Abstract
AimTo understand how disturbance—here defined as a transient reduction in competition—can shape plant distributions along elevation gradients. Theory suggests that disturbance may increase elevation ranges, especially at the lower range limits, through reduced competitive exclusion. Nevertheless, to date this relationship remains unclear.LocationMountains of Costa Rica.MethodsWe compared the elevation range of woody stems over 10 cm dbh (“trees”) observed in plots along two transects spanning a range of elevations in secondary (regrowth) and old‐growth forest (409 and 249 species, respectively). We also estimated these elevation ranges using nationwide data. In addition, we examined the influence of stem size and plot scale basal area (as a measure of competition) on species elevation range limits in the two gradients.ResultsIn general, tree species ranges increased with elevation. Species in the secondary forest had broader elevation ranges (100–318 m broader than species in the old‐growth forest; Wilcoxon: p‐value <.001). Also, in the secondary transect, individuals with greater diameters had broader elevation ranges than those observed as smaller trees (137 m broader; Kruskal–Wallis: p‐value = .03). The lower range limit of species occurred more frequently in plots with lower (vs. higher) basal area than expected by chance in both forest types. We also observed higher elevation upper limits in old growth, but not in secondary forests, with lower (vs. higher) basal area.Main conclusionDisturbance relaxes the constraints imposed by competition and extends effective elevation ranges of species, particularly those in secondary forest, to warmer and cooler climates (minimum increase equivalent to about 0.6–1.4°C). Thus, suitable disturbance may assist species persistence under climate change. We believe this is the first study indicating a consistent relation between disturbance and woody plant species distributions along elevation gradients.
Highlights
The idea that tree species distribution patterns in tropical forest are influenced by disturbance is long established—many observations indicate a context-dependent effect of competition on species persistence along environmental gradients (Budowski, 1965, Van Steenis, 1958 see further examples in Sheil, 2016)
Our comparison of elevation ranges of tree species in secondary and old-growth forest represents an exceptional opportunity for an initial exploration of how disturbance histories may influence species distributions
We have found patterns that appear largely consistent with how we expect competition may influence the upper and lower distribution of tree species in the mountains of Costa Rica
Summary
The idea that tree species distribution patterns in tropical forest are influenced by disturbance is long established—many observations indicate a context-dependent effect of competition on species persistence along environmental gradients (Budowski, 1965, Van Steenis, 1958 see further examples in Sheil, 2016). Plant species distributed over an extended environmental gradient, such as elevation, are typically thought to sort themselves according to a competitive hierarchy in which inferior competitors are displaced to sites supporting less optimal growth (i.e., higher or lower elevations; Sheil, 2016; Shipley & Keddy, 1994; Wisheu, 1998) This reasoning follows from observations that a trade-off occurs between the competitive ability of a species and its ability to persist under limiting environmental conditions (Michalet et al, 2006; Morin & Chuine, 2006; Salguero-Gómez et al, 2016). We evaluated the relationship between species elevation range limits and local (plot defined) basal area with the prediction that range limits will be more frequent in lower versus higher basal area plots (representing lower vs. higher competition)
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