Occurrence of Density-Dependent Height Repression within Jack Pine and Black Spruce Populations

Peter Newton

doi:10.3390/f6072450

Abstract

The objective of this study was to investigate the occurrence of density-dependent height relationships in jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) B.S.P.) populations. After assessing and ruling out the presence of consequential spatial correlation effects, the analysis consisted of analyzing the relationship between mean dominant height and initial planting density within 28 Nelder plots located in the central portion of the Canadian Boreal Forest Region. Employing remeasurement data obtained at periodic intervals (16, 20 and 40–41 years post-establishment) across a stand density gradient ranging from a minimum of 1425 stems/ha to a maximum of 28,621 stems/ha, graphical and simple linear regression analyses were used to quantify the stand height–density relationship by species, plot and measurement year. The results indicated the presence of density-dependent effects on height development for both species: 65% of the 83 jack pine relationships and 89% of the 27 black spruce relationships had significant (p ≤ 0.05) and negative slope values. In regards to jack pine for which the data permitted, the occurrence and magnitude of the observed height repression effect increased over time. The asymptotic height repression effect for jack pine was 24% greater than that for black spruce. The results are discussed within the context of the applicability of the density-independent height growth assumption and potential implications for site quality estimation and thinning response modeling.

Highlights

Jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) B.S.P.) stand-types occupy a wide range of sites throughout the central portion of the Canadian Boreal Forest Region [1].These species are vital to the short and long term economic well-being of numerous single-industry communities and are currently the preferred reforestation species throughout the area [2]
Given the modelling enhancements and associated consequences in terms of volumetric productivity which may arise from acknowledging the existence of a density-dependent height growth repression effect, the objective of this study was to determine if density-dependent repression relationships were present in density-stressed jack pine and black spruce populations
Due to potential edge effects, inferences were limited to the patterns shown between the nominal initial spacings of

Summary

Introduction

Jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) B.S.P.) stand-types occupy a wide range of sites throughout the central portion of the Canadian Boreal Forest Region [1]. These species are vital to the short and long term economic well-being of numerous single-industry communities and are currently the preferred reforestation species throughout the area [2]. Specific decisions regarding initial spacing and thinning treatments for a given site, management intensity and objective, are commonly determined using stand density management decision-support models (e.g., [6,7]). The site index and yield forecasting currently embedded within these stand-level decision support models are largely driven by species-specific dominant height—

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