LIVESTOCK GRAZING REDUCES SOIL QUALITY AND THREATENS RECOVERY OF A DEGRADED ANDEAN ARAUCARIA FOREST.
Oscar Crovo1, Clara da Costa-Reidel1, Francisco Montecino1, Rolando Rodríguez2, Felipe Aburto1*
1 Laboratorio de Investigación en Suelos, Aguas y Bosques (LISAB). Departamento de Silvicultura, Universidad de Concepción, Facultad de Ciencias Forestales.
2 Departamento de Manejo de Bosques y Medioambiente, Universidad de Concepción, Facultad de Ciencias Forestales, Concepción, Chile.
* feaburto@udec.cl, Victoria 631, Facultad de Ciencias Forestales, Barrio Universitario, Concepción, Chile
ABSTRACT
Araucaria araucana is an iconic long-lived endangered tree species exclusively distributed in Southern Chile and Argentina. Araucaria forests provide a myriad of ecosystem benefits to local aboriginal Mapuche-Pehuenche communities. Among the main current threats for Araucaria forests are the increasing frequency and severity of wildfires and overgrazing. This study evaluates the effect of uncontrolled livestock grazing on soil quality indicators linked to critical functions relevant to forest regeneration and ecosystem service provision. We also aim to determine a set of sensitive soil quality indicators to grazing pressure, so they are useful as early indicators of degradation or restoration practices’ effectiveness. This study evaluated twenty soil quality indicators in two contiguous degraded forest areas with contrasting grazing pressure. We observed a substantial shift in forest structure, a reduction in tree coverage on the overgrazed sites. Overgrazing has significantly affected most soil physical, chemical, and biological quality indicators making soil conditions less suitable for seed germination and sapling establishment. We also observed an alteration in C, N, and P biogeochemical pools. Besides, soil physical indicators alterations suggest changes in these soils’ hydrological behavior, potentially reducing water storage, availability, and increasing runoff. We show that uncontrolled grazing in native protected areas degrades soils and forest health, restricting forest regeneration and potentially accelerating erosive processes. Our results emphasized the need for an improved conservation plan for these forests that systematically evaluates and monitors livestock grazing and its direct and indirect effects, including soil quality.
Keywords : soil health, overgrazing, tree regeneration, mountainous forest, volcanic soils
INTRODUCTION
Mountain forest ecosystems are a complex socioecological system where competitive land-uses, management practices, and biodiversity conservation are in a continuous quarrel (Concostrina‐Zubiri et al., 2017; Renison et al., 2010). Most of the ecosystem services that forests provide, such as clean water provision, carbon sequestration, nutrient cycling, and biodiversity conservation, depend on maintaining adequate soil functioning and quality (Dominati et al., 2010; Wu, 2013). However, large areas of these natural forest ecosystems have been pushed to a limit where soil conservation and functioning are at risk. The main drivers for forest ecosystem degradation processes are timber extraction and overgrazing, which affect both soil quality and natural forest regeneration and successional processes.
In many South American mountainous areas, where grazing is a relevant activity, there have been reports of land and forest degradation (e.g., Renison et al. (2010)). In the past decades, researchers have shown strong evidence of the negative impacts of overgrazing on plant communities and a few other on soil degradation (Concostrina‐Zubiri et al., 2017; Greenwood & McKenzie, 2001; Krümmelbein et al., 2009; Manzano & Návar, 2000; Suet al.,2004). The reduction of canopy cover, the destruction of topsoil structure and soil compaction followed by a decrease in soil infiltration and chemical properties (Krümmelbein et al., 2009; Steffens., 2008) induced by grazing has led to accelerated erosion and land degradation in many regions around the world (Steffens et al., 2008).
Zamorano-Elgueta et al. (2012) studied cattle activity effectsAraucaria araucana (Molina) K. Koch forests in the Chilean coastal mountain range, finding that overgrazing produced soil compaction and diminished tree recruitment. On the Argentinian side of the Cordillera de los Andes, Renison et al. (2010) found that domestic livestock is indeed the primary driver of forest and soil degradation. Currently, there is no governmental regulation concerning the use of forests for pasturing animals in Chile (Dube et al., 2016). Thus, forest and soil degradation could become worse in the future decades. The control of these potentially irreversible soil degradation processes is critical for Araucaria forests as this is an endangered species (Premoli et al., 2013) with innumerable cultural and environmental value. Moreover, Araucaria is an internationally protected species in both Chile and Argentina through its listing in I appendix of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Soil quality indicators for soil derived from volcanic materials have been relatively less studied than for other soil types, with a few exceptions (e.g., Alfaro et al. 2018, Valle and Carrasco 2018 Zuñiga et al., 2015). Valle and Carrasco (2018) tested a complete set of soil quality indicators in three volcanic soils identifying a group of them sensitive to contrasting land-use changes (native forest to prairies and cropland). The main parameters highlighted for these authors were bulk density, water retention-derived properties, SOC, P-Olsen, extractable Al, and base saturation.
In this study, we assessed the effect of exotic livestock overgrazing inAraucaria forests’ soil quality, using the relatively recently created Ralco National Reserve (Biobio Region, Chile) as a study site. This National Reserve was created for environmental conservation considering the Mapuche-Pehuenche local indigenous communities’ historical use for livestock grazing and other relevant cultural services like collecting araucaria tree seed (piñon).
Here we aim to evaluate the effect of grazing in critical soil properties related to ecosystem functions that sustain forest regeneration. We also seek to identify which properties are more sensitive to this impact. We hypothesized that livestock grazing had hampered soil quality in these weakly developed volcanic soils, affecting critical functions to plant recruitment and forest health. We expect that the soil properties identified here will help build a robust and sensitive set of soil quality indicators that could alert land managers of ongoing degradation in similar ecosystems across the Andean Region.
2. MATERIALS AND METHODS