Citation: Rivero-Villar, A.; de la Peña-Domene, M.; Rodríguez-Tapia, G.; Giardina, C.P.; Campo, J. A Pantropical Overview of Soils across Tropical Dry Forest Ecoregions. Sustainability 2022, 14, 6803. https:// doi.org/10.3390/su14116803 Academic Editor: Ivo Machar Received: 9 March 2022 Accepted: 12 May 2022 Published: 2 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article A Pantropical Overview of Soils across Tropical Dry Forest Ecoregions Anaitzi Rivero-Villar 1 , Marinés de la Peña-Domene 1,2 , Gerardo Rodríguez-Tapia 1 , Christian P. Giardina 3 and Julio Campo 1, * 1 Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico; anaitzirv@iecologia.unam.mx(A.R.-V.); marinespd@iteso.mx (M.d.l.P.-D.); gerardo@iecologia.unam.mx (G.R.-T.) 2 Centro Interdisciplinario para la Formación y Vinculación Social, Instituto Tecnológico y de Estudios Superiores de Occidente, Tlaquepaque 45604, Mexico 3 Institute of Pacific Islands Forestry, USDA Forest Service, Hilo, HI 96720, USA; christian.p.giardina@usda.gov * Correspondence: jcampo@ecologia.unam.mx; Tel.: +52-55-56229027 Abstract: Pantropical variation in soils of the tropical dry forest (TDF) biome is enormously high but has been poorly characterized. To quantify variation in the global distribution of TDF soil physical and chemical properties in relation to climate and geology, we produced a synthesis using 7500 points of data with gridded fields representing lithologic, edaphic, and climatic characteristics. Our analyses reveal that 75 TDF ecoregions across five biogeographic domains (Afrotropical, Australasian, Indo- Malayan, Neotropical, and Oceanian) varied strongly with respect to parent material: sediment (57%), metamorphic (22%), volcanic (13%), and plutonic (7%). TDF ecoregions support remarkably high variability in soil suborders (32), with the Neotropical and Oceanian realms being especially diverse. As a whole, TDF soils trend strongly toward low fertility with strong variation across biogeographic domains. Similarly, the exhibited soil properties marked heterogeneity across biogeographic domains, with soil depth varying by an order of magnitude and total organic C, N, and P pools varying threefold. Organic C and N pool sizes were negatively correlated with mean annual temperature (MAT) and positively correlated with mean annual precipitation (MAP). By contrast, the distribution of soil P pools was positively influenced by both MAT and MAP and likely by soil geochemistry, due to high variations in soil parent material across the biogeographic domains. The results summarized here raise important questions as to how climate and parent material control soil biogeochemical processes in TDFs. Keywords: carbon; Entisols; nitrogen; phosphorus; soil climate relationships; soil fertility; Ultisols 1. Introduction Tropical landscapes are characterized by enormously high edaphic diversity, with soils ranging from pedologically young Entisols and Inceptisols to pedologically old Ultisols and Oxisols [1–3]. This edaphic variation exerts strong control over ecosystem functioning and dynamics [4], including in the tropical dry forest (TDF) biome, which exhibits high soil het- erogeneity. To date, reviews portray TDFs as being dominated by medium- to high-fertility status soils e.g., [5,6], likely because TDF soils are generally less weathered compared to those found in more humid tropical climates, including tropical rain, wet, or moist forests or in tropical savannas [7,8]. This generalization may obscure the highly heterogeneous nature of TDF soils as a result of the wide variety of climate, parent material, topography, and vegetation that defines the TDF biome [9]. So, for TDF soils, as elsewhere, local to regional scale variation relates to both abiotic (edaphic properties, climatic conditions) and biotic (vegetation) conditions [10,11]. Variation in these variables and their interactions across TDFs result in very high heterogeneity in soil properties and soil-ecological processes and, consequently, highly dynamic biogeochemistry [12–15]. This dynamic condition in TDFs is accentuated by severe anthropogenic land use changes [16,17] that can expose Sustainability 2022, 14, 6803. https://doi.org/10.3390/su14116803 https://www.mdpi.com/journal/sustainability