Road dust correlated with decreased reproduction of the endangered Utah shrub Hesperidanthus suffrutescens

Authors: LEWIS, MATTHEW - Bureau Of Land Management; SCHUPP, EUGENE - Utah State University; Monaco, Thomas

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2017
Publication Date: 12/1/2017
Citation: Lewis, M.B., Schupp, E.W., Monaco, T.A. 2017. Road dust correlated with decreased reproduction of the endangered Utah shrub Hesperidanthus suffrutescens. Western North American Naturalist. 77:430-439.

Interpretive Summary: Roads associated with energy development have fragmented much of the Colorado Plateau and elsewhere. Beyond reducing available habitat, spreading exotic species, and creating barriers to dispersal, unpaved roads also increase dust loads on plants and potentially disrupt pollinator behavior, which may reduce growth and reproduction. We studied the effects of an unpaved road on reproduction of an endangered Utah endemic shrub. We measured the size and reproductive output of 156 plants and dust deposition in plots at increasing distances from the road. We also hand outcrossed 240 flowers from 80 plants to help determine if any reduced reproduction is due to pre or post-pollination mechanisms. Additionally, we experimentally dusted 3 leaves on 30 plants (n=90) and measured stomatal conductance pre-dust and post-dust. We also dusted 3 flowers on 10 plants (n=30) prior to hand pollination and measured fruit set. Generalized linear mixed models were used to examine the relationship between reproduction and dust deposition. When controlling for plant size and distance from the road, fruit set was negatively correlated with increasing levels of dust depositon (F1,15=5.26, p=0.036). The number of seeds per plant, mean plant seed weight, and the proportion of hand-pollinated flowers that set fruit were also negatively correlated with dust, although not significantly. Dusting significantly reduced stomatal conductance (F1,58=87.56, P<0.001). Eighty percent (24/30) of hand pollinated flowers set fruit after dusting. These results demonstrate that road dust reduces H. suffrutescens reproduction, although mechanisms are not clear. Although dust negatively affected physiological processes, hand pollination results suggest dust might be disrupting pollination. This study highlights the need for further research into the effects that roads and dust have on nearby plants while strongly suggesting negative consequences for the conservation of an endangered shrub in Utah's Uinta Basin.

Technical Abstract: Roads associated with energy development have fragmented much of the Colorado Plateau and elsewhere. Beyond reducing available habitat, spreading exotic species, and creating barriers to dispersal, unpaved roads also increase dust loads on plants and potentially disrupt pollinate behavior, which may reduce growth and reproduction. We studied the effects of an unpaved road on reproduction of an endangered Utah endemic shrub. We measured the size and reproductive output of 156 plants and dust deposition in plots at increasing distances from the road. We also hand outcrossed 240 flowers from 80 plants to help determine if any reduced reproduction is due to pre or post-pollination mechanisms. Additionally, we experimentally dusted 3 leaves on 30 plants (n=90) and measured stomatal conductance pre-dust and post-dust. We also dusted 3 flowers on 10 plants (n=30) prior to hand pollination and measured fruit set. Generalized linear mixed models were used to examine the relationship between reproduction and dust deposition. When controlling for plant size and distance from the road, fruit set was negatively correlated with increasing levels of dust deposition (F1,15=5.26, p=0.036). The number of seeds per plant, mean plant seed weight, and the proportion of hand-pollinated flowers that set fruit were also negatively correlated with dust, although not significantly. Dusting significantly reduced stomatal conductance (F1,58=87.56, p<0.001). Eighty percent (24/30) of hand pollinated flowers set fruit after dusting. These results demonstrate that road dust reduces H. suffrutescens reproduction, although mechanisms are not clear. Although dust negatively affected physiological processes, hand pollination results suggest dust might be disrupting pollination. This study highlights the need for further research into the effects that roads and dust have on nearby plants while strongly suggesting negative consequences for the conservation of an endangered shrub in Utah's Unita Basin.