Common reed (Phragmites australis) is a nonnative invasive perennial grass that is problematic in aquatic and riparian environments across the United States. Common reed often forms monotypic stands that displace native vegetation which provide food and cover for wildlife. To help maintain native habitats and manage populations of common reed in the United States, an understanding of its life history and starch allocation patterns are needed. Monthly biomass samples were harvested from sites throughout the Mobile River delta in southern Alabama, USA from January 2006 to December 2007 to quantify seasonal biomass and starch allocation patterns. Total biomass of common reed throughout the study was between 1375 and 3718 g m⁻² depending on the season. Maximum aboveground biomass was 2200 ± 220 g m⁻² in October of 2006 and 1302 ± 88 g m⁻² in December of 2007. Maximum belowground biomass was seen in November of 2006 and 2007 with 1602 ± 233 and 1610 ± 517 g m⁻² respectively. Biomass was related to ambient temperature, in that, as temperature decreased aboveground biomass (p  =  0.05) decreased. Decreases in aboveground biomass were followed by an increase in belowground biomass (p < 0.01). Starch comprised 1 to 10% of aboveground biomass with peak temporary storage occurring in July and August 2006 and September to November of 2007. Belowground tissues stored the majority of starch for common reed regardless of the time of year. Overall, belowground tissues stored 5 to 20% of total starch for common reed with peak storage occurring in December 2006 and October 2007. Starch allocation to belowground tissues increased as temperatures decreased. Understanding seasonal life history patterns can provide information to guide management strategies by identifying the vulnerable points in biomass and starch reserves in common reed.

Nomenclature: Common reed, Phragmites australis (Cav.) Trin. ex Steud PHRCO.

Management Implications: Common reed is an invasive grass that continues to spread across the United States. The genetic haplotype I is the dominant form of this species along the Gulf Coast of the United States. During this two year study, common reed biomass fluctuated seasonally, though maximum biomass exceeded 3700 g m⁻². Biomass allocation was influenced by seasonal temperatures in that aboveground biomass peaked in early fall, followed by a peak in belowground biomass. The peak in belowground biomass allocation corresponded to increased starch allocation to underground tissues. Understanding these seasonal life history patterns can provide information to guide management strategies by identifying the vulnerable points in biomass and starch reserves in common reed. Based on these data it may be beneficial to implement management techniques in early spring when starch reserves in belowground tissues are being used to support shoot growth. Aboveground biomass during this time would be reduced as plants would be small, and therefore, may be more susceptible to management.