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Floristic Similarity (floristic + similarity)

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Life Sciences	64%

Selected Abstracts

Importance of soils, topography and geographic distance in structuring central Amazonian tree communities

JOURNAL OF VEGETATION SCIENCE, Issue 6 2008
Stephanie A. Bohlman
Abstract Question: What is the relative contribution of geographic distance, soil and topographic variables in determining the community floristic patterns and individual tree species abundances in the nutrient-poor soils of central Amazonia? Location: Central Amazonia near Manaus, Brazil. Methods: Our analysis was based on data for 1105 tree species (, 10 cm dbh) within 40 1-ha plots over a ca. 1000-km2 area. Slope and 26 soil-surface parameters were measured for each plot. A main soil-fertility gradient (encompassing soil texture, cation content, nitrogen and carbon) and five other uncorrelated soil and topographic variables were used as potential predictors of plant-community composition. Mantel tests and multiple regressions on distance matrices were used to detect relationships at the community level, and ordinary least square (OLS) and conditional autoregressive (CAR) models were used to detect relationships for individual species abundances. Results: Floristic similarity declined rapidly with distance over small spatial scales (0,5 km), but remained constant (ca. 44%) over distances of 5 to 30 km, which indicates lower beta diversity than in western Amazonian forests. Distance explained 1/3 to 1/2 more variance in floristics measures than environmental variables. Community composition was most strongly related to the main soil-fertility gradient and C:N ratio. The main fertility gradient and pH had the greatest impact of species abundances. About 30% of individual tree species were significantly related to one or more soil/topographic parameters. Conclusions: Geographic distance and the main fertility gradient are the best predictors of community floristic composition, but other soil variables, particularly C:N ratio, pH, and slope, have strong relationships with a significant portion of the tree community. [source]

The biogeography of seaweeds in Southeast Alaska

JOURNAL OF BIOGEOGRAPHY, Issue 3 2009
Sandra C. Lindstrom
Abstract Aim, This article reviews the history of seaweed collections in Southeast Alaska from the early Russian explorers to contemporary efforts. It summarizes other studies of Southeast Alaskan seaweeds from a biogeographical perspective, and compares the known seaweed flora near three population centres (Ketchikan, Sitka and Juneau) with those of other regions within Alaska, and with nearby regions. Location, For this article, Southeast Alaska includes all inside and outside waters of the Alexander Archipelago from Dixon Entrance (54°40, N, 133°00, W) to Icy Point (58°23,10, N, 137°04,20, W). Methods, The literature on seaweeds occurring in Southeast Alaska is reviewed from a biogeographical perspective, and herbarium records for Southeast Alaska from the Alaska Seaweed Database project are used to provide an overview of the biogeography of the area. Records for the population centres of Ketchikan, Sitka and Juneau are compared with records from other areas within Alaska and with nearby regions to determine floristic similarities. Results, Southeast Alaska has the most diverse seaweed flora of any region of Alaska. A list of species known to occur in Southeast Alaska is appended (in Supplementary Material) and includes their reported occurrences in three population centres (Juneau, Ketchikan and Sitka). Recognition of at least three distinct biogeographical areas associated with these three centres is supported by a comparison of their floras with those of other regions in the North Pacific. A close relationship of some species with conspecifics in the north-west Atlantic is also noted. In contrast, ecological, physiological and genetic differentiation of Southeast Alaskan seaweeds from conspecifics in Washington State or even from different areas of Southeast Alaska are documented. A ShoreZone coastal habitat system, which is being implemented to inventory and map the entire shoreline of Southeast Alaska, is defining new biogeographical units called ,bioareas' on the basis of the distribution of canopy kelps and lower intertidal algal assemblages. Main conclusions, Southeast Alaska has the most diverse seaweed flora of any region of Alaska. This is a reflection of its extensive coastline, with varied past and present environmental conditions. Different parts of Southeast Alaska show similarities to different areas outside Southeast Alaska. Despite this, much remains to be learned about the biogeography of seaweeds in Southeast Alaska, and many questions remain to be answered. [source]

Distance Decay of Tree Species Similarity in Protected Areas on Terra Firme Forests in Colombian Amazonia

BIOTROPICA, Issue 5 2009
Álvaro Duque
ABSTRACT In this study, we investigated the pattern of floristic similarity as a function of geographical distances and environmental variability in well-drained uplands (terra firme) in Colombian Amazonia. The study site comprised three National Natural Parks, Tinigua, Chiribiquete, and Amacayacu, located in different geological units that represent a soil fertility gradient linked to parental materials. Differences in species richness between sites were compared using rarefaction analysis. A clear floristic transition appeared in the east,west direction following a soil fertility gradient along the first PCoA axis. In multiple regression analyses based on distance matrices, both geographical distances and geology explained 64 percent of the total floristic variation. Geographical distances alone accounted for 12 percent of variation in floristic similarities among plots, while geology alone accounted for 1 percent, and the joint effect of both explained 51 percent of the floristic variation. The species richness trend supports the existence of a latitudinal corridor southward of the geographical Equator in the Amazon basin, where tree diversity reaches the maximum expected values. A coupled effect of stochastic dispersal limitation and habitat specialization would certainly appear to be an appropriate explanation for tree species turnover in terra firme forests in Colombian Amazonia, strongly emphasizing that competition and neutrality must be supplementary rather than mutually exclusive processes. This result pinpoints the effect of dispersal on floral mixing as an ongoing active process for structuring tree communities in NW Amazonia, and the size of the reserves as a relevant issue to protect rare species from extinction by chance. [source]

Assessing the relationship between forest types and canopy tree beta diversity in Amazonia

ECOGRAPHY, Issue 4 2010
Thaise Emilio
Planning of conservation priorities has often taken mapped forest types as surrogates for biological complementarity. In the Brazilian Amazon, these exercises have given equal weight to each forest type as if they were all equally distinct. Here, we examine floristic similarity between forest types to assess the reliability of vegetation maps as a surrogate for canopy tree-community composition. We analyzed floristic differences at the genus level between twelve Amazonian forest types using 1184 one-hectare inventories of large trees with three complementary approaches. First, we compared a map of floristic composition, from a uni-dimensional NMDS ordination of the inventories, with a map of coarser-level forest types commonly recognized as distinct by classification systems across Amazonia. Using Mantel and means-difference tests, we next examined the distance-decay of floristic similarity for all paired samples and for the pairs drawn from within and between twelve more finely divided forest types. Finally, we examined the degree of floristic separation of each pair of the twelve forest types using non-parametric analysis of variance. Maps of floristic composition and coarse-level forest types were highly congruent. At the finer level of classification, similarity was only slightly higher when pairs were drawn from the same versus from different forest types. This was true for all geographic distances. Nonetheless, eighty percent of the 66 paired combinations of forest types were significantly different in the unreduced genus-space and nearly half showed little or no overlap in a two-dimensional ordination. Three types were most distinct from all others: white sand, seasonally dry, and bamboo-dominated forests. Here, we show that forest types exhibit variable degrees of separation. For this reason, treating all fine-level forest types as equally distinct results in poor representation of canopy tree beta diversity. We recommend explicitly considering the degree of floristic separation between all forest types , as presented here for Amazonian flora , as a way to improve the use of this biodiversity surrogate. [source]

Dry spots and wet spots in the Andean hotspot

JOURNAL OF BIOGEOGRAPHY, Issue 8 2007
Timothy J. Killeen
Abstract Aim, To explain the relationship between topography, prevailing winds and precipitation in order to identify regions with contrasting precipitation regimes and then compare floristic similarity among regions in the context of climate change. Location, Eastern slope of the tropical Andes, South America. Methods, We used information sources in the public domain to identify the relationship between geology, topography, prevailing wind patterns and precipitation. Areas with contrasting precipitation regimes were identified and compared for their floristic similarity. Results, We identify spatially separate super-humid, humid and relatively dry regions on the eastern slope of the Andes and show how they are formed by the interaction of prevailing winds, diurnally varying atmospheric circulations and the local topography of the Andes. One key aspect related to the formation of these climatically distinct regions is the South American low-level jet (SALLJ), a relatively steady wind gyre that flows pole-ward along the eastern slopes of the Andes and is part of the gyre associated with the Atlantic trade winds that cross the Amazon Basin. The strongest winds of the SALLJ occur near the ,elbow of the Andes' at 18° S. Super-humid regions with mean annual precipitation greater than 3500 mm, are associated with a ,favourable' combination of topography, wind-flow orientation and local air circulation that favours ascent at certain hours of the day. Much drier regions, with mean annual precipitation less than 1500 mm, are associated with ,unfavourable' topographic orientation with respect to the mean winds and areas of reduced cloudiness produced by local breezes that moderate the cloudiness. We show the distribution of satellite-estimated frequency of cloudiness and offer hypotheses to explain the occurrence of these patterns and to explain regions of anomalously low precipitation in Bolivia and northern Peru. Floristic analysis shows that overall similarity among all circumscribed regions of this study is low; however, similarity among super-humid and humid regions is greater when compared with similarity among dry regions. Spatially separate areas with humid and super-humid precipitation regimes show similarity gradients that are correlated with latitude (proximity) and precipitation. Main conclusions, The distribution of precipitation on the eastern slope of the Andes is not simply correlated with latitude, as is often assumed, but is the result of the interplay between wind and topography. Understanding the phenomena responsible for producing the observed precipitation patterns is important for mapping and modelling biodiversity, as well as for interpreting both past and future climate scenarios and the impact of climate change on biodiversity. Super-humid and dry regions have topographic characteristics that contribute to local climatic stability and may represent ancestral refugia for biodiversity; these regions are a conservation priority due to their unique climatic characteristics and the biodiversity associated with those characteristics. [source]

Bat species diversity and distribution in three vegetation communities of Meru National Park, Kenya

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2004
Paul W. Webala
Abstract Diversity and distribution of bats was determined in four vegetation types in and around Meru National Park, Kenya between September 2000 and February 2001. Bat-habitat studies were based on plant species dominance, cover and farming activities. Bats were captured using standard mist nets (18 m long × 2 m high) erected on poles averaging 3 m. Vegetation was broadly grouped as Acacia or Combretum wooded grassland, or Acacia,Commiphora bushland and studied using the Braun-Blanquet method. Analysis of floristic similarity showed five vegetation species assemblages in the three broad categories. Four hundred and ninety-five bats representing eleven genera in seven families were recorded. These were Epomophorus labiatus, E. wahlbergi, Cardioderma cor, Lavia frons, Myotis welwitschii, Scotoecus hirundo, S. leucogaster, Pipistrellus kuhlii, Mops condylurus, Chaerephon bemmeleni, Mormopterus sp., Hipposideros caffer, H. commersoni, Nycteris arge and Rhinolophus landeri. This was the first record of N. arge, M. welwitschii, C. bemmeleni and a Mormopterus species in eastern Kenya. The Combretum community was most equitable (E = 0.51) with nine bat species records, while farming areas had only four. The low species richness and increased dominance of a few generalist species on farms may be indicative of different levels of disturbance. Résumé On a déterminé la diversité et la distribution des chauves-souris dans quatre types de végétation dans et autour du Parc National de Meru, au Kenya, entre septembre 2000 et février 2001. Les études de l'habitat des chauves-souris se basaient sur la dominance et le couvert de certaines espèces végétales et sur les activités agricoles. On a capturé les chauves-souris en utilisant les filets standards (18m de long sur 2 m de haut) fixés sur des piquets d'environ 3 m de haut. La végétation fut grossièrement regroupée en prairie arborée à Acacia ou à Combretum, ou en brousse à Acacia-Commiphora, et étudiée suivant la méthode Braun-Blanquet. L'analyse des similarités floristiques a montré cinq assemblages d'espèces végétales dans ces trois grandes catégories. On a relevé 495 chauves-souris représentant onze genres appartenant à sept familles. Ce sont: Epomophorus labiatus, E. wahlberghi, Cardioderma cor, Lavia frons, Myotis welwitschii, Scotoecus hirundo, Scotophilus leucogaster, Pipistrellus kuhlii, Mops condylurus, Chaerephon bemmeleni, Mormopterus sp., Hipposideros caffer, H. commersoni, Nycteris arge et Rhinolophus landeri. Ce sont les premiers cas rapportés pour N. arge, M. welwitschii, C. bemmemeni et pour une espèce de Mormopterus dans l'est du Kenya. La communautéà Combretum était la plus équitable (E = 0,51), avec neuf espèces de chauves-souris rapportées, alors que les aires cultivées n'en comptaient que quatre. La faible richesse en espèces et la dominance croissante de quelques espèces généralistes dans les fermes pourraient indiquer divers degrés de perturbation. [source]

Drivers of lowland rain forest community assembly, species diversity and forest structure on islands in the tropical South Pacific

JOURNAL OF ECOLOGY, Issue 1 2010
Gunnar Keppel
Summary 1.,Testing the comparative strength and influence of age and area of islands, proximity of source propagules and disturbances on community assembly, species diversity and vegetation structure has proved difficult at large scales. The little-studied rain forests in the Tropical South Pacific (TSP) provide a unique study area to investigate determinants of community dynamics, with islands varying in age, isolation, area and cyclone frequency. We tested the effects of biogeographical factors and cyclone frequency on the species composition, species diversity and forest structure of old-growth rain forest using 1-ha inventory plots on 12 islands between New Guinea and the Solomon Islands. 2.,As predicted by the General Dynamic Model of Oceanic Island Biogeography, the biogeographical variables of archipelago age and island area are the most important factors affecting species richness and diversity, with older and larger islands having higher richness and diversity. There is no significant effect of cyclone frequency on species diversity. 3.,The theory that diversity drives endemism is not supported in this system as endemism is not correlated with species diversity. Instead, age and isolation of an island best explain patterns of endemism, with the latter suggesting dispersal limitations between archipelagos. 4.,Proximity to source area influences species composition of lowland tropical rain forests in the TSP, which is also supported by a strong correlation between geographic distance and floristic similarity. Vector-fitting onto non-metric multidimensional scaling suggests that archipelago age and cyclone frequency may, in addition to proximity to source area, influence species composition. This implies that a species' tolerance to cyclones affects its abundance at different cyclone frequencies. 5.,Synthesis. Both biogeographical variables (island area and isolation) and cyclone frequency appear to affect community assembly in lowland rain forests in the TSP. While species are hence not ecologically equivalent, interspecific ecological differences do not seem to affect the overall patterns of species diversity, which are mostly determined by biogeographical variables, as predicted by the neutral theory. [source]

Effects of mesoscale environmental heterogeneity and dispersal limitation on floristic variation in rain forest ferns

JOURNAL OF ECOLOGY, Issue 1 2006
MIRKKA M. JONES
Summary 1Field studies to evaluate the roles of environmental variation and random dispersal in explaining variation in the floristic composition of rain forest plants at landscape to regional scales have yet to reach a consensus. Moreover, only one study has focused on scales below 10 km2, where the effects of dispersal limitation are expected to be easiest to observe. 2In the present study, we estimate the importance of differences in some key environmental variables (describing canopy openness, soils and topography) relative to the geographical distances between sample plots as determinants of differences in pteridophyte (ferns and fern allies) species composition between plots within a c. 5.7 km2 lowland rain forest site in Costa Rica. 3To assess the relative importance of environmental vs. geographical distances in relation to the length of environmental gradient covered, we compared the results obtained over the full range of soil types, including swamps, with those for upland soils alone. 4Environmental variability was found to be a far stronger predictor of changes in floristic differences than the geographical distance between sample plots. In particular, differences in soil nutrient content, drainage and canopy openness correlated with floristic differences. 5The decline in mean floristic similarity with increasing geographical distance was stronger than proposed by the random dispersal model over short distances (up to c. 100 m), which is probably attributable to both dispersal limitation and environmental changes. The scatter around the mean was large at all distances. 6Our initial expectation was that the effects of dispersal limitation (represented by geographical distance) on observed patterns of floristic similarity would be stronger, and those of environmental differences weaker, than at broader spatial scales. Instead, these results suggest that the niche assembly view is a more accurate representation of pteridophyte communities at local to mesoscales than the dispersal assembly view. [source]

Seed bank, seed dispersal and vegetation cover: Colonization along a newly-created river channel

JOURNAL OF VEGETATION SCIENCE, Issue 5 2006
A.M. Gurnell
Stace (1999) Abstract Question: What is the relative importance of the initial seed bank and subsequent seed dispersal for floristic composition of bank vegetation two years after creation of a newly-cut reach of a river channel? Location: River Cole, West Midlands, United Kingdom. Methods: We took bank and bed sediment samples from a 0.5-km reach of a new river channel cut into intact flood-plain. After river diversion, seed samples deposited on artificial turf mats placed on the river banks and flood-plain edge were taken in summer and winter 2002 and 2003. Seed rain samples from funnel traps were taken during summer 2002 and 2003. We undertook greenhouse germination trials to assess viable seed species within these samples. In summer 2004, we surveyed river bank vegetation. Agglomerative cluster analysis was used to investigate floristic similarity between seed bank, seed rain, seed deposition samples and final bank vegetation cover. DCA was used to explore contrasts between the samples and to assess whether these reflected interpretable environmental gradients. Results: Seed rain samples contained a small subset of species in the summer depositional samples. 38 species were found within the final vegetation, the seed bank, and at least one of the four sets of depositional samples; a further 30 species not present in the seed-bank samples were present in at least one of the four sets of depositional samples and the final vegetation. Floristic composition of the vegetation was most similar to the depositional samples from winter 2002 and 2003 and summer 2003. DCA axis 1 reflected a time sequence from seed-bank samples through depositional samples to the final vegetation. Conclusions: Newly cut river banks were colonized rapidly. Seed remobilization and hydrochorous transport from the upstream catchment are important for colonization. Species richness was highest in samples deposited during winter when high river flows can remobilize and transport viable seeds from upstream. This process would also have enhanced the species richness of seed production along the banks during the second summer (2003). [source]

Propagule banks and regenerative strategies of aquatic plants

JOURNAL OF VEGETATION SCIENCE, Issue 1 2004
Isabelle C.S. Combroux
Lambinon et al. (1992); Wiegleb & Kaplan (1998) for Potamogeton species and Corillon (1975) for Characeae Abstract. The role of the propagule bank in aquatic plant maintenance was studied in two riverine wetlands. Four sites were selected, characterized respectively by flooding, drying up, both disturbances operating, and neither operating. Our hypothesis was that recolonization after drying up would mostly involve seeds and buds from the propagule bank, whereas recolonization after floods would mostly involve rhizomes. Dry sites were characterized by a high density of seeds, and a high similarity between seed species and established vegetation. Unspecialized fragments remaining in wet parts of the sediment probably also contribute to species maintenance. Species maintenance in sites subjected to flooding was highly dependent on deeply anchored rhizomes, as indicated by the strong floristic similarity between species that occur in the established vegetation and rhizomes in the bank. Regeneration of the community after scouring floods also involved seeds, some species being able to flower under water. When scouring flooding and drying up were superimposed, regenerative strategies exhibited in the bank did not simply result from the ,addition' of the two disturbance effects. When the disturbances did not occur too closely together in time, species were able to survive either by: (1) producing many propagules under aquatic conditions or (2) coping with the temporal variability by producing several types of propagules. [source]

Road Slope Revegetation in Semiarid Mediterranean Environments.

RESTORATION ECOLOGY, Issue 1 2007
Part I: Seed Dispersal, Spontaneous Colonization
Abstract The importance of neighboring vegetation as a seed reservoir for spontaneous colonization of adjacent road slopes was analyzed in a semiarid region of east Spain. Two independent methodological approaches were used to examine the relative contribution of seed from neighboring vegetation and the efficiency of different seed dispersal strategies in plant colonization. We first used a randomization test to compare floristic similarity between road slopes, neighboring flora, and local flora (the regional species pool found in the same climate and soil conditions as the road slopes). Second, we compared seed dispersal mechanisms of road slope vegetation with those of the surrounding area using frequency analysis. Species composition of road slopes was more similar to that of the flora of adjacent surrounding areas than expected by chance. Anemochorous (wind-dispersed) plants were over-represented in road slopes 8 years after road slopes were built. We concluded that seed dispersal from neighboring vegetation is an important factor in the vegetative colonization of road slopes. However, this initial species pool was also strongly shaped by the harsh environmental conditions of roadcuts and southern aspect. These results have important implications in road slope restoration because they suggest that naturally vegetated areas should be maintained adjacent to road slopes to enhance seed immigration from species adapted to local site conditions, which will accelerate the successional process. The application of this single reclamation strategy and mixed strategies that combine the use of natural colonization and soil amendment for road slope restoration in Mediterranean environmental conditions is discussed. [source]

Distance Decay of Tree Species Similarity in Protected Areas on Terra Firme Forests in Colombian Amazonia

Patterns of Floristic Differentiation among Atlantic Forests in Southeastern Brazil and the Influence of Climate,

BIOTROPICA, Issue 4b 2000
Ary T. Oliveira-Filho
ABSTRACT The tree flora of southeastern Brazilian Atlantic forests was investigated according to two main aspects: (a) the variations in floristic composition of bodi rain and semi-deciduous forests were analyzed in terms of geographic and climatic variables by performing multivariate analyses on 125 existing floristic checklists; and (b) the links of both rain and semi-deciduous forests to Amazonian forests and Cerrados (woody savanna) were assessed. All analyses were performed at the species, genus, and family levels. The information obtained for the 125 forest areas was organized into an environmental database containing geographic and climatic records, and a floristic database containing binary presence records for 2532 species, 520 genera, and 106 families. Canonical correspondence analyses (CCA) were utilized to assess the relationship between geographic and climatic variables, and tree flora composition. Venn diagrams and cluster analyses were used to assess the floristic links to Amazonian forests and Cerrados. The following patterns were detected at all three taxonomic levels: (a) the differentiation between rain and semi-deciduous forests is floristically consistent and strongly correlated with rainfall regime, although transitions may be abrupt to gradual; (b) a north,south differentiation exists for both rain and semi-deciduous forests, probably caused by variations in both temperature and rainfall regime; (c) The flora of semi-deciduous forests also changes with increasing distance from the ocean and the associated increasing rainfall seasonality; and (d) elevation and associated temperatures are strongly correlated with the internal differentiation of both rain and semi-deciduous forests. To a considerable extent, the tree flora of semi-deciduous forests is a subset of the rain forest flora, probably extracting species that are able to cope with a longer dry season. There is greater floristic similarity at the species level between Atlantic rain and semi-deciduous forests than between any of these and either Amazonian rain forests or Cerrados. Nevertheless, semi-deciduous forests and Cerrados show stronger links, particularly at the generic and familial levels. Therefore, rhere is little floristic ground for viewing Atlantic rain forests as being closer to their Amazonian counterparts than to the adjacent semi-deciduous forests. The most appropriate view of rain and semi-deciduous forests in southeastern Brazil is that of a continuum in tree species distribution. We suggest that the definition of Atlantic forests should be as comprehensive as that of Amazonian forests. RESUMO A flora arbórea das florestas Atlãnticas do sudeste do Brasil é investigada sob dois aspectos principals: (a) as varia¸ões em composi¸ão florística de florestas ombrófilas e semidecíduas são analisadas sob a ótica de variáveis geográficas e climáticas por meio de análises multivariadas de 125 listagens florísticas existentes na literatura; e (b) os la¸os das florestas ombrófilas e semidecíduas com as florestas Amazõnicas e cerrados são avaliados. Todas análises foram feitas nos níveis de espécie, gênero e família. A informa¸ão obtida para as 125 áreas de floresta foi organizada em um banco de dados ambientais, contendo registros geográficos e climáticos, e um banco de dados florísticos, contendo registros binários de presen¸a para 2532 espécies, 520 gêneros e 106 famílias. Análises de correspondência canõnica (ACC) foram utilizadas para avaliar as rela¸ões entre variáveis geográficas e climáticas e a composi¸ão da flora arbórea. Diagramas de Venn e análises de agrupamento foram utilizados para avaliar os la¸os florísticos com florestas Amazõnicas e cerrados. Os seguintes padrões foram detectados para todos os níveis taxonõmicos: (a) A diferencia¸ão entre florestas ombrófilas e semidecíduas é floristicamente consistente e fortemente correlacionada com o regime de chuvas, embora as transi¸ões possam ser abruptas a graduais; (b) Há uma diferencia¸ão norte-sul tanto para florestas ombrófilas como semidecíduas, provavelmente causada por varia¸ões em temperatura e regime de chuvas; (c) A flora das florestas semidecíduas também muda com a distãncia do oceano e o correspondente aumento da dura¸ão da esta¸ão seca; e (d) Altitude e suas correspondentes varia¸ões de temperatura são fortemente correlacionadas com a diferencia¸ão interna tanto das florestas ombrófilas como semidecíduas. A flora arbórea das florestas semidecíduas é, em boa medida, um sub-conjunto da flora das florestas ombrófilas, provavelmente extraindo espécies capazes de enfrentar uma esta¸ão seca mais prolongada. Há mais similaridade florística, no nível de espécies, entre florestas Atlãnticas ombrófilas e semidecíduas do que entre qualquer destas e as florestas Amazõnicas, ou mesmo os cerrados. No entanto, florestas semidecíduas e cerrados mostram la¸os florísticos mais fortes, particularmente nos níveis de gênero e família. Portanto, há pouco fundamento florístico para se pensar nas florestas ombrófilas Atlãnticas como mais próximas de suas correspondentes Amazõnicas do que de suas vizinhas semidecíduas. A abordagem mais correta para florestas ombrófilas e semidecíduas do sudeste brasileiro é de um contínue de distribui¸ão de espécies. Sugerimos, portanto, que a defini¸ão de florestas Atlãnticas deve ser tão abrangente quanto a das florestas Amazõnicas. [source]