Pollination partial recovery across monospecific plantations of a native tree (Inga vera, Leguminosae) in the Atlantic forest: Lessons for restoration

Abstract

In the last decades several approaches have been adopted for tropical assisted forest restoration from monospecific plantations to the establishment of highly-diverse tree stands. However, the long-term viability of restored forest and their capacity to provide the required services demand continuous evaluation to guide future initiatives. We aimed to evaluate the existence of pollination recovery in monospecific tree plantations in a hyper fragmented landscape of the Atlantic forest in northeast Brazil. By using Inga vera as a model species, we compared several relevant aspects relative to tree reproduction such as reproductive phenology, floral structures, nectar consumption, fruit- and seed-set, between monospecific plantations and native conspecific populations. Populations of I. vera from both native forest stands and planted areas flowered in overlapping periods in the dry season, while fruiting occurred at the beginning of the rainy season. Flowers of planted populations were significantly larger (11% in the size of the calyx, corolla and androecium – staminal tube and filaments) relative to natural populations. Flowers of both planted and natural populations secrete ca. 46 μl of nectar with concentration of 20.2% and 45.8 mg of sugars throughout the anthesis. However, the average volume of nectar consumed by visitors per flower in planted populations was 30% lower than in natural populations. The frequency of pistils with pollen tubes and the average number of seeds per fruit were similar between natural and planted populations. Nevertheless, surprisingly, the natural fruit set was 49% lower in planted relative to natural populations. Lower consumption of nectar and natural fruit set in planted populations of I. vera, in relation to the natural populations, indicate a partial recovery of the pollination process through the practice of planting single species of a tree in clusters of individuals. Our results add some doubts about the long-term viability and the ability of monospecific plantations in delivering services such as increased pollination capacity in human-modified landscapes.