice vegetation of cliffs in north-east Ireland was carried out using a sampling programme based on multivariate land classification. The composition of the vegetation was shown to be determined primarily by distance from the sea, elevation and rock type. The chemical composition and physical structure of the cliffs, together with environmental gradients associated with aspect, elevation and nearness to the sea provide a wide range of habitats in which plants coexist. Certain types of cliff vegetation contained associations of species with a contrasting ecology, such as arctic–montane, maritime, woodland, calcicole and calcifuge plants. The positions of these species in ordination space were found to be unique but overlapping. A model is described to account for these observations. It proposes that species dominance in cliff habitats is prevented by factors such as physical disturbance and that plants are able to coexist in cliff habitats which meet their common environmental tolerances and preferences. The model predicts that cliff habitats with the greatest diversity of species are likely to be subject to less extremes of environmental variability. These habitats include inland sites with nutrient enrichment by sea spray, north-facing sites, seepage sites, base-rich sites, low elevation sites and sites with a heterogeneous physical structure.     

Plasticity of nest-site selection in the trumpeter finch: A comparison between two different habitats

In habitats with more predators, a species is expected to breed in safer sites and be less successful than in predator-impoverished habitats. We tested this hypothesis by studying nest-habitat selection and nest predation in two populations of Trumpeter finch (Bucanetes githagineus). One breeds in a predator-rich habitat (Tabernas, Iberian Peninsula), and the other is found on an island with fewer predators (La Oliva, Canary Islands). In both localities, we studied the features of nests in two different substrates, on the ground and in cliffs, including visibility and position in the cliff. We measured the habitat characteristics in a series of plots around the ground nests and compared them to random points. We also studied the influence of nest features and habitat selection on predation of both nest types. Trumpeter finches built more nests in cliffs in Tabernas, probably because there are more cliffs available there. In this locality, the patches selected for ground nesting had below-average vegetation cover, lower vegetation height, and were on steeper slopes. In La Oliva, they selected above-average vegetation height and steeper slopes. Cliff nests were less predated than ground nests in La Oliva, but not in Tabernas. The only variable that affected survival rates in Tabernas was the height of vegetation around ground nests, with nests in lower vegetation having higher survival rates. These results suggest that locality-related differences in habitat selection by vegetation height could be related to the different predator assemblages present in any given area, though we cannot rule out confounding influences of other differences between the two sites.     

郑州郊区崖沙燕(Riparia riparia)的巢址选择

2014年3—8月,采用样方法对分布于河南省郑州市郊区的4处崖沙燕(Riparia riparia Linnaeus 1758)营巢地的13个生境因子进行了调查,测定了巢址样方和对照样方各160组数据,并利用Mann-Whitney U检验对这些数据的显著水平进行了检验;最后采用逐步判别分析(stepwise discriminate analysis)方法确定影响崖沙燕巢址选择的主要生态因子,并建立了标准化的典则判别函数。结果表明,1)崖沙燕洞巢的洞口横径(8.46±0.79)cm,纵径(8.30±0.79)cm,巢洞深(87.80±11.97)cm,巢室长径(11.25±1.33)cm,短径(10.43±1.33)cm,巢室高(9.99±1.33)cm;2)巢址样方与对照样方在植被均高、植被密度、坡位、坡度、崖高、崖长、崖龄及干扰度等8个方面差异达到显著水平,崖沙燕偏好选择的洞巢周围植被较高(97.24±8.42)cm,植被密度较大(64.34±7.15)株/m~2,坡度较大(83.78±0.35)°、上坡位(1.41±0.04)、崖较高处(7.54±0.13)m、崖壁较长(51.18±3.54)m、崖龄较短(2.41±0.05)月及人类干扰较低(1.94±0.06);3)逐步判别分析结果表明,影响崖沙燕营巢地选择的主要生境因子是坡位、崖龄和干扰度,标准化的典则判别函数为y=0.753×坡位+0.681×崖龄+0.288×干扰度。建议在城市化建设过程中针对崖沙燕的巢址选择特性建立合理的保护措施。     

Burrows of Paragnathia (Crustacea: Isopoda) and bledius (Arthropoda: Staphylinidae) Enhance cliff erosion

In coastal cliffs consisting of Pliocene fine‐grained clastic sediments at El Rompido, Huelva, Spain we discovered around the high water line an extensive zone of about 1.5 m in height burrows that were made by up to 4 mm long isopods Paragnathia formica (Hesse) and small 5 mm long staphylinid beetles (Bledius cf. corniger Rosenhauer). The burrowing zone was crowded with irregular burrows 2–5 mm in diameter and extended some 5 cm deep in the cliff. The base of the cliff showed a clear (bio)erosional notch due to this burrowing activity, comparable to those produced by marine boring and scraping organisms in, for example, calcareous rocks. This indicates that the activity of Paragnathia and Bledius helps in eroding the cliffs, a phenomenon not published earlier as far as we know. A comparable but less extensive burrowed zone was found farther upstream near Cartaya. Their presence around the high tide zone also might prove these burrows to be good markers of former high tide lines in older cliffs.     

THE INFLUENCE OF HABITAT ON THE DISTRIBUTION AND ABUNDANCE OF PEREGRINE AND LANNER FALCONS IN SOUTH AFRICA

Jenkins, A.R. 1994. The influence of habitat on the distribution and abundance of Peregrine and Lanner Falcons in South Africa. Ostrich 65: 281–290.

The distribution and abundance of Peregrine and Lanner Falcons in South Africa was compared using recorded sightings from various sources, including the Southern African Bird Atlas Project. Falcon distributions were compared with the distribution of cliffs and vegetation, to quantify differences in the habitat preferences of the two species in the breeding and the non-breeding seasons. Lanner Falcons outnumbered Peregrine Falcons in most areas by at least 10:1. Peregrine Falcons were more habitat specific than Lanner Falcons, in terms of topographic and biotic requirements. Peregrine Falcons were largely restricted to high cliff areas throughout the year and there probably were no large-scale seasonal movements within the population. The bulk of the resident Peregrine Falcon population was found in the fynbos biome, in the southwestern Cape. Outside of this area, Peregrine Falcons were concentrated in woodlands. Lanner Falcons were less dependent on high cliffs, although cliff availability was important in defining the ranges of both species. Lanner Falcons were most common in the sour grasslands in the east of the country in the breeding season, with apparent movements in the non-breeding season into the fynbos, the Nama Karoo and the southern Kalahari. Overall, Peregrine Falcons favoured relatively closed habitats and Lanner Falcons favoured relatively open habitats. The differences in the two species' habitat preferences are proximate factors influencing distribution and abundance.     

Syntaxonomic revision of chasmophytic vegetation of the Centaureo cuspidatae-Portenschlagiellion ramosissimae (Southeastern Adriatic)

Abstract

The Centaureo-Portenschlagiellion describes the cliff vegetation of the Southeastern Adriatic. This habitat type harbours many endemic taxa and has a high value for biodiversity conservation. Notwithstanding its importance, knowledge of the syntaxonomy of this alliance is still poor. This article aims at revising the synchorological, coenological and floristic relationships of the associations of the Centaureo-Portenschlagiellion. The revision is based on a data set of 103 relevés of Mediterranean xerothermic cliffs from Croatia, Bosnia i Herzegovina and Montenegro. The relevés were clustered by using the Flexible beta method. An indicator species analysis was used to identify the diagnostic taxa of the main clusters of relevés and non-metric multidimensional scaling ordination was undertaken to visualize the floristic relationships among them. Results revealed that only seven associations belong to the Centaureo-Portenschlagiellion, whereas the others already described in phytosociological literature were invalidly described or should be treated as syntaxonomic synonyms of the previous ones. Two associations (Inulo-Centaureetum cuspidatae and Portenschlagiello-Campanuletum portenschlagianae) were reduced to the rank of subassociations of the Moltkio-Inuletum verbascifoliae. Two other subassociations were described for the first time. Data provided with this revision may be considered as essential base-line information that should aid in evaluating the state of this vegetation type in the future.     

Evidence for the widespread occurrence of ancient forests on cliffs

Aim The objective of this work was to determine if the existence of ancient forests on cliffs was specific to the Niagara Escarpment, Canada, or part of a globally widespread pattern. Location Sixty‐five cliff sites were visited in five countries in the temperate climatic zone, and trees were sampled for age and growth rate on forty‐six of these. Methods Two hundred and twenty‐four core samples or cross‐sections were taken from trees on cliffs that varied in height, aspect, rock‐type, and exposure. General observations were also made of regeneration of the tree species forming the mature canopy, and other habitat conditions. Results The evidence shows that ancient slow‐growing forest occurs on most cliffs. Age and growth rate distributions were similar at all treed sites. Small‐statured Thuja, Juniperus, or Taxus stems with age estimates in excess of 1000 years were found in the United States, the United Kingdom and France, and small Pinus and Quercus stems nearly 400 years in Germany. There was a high rate of recurrence of plants in the genera Polypodium, Asplenium, Cystopteris, Campanula, Rosa, Prunus, Hedera, and Sorbus. Most of the sites appear to be habitats of completely natural origin. Conclusions We conclude that ancient natural forest is a normal feature of cliffs, at least in the temperate zone.     

Effects of rock climbing on plant communities on exposed limestone cliffs in the Swiss Jura mountains

Abstract. Exposed cliffs of the Swiss Jura mountains harbour a highly diverse flora with many rare and endangered plant species. Many cliffs are frequently visited by rock climbers. We examined the impact of rock climbing on vascular plants in the lower part of four cliffs of the Gerstelflue (NW Switzerland) by comparing the vegetation of climbed and unclimbed areas. In climbed areas plant cover and species density were reduced. Similarly, the density of forbs and shrubs decreased, whereas the density of ferns tended to increase. In addition, rock climbing caused a significant shift in plant species composition and altered the proportions of different plant life forms. Rock climbing can be a threat to sensitive plants of the limestone cliff community.     

Nitrate reductase activity in vegetation below an arctic bird cliff,Svalbard, Norway

Abstract. Vegetated sites below bird-nesting cliffs are uniquely nutrient-rich habitats in the otherwise nutrient-poor arctic environment. Plants from six distinct vegetation zones below such a cliff at 79° N, Svalbard, Norway, were collected for analysis under greenhouse conditions. Leaf nitrate reductase activity (NRA) was analysed in 42 species representing 25 % of the Svalbard vascular flora. The species mean NRA values ranged from 0.37 to 8.34 μmols of nitrite ions formed per gram of plant fresh weight per hour. Species in the vegetated zone growing closest to recent guano deposits had the highest NRA values, (mean = 4.47) whereas plants growing farther below the cliff had significantly lower values (mean = 0.55). A similar pattern was detected in a duplicate set of plants induced with 15 mM KNO₃; vegetation zone means for NRA ranged from 5.08 to 0.98 μmols of nitrite ions formed per gram of plant fresh weight per hour. Maximally induced species NRA values were highest in the first zones below the cliff and decreased downslope. This gradient paralleled the steep soil nitrate gradient, which decreased from 13.84 mg/l at the cliffbase to 1.03 mg/l downslope. Correspondingly, soil ammonium ions in the vegetation zones ranged between 1.96 mg/l at the cliff-base to 0.03 mg/l downslope. Correlations between NRA and soil nitrate provide a systematic basis for assigning scalar ‘nitrogen figures’ as indicators of habitat preference, here for the first time applied to arctic species.     

Characteristics of Peregrine and Lanner Falcon nesting habitats in South Africa

Jenkins, A.R. 2000. Choracteristics of Peregrine and Lanner Falcon nesting habitots in South Africa. Ostrich 71 (3&4): 416-424. Peregrine Falcon, Falco peregrinus, and Lanner Falcon, F. biarmicus, nesting habitats in South Africa are described in terms of nest ledge, nest cliff and scree slope parameters, ond the environmental context of each site. Data were collected in a tropical study area where Peregrines and Lannen occurred in sympatry, from an allopatric south temperate Peregrine population, and opportunistically for bath species from other sites throughout the country. Elevation, ledge size, cliff size ond vegetation structure accounted for about 80%of the variation in falcon nesting habitots between species and between populations within species. Peregrines used larger nest ledges on higher, more elevated cliffs than Lanners, overlooking mare open, structurally complex Vegetation. Temperate Peregrines used smaller ledges on lower cliffs, overlooking vegetation that provided less refuge for overflying prey than subtropical pairs. Temperote Peregrines selected nest sites to minimize the negative effects of spring roinfall. Tropical Peregrines may have selected sites to maximize hunting and provisioning efficiency.