Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests
This study presents two stand-density indices (SDIs) based on exponential density decline as a function of quadratic mean diameter for all species combined in mixed-species forests with 22 species mix grouped in four species groups. The exponential-based density–diameter relationship, as w...
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Online Access: | http://www.mdpi.com/1999-4907/10/1/9 |
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doaj-fff781b4e29c422cb5d64b8b9f03f44c2020-11-24T21:28:54ZengMDPI AGForests1999-49072018-12-01101910.3390/f10010009f10010009Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species ForestsGerónimo Quiñonez-Barraza0Hugo Ramírez-Maldonado1Campo Experimental Valle del Guadiana, Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias (INIFAP), Carretera Durango-Mezquital Km 4.5, Durango 34170, MexicoUniversidad Autónoma Chapingo, Carretera México-Texcoco Km 38.5, Texcoco 56230, MexicoThis study presents two stand-density indices (SDIs) based on exponential density decline as a function of quadratic mean diameter for all species combined in mixed-species forests with 22 species mix grouped in four species groups. The exponential-based density–diameter relationship, as well the density index corresponding to the slope or instantaneous mortality rate parameters, was compared with those based on power-law density–diameter relationship. A dataset of 202 fully stocked circular plots at maximum density was used for fitting the models, and a dataset of 122 circular plots was used for validation stand density index for all species combined of mixed-species stands. The dataset for validation was independent of dataset for model development. The first stand-density index showed a density management graphic (DMG) with a variable intercept and common instantaneous mortality rate, and the second index showed a DMG with common intercept and variable mortality rate. Additionally, the value of the initial density of the fitted line was more realistic than those generated by the potential model for all species combined. Moreover, the density management diagrams showed a curvilinear trend based on the maximum stand density index in graphical log–log scale. The DMGs could be interpreted as forest scenarios based on variable initial density and common management objectives or the same density and different management objectives for forest-rotation periods involving all species combined in mixed-species stands. The fitting of exponential and potential equations for species or species groups showed that the density–size relationships in mixed-species forests should be modeled for all species combined because the disaggregation of mixture species represented a weak tendency for each species or species group and the resultant fitted equations were unrealistic.http://www.mdpi.com/1999-4907/10/1/9exponential equationdensity management graphicmaximum density lineself-thinning |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Gerónimo Quiñonez-Barraza Hugo Ramírez-Maldonado |
spellingShingle |
Gerónimo Quiñonez-Barraza Hugo Ramírez-Maldonado Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests Forests exponential equation density management graphic maximum density line self-thinning |
author_facet |
Gerónimo Quiñonez-Barraza Hugo Ramírez-Maldonado |
author_sort |
Gerónimo Quiñonez-Barraza |
title |
Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests |
title_short |
Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests |
title_full |
Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests |
title_fullStr |
Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests |
title_full_unstemmed |
Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests |
title_sort |
can an exponential function be applied to the asymptotic density–size relationship? two new stand-density indices in mixed-species forests |
publisher |
MDPI AG |
series |
Forests |
issn |
1999-4907 |
publishDate |
2018-12-01 |
description |
This study presents two stand-density indices (SDIs) based on exponential density decline as a function of quadratic mean diameter for all species combined in mixed-species forests with 22 species mix grouped in four species groups. The exponential-based density–diameter relationship, as well the density index corresponding to the slope or instantaneous mortality rate parameters, was compared with those based on power-law density–diameter relationship. A dataset of 202 fully stocked circular plots at maximum density was used for fitting the models, and a dataset of 122 circular plots was used for validation stand density index for all species combined of mixed-species stands. The dataset for validation was independent of dataset for model development. The first stand-density index showed a density management graphic (DMG) with a variable intercept and common instantaneous mortality rate, and the second index showed a DMG with common intercept and variable mortality rate. Additionally, the value of the initial density of the fitted line was more realistic than those generated by the potential model for all species combined. Moreover, the density management diagrams showed a curvilinear trend based on the maximum stand density index in graphical log–log scale. The DMGs could be interpreted as forest scenarios based on variable initial density and common management objectives or the same density and different management objectives for forest-rotation periods involving all species combined in mixed-species stands. The fitting of exponential and potential equations for species or species groups showed that the density–size relationships in mixed-species forests should be modeled for all species combined because the disaggregation of mixture species represented a weak tendency for each species or species group and the resultant fitted equations were unrealistic. |
topic |
exponential equation density management graphic maximum density line self-thinning |
url |
http://www.mdpi.com/1999-4907/10/1/9 |
work_keys_str_mv |
AT geronimoquinonezbarraza cananexponentialfunctionbeappliedtotheasymptoticdensitysizerelationshiptwonewstanddensityindicesinmixedspeciesforests AT hugoramirezmaldonado cananexponentialfunctionbeappliedtotheasymptoticdensitysizerelationshiptwonewstanddensityindicesinmixedspeciesforests |
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