Variations in aboveground vegetation structure along a nutrient availability gradient in the Brazilian pantanal

Forest expansion into seasonally flooded (hyperseasonal) savanna of the Brazilian Pantanal has been occurring for decades. Our goal was to evaluate how ecosystem physiognomy varied across a nutrient availability gradient and if hyperseasonal savanna had adequate nutrient stocks to support forest expansion. We quantified soil properties, aboveground ecosystem structure, and nutrient stocks of three savanna and three forest stands in the Pantanal of Mato Grosso, Brazil, and used correlation analysis to assess how aboveground vegetation structure varied across a soil nutrient availability gradient. Wood and foliage carbon storage and leaf area index were positively correlated with soil extractable phosphorus (P), calcium (Ca2+), and magnesium (Mg2+) concentrations but not soil organic matter or texture. Soil profiles indicated that vegetation enriched surface P and K+ availability but not Ca2+ and Mg2+. Savanna ecosystems had adequate K+, Ca2+, and Mg2+ to support gallery and riparian forests but not palm forest, while the savanna P stock was inadequate to support forest expansion. Hyperseasonal savanna has adequate nutrients (except P) to support forest expansion. Forest trees likely invade P-deficient savanna by surviving in P-rich microsites. Over time, biotic enrichment of soil may accelerate forest expansion into P-poor savanna.