Abstract
Dicksonia sellowiana Hook. (Dicksoniaceae) is target of extractive exploitation and is threatened with extinction. We analyzed the population structure, the spatial distribution pattern of D. sellowiana and its relationship with environmental parameters within three fragments of Araucaria Forest in Rio Grande do Sul, Brazil. The fragments are of different sizes, namely, large (H1LF) with 246 ha, medium (H2MF) with 57 ha and small (H3SF) with 5.2 ha. Within each site, 1 ha was delimited, divided into 100 subplots (100 m2), of which 20 were selected with a draw. In each subplot, counting of the individuals, the registration of the caudice height and the coverage of leaves (SC) (m2), measurements of photosynthetically active radiation (PAR), canopy opening degree (CO), soil moisture (SM) and litter thickness (LT). The temperature (T) was measured inside each site. A total of 792 plants were sampled, of which 551 were concentrated in H1LF, 108 in H2MF and 133 in H3SF. An average of 1320 ha-1 individuals were estimated. Of the total including the three fragments, 96.9% of the individuals are in the first class of height (up to 0.8 m), indicating a great potential of population development. The spatial distribution pattern (AI) was aggregated in the three populations and the plants presented a heterogeneous total coverage, between 4.73 m2 (H2MF) and 2,223.47 m2 (H1LF). The highest values of SC and SM were more related to the distribution of individuals in H1LF whereas the opposite was recorded in H2MF. The highest values of PAR, LT and CO correlated with the distribution of D. sellowiana in H3SF. In addition to revealing that the H1LF population is among the most dense in southern Brazil, the results demonstrated a significant structural distinction between the interior populations of the fragments, in spite of them being located near to one another and being part of the same natural field matrix.
Highlights
The arborescent fern Dicksonia sellowiana Hook. (Dicksoniaceae), known as Xaxim, is the subject of extractive exploitation
In the 6,000 m2 of the three sites, 792 individuals were sampled, and the highest abundance was recorded in the H1LF, which concentrated 69.6% of the total (551), while in H2MF and H3SF 108 and 133 individuals occurred, respectively
When the sites were considered in isolation, the density estimation corresponded to 2,755 individuals ha-1 in H1LF, 540 in H2MF and 665 in H3SF
Summary
The arborescent fern Dicksonia sellowiana Hook. (Dicksoniaceae), known as Xaxim, is the subject of extractive exploitation. (Dicksoniaceae), known as Xaxim, is the subject of extractive exploitation It is listed in the Brazilian List of Flora Species Threatened by Extinction in accordance with MMA Ordinance N. 52.109/2014 (Fundação Zoobotânica do Rio Grande do Sul, 2014) This species occurs from southern Mexico in North America, in Central America, in Venezuela, Colombia, southern Bolivia, Paraguay, Uruguay and Brazil in South America (Tryon and Tryon, 1982). It was observed that, on a local scale, D. sellowiana promotes biological diversity by increasing habitat heterogeneity It facilitates the coexistence of species both by inhibiting the dominance of some woody plants and by providing habitat for the establishment of epiphytes and hemiepiphytes, which enlarges the diversity of plants in the forest (Negrão et al, 2017). Due to the presence of a porous mass of adventitious roots that holds great humidity (Cortez, 2001), the species is fundamental to the reproductive success of ferns (Becker et al, 2015) and constitutes an exclusive (Becker et al, 2015; Mallmann and Schmitt, 2014) or preferential microhabitat for some species (Schmitt et al, 2005; Cortez, 2001)
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