How have we studied seed rain in grasslands and what do we need to improve for better restoration?

Seed rain, the number of seeds reaching an area, is a process that plays a key role in recruitment and regeneration in plant communities. A better understanding of seed rain dynamics is therefore a critical step for restoration practices. A wide variety of methods to study seed rain in grasslands are available, but there is little agreement to which is the most appropriate one. Here, we (1) assessed where, how, and why research on seed rain has been carried out; (2) examined how methodological design and results have been reported; and (3) provided guidelines for future research on seed rain in grasslands. We built a database of 185 papers from a systematic literature survey between 1980 and November 2016 and we found a remarkable unbalance of the numbers of studies between grassland types, which becomes even more dissimilar across global climatic ranges when the area covered by each grassland type is addressed. We also found a great disparity of methods and data being reported across studies. Despite recent progress in understanding seed rain dynamics, large knowledge gaps in important issues such as the role of native dispersers, method efficiency, and application of mechanistic models still persist. Finally, we propose guidelines for the implementation of minimum standardized methodology and data reporting, which will foster higher quality, transparency, reproducibility, and value of seed rain studies and grassland restoration.