Changes in Soil Hydro-Physical Properties and SOM Due to Pine Afforestation and Grazing in Andean Environments Cannot Be Generalized

Abstract

Andean ecosystems provide important ecosystem services including streamflow regulation and carbon sequestration, services that are controlled by the water retention properties of the soils. Even though these soils have been historically altered by pine afforestation and grazing, little research has been dedicated to the assessment of such impacts at local or regional scales. To partially fill this knowledge gap, we present an evaluation of the impacts of pine plantations and grazing on the soil hydro-physical properties and soil organic matter (SOM) of high montane forests and páramo in southern Ecuador, at elevations varying between 2705 and 3766 m a.s.l. In total, seven study sites were selected and each one was parceled into undisturbed and altered plots with pine plantation and grazing. Soil properties were characterized at two depths, 0–10 and 10–25 cm, and differences in soil parameters between undisturbed and disturbed plots were analyzed versus factors such as ecosystem type, sampling depth, soil type, elevation, and past/present land management. The main soil properties affected by land use change are the saturated hydraulic conductivity (Ksat), the water retention capacity (pF 0 to 2.52), and SOM. The impacts of pine afforestation are dependent on sampling depth, ecosystem type, plantation characteristics, and previous land use, while the impacts of grazing are primarily dependent on sampling depth and land use management (grazing intensity and tilling activities). The site-specific nature of the found relations suggests that extension of findings in response to changes in land use in montane Andean ecosystems is risky; therefore, future evaluations of the impact of land use change on soil parameters should take into consideration that responses are or can be site specific.

Impact of tussock grasses removal on soil water content dynamics of a tropical mountain hillslope

“…It is important to mention that our emulation acts like an intensive version of the extensive grazing in páramos ecosystems because in Mean SWC diff suggests that there were no impacts in the mean SWC of Experimental transect due to the emulation (Figure 4). This agrees with other studies at páramo ecosystems, where the effects of extensive grazing on SWC of Andosols were analyzed [extensive grazing < 0.2 animals ha -1 reported in Marín et al (2018); intensive grazing: 2 -3 animals ha -1 reported in Crespo et al (2010)]. For example, Harden, Hartsig, Farley, Lee, and Bremer (2013) found in pairs of plots at north and south of the Ecuadorian Andes that alpacas grazing does not affect the hydrology of Andosols.…”

“…At these depths, soil corresponds to Andosols that have a high content of organic matter (57.41%). This is similar to the findings ofMarín et al (2018) for Andosols soils between 0 and 35 cm of depth with tussock grasses cover in Southern Ecuador (0.69 -0.67 cm 3 cm -3 ). In the studied hillslope, the lower SWC were found from 65 to 75 cm of depth (mean SWC = 0.44 cm 3 cm -3 ) in C horizon where the organic matter content is low (6.52%).…”

“…Previous studies have documented that Andosols with native tussock grasses cover in the Andes Mountains and specifically in the observatory have a high water-storage capacity (e.g., Podwojewski et al, 2002;Quichimbo et al, 2012). This is due to Andosols physical properties such as the high content of organic matter (> 30%; Buytaert et al, 2005) and low bulk density (< 0.6 gr cm -3 ; Marín et al, 2018;Poulenard, Podwojewski, & Herbillon, 2003); despite being soils of low depth (≤ 1 m). We have deepened this knowledge through the analysis of SWC During the period of this study, soils at the hillslope did not reach the saturation point (except C 10 ).…”

“…First, it leads to soil compaction, increasing soil bulk density (Célleri & Feyen, 2009) and reducing soil water storage (Podwojewski et al, 2002) and water yield with respect to its original state (Crespo et al, 2010). In fact, extensive grazing [< 0.2 animals ha −1 reported by Marín et al, (2018)] is the most common activity in páramo ecosystems (Buytaert, Iñiguez, & Bièvre, 2007) and is the cause of vegetation lost, but without soil compaction. In fact, extensive grazing [< 0.2 animals ha −1 reported by Marín et al, (2018)] is the most common activity in páramo ecosystems (Buytaert, Iñiguez, & Bièvre, 2007) and is the cause of vegetation lost, but without soil compaction.…”

“…Second, tussock grasses are almost completely eaten by livestock, leaving the land in almost bare soil conditions. In fact, extensive grazing [< 0.2 animals ha −1 reported by Marín et al, (2018)] is the most common activity in páramo ecosystems (Buytaert, Iñiguez, & Bièvre, 2007) and is the cause of vegetation lost, but without soil compaction. Vegetation lost possibly affects SWC and water yield of páramo ecosystems.…”