Final Report - Center for Invasive Plant Management

seedling recruitment and fecundity. All individuals in each of these populations will bepermanently marked, and their locations mapped. Plants will be divided into four to sixsize classes based on the number of tillers and reproductive status. Size classes willinclude a seedling stage (single tiller), a juvenile stage (multiple tillers, no evidence ofpast or present sexual reproduction), and from one to three adult stages (sexualreproduction evident) that are based on estimated tiller number. Fecundity will beestimated for each adult size class based on the number of culms and florets per culm.Any seedling found in each delineated population area will be permanently marked,measured. Data for each population will be analyzed for the size classes described abovein Lefkovich transition matrices as described by Caswell (2000). Matrices will be used toestimate average transition probabilities, elasticities and sensitivity measures, and theaverage growth rate (λ) over the three seasons of this study. Average population growthrates will be tested using a paired t-test and a split plot ANOVA using the GLMprocedure of SAS (SAS 2001). The elasticity and sensitivity parameters will provide anassessment of the critical life history stages (i.e., that have the largest influence on λ:Caswell 2000), which will provide valuable information for targeted control measures.Once the source or sink status of each population is more firmly established from geneticdiversity and assignment tests, we will used pooled samples across populations of thesame type to obtain more robust estimates of the transition probabilities and growth rateparameters for each class of population.ResultsSynopsis of resultsSites were sampled for total density and reproductive effort per plant inpopulations that were central or peripheral to locations of the original introduction offalse brome in the Willamette valley. These same sites had previously been sampled forgenetic diversity at 10 microsatellite loci. Site location was not a very good predictor ofpopulation density or the reproductive effort per plant, but reproductive effort tended tobe higher for populations with higher genetic diversity.BackgroundGrasses make up a large proportion of invasive plants and are capable ofdisturbing ecological processes and native plant community structure (D'Antonio andVitousek 1992). A perennial bunch grass, Brachypodium sylvaticum, also known as falsebrome, was introduced into the Pacific Northwest in the early 1900’s. Within the lastfifteen years this species has rapidly become an aggressive invader in the Western US(Kaye 2003; Rosenthal et al. 2008 ; Ramakrishnan unpublished data). Previous work hasestablished that this species was introduced into two locations in the Willamette Valley ofOregon, and that invasive genotypes are hybrids from recombination of genotypesderived from several locations in Western Europe (Rosenthal et al. 2008). Due to therelatively recent introduction and spread of B. sylvaticum, its amenability to bothgreenhouse and genetic studies, and the large network of managers involved, this grass isan ideal system for assessing the ecological and genetic characteristics associated withinvasion.The goals of this project were two-fold: 1) to establish demographic plots forcharacterization of population size distributions and reproductive effort for sites having