Wood Basic Density Variation Along Pinus occidentalis , Swartz, and Pinus caribaea , var. Caribaea, Morelet tree stems

Abstract

Pinus occidentalis and Pinus caribaea are important conifers in La Sierra, Dominican Republic, used to recover degraded ecosystems. A study on their wood density obtained from stem discs at three relative heights (RH) as a composite sample showed that wood density increased with age class for both species and decreased with RH in the stem. A mixed repeated measures analysis of variance, followed by a regression approach to the effects model, indicates a statistically significant interaction between species, age class (AC), RH, [ , P ≤0.000, partial =0.814]. Simple bidirectional interactions between factors and all simple main effects are statistically significant. Basic density (BD) increased with age class for both species and decreased with RH in the stem. Pinus occidentalis had a 14.6% higher average wood density and is endemic. Therefore, efforts must be made to provide better silvicultural practices so that its population continues to be a viable asset.

Keywords:
analysis of variance; conventional densitometry; repeated measures analysis; wood physical properties

INTRODUCTION

In “La Sierra”, Dominican Republic (DR), two conifer species, Pinus occidentalis , Swartz, and Pinus caribaea var. caribaea, Morelet play very important roles, economically, ecologically, and socially. P. occidentalis is endemic of La Hispaniola ( Hubbel et al., 2018 ), and is considered highly suitable for structural timber applications and developing value-added solid timber products ( Klotz & Torres 1991 ). P. caribaea original habitat is in Pinar del Rio Province and Isla de la Juventud, western Cuba. It was introduced to the Sierra region around 1980, mostly replacing the endemic P. occidentalis in plantation establishment operations at lower elevations. Both species are classified within the genus Pine , Subgenus Pinus , Section Trifoliae, and Subsection Australes.

Little is known about the interaction between species, age, and RH with respect to their effects on basic density (BD) traits along the stem in P. occidentalis and P. caribaea in the study region. Therefore, detailed quantitative knowledge of variation in BD among these species and individual trees is required and should be valuable information for local forest managers.

Wood density (WD) varies among tree species ( Li et al., 2020 ). Oliveira et al. ( 2022 ), as cited in Guo et al. ( 2024 ), state that even in the same region, WD varies between and within trees due to different environments. Density was correlated with mean annual precipitation, temperature, evapotranspiration, and soil water storage capacity ( Lima-Costa et al., 2020 ; Oliveira et al., 2022 ). Gonçalves-Rocha et al. ( 2020 ) observed water deficit in the soil being the most significant variables with potential to estimate the BD in eucalyptus clones. Within a tree, WD usually increases from juvenile to mature wood in the radial direction and decreases from root to branch in the axial direction ( Venega et al., 2023 ), although there are exceptions.

Conifer species from the Picea , Pinus , or Pseudostuga genera used in plantations worldwide have overall denser wood than most planted angiosperms ( McCulloh et al. 2019 ). Topanotti et al. ( 2021 ) evaluated WD at different stem heights of Pinus taeda , L. managed under shelterwood silviculture and found that this treatment affected WD. Within a tree, WD usually increases from juvenile to mature wood in the radial direction and decreases from root to branch in the axial direction ( Venega et al., 2023 ), but there are exceptions. The same effect has been reported by Beets et al. ( 2020 ) in Pinus radiata , D., although these authors also report an inverse effect for Pseudotsuga menziesii , (Mirbel) Franco in New Zealand.

Earlywood density of conifer species remains stable, whereas latewood density increases with age and from pith to bark ( Moreno-Fernández et al., 2018 ). Morgado-González ( 2019 ) investigated radial changes in WD of Pinus hartwegii , Lindley. Their results indicate that changes in WD are influenced by altitude, but the level of change depends on exposure. Vaughan et al. ( 2019 ) informed of climatic fluctuations having a strong effect on Pinus ponderosa , Engelm density. For Pinus halepensis Miller, Hevia et al. ( 2020 ) found that climate at provenance and not planting site was more relevant for WD fluctuations. In Pinus elliottii , Engelm. temperature displayed higher correlations with WD than precipitation ( Li et al., 2020 ).

We were interested in assessing the effects of these two species and the factors, age class (AC) and RH on the variation of BD along tree stems. The overall objective of this study was to assess inter-tree, intra-tree, and inter-species BD variation within the stem of P. occidentalis and P. caribaea trees planted in La Sierra, Dominican Republic (DR), as an initial assessment of the quality of their wood and timber potential. Specifically:

• BD variation between species.

• BD variation within trees at three RHs in each species.

• BD variation within trees belonging to three different age classes from each species.

• The presence of any interaction effects between these three factors.

To our knowledge, no information concerning P. occidentalis in this respect exists, and there are no records of BD comparisons between these two species.

MATERIALS AND METHODS

2.1. Study Area

Data for this comparative observational study was collected in six plantations of P. caribaea and P. occidentalis, growing side by side within La Sierra, DR, aged between 5 and 34 years. La Sierra is located between UTM coordinates 251748 m E - 325795 m E and 2116888 m N - 2156996 m N. Slopes range from zero to 70 percent. The elevation ranges from 400 m to 1000 meters above sea level. The average annual temperature is 24 ºC, varying between maximum and minimum of less than 10 ºC ( Bueno & Bevilacqua, 2013 ).

2.2. Destructive sampling

Thirty trees were selected, 15 for each species and 5 per species in each age class (AC). Three ACs were considered: 5-14, 15-24, and 25-34 years. The trees selected for destructive sampling were healthy and without apparent defects. For sampling at 0.1, 0.5, and 0.8 relative heights, the total tree height of the stem was considered from 0.1 meters on the stump to the treetop ( Figure 1 ). For each tree, one-inch-thick discs at the three RH were obtained. On each disc, subsamples were dissected, taking one portion from heartwood wood and two portions from sapwood to form a composite sample at each RH.

Figure 1.
Tree stem scheme showing relative heights 0.1 (10% RH), 0.5 (50% RH), and 0.8 (80% RH), and total tree height (H), considered from 0.1 meters on the stump to the treetop.

A summary of tree characteristics, including normal diameter (d.b.h, cm), tree total height (H, m), and stem height at 0.1, 0.5, and 0.8 relative heights for each species, is presented in Table 1 .

Table 1.
Summary of tree characteristics for each species.

	d.b.h	H	RH-0.1	RH-0.5	RH-0.8
Species	(cm)	(m)	(m)	(m)	(m)
P. caribaea	11.40	4.74	0.47	2.37	3.79
	13.20	8.75	0.88	4.38	7.00
	12.70	11.12	1.11	5.56	8.90
	19.40	15.35	1.54	7.68	12.28
	17.20	13.90	1.39	6.95	11.12
	22.40	13.64	1.36	6.82	10.91
	17.50	17.80	1.78	8.90	14.24
	21.00	19.45	1.95	9.73	15.56
	19.80	19.14	1.91	9.57	15.31
	25.50	21.04	2.10	10.52	16.83
	30.70	27.30	2.73	13.65	21.84
	25.00	18.97	1.90	9.49	15.18
	35.00	22.90	2.29	11.45	18.32
	23.10	21.10	2.11	10.55	16.88
	27.00	22.95	2.30	11.48	18.36
P. occidentalis	10.50	11.50	1.15	5.75	9.20
	12.10	10.80	1.08	5.40	8.64
	16.50	12.80	1.28	6.40	10.24
	10.50	12.25	1.23	6.13	9.80
	17.50	8.70	0.87	4.35	6.96
	17.00	11.50	1.15	5.75	9.20
	15.70	15.60	1.56	7.80	12.48
	22.70	15.30	1.53	7.65	12.24
	23.50	22.00	2.20	11.00	17.60
	19.00	18.17	1.82	9.09	14.54
	23.50	21.20	2.12	10.60	16.96
	27.00	15.90	1.59	7.95	12.72
	27.50	21.80	2.18	10.90	17.44
	21.50	14.53	1.45	7.27	11.62
	21.00	14.65	1.47	7.33	11.72

Although several methods are used to measure wood density, the standard way is to calculate the ratio between the dry weight of wood divided by the green volume of the same wood (Zobel & Jett 1995 ). The following protocol was used to measure basic density in our samples.

1) One-inch-thick discs at the three RH were obtained for each tree. On each disc, 0.5 x 0.5 x 1-inch subsamples were dissected, taking one portion from heartwood and two portions of sapwood to form a composite sample at each RH, measuring density on each portion and averaging these three densities to represent the density at each RH, ensuring they represented the wood’s variability.

2) The fresh (green) volume (cm ³ ) was measured by water displacement using an Electronic Densimeter model MD-300S (Advanced Testing Technologies, QMS Inc., 1840 Gateway Drive, Suite 200, San Mateo, CA 94404, USA), after soaking each of the subsamples in water until they reached maximum hydration.

3) The subsamples were oven-dried until a constant weight with a humidity percentage of at least 30% was achieved at an average temperature of 110 ºC. Oven-dried weight (g) were obtained using a high-precision analytical balance (Radwag model XA 220.r2, Torunska 5, 26-600 Radom, Poland). Moisture content (%) was obtained using a mini-Ligno model E/D pin moisture meter (Lignomat USA LTD, 14345 NE Morris Ct., Portland OR 97230, USA).

4) Basic density was calculated using the formula,

$$\mathrm{Basic\; Density}=\frac{\mathrm{Oven\; -\; Dry\; Mass}}{\mathrm{Green\; Volume}}$$

2.3. Statistical analysis

A three-way mixed ANOVA was performed using the GLM procedure for repeated measurements (SPSS IBM Corp. 2017), to understand the effects of species, AC, and RH, on the variability of BD within stem. The main purpose was to understand group differences between intra-subjects factor (RH) and groups formed by combination of two inter-subject factors (Species and AC). Furthermore, we examined the nature of bidirectional interactions and simple main effects. The sum of squares for a factor effect in each instance is the difference between error sums of squares for reduced and full models, and the associated degrees of freedom are the difference between respective degrees of freedom for these error sums of squares.

The assumption of normality was evaluated using Shapiro-Wilk test ( Shapiro and Wilk 1965 ), for each combination of groups of the three factors: species, AC (intra-subjects), and RH (inter-subjects). The homogeneity of variances assumption was evaluated using Levene’s test ( 1960 ), and the sphericity assumption using Mauchly test ( 1940 ). Post hoc tests to assess differences between specific averages were conducted employing the Bonferroni procedure (Bonferroni 1936 ).

RESULTS

BD values were normally distributed as assessed by Shapiro-Wilk’s test ( P >0.05). Inspection of box plots for values greater than 1.5 box-lengths from the edge of the box indicates the absence of outliers in the data. Figure 2 depicts realized BD values at RHs of 0.1, 0.5, and 0.8 for P. caribaea (Panel A) and P. occidentalis (Panel B), respectively. In Table 2 we present general descriptive statistics of the relationship between within-subject and inter-subject factors on variation of BD in these two species .

We found homogeneity of variances on BD values for factor combinations at 0.1 and 0.8 RHs (P=0.587 and P=0.288), respectively, but not at RH 0.5 (P=0.011), as assessed by Levene’s test for equality of variances ( Levene 1960 ). However, we have equal sample size, and the three-way mixed ANOVA is robust to variance heterogeneity in these circumstances. Mauchly’s test of sphericity indicated that the assumption of sphericity is not violated, =3.684, P=0.158.

Figure 2.
Realized BD values at RH of 0.1, 0.5, and 0.8 and age classes 5-14, 15-24, and 25-34 for P. caribaea (Panel A) and P. occidentalis (Panel B).

Table 2.
General descriptive statistics of the relationship between within-subjects and inter-subjects’ factors on the variation of BD in the two species P. caribaea and P. occidentalis .

					Confidence Interval (95%)
Species	AC	RH	Mean	Standard Error	Lower Limit	Upper Limit
P. caribaea	5-14	0.1	0.597	0.002	0.593	0.601
		0.5	0.521	0.002	0.516	0.526
		0.8	0.500	0.001	0.498	0.503
	15-24	0.1	0.830	0.002	0.826	0.834
		0.5	0.738	0.002	0.733	0.743
		0.8	0.688	0.001	0.685	0.691
	25-34	0.1	0.912	0.002	0.908	0.916
		0.5	0.781	0.002	0.776	0.786
		0.8	0.697	0.001	0.694	0.700
P. occidentalis	5-14	0.1	0.701	0.002	0.697	0.705
		0.5	0.617	0.002	0.612	0.622
		0.8	0.601	0.001	0.599	0.604
	15-24	0.1	0.958	0.002	0.954	0.962
		0.5	0.803	0.002	0.798	0.808
		0.8	0.698	0.001	0.695	0.701
	25-34	0.1	1.043	0.002	1.039	1.047
		0.5	0.972	0.002	0.967	0.977
		0.8	0.862	0.001	0.859	0.864

• ^AC:
  Age class; RH: Relative height.

Results in Table 3 indicate that for alpha = 0.05, there is a statistically significant three-way interaction for stem BD, between the factors RH, species, and AC; , P ≤0.000, partial =0.954. It also shows that simple bidirectional interaction RH*species is statistically significant, , P ≤0.000, partial =0.814, as it is also the simple two-way interaction RH*AC, , P ≤0.000, partial =0.954.

Table 3.
Inter-subject effect tests for the dependent variable (BD) with assumed sphericity. Intra-subject factor (AR) and its interactions with inter-subject factors are included. Observed Power is calculated for alpha = 0.05.

Origen	Type III sum of squares	df	Avg. Square	F	Sig.		Non centrality Parameter	Obs. Power
RH	0.420	2	0.210	11589.8	0.000	0.998	23663.6	1.00
RH*Specie	0.004	2	0.002	105.2	0.000	0.814	211.7	1.00
RH*AC	0.037	4	0.009	514.9	0.000	0.977	2105.4	1.00
RH*Specie*AC	0.018	4	0.005	250.3	0.000	0.954	1020.0	1.00
Error (RH)	0.001	48	1.8E-5

• ^RH:
  Relative Height
• ^AC:
  Age Class
• ^df:
  Degrees of Freedom
• Partial Eta Squared
• ^Obs.:
  Observed

Figure 3 shows that, for the three RHs, BD increases with AC. Lines that identify the species are not parallel. Two-way interactions between “species” and “AC” are different at RHs 0.1, 0.5, and 0.8. suggesting the existence of different two-way interactions amid Species*AC at different levels of RH. BD is higher in all AC and RH for P. occidentalis , except when RH is 0.5 in AC 15-24. For AC 25-34 and RH 0.8 (panel A), average BD for P. occidentalis differs substantially from that of P. caribaea . This pattern is repeated on panel (B). In panel (C), at RH 0.5, species BD averages are similar, and differences are substantial at RHs 0.1 and 0.8.

Figure 3.
Means plots showing that there is a two-way interaction between “species” and “AC” when either “RH” is 0.1 (panel A), 0.5 (panel B), or 0.8 (panel C). Patterns differences confirmed graphically the presence of a three-way interaction of “species”, “AC” and “RH” on “BD” for P. occidentalis and P. caribaea .

In Table 4 all possible pairwise comparisons for simple main effects between each group average are presented. Regarding species, BD had an average value of 0.696 g.cm ³ for P. caribaea and 0.806 g.cm ³ for P. occidentalis . Mean differences are statistically significant (-0.110±0.001), P ≤0.000. All mean comparisons adjusted as a family by the Bonferroni correction, are statistically significant ( P ≤0.000).

Table 4.
All possible mean comparisons between each group average, based on estimated marginal means for BD data of P. caribaea and P. Mean comparisons are adjusted as a family by Bonferroni correction .

							Confidence Interval (95%) for Mean Difference
Species	RH	AC (I)	AC (J)	Mean Difference (I-J)	Stand. Error	Sig.	Lower Limit	Upper Limit
P. caribaea	0.1	5-14	15-24	-0.233*	0.003	0.000	-0.240	-0.226
			25-34	-0.314*	0.003	0.000	-0.321	-0.307
		15-24	25-34	-0.081*	0.003	0.000	-0.088	-0.074
	0.5	5-14	15-24	-0.217*	0.003	0.000	-0.226	-0.208
			25-34	-0.260*	0.003	0.000	-0.269	-0.252
		15-24	25-34	-0.043*	0.003	0.000	-0.052	-0.035
	0.8	5-14	15-24	-0.187*	0.002	0.000	-0.192	-0.183
			25-34	-0.197*	0.002	0.000	-0.201	-0.192
		15-24	25-34	-0.009*	0.002	0.000	-0.014	-0.004
Pinus occidentalis	0.1	5-14	15-24	-0.257*	0.003	0.000	-0.264	-0.250
			25-34	-0.342*	0.003	0.000	-0.349	-0.335
		15-24	25-34	-0.085*	0.003	0.000	-0.092	-0.078
	0.5	5-14	15-24	-0.186*	0.003	0.000	-0.195	-0.178
		15-24	25-34	-0.355*	0.003	0.000	-0.363	-0.346
			25-34	-0.168*	0.003	0.000	-0.177	-0.160
	0.8	5-14	15-24	-0.096*	0.002	0.000	-0.101	-0.092
			25-34	-0.260*	0.002	0.000	-0.265	-0.255
		15-24	25-34	-0.164*	0.002	0.000	-0.169	-0.159

• ^*.
  The mean difference is significant at the .05 level
• ^AC:
  Age class
• ^RH:
  Relative height
• ^{Sig.: Stand.:}
  Standard; Statistical significance

Figure 4 displays all estimated means for both species at different levels of RH and AC. BD is greater in P. occidentalis for all combinations of RH and AC except at RH 0.8 and AC 15-24. For both species, BD increases with AC. Within individual trees, it decreases as RH increases.

Figure 4.
Estimated means for P. occidentalis and P. caribaea at different levels of the between-subjects factor AC, and the within-subjects factor RH. BD is higher for P. occidentalis at all combinations of the above factors except AC 15-24 and RH 0.8.

More significant differences in means (± standard error) were found for P. occidentalis at 0.5 RH, between AC 5-14 and 25-34 (-0.355±0.003) g.cm ³ ( P ≤0.000), followed by mean difference at 0.1 RH, between the same AC (-0.342±0.003) g.cm ³ ( P ≤0.000). For P. caribaea the greatest difference among means was found at 0.1 RH, between AC 5-14 and 25-34 ( P ≤0.000).

DISCUSSION

WD differs among different species. Its allocation in trees depends on many factors, but mainly on the tree species ( Jakubowski & Dobroczynski, 2021 ). Li et al. ( 2024 ) study revealed that at a global scale, species explained 7.7% of total WD variation for angiosperms and gymnosperms combined. When gymnosperms were considered separately, species explained 21.3%.

Overall, the average BD was 14.6% higher for P. occidentalis (0.806±0.137 g.cm ^-3 ) than that for P. caribaea (0.696±0.117 g.cm ^-3 ). Mean difference ± standard error is statistically significant (-0.110±0.001), P ≤0.000. BD is greater in P. occidentalis at 0.1, 0.5, and 0.8 RHs, with corresponding values of 0.901±0.150, 0.797±0.150, and 0.720±0.111 g.cm ³ ; as compared to P. caribaea , which attained respective values of 0.780±0.138, 0.680±0.118, and 0.628±0.094 g.cm ³ . Higher similar BD values (>0.650 g.cm ^-3 ) were found in 62% of 108 species of the northern Brazilian Amazon by Farias et al. ( 2023 ). Increased WD relates to greater wood strength and greater ability of the material to resist forces ( Horácek et al., 2017 ).

Sample trees from both species had an average age of 19 years, and both exhibited higher average BD than the equivalent quantity reported by Demol et al. ( 2021 ) for Pinus sylvestris L in Belgium, who found average wood BD values of 0.461 g.cm ⁻³ . Szaban et al. ( 2023 ) compared the stem density of several P. sylvestris provenances in Poland, finding values ranging from 0.418 g.cm ^-3 to 0.451 g.cm ^-3 . Tomczak et al. ( 2023 ) reported P. sylvestris’ s density values ranging from 0.491±0.083 to 0.495±0.076 g.cm ^-3 .

How do stem wood BD of P. occidentalis and P. caribaea compare with other species in the same taxonomic group? Pinus echinata Mill, Pinus elliottii Engelm, Pinus palustris Mill, and Pinus taeda L, were studied by MacFarlane ( 2020 ) who reported values of 0.460, 0.484, 0.497 and 0.464 g.cm ^-3 , respectively, lower than wood BD from both studied species. Kimberley et al. ( 2016 ) conveyed an average density value of 0.410 g.cm ³ for genetically improved P. radiata , and Pompa-Garcia et al. ( 2021 ) reported minimum and maximum WD values of 0.450±0.004 and 0.950±0.014 g.cm ^-3 for Pinus lumholtzii , B.L. Robinson et Fernald.

It is well-documented that most Pinus and other conifer species exhibit a decrease in BD at increasing heights along the stem. On average, BDs decreased as RHs increased for P. occidentalis and P. caribaea . Between 0.1 and 0.5 RHs, percentage decreases were 11.54 % and 12.82%; between 0.1 and 0.8 RHs, percentage decreases were 19.49 % and 20.09%, respectively. BD variation ranged in P. occidentalis from 0.901±0.002 to 0.720±0.001 g.cm ³ and from 0.780±0.002 to 0.628±0.001 g.cm ³ for P. caribaea . This agrees with results reported by Djomo et al. ( 2017 ) in tropical African species, where WD variation can be, on average, from 15% to 30% greater at the tree base than the top portion of the stem.

Billard et al. ( 2021 ) assessed two softwood species Abies alba Mill and Pseudotsuga menziesii (Mirbel) Franco, finding that BD was most of the time highest at the tree’s base for both species, showing a substantial decrease from the base along with an increase towards the top. of the tree, especially for A. alba . Demol et al. ( 2021 ) found a general decline in BD from stump to tip in Fagus sylvatica , Larix decidua , and P. sylvestris . These authors reported BD ranging from 0.463 g.cm ⁻³ at breast height to 0.391 g.cm ⁻³ at the highest height assessed for P. Sylvestri . MacFarlane ( 2020 ) reported the same decreasing pattern in Pinus massoniana Lamb. Rodríguez-Gamir et al. ( 2021 ) found a decreasing WD gradient from base to crown in P. radiata stands in New Zeeland.

Minini et al. ( 2022 ) sampled and measured 576 trees of 83 species in 28 natural ecosystems in the Atlantic Forest ecosystems of Brazil. BWD was the same at normal diameter (DBH) and 0.5 RH within the stem. The variability in density along the stem differs by wood type. It decreases in species with medium- and high-density wood ( Romero et al., 2024 ), this being the case for P. occidentalis and P. caribaea .

BD increased significantly with the age of trees in both species. Between AC 1 (5 to 14 years) and AC 2 (15 to 24 years) a percentage increase was registered at 27.64% and 39.36% for both P. occidentalis and P. caribaea , respectively. The percentage increase between AC 1 and 3 (25 to 34 years) was approximately similar for P. occidentalis and P. caribaea (49.34% and 47.29%), and between AC 2 and AC 3, it was 17.75% and 5.67%. Within P. massoniana stems in a similar age range to our sampled trees (5-29 years), WD of each relative height in mature trees was significantly higher than that of younger trees, being 10% higher in the oldest age class compared to the youngest one ( Deng et al., 2014 ). As stated by Dobner et al. ( 2018 ), mean density of a tree is, among other factors, directly related to its cambial age. At same harvest age, P. taeda WD exhibited mean density of 0.530 g.cm ³ . Increases in latewood WD of P. taeda related to aging were reported at 0.45 g.cm ³ ± 0.07 ( Ortega-Rodríguez & Tomazello-Filho, 2018 ).

P. taeda averaged whole-tree BD increased from 0.471 g.cm ³ at age 10 to 0.516 g.cm ³ at age 30, being changes with age for the first log more pronounced, with BD increasing from 0.484 g.cm ³ at age 10 to 0.562 g.cm ³ at age 30 ( Dahlen et al., 2018 ). In another study, Schimleck et al. ( 2018 ) reported increases from 0.538 and 0.589 g.cm ³ for 13 and 22-year-old P. taeda trees. The age of trees compared in both P. taeda studies corresponds to our age classes 1 and 2. Related percent increases on density as related to age for both studies were lower (9.55% and 9.48%) as compared to our results between AC1 and AC2 (27.64% for P. occidentalis and 39.36% for P. caribaea ). WD for all heights increases with age, which is the most common pattern in conifers ( Topanotti et al., 2021 ).

The higher stem wood BD value for P. occidentalis , compared to P. caribaea , corroborates empirical local end users’ perception regarding the strength of both species. However, perhaps the main reason is the rapid growth of P. caribaea . When comparing the mean annual increment (MAI) of the trees in the study in terms of diameter at breast height, P. caribaea has, on average, 8.83 %, 5.51%, and 21% greater growth than P. occidentalis in young, intermediate, and older stands, respectively. In terms of tree height, P. occidentalis MAI is 8% higher than P. caribaea in young-age stands, but the latter was superior in intermediate and older stands (13% and 31% greater MAI), respectively. Rodríguez-Gamir et al. ( 2021 ) found that in P. radiata, greater WD was negatively related to growth rates.

CONCLUSION

In this study, the effects of “conifer species” and the factors of “age class” and “relative height” on the variation of wood basic density along tree stem growing in forest plantations within La Sierra, Dominican Republic, were assessed using a three-way repeated measures mixed ANOVA. The results indicate a significant statistical effect of these three factors and the presence of statistically significant interactions among them.

The results also indicate that the intrasubject factor “relative height” was the largest, with a Partial Eta Square value of =0.998, followed by the effect of the interaction between “relative height” and “age class” (=0.997), and the tree factors interaction (Species*RH*AC), with =0.954.

Overall, the average BD was 14.6% higher for P. occidentalis (0.806 ± 0.137 g/cm3) than that for P. caribaea (0.696 ± 0.117 g/cm ³ ). BD was greater in P. occidentalis than P. caribaea at 0.1, 0.5, and 0.8 RHs, with a percent difference of 14.40, 15.84, and 13.65, respectively. Realized average values at each of the RHs 0.1, 0.5, and 0.8 were, respectively, 0.780 g/cm ³ , 0.680 g/cm ³ , and 0.628 g/cm ³ for P. caribaea , and 0.901 g/cm ³ , 0.797 g/cm ³ , and 0.720 g/cm ³ , for P. occidentalis .

On average, BD decreased as relative height increased. For P. caribaea , the percentage decrease differences between 0.1 and 0.5, 0.1 and 0.8, and 0.5 and 0.8 relative heights were 13.70, 21.59, and 7.95. For P. occidentalis , the respective percentage decrease differences were 12.25, 22.33, and 10.15 . This pattern is common in conifers species.

BD increased significantly with the age of trees in both species. Between AC 1 (5 to 14 years) and AC 2 (15 to 24 years), a percentage increase was registered at 27.64% and 39.36% for both P. occidentalis and P. caribaea , respectively. The percentage increase between AC 1 and 3 (25 to 34 years) was approximately similar for P. occidentalis and P. caribaea (49.34% and 47.29%). Between AC 2 and AC 3, it was 17.75% and 5.67%.

Future research should prioritize studying wood density, including analyzing the effects of radial variation and diameter class within the same species. A large sample size that includes individuals from the same and different species will facilitate the analysis of horizontal structure.

ACKNOWLEDGMENTS

We recognize the effort and contribution of the acquisitions department and administrative staff of the Vice-Rectory of Research and Innovation at PUCMM and the contributions of field personnel such as Esclaudys Perez Gonzales, José Reyes, Cristian Goris, and Roque Herrera. We are incredibly grateful to Luis Eduardo Peralta for his support throughout the process and to Pablo Ovalles for his valuable collaboration.

REFERENCES

• Beets PN, Kimberley MO, Oliver GR, Pearce SH. Predicting wood density of growth increments of Douglas-fir stands in New Zealand. New Zealand Journal of Forestry Science 2020; 48:1-11. https://doi.org/10.1186/s40490-018-0112-z .
  » https://doi.org/10.1186/s40490-018-0112-z
• Billard A, Bauer R, Mothe F, Colin F, Deleuze C, Longuetaud F. Vertical variations in wood basic density for two softwood species. Eur. J. Forest Res. 2021; 140:1401–1416. https://doi.org/10.1007/s10342-021-01402-y .
  » https://doi.org/10.1007/s10342-021-01402-y
• Bonferroni CE. Teoria statistica delle classi e calcolo delle probabilità. 1st ed. Pubblicazioni del R Istituto Superiore di Scienze Economiche e Commerciali di Firenze; 1936.
• Bueno SW, Bevilacqua E. Diameter growth prediction for individual Pinus occidentalis Sw. trees. iForest-Biogeosciences and Forestry 2013; 6:209-216. https://doi.org/10.3832/ifor0843-006 .
  » https://doi.org/10.3832/ifor0843-006
• Dahlen J, Auty D, Eberhardt TL. Models for predicting specific gravity and ring width for Loblolly Pine from intensively managed plantations, and implications for wood utilization. Forests 2018; 9:292. https://doi.org/10.3390/f9060292 .
  » https://doi.org/10.3390/f9060292
• Demol M, Calders K, Krishna-Moorthy SM, van den Bulcke J, Verbeeck H, Gielen B. Consequences of vertical basic wood density variation on the estimation of aboveground biomass with terrestrial laser scanning. Trees 2021; 35:671-684. https://doi.org/10.1007/s00468-020-02067-7 .
  » https://doi.org/10.1007/s00468-020-02067-7
• Deng X, Zhang L, Lei P, Xiang W, Yan W. Variations of wood basic density with tree age and social classes in the axial direction within Pinus massoniana stems in Southern China. Annals of Forest Science 2014; https://doi.org/10.1007/s13595-013-0356-y .
  » https://doi.org/10.1007/s13595-013-0356-y
• Djomo AN, Ngoukwa G, Zapfack L, Chimi CD. Variation of wood density in tropical rainforest trees. Forests 2017; 4:2. https://doi.org/10.18488/journal.101.2017.42.16.26 .
  » https://doi.org/10.18488/journal.101.2017.42.16.26
• Dobner M, Huss J, Tomazello-Filho M. Wood density of Loblolly Pine trees as affected by crown thinnings and harvest age in southern Brazil. Wood Science Technology 2018; 52:465-485. https://doi.org/10.1007/s00226-017-0983-9 .
  » https://doi.org/10.1007/s00226-017-0983-9
• Farias HLS, Pequeno PACL, Silva WR, Melo VF, Carvalho LCDS, Perdiz RDO, et al. Amazon forest biomass: intra- and interspecific variability in wood density drive divergences in Brazil’s far north. iForest-Biogeosciences and Forestry 2023; 16:95-104. https://doi.org/10.3832/ifor4137-016 .
  » https://doi.org/10.3832/ifor4137-016
• Rodríguez-Gamir J, Xue J, Meason DF, Clearwater M, Clinton PW, Domec JC. Interclonal variation, coordination, and trade-offs between hydraulic conductance and gas exchange in Pinus radiata: consequences on plant growth and wood density, Journal of Experimental Botany 2021; 72(7):2419-2433. https://doi.org/10.1093/jxb/eraa587 .
  » https://doi.org/10.1093/jxb/eraa587
• Gonçalves-Rocha SM, Baptista-Vidaurre G, Macedo-Pezzopane JE, Félix-Almeida MN, Lorenzato-Carneiro R, Camargo-Campoe O, et al. Influence of climatic variations on production, biomass and density of wood in eucalyptus clones of different species. Forest Ecology and Management 2020; 473:118290. https://doi.org/10.1016/j.foreco.2020.118290 .
  » https://doi.org/10.1016/j.foreco.2020.118290
• Guo P, Zhao X, Wang X, Feng Q, Li X, Tan Y. Wood Density and Carbon Concentration Jointly Drive Wood Carbon Density of Five Rosaceae Tree Species. Forests 2024; 15:1102. https://doi.org/10.3390/f15071102 .
  » https://doi.org/10.3390/f15071102
• Hevia A, Campelo F, Chambel R, Vieira J, Alía R. Which matters more for wood traits in Pinus halepensis Mill., provenance or climate? Annals of Forest Science 2020; 77:55-67. https://doi.org/10.1007/s13595-020-00956-y .
  » https://doi.org/10.1007/s13595-020-00956-y
• Horácek P, Fajstavr M, Stojanović M. The variability of wood density and compression strength of Norway spruce ( Picea abies /L./Karst.) within the stem. Beskydy 2017; 10:17-26. http://dx.doi.org/10.11118/beskyd201710010017 .
  » https://doi.org/10.11118/beskyd201710010017
• Hubbel KL, Ross-Davis AL, Pinto JR, Burney OT, Davis AS. Toward Sustainable Cultivation of Pinus occidentalis Swartz in Haiti: Effects of Alternative Growing Media and Containers on Seedling Growth and Foliar Chemistry. Forests 2018; 9:14. http://dx.doi.org/10.3390/f9070422 .
  » https://doi.org/10.3390/f9070422
• IBM CORP. IBM SPSS Statistics for Windows, Version 25.0. 2017 Armonk, N.Y. IBM Corp.
• Jakubowski M, Dobroczynski M. Allocation of wood density in European Oak (Quercus robur L.) trees grown under a canopy of Scots Pine. Forests 2021; 12:712. https://doi.org/10.3390/f12060712 .
  » https://doi.org/10.3390/f12060712
• Kimberley MO, Moore JR, Dungey HS. Modelling the effects of genetic improvement on radiata pine wood density. New Zealand Journal of Forestry Science 2016; 46:8-21. https://doi.org/10.1186/s40490-016-0064-0 .
  » https://doi.org/10.1186/s40490-016-0064-0
• Klotz UW, Torres JG. Comportamiento del Pinus occidentalis Sw. en la Zona de Moncion, La Celestina y San José de las Matas. 1st ed. Plan Sierra y Servicio de Cooperación Social Tecnica (DED). San José de las Matas; 1991.
• Kutner MH, Nachtsheim CJ, Neter JK, Li W. Applied Linear Regression Models. 5th Edition. McGraw-Hill/Irwin, The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York; 2005.
• Levene H. Robust tests for equality of variances. In Ingram Olkin; Harold Hotelling; et al. (eds.). Contributions to Probability and Statistics: Essays in Honor of Harold Hotelling. Stanford University Press; 1960. https://www.scirp.org/reference/referencespapers?referenceid=2488563 .
  » https://www.scirp.org/reference/referencespapers?referenceid=2488563
• Li Y, Ding X, Jiang J, Luan Q. Inheritance and correlation analysis of pulpwood properties, wood density, and growth traits of Slash Pine. Forests 2020; 9:493. https://doi.org/10.3390/f11050493 .
  » https://doi.org/10.3390/f11050493
• Li F, Qian H, Sardans J, Amishev DY, Wang Z, Zhang C, et al. Evolutionary history shapes variation of wood density of tree species across the world. Plant Diversity 2024; 46(3):283-293. https://doi.org/10.1016/j.pld.2024.04.002 .
  » https://doi.org/10.1016/j.pld.2024.04.002
• Lima-Costa SE, do Santos RC, Baptista-Vidaurre G, Oliveira-Castro RV, Gonçalves-Rocha SM, Carneiro RL, et al. The effects of contrasting environments on the basic density and mean annual increment of wood from eucalyptus clones. Forest Ecology and Management 2020; 458:117807. https://doi.org/10.1016/j.foreco.2019.117807 .
  » https://doi.org/10.1016/j.foreco.2019.117807
• Mauchly JW. Significance Test for Sphericity of a Normal n-Variate Distribution. The Annals of Mathematical Statistics 1940; 11:204-209. https://doi.org/10.1214/aoms/1177731915 .
  » https://doi.org/10.1214/aoms/1177731915
• McCulloh KA, Domec JC, Johnson DM, Smith DD, Meinzer FC. A dynamic yet vulnerable pipeline: integration and coordination of hydraulic traits across whole plants. Plant, Cell & Environment 2019; 42:2789-2807. https://doi.org/10.1111/pce.13607 .
  » https://doi.org/10.1111/pce.13607
• MacFarlane DW. Functional Relationships Between Branch and Stem Wood Density for Temperate Tree Species in North America. Front. For. Glob. Change 2020; 3:63. https://doi.org/10.3389/ffgc.2020.00063 .
  » https://doi.org/10.3389/ffgc.2020.00063
• Minini D, da Silva JGM, Paula RR, Gonçalves-Rocha SM, Silveira-Filhod TB, Gaui TD, et al. Insights about wood density in Atlantic Forest ecosystems: spatial variability and alternative measurement. Can. J. For. Res. 2022; 52:1212-1223. dx.doi.org/10.1139/cjfr-2022-0061.
  » https://doi.org/10.1139/cjfr-2022-0061.
• Morgado-González G, Gómez-Guerrero A, Villanueva-Díaz J, Terrazas T, Ramírez-Herrera C, Hernández de la Rosa P. Densidad de la madera de Pinus hartwegii Lind. en dos niveles altitudinales y de exposición. Agrociencia 2019; 53:645-660. https://www.researchgate.net/publication/334191248 .
  » https://www.researchgate.net/publication/334191248
• Moreno-Fernández D, Hevia A, Majada J, Cañellas I. Do Common Silvicultural Treatments Affect Wood Density of Mediterranean Montane Pines? Forests 2018; 9:80. https://doi.org/10.3390/f9020080 .
  » https://doi.org/10.3390/f9020080.
• Oliveira GMV, de Mello JM, de Mello CR, Soares-Scolforo JR, Pereira-Miguel E, Campos-Monteiro E. Behavior of wood basic density according to environmental variables. J. For. Res. 2022; 33:497-505. https://doi.org/10.1007/s11676-021-01372-2 .
  » https://doi.org/10.1007/s11676-021-01372-2
• Ortega-Rodríguez DR, Tomazello-Filho M. Clues to wood quality and production from analyzing ring width and density variabilities of fertilized Pinus taeda trees. New Forests 2018; 50:821-843. https://doi.org/10.1007/s11056-018-09702-9 .
  » https://doi.org/10.1007/s11056-018-09702-9.
• Pompa‑Garcia M, Hevia A, Camarero J. Minimum and maximum wood density as proxies of water availability in two Mexican pine species coexisting in a seasonally dry area. Trees 2021; 35:597-607. https://doi.org/10.1007/s00468-020-02062-y .
  » https://doi.org/10.1007/s00468-020-02062-y
• Romero FMB, de Nazaré Oliveira Novais, T., Jacovine LAG, Bezerra EB, de Castro Lopes RB, de Holanda JS, et al. Wood Basic Density in Large Trees: Impacts on Biomass Estimates in the Southwestern Brazilian Amazon. Forests 2024; 15:734. https://doi.org/10.3390/f15050734 .
  » https://doi.org/10.3390/f15050734
• Schimleck L, Antony F, Dahlen J, Moore J. Wood and Fiber Quality of Plantation-Grown Conifers: A Summary of Research with an Emphasis on Loblolly and Radiata Pine. Forests 2018; 9:298. https://doi.org/10.3390/f9060298 .
  » https://doi.org/10.3390/f9060298
• Shapiro SS, Wilk MB. An analysis of variance test for normality (complete samples). Biometrika 1965; 52:591-611. http://links.jstor.org/sici?sici=0006444%28196512%2952%3A3%2F4%3C591%3AAAOVTF%3E2.0.CO%3B2-B ).
  » http://links.jstor.org/sici?sici=0006444%28196512%2952%3A3%2F4%3C591%3AAAOVTF%3E2.0.CO%3B2-B
• Szaban J, Jelonek T, Okinczyk A, Kowalkowski W. Results of a 57-year-long research on variability of wood density of the Scots Pine (Pinus sylvestris L.) from different provenances in Poland. Forests 2023; 14:480. https://doi.org/10.3390/f14030480 .
  » https://doi.org/10.3390/f14030480
• Tomczak A, Jelonek T, Pazdrowski W, Grzywinski W, Mania P, Tomczak K. The effects of wind exposure on Scots Pine Trees: Within-Stem Variability of Wood Density and Mechanical Properties. Forests 2023; 11:1095. https://doi.org/10.3390/f11101095 .
  » https://doi.org/10.3390/f11101095
• Topanotti LR, Vaz DR, Chaves-Carvalho SP, Rios P, Tomazello‑Filho M, Dobner M, et al. Growth and wood density of Pinus taeda L. as affected by shelterwood harvest in a two‑aged stand in Southern Brazil. European Journal of Forest Research 2021; https://doi.org/10.1007/s10342-021-01372-1 .
  » https://doi.org/10.1007/s10342-021-01372-1
• Vaughan D, Auty D, Kolb TE, Meador AJS, Mackes KH, Dahlen J, et al. Climate has a larger effect than stand basal area on wood density in Pinus ponderosa var. scopulorum in the southwestern USA. Annals of Forest Science 2019; 76:85-97. https://doi.org/10.1007/s13595-019-0869-0 .
  » https://doi.org/10.1007/s13595-019-0869-0.
• Venega RdS, da Silva RC, Sousa TO, Ferreira-Saraiva K, Gomes-Colares CJ, Loiola PL, et al. Energy quality of wood and charcoal from the stem and root of Eucalyptus spp. Floresta e Ambiente 2023; 30(1):e20220031. https://doi.org/10.1590/2179-8087-floram-2022-0031 .
  » https://doi.org/10.1590/2179-8087-floram-2022-0031
• Zobel BJ, Jett JB. The Importance of Wood Density (Specific Gravity) and Its Component Parts. In: Genetics of Wood Production. Springer Series in Wood Science. Springer, Berlin, Heidelberg; 1995. https://doi.org/10.1007/978-3-642-79514-5_4 ]
  » https://doi.org/10.1007/978-3-642-79514-5_4

• DATA AVAILABILITY
  The authors will make the raw data supporting this article’s conclusions available upon request.
• FINANCIAL SUPPORT
  This research was funded by the Ministry of Higher Education, Science, and Technology of the Dominican Republic, National Fund for Innovation and Scientific and Technological Development, grant number FONDOCyT 2018-2019-2B4-088. The APC was funded by Pontificia Universidad Católica Madre y Maestra (No. 121-2019-PUCMM).

Edited by

• Associate editor:
  Fernando Gomes

Data availability

The authors will make the raw data supporting this article’s conclusions available upon request.

Publication Dates

• Publication in this collection
  31 Jan 2025
• Date of issue
  2025

History

• Received
  31 July 2024
• Accepted
  04 Dec 2024