Using tree population size structures to assess the impacts of cattle grazing and eucalypts plantations in subtropical South America

Abstract

To evaluate the effects of distinct management of the matrix in which forest fragments are found upon plant populations thriving in forest remnants in south Brazil, we assessed the conservation status of populations of four woody species (Campomanesia rhombea, Diospyros incontans, Myrciaria cuspidata and Sebastiania commersoniana) through analyses of size structure. Analyzes were carried out at two scales. At a local scale, we consider populations in fragments surrounded by pastures or eucalypts forest plantations, and at a regional scale we also consider larger forest tracts taken as reference areas (Rio Grande do Sul Forest Inventory databank). Population size structures were summarized using the symmetry of height distributions. Small individual size classes prevailed at the local scale in fragments surrounded by eucalypts plantations, whereas in areas exposed to cattle ranching, populations of the same species consistently lack small individuals. At the regional scale, populations in fragments surrounded by pastures presented greater skewness (prevalence of small plants) than populations in reference areas, while populations surrounded by eucalypts plantations presented intermediate skewness. These results reinforce the notion that plantations have a higher conservation value for forest ecosystems than other commercial land uses, like cattle ranching.

Effects of Environmental Changes on the Occurrence of Oreomunnea mexicana (Juglandaceae) in a Biodiversity Hotspot Cloud Forest

“…In this region, the inverse J-shaped population structure of the species suggests a favorable regeneration and a mature stable system according to de Souza et al [51]. However, aggregate spatial structures of the species suggest that abiotic processes such as habitat heterogeneity, disturbances or other stochastic events contribute to nonrandom distributions of trees.…”

Native forest management in subtropical South America: long-term effects of logging and multiple-use on forest structure and diversity

“…In a longer time scale, logged fragments may suffer from hampered succession due to dispersal limitation (Barlow et al 2006) and pervasive edge effects (Broadbent et al 2008) that promote widespread and permanent tree canopy openings (Souza and Martins 2005), elevated tree mortality (Laurance et al 2002) and favored population growth of pioneer species (Dupuy and Chazdon 1998;Laurance et al 2006), among other changes. Pervasive edge effects in the study region have been found to contribute to forest degradation elsewhere and include cattle grazing and trampling (Eyre et al 2010;Souza et al 2010), fire, hunting, firewood extraction, and seed harvesting (Guerra et al 2002;Silveira et al 2007). As has been found in other ecoregions (Santos et al 2008;Pütz et al 2011), degradation was more pronounced in smaller fragments, which are more susceptible to edge effects (Broadbent et al 2008).…”

“…Our results indicate that Angiosperms, on the other hand, may be more prone to ecologicallybased management plans aiming at selective logging, as indicated by its resilience to disturbance as a group and the formerly heavily-logged Ocotea in particular. The ecological sustainability of such exploitation, however, is likely to rely on more careful and biodiversityoriented management (Bawa et al 1998;Putz et al 2001;Fonseca et al 2009), that should include: (a) reduced logging intensities (Sist et al 1998;Chapman et al 2000;Barlow et al 2006;Eyre et al 2010), possibly up to 15 % of each stand basal area (Sist and Nguyen-Thé 2002), (b) adoption of careful planning of logging strategies aiming at minimizing operational impacts during felling and yarding, like reduced-impact logging (Sist et al 1998), (c) adoption of rotation times longer (at least 55 years) than those employed in experimental A. angustifolia plantations (45 years, Guerra et al 2002) (Horne and Hickey 1991;Sist et al 1998;Kariuki et al 2006;Sebbenn et al 2008;Fonseca et al 2009;Eyre et al 2010), (d) setting aside at least 10 % or a minimum of 25 ha (Pütz et al 2011) of managed forests as unlogged refugia for species conservation and as colonist sources (Barlow et al 2006), (e) restriction of forest management to fragments larger than the prudential and tentative threshold size of 100 ha, (f) sustainable harvesting of non timber forest products (Guerra et al 2002;Silveira et al 2007), (g) development of locally based ecotourism, (h) the regulation and generalization of landowners payment for ecosystem services, (i) livestock exclusion from forest remnants, in order to allow the maintenance of understory biodiversity (Fonseca et al 2009) and overstory natural regeneration (Eyre et al 2010;Souza et al 2010), and (j) restrict human access other than touristic to managed forests in order to avoid associated degrading effects like hunting and fire (Toivonen et al 2011). Each of these points represents a research agenda of great conservation relevance in itself.…”

“…30-40 years of post-harvesting undisturbed succession (Horne and Hickey 1991;Panfil and Gullison 1998;Gerwing 2002;Kariuki et al 2006). Fragmentation and chronic disturbance, however, degrade forest fragments and keep them at early successional stages (Putz et al 2001;Santos et al 2008;Pütz et al 2011), with higher tree density, reduced basal area and scarce or absent regeneration (Gerwing 2002;Laurance et al 2002;Souza and Martins 2005;Broadbent et al 2008;Santos et al 2008;Eyre et al 2010;Souza et al 2010;Pütz et al 2011;Toivonen et al 2011). Structure of recentlylogged forests is expected to lie in between that of control and fragments.…”

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).…”