Forest Structure, Nutrients, and Pentaclethra macroloba Growth after Deforestation of Costa Rican Lowland Forests

Succession following deforestation in Neotropical forests has been investigated extensively, yet rarely have studies connected nutrient dynamics with vegetation. This study was conducted in lowland wet forests of Maquenque, Costa Rica. The objectives were (1) to compare carbon (C), nitrogen (N), and phosphorus (P) characteristics and understory vegetation diversity between regenerating forests and primary forests; and (2) to use these variables to evaluate P. macroloba’s successional role. Four 300？m2 plots were established in primary and secondary forests where P. macroloba was the dominant N-fixing tree. Soil and vegetation data were collected from 2008 to 2010. Values of indicators of C, N, and P cycle activity were generally greater in primary than in secondary forest soils. Efficiency of organic C use and the relative contribution of respiration and organic C to soil biomass were also greater in the primary forest. These trends corresponded with greater richness, biomass, and cover of total and leguminous plant species, greater volume of P. macroloba in primary stands, and greater density of P. macroloba in secondary stands. As cleared regions of former primary forest regenerate, P. macroloba is the important dominant N-fixing tree and a critical driver of C, N, and P recuperation and ecosystem recovery. 1. Introduction Tropical forests originally covered up to 99% of the land in Costa Rica [1]. Approximately 90% of the original forests in Costa Rica have been destroyed in recent decades, and approximately 46% of the total area has been converted into cattle pasture [1, 2]. In the Northern Zone of Costa Rica, four decades of deforestation have resulted in the loss of about 70% of the lowland forests [2–7]. The resulting fragmentation has yielded concern among regional scientists regarding whether the remaining primary forests will be able to regenerate at a rate matching the deforestation [7]. Today, tropical forest land is characterized by an expanding proportion of secondary forests [8]. As the area of the secondary forests grows at the cost of primary forests, the secondary forests will have to be managed and used in the future [9]. Rates of recovery for abandoned farmland in tropical areas are accelerated if prior land-use intensity was low, areas recovering are small in size, soils are fertile, and there are remnant forests nearby [10]. However, many areas cleared and used as pasture in Costa Rica have suffered such a severe deterioration of soils that forest successional processes are hindered. Instead of forests returning to the area,