DOI: 10.5061/dryad.0gb5mkkzt
title: Data from: Changes in beta diversity and species functional traits differ between saplings and mature trees in an old growth forest

description: 1. Invasion by generalist tree species can cause biotic homogenization and
 such community impoverishment is likely more important in rare forest
 types.  We quantified changes in tree diversity within Carolinian
 (range in Central Hardwoods), northern (range reached Northern
 hardwood-conifer/Boreal-spruce-fir) and central species (range in Central
 Hardwood region and Northern hardwood-conifer) in an old forest in
 southern Canada at points surveyed 24 years apart. 2. We asked: How did
 mature tree and sapling composition and abundance change for the 3
 species’ groups? Did those changes lead to biotic homogenization? Can
 species’ changes be explained by community traits? We tested for
 differences in temporal and spatial tree β-diversity, as well as forest
 composition and structure, using univariate/multivariate analyses and a
 community trait-based approach to identify drivers-of-change. 3. Major
 increases occurred in abundance for mature Acer rubrum (northern), while
 others decreased (Fraxinus americana, Populus grandidentata); declines
 were found in A. saccharinum (central) and Cornus florida
 (Carolinian).  Species composition of saplings, but not mature
 trees, changed due to replacement; no evidence for biotic homogenization
 existed in either cohort.  As a group, northern mature tree
 species increased significantly, while central species declined; saplings
 of Carolinian species declined.  4. Shade-tolerance in mature
 trees increased, reflecting successional changes, while drought-tolerance
 decreased perhaps due to changing temperatures, altered precipitation or
 ground water levels.  Saplings showed declines in all traits,
 probably because of compositional change.   5. Our results
 demonstrated that saplings can more closely reflect change in forest
 dynamics than mature trees, especially over short time periods. 
 Based on sapling trends, this remnant could ultimately transition to a
 mesophytic hardwood stand dominated by A. rubrum and other shade-tolerant
 species, creating a more homogeneous forest.  6. While
 encouraging regeneration for Carolinian and central tree species could
 ensure high levels of diversity are conserved in the future, it is
 important that this is balanced with the primary management goal of
 maintaining the older-growth characteristics of the forest.
description: Data were collected in Backus Woods, Norfolk County, Ontario,
 Canada (42<sup>o</sup> 40 N and 80<sup>o</sup> 29
 west), within the Lake Erie Lowland Ecoregion.  A permanent grid of iron
 stakes was established by the Long Point Region Conservation Authority
 (LPRCA) in 1983; stakes were installed from east to west (bearing
 240<sup>o</sup>) at 50 m intervals along a series of parallel
 rows, 100 m apart.  Trees were surveyed at 397 grid points (totalling
 3,176 sampled mature trees and saplings) in 1985 and 2009. 
 Each of the permanent grid points was used as a starting point to
 quantify tree species abundance using the point distance sampling method.
 Point distance methods involved first, dividing the area around each grid
 point into four quadrants in each compass direction.  Within each of these
 quarters the closest tree was located, identified to species, and the
 distance of the tree from the sampling point and its diameter at breast
 height measured (dbh 1.3 m).  We treated mature trees (≥10 cm dbh) and
 saplings (&lt;9.9 cm dbh) separately.   Mature
 trees and saplings were identified to species. A total of 38 tree species
 was identified during the two surveys. We pooled the hybrid <i>Acer
 x freemanii</i> with <i>A. saccharinum </i>because we
 suspected observer bias; we also pooled <i>Fraxinus
 profunda</i> with <i>F. pennsylvanica</i> as the former
 was not recognized as a distinct species until 1992.  Because we were also
 interested in analyzing changes in abundance of rare tree species, we had
 to account for potential biases in our sampling due to differences in grid
 point locations, and so eliminated extremely rare species that occurred at
 less than 1% of grid points. This selection retained 28 species.
description: Some minor differences between years occurred in the locations
 used to initiate sampling. In 1985, surveyors tried to avoid disturbance
 to vegetation caused by the installation of stakes and so they began the
 point quarter distance sampling at a point away from the stake (mean
 distance 7.41 m).  In 2009, the stake or grid point itself was used as the
 starting point for the point quarter distance sampling. To minimize
 variation due to these slight differences in vegetation sampling locations
 between years, we therefore examined the community as a whole by combining
 multiple stakes, not analyzing individual stakes. To do so, we constructed
 a fishnet overlay (cells of grid points) to group sampled grid points in
 ArcGIS. We optimized the location and the mesh size of the fishnet to
 contain the maximum number of grid points per cell with a minimum
 criterion of 10 grid points per cell. We used this optimized fishnet for
 both years so that despite slight variation in the location of sampled
 grid points (mostly 6 m offsets), grid points belonged to the same cell in
 both years. These new 20 cells, containing between 11 and 18 sampled grid
 points, were used as sample units in all subsequent analyses.
 One file is attached (Backus Woods data) with 6 data
 sheets: 1) Sheet 1 = Backus_data - all tree
 data  2) Sheet 2 = bw_saplings - sapling data
 3) Sheet 3 = bw_groups - tree species classified as
 'Carolinian', 'Central' and 'Northern' (see
 Methods above) 4) Sheet 4 = bw_traits - TolS (shade
 tolerance), TolD (drought tolerance), TolW (waterlogging tolerance), SeedW
 (seed mass) 5) Sheet 5 = block_id (cell to which each
 gridpoint belonged) 6) Sheet 6 =
 plotcells_all