Estrutura e dinâmica populacional de Lychnophora pinaster MART. em campos rupestres no sul de Minas Gerais

Abstract

The Brazilian rocky grasslands is a predominantly herbaceous-shrub vegetation with trees no taller than two meters. Typical species occur in complex vegetation mosaics shaped by micro relief, alternating rocky outcrops and shallow soils. Species of the genus Lychnophora are endemic to these rocky grasslands and suffer intense speciation due to the geographical barriers typical of the disjoint distribution of this type of environment. Lychnophora pinaster Mart. is one of the endemic endangered species of rocky grasslands of Minas Gerais. The species Lychnophora pinaster is considered a vulnerable species, due to the decline of its populations associated to the excessive exploitation, due to its medicinal properties and loss of its habitat (monocultures, tourism, mining and the advance of constructions). Thus, the objective of this work was to analyze the structure, spatial distribution and population dynamics of the Lychnophora pinaster species in the rocky grasslands in the South of Minas Gerais, as well as the soil variables that contribute or restrict its abundance and growth. The study areas are located in the municipalities of Itumirim and Carrancas, on the Alto do Rio Grande plateau, in the south of Minas Gerais. Permanent plots (20 m × 10 m) in the number of 30 were placed in two parallel continuous lines in each one of both areas. The data sampled included number and height of individuals, and diameter at ground level (DNS). The soil variables measured were pH, K, Ca, Al, P, Mg, SB, T, V, t, m, M.O. and Prem of each area. The populations of Itumirim and Carrancas presented an aggregate distribution pattern. The total number of individuals of L. pinaster measured was 3293 at Itumirim and 2857 at Carrancas. A high concentration of individuals in the smaller classes (both, height and diameter) was observed in both populations. In Itumirim individuals with smaller diameter and height were more abundant respectively in soil and gravel, whereas in Carrancas the individuals of smaller diameter and size were concentrated respectively in soil and rock slit. Larger individuals were more common on rock and rock crevices in both areas. The mortality rate was around 4% for both populations, and far below the recruitment rate, which for the population of Itumirim was 11.91% and Carrancas 14.29%. The loss in basal area was lower (6.25% for Carrancas and 5.91% for Itumirim) than the gain in basal area (17.04% for Carrancas and 24.03% for Itumirim) due to higher recruitment than mortality to the growht of survivors. Rates of recruitment, mortality, ingrowth and outgrowth were higher for smaller classes in both areas. When analyzing the dynamics of the two populations in the different substrates, both areas had a higher recruitment in the soil, however, the mortality was higher in the rock in Itumirim and in the rock crevice in Carrancas. In relation to the environmental variables, it is observed that Prem, ot, SB, and Fe positively affect the growth rate of the population of Itumirim and Carrancas, the recruitment rate is positively influenced by Prem and t. The models had poor explanation for density of individuals, diameter, height and mortality rate. We suggest new studies with smaller scales in terms of of soil collection, also analyzing water quantity and competition for exploring some of these not explained patterns.