Table 2 Comparison of the three methods in terms of equipment, procedures, costs, and operators needed. Costs are to be considered a tentative estimation; they may vary a lot according to the availability of cameras and laboratory equipments of research units. Travel expenses are calculated in case of the sampling site located within 100 km and a day in the field is about 6 working hours

Materials

Litter trap; bags; fan-forced oven; sieve, scale, and lab tools

Frame 50 × 50 cm

Reflex camera and lens; tripod; frame 50 × 50; SD card; laptop

Collection process

Installation of the LT; seed collection; separation of reproductive parts from total litter; drying of the seeds in oven (in case of biomass determination); seed count

Positioning of the frame on the ground; visual on field seed count

Positioning of the frame on the ground; tripod/camera setup; picture shooting; images download; visual on screen seed count

Storage

Physical storage of the seeds (not permanent)

_

Electronic storage of the images (permanent)

Permissions

Authorizations are required to place LT in the forest

No authorizations required

No authorizations required

Location

LT are installed in fixed locations

Frames are portable and can be easily moved

Frames and cameras are portable and can be easily moved

Operators

1–2

1

1

Estimated time per sample

2 h per trap (collection, separation, count) + 24 h in case of overdrying (seed biomass)

6 min per quadrat

6 min per quadrat (2 min shooting, up to 4 min for image download and on screen counting)

Equipment costs

250 Euros for each trap

In case of biomass determination: 5000 Euro for laboratory equipments (fan-forced oven, digital scale, storage)

20 euro per frame

2000 euros for a reflex camera, lens, SD cards + 20 euros per frame

Costs per sample (Euros)

2

 < 1

 < 1

Samples per day (N)

18–25

40

40

Travel cost (Euros)

35

35

35