Large-scale impacts of herbivores on the structural diversity of African savannas

Abstract

African savannas are undergoing management intensification, and decision makers are increasingly challenged to balance the needs of large herbivore populations with the maintenance of vegetation and ecosystem diversity. Ensuring the sustainability of Africa's natural protected areas requires information on the efficacy of management decisions at large spatial scales, but often neither experimental treatments nor large-scale responses are available for analysis. Using a new airborne remote sensing system, we mapped the threedimensional (3-D) structure of vegetation at a spatial resolution of 56 cm throughout 1640 ha of savanna after 6-, 22-, 35-, and 41-year exclusions of herbivores, as well as in unprotected areas, across Kruger National Park in South Africa. Areas in which herbivores were excluded over the short term (6 years) contained 38%-80% less bare ground compared with those that were exposed to mammalian herbivory. In the longer-term (> 22 years), the 3-D structure of woody vegetation differed significantly between protected and accessible landscapes, with up to 11-fold greater woody canopy cover in the areas without herbivores. Our maps revealed 2 scales of ecosystem response to herbivore consumption, one broadly mediated by geologic substrate and the other mediated by hillslope-scale variation in soil nutrient availability and moisture conditions. Our results are the first to quantitatively illustrate the extent to which herbivores can affect the 3-D structural diversity of vegetation across large savanna landscapes.ecological sustainability ͉ ecosystem heterogeneity ͉ Kruger National Park ͉ park management ͉ protected areas ͉ South Africa ͉ vegetation structure

Influence of plant resistance traits in selectiveness and species strength in a tropical plant‐herbivore network

“…Th e increased precipitation during the wet season is likely to promote greater quality and quantity of host plants ( Reich et al, 1997 ;Asner et al, 2009 ;Janecke and Smith, 2011 ;López-Carretero et al, 2014 ), providing a fair variety of microhabitats and resources favoring richness and abundance of herbivores ( Janzen, 1993 ;Fernandes et al, 2004 ;Yarnes and Boecklen, 2005 ;López-Carretero, 2010 ;López-Carretero et al, 2014 ), and a homogeneous distribution of food resources for all herbivore species ( Lewinsohn et al, 2005 ;Lewinsohn and Roslin, 2008 ). Th ese factors are likely to be translated into increased plant species strength and herbivore selectiveness (or specialization) in the network.…”

The development of agriculture in the Americas: an ecological perspective

“…For example, in Kruger National Park in South Africa, herbivores over 5kg were excluded from two plots (220 and 230 ha) for 36 and 40 years. There was a large increase in plant biomass in the enclosures with no large herbivores, suggesting that the additional NPP went into plant matter instead of more small herbivores (Asner et al 2009). In North America, Bison did eventually consume some of the liberated NPP, but only later (Meagher 1986), following extensive physiologi- (Balter 2007).…”

Bases ecológicas para implementar un sistema de uso silvopastoral en la región patagónica de Aysén, Chile

“…Ejemplos bien conocidos y estudiados de estos sistemas existen en la región central de Chile (espinales; Ovalle et al 1990, Aronson et al 2002, Muñoz et al 2006), California (McNaughton 1968, Roche et al 2012) y Australia (Dorrough et al 2006, Barnes et al 2009, Le Brocque et al 2009). Las sabanas naturales como ecosistemas donde coexiste la vegetación herbácea y la arbustiva y los grandes herbívoros también se han estudiado, en África (McNaughton 1979, Knoop y Waker 1985, Belsky et al 1989, Mordelet y Menaut 1995, Ong y Leakey 1999, Ludwig et al 2004, Sankaran et al 2005, Treydte et al 2007, Asner et al 2009) y en Norteamérica (McNaughton 1968, Belsky y Canham 1994, McPherson 1997, Jose et al 2004. En estas regiones y en otras más templadas también existen sistemas de uso ganadero que incorporan el arbolado (Cooper et al 1996, Feldhake 2001, Alavalapati et al 2004, Mosquera-Losada et al 2006, Guevara-Escobar et al 2007, Benavides et al 2009), con importantes beneficios para las características productivas de las comunidades herbáceas, la diversidad biológica y la provisión de servicios ambientales (Young 1989, Sanchez 1995, Etienne 1996, Altieri 1999, Jose et al 2004, Palma et al 2007, Benavides et al 2009, Jose 2009, Pastur et al 2012).…”

“…Al efecto del arbolado sobre las estructura de los pastizales hay que añadir el importante efecto ocasionado por el pastoreo de grandes herbívoros silvestres y ganado doméstico, sobre todo vacuno (Kho et al 2001, Clarke 2003, Abule et al 2005, Dorrough et al 2006, Barnes et al 2009). La presencia de estos herbívoros condiciona también la dinámica de regeneración natural del bosque y la vegetación bajo el dosel , Cavieres y Fajardo 2005, Asner et al 2009). …”

“…El pastoreo con ganado es uno de los factores más importantes en la estructura y dinámica de las comunidades de pastizal, modificando su composición florística y diversidad (Crawley 1983, McNaughton 1985, Milchunas et al, 1988, Pacala y Crawley 1992, Milchunas y Lauenroth 1993, Hobbs 1996, Collins et al 1998, Stohlgren et al 1999, Adler et al 2001, Díaz et al 2001, Olff y Ritchie 1998, De Bello et al 2006, Asner et al 2009), así como su biomasa y tasa de renovación (Margalef 1974, McNaughton 1979, Huntly 1991, Oesterheld et al 1992, Milchunas y Lauenroth 1993, de Mazancourt et al 1998, de Mazancourt y Loreau 2000, Leriche et al 2001). …”