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. 2017 May 24;12(5):e0177060.
doi: 10.1371/journal.pone.0177060. eCollection 2017.

Land use history and population dynamics of free-standing figs in a maturing forest

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Land use history and population dynamics of free-standing figs in a maturing forest

Larissa Albrecht et al. PLoS One. .

Abstract

Figs (Ficus sp.) are often considered as keystone resources which strongly influence tropical forest ecosystems. We used long-term tree-census data to track the population dynamics of two abundant free-standing fig species, Ficus insipida and F. yoponensis, on Barro Colorado Island (BCI), a 15.6-km2 island in Lake Gatún, Panama. Vegetation cover on BCI consists of a mosaic of old growth (>400 years) and maturing (about 90-150 year old) secondary rainforest. Locations and conditions of fig trees have been mapped and monitored on BCI for more than 35 years (1973-2011), with a focus on the Lutz Catchment area (25 ha). The original distribution of the fig trees shortly after the construction of the Panama Canal was derived from an aerial photograph from 1927 and was compared with previous land use and forest status. The distribution of both fig species (~850 trees) is restricted to secondary forest. Of the original 119 trees observed in Lutz Catchment in 1973, >70% of F. insipida and >90% of F. yoponensis had died by 2011. Observations in other areas on BCI support the trend of declining free-standing figs. We interpret the decline of these figs on BCI as a natural process within a maturing tropical lowland forest. Senescence of the fig trees appears to have been accelerated by severe droughts such as the strong El Niño event in the year 1982/83. Because figs form such an important food resource for frugivores, this shift in resource availability is likely to have cascading effects on frugivore populations.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Map of the area around Barro Colorado Island before flooding (adapted from [38]).
This map depicts the natural course of the Chagres River (flowing southeast to northwest) and positions of former settlements. Land areas remaining after the filling of artificial Lake Gatún in 1914 are shaded in gray. The remaining white background represents the modern lake. Also indicated are the railway to the north (the black dash-dotted line) and the planned course of the Panama Canal (thick solid black line). Topographic contours, from the original map, in meters above sea level.
Fig 2
Fig 2. Distribution of Ficus insipida and F. yoponensis on Barro Colorado Island.
Depicted is the relative age of the forest from young (white) to old (black) forest as determined from an aerial photo from 1927 (compiled by R. Stallard and D. Kinner 2002). Secondary forest is about 90–150 years old, primary forest at least 400–600 years. The black circle marks the position of the Lutz Catchment, the white rectangle indicates the 50-ha forest-dynamics plot.
Fig 3
Fig 3. Results of the fig census in the Lutz Catchment.
(a) Trees and saplings of Ficus insipida and F. yoponensis found alive in the Lutz Catchment in 1973 and (b) in 2011.
Fig 4
Fig 4. Mortality of fig trees in the Lutz Catchment.
(a) Annual rainfall on BCI. Rainfall data are provided by the Environmental Studies Program (ESP). (b) Fig tree count per census year (light grey: F. yoponensis, dark grey: F. insipida). (c) Number of dead fig trees and (d) fig mortality in percent per year, estimated with relaxed cubic splines.

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