Journal of Vegetation Science 20: 424–432, 2009 & 2009 International Association for Vegetation Science Ecological consequences of a massive flowering event of bamboo (Chusquea culeou) in a temperate forest of Patagonia, Argentina Marchesini, Victoria A.1Ã; Sala, Osvaldo E.2 & Austin, Amy T.1,3 1IFEVA-CONICET and Faculty of Agronomy, University of Buenos Aires, Av. San Martı´n 4453 Buenos Aires (C1417DSE); Argentina; 2Department of Ecology and Evolutionary Biology, Brown University, Box G-W Providence, RI 02912, USA; E-mail [email protected]; 3E-mail [email protected]; ÃCorresponding author; Fax 15411 4514 8730; E-mail [email protected] Abstract Keywords: Bamboo flowering; Forest regeneration; Light availability; Nothofagus forest; Seedling demography. Question: What changes occur as a consequence of the massive flowering and senescence of the dominant unders- Nomenclature: Clark (1989) . tory species of bamboo, Chusquea culeou (E. Desvaux)? In this study, we documented some of the ecological consequences of this rare event that occurred in 2001, Abbreviations: PAR 5 Photosynthetically Active Radiation. the previous flowering having occurred more than 60 years ago. Introduction Location: Nothofagus temperate forest, Patagonia, Argen- tina. Understory vegetation has been recognized to exert a profound influence on the structure and dy- Methods: We assessed changes in environmental variables namics of diverse forests around the world (Veblen and bamboo biomass post-flowering in an old-growth 1982; Young 1991; Taylor et al. 2004), and in South southern beech forest. In addition, we monitored the America, bamboo grass species are one of the most demography of emergent Ch. culeou seedling and Notho- conspicuous species dominating the forest unders- fagus nervosa saplings, comparing non-flowered (live tory (Clark 1989; Judziewics et al. 1999). Because understory) and flowered (senescent understory) patches within the forest matrix. of their rapid growth, large biomass, and high litter production (Veblen 1982; Christanty et al. 1996), it has been suggested that bamboos could play an Results: Bamboo flowering dramatically increased light availability in the forest understory but, surprisingly, important role in forest ecosystems, affecting com- other environmental changes were not observed. Bamboo petitive interactions, nutrient turnover, and forest seedlings emerged in both patch types, and experienced regeneration (Taylor & Zisheng 1987). gradual but modest mortality through time. Bamboo A particular feature of most bamboo species is dieback promoted higher survivorship and an increment an unusual life cycle, which varies from 3 to 120 in biomass, height, number of leaves and buds in the years (McClure 1993), ending with a single re- saplings of Nothofagus nervosa. productive event that leads to massive flowering and seed production (McClure 1993; Keeley & Bond Conclusion: The high density of bamboo seedlings 5 years 1999). In general, these synchronized flowering epi- after the flowering event and the independence of emer- sodes involve a large fraction of the population, gence from environmental variables suggest that although occasionally, patches of non-flowered understory regeneration is a gradual process that is not clumps remain. Seed production during flowering strongly regulated by initial seedling density or resource events is copious; for example, Gonza´lez & Donoso limitation. In contrast, microenvironmental conditions À 1 created after the flowering event significantly increased (1999) estimated an input of 50 million seeds ha Nothofagus sapling growth and survival. These results during the flowering of Chusquea quila in a southern suggest that overstory forest regeneration could be en- beech forest in Chile, and frequently there is an as- hanced in this temperate forest in the first years after this sociated explosion of granivores (Jansen 1976; infrequent bamboo flowering event. Gallardo & Mercado 1999; Jaksic & Lima 2003). - Ecological consequences of a massive flowering event of bamboo - 425 Bamboo flowering events have been recorded for temperatures in the forest understory. In addition, centuries, especially in Asia (Gadgil & Prasad 1984; we hypothesized that soil water availability would Taylor & Zisheng 1993), but in the Americas, re- increase due to decreased evapotranspiration by the cords are scarce (Seifriz 1950; Filgueiras 1988). Due understory bamboo. Finally, we tested predictions to long vegetative periods and unpredictable flow- that these environmental changes would alter forest ering episodes, little is known about the ecological conditions, increasing bamboo seedling and overs- impact of this phenomenon on forest dynamics, tory sapling survival and growth in areas of bamboo particularly in the first years post-flowering. The flowering and dieback. extensive germination and seedling establishment after flowering events suggests that regulation by Methods density-dependent effects could be important fac- tors controlling the final population size and Study site distribution of bamboo in the understory (Makita 1996). In 1998, the Forest Service of the Lanı´n Na- In North and South America, Chusquea is one tional Park in the Neuque´n Province of Argentina of the most diverse genera of woody bamboos, ex- (41110S, 71121W) observed some isolated flowered tending from Mexico to the Patagonian forests of patches of Ch. culeou in the south-central portion of Argentina and Chile (Clark 1989; Judziewics et al. the park (Sanguinetti & Garcı´a 2001). During spring 1999). In many of these temperate forests, Chusquea and summer of 2000-2001, the flowering event of is the dominant vegetation growing below a Notho- Ch. culeou extended over more than 200 000 ha of fagus spp. overstory (Veblen 1982). In particular, temperate Nothofagus forests of Patagonia, princi- Chusquea culeou has the most widespread distribu- pally between 391-401S (Kitzberger et al. 2007; tion, ranging between 351S and 471S (Parodi 1941; Raffaele et al. 2007). The massive flowering and sub- Veblen et al. 1996). The dense aggregation of culms sequent dieback took place in both humid and dry in the understory can reach 2 to 6 m in height in a zones, in high and lowland sites, and involved non- matter of months (Veblen et al. 1980; Pearson et al. disturbed areas as well as those affected by grazing 1994). Veblen (1982) observed the influence of and recurrent fires (Sanguinetti & Garcı´a 2001). Chusquea tenuiflora on tree sapling establishment in Field sampling was conducted from January Chilean forests, with increased tree recruitment in 2003 to March 2006, at several points during spring, areas without a bamboo understory. Similarly, stu- summer, and fall. The study site is an undisturbed dies in temperate forests of Asia associated tree forest in the Yuco Station of Lanı´n National Park, sapling density and growth with the presence of un- near San Martı´n de los Andes (800 m a.s.l). This derstory bamboo (Nakashizuka 1988; Taylor & temperate forest site includes two deciduous tree Zisheng 1992; Narukawa & Yamamoto 2002). Fi- species, Nothofagus obliqua and N. nervosa, and one nally, recent studies after flowering events in evergreen species, N. dombeyi (Veblen et al. 1996; temperate Chilean forests have shown high sapling Marchelli & Gallo 1999). The site has nearly density of overstory species in flowered areas (Gon- equivalent proportions of the three Nothofagus spp, za´lez et al. 2002; Holz & Veblen 2006). as represented by basal area (Vivanco & Austin Like many other bamboos, Ch. culeou exhibits 2008), and Ch. culeou almost completely dominates gregarious and synchronous reproduction, an event the understory, except for rare shrub (Aristotelia that occurred most recently in 2001 in the north- chilensis and Azara microphylla) and herbaceous western Patagonian region of Argentina. Historic species (Osmorrhiza chilensis and Alstroemeria aur- records from Pearson et al. (1994) for temperate ea) (Dezzotti et al. 2003). Annual precipitation is forests in northwest Patagonia indicate that the last 2300 mm, and mean temperature ranges between flowering events of Ch. culeou occurred in 1900 and 31C during winter and 151C in summer (Estacio´n 1938. As the last flowering occurred more than 60 Meteorolo´gica Estancia Quechuquina, Neuque´n years ago, there is little information on the ecologi- Province, Argentina). Soils are Andisols, derived cal consequences in these temperate forests. In this from volcanic ash, with a high content of silt, clay, study, we examined changes in a native old-growth and organic matter (Dezzotti et al. 2003). Nothofagus forest after the recent Ch. culeou massive flowering. Specifically, we tested predictions that, as Experimental design a result of bamboo flowering, microenvironmental conditions would be substantially altered, with in- In order to evaluate the magnitude of the flow- creases in light availability, and air and soil ering event at a local scale, we randomly established 426 Marchesini, V.A. et al. 21 transects of 50 m within the site. In each transect, Environmental variation as a consequence of bamboo we counted the total number of bamboo culms flowering touching the tape, and identified them as non-flow- ered (live) and flowered (senescent). Considering We measured light, air and soil temperature, these categories, we estimated the overall percentage relative air humidity, and soil water content in live of non-flowered and flowered bamboo within the and senescent bamboo patches. Three dataloggers study site. per patch type were installed to