Athel (Tamarix aphylla) and Athel hybrid (Tamarix aphyllaX Tamarix ramosissima)Establishment and Control at Lake Mead National Recreation Area

Athel is a large evergreen ornamental tree that has been planted throughout the Southwest since the 1950’s. Athel was considered benign because it was thought to produce non-viable seed unlike its invasive relative, tamarisk. However, athel began establishing in the wild from seed on Lake Mead in 1983. Lake Mead NRA has been actively controlling athel since November 2004 along the high water mark of Lake Mead shoreline (439 miles) to prevent it from spreading throughout the Colorado River Drainage. The NPS contracts Nevada Conservation Corp crews and the Lake Mead Exotic Plant Management Team to implement the control efforts of athel and the hybrid. Since 2004 Lake Mead NRA has controlled 72,156 athel and 11,749 hybrids. Control methods have been effective and follow up monitoring and retreatment is planned during the 2009 field season. Based on observations at Lake Mead NRA, the invasive potential of athel is high, particularly in light of its hybridization potential with tamarisk thus creating a new noxious weed. Natural resource land managers should be vigilant in monitoring current athel populations to ensure they do not become invasive or hybridize with tamarisk

Mojave Applied Ecology Notes Fall 2008

Effects of wildfires in Joshua Tree National Park, Blackbrush masting volunteer seed collection effort, new book chapter on Mojave revegetation, Natural Areas Association presentations

Relationship between 30-year temperature average and fruit and seed mass across the 10 study sites using regression analysis.

<p>Relationship between 30-year temperature average and fruit and seed mass across the 10 study sites using regression analysis.</p

Pearson correlation coefficients indicating the direction and the significance of the relationships between climate variables and stand structure and reproduction of Joshua tree across the 10 study sites.

<p>Pearson correlation coefficients indicating the direction and the significance of the relationships between climate variables and stand structure and reproduction of Joshua tree across the 10 study sites.</p

Reproductive ecology and stand structure of Joshua tree forests across climate gradients of the Mojave Desert

<div><p>Climate change is restructuring plant populations and can result in range shifts depending on responses at various life stages of plants. In 2013, a widespread and episodic flowering event provided an opportunity to characterize how Joshua tree’s reproductive success and population structure vary in response to the climate variability across its range. We examined the reproductive success and stand structure of 10 Joshua tree populations distributed across the Mojave Desert. Joshua tree density varied by more than an order of magnitude across sites. At 8 of the 10 sites, nearly 80% of the Joshua trees were in bloom, and at the other two 40% were in bloom. The range of seed production and fruit set across the study populations varied by more than an order of magnitude. Fruit production occurred at all of our study sites suggesting that yucca moth pollinators were present at our sites. Increasing temperature had strong positive correlations with the number of trees in bloom (R² = 0.42), inflorescences per tree (R² = 0.37), and fruit mass (R² = 0.77) and seed size (R² = 0.89. In contrast, temperature was negatively correlated with Joshua tree stand density (R² = -0.80). Positive correlations between temperature and greater flower and seed production suggest that warming may positively affect Joshua Tree reproduction while negative relationships between temperature and stand density are suggestive of potential constraints of warmer temperatures on establishment success.</p></div

Relationship between average warmest month temperature and stand characteristics across the 10 study sites using regression analysis.

<p>Relationship between average warmest month temperature and stand characteristics across the 10 study sites using regression analysis.</p

Relationship between 30-year temperature average and fruit and seed mass across the 10 study sites using regression analysis.

<p>Relationship between 30-year temperature average and fruit and seed mass across the 10 study sites using regression analysis.</p

Map of Joshua tree’s range in the southwestern US (gray polygons) and our 10 study locations across the range of that distribution.

<p>Data for the mapping the distribution of Joshua tree was obtained from the following database: <a href="https://databasin.org/datasets/b74f96cc008d4c7398ea0ef0bb6b4078" target="_blank">https://databasin.org/datasets/b74f96cc008d4c7398ea0ef0bb6b4078</a>.</p

Variation in reproductive characteristics across the 10 study sites.

<p>Mean values presented with ± 1 SE. F-statistics and P-values presented that test the significance of variability in reproductive characteristics across the 10 study sites. Sites are ordered from hottest to coolest from left to right. Letters in parentheses behind each site represent range location: northeast (NE), northwest (NW), southeast (SE), central (C), south (S), west (W), Multiple mean comparisons conducted using Tukey’s HSD with different letters between sites denoting significant mean differences.</p