Rodent mediated seed dispersal of Joshua tree (Yucca brevifolia)

The Joshua tree is a charismatic and popular symbol of the Mojave Desert. Despite its popularity, we know little about the ecology of this species. The seed dispersal of Joshua tree, in particular, has not been thoroughly studied to this point. Here I examine the possible mechanisms acting to disperse Joshua tree seeds and their resulting fate. I hypothesized that Joshua tree seeds are cached by scatter-hoarding rodents and that other dispersal syndromes are unlikely. The majority of Joshua tree fruits monitored were taken directly from Joshua tree canopy by white-tailed antelope ground squirrels, and seeds and fruits on the soil surface were quickly removed by animals. Rodents given seeds labeled with scandium -- 46 cached them between 0.1 cm and 4.1 cm deep. Seedling emergence was most common for seeds planted between 1 cm and 3 cm in the field, and at 1 cm in a growth chamber. Seeds placed on the soil surface were unlikely to germinate. Anemochory is unlikely because the wind speeds required to move Joshua tree seeds and fruits across the soil surface were high (mean 43.6 km/h and 31.9 km/h respectively), and rodents are likely to remove seeds before abiotic burial. These data show that the most common fate of Joshua tree seeds is hoarding by rodents. Caches made by rodents are an effective means of dispersal for Joshua tree.;Key words: Joshua tree, Yucca brevifolia, white-tailed antelope ground squirrel, scatter-hoarding, Mojave Desert, seed dispersal...