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Forest Mensuration II Lecture 11: Stocking and Stand Density Nick Buda Northwest Science and Information Ontario Ministry of Natural Resources November 16th, 2005 Lakehead University Reference: Avery, T.E. and H.E. Burkhart. 2002. Forest Measurements 5th Ed. Chapter 15, pp. 321-336.

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Context “The stocking in this stand is too low.” “Plant this area to jack pine at 1700 stems/hectare” “Mark this stand to remove about 15 m 2 /ha of hard maple” “This stand is fully stocked” “This stand is understocked” “This stand is overstocked” Context Definitions Density Stocking Summary

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Definitions Density: A quantitative term describing the degree of stem crowding within a stocked area* Can be expressed in absolute or relative terms Simply put: a measure of the amount of tree vegetation on a unit of land area Examples: 1700 stems/ha or 35 m 2 /ha, more… Context Definitions Density Stocking Density Stocking Summary

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Definitions Stocking: Refers to the adequacy of a given stand density to meet some management objective * – Understocked, fully stocked, overstocked A stand considered “overstocked” for one management objective could be “understocked” for another Important to decide what constitutes full stocking - makes the use of this term confusing “Stocking” and “density” are often applied interchangeably - they are NOT the same thing Context Definitions Density Stocking Density Stocking Summary

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Density Density Relationships (for given species, site and time period) As Density Increases, Spacing Average stem diameter Crown Width Live Crown Ratio GTV per tree MV per tree Decrease Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary Increase Gross Total Volume per hectare Merchantable Volume per hectare After White (2004)

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Density Measures: Stems per unit area Basal Area Volume Various Indices Absolute vs. Relative Measures Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary

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Stand Density Stems per unit area: Very useful in developing silvicultural prescriptions Variable density yield tables e.g. 1700 stems per hectare, 2500 sph, 500 stems/ha, etc. Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary

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Stand Density Basal Area A good, objective expression of density - very commonly used - e.g. point sampling Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary

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Stand Density Stand Density Index A measure of density based on 2 parts of BA - density and diameter of average tree Has been used in variable-density yield tables BA simpler and easier to use 3/2 Law of Self Thinning Foundation of Stand Density Management Diagrams (DMDs) Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary

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Stand Density Relative Spacing Average distance between trees divided by the average height of the dominant canopy Main uses - mortality models & thinning schedules Tendency to decrease with age Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary

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Stand Density Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary Crown Competition Factor Reflects area available to average tree in a subject stand, relative to maximum area it would use if open-grown Establish crown width- dbh relationship Compute maximum crown area (%ha) Sum MCA values for each dbh class and divide by stand area

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Point Density Context Definitions Density Relationships Measures Stems/unit area Basal Area SDI & 3/2 Law Relative Spacing CCF Point Density Stocking Summary Stand density measures give an idea of the average density or competition for the whole stand Point density measures provide a competition index for a specific tree or point within a stand 3 main types: – Area-overlap - competion influence zone around tree - competition stress a result of overlaps in zone – Distance-weighted size ratio - idea that large trees close to subject tree exert more stress than small trees far away – Polygon (area-available)

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Stocking Recall: stocking refers to the adequacy of a given density to meet some management objective Problem: What should constitute full stocking for a given species on a given site for a given management objective? Fully-stocked or “normal stand”: Hypothetically, a stand in which tree crowns are fitted together so that no sunlight is wasted and each crown is matched with a root system that fully utilizes the soil Context Definitions Density Stocking Full Stocking Normality Regeneration Mature Stands Stocking Guides Summary

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Stocking Regenerating Stands Stocking thought of as a measure of site occupancy i.e. The proportion of available areas occupied by tree seedlings (so as to result in a fully-stocked stand at maturity) Available area = growing space for one tree Context Definitions Density Stocking Full Stocking Normality Regeneration Mature Stands Stocking Guides Summary

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Stocking Regenerating Stands A percentage based stocking figure does not tell you much about the distribution of the trees in a stand: Context Definitions Density Stocking Full Stocking Normality Regeneration Mature Stands Stocking Guides Summary 2000 trees/ha 0 trees/ha Clumped - 50% stocked 1000 trees/ha Uniform - 50% stocked

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Stocking Mature Stands Essentially comparing the density of a subject stand to that of an “ideal” or reference stand – Volume – Basal Area – An Example Context Definitions Density Stocking Full Stocking Normality Regeneration Mature Stands Stocking Guides Summary

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Stocking Guides Context Definitions Density Stocking Full Stocking Normality Regeneration Mature Stands Stocking Guides Summary

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Context Definitions Density Stocking Full Stocking Normality Regeneration Mature Stands Stocking Guides Summary In a nutshell: “…density tells what is, and stocking tells how this density relates to someone’s notion of what ought to be, usually in terms of percentages” Smith et al. (1997)

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