Are they two seeds in a pod? Comparing seed rain recovery in grasslands using artificial grass carpets versus sticky traps

Premise: Seed dispersal is a critical process for plant community
assembly; however, natural rates of seed arrival are rarely quantified
compared with other assembly mechanisms, especially in herbaceous
communities. Methods: Here we compare the utility of artificial grass
carpet squares (“artificial grass”) for capturing seed rain with classic
“sticky trap” methods. We placed paired sticky traps and artificial grass
squares in two grassland ecosystems, added known numbers of seeds of
multiple species to each trap, and recovered seeds at one-week, one-month,
and two-month intervals. Results: We found that both trap types lost seeds
through time at similar rates, but each trap type had advantages and
disadvantages. Overall, sticky traps retained more seeds and measured
primary dispersal, but recovering seeds was difficult and hindered by
debris stuck to the traps. Alternatively, artificial grass traps measured
effective dispersal as more seeds were lost through time to secondary
dispersal and granivory, but recovered seeds could be handled easily and
retained for long-term storage and germination. Discussion: We encourage
the broad adoption of seed rain studies to improve links between
theoretical and empirical community ecology. Both sticky traps and
artificial grass traps are useful in measuring seed rain in grasslands but
vary in the types of information they provide.