Dean S. DeBell

Tree growth and stand development in short-rotation Populus plantings: 7-year results for two clones at three spacings

Two Populus hybrids (11-11 and D-01) were planted in monoclonal block plantings at three spacings (0.5, 1.0, and 2.0 m) near Olympia, Washington, and evaluated over a 7-year period for individual tree growth rates and above-ground stand productivity. Differences were substantial between clones and among spacings in both individual tree characteristics (height and diameter growth) and stand productivity (leaf area, basal area, or biomass production). Relative differences in growth between the clones tended to increase with spacing. Woody biomass production of clone 11-11 averaged 18.2 Mg ha−1 yr−1 at the 1.0 m spacing, whereas clone D-01 averaged only 10.1 Mg ha−1 yr−1 at that spacing. The clones differed in phenology of height and diameter growth, maximum rate of periodic height growth, tendency to produce sylleptic branches, partitioning of woody biomass, and sensitivity of growth rates to competition. All of these characteristics have important influences on the productivity of short-rotation plantations.

Tree growth and stand development of four Populus clones in large monoclonal plots

Four clones of Populus were planted in replicated monoclonal plots near Olympia, WA, to evaluate their suitability for use in short-rotation culture. All clones were easily established and had minimal problems from damaging agents during the first five years. Observed differences among clones in pattern and amount of growth appeared to be associated with differences in number and density of buds, sylleptic branching, and phenology. In addition, differences in drought tolerance and stockability may also have influenced clonal differences in annual growth and stand productivity. Individual tree growth was limited by the dense 1.0-m spacing, but the best-growing clones averaged 13 to 16 m tall, 7 to 9 cm in breast-high diameter (1.3 m), and produced stand basal areas exceeding 38 m2ha-1at 8 years. Mortality was negligible for 7 years, after which various combined effects of competition, stem borer damage (Cryptorhyncus lapathi), and a severe windstorm caused mortality ranging from 18 to 36% in the three fastest growing clones.

Above- and below-ground characteristics associated with wind toppling in a young Populus plantation

Abstract Damage from a dormant-season windstorm in a 3-year-old Populus research trial differed among four clones and three spacings and between monoclonal and polyclonal plots. Clonal differences in susceptibility to toppling (or leaning) were associated with both above- and below-ground characteristics. Susceptible clones had less taper in the lower stem and more weight in branches on the upper stem. The most susceptible clone also had the most above-ground biomass per unit of cross-sectional root area. The other susceptible clone had the least root system development in the windward quadrants. Wind toppling was least at the closest spacing. Apparently, mutual support was more important than individual tree characteristics from which the most damage would be expected at the closest spacing. Differences between paired trees of the same clone and spacing which did or did not topple were primarily associated with distribution of root systems by compass quadrant or depth. At the closest spacing where crown sway would have been minimized, trees which did not topple had greater cross-sectional root area in the windward direction than trees which did topple. At the widest spacing where crown sway would have been greatest, windfirm trees had greater cross-sectional root area than non-windfirm trees in both the windward and leeward directions. Toppling was reduced in polyclonal plots; this reduction may have been the result of more rapid stand differentiation in the polyclonal plots or reduction in the “domino effect” by inclusion of more windfirm clones in the mixture.

Wood density of Eucalyptus saligna grown in Hawaiian plantations: effects of silvicultural practices and relation to growth rate

Summary We evaluated effects of chemical fertilizer, spacing, and interplanted nitrogen-fixing trees on wood density and diameter growth of 15-year-old Eucalyptus saligna trees. The trees were grown in silvicultural trials established on former sugarcane land on the island of Hawaii. Elevation was 480 m, slopes were gentle, and annual rainfall averaged 4600 mm at the trial locations. Breast-high increment core samples were obtained by boring more than 100 dominant and codominant trees. Diameters of individual trees ranged from 16.4 to 45.9 cm, and cross-sectional wood densities from 349 to 496 kg m−3. Silvicultural treatment means for 15-year diameter ranged from 24.2 to 35.6 cm, and means for cross-sectional wood density from 400 to 424 kg m−3. Wider spacing (4 m by 4 m vs. 2 m by 2 m) increased mean diameter by 34% without decreasing, and may have increased, wood density. Level of chemical fertilization did not affect wood density, and mean diameter of trees sampled in the two fertilizer treatments was identical. When compared to chemical fertilization, interplanting of N-fixing Albizia trees increased mean diameter by 37% but did not alter wood density. Regression and covariance analyses indicated that growth rate per se (as evidenced by 15-year diameter) had negligible influence on wood density. Pith-to-bark profiles of wood density revealed that trees with rapid growth had more uniform wood density patterns across the radii. We conclude that diameter growth (hence, productivity) can be increased substantially through supplemental nitrogen and increased growing space without decreasing wood density; moreover, wood density may be slightly increased with additional growing space. Moreover, rapid growth—whether associated with improved nutrition or increased growing space—will result in wood with a more uniform density from pith to bark.

Comparison of diameter-distribution-prediction, stand-table-projection, and individual-tree-growth modeling approaches for young red alder plantations

Abstract A red alder planting spacing study was used to compare three modeling approaches that have been successfully used for other tree species. These three approaches predict stand structure and dynamics in plantations that are 7 to 16 years old, with planting densities of 976 to 13 899 trees/ha. The diameter-distribution-prediction approach tended to over-predict the diameter at breast height (dbh) for larger trees in stands planted at low density and to under-predict dbh for smaller trees in stands planted at high density. This approach may be useful for comparing planting densities when a tree list is not available. The stand-table-projection approach tended to under-predict dbh for smaller trees in young stands planted at low density and to over-predict dbh for smaller trees in young stands planted at high density. This approach, however, provided consistency between stand- and tree-level growth projections, and should be useful for comparing planting densities when a tree list is available. The individual-tree-growth approach provided the best representations of observed diameter distributions at all planting densities, stand ages, and growth intervals. This approach may be best suited for stands that have been thinned, stands with mixtures of species, and stands with heterogeneous size classes.

Growing Populus biomass: Comparison of woodgrass versus wider-spaced short-rotation systems

Abstract Growth and yield of Populus were examined in a 5-year test of five spacing-harvest regimes in western Washington. Two hybrid clones (D-O1 and H-11) were planted at two woodgrass spacings (0.18 and 0.3 m) and three wider spacings (0.5, 1.0 and 2.0 m). All treatments were replicated three times in a randomized block design; all plots were fertilized, irrigated, and weeded uniformly. Mean annual harvest yields in the woodgrass treatments did not differ significantly between the two clones (D-O1 and H-11) or two spacings (0.18 and 0.3 m), averaging 6.4 to 7.0 Mg ha −1 (tonnes ha −1 ) over the 5-year period. The highest yield in woodgrass treatments was produced in the second year (first year of coppice), and it declined thereafter. Cumulative growth in the wider spacings was significantly greater than in the two woodgrass spacings. Per hectare yields of clone H-11 in the wider spacings at age 5 were two to three times greater than cumulative yields obtained with annually cut woodgrass, averaging 15.7 to 18.8 Mg ha −1 yr −1 . Fifth-year increments in all wider spacings (0.5, 1.0 and 2.0 m) of clone H-11 exceeded 30 Mg ha −1 . Yields of clone D-01 in the wider spacings ranged from 8.1 to 10.9 Mg ha −1 yr −1 , and thus were also substantially greater than cumulative yields of woodgrass. We conclude that annually harvested woodgrass shows little promise as a viable system for growing Populus for biomass. On the other hand, yields in the wider spacings with a longer harvest cycle were substantially higher than previously expected, especially for clone H-11. Thus, possibilities for application of the wide-spaced regimes and longer cutting cycles appear promising.

Growth and early stand development of intensively cultured redalder plantings

This study evaluates the performance of Alnus rubra inthree square spacings (0.5-, 1.0- and 2.0-m), two irrigationregimes (low and high), and two pre-planting fertilizer treatments (0 and 300 kg P ha−1). Initial survival and growthwere excellent, and differences among various cultural treatmentswere apparent by the end of the second growing season. At ageten, mean tree sizes in specific regimes ranged from 4.8 cm to11.5 cm in diameter and 7.7 m to 13.1 m in height, with largesttrees produced in regimes with wide spacing and high irrigation. Beneficial effects of fertilizer were minimal and were limitedprimarily to enhanced early survival during the first two yearsin the closest spacing. Growth of the plantings was greater thanthat estimated for fully stocked, natural stands of the same ageand site index (or height). Data from our study provided generalconfirmation of the level and slope of the tree size-standdensity lines currently used in density management guidelines foralder, except that mortality in the densest spacing occurred atdiameters smaller than those assumed to indicate the thresholdfor inter-tree competition. This difference, however, waslessened by irrigation.

Dry weight partitioning among 36 open-pollinated red alder families

Abstract Six trees of each of 36 red alder ( Alnus rubra Bong.) open-pollinated families were harvested from a genetic test plantation in September of the second field season and analyzed for growth and dry weight partitioning. Families from elevations greater than 300 m were significantly shorter than from those below 300 m and tended to be in intermediate or suppressed positions in the plantation canopy. Families from the most southerly drainage system, Santiam, were smaller than those from the more northerly drainages. When low elevation families (those from less than 300 m; 24 of the 36 families met this criterion) were analyzed separately, no statistically significant variation was found among the growth traits. In contrast, significant family variation was found in all of the dry weight partitioning traits and relative crown class. Family heritability (h 2 ) values for low elevation families varied from 0·00 to 0·39 for growth traits and from 0·39 to 0·69 for dry weight partitioning traits. At this age and stage of plantation development, there seemed to be more variation in dry weight partitioning than growth of low elevation red alder families. Family means of the dry partitioning traits varied from as little as 5% to as much as 20% around the population means; hence, it appears that variation in some partitioning traits is large enough to be of practical significance in breeding and tree improvement programs.