THE INFLUENCE OF STAND CONDITIONS ON TREE FORM Sean M. Garber and Aaron R. Weiskittel Oregon State University June 21, 2004

INTRODUCTION A goal of silvicultural research is to detect changes in growth. Changes in stand conditions affect diameter and sometimes height: –Density (spacing and thinning) –Social position within the stand –Control of competing vegetation –Fungal diseases

INTRODUCTION Consequently stem volume also responds to these stand conditions.

INTRODUCTION Existing volume and taper equations: –Most are functions of only DBH and HT; –Regional development; –May not include intensively managed stands or other dramatically altered stand conditions; –Averages lose subtle differences.

INTRODUCTION Questions: –Is there an affect of stand conditions above and beyond the effect on DBH and height? –Does this influence the ability to discern growth differences among treatments in silvicultural studies?

INTRODUCTION DBH HT

METHODS Analytically assessed stem form on four separate studies: –Two vegetation management studies –A western larch LOGS thinning study –Two mixed-species spacing trials –Study of Swiss needle cast

METHODS Kozak variable-exponent taper model applied in all studies: d = γ 1 DBH γ 2 X C + ε Represents shape

METHODS Shape component (X C ) –X varies from 0 (top), 1 (p), > 1 below p. –C = linear function of: Z = stem position (h/HT) DBH/HT Treatment variables

Model dynamics Positive term Negative term

METHODS Sample trees were climbed or felled: –Sampled across range of within treatment DBH; –DBH, HT, HCB, and CW measured; –Upper stem diameters (ib and ob) and height measured.

METHODS Autocorrelation accounted for in two ways: –Model fit by tree and parameters modeled using SUR. –Model fit using GNLS with CAR(1) Multicollinearity was also a problem –Screened to reduce VIF

Douglas-Fir Stem Taper Under Early Vegetation Control Study part of the Vegetation Management Research Cooperative, Oregon State University.

INTRODUCTION As trees develop under intensive management: –Form differs from a cone (  /12)D 2 H, –Trees large enough for existing volume or taper equations.

Summit Marcola

Vegetation Management sites Study description –Planted in 1993, –Completely randomized design, –8 treatments, –3 replicates, –Plot area = ac, –49 seedlings planted at 9.8 ft square spacing.

METHODS Treatments –No herbicide, –4 ft 2 full control, –16 ft 2 full control, –36 ft 2 full control, –64 ft 2 full control, –100 ft 2 full control, –100 ft 2 woody vegetation control, –100 ft 2 herbaceous vegetation control.

METHODS Diameter outside bark was collected at tree base, breast height, 8 ft, and every 4 ft above 8 ft. Observed DOB’s were modeled using variable-exponent model using GNLS. C was a function of site, area treated, and target vegetation.

RESULTS Modeling –Model fits were excellent (R 2 > 0.95); –Impact of autocorrelation eliminated w/ CAR(1); –Multicollinearity present, albeit small. Treatment variables –Area treated and herb control significant

Stem Taper in a Western Larch Levels-of-Growing- Stock Thinning Study From Lennette A.P Twenty-five-year responses of Larix occidentalis stem form to five stand density regimes in the Blue Mountains of eastern Oregon. M.S. Thesis, Oregon State University. 59 p.

METHODS Study description –Established in 1933, –Completely randomized design, –5 treatments, –2 replicates, –Plot area = 0.4 ac, –Thinned in 1966, 1975, and 1985

METHODS Treatments based on bole surface area (BSA) targets: BSA ( ft 2 /ac ) SDIRelative density 5, , , , ,

METHODS Data analysis: –Parameters fit by tree; –Parameters tested among treatments by MANOVA; –Parameters modeled using SUR.

RESULTS Stem form responded to thinning: –C = a 1 sin -1 (Z) + a 2 Z 2 ; –MANOVA suggested differences among the treatments; –Parameters increased w/ thinning intensity: a 1 = f (DBH/HT) a 2 = f (CR)

BSA: 15,000 to 25,000 BSA 10,000 BSA 5,000

RESULTS CR improved model fit after accounting for DBH/HT Treatment variables did not account for additional variation beyond DBH/HT and CR.

Increasing thinning intensity

Stem Taper in Two Mixed- Species Spacing Trials From Garber, S.M. and Maguire, D.A Modeling stem taper of three central Oregon species using nonlinear mixed-effects models and autoregressive error structures. For. Ecol. Manage. 179:

Study sites Two study sites located at Pringle Falls EF on the Deschutes National Forest: –Pringle Butte (34 years) Lodgepole pine and Ponderosa pine 4500 feet elevation, west aspect, and dry SI 100 = 100 ft (Barrett 1978) –Lookout Mountain (27 years) Grand Fir and Ponderosa pine 5100 feet elevation, east aspect, and “more mesic” SI 100 = 110 ft (Barrett 1978)

Experimental Design Completely randomized split-plot design –Whole plot factor: spacing –Split-plot factor: species composition Replacement series setup –Only one mixture 50:50 GF MX PP Whole plot Split plot PP P PP F F F F MX

INTRODUCTION Mixed-species stand development: –Spacing More spacing, less stratification –Species composition PP over GF LP over PP From Garber, S.M. and Maguire, D.A Stand productivity and development in two mixed- species spacing trials in the central Oregon Cascades. For. Sci. 50:

Top height growth across spacing

RESULTS Modeling –Model fits were excellent (R 2 > 0.95); –Impact of autocorrelation eliminated w/ random effects and CAR(1). Profiles –Showed differences among spacing; –Slight differences between pure and mixed stands.

SPACING

SPECIES COMPOSITION Mix PP (subordinate) Pure PP

SPECIES COMPOSITION Pure PP Mix PP (dominant)

DOUGLAS-FIR STEM TAPER & SNC Part of the Swiss Needle Cast Cooperative, Oregon State University. From Weiskittel, A.R Alterations in Douglas-fir crown structure, morphology, and dynamics imposed by Swiss needle cast in the Oregon Coast Range. M.S. Thesis, Oregon State University. 389 p.

INTRODUCTION SNC disrupts normal needle physiology, leading to premature loss of foliage 10 yrs of extensive defoliation has dramatically altered Douglas-fir crown structure & morphology –modified age class structure and vertical location of foliage –reduced branching –increased crown recession rates

HYPOTHESES loss of foliage has decreased stem increment in the crown increased crown recession rates modified stem form stem taper equations require additional SNC covariates

METHODS 105 trees from 31 plots destructively sampled –DBH; 12 – 65 cm –Relative density; –Site index; 27.7 – yr –Foliage retention; 1.2 – 4.4 yrs 3 to 4 trees/plot & 10 to 15 discs/tree

ANALYSIS utilized modified Kozak’s equation –includes Z, DBH Z, DBH/HT, FOLRET –little correlation between covariates –continuous AR1 error structure tree volume predicted using the developed equation and Bruce & Demars (1974) equation –results compared graphically and statistically

RESULTS R 2 of 0.95 parameters all highly significant (p<0.001) likelihood ratio test also suggested that foliage retention significantly improved model fit (p<0.0001) for a given DBH/HT, foliage retention significantly reduced dibs throughout the stem, except below BH

RESULTS

DISCUSSION Does relative stem form change w/ stand conditions? –Differences in profiles after accounting for DBH and HT. –Treatments variables significant after accounting for DBH/HT: Vegetation treatment; Thinning level; Foliage retention.

DISCUSSION StudyShape changeConsequences ↑ Veg. controlMore NeoloidOverestimate ↑ ThinningMore NeoloidOverestimate ↑ SpacingMore NeoloidOverestimate ↑ DominanceMore NeoloidOverestimate ↑ SNCMore NeoloidOverestimate Does relative stem form change w/ stand conditions?

DISCUSSION Do these changes affect results of silvicultural studies? –Significant difference between volumes estimated from SNC equations and Bruce- DeMars; –Bias a function of top height, DF QMD, FOLRET, and CLSA; –Mean volume losses due to SNC were 31%.

DISCUSSION Mechanisms –Differential basal area growth rate along the stem differences among treatments. Stem growth rate responds to increased resources; Response increases w/ decreasing stem height. –Swiss needle cast Reduces tree leaf area (thins crown) Decreases upper stem growth

Curves diverge

DISCUSSION Measure upper stem diameters. –Assess existing volume or taper equations. –Develop new site-specific equations. Incorporate crown ratio into the model Include stand or treatment variables into models.

THE END Any questions?

VMRC literature Ketchum et al The impacts of weed control on young Douglas- fir taper and volume calculations. Pp in Annual Report, Vegetation Management Research Cooperative, College of Forestry, Oregon State University, Corvallis, OR, USA. Maguire et al Stem form responses to differing areas of weed control around planted Douglas-fir trees. Pp in Annual Report, Vegetation Management Research Cooperative, College of Forestry, Oregon State University, Corvallis, OR, USA.