Soil health indicators for monitoring forest ecological restoration: a critical review

Abstract

Forest restoration is considered among the most affordable and effective practices to address ecosystem and biodiversity loss and mitigate the impacts of human-induced global change. Soils are intrinsically complex systems that mediate and regulate multiple processes and functions vital for forest ecosystem restoration. Although monitoring soil attributes are critical for evaluating the success of forest restoration projects, research, and development of soil function indicators are still limited. Here, we have reviewed the most commonly reported soil indicators in forest restoration research and their recovery trajectory on a global scale. We also identified and discussed less frequently used indicators that have the potential for monitoring ecosystem recovery. We found that soil indicators have considerably increased in the literature. However, research is regionally concentrated, and a significant proportion of publications neither considered reference ecosystems (41%) nor provided basic information about soil types (<21%). The most reported indicator types were chemical (76%) (e.g., soil carbon, nitrogen, and pH). A significant proportion of the studies (46%) performed long-term evaluations (>15 years) of indicators. The majority of the indicators tended to resemble the levels of the reference ecosystem in the long term, with a few exceptions (e.g., water content and bulk density). We identified several less used but more integrative indicators with great potential for monitoring forest ecosystem recovery (e.g., aggregate stability, oxidizable carbon, soil respiration, and enzyme activity). Our results emphasize the need to effectively develop standardized soil health indicators to monitor ecosystem recovery under different conditions and expand their use in underrepresented regions.

Forty years of soil research funded by the European Commission: Trends and future. A systematic review of research projects

“…However, as forests became more important as sources of fuel, wood products, research began to evolve to consider forest soils separately, and in light of their capacity to provide important products, and more recently important ecosystem goods and services. While the number of forest soil indicators has considerably increased in the literature, there are significant knowledge gaps on forest soil processes and soil monitoring is not sufficiently harmonized (Gatica‐saavedra et al, 2022), which limits the EU's ability to soil‐related ecosystem services and to reach climate policy targets.…”

Forest Wildfires in Chile: Effects on Soil Degradation and Damage Mitigation

“…In our opinion, there is an urgent need of mapping soil resources in these areas with a special focus on delivering soil indexes of fire degradation susceptibility. Monitoring the recovery of soil indicators is essential for an adequate assessment of ecosystem recovery after restauration practices have been implemented [27,50]. Any future government regulation considering mechanisms or subsidies for reforestation of burned forests, should include mandatory monitoring plans of soil and ecosystem recovery.…”

Soil Respiration and Bacterial Changes after a Wildfire in Mediterranean-Type Ecosystems

“…Soil respiration rates indirectly shows the level of soil fertility and functionality (Yiqi and Zhou, 2010). Therefore, soil respiration rates are constantly evaluated as a key indicator during soil quality and degradation studies (Paz-Ferreiro and Fu, 2016), and consequently constitute a key indicator in forest ecological restoration monitoring and research (Gatica-Saavedra et al, 2023).…”