Effects of the occurrence of a cyclone and the dominance of a bamboo species on the dynamics of subtropical forest fragments

Abstract

With the intensification of global warming, the occurrence of large-scale natural events is becoming even more common in tropical regions, which can impact the structure of plant communities. In this study, we evaluated the isolated and combined effects of an extratropical cyclone and the dominance of a native bamboo species (Merostachys skvortzovii) on floristic composition, diversity, demographic rates and the increment of trees in Atlantic Forest fragments in Southern Brazil. In 2014 (T1) and 2016 (T2), we sampled 56 plots of 200 m² for the effects of an extratropical cyclone in 2009 (T0). We also evaluated another 60 plots of the same size not in the direct path of this cyclone. Half of the plots in each group were covered by dense groupings of bamboos, as a result of past human activities, which could potentially limit natural regeneration. We observed an increase in richness and diversity indices (H 0 and 1/D) from the first (T0) to the following assessments (T1 an T2) on the sites affected by the cyclone, when compared to non-affected sites. After the cyclone, both density and basal area they decreased, but there was an increase in recruitment, mortality, turnover rates and basal area, as well as basal increment. The diameter increment on surviving individuals was higher in cyclone-affected sites than in nonaffected sites. Bamboo cover did not affect richness or demographic rates (except mortality between T0 and T1). Natural impacts of this nature can lead to significant alterations of demographic rates, allowing the input of new species and influencing the pace of demographic processes.

How do trees survive a cyclone? The relative role of individual and site characteristics over mortality

“…Based on our results, there is a positive correlation between bamboo presence and tree mortality. This bamboo species thrives in forest areas with open canopies (Liebsch et al 2019). Due to the high degree of fragmentation and degradation of the forest remnants in the region, the populations of bamboos largely occupied the clearings of the forests (Liebsch et al 2021).…”

“…Finally, we considered the presence or absence of the native bamboo species (Merostachys skvortzovii Sendulsky) as a predictor of disturbance. Because this species is a fast-growing, strong competitor in areas with open canopies, its presence can indicate open canopy conditions and affect regeneration/colonisation of other species after the cyclone disturbance in a site (Liebsch et al 2019).…”

“…In just one southern Brazilian state, Santa Catarina, 45 extreme atmospheric events like cyclones and waterspouts were registered between 1976 and 2003 (Marcelino et al 2009), including more recent cyclone events in 2009, 2019, and 2020. As cyclones were historically rare disturbances in this region, their impacts on the forest and how plant communities recover from these events are poorly known, despite some previous works addressing it (Beckert et al 2014;Santos et al 2015;Liebsch et al 2019).…”

“…The immediate effects of cyclone passage on forest communities are loss of leaves, branch and trunk breakage, individual mortality, loss of biomass, changes in soil and microclimate, among others (Walker et al 1992;Everham & Brokaw 1996; Vandermeer et al 2000;Pascarella et al 2004). Such effects can last for a long timedecades or even centuries (Hibbs 1983;Foster 1988;Burslem et al 2000) by affecting species recruitment, regeneration capacity through regrowth and changes in floristic composition (Turner et al 1998;Lugo 2008;Liebsch et al 2019). The damage level on a given site depends on the cyclone intensity, the characteristics of the trees in that site (Niklas 2000;Butler et al 2012;Uriarte et al 2019) and the successional status of the community encompassing the site (Odum 1969).…”