Phenological cycles in the Pantanal woody communities: Responses to climate and soil moisture seasonality

Phenological data collection and analyses Sampling design and collection. The study area is located along the margins and flood- plains of the Cuiaba´ River and its tributary, the Piraim River, within the SESC Baı´a das Pedras. It belongs to the Cuiaba´ fluvial fan system, the second largest megafan of the Pantanal Basin [43]. This area is part of the SESC Pantanal Ecological Station, located in the municipality of Pocone´ (Mato Grosso, Brazil), and it is dedicated to ecotourism and scientific research. Cover- ing 4,200 hectares, it hosts the Advanced Research Base for Pantanal Studies of the Federal University of Mato Grosso. This study was performed during the annual hydroclimatic cycle from July 2017 to July 2018 in the northern Pantanal (16˚30’S and 56˚25’W). This period represents normal to mod- erately wet conditions intercepted with intense rainy periods lasting from nearly 2–4 months [44], considering that the cumulative annual average precipitation in the region was 1,516 mm from 1991–2020 [45]. The vegetation communities of the study area represent mosaics of dif- ferent forest and savanna formations in the northern Pantanal and other subregions [17]. Observations of phenological aspects were made in seven communities, namely, Seasonally Flooded Woodland, also known as Parkland Savanna (PS); Low Tree and Shrub Savanna (Cer- rado Savanna—CS); Low Tree and Shrub Savanna, invaded by Trees (Invaded Savanna—IS); Shrubland (SHB); the Alluvial Seasonal Semideciduous Forest (ASDF); the Lowland Seasonal

Semideciduous Forest (LSDF); and the Semi-evergreen Monodominant Forest of Vochysia divergens (MF) [46]. Parkland Savanna occurs in areas experiencing short-term flooding from rainfall accumu- lation lasting only a few weeks, with depths reaching less than 50 cm, and is distributed along abandoned lobes on fluvial fans [43,47]. These woodland savannas usually encompass a single tree or shrub species over a grassy layer, featuring typical species such as Byrsonima cydoniifo- lia scrub, Curatella americana, Handroanthus heptaphyllus, and T. aurea, which create spots of monodominant formations. The presence of species such as the spiny Machaerium hirtum and the palm Copernicia alba gives these formations physiognomic similarities with the Steppic Park Savanna (Humid Chaco) of the southern Pantanal (Silva and Caputo 2010, Polido and Sartori). The treelet B. cydoniifolia ("canjiqueiral") is associated with sandy soils, whereas C. alba is associated with calcium- or sodium-rich patches [48]. Cerrado Savanna (Low Tree and Shrub Savanna) is composed of herbaceous and shrubby plants, palms, and isolated trees up to 8 m tall, including species such as Cupania vernalis, Ery- throxylum anguifugum, Eugenia florida, Genipa americana, and Tabebuia aurea. This vegeta- tion community typically occurs when flooding lasts less than 3 months and when the floodwater is up to 1 m deep. These dynamic habitats feature species with high tolerance to floods and droughts [47]. The reduction in flooding and soil moisture leads to species turn-

over, with some species, such as the less flood-tolerant Callisthene fasciculata, becoming dominant. Invaded Savanna (locally called campo sujo) by native trees and shrubs exemplifies the Pan- tanal vegetation dynamics regulated by multiannual dry and wet periods that result in a reor- ganization of the spatial distribution of vegetation communities and species [47]. Multiple wet years drive the expansion of pioneer and native riparian tree V. divergens over flooded open- canopy savannas and natural grasslands, reducing herbaceous diversity and evolving into a semi-evergreen monodominant forest [49]. In this woody encroached community, flooding lasts 3–6 months in wet years, and the soil can remain waterlogged in the dry season, with establishment benefitting from low wildfire regimes [50]. Shrublands are usually characterized by encroachment stages of a set of shrubby species over grasslands and savanna areas, such as the entangling Combretum lanceolatum and C. PLOS ONE Phenological cycles in the Pantanal woody communities PLOS ONE | https://doi.org/10.1371/journal.pone.0316011 February 7, 2025 4 / 30