Strong floristic distinctiveness across Neotropical successional forests

Abstract

Forests that regrow naturally on abandoned fields are important for restoring biodiversity and ecosystem services, but can they also preserve the distinct regional tree floras? Using the floristic composition of 1215 early successional forests (≤20 years) in 75 human-modified landscapes across the Neotropic realm, we identified 14 distinct floristic groups, with a between-group dissimilarity of 0.97. Floristic groups were associated with location, bioregions, soil pH, temperature seasonality, and water availability. Hence, there is large continental-scale variation in the species composition of early successional forests, which is mainly associated with biogeographic and environmental factors but not with human disturbance indicators. This floristic distinctiveness is partially driven by regionally restricted species belonging to widespread genera. Early secondary forests contribute therefore to restoring and conserving the distinctiveness of bioregions across the Neotropical realm, and forest restoration initiatives should use local species to assure that these distinct floras are maintained.

Fig. 1.. Clustering of landscapes based on the species composition of early successional communities.

(A) Higher-level clusters (four floristic groups) explaining 60% of the variation in floristic species composition. (B) Lower-level groups explaining 90% of the variation in floristic species composition (14 floristic groups). The location of moist and dry forests as well as the two major biogeographical barriers [the Andes at the northwest of South America and the dry savannas (beige background)] are shown in (A) and (B). For each cluster level, the dendrogram provided shows the mean Simpson dissimilarity values and relationships among the four higher-level clusters (C) and among the 14 lower-level groups (D). Please note different scales of Simpson dissimilarity in (C) and (D). The consensus cluster with landscapes as tips is provided in fig. S1. CA, Central America; SA, South America.

Fig. 2.. Species frequency and occurrence across floristic groups.

(A) Contribution of each floristic group to the species shared across Neotropical early successional communities. The bars show the proportion of species shared between at least two floristic groups (434 species) that occur in a given floristic group. For example, the group Wet Central America contains 47% of the species shared with at least one other group. The number of landscapes included in each floristic group is indicated on the right side of the bars. (B) Rank-frequency curve for the 2163 species in the database. (C) List of the most widespread species, which occur in five or more floristic groups, and their occurrence in the 14 floristic groups. Species names are ordered according to the number of floristic groups they occur, followed by alphabetic order. Colors refer to the four higher-level floristic clusters in Fig. 1: Dry Forest—Caatinga (yellow), Southern South America (purple), Equatorial Moist Forests (orange), and Middle America (blue).

Fig. 3.. Relative importance of factors for the classification of floristic groups based on species occurrence.

Factors associated with the four higher-level clusters (A) and the 14 lower-level groups (B). The most important factors for predicting the classification are the ones that yield the largest decrease in Gini coefficient and in accuracy when they are left out of the model. Labels are provided for the significant factors.