Understanding the Physiochemical Behaviour and Hydrological Response of Pine and Oak Vegetation: A Plot-scale Study

Abstract

An ecosystem is the unit of ecology, and any forest stands to become the parts of that particular ecosystem. For example, oak and pine forest ecosystems differ significantly. This study was conducted to understand the physio-chemical difference between the oak and pine ecosystems. To understand these differences, a watershed- and plot-scale approach was applied. Field experiment was set up in the Almora region of central Himalayan forests, Uttarakhand, India. For each ecosystem, three pots of 3m ×1.5m were constructed with sheet metal borders to alienate the runoff. In each plot, an HS flume, a water level sensor, and a zero-tension pan lysimeter were installed for stage/discharge and leachate measurements. For the watershed scale study, an H-flume and a stilling well were installed at the outlet of the draining stream. To understand the physio-chemical analysis of soil and runoff samples for both oak and pine ecosystems, 10 core and 18 disturbed soil samples were collected outside the boundaries of the plots. Similarly, after rainfall events, leachate and runoff samples were collected and analyzed for chemical composition. In-situ soil, as well as laboratory experiments, were performed for the estimation of soil physical properties. Results of the mini-disk infiltrometer test show that estimated values of hydraulic conductivity were higher for the pine forest (17.28 cm / d to 49.48 cm / d) as compared to the oak forest (1.86 cm / d to 7.98 cm /d). In contrast, sorptivity was found to be more for the oak ecosystem (1.76 to 4.09 cm / day1/2) than the pine ecosystem (0.26 to 1.91 cm / day1/2). Gravimetric analysis results showed that during the infiltrometer experiments, the oak ecosystem contained higher forest floor moisture contain (35.7 % to 43.7 %) than the pine system (4.17 % to 10.58 %). The empirical relationship established shows that for the oak ecosystem soil moisture content has a positive correlation with hydraulic conductivity and soil sorptivity. The tapped cylinder method of bulk density experiments results showed that the pine ecosystem was more compacted (bulk density range: 1.34 to 1.75 g/cc) than the oak ecosystem (bulk density range: 1.35 g/cc to 1.54 g/cc). This implies that oak ecosystem soils were more porous (0.41 to 0.48) than the pine forest soils (0.33 to 0.48). Further, the results of pressure plate experiments to understand the soil moisture retention curves (SMRC) explained that oak ecosystem soil structure has a higher potential to retain water as compared to the pine ecosystem. The developed SMRCss was helpful to support the established relationships between soil physical properties of both ecosystems. The results of the chemical analysis for the leachate and runoff samples showed that the pine ecosystem slightly acidic leachate and runoff (pH 6.68 and EC 63.4 μs/cm). Other results of base cations (Sodium and Potassium) and base anion (Sulphate) supported the hypothesis that both forest ecosystems are chemically different from each other. A study at watershed scale shows that in low flow duration oak watershed stream water yield more water than the pine watershed stream water yield.