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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Research Project #429070

Research Project: Factors Influencing the Establishment, Spread and Management of Invasive Ludwigia Species

Location: Invasive Species and Pollinator Health

Project Number: 2030-22000-029-08-I
Project Type: Interagency Reimbursable Agreement

Start Date: Jul 10, 2015
End Date: Sep 30, 2017

Recent aggressive spread of Ludwigia species (Onagraceae) has impacted aquatic and riverine ecosystems in Pacific west states and Florida (FL). Aquatic Ludwigia taxa are considered among the most aggressive plant invaders in the world, rapidly form dense floating mats that degrade water quality, increase flood risk, alter fish and wildlife habitat, and displace native vegetation. Rapid expansion of Ludwigia on the Russian River, and in the Sacramento-San Joaquin Delta and Willamette Valley has resource managers concerned. A similar rapid expansion of two Ludwigia species has been observed in FL on the St John’s River and Kissimmee Chain of Lakes. Continued expansion of invasive Ludwigia into key resources such as the Sacramento Delta and key restoration projects such as the Kissimmee River restoration and acquired lands under the Comprehensive Everglades Restoration Program looks to be inevitable. Current management efforts are limited and there is no consensus on best management practices. There are few published studies regarding invasion biology and management of Ludwigia. Closely related, invasive Ludwigia of varying ploidy levels may look similar, but their potential differential adaptations and tolerances to environmental conditions and biological control taxa are unknown, and will require unique management approaches. Biological and ecological data and how they vary with ploidy level of species are needed to optimize control efforts across systems. Colonization dynamics and potential changes in distribution are poorly understood in the context of global environmental change. As pressure increases to manage a variety of Ludwigia cytotypes, there is a need to develop baseline biology data to optimize control efforts in a variety of lotic and lentic sites. The USDA ARS invasive plant research group in Davis, California is conducting research on Ludwigia invasions, and given the proximity of their lab to the key invasion sites in California and their prior experience in working with this plant under both field and lab conditions, they provide unique experience, geographical proximity, and capabilities to generate information to improve long-term management strategies. Current ARS infrastructure dedicated to Ludwigia research (laboratory, greenhouse, mesocosm facilities) and prior field monitoring studies through the West Coast establishes this group as a strong collaborative partner to address Ludwigia issues in the West. Objectives are to: 1) evaluate links between weed demographic and hydrochorous dispersal processes and environmental factors (i.e. flow regimes, climate change) affecting colonization and expansion of L. hexapetala in the Russian River; 2) evaluate the effects of increasing temperature on the germination/emergence of invasive Ludwigia spp. from invaded watersheds with contrasting latitudes/climates in, and how recruitment may differ between genotypes to inform restoration and management implications of seed bank and germination under changing environmental conditions; and 3) identify and determine distribution of complex, problematic Ludwigia species in FL, southeast USA.

Obj. 1. Hypotheses: a) dispersal of asexual ramets follows nonlinear responses in watersheds; b) ramet size determines dispersal distance; c) establishment relates to ramet size, origin. Rationale: Hydrochorous dispersal and colonization of L. hexapetala ramets in the Russian River may be heterogeneous with respect to watershed position, and require atypical prioritization of management. Approach: 1) collect/characterize ramets monthly along random transects in discrete river reaches; evaluate propagule pressure, dispersal patterns and reach influence 2) Release marked replicates each of 2 size classes of ramets at 2 river reach sites, analyze dispersal distance and end-location, and model ramet length as a function of colonized habitat type; and 3) test effect of ramet origin, landing time and substrate type on colonization success in a field experiment at 3 river reach sites using ramets secured to 2 different substrates in May, July, Sept. (90 ramets/study reach), and determine survival and fitness. Results (a-c) will be evaluated with generalized linear mixed models and logistic regression. Obj. 2. Hypotheses: a) Germination of Ludwigia seeds will increase with increasing temperature; b) seedling emergence and survival will be greatest in polyploid species. Rationale: Recruitment dynamics of Ludwigia cytotypes are poorly understood in the context of global climate change. Environmental changes may alter reproductive strategies, promoting greater sexual reproduction. Approach: Mature capsules will be collected from multiple L. peploides (diploid) and L. hexapetala (decaploid) populations from cross-latitudinal watersheds. Laboratory trials on experimental seedbanks will include pot studies and/or controlled environment growth chambers using randomly designed, replicated treatments across temperature gradients. Germinants will be counted and recorded, mass of surviving seedlings will be determined, and final germination percentage, mean time to germination, germination rate will be calculated. Effects of ploidy, temperature, seed production site and their interactions on germination responses will be determined. Obj 3. Goal: Determine taxonomy of invasive Ludwigia species in Florida. Task, study sites, methods were initiated in previous agreement. Rationale: Accurate identification of invasive plant species and their distribution is an essential for the development of biological control and integrated management. Taxonomic confusion and recent ecological risk assessments point to the need for further study of the biosystematics of the genus and cytotypes invading FL watersheds. Approach: Voucher specimens for morphometric assessment and plant tissue samples will be collected from subpopulations randomly selected and widely separated in St Johns River, Kissimmee River/Lakes, and Lake Okeechobee. Live tissue will be propagated in a greenhouse for chromosome counts. Meristematic tissue will be prepared, and somatic chromosome numbers will be determined from composite image analysis of cells. Morphological characters will be quantified and statistically analyzed for differences among cytotypes.