DOI: 10.5061/dryad.b2rbnzst1
title: Marked tree demographic variation along subtle elevation differences partially explains species' habitat associations in an Amazonian forest

description: It is widely recognized that large-scale topographic variation affects the
 distribution of tree diversity, yet the effects of topography at smaller
 scales are less appreciated but can be no less consequential. We evaluated
 how small-scale topographic variation affects tree demography and
 diversity in a hyperdiverse Amazonian forest where species distributions
 respond strongly to elevation differences as small as 22 meters. For
 topographically structured species distributions to arise, species should
 grow and survive (perform) better in the topographic habitat they are
 associated with (best-at-home hypothesis), and they should outperform
 other species that are found, but not strongly aggregated, on that habitat
 (resident-advantage hypothesis). Here, we tested these demographic
 hypotheses using data on the growth and mortality of 79,911 trees (352
 species) among three topographic habitats (valleys, slopes, and ridges) in
 the 25-ha Amacayacu Forest Dynamics Plot. Despite the small variation in
 elevation, there was significant community-level variation in growth and
 mortality among topographic habitats: trees growing in valleys, where soil
 moisture is higher, had significantly higher growth and mortality rates
 than those growing on slopes and ridges. However, tree growth rates did
 not depend on, and mortality rates varied inconsistently with, species’
 habitat association. Our results partially support the best-at-home or
 resident-advantage hypotheses for valley-associated species, which grew
 best in their home habitat (valleys) than elsewhere and had lower
 mortality there compared to slope-associated or generalist species
 (foreigners). For slope- and ridge- associated species our results did not
 support these hypotheses at the community level. Species-specific analyses
 revealed that 73 out of the 352 species analyzed at the community level
 supported either hypothesis. Synthesis. Our findings show that even small
 differences in elevation can lead to biologically meaningful variation in
 resource access that translates into significant differences in tree
 growth and survival. However, resource access could not fully explain the
 patterns of topographically driven demographic variation we observed.
 While certain species may still exhibit home and resident advantages in
 specific habitats, even when community-level averages partially reflect
 this pattern, alternative hypotheses are likely driving the patterns
 observed at the community level.
description: Study area<br>The dataset originates from the Amacayacu
 Forest Dynamics Plot (AFDP), a 25-hectare tropical wet forest plot in the
 Northwestern Amazon (3°48ʹS, 70°16ʹW). The AFDP, part of the Forest Global
 Earth Observatory (ForestGEO), features a unimodal rainfall regime (~3,216
 mm/year), high humidity (86%), and a mean annual temperature of 25.8 °C.
 The plot encompasses diverse topographic habitats including ridges,
 slopes, and valleys, with generally poor, acidic soils dominated by
 kaolinite and quartz minerals. Forest
 censuses<br>Two full censuses were conducted: the first from August
 2007 to April 2009, and the second from August 2014 to November 2015. All
 woody plants ≥10 mm diameter at breast height (DBH; 1.3 m) were mapped,
 tagged, measured, and identified taxonomically, with vouchers deposited at
 the Herbario Amazónico Colombiano (COAH). Topographic
 Habitat Classification<br>Three topographic habitats—ridges, slopes,
 and valleys—were defined using hierarchical clustering based on elevation,
 slope, and convexity metrics at a 20 m × 20 m quadrat scale, derived from
 a 5-m resolution topographic survey. These habitats account for
 approximately 25%, 31%, and 44% of the plot area, respectively.
 Species habitat associations<br>Species preferences for the
 three habitats were tested using a Torus Translation test on 106,230 trees
 of 441 species. Species with fewer than 10 individuals per habitat were
 excluded. Associations were identified based on deviations from null model
 expectations; species were classified as positively associated, neutral,
 or repelled from each habitat. Growth rate
 estimation<br>Tree growth rate (G) was calculated as the annualized
 difference in DBH between censuses, applying taper corrections for
 measurements taken at non-standard heights. Wood specific gravity values
 were assigned based on taxonomic identity. Extreme growth outliers were
 excluded, and growth rates were transformed using a modulus power
 transformation (t = 0.39) to reduce skewness before statistical
 analyses. Mortality assessment<br>Mortality was
 recorded as a binary variable (dead/alive) based on the absence of live
 foliage and other vitality indicators. Instantaneous mortality rates (%
 per year) were calculated from the probability of death between censuses.
 The final dataset used for modeling included 352 species with 68,380
 individuals for growth analyses and 79,911 individuals (12,943 dead) for
 mortality analyses.
description: # Marked tree demographic variation along subtle elevation differences
 partially explains species' habitat associations in an Amazonian
 forest Dataset DOI: [10.5061/dryad.b2rbnzst1](10.5061/dryad.b2rbnzst1) ##
 Description of the data and file structure The data consists of two
 databases: one for mortality (`m.csv`) and another for growth (`g.csv`).
 The mortality database is at the tree level (one row per tree), whereas
 the growth database is at the stem level (one row per stem, with multiple
 rows per tree in the case of multi-stemmed trees). ### Files and variables
 #### File: g.csv **Description:**  ##### Variables * tag: Individual tree
 tag * stemtag: Stem identifier. Note that a tree can have multiple stems.
 * Species: Species code used to identify unique species names. *
 dbh: Diameter at breast height (1.30 m) of the stem at time 1, measured in
 millimeters. * G: Estimated growth rate in millimeters. G was estimated as
 (dbh*2 - dbh*1)/(time_*diff) where dbh1 and dbh2 correspond to the
 diameter measurement in the first and second census, respectively;
 time_*diff is the time difference in years between censuses. *
 G_T: Transformed growth estimates using the modulus function with power
 t=0.39. * Habitat: Habitat where the tree is located. *
 Habitat_association: Habitat to which the tree species is statistically
 associated based on the Torus Translation test. #### File: m.csv
 **Description:**  ##### Variables * tag: Individual tree tag *
 stemtag: Stem identifier. Note that a tree can have multiple stems. *
 Species: Species code used to identify unique species names. *
 dbh: Diameter at breast height (1.30 m) of the stem at time 1, measured in
 millimeters. - M: Observed mortality status, binary variable: 1 indicates
 dead, 0 indicates living trees. - Habitat: Habitat where the tree is
 located. - Habitat_association: Habitat to which the tree species is
 statistically associated based on the Torus Translation test.