Correction: Spatial Distribution Patterns in the Very Rare and Species-Rich Picea chihuahuana Tree Community (Mexico).

[This corrects the article DOI: 10.1371/journal.pone.0140442.]

Spatial structure of <i>Picea chihuahuana</i> M. in the 50 x 50 m plots in the 12 study locations, based on the neighbourhood-based Clark-Evans index (<i>CE</i>), Uniform Angle index (W¯), and Mean Directional index (R¯) (<i>P</i> values estimated with 10,000 permutations) and univariate <i>L</i>-function

<p>Note: Significant results after Bonferroni correction are shown in bold type. <math><mrow><mi>W</mi></mrow><mo>¯</mo></math> and <math><mrow><mi>R</mi></mrow><mo>¯</mo></math> failed in some plots because of an insufficient number of trees (repetitions) for the calculations.</p><p>. The 99% simulation envelope (dashed red lines) for the CSR hypothesis was calculated by the Monte Carlo Method (Besag 1977), with 1,000 simulations (distance interval equals 0–12 m). <i>N</i> equals the number of <i>Picea chihuahuana</i> M. trees in the plot. 1) La Tinaja (<i>TN</i>), 2) El Ranchito (<i>RC</i>), 3) El Cuervo (<i>CV</i>), 4) Talayote (<i>TY</i>), 5) Las Trojas (<i>TR</i>), 6) El Venado (<i>VN</i>), 7) La Quebrada (<i>LQ</i>), 8) Paraje Piedra Rayada (<i>PPR</i>), 9) Quebrada de los Durán (Arroyo del Indio Ignacio) (<i>QD</i>), 10) Cebollitas (<i>CB</i>), 11) San José de las Causas (<i>SJ</i>), and 12) La Pista (Arroyo de La Pista) (<i>LP</i>).</p

Analysis of spatial tree structure in 50 x 50 m plots in the 12 locations including all tree species (species shown [44]) and based on the neighbourhood-based Clark-Evans index (<i>CE</i>), Uniform Angle index (W¯), and Mean Directional index (R¯).

<p>Note: Significant results after Bonferroni correction are shown in bold type. ^cl indicates a clustering pattern in the plot.</p><p><i>P</i> values estimated with 10,000 permutations. 1) La Tinaja (<i>TN</i>), 2) El Ranchito (<i>RC</i>), 3) El Cuervo (<i>CV</i>), 4) Talayote (<i>TY</i>), 5) Las Trojas (<i>TR</i>), 6) El Venado (<i>VN</i>), 7) La Quebrada (<i>LQ</i>), 8) Paraje Piedra Rayada (<i>PPR</i>), 9) Quebrada de los Durán (Arroyo del Indio Ignacio) (<i>QD</i>), 10) Cebollitas (<i>CB</i>), 11) San José de las Causas (<i>SJ</i>), and 12) La Pista (Arroyo de La Pista) (<i>LP</i>).</p

Spatial Distribution Patterns in the Very Rare and Species-Rich <i>Picea chihuahuana </i>Tree Community (Mexico)

<div><p>The very rare Mexican <i>Picea chihuahuana</i> tree community covers an area of no more than 300 ha in the Sierra Madre Occidental. This special tree community has been the subject of several studies aimed at learning more about the genetic structure and ecology of the species and the potential effects of climate change. The spatial distribution of trees is a result of many ecological processes and can affect the degree of competition between neighbouring trees, tree density, variability in size and distribution, regeneration, survival, growth, mortality, crown formation and the biological diversity within forest communities. Numerous scale-dependent measures have been established in order to describe spatial forest structure. The overall aim of most of these studies has been to obtain data to help design preservation and conservation strategies. In this study, we examined the spatial distribution pattern of trees in the <i>P</i>. <i>chihuahuana</i> tree community in 12 localities, in relation to i) tree stand density, ii) diameter distribution (vertical structure), iii) tree species diversity, iv) geographical latitude and v) tree dominance at a fine scale (in 0.25 ha plots), with the aim of obtaining a better understanding of the complex ecosystem processes and biological diversity. Because of the strongly mixed nature of this tree community, which often produces low population densities of each tree species and random tree fall gaps caused by tree death, we expect aggregated patterns in individual <i>Picea chihuahuana</i> trees and in the <i>P</i>. <i>chihuahuana</i> tree community, repulsive <i>Picea</i> patterns to other tree species and repulsive patterns of young to adult trees. Each location was represented by one plot of 50 x 50 m (0.25 ha) established in the centre of the tree community. The findings demonstrate that the hypothesis of aggregated tree pattern is not applicable to the mean pattern measured by Clark-Evans index, Uniform Angle index and Mean Directional index of the uneven-aged <i>P</i>. <i>chihuahuana</i> trees and <i>P</i>. <i>chihuahuana</i> tree community and but to specific spatial scales measured by the univariate <i>L</i>-function. The spatial distribution pattern of <i>P</i>. <i>chihuahuana</i> trees was found to be independent of patches of other tree species measured by the bivariate <i>L</i>-function. The spatial distribution was not significantly related to tree density, diameter distribution or tree species diversity. The index of Clark and Evans decreased significantly from the southern to northern plots containing all tree species. Self-thinning due to intra and inter-specific competition-induced mortality is probably the main cause of the decrease in aggregation intensity during the course of population development in this tree community. We recommend the use of larger sampling plots (> 0.25 ha) in uneven-aged and species-rich forest ecosystems to detect less obvious, but important, relationships between spatial tree pattern and functioning and diversity in these forests.</p></div

Analysis of spatial structure of the suppressed and dominant trees in 50 x 50 m plots containing all tree species(species shown [44]),in the 12 study locations, based on the neighbourhood-based Clark-Evans index (<i>CE</i>), Uniform Angle index (W¯), and Mean Directional index (R¯).

<p>Note: Significant results after Bonferroni correction are shown in bold type. ^<b>cl</b> indicates a clustering pattern in the plot. <math><mrow><mi>W</mi></mrow><mo>¯</mo></math> and <math><mrow><mi>R</mi></mrow><mo>¯</mo></math> failed in some plots because of insufficient numbers of trees (repetitions) for the calculations.</p><p><i>P</i> values estimated with 10,000 permutations. <i>N</i> equals the tree number in the plot. 1) La Tinaja (<i>TN</i>), 2) El Ranchito (<i>RC</i>), 3) El Cuervo (<i>CV</i>), 4) Talayote (<i>TY</i>), 5) Las Trojas (<i>TR</i>), 6) El Venado (<i>VN</i>), 7) La Quebrada (<i>LQ</i>), 8) Paraje Piedra Rayada (<i>PPR</i>), 9) Quebrada de los Durán (Arroyo del Indio Ignacio) (<i>QD</i>), 10) Cebollitas (<i>CB</i>), 11) San José de las Causas (<i>SJ</i>), and 12) La Pista (Arroyo de La Pista) (<i>LP</i>).</p

Summary of statistical tests of spatial tree structure, null hypothesis, interpretation and related ecological questions; <i>CE</i> = neighbourhood-based Clark-Evans index, W¯ = Uniform Angle index, R¯ = Mean Directional index, LU(r) = univariate L-function, and <i>LB</i>(<i>r</i>) = bivariate <i>L</i>-function.

<p>Summary of statistical tests of spatial tree structure, null hypothesis, interpretation and related ecological questions; <i>CE</i> = neighbourhood-based Clark-Evans index, <math><mrow><mi>W</mi></mrow><mo>¯</mo></math> = Uniform Angle index, <math><mrow><mi>R</mi></mrow><mo>¯</mo></math> = Mean Directional index, LU(r) = univariate L-function, and <i>LB</i>(<i>r</i>) = bivariate <i>L</i>-function.</p

Analysis of spatial tree structure in 50 x 50 m plots in the twelve locations including all tree species using the univariate (for all trees, smaller trees of all species [44](< 23.2 cm diameter at the breast height (DBH)), larger trees (≥ 23.2 m DBH), and bivariate versions of the L-function (spatial pattern of <i>Picea chihuahuana</i> (Pch) vs. other tree species, pattern of smaller vs. larger trees and of smaller Pch (< 29.3 cm DBH) vs. larger Pchtrees (≥ 29.3 cm DBH)).

<p>The 99% simulation envelope (dashed red lines) for the CSR hypothesis (for the univariate <i>L</i>-function) and for spatial independence hypothesis (for the bivariate <i>L</i>-function) was calculated by the Monte Carlo Method (Besag 1977), with 1,000 simulations (distance interval equals 0–12 m).1) La Tinaja (<i>TN</i>), 2) El Ranchito (<i>RC</i>), 3) El Cuervo (<i>CV</i>), 4) Talayote (<i>TY</i>), 5) Las Trojas (<i>TR</i>), 6) El Venado (<i>VN</i>), 7) La Quebrada (<i>LQ</i>), 8) Paraje Piedra Rayada (<i>PPR</i>), 9) Quebrada de los Durán (Arroyo del Indio Ignacio) (<i>QD</i>), 10) Cebollitas (<i>CB</i>), 11) San José de las Causas (<i>SJ</i>), and 12) La Pista (Arroyo de La Pista) (<i>LP</i>).</p

Location of the study area on the Sierra Madre Occidental, Durango (Mexico).

<p>Map of the 12 locations of the <i>Picea chihuahuana</i> Martínez tree community under study in the States of Durango and Chihuahua (Mexico)<b>:</b> 1) La Tinaja (<i>TN</i>), 2) El Ranchito (<i>RC</i>), 3) El Cuervo (<i>CV</i>), 4) Talayote (<i>TY</i>), 5) Las Trojas (<i>TR</i>), 6) El Venado (<i>VN</i>), 7) La Quebrada (<i>LQ</i>), 8) Paraje Piedra Rayada (<i>PPR</i>), 9) Quebrada de los Durán (Arroyo del Indio Ignacio) (<i>QD</i>), 10) Cebollitas (<i>CB</i>), 11) San José de las Causas (<i>SJ</i>), and 12) La Pista (Arroyo de La Pista) (<i>LP</i>).Data sources: Own compilation based on freely-accessible digital maps from INEGI, Mexico (<a href="http://www.inegi.org.mx/geo/contenidos/mapadigital/" target="_blank">http://www.inegi.org.mx/geo/contenidos/mapadigital/</a>).</p

Analysis of spatial structure of the suppressed and dominant trees in 50 x 50 m plots containing all <i>Picea chihuahuana M</i>. trees, in the 12 study locations, based on the neighbourhood-based Clark-Evans index (<i>CE</i>), Uniform Angle index (W¯), and Mean Directional index (R¯).

<p>Note: Significant results after Bonferroni correction are shown in bold type. <i>CE</i>, <math><mrow><mi>W</mi></mrow><mo>¯</mo></math> and <math><mrow><mi>R</mi></mrow><mo>¯</mo></math> failed in some plots because of insufficient numbers of trees (repetitions) for the calculations.</p><p><i>P</i> values estimated with 10,000 permutations. <i>N</i> equals the tree number in the plot. 1) La Tinaja (<i>TN</i>), 2) El Ranchito (<i>RC</i>), 3) El Cuervo (<i>CV</i>), 4) Talayote (<i>TY</i>), 5) Las Trojas (<i>TR</i>), 6) El Venado (<i>VN</i>), 7) La Quebrada (<i>LQ</i>), 8) Paraje Piedra Rayada (<i>PPR</i>), 9) Quebrada de los Durán (Arroyo del Indio Ignacio) (<i>QD</i>), 10) Cebollitas (<i>CB</i>), 11) San José de las Causas (<i>SJ</i>), and 12) La Pista (Arroyo de La Pista) (<i>LP</i>).</p