The impact of adaptive forest management on water fluxes and growth dynamics in a water-limited low-biomass oak coppice

Abstract

Marginal semi-arid forests in areas currently affected by climate change are a challenge to forest management, which has to focus on key functional traits that can effectively contribute to resistance under extreme drought. We studied the effects of thinning in a marginal forest by quantifying functional responses relating to growth, carbon and water fluxes. Two experimental plots were established, one thinned in 2012 and the other one left as a control. The environmental conditions varied substantially during the 4-year study period, although dry years predominated. There were signs of dieback in the control with a decreasing inter-annual trend in LAI, as opposed to the treated plots, where LAI by the end of the study almost reached pre-thinning levels. Sap flow and transpiration were greatly enhanced by the treatment, with thinned trees transpiring 22.4 l tree -1 day -1 in the growing season, about twice the control figures. The seasonal patterns of transpiration and soil moisture were uncoupled, indicating a contribution of deep groundwater to the former flux. In the control, limitations to water and carbon dynamics (canopy conductance) occurred at soil moisture values below 16%, whereas in the thinned trees these limitations appeared when soil moisture dropped below 10%.Overall, oaks' transpiration was enhanced with thinning to the point that stand-water use surpassed that of the control by the second half of the study period, averaging 24% of gross rainfall in both plots. Soil evaporation increased from 12 to 20% of gross rainfall after treatment in the overall period. The treatment had a profound watering effect in this marginal forest, led by fewer trees using the same amount of water as those in the untreated overstocked plot. This research may provide guidelines for ecohydrology-oriented silviculture in stands experiencing tree encroachment and transformation into shrublands that are more prone to global change-induced disturbances.

Effectiveness of water-oriented thinning in two semiarid forests: The redistribution of increased net rainfall into soil water, drainage and runoff

“…Samp.). Both sites have been previously defined in terms of vegetation, climate, soils and other bio-geographical traits (del Campo et al, 2018(del Campo et al, , 2019. Table 1 summarizes key information according to the objectives of this work.…”

“…In order to explain this conflicting result, we must pay attention to the antecedent soil moisture (st_rel), which was significantly improved by 10% (about 5% in absolute value) with the thinning treatment (Figure 4), and it was the most important variable in explaining the rate of Pg which is diverted into the different BHP (RI of 29% on average, Figure 3). This means that the eco-hydrological impact of forest management should be better evaluated in terms of changes in the soil water content, which is in fact one of the most important changes following thinning treatments (Breda et al, 1995;del Campo et al, 2014;Cabon et al, 2018;del Campo et al, 2019).…”

Drought Effects on Tectona grandis Water Regulation Are Mediated by Thinning, but the Effects of Thinning Are Temporary

“…Although teak can grow well on high nutrient soils in Panama, teak has been associated with dry and degraded soils that are often accompanied with low infiltration rates and high overland flow rates during rain events (Ribolzi et al, 2017, see exceptions: Fernández-Moya et al, 2013, 2014, raising concerns of how teak may affect important ecosystem services in Panama (i.e., water quality, water supply, and carbon sequestration). Although teak is a dry season deciduous and occurs in dry areas across its natural range, with respect to ecosystem services, planting teak in areas of water scarcity, in particular, is of concern given their relatively high transpiration rates and low water use efficiency (Cernusak and Aranda, 2007).…”

“…With predicted increases in temperature, in particular, understanding at what threshold tree water use begins to decline at high temperatures and VPDs is crucial for modeling future stand and landscape level responses to a changing climate. While precipitation and soil moisture are sometimes decoupled from transpiration on seasonal timescales (del Campo et al, 2019), deficits in soil moisture can still affect long term transpiration trends and growth of trees (Detto et al, 2018).…”

“…While the effects of thinning are generally considered in terms of growth, recent growing concern over water resources has sparked increasing attention on the effects of thinning as a tool to manage plantations for desirable productivity and water yield outcomes (Lagergren et al, 2008;Gavinet et al, 2019). At the individual tree level, thinning may increase tree water use due to a reduction in competition for resources and an increase in radiation hitting previously shaded leaves (Lagergren et al, 2008;del Campo et al, 2019). However, stand-level transpiration following thinning depends on many factors.…”