1

RELATIVE DENSITYRELATIVE DENSITYAND ITS USE IN THINNINGAND ITS USE IN THINNING

Ralph D. NylandDepartment of Forest and Natural Resources Management

SUNY College of Environmental Scienceand Forestry

Syracuse, NY 13210

Nyland - 2010

All rights reservedUse of all or parts of this permission prohibited

without express consent of Ralph D. Nyland

Background reading:

Chapter 17, in Nyland, R.D. 2002. Silviculture: Concepts and Applications.Waveland Press. Long Grove, IL. 2ed.

Sources cited:

Dale, M.E. 1968. Growth response from thinning young even-aged white oak stands. US For. Serv. Res. Rpt. NE-112

Daniel, T.W. J.A. Helms, and F.S. Baker. 1979. Principles of Silviculture. McGraw—Hill Book. Co. NY. 2ed.

Mar:Moller, C. 1954. The influence of thinning on volume increment. 1. Results of investigations. Pp. 5-32, in Thinning Problems and Practices in Denmark. SUNY Coll. For. at Syracuse, World For. Ser. Bull. No. 1, Tech. Publ. No. 76.

Marquis. D.A. 1986. Thinning Allegheny hardwood pole and small sawtimber stands. Pp. 68-84, in Guidelines for Managing Immature Appalachian Hardwood Stands. H.C. Smith and M. Eyes (Ed.). W. Va. Univ./, Morgantown. Soc. Am. For. Publ. 86-02.

Marquis, D.A., R.L. Ernst, and S.L. Stout. 1984. Prescribing silvicultural treatments in hardwood sands of the Alleghanies.US For. Serv. Gen. Tech. Rpt. NE-96.

Nyland,. R.D. 2002. Silviculture: Concepts and Applications. McGraw-Hill Book Co. NY. 2ed.

Roach, B.A. and S.F. Gingrich. 1968. Even-aged silviculture for upland central hardwoods. US Dept. Agric., Agric Handbk. No.355.

Roach, B.A. 1977. A stocking guide for Allegheny hardwoods and its use in controlling intermediate cuttings. US For. Serv. Res.Rpt. NE-373.

2

Reukema, D.L., and D. Bruce. 1977. Effects of thinning on yield of Douglas-fir: Concepts and some estimates obtained by simulation. US For. Serv. Gen. Tech. Rpt. PNW-58.

Steneker, G.A., and J.M. Jarvis. 1966. Thinning in trembling aspen stands in Manitoba and Saskatchewan. Can. Dept. For. Publ. No. 1140.

Stout, S.L. and R.D. Nyland. 1986. Role of species composition in relative density measurement in Allegheny hardwoods. Can. J. For. Res. 16:574-579.

Stout, S.L. 1990. Progress report for relative stand density in northern hardwoods throughout the Northeast. USFor. Serv. Northeast. For. Expt. Stn. 4110-FS-NE-1152-119.

Stout, S.L. and R.D. Nyland. 1986. Role of species composition in relative density measurement in Allegheny hardwoods. Can. J. For. Res. 16:574-579.

WHY THIN …- Improve sawtimber production

... get larger trees in less time

... increase board-foot yields

... enhance stand-wide quality and value

... influence species composition

- Promote stand development... enhance habitat for plants and animals... alter visual qualities... facilitate other non-market uses... move toward “old-growth” conditions

- Influence hydrologic characteristics (water quality and yields)

- Promote tree vigor and stand health (growth and resiliency)

- Stimulate seed production (like preparatory cutting)

- Promote litter decomposition (release nutrients)

3

To influence stand development in favor of a landowner’s objectives ...

How to measure success ...

- volume and value realized- tree growth rates and sizes- tree vigor and health- stand structural features- diameter and height distributions

- number and sizes of understory plants- amount of coarse woody debris- homogeneity of structural features (orderliness or

“neatness”)- thickness and composition of soil organic layers

- light levels near the ground- ease of movement through a stand- degree and distance of visibility (fewer stems and brighter

understory)

Socialinterests

Timbervalues

Ecologicfactors

4

… depending on the objectives for management

AMaximumstocking

Expected development of unthinned oak stands

... the curve shows the maximum basal areafor stands with a specified number/acre

Remember this critical concept …Developed primarily for timber objectives …

5

Mar:Möller 1954 … with full net production at about 60% relative density

ALSO, we need some minimum stocking for full site utilization …

A

B For FULL site utilization

Suggesting a minimum stocking AFTER thinning ...

6

MortalityHIGH>80%

But with mortality increasing with REL DEN >80% ...

Giving us a zone for rational action ...

Nyland 2002

7

B-level relative density gives you ...

- full net cubic-foot production

... per acre per year

- enhanced individual tree growth

... commensurate with full net cubic volumeproduction per acre per year

Keep stands in the GREEN zone

To realize full net production ...

… with the associated ecologicconditions that follow

8

… altering stand conditions to serve the objectives

Roach and Gingrich 1968

So we can use the stocking guideas an aid in planning thinning ...

FOR OAK STANDS

9

But Roach tried it with Allegheny hardwoods ...

... with poor results

After Roach 1977

Until he accounted for species composition ...

... separating

CAPS (bc, wa, and tulip-poplar)

OTHERS (all other species)

… demonstrating that species composition made a difference

10

With a separate line for each species group ...

... each A line to representa different proportionof basal area in CAPs

Roach 1977

And then adding a family of B lines ...

... one for each species group(set at 60% of each A line)

B

11

... and this worked wellin most cases

… to 60% relative density

12

So Stout asked ...

… WHAT IF I add additional species groups

But experience suggested that this guide needed enhancement ...

... particularly to account for stands with lots of red maple

She approached it using the tree-area ratio (TAR) …

TREE-AREA RATIO (TAR)

- a mathematical device for apportioning

ground area using stem diameters

- where the area of a stand is expressed as

a function of ΣD & ΣD2

- Σ (TAR) of all trees present = 1.00

13

RELATIVE DENSITY = Σ (TAR)

- expressed in CENTACRES

- the TAR’S for different species can be compared to

determine how to best account for species composition

in assessing competition within forest stands

- TAR differed between CAPS & two other species groups

See Stout and Nyland 1986

Stand relative density = ∑ (Tree relative density)

Tree relative density = ƒ (Tree diameter and species)

Individual tree

relativ

e density

... in ce

ntacres

Stout and Nyland 1986

14

So three groups for Allegheny hardwoods ...

CAPS – bc, wa, & tulip-poplar

HM-BE – hm, be, stm, oaks except ro

OTHER – all other species

… we use these for other northern hardwoods as well

... the hm-be group

This defines the contribution of individual trees to stand relative density (by species) …

... e.g., for 16-inch treeStout and Nyland 1986

... the CAPS

... the red maple group

15

Stout, USFS, 1990

The number, shape, and position of the lines depends uponthe species mix and regional conditions ...

But Stout found that even this improvement needed refinement …

So we use this set for hardwood stands in NYS …

Stout, USFS, 1990

16

SO HOW TO USE IT ...

... in practical applications

Tim Davis 2001

SO COMPLICATED ...

Marquis et al. 1984

RD factorsincluded

Try this field tally sheet ...

17

AcceptableGrowing

Stock

Quality considered ...

UnacceptableGrowing

Stock

Poor trees as well ...

18

And species group

Also by diameter classwithin each group

19

An example ...

... a typical field tally

Here we calculate relative density rather than getting it from a chart...

See instruction sheetfor guidance in makingthese calculations …

20

And based on the findings, we canprepare a marking guide to controlthe thinning …

NOTE: Remove up to 35% RD …

… butbut don’t reduce the standbelow 60%

21

From the distribution of cut chart …

And how much to cut from each size class ….

… taking a trial distributionof cut from this chart

… in this case forDM = 14 inches

Marquis et al. 1984

For a crown thinning …

22

From the distribution of cut chart …

32.16 * 0.63 = 20.26

And how much to cut from each size class ….

… to see how a cut of this kind wouldmatch actual conditions in the stand

BUT check the UGS …

23

The proposed cutwould NOT reduce the ST UGS adequately

… so we make an adjustment tofit the real situation

24

… expressed as a % of what we have

… and finally expressed as a marking guide

25

Then we go back and convert itto basal area removed …

Our guide

Our prescription ...

26

100% of potentialgross growth

% of maximum possible basal area

% o

f max

imum

cur

rent

gro

ss g

row

th

After Mar:Möller 1954

... at about 60% relative density we getfull gross cubic-foot volume growth

Insuring full site utilization …… and a full level of production

Mortality

And control of mortality as well ...

The B line on stocking charts set at the best estimate of a stand density where

net P.A.I. peaksfor stands at different ages

27

Helms, Daniel, and Baker 1979

60%

30-35%

... for a stand

... for a tree

Examine some real responses from thinning trials ...

Stand

Tree

Marquis 1986

28

Steneker and Jarvis 1966

Dale 1968

Stand-level cubic-foot volume production like this ...

In older managed stands bd ft production seems topeak at a somewhat higherresidual relative density ...

… but this still needs betterdefinition

Marquis 1986

29

Marquis 1986

... mostly the smallertrees of poor crownpositions die

80%

With stocking below 80% ...

Marquis 1986

60%

… FEW epicormics instands with at least60% relative density

With stocking above 60% ...

30

Giving us a model for management ...

... keep stands in the green zoneNyland 2002

Keep stands in the GREEN zone

Primarily ...

31

Reukema and Bruce 1977

The same basic idea ...

... for Douglas-fir

And note this for northern hardwoods ...

ResidualBASAL AREAincreased witheach thinning ...

For the stages of developmentportrayed, the optimum residualbasal area should be increasedfrom about 62 to 80 ft2/ac …

… if periodically thinned to 60% RD

32

To give you this ...

Additional volume ralizedwith regular thinning

Excess trees removedduring thinning

Post-thinningBA/ac higher each time

Full site utilization ...

33

... but we must have one somewhere near here After Nissen 2010