Role of nurse plants in Araucaria Forest expansion over grassland in south Brazil

Abstract

Araucaria Forest expansion over grassland takes place under wet climate conditions and low disturbance and it is hypothesized that isolated trees established on grassland facilitate the establishment of forest woody species beneath their canopies. Forest with Araucaria angustifolia is a particular type of Brazilian Atlantic Forest and the main forest type on the highland plateau in south Brazil, often forming mosaics with natural Campos grassland. The objectives of this paper were to evaluate the role of isolated shrubs and trees as colonization sites for seedlings of Araucaria Forest woody species on grassland, to determine which species function as preferential nurse plants in the process and the importance of vertebrate diaspore dispersal on the structure of seedling communities beneath nurse plants. The study was conducted in São Francisco de Paula, Rio Grande do Sul State, where we sampled isolated shrubs and trees in natural grassland near Araucaria Forest edges. Seedlings were counted and identified, and seedling diaspore dispersal syndromes, size and colour were registered. We detected 11 woody species with a potential role in nucleating grassland colonization by forest species. Beneath the canopies of nurse plants more forest species seedlings were found compared with open field grassland and the seedlings had diaspores mostly dispersed by vertebrates. Also, more seedlings were found under the canopy of A. angustifolia than beneath other nurse plant species. We conclude that A. angustifolia trees established on grassland act as nurse plants, by attracting disperser birds that promote colonization of the site by other forest species seedlings, and that under low level of grassland disturbance, conservation of frugivorous vertebrate assemblages may increase forest expansion over natural grassland and also facilitate the regeneration of degraded forest areas.

Neotropical rainforest restoration: comparing passive, plantation and nucleation approaches

“…In a review of system patchiness, it was determined that ''scattered trees'' act as keystone structures capable of increased landscape connectivity and function as restoration nuclei (Manning et al 2006). Araucaria pine trees that establish in Brazilian grasslands can attract bird species known to disperse seeds of forest species (Duarte et al 2006). Slocum (2001) described similar patterns with the formation of ''tree islands'' in abandoned pastures from ''focal trees'' in Costa Rica.…”

White grubs (Coleoptera, Melolonthidae) in the "Planalto Region", Rio Grande do Sul state, Brazil: Key for identification, species richness and distribution

“…Latosol is the predominant soil type in the region, but also occur Argisol in the west (Streck et al 2008). The Planalto is represented by the combination of two floristic ecoregions, the Brazilian Araucaria moist forests and "Campos" moist grasslands, both with secondary vegetation and agricultural activities (Duarte et al 2006). The Brazilian Araucaria moist forests have a predominance of Araucaria angustifolia, Podocarpus lambertii and Ilex paraguariensis.…”

Dinâmica de habitats na região subtropical da América do Sul: determinantes socioeconômicos e padrões de paisagem em um ecótono floresta-campo

“…Southern Atlantic forests have been shown to colonize grasslands through direct succession from fragment edges and natural patches under grazing and fire exclusion (Oliveira and Pillar, 2005) or through nucleation around isolated Araucaria angustifolia trees growing in grasslands (Duarte et al, 2006).The conservation status of small forest patches in the southern extreme of the Atlantic Forests, however, is generally impaired by cattle grazing (Souza et al, 2010) and other non-sustainable uses (Souza et al, 2012). Biodiversity conservation has been shown to be much increased, however, under minimally protected areas (Souza et al, 2012).…”

“…The Pampa grasslands biological diversity is differentiated along moisture/microtopographic gradients (Focht and Pillar, 2003), and hence grassland loss should affect distinct sets of species depending on the spatial distribution of land conversion. Forested areas, on the other hand, seem to have expanded (Duarte et al, 2006;Hansen et al, 2013;Hendges et al, 2012;Scariot et al, 2015), possibly for socioeconomic reasons related to rural exodus and ageing smallholder rural populations (Schneider, 1994). Up to now, land use changes in southern Brazil have been poorly documented compared to other regions of Brazil, and the socioeconomic drivers of these changes have scarcely been investigated (see Naumov, 2005 for a general review).In the transitional forestgrassland region of southern Brazil (northern Rio Grande do Sul), small-scale family agriculture concentrates on beans, manioc, pork, and chicken production, and coexists with extensive business agriculture concentrated on soy, corn, tobacco, wheat, and cattle ranching (Rio Grande do Sul, 2012).…”