DOI: 10.5061/dryad.vq83bk3tm
title: Not all trees can make a forest: tree species composition and competition control forest encroachment in a tropical savanna

description: Forest encroachment into savannas is a widespread phenomenon, the rate of
 which may depend on soil conditions, species composition, or changes in
 stand structure. As savanna specialist trees are replaced by generalist
 species, rates of stand development may increase. Because generalists can
 persist in forests, they are likely to grow more quickly and survive
 longer in dense stands, compared to savanna specialists. Furthermore, the
 faster growth rates of generalists may allow them to overtop and
 outcompete savanna specialists, causing rapid species turnover. We
 measured growth and survival of 6147 individuals of 112 species of savanna
 and generalist tree species over a period of 10 years in an ecological
 reserve in Assis, São Paulo State, Brazil. We modeled growth and mortality
 as a function of soil texture and nutrients, tree size, competitive
 neighborhood, and membership in savanna or generalist (species which can
 persist in forests and savannas) functional groups. Tree growth and
 survival was strongly influenced by competition, as estimated by the basal
 area of trees taller than a focal tree. At the stand level, savanna
 species are unable to contribute basal area growth in closed stands, while
 generalist species continue to increase in basal area even at high stand
 basal area. This phenomenon is driven by differences in growth and
 mortality. Generalists grew faster than savanna species, both in height
 and diameter. This difference in growth rates led to savanna species
 becoming suppressed more rapidly than generalists. When suppressed,
 savanna species were more than twice as likely to die than were
 generalists. Soils had inconsistent and mostly weak effects which were
 difficult to separate from gradients of stand structure. Synthesis: We
 demonstrate that the presence of generalist trees accelerates rates of
 basal area accumulation due to their greater growth rates and tolerance of
 shading. Generalists outcompete savanna trees by growing faster in the
 open and overtopping savanna specialists. Due to the slow growth and high
 mortality of savanna species in the shade, they are unable to form
 closed-canopy stands. Accounting for differences among functional types
 and development of vegetation structure is critical for modeling forest
 encroachment.
description: This dataset consists of three files: individual tree data,
 plot-level data, and soils data (also collected at the plot
 level). Tree_data_EEcAssis.xlsx: Thirty plots were
 established in 2006 along a gradient from open savanna to closed forest.
 Each plot comprised 20 x 50 m, within which all trees &gt; 5 cm DBH
 were sampled. For each tree, DBH, height, and species identity were
 recorded. Individual trees were tagged and resurveyed in 2011 and 2016,
 along with any new recruits into the 5 cm size class. 
 Soil_EEcAssis_All data.xlsx: Within each plot, soil structure and
 chemistry were sampled at a depth of 0-20 cm and 60-80 cm. Samples were
 commingled to produce one sample per plot. 
 Plot_data_EEcAssis.xlsx: Some variables are summarized to the
 plot level in this spreadsheet, to facilitate analysis. 
 For details on data collection, see Assis, et al. (2011) and
 Honda & Durigan (2016).  Assis, A. C. C., R. M.
 Coelho, E. da Silva Pinheiro, and G. Durigan. 2011. Water availability
 determines physiognomic gradient in an area of low-fertility soils under
 Cerrado vegetation. Plant Ecology 212:1135–1147. Honda,
 E. A., and G. Durigan. 2016. Woody encroachment and its consequences on
 hydrological processes in the savannah. Phil. Trans. R. Soc. B
 371:20150313.
description: Plot_data_EEcAssis.xlsx<br> Plot-level summary data,
 including soils data and variables derived from tree
 inventories.<br> Rows are color-coded by vegetation structure:
 straw: savanna; orange: cerrado sensu stricto; green: cerradão.<br>
 Soil size classes follow Camargo, et al. (1986)
 Columns: Plot: plot identifier<br> TBA
 2011 m2 ha-1 : toal tree basal area in 2011<br> Total sand %: soil %
 sand<br> Clay %: soil % clay<br> Silt %: soil % silt<br>
 Coarse sand % : soil % coarse sand<br> Fine sand %: soil % fine
 sand<br> Base saturation V% 0-20cm: base saturation in the 0-20 cm
 soil layer<br> Base saturation V% 60-80cm: base saturation in the
 60-80 cm soil layer<br> Canopy cover %: canopy cover estimated from
 satellite images<br> Canopy oppeness %: 1 - canopy cover<br>
 Transprecipitation 2006 %: rain throughfall; estimated following Honda and
 Durigan (2016).<br> soil humidity 0-20cm %: soil moisture in 0-20cm
 soil layer<br> Diameter increment cm/yr: mean growth increment of
 trees, calculated using only positive growth
 ------------------------------------------<br>
 Soil_EecAssis_All_data.xlsx<br> Plot-level soil variables, estimated
 for the 0-20 cm layer and 60-80 cm layer (different tabs)<br> For
 details, see Assis et al. (2011).  Columns:
 Plot number: plot identifier<br> Soil Depth: soil layer
 (0-20 cm or 60-80 cm)<br> Coarse Sand: soil % coarse sand<br>
 Fine sand: soil % fine sand<br> Clay: soil % clay<br> Silt:
 soil % coarse silt<br> Clay + Silt: % total fines<br>
 Moisture: soil moisture<br> P(resin): Phosphorus concentration
 (measured using resin)<br> Organic Matter: Organic matter <br>
 pH: pH<br> K: Potassium concentration<br> Ca: Calcium
 concentration<br> Mg: Magnesium concentration<br> H+Al: Sum of
 Hydrogen and Aluminum concentrations<br> Al: Aluminum
 concentration<br> Sum of bases: Sum of nutrient cation
 conetrations<br> Cation exchange capacity: Cation exchange
 capacity<br> Base Sat: Proportion of cation exchance sites bound
 with bases<br> Al Sat: Proportion of cation exchance sites bound
 with Aluminum<br> Cu: Copper concentration<br> Zn: Zinc
 concentration<br> Mn: Manganese concentration<br> Fe: Iron
 concentration<br> B: Boron concentration
 ----------------------------------------------------<br>
 Tree_data_EEcAssis.xlsx<br> Individual tree data from three
 inventories (2006, 2011, and 2016). Columns:
 Old number: Tree identifier<br> Current number: Tree
 identifier<br> Plot: Plot identifier<br> Subplot: Subplot
 identifier (subplots 1-10 within each plot)<br> a=2006; n=2011;
 nv=2016: indicates which year the tree was added to the
 inventory<br> Alive2011: indicates whether the tree was alive in
 2011 (v) or dead (m)<br> Alive2016: indicates whether the tree was
 alive in 2016 (v) or dead (m)<br> Family: Family of the
 species<br> Species (names not updated): Scientific name and
 authority of species<br> C=Cerrado; G=generalist;: Indicates whether
 the species is a cerrado specialist or generalist<br> Shade
 Tolerance: Is the species shade tolerant (T) or intolerant (I)<br> H
 2016 m: Height of tree in 2016<br> DAP1/16 : DAP7/16: Diameters at
 beast height of stems of individual tree<br> G2016 (m2):
 Cross-sectional area of tree, calculated from individual tree
 diameters<br> dg2016 (cm): Effective diameter, calculated from
 cross-sectional area columns repeat for each sample interval (2011 and
 2006)<br> dbh annual increment(cm)_10 years: Change in tree diameter
 from 2006 to 2016. Only includes trees which were alive in 2006 and
 2011. References: Assis, A. C. C.,
 Coelho, R. M., da Silva Pinheiro, E., & Durigan, G. (2011). Water
 availability determines <br>     physiognomic gradient in an area of
 low-fertility soils under Cerrado vegetation. Plant Ecology,
 212(7), <br>     1135–1147.
 https://doi.org/10.1007/s11258-010-9893-8 Honda, E. A.,
 & Durigan, G. (2016). Woody encroachment and its consequences on
 hydrological processes in <br>     the savannah. Phil. Trans. R.
 Soc. B, 371(1703), 20150313.
 https://doi.org/10.1098/rstb.2015.0313 Camargo AO,
 Moniz AC, Jorge JA, Valadares JMAS (1986) Métodos de análise química,
 mineralôgica e física de<br>     solos do Instituto Agronômico de
 Campinas. Instituto Agronômico, Campinas, SP (Boletim Técnico,
 106)