Proceedings of the 21st Asian Pacific Weed Science Society Conference (Editors: B. Marambe, U.R. Sangakkara, W.A.J.M. De Costa, and A.S.K. Abeysekara), 2-6 October 2007, Colombo, Sri Lanka. EFFECT OF SEEDLING EMERGENCE TIME ON THE PERFORMANCE OF MAYWEED (Anthemis cotula L.): AN ALIEN INVASIVE SPECIES IN KASHMIR HIMALAYA I. Rashid, Z. Reshi and B.A. Wafai Department of Botany, University of Kashmir, Srinagar, J&K, India [email protected] Abstract: Biological invasions, caused by non-native invasive species are a major factor contributing to ecosystem perturbations and hence are being actively pursued worldwide. Mayweed (Anthemis cotula L.), a native of southern Europe-West Siberia is an aggressive invasive species in Kashmir Himalaya, India. Among the myriad of attributes, seedling emergence time is critical to its successful colonization of habitats with varying levels of soil disturbance. Field studies revealed that the species recruits individuals over an extended period of time from September to May. This recruitment period is interspersed by harsh snowy winter (December-February) and hence the established plants of the species are constituted of pre-winter and post-winter populations, with former contributing to the fitness component of its life history and latter to the survival component. Except for number of achenes per capitulum and achene weight, all other investigated parameters such as stem height, number of primary branches per plant and number of capitula per plant were significantly higher in individuals belonging to pre-winter population in than the individuals constituting the post-winter plants. Fecundity of pre-winter individuals was further enhanced if decapitated by a specific herbivore that results in over-compensatory growth. Thus, seedling emergence time is of pivotal importance to the establishment, colonization and spread of this obnoxious invasive weed in the Kashmir Himalaya. Key words: A. cotula, emergence time, invasiveness Introduction Biological invasion by alien species are among the most important driving forces of evolution on our human-dominated planet and distinctive features of this evolution now include homogenization of biota, proliferation of opportunistic species and decline of biodiversity (Eppstein and Molofsky, 2007). The growing awareness of the biological, economic and social impacts of invasive plant species has propelled the current staggering interest in identification of life-history and ecological traits that contribute to invasiveness of some species in their non-native range. This interest is further fuelled by the central importance of such studies in providing a scientific basis for the development of strategies aimed at prevention and management of invasive species (Richardson and Pyšek, 2006). While species invasiveness has been associated with a variety of individual traits such as high seed production, dispersal, vegetative reproduction, broad tolerance or phenotypic plasticity (Baker, 1965; Sutherland, 2004; Pyšek and Richardson, 2007), yet seedling emergence time, known to significantly influence survival, growth, competitive ability and ultimately fitness of established adult plants (Geber and Griffen, 2003), has been rarely considered as a key trait contributing to invasiveness of the species with protracted seedling recruitment pattern. The present study thus, examined the influence of emergence date of Anthemis cotula seedlings on the vegetative, reproductive and fitness attributes of adult plants, and the relationship between phenotypic variation in germination time to environmental factors, and invasiveness of the species in the Kashmir Himalaya. 408 Proceedings of the 21st Asian Pacific Weed Science Society Conference (Editors: B. Marambe, U.R. Sangakkara, W.A.J.M. De Costa, and A.S.K. Abeysekara), 2-6 October 2007, Colombo, Sri Lanka. Materials and Methods Study species Mayweed (Anthemis cotula L.), also known as Stinking Chamomile, is an annual bushy, branched ill-scented herb of the Asteraceae. It is native to southern Europe-west Siberia but at present has cosmopolitan distribution (Erneberg, 1999). This invasive species can follow a winter or summer life cycle resulting in the formation of two distinct (pre and post-winter) populations. After emergence in the fall, A. cotula forms a basal rosette for winter survival. In a winter annual life cycle, the rosette bolts in the spring, growing to a height of about 25-125 cm. Capitula are 15-30 mm in diameter and contain white neuter ray florets and yellow hermaphroditic disc florets. The plant is strongly self- incompatible and mostly pollinated by insects. Study area The study was carried out in the Mirza Bagh campus of the University of Kashmir, Srinagar, J&K, India, lying within the geographical co-ordinates of 34° 5' to 34° 6' N latitude and 74° 8' to 74° 9' E longitude at an altitude of 1,586 meters above mean sea level. This three hectare area is an abandoned wasteland previously occupied by grassland that now supports vegetation dominated by A. cotula. The temperature at the study site ranges from an average daily maximum of 22°C and minimum of 3°C. It receives annual precipitation of about 70 cm, mostly in the form of snow during winter months. Sampling In June 2003, three study sites within the Mirza Bagh campus designated as S1, S2 and S3 were selected for studies of seedling establishment, survival and reproductive differences among the individuals of pre-winter and post-winter populations. Average distance between the three study sites ranged from 75 to 100 m. Seedlings emergence pattern in A. cotula was -2 monitored in three randomly laid permanent quadrats (1m ) at each study site, which were surveyed after an interval of 15 days during the study period from the stage of seedling recruitment to maturation i.e. from September 2003 to July 2004, except during the period when the entire study area was covered with snow. The seedlings, after attaining distinctive appearance, were marked using color paint following Khushwaha et al. (1981). The marked seedlings were again counted on the subsequent census to record mortality and survival of the individuals. The seedlings without color marking on each sampling date constituted the new recruits which after counting were marked with the color paint in the permanent quadrats to distinguish between previous and new recruits on successive sampling dates. Mortality data of pre-winter and post winter individuals was used to construct population survivorship curves. At maturity, just prior to dispersal of achenes, data on attributes, namely stem height, number of primary branches per plant, number of capitula per plant, number of achenes per capitulum and average weight of 1000 achenes per plant were recorded. Data were statistically analyzed using SPSS version 10.0. Results Seedling recruitment pattern Seedling emergence in A. cotula, a winter annual, starts in early autumn (September) and lasts till spring (May). During this entire period, recruitment occurs in two main pulses. The recruitment pattern shows a relationship with temperature and precipitation (Figure 1). A major pulse of recruitment occurs in autumn prior to onset of winter (December-February) and a minor pulse occurs during spring (April). 409 Proceedings of the 21st Asian Pacific Weed Science Society Conference (Editors: B. Marambe, U.R. Sangakkara, W.A.J.M. De Costa, and A.S.K. Abeysekara), 2-6 October 2007, Colombo, Sri Lanka. 25 80 Precipitation 70 Temperature Temperature (°C) 20 No. of No. of seedlings emerged 60 and seedlings Precipitation emerged (cm) 15 50 40 0 10 30 20 5 10 0 0 Se Oc No De Ja Fe Ma Ap Ma Ju Ju p t v c n b r r y n l Months (1st Sept. 2003 -15th Jul. 2004) Figure 1. Temporal Variation in seedling emergence (Mean ± SD) of A. cotula (continuous line) in relation to temperature and precipitation (bars). There was an irregular mortality pattern in the populations investigated. The population size was higher during autumn and thereafter declined considerably. Since the established populations of A. cotula in the Kashmir Himalaya consist of individuals of both the pre- as well as the post-winter seedlings, the numbers surviving during the study period at each site are presented as survivorship curves (Figure 2). Pre-winter population exhibits a Type II curve while as post-winter population showed Type I survivorship curve. 14 8 Pop 3 ) Pop 2 6 -2 12 Pop 1 4 10 2 0 8 AMJ J 6 4 Log (number of individuals m 2 0 SONAMJ J Months (Sep.03 - Jul.04) Figure 2. Survivorship curves for pre (main) and post-winter (inset) populations in A. cotula in Kashmir Himalaya. 410 Proceedings of the 21st Asian Pacific Weed Science Society Conference (Editors: B. Marambe, U.R. Sangakkara, W.A.J.M. De Costa, and A.S.K. Abeysekara), 2-6 October 2007, Colombo, Sri Lanka. Emergence time and fitness attributes The individuals of the two populations differed significantly in respect of vegetative parameters, such as stem height (p<0.0001), number of primary branches per plant (p<0.0001), total number of branches per plant (p<0.0001) and reproductive attributes such as number of capitula per plant (p<0.0001) and number of achenes per plant (p<0.0001). However, statistically insignificant differences between the two populations were recorded in the number of secondary branches per primary branch (p<0.047) and average achene weight (p<0.033). Particularly important was the significant increase in the numbers of primary branches per plant in individuals of pre-winter population because it influenced the number of capitula and hence the number of reproductive propagules and subsequent invasiveness of the species in the Kashmir Himalaya (Table 1). Table 1. Comparison of vegetative and reproductive attributes of pre- and post-winter populations of A. cotula across different study sites. (Mean ± SD based on 3 replicates). Attribute Population Pop 1 Pop 2 Pop 3 Pre-winter 91.80 ± 6.92 87.87 ± 5.94 87.47 ± 5.07 Stem height (cm) Post-winter 42.00 ± 5.06 36.67 ± 5.62 37.56 ± 2.70 No.