Forest regeneration can positively contribute to local hydrological ecosystem services: Implications for forest landscape restoration

Abstract

Governments are increasingly committing to significant forest restoration. While carbon sequestration is a major objective, the case for restoration often includes benefits to local communities. However, the impacts of forest restoration on local hydrological services (e.g. flood and erosion risk, stream flow during dry periods) are surprisingly poorly understood. Particularly limited information is available on the impacts of passive tropical forest restoration following shifting cultivation. The outcome depends on the trade‐off between the improved soil infiltration capacity (reducing overland flow and increasing soil and groundwater recharge) and greater evapotranspiration (diminishing local water availability). Using measurements from highly instrumented plots under three vegetation types in the shifting cultivation cycle in Madagascar's eastern rainforests (forest, tree fallow and degraded abandoned agricultural land), and infiltration measurements for the same vegetation types across the landscape, we explore the impacts of forest regeneration on the ecohydrological processes that underpin locally important ecosystem services. Overland flow was minimal for the tree fallow (similar to the forest) and much lower than for the degraded land, likely leading to a lower risk of erosion and flooding compared to the degraded land. Conversely, evapotranspiration losses were lower for the tree fallow than the forest, leading to a higher net recharge, likely resulting in more streamflow between rainfall events. These results demonstrate that young regenerating tropical forest vegetation can positively contribute to locally important hydrological ecosystem services. Allowing tree fallows to recover further is unlikely to further reduce the risk of overland flow but may, at least temporarily, result in less streamflow. Synthesis and applications. Encouraging natural regeneration is increasingly seen as a cost‐effective way to deliver forest landscape restoration. Our data suggest that increasing the abundance of young secondary forest in the tropics, by increasing fallow lengths in the shifting cultivation cycle, could make a positive contribution to locally important hydrological ecosystem services (specifically reducing overland flow and therefore erosion and flooding, while maintaining streamflows). Such empirical understanding is needed to inform the models used for planning forest landscape restoration to maximize benefits to local communities.

Contrasts in Top Soil Infiltration Processes for Degraded vs. Restored Lands. A Case Study at the Perijá Range in Colombia

“…The variation in K s for AR indicates that locally IOF will occur, but this flow may infiltrate at locations where the values are much higher (mean K s of 240 mm h −1 , standard deviation 212), and it is unlikely that IOF will occur at RF (mean K s of 324 mm h −1 , standard deviation 173 mm h −1 ). The latter is in line with research elsewhere [15,16,23,24]. To have a better understanding of hillslope scales it is recommended to apply larger scale measurements of overland flow, subsurface processes, and precipitation measurements.…”

“…Recent literature reviews have indicated that tree planting in the tropics can improve the water infiltration in degraded soils [3,7,15,16]. Most field studies in forests undergoing restoration [8,[17][18][19][20][21] have measured water infiltration on the top-oil focusing on the saturated soil hydraulic conductivity (K s ), only a few scientific works [22][23][24][25][26] have investigated the preferential flow pathways, explaining the water movement through the soil profile. Usually, preferential flow pathways are identified by dye tracer experiments, which have been important in hydrology to understand the water cycle, subsurface flows, and transport processes [27,28].…”

Upscaling tropical restoration to deliver environmental benefits and socially equitable outcomes

“…Natural regeneration can also provide many ecosystem service benefits, including hydrological regulation 39,40 (Figure 3C) (A) The Great Green Wall initiative aims to reduce land degradation, improve climate adaptation, and strengthen food security by restoring arid-resistant landscapes in a $15 km wide belt across 7,775 kilometres of Africa. Costing $US$43 billion by completion, 16% of the project was underway in 2020 8 .…”

“…Error bars indicate 95% confidence intervals; effects are significant (P < 0.05) if confidence interval does not overlap zero. Plots redrawn from: (A) 19 ; (B) 32 ; (C) 39 ; and (D) 54 ; data from 40 .…”

“…In Mexican dry forests, early secondary regrowth results in farmer losses of $168 ha À1 yr À1 in cattle fodder as thorny vegetation encroaches onto pasture, yet over time, older secondary forests (>25 years) deliver globally valuable carbon stocks and $$80 ha À1 yr À1 in forest-derived products and fodder 42 . Similarly, while young regenerating fallows in eastern Madagascar return key hydrological services (Figure 3C), more biodiversityand carbon-rich older forest does not further reduce the risk of overland flow and might reduce streamflow through evapotranspiration 39 .…”