Abstract
In California, vernal pools are key to native flora and fauna biodiversity; therefore, the presence of invasive plant species in vernal pools can negatively affect the maintenance of native plant species diversity. The majority of research conducted on vernal pool restoration projects with exotic plant species has focused on the exotic grass species that invade from the surrounding uplands. However, exotic wetland species are also a growing threat to vernal pools. Two manual removal treatments were utilized to determine the most effective method of restricting Lythrum portula growth while increasing overall native plant species richness and abundance. The following hypotheses were tested in this study: H1: Hydroperiod, algal crust, hoofprints, and bare soil will decrease L. portula abundance. H2: Species richness of native vernal pool endemic plant species will be greater in natural vernal pools than in created (invaded and not invaded) vernal pools. H3: Created vernal pools invaded by L. portula will have lower species cover, lower species richness and a different plant species composition than created vernal pools not invaded by L. portula. H4: Removal of L. portula will increase native species abundance and richness This study took place at Van Vleck Ranch Mitigation Bank in the town of Rancho Murieta in eastern Sacramento County, California. A total of 20 experimental 1 m x 1 m plots were created in fifteen created and natural vernal pools. The 1 m2 plots were divided into a manipulated removal treatment plot and a paired non-removal control plot. A dormant season scraping removal treatment was conducted in October 2013 in all fifteen vernal pools in this study. Natural and created vernal pools that do not contain L. portula are included in the scraping removal experiment as a control. Beginning in April 2014, removal of L. portula through hand pulling and clipping was conducted and maintained in a manipulated removal treatment plot and paired non-removal control plot in five created vernal pools invaded by L. portula. The removal of L. portula through clipping was shown to benefit ten vernal pool endemic plant species by allowing for higher mean abundance in the clipped plots (Hypothesis 4). This study provides insight into L. portula as a new vernal pool invader and determines which removal treatments are the most effective in restricting L. portula growth while increasing overall native plant species richness and abundance. Further research of L. portula’s growth patterns, niche, and physiology is required. Research into other direct and controlled invasive species removal techniques that reduce the cover of L. portula in the field would be beneficial.