Greenhouse gas fluxes from an oil palm plantation on mineral soil in Indonesia undergoing riparian restoration

<p>Oil palm (OP) growers are under pressure to reduce their environmental impact. Ecosystem function and biodiversity are at the forefront of the issue, but what effect do changes in management practices have on greenhouse gas (GHG) fluxes from plantations? </p><p>The Riparian Ecosystem Restoration in Tropical Agriculture (RERTA) Project is a collaboration between the University of Cambridge and the SMART Research Institute in Riau, Indonesia. This project explores the ecological changes resulting from the restoration of riparian margins between plantations and watercourses. Four management strategies were applied on both sides of a river to create 50m riparian buffers, 400m in length: (1) A control treatment of no restoration, the removal of mature OP and replanting of young OP to the river margin; (2) Little to no agricultural management of mature OP; (3) Clearance of mature OP and enrichment planting with native forest trees; (4) Little or no agricultural management of mature OP and enrichment planting with native forest trees. Here we present a specific objective to investigate the effect of riparian restoration – and related changes in soil characteristics, structure and vegetation cover – on fluxes of N<sub>2</sub>O, CH<sub>4</sub> and CO<sub>2</sub> from mineral soils.</p><p>The experimental site began as a mature OP plantation, with monthly background measurements taken between January and April 2019. Palms were felled in April 2019 and monthly sampling was resumed when replanting and restoration began, in October 2019. We measured GHGs using static chambers; 6 in each riparian treatment and 16 in the actual OP plantation, 40 chambers in total. Samples were analysed using GC-FID/µECD.</p><p>Background measurements before felling showed high variability, but indicated no difference between the four experimental plots and the rest of the plantation. Fluxes measured following replanting were also highly variable, with no significant differences observed between treatments. N<sub>2</sub>O fluxes were relatively low before felling as the mature palms were no longer fertilised. Higher emissions were seen in the disturbed immature OP and forest tree treatments following replanting. Though the sites appeared to recover quickly and emission fluxes decreased after a few months, presumably as the soil settled and new vegetation began to grow. CH<sub>4</sub> uptake was seen in the immature OP treatment immediately after replanting. In subsequent months no clear trends of CH<sub>4</sub> uptake or emission were observed, with the greatest variability generally seen in the forest tree treatment. CH<sub>4</sub> emissions increased in October 2020 with the beginning of the rainy season, most notably in mature OP and mature OP with forest tree treatments. Following restoration CO<sub>2</sub> emissions were higher in treatments with established plant communities – mature OP and mature OP with forest trees.</p><p>These results suggest that riparian restoration had no significant effect on GHG fluxes from mineral soils, and would not alter the overall GHG budget of a plantation. If there is no additional GHG burden and riparian restoration results in enhancing biodiversity and ecosystem services as well as improving water quality, it will be a viable management option to improve the environmental impact of an OP plantation.</p>

Supporting evidence varies for rangeland management practices that seek to improve soil properties and forage production in California

California is increasingly investing in policies and programs that promote soil stewardship on natural and working lands as a way to help achieve multiple goals, including improved forage production and climate change mitigation. To inform the growing expectations for rangeland management activities to promote such services, we conducted an evidence synthesis assessing how four commonly suggested practices (silvopasture, prescribed grazing, compost application and riparian restoration) affect a suite of soil properties and plant-related metrics throughout the state. We extracted data on soil properties that are potentially responsive to management and relevant to soil health. We also extracted data on aboveground forage production, forage nitrogen content and herbaceous species richness. Our search resulted in 399 individual soil observations and 64 individual plant observations. We found that the presence of oaks had the largest effects on soil properties, with soil organic carbon, microbial biomass and other measures of soil fertility increasing beneath oak canopies. The presence of grazing increased compaction and total nitrogen, and decreased pH. Compost applications did not significantly affect any of the measured soil properties, but did boost forage production. Due to a lack of published data, we were unable to characterize the influence of rangeland riparian restoration on any of the soil or plant metrics in our review.

Prioritizing riparian corridors for ecosystem restoration in urbanizing watersheds

Background Riparian corridors can affect nutrient, organic matter, and sediment transport, all of which shape water quality in streams and connected downstream waters. When functioning riparian corridors remain intact, they provide highly valued water quality ecosystem services. However, in rapidly urbanizing watersheds, riparian corridors are susceptible to development modifications that adversely affect those ecosystem services. Protecting high quality riparian corridors or restoring low quality corridors are widely advocated as watershed level water quality management options for protecting those ecosystem services. The two approaches, protection or restoration, should be viewed as complementary by watershed managers and provide a foundation for targeting highly functioning riparian corridors for protection or for identifying poorly functioning corridors for restoration. Ascertaining which strategy to use is often motivated by a specific ecosystem service, for example water quality, upon which watershed management is focused. We have previously reported on a spatially explicit model that focused on identifying riparian corridors that have specific characteristics that make them well suited for purposes of preservation and protection focused on water quality. Here we hypothesize that focusing on restoration, rather than protection, can be the basis for developing a watershed level strategy for improving water quality in urbanizing watersheds. Methods The model described here represents a geographic information system (GIS) based approach that utilizes riparian characteristics extracted from 40-meter wide corridors centered on streams and rivers. The model focuses on drinking water reservoir watersheds that can be analyzed at the sub-watershed level. Sub-watershed riparian data (vegetation, soil erodibility and surface slope) are scaled and weighted based on watershed management theories for water quality, and riparian restoration scores are assigned. Those scores are used to rank order riparian zones –the lower the score the higher the priority for riparian restoration. Results The model was applied to 90 sub-watersheds in the watershed of an important drinking water reservoir in north central Texas, USA. Results from this study area suggest that corridor scores were found to be most correlated to the amount of: forested vegetation, residential land use, soils in the highest erodibility class, and highest surface slope (r2 = 0.92, p < 0.0001). Scores allow watershed managers to rapidly focus on riparian corridors most in need of restoration. A beneficial feature of the model is that it also allows investigation of multiple scenarios of restoration strategies (e.g., revegetation, soil stabilization, flood plain leveling), giving watershed managers a tool to compare and contrast watershed level management plans.

Changes in Vegetation and Geomorphological Condition 10 Years after Riparian Restoration

Riparian restoration is an important objective for landscape managers seeking to redress the widespread degradation of riparian areas and the ecosystem services they provide. This study investigated the long-term outcomes of ‘one-off’ restoration activities undertaken in the Upper Murrumbidgee Catchment, NSW, Australia. The objective of the restoration was to protect and enhance riparian vegetation and control erosion, and consequently reduce sediment and nutrient delivery into the Murrumbidgee River. To evaluate the outcomes 10 years after restoration, rapid riparian vegetation and geomorphological assessments were undertaken at 29 sites spanning the four different restoration methods used (at least five replicates per treatment), as well as at nine comparable untreated sites. We also trialed the use of aerial imagery to compare width of riparian canopy vegetation and projective foliage cover prior to restoration with that observed after 10 years. Aerial imagery demonstrated the width of riparian canopy vegetation and projective foliage cover increased in all restored sites, especially those with native plantings. The rapid assessment process indicated that 10 years after riparian restoration, the riparian vegetation was in a better condition at treated sites compared to untreated sites. Width of riparian canopy vegetation, native mid-storey cover, native canopy cover and seedling recruitment were significantly greater in treated sites compared to untreated sites. Geomorphological condition of treated sites was significantly better than untreated sites, demonstrating the importance of livestock exclusion to improve bank and channel condition. Our findings illustrate the value of ‘one-off’ restoration activities in achieving long-term benefits for riparian health. We have demonstrated that rapid assessments of the vegetation and geomorphological condition can be undertaken post-hoc to determine the long-term outcomes, especially when supported with analysis of historical aerial imagery.

Modeling Riparian Restoration Impacts on the Hydrologic Cycle at the Babacomari Ranch, SE Arizona, USA

This paper describes coupling field experiments with surface and groundwater modeling to investigate rangelands of SE Arizona, USA using erosion-control structures to augment shallow and deep aquifer recharge. We collected field data to describe the physical and hydrological properties before and after gabions (caged riprap) were installed in an ephemeral channel. The modular finite-difference flow model is applied to simulate the amount of increase needed to raise groundwater levels. We used the average increase in infiltration measured in the field and projected on site, assuming all infiltration becomes recharge, to estimate how many gabions would be needed to increase recharge in the larger watershed. A watershed model was then applied and calibrated with discharge and 3D terrain measurements, to simulate flow volumes. Findings were coupled to extrapolate simulations and quantify long-term impacts of riparian restoration. Projected scenarios demonstrate how erosion-control structures could impact all components of the annual water budget. Results support the potential of watershed-wide gabion installation to increase total aquifer recharge, with models portraying increased subsurface connectivity and accentuated lateral flow contributions.