Regeneration Stratum Research Articles

Effects of Vegetable Cover on the Regeneration Process in Degraded Dry Forest in Brazil

ABSTRACTThe Brazilian Caatinga is among the most diverse dry forests in the world, yet half of its original coverage has been degraded. Natural regeneration is influenced by climatic and edaphic conditions, as well as the existing adult stratum. Despite its significance, this process remains poorly understood in the Caatinga. Thus, our study aimed to analyze how anthropogenic disturbance, vegetation cover, and soil properties affect the regenerating stratum under different levels of Caatinga vegetation cover. The research was conducted in the driest region of Brazil. The selected sites represent low (Area I) and high (Area II) normalized difference vegetation index. Six vegetable plots (50 × 20 m each) were delimited to study adult stratum, and four vegetable plots (10 × 10 m each) to regeneration stratum. Topsoil was sampled in all vegetable plots. Our results reveal interactions between soil characteristics and the adult and regenerating strata. Area II exhibited higher diversity and a greater number of exclusive species, while Area I was dominated by species more resistant to limiting conditions, such as Aspidosperma pyrifolium Mart. & Zucc. The C and N content in the soil showed a positive and significant correlation with the diversity of the regenerating stratum. The data suggest that the area with less vegetation cover, richness, and diversity shows signs of desertification.

EFEITOS DO FOGO NA REGENERAÇÃO NATURAL EM FLORESTA ESTACIONAL SEMIDECIDUAL

ABSTRACT Forest fire is considered a relevant environmental and ecological issue worldwide, as it causes population, ecosystem, and economic impacts, making monitoring and additional research necessary to understand post-fire forest recovery. Thus, the aim of this study was to evaluate the changes that occurred in the natural regeneration stratum in a fragment of Atlantic Forest in the municipality of Viçosa (MG), with and without the occurrence of fire. The phytosociological parameters and the functional diversity of the plant community were evaluated through 20 plots, 10 in the burnt area and 10 in the unburnt area, in 2018 and 2019, to follow the natural regeneration. There were collected, in the burnt and unburnt areas, respectively, 113 and 126 individuals, 23 and 16 species, and 13 and 9 botanical families. Piper sp.1, showed the highest values for the parameters: relative density, absolute frequency, and cover value, occurring in 100% of the plots. Areas with occurrence of fire present higher species richness. Species of the genus Piper occur frequently in areas of Semideciduous Seasonal Forest with signs of disturbance. The highest Shannon diversity and Pielou equitability indexes were found in the burnt area. The Jaccard index and the cluster analysis confirm the formation of groups with low similarity, showing floristic heterogeneity between the two areas, and the disturbance caused by fire is considered an important aspect for this floristic differentiation to occur. Therefore, the occurrence of forest fire in areas of Atlantic Forest increased the diversity values of species, with an increase in the equitability index, showing low floristic similarity between burnt and unburnt areas.

Influence of Environmental Variables on the Natural Regeneration of a Forest under Restoration after Bauxite Mining and in a Reference Ecosystem in Southeastern Brazil

The shrub-tree floristic composition of the natural regeneration stratum of a bauxite mine in the process of restoration and in a reference ecosystem (remnant of a preserved secondary Seasonal Semi-Deciduous Forest) were analysed to evaluate forest restoration conditions after five years of planting. The influence of canopy openness, accumulated leaf litter and soil attributes in the regeneration stratum were also investigated in both the forests. The floristic composition of the regeneration stratum in the forest under restoration (16 species and 5,083 individuals ha-1) and in the reference ecosystem (58 species and 26,250 individuals ha-1) are distinct due to the difference in the environmental variables. Results showed that the reference ecosystem favours the presence of species that tolerate environments with greater shading and higher aluminium and organic matter content in the soil like Psychotria carthagenensis Jacq., while the forest under restoration favours the presence of species adapted to fertile soils and those that tolerate greater luminosity like Vernonanthura phosphorica (Vell.) H.Rob.

Changes caused by forest logging in structure and floristic diversity of natural regeneration: Relationship between climate variables and forest dynamics in the eastern Amazon

Several studies indicate that the Amazon rainforest is home to the greatest biodiversity of tree species on the planet. The unique quality of this forest typology is under constant threat of change owing to the behavior of climate variables and different anthropic activities that occur in the biome itself. Therefore, it is essential to conduct studies that clarify the factors that affect the formation of forests in this ecosystem and to validate the use of forest resources by society through appropriate forest management practices. Thus, this study aimed to answer how the structure, composition and floristic diversity of the forest are influenced by forest logging in different phases of development of a local Amazonian forest, and whether there is a relationship between these attributes and regional and global climate factors. This study assessed the dynamics of natural regeneration of 36 permanent plots over 33 years after logging in the Tapajós National Forest in Belterra, State of Pará, Brazil. The plots studied were measured in 1981, 1983, 1985, 1987, 1992, 1997, 2007, and 2012. All individuals with height greater than 30 cm and diameter at breast height <10 cm were monitored in three regeneration strata (seedlings, saplings, and small trees) and three forest classes (gap-phase forest, growing forest, and old-growth forest). Density, floristic similarity according to the Sørensen Index, and floristic diversity according to the Hill series were analyzed. Climate variables such as mean annual compensated temperature; total annual precipitation, and Oceanic Niño Index were correlated with the mortality, recruitment, and density of growing trees. An ANOVA for count data verified that the density of individuals differed over time since logging among the regeneration strata and forest classes analyzed. Likewise, the diversity profiles generated from the Hill series were significantly different from each other, and the floristic similarity varied between regeneration strata over time. For the forest classes, the similarity values ranged between 50% and 96%. The gap-phase forest areas had the lowest similarity values, with some 100% dissimilar surveys. However, there was an exponential reduction in similarity over time in the different forest classes. The results indicate that logging promotes significant changes in floristic structure and diversity in different strata of natural regeneration and forest classes over time. Additionally, no correlation was found between climate variables and the natural regeneration dynamics in the Tapajós National Forest.

Response of taxonomic and functional diversity to disturbance severity in temperate hardwood forests

AbstractAims:Quantify changes in taxonomic and functional diversity (FD) and identity to determine if responses to a disturbance severity gradient follow a “colonization/competition” hypothesis: diversity will (a) increase with disturbance severity as more open conditions favor species with traits linked to colonization; and (b) become more similar between regeneration and overstorey layers as environmental filtering favors species with traits linked to increasing competition for light.Location:North Carolina, USA.Methods:Taxonomic (richness [S], evenness [E], and Shannon diversity [H′]) and functional diversity (richness [FRic], evenness [FEve], and dispersion [FDis]) and identities were calculated for regeneration and overstorey before and after restoration treatments: control (CONT); “undesirable” subcanopy stems removed via herbicide (HERB); repeated burning (RRXF); and timber harvest followed by burning (HARV).Results:In the overstorey, HARV affected taxonomic and FD. In HARV, S and H′ were lower than in other treatments. At high levels of species richness, FEve was lower in HARV than in HERB and RRXF. Similarly, at high levels of species richness, FDis was greater in HARV than other treatments. In the regeneration layer, taxonomic and FD did not differ across treatments during any of the post‐treatment years. In the regeneration stratum, HARV increased the means of traits associated with rapid post‐disturbance establishment, carbon capture, and maximum height. Greater dissimilarity in composition between the overstorey and regeneration suggests stronger treatment effects on regeneration in HARV than less severe treatments.Conclusion:Patterns do not support the hypothesis that taxonomic diversity increases with disturbance severity or decreases with time after disturbance in the regeneration layer. Of the restoration treatments tested in this study, only HARV affected aspects of functional identity of the regeneration stratum; even so, FD remained unchanged. In mixed Quercus forests, functional identity rather than taxonomic or FD may provide insight into nuanced effects of restoration treatments on ecosystem function.

Soil carbon and nitrogen stocks and the quality of soil organic matter under silvopastoral systems in the Brazilian Cerrado

This study investigated soil carbon and nitrogen stocks and quality of soil organic matter in an Eutric Haplic Cambisol four years after the conversion of degraded pastures into silvopastoral systems in the Brazilian Cerrado. The integrated production systems were composed of marandu grass (Urochloa brizanta) and Eucalyptus cloeziana or Eucalyptus urograndis. These systems were compared with areas of regenerating stratum and native vegetation of the Cerrado biome. A randomized statistical design was used, and soil chemical and biological attributes and soil CO2 efflux were evaluated (p < 0.05). After four years of implantation, soil carbon and nitrogen stocks increased in silvopastoral systems in relation to regeneration stratum, but were still lower than those in native vegetation. The chemical and granulometric soil fractionations indicated that carbon was protected in the most stable soil organic matter fractions (humin and silt + clay). There was an increase in soil microbial carbon during the rainy season and the metabolic quotient during the dry period. The deposition of plant material and soil tillage in silvopastoral systems composed of marandu grass (Urochloa) and Eucalyptus cloeziana contributed to an increase in soil microbial carbon at the 10–20 cm soil layer. The soil CO2 efflux, during the rainy and dry seasons, was similar between both silvopastoral systems and native vegetation, probably indicating greater diversity of organisms and roots in these systems than in regeneration stratum. We conclude that the introduction of integrated systems improved soil quality, allowing greater protection of soil organic matter.

White ash (Fraxinus americana) survival in the core of the emerald ash borer (Agrilus planipennis) invasion

Despite catastrophic ash (Fraxinus spp.) mortality observed by the mid-2000s in the epicenter of the emerald ash borer (EAB) (Agrilus planipennis Fairmaire) invasion in southeast Michigan, we noticed numerous live white ash (Fraxinus americana L.) in some forests in this region. In 2015, we inventoried overstory trees and regeneration in 28 white ash sites spanning 11 counties. White ash survival ranged from 0% to 100% of stems. Overall, 75% of 821 white ash trees, ranging from 10.0 to 44.0 cm diameter at breast height, and 66% of the white ash basal area, ranging from 0.3 to 3.5 m2·ha–1, were alive. Nearly all live white ash had signs of previous EAB colonization, but 83% had healthy canopies (≤10% canopy dieback). Green ash trees were recorded in 27 sites, but 92% were killed by EAB. Model selection indicated that variation in white ash survival was related to white ash abundance and distance of sites from the original EAB epicenter but not to green ash related variables or to the distance of sites from the Asian parasitoid release or recovery locations. Regeneration strata were dominated by white ash, suggesting that some white ash populations may persist in post-invasion areas.

Rehabilitation silviculture in a high-graded temperate mixedwood stand in Quebec, Canada

Vast areas of hardwood and mixedwood forests of eastern North America have been high-graded in the past and need silvicultural treatments to increase their value and productivity. To rehabilitate a high-graded temperate mixedwood stand, in Quebec, Canada, we used a split–split-split plot design with three replicates to assess different seed-tree and strip cutting systems, in combination with scarification and planting. The experiment consisted of three regeneration cuts in main plots: 10 seed-trees/ha, 40 seed-trees/ha and a 40-m wide strip clearcut (0 seed-tree/ha) with 60 seed-trees/ha in leave strips, thereby resulting in four levels of tree retention, and all included understory brushing. We applied two types of scarification (patch scarification or disk-trenching) to subplots, two regeneration modes (natural regeneration or planting with white spruce [Picea glauca]) to sub-subplots and two mechanical release treatments (softwood or mixedwood production) to planted sub–sub-subplots. Density of seed-trees did not affect the natural regeneration dynamics after 5 years, but disk-trenching was more efficient for the establishment of yellow birch (Betula alleghaniensis) and sugar maple (Acer saccharum). Few seed-trees of desirable white spruce were present and most died standing, confirming the importance of supplemental planting. Height growth of planted seedlings was 15% higher in the 0 and 10 (26–27 cm/year) than in the 40 and 60 (23 cm/year) seed-trees/ha treatments, and release doubled mean height growth (33.1 vs. 16.6 cm/year). Despite intensive site preparation, pre-established beaked hazel (Corylus cornuta) and mountain maple (Acer spicatum) were present at high densities in the regeneration stratum. Controlling this recalcitrant layer might be the greatest challenge for rehabilitating degraded stands of the mixedwood forest, especially since the use of herbicides is prohibited on Quebec’s public lands.

Regeneração de agroflorestas: a importância da cobertura arbórea na transição florestal

Este estudo analisou e descreveu a composição, riqueza e diversidade de espécies do componente arbustivo-arbóreo nos diferentes estratos florestais de um sistema agroflorestal abandonado (~3 ha), situado em área urbana de Floresta Atlântica, no município de Juiz de Fora (MG), Brasil. Partiu-se da premissa de que o estrato arbóreo remanescente tende a auxiliar o processo de regeneração natural e sucessão florestal. Foram alocadas aleatoriamente 25 parcelas de 20 x 20 m para a análise do estrato arbóreo e subparcelas de 5 x 5 m para a análise do estrato regenerante. Observou-se uma comunidade com forte dominância específica e baixo índice de diversidade de espécies (H’) em comparação com florestas secundárias de mesma fitofisionomia na região. As análises demonstraram que a presença de indivíduos de grande porte que remanesceram no local após o processo de desbaste do sub-bosque tende a auxiliar e acelerar o processo de regeneração natural e sucessão ecológica.

Invasão de palmeira australiana no sub-bosque de uma floresta plantada, Viçosa, MG

O objetivo desse trabalho foi avaliar a regeneração natural e a abundância de espécies exóticas no sub-bosque de um plantio experimental de Araucaria angustifolia, em Viçosa, MG. A amostra correspondeu a 40 parcelas de 2 m x 2 m, onde mediu-se o diâmetro ao nível do solo (DNS) de todos os indivíduos arbustivo-arbóreos com diâmetro ≤ a 5,0 cm e altura ≥ a 0,5 m. Foram calculados os parâmetros fitossociológicos e os índices de diversidade e equabilidade. As espécies foram classificadas quanto à forma de vida, classe sucessional e síndrome de dispersão. Foram amostrados 980 indivíduos, sendo observada maior proporção de espécies arbustivas, típicas de sub-bosque e zoocóricas. A espécie exótica Archontophoenix cunninghamiana, conhecida como palmeira australiana, obteve o terceiro maior valor de importância, a maior dominância e 19,25% da área basal total, valor consideravelmente maior que o das demais espécies. A. cunninghamiana foi caracterizada como uma espécie exótica invasora que domina o estrato de regeneração natural. A inibição da sucessão natural pela presença de espécies exóticas, como A. cunninghamiana, precisa ser monitorada, visando eliminar as espécies-problema, para garantir a continuidade do processo de sucessão.

NATURAL REGENERATION STRATUM AS AN INDICATOR OF RESTORATION IN AREA OF ENVIRONMENTAL COMPENSATION FOR MINING LIMESTONE, MUNICIPALITY OF BARROSO, MG, BRAZIL

ABSTRACT This study was conducted in a forest under restoration process, which belongs to the company Holcim Brasil S/A, in the municipality of Barroso, state of Minas Gerais (21º00'to 22º00'S and 43º00' to 44º00'W), where 40 plots (2 x 2 m) were set, spaced at 10 m, forming eight strata parallel to the watercourse present in the area. Floristic composition and natural regeneration stratum were characterized, and the formed strata allowed evaluating whether the riparian vegetation and watercourse influence on the local regeneration. It was found 162 individuals of 13 families, 18 genera and 22 species, and 10,125 individuals/ha were estimated. Successional classes from pioneer and early secondary and zoochory dispersion syndrome prevailed among species and individuals. The watercourse and riparian vegetation did not exercise significant influence (p&gt; 0.05) on the number of species and regenerating individuals among the different strata of the forest. The diversity index of Shannon-Wiener (H') and equability of Pielou (J') were 2.691 and 0.870, respectively. The species Psidium guajava and Myrtaceae families presented the highest VI (value of importance). Natural regeneration analysis showed the low floristic diversity in the area, suggesting that corrective management actions should be adopted.

PHYTOSOCIOLOGY AND STRUCTURAL CHARACTERIZATION OF WOODY REGENERATION FROM A REFORESTATION WITH NATIVE SPECIES IN SOUTHEASTERN BRAZIL

ABSTRACT In Brazil, specifically in São Paulo State, there are guidelines based on the high diversity of tropical forests that instructs the restoration projects in the state (current SMA 32/2014). The main goal of this study was verify the importance and effectiveness of the high diversity of arboreal species originated from a reforestation, and its influence in a woody regenerating composition. We developed a phytosociologic study in a woody regenerating stratum of a nine year old reforestation at a Private Reserve of Natural Heritage (RPPN), in Mogi-Guaçu, São Paulo State. All specimens with height &gt; 30 cm and Diameter at Breast Height (DBH) &lt; 5 cm were evaluated. The woody regenerating diversity was smaller than the overstory diversity and the species composition was similar to the overstory. The Simpson index (1-D) was 0.85, Shannon index (H') was 2.46 and the Pielou index (J') was 0.60. The zoochoric dispersion syndrome was major among the species. Our results suggest that the use of high diversity of native seedlings in a reforestation leads to high diversity of species in woody regeneration stratum, after one decade of planting.

Structure and regeneration capacity of a urban forest fragment

Understanding the plant communities affected by human activities related to urbanization is an important tool to conserve these. In this way, this study on an urban forest fragment aimed to evaluate, through a phytosociological study and investigation of the germination of the seed bank, the current forest structure, the successional strata, and the regenerative capacity of the remnant. Three different stages comprised this research, the first with a floristic survey of the entire forest remnant, then the phytosociological study of the canopy (PAP above 10 cm) and regeneration strata (PAP 5-10 cm), and at last, the study on the seed bank. The phytosociological survey of the canopy stratum presented 1,368 individuals, with 41 species distributed into 24 families. The stratum of natural regeneration had 665 individuals, being 38 species distributed into 24 familie s. The seed bank was made up by only 8 native species, and 3 exotic species. The floristic diversity of the seed bank in all samples was low due to few species provide seeds to the soil. In addition, the strata and the seed bank had a low similarity, confirming thus the fragility and the need for preservationist attitudes.

Partitioning the Effect of Release and Liming on Growth of Sugar Maple and American Beech Saplings

In northeastern North America, a growing number of studies report on the regeneration failure of sugar maple (SM, Acer saccharum Marsh.) in some SM-dominated stands coupled with a marked increase in abundance of American beech (AB, Fagus grandifolia Ehrh.) in the regeneration stratum, suggesting change in forest composition toward AB dominance. The effect of release (removing all competitors within 1 m of their crown perimeters) and liming (3 Mg ha‐1 of CaCO3) on growth of SM and AB saplings was experimentally tested to partition the effect of intertree competition and soil fertility on the growth dynamics of these two species at the sapling stage. Lime application had the desired effect on soil chemistry, expressed notably as a four-fold increase in calcium concentrations of the upper soil layer (0‐12 cm) and a 63% decrease in exchangeable acidity. Seven years following treatments, biomass growth response of AB saplings to release was 1.5 times higher than that of SM. In contrast, liming increased biomass growth of SM saplings (approximately 2 times compared with unlimed saplings), while there was no effect on AB growth. Also, the availability of light and of soil Ca interacts to increase growth of SM saplings. Our results confirm that SM is more sensitive to calcium availability than AB. Various forest management strategies are discussed in light of these experimental results.

Structural diversity of abandoned chestnut (Castanea sativa Mill.) dominated forests: Implications for forest management

Components of structural diversity of abandoned chestnut (Castanea sativa Mill.)-dominated and co-dominated forests along an altitudinal gradient in the Belasitsa mountain region of Southwest Bulgaria were evaluated, including: (i) tree species composition; (ii) differentiation in diameter, height and age; (iii) tree crown defoliation and light transmission; and (iv) regeneration composition and abundance. Competition between tree species and its influence on current stand structure were analysed. Lack of management had triggered rapid structural and successional development in formerly chestnut mono-dominated forests which have now been invaded by midseral and later seral vegetation dominated by European beech (Fagus sylvatica L.) and sessile oak (Quercus petraea Liebl.). Distribution of sample plots according to diameter differentiation for chestnut showed positive differentiation values (dominance of chestnut with respect to other species) in 43 of a total of 46 plots sampled. Structure is much more balanced in terms of height differentiation. In the absence of management, chestnut blight has been a major stress factor and is likely an important driver of chestnut decline. The proportion of chestnut trees infected by chestnut blight disease exceeded 80% in 28 plots. Nearly one third (31%) of all sampled trees were characterized by a degree of defoliation of more than 60%. Despite the low levels of light at the forest floor, the density of the regeneration stratum was relatively high (averaging 19,300ha–1). An important finding is the retained regeneration potential of chestnut (31% of all seedlings). Chestnut seedlings, however, appeared to be poorly adapted to shading and rapidly declined in density and growth while seedlings of most competitors survived longer and dominated the regeneration stratum.

Forest transformation resulting from an exotic pathogen: regeneration and tanoak mortality in coast redwood stands affected by sudden oak death

Sudden oak death is dramatically altering forests throughout coastal California, but little is known about the communities that are assembling in affected areas. This emerging disease, caused by the exotic pathogen Phytophthora ramorum (S. Werres, A.W.A.M. de Cock), has had especially severe effects on tanoak ( Notholithocarpus densiflorus (Hook. &amp; Arn.) Manos, Cannon &amp; S.H. Oh), a broadleaf evergreen that is abundant in forests dominated by coast redwood ( Sequoia sempervirens (D.Don) Endl.). Tanoak, a valuable food source to numerous wildlife species, is unlikely to successfully regenerate in diseased areas, and thus, affected redwood forests are transitioning to a novel state. In this study, to predict which species might replace tanoak, we investigated regeneration patterns in heavily impacted stands in Marin County, California. Our main findings were as follows: (i) despite reductions in canopy cover, there is no evidence that any species other than tanoak has exhibited a regenerative response to tanoak mortality, (ii) the regeneration stratum was dominated by redwood and tanoak (other tree species were patchy and (or) scarce), and (iii) some severely affected areas lacked sufficient regeneration to fully re-occupy available growing space. Our results indicate that redwood is likely to initially re-occupy the majority of the ground relinquished by tanoak, but also provide evidence that longer-term trajectories are unresolved, and may be highly responsive to management interventions.

Inventário florístico florestal de Santa Catarina (IFFSC): aspectos metodológicos e operacionais

The purpose of this study is to contribute to the discussion on regional and national forest inventories, aiming mainly on aspects of methodos and operational. The Floristic and Forest Inventory of Santa Catarina State (IFFSC) is an initiative of the state government and it was conceived in order to attend requirements of environmental laws. A pilot inventory took place in 2005; then the methodology was fitted to the proposal of the National Forest Inventory (IFN-BR) in discussion at the time. IFFSC is carried out since 2007 in all natural forest formations all over the state’s territory, including floristic sampling (collection of fertile trees, shrubs and herbs within the sample unit and in its surroundings) and survey of vascular epiphytes by specialized crews. The inventory applies a systematic sampling, with sample units containing clusters of four crosswise 1,000 m² plots (20 m x 50 m), distributed systematically at the intersections of a 10 km x 10 km grid all over the state’s territory (a 5 km x 5 km grid is applied on highly fragmentized Seasonal Deciduous Forests). Methodological details and some important operational issues are discussed beyond the four years experience of IFFSC. Major sampling intensity and lower diameter and height thresholds (in the arboreal and regeneration strata) than in the nationwide inventory proposal (IFN-BR), as well as the execution of a floristic survey within and around the sample plots, showed to be important to record plant diversity of Santa Catarina’s forests. doi: 10.4336/2010.pfb.64.291

Structure of mixed ombrophyllous forests with Araucaria angustifolia (Araucariaceae) under external stress in Southern Brazil

This study is part of the Floristic and Forest Inventory of Santa Catarina, conceived to evaluate forest resources, species composition and structure of forest remnants, providing information to update forest conservation and land use policy in Southern Brazilian State of Santa Catarina (95 000 km2). In accordance to the Brazilian National Forest Inventory (IFN-BR), the inventory applies systematic sampling, with 440 clusters containing four crosswise 1 000m2 plots (20 x 50m) each, located on a 10 x 10km grid overlaid to land use map based on classification of SPOT-4 images from 2005. Within the sample units, all woody individuals of the main stratum (DBH > or = 10cm) are measured and collected (fertile and sterile), if not undoubtedly identified in field. Regeneration stratum (height > 1.50m; DBH < 10cm) is registered in 100m2 in each sample unit. Floristic sampling includes collection of all fertile trees, shrubs and herbs within the sample unit and in its surroundings. This study performs analysis based on 92 clusters measured in 2008 within an area of 32320km2 of mixed ombrophyllous forests with Araucaria angustifolia located at the state's high plateau (500m to 1 560m above sea level at 26 degrees 00'-28 degrees 30' S and 49 degrees 13'-51 degrees 23' W). Mean density (DBH > or = 10cm) is 578 individuals/ha (ranging from 85/ha to 1 310/ha), mean species richness in measured remnants is 35 (8 to 62), Shannon and Wiener diversity index (H') varies between 1.05 and 3.48. Despite high total species diversity (364 Magnoliophyta, five Coniferophyta and one tree fern) and relatively high mean basal area (25.75m2/ha, varying from 3.87 to 68.85m2/ha), the overwhelming majority of forest fragments are considered highly impacted and impoverished, mostly by logging, burning and extensive cattle farming, turning necessary more efficient protection measures. Basal area was considered an appropriate indicator for stand quality and conservation status.

Relações entre a distribuição das espécies de diferentes estratos e as características do solo de uma floresta aluvial no Estado do Paraná, Brasil

Entre os fatores que influenciam a distribuição de espécies nas comunidades vegetais localizadas em regiões ribeirinhas, as características do solo são consideradas os mais importantes. No presente estudo, foram avaliadas a composição florística, a diversidade e a estrutura de três estratos da vegetação e suas relações com as características do solo em um fragmento de floresta aluvial na bacia do rio Iguaçu, no estado do Paraná. Buscou-se verificar se a estrutura e a diversidade da floresta nos diferentes estratos podem ser explicadas por fatores edáficos e hídricos. Caracterizaram-se os parâmetros estruturais e a composição florística de três estratos da vegetação % de regeneração (20 cm &lt; altura &lt; 1,30 m; 80 sub-parcelas de 1 m×1 m), intermediário (perímetro à altura do peito - PAP &lt; 15 cm, altura &gt; 1,30 m; 20 sub-parcelas de 5 m×5 m) e superior (PAP &gt; 15 cm, 20 parcelas de 10 m×10 m) - e correlacionaram-se as abundâncias das espécies com os parâmetros do solo e do lençol freático de cada parcela. A floresta caracterizou-se por baixa diversidade (H' = 2,36 no estrato de regeneração, 2,49 no estrato no estrato intermediário e 1,59 no estrato superior) e alta similaridade florística entre estratos (índices de similaridade de Sørensen &gt; 0,65). As relações entre a distribuição espacial das espécies e as características do solo foram distintas entre estratos: no estrato superior correlacionou-se com a profundidade do lençol freático e o teor de matéria orgânica; no intermediário, com profundidade do lençol e teor de alumínio, porém no estrato inferior nenhum dos fatores ambientais analisados explicou a distribuição das espécies. Os resultados sugerem que a estrutura e a composição florística destas comunidades aluviais refletem os diferentes níveis de interação ao longo do ciclo de vida dos indivíduos.

Fitossociologia dos estratos arbóreo e de regeneração natural em um povoamento de acácia-negra (&lt;i&gt;Acacia mearnsii&lt;/i&gt;, De Wild.) na região da Floresta Estacional Semidecidual do Rio Grande do Sul.

O presente estudo analisa a composição e a estrutura da regeneração de espécies nativas arbóreas em um povoamento de acácia-negra, estabelecido há 16 anos em área ripária, e verifica a possibilidade da acácia-negra constituir-se numa invasora desse ambiente. O estrato arbóreo (circunferência a 1,3 m de altura (CAP) ≥15 cm) foi avaliado em 12 parcelas de 100 m2, alocadas em quatro blocos perpendiculares a maior pendente da área. O estrato de regeneração natural (0,3 m de altura a CAP &lt;15 cm) foi amostrado em duas subparcelas de 9 m2, demarcadas em vértices opostos de cada parcela. O estrato arbóreo apresentou 26 espécies de 14 famílias e o estrato de regeneração natural 49 espécies de 23 famílias. O índice de diversidade de Shannon para espécie, considerando as parcelas como um todo, foi de 2,60 e 3,06 para os estratos arbóreo e de regeneração natural respectivamente. Entre as espécies nativas, Casearia sylvestris, Myrsine lorentziana e Zanthoxylum petiolare apresentaram o maior valor de importância no estrato arbóreo e Faramea marginata, Myrsine lorentziana e Myrcia glabra a maior densidade no estrato de regeneração natural. As características ecológicas das espécies encontradas nos diversos estratos de altura indicaram que o processo de sucessão florestal está em evolução. A acácia-negra não se regenerou na área e as árvores plantadas estão em senescência, sendo encontradas somente cem plantas/ha, que representa apenas 4,5% da população original. Dessa forma, a acácia-negra não se constitui numa possível invasora desse ambiente.