Systematic review of field research reveals critical shortfalls for restoration of tropical grassy biomes

Scientists and policymakers are becoming aware of the pressing need to
restore tropical grassy biomes (TGB), which are home to unique
biodiversity and provide essential ecosystem services to hundreds of
millions of people. However, TGB face increasing threats, including the
forest- and tree-centric approaches that promote their degradation though
we still lack a systematic assessment of where and how TGB restoration
research has been done to guide policy and practice. We synthesised
knowledge on field restoration experiments by conducting a systematic
literature review to map TGB restoration field studies, examine the
association of restoration techniques and degradations sources, and
investigate the diversity of indicators used to monitor restoration
outcomes.  TGB restoration was concentrated in Brazilian and
Australian savannas, with large blindspots in Asia, Africa, and northern
and western South America. Studies were largely context-dependent, with an
inconsistent usage of restoration techniques to different sources of
degradation. Less than half of the indicators evaluated were monitored
consistently through time, often using a low-dimensional approach related
to ecosystem functioning. Few studies manipulated fire, herbivores, and
soils, the key drivers for the re-establishment of TGB dynamics.
Unfortunately, many studies lacked negative (degraded ecosystems),
positive (reference ecosystems) controls, or both, impairing attempts to
robustly determine restoration outcomes.  Our overview of field
research on TGB restoration highlights that research needs improvement to
refine our ability to assess, plan, implement, and monitor restoration.
Severe issues with experimental designs and data reporting are identified
as barriers to finding generality and upscale TGB restoration to meet the
goals of the UN Decade on Ecosystem Restoration.  Synthesis and
implications: Our synthesis calls for enhanced field experiments,
transparent data reporting, and quantitative syntheses to guide
large-scale TGB restoration. The overall lack of knowledge on improving
resilience and measuring outcomes hampers meaningful comparisons between
studies and hinders synthetic views essential for determining appropriate
restoration techniques for different degradation sources and suitable
monitoring indicators. To overcome the scarcity of reliable and
transparent data supporting TGB restoration, we propose a simple checklist
for minimum research reporting information and a more complete
multilingual standardized guideline.