Data from: Rare frost events reinforce tropical savanna-forest boundaries

Hoffmann, William A., North Carolina State University

Flake, Samuel W., North Carolina State University

Abreu, Rodolfo C.R., North Carolina State University

Pilon, Natashi A.L., State University of Campinas

Rossatto, Davi R., Sao Paulo State University

Durigan, Giselda, Laboratório de Ecologia e Hidrologia FlorestalFloresta Estadual de Assis, Instituto Florestal Assis Brazil

Abreu, Rodolfo C. R., North Carolina State University

Published Jul 13, 2019 on Dryad. https://doi.org/10.5061/dryad.56hb7gf

Cite this dataset

Hoffmann, William A. et al. (2019). Data from: Rare frost events reinforce tropical savanna-forest boundaries [Dataset]. Dryad. https://doi.org/10.5061/dryad.56hb7gf

Abstract

1) The ability of vegetation to ameliorate or exacerbate environmental extremes can generate feedbacks that mediate the distribution of biomes. It has been suggested that feedbacks between vegetation and frost damage may be important for maintaining savanna, particularly at the edge of the tropics. 2) We quantified frost damage and air temperature across a network of 30 permanent plots distributed across tropical savanna-forest boundaries in Brazil during an uncommonly hard frost. 3) Tree cover strongly buffered temperatures during frost events, such that forest sites were up to 5°C warmer than nearby sites occupied by open shrub savanna. Consequently, in forest, woody plants were not damaged, but in savanna there was extensive dieback of trees and shrubs. Within savanna, frost had disproportionately large effects on small individuals, likely due to colder temperatures near the ground and the lower thermal mass of thin stems. Across species, frost tolerance was strongly correlated with latitudinal range limit, revealing the importance of minimum temperature as a species filter at the regional scale. Counterintuitively, savanna species, which are adapted to open habitats where frost is more likely, were more vulnerable to cold than were forest species and experienced more than twice the amount of leaf damage as co-occurring forest species. 4) Synthesis: Frost reinforces the effects of fire on vegetation structure by preferentially damaging trees in open environments and generating high loads of dead, flammable fuels. However, frost does not currently occur with sufficient frequency in the region to maintain open savanna by itself. Nevertheless, it occurs with sufficient frequency and severity that it likely acts as a partial environmental filter and evolutionary pressure for some of the most frost-sensitive species.

Usage notes

r code for analyses

FrostAnalyses.r

Phylogenic tree of principal species.

This is the phylogenetic tree used for performing phylogenetically corrected tests.

FrostPhylogeny.txt

Species data for phylogenetic analyses

A) species: binary latin name. B) T50: The estimated temperature at which 50% of individuals were damaged (C). C) Type: s = savanna specialist, f = forest specialist or generalist. D) Lat: Latitude of southern range limit (degrees) E) Bio6: The climatological mean temperature of the coldest month from the WorldClim 2.0 database (http://www.worldclim.org/) at the cold limit of the species range.

FrostTraits.csv

Data file with individual-level frost damage data.

This file contains the following fields:A) P: Plot identifier number. B) PlotBasalArea: Tree basal area of the plot (m^2/ha). C) MinTemp: Predicted minimum air temperature on the coldest night at height of 1 m (C). D) Phys: Physiognomy of the plot 0 = shrub savanna, 1 = tree savanna, 2 = forest. E) TagNumber: Identifier number for trees that were permanently tagged. F) Species: Binomial latin name. G) Species.Code: Four-letter abbreviation of species. H) Type: S = savanna specialist, F = forest specialist or generalist. I) InitialHeight: Height prior to frost (cm) J) FinalHeight: Height one year after frost (cm) K) LeafDamage: Fraction of leaf area damaged, as visually estimated several days after the coldest frost event (cm). L) DiebackHeight: The height from which the stem resprouted, as determined one year after the severe frost (cm). M) Dieback.length: The loss amount of stem height lost due to dieback (cm). N) CrownExposure: A unitless index of canopy exposure: 1 = receiving no direct light; 2 = receiving some direct lateral light; 3 = receiving some direct overhead light, but with <90% of the crown exposed to overhead light; 4 = receiving direct overhead light on >90% of the vertical projection of the crown; 5 = receiving direct light on all sides (an emergent tree or open-grown savanna tree). O) dieback.binary: A binary indicator of damage. 0 = no damage; 1 = damaged. A plant was considered damaged if it exhibited at least 50% leaf damage. For individuals without leaf damage data, an individual was considered damaged if it exhibited any amount of stem dieback. P) RegrowthLength: The recovery of height, from the point of dieback, for plants experiencing any amount of stem dieback (cm) Q) NetChange: The net increase or decrease in height as determined one year after the severe frost (cm). This net change is equal to InitialHeight-FinalHeight and is also equal to RegrowthLength-Dieback.length.

FrostDamage.csv

Funding

National Science Foundation, Award: DEB1354943

Location

22.807560S

49.238842W

Brazil

São Paulo