DOI: 10.5061/dryad.4n7n883
title: Data from: Frost maintains forests and grasslands as alternate states in a montane tropical forest-grassland mosaic; but alien tree invasion and warming can disrupt this balance

description: 1. Forest-grassland mosaics, with abrupt boundaries between the two
 vegetation types, occur across the globe. Fire and herbivory are widely
 considered primary drivers that maintain these mosaics by limiting tree
 establishment in grasslands, while edaphic factors and frosts are
 generally considered to be secondary factors that reinforce these effects.
 However, the relative importance of these drivers likely varies across
 systems. In particular, although frost is known to occur in many montane
 tropical mosaics, experimental evidence for its role as a driving factor
 is limited. 2. We used replicated in-situ transplant and warming
 experiments to examine the role of microclimate (frost and freezing
 temperatures) and soil in influencing germination and seedling survival of
 both native forest trees and alien invasive Acacia trees in grasslands of
 a tropical montane forest-grassland mosaic in the Western Ghats of
 southern India. 3. Seed germination of both native and alien tree species
 was higher in grasslands regard-less of soil type, indicating that
 germination was not the limiting stage to tree establishment. However,
 irrespective of soil type, native seedlings in grasslands incurred high
 mortality fol-lowing winter frosts and freezing temperatures relative to
 native seedlings in adjoining forests where freezing temperatures did not
 occur. Seedling survival through the tropical winter was thus a primary
 limitation to native tree establishment in grasslands. In contrast, alien
 Acacia seedlings in grasslands incurred much lower levels of winter
 mortality. Experimental night-time warming in grasslands significantly
 enhanced over-winter survival of all tree seedlings, but increases in
 recruitment were much greater for alien Acacia than for native tree
 seedlings. 4. Synthesis: Our results provide evidence for a primary role
 for frost and freezing temperatures in limiting tree establishment in
 grasslands of this tropical forest-grassland mosaic. Future increases in
 temperature are likely to release trees from this limitation and favour
 tree expansion into grasslands, with rates of expansion of non-native
 Acacia likely to be much greater than that of native trees. We suggest
 that studies of frost limitation to plant establishment are needed across
 a range of tropical ecosystems to re-evaluate the general importance of
 frost as a driver of vegetation transitions in the tropics.
description: Nilgiri_germination_dataData on native and invasive tree species germination across the habitats and soils recorded from the replicated in-situ experiment in the Nilgiri Hills of the Western GhatsNilgiri_seedling survival across habitat and soil_dataData on survival of native and invasive tree species seedlings across the habitats and soils recorded from the replicated in-situ experiment in the Nilgiri hills of the Western Ghats.Nilgiri_ seedling survival_experimental warming_dataData on the survival of native and invasive tree species seedlings in the control and experimental warming treatment recorded from the replicated in-situ experiment in the Nilgiri hills of the Western Ghats.