Environmental filters influence functional structure and growth of monodominant forest patches in the Pantanal floodplain

Abstract

In the tropics, the occurrence of monodominant stands interspersed with mixed forest or savanna formations, with high species diversity is an issue that still challenges ecologists. Despite several studies on this topic, there is still no explanation for all aspects of this phenomenon. Some key factors have been pointed out and two general approaches have been discussed. Firstly, the lack of disturbance, where species that are better competitors stand out in most advanced stages of succession, and secondly, the presence of environmental filters, such as fire, flood and poor soils, which exclude less tolerant species. Environmental filters can influence strategies for use of nutrients by plants, varying between aquisitive or conservative strategies. For this reason, in this thesis we show, in three chapters, how environmental filters influence the structure of the community and individual traits in monodominant stands of Leptobalanus parvifolius (Huber) Sothers & Prance (= Licania parvifolia Huber, recently synonymized, see Sothers et al. 2016) in the Pantanal floodplain, in central South America. In addition, given the importance of climate for tree growth, we analysed growth rings to verify if EL Niño and precipitation events and flooding, influence the establishment and growth of L. parvifolius individuals. We found that L. parvifolius dominance increases with greater flooding, greater soil fertility and greater livestock disturbance, or in less fertile and more flooded soils, but without livestock. A plausible explanation is that floods and livestock disturbances can prevent the establishment of other species in more fertile soils and, therefore, can facilitate the establishment and increase the L. parvifolius dominance. Tree individuals in more flooded areas have conservative strategies (slower growth), while in less flooded areas they resort to acquisitive strategies (faster growth). This result may represent higher productivity and nutrient cycling in less flooded areas. Thus, monodominant stands of L. parvifolius are niche-structured along environmental gradients. This may be related to the plasticity of the dominant species, which may be an important factor for the monodominance of L. parvifolius and other species in the Pantanal. The flooding in the region seems not strong enough to really affect the growth of L. parvifolius. The establishment of L. parvifolius individuals occurs mainly in years with flooding duration between 30 and 110 days. In turn, El Niño events have a significant negative influence on the growth of L. parvifolius. The expected climate changes and consequent increase in El Niño events can drastically modify the hydrology and climate of the Pantanal, which can compromise the establishment and growth of monodominant species, causing drastic changes in the floodplain landscape.