Abstract Detail



Ecology

Houghton, Sydney [1], Meyer, Susan [2], Stevens, Michael T. [1].

Seed Pod Wind Dispersal of Holmgren’s Milk-vetch Astragalus holmgreniorum.

Astragalus holmgreniorum is an endemic perennial herb of the northern Mojave Desert near St. George, Utah. Populations occur at elevations between 750-900 meters in areas that are gently sloping, with gravelly sandy loam soils. Soil surface is composed of small stone and gravel deposits with low amounts of living cover. The plants are generally found on the skirt edges of washes and individuals are widely dispersed, suggesting wind as a mechanism of dispersal. The fruits start out as fully bilocular, trigonously-compressed legumes with the ventral side of the fruit wall folded inward to form a double walled partition between the valves. Once ripe seeds are produced, the pod becomes coriaceous and partially dehisces from both ends. The ventral side sulcus separates, exposing the inner partition and allowing the ends of the pod to curve dorsally. The morphological characteristics of the pods at this stage exhibit aerodynamic qualities. This study was performed to determine if wind dispersal is possible and if seeds are dispersed individually from the pods as a consequence. A runway was designed with different substrates: sand, small gravel, and medium gravel. Three degrees of slope were tested: no slope, upslope and downslope. Three speeds of wind velocity (4.3 m/s, 7.1 m/s, 10.7 m/s) were provided by a fan to mimic environmental conditions in a controlled laboratory setting. For each treatment combination a new group of pods was tested. In total, 324 individual seed pods were trialed at two orientations to the wind. Pod mass was recorded before and after running trials to quantify any seed loss. Results showed that the pods have significant ability to move in the wind. On average, it took 3.73 seconds for pods to reach a distance of 152.4 cm. The percentage of pods that reached this distance varied according to surface attributes: on sand 50%reached this distance, while only 27%of seed pods reached this distance on small gravel. Seed loss averaged 24.5% across all substrates. This investigation fills knowledge gaps in dispersal processes and shows how environmental conditions affect such processes. This information is valuable for conservation efforts of this federally listed endangered species.


1 - Utah Valley University, Biology, 800 West University Parkway, Orem, UT, 84058, USA
2 - USFS SHRUB SCIENCES LABORATORY, 735 North 500 East, Provo, UT, 84606, United States

Keywords:
Astragalus
seed dispersal
endangered
Conservation.

Presentation Type: Oral Paper
Number:
Abstract ID:678
Candidate for Awards:Ecological Section Best Undergraduate Presentation Award


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