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