Use of Cupressus lusitanica for Afforestation in a Mediterranean Climate: Biomass Production and Wood Quality

Abstract

The selection of tree species for afforestation in Mediterranean environments involves challenges related to adaptability, impact on soil properties, and overall environmental quality. Cupressus lusitanica has been recognized for its rapid growth, environmental resilience, and versatile applications, positioning it as a promising candidate for these regions. Although it has been used for afforestation in Northeast Portugal since the 1990s, no comprehensive studies have evaluated its performance under local conditions. To address this knowledge gap, this study assessed a 14-year-old C. lusitanica stand in Northeast Portugal. The wood’s anatomical, physical, chemical, and mechanical properties, as well as biomass production, were evaluated. The species showed superior radial growth and adaptability compared with other species under similar environmental conditions. Despite exhibiting lower fiber length (1.6 mm) and basic wood density (404 kg/m³), shrinkage values fell within the typical range for softwoods. Nevertheless, a marked tendency for warping was observed. The extractive content was relatively high (5.1%), with the ethanol-soluble fraction being predominant (3.6%). Mechanical tests revealed low values for both Modulus of Elasticity (MOE) (3592.5–3617.1 MPa) and Modulus of Rupture (MOR) (57.7–68.9 MPa), with both properties significantly influenced by knot presence. Given the results obtained, the species C. lusitanica, despite its low wood density and potential limitations in use, exhibits remarkable growth and adaptability, which confer a high potential for biomass production and carbon sequestration, as well as potential applications of its wood in reconstituted panels and fiber- or particle-based boards.

1. Introduction

It is well established that forests play a crucial role in the restoration of degraded areas and contribute significantly to combating climate change through atmospheric carbon sequestration. Among the numerous well-known forest management practices—such as shortening rotation cycles, applying thinning regimes of varying intensities, and promoting structural diversity—the selection of the most suitable tree species, with the greatest potential to generate positive outcomes toward sustainability goals, stands out as one of the most effective strategies [1].

This is particularly relevant considering that global warming directly affects wood quality by influencing the formation of earlywood and latewood, the arrangement of fibers, the rate of cell division, and, consequently, both growth velocity and carbon capture capacity [2].

In addition to Quercus suber L., Quercus rotundifolia Lam., and Pinus pinea L., species widely recognized for their adaptation to Mediterranean environments, there remains a lack of comprehensive knowledge regarding the adaptation, growth performance, and wood quality of other species under that environment. Among these, C. lusitanica Mill., stands out as a species long introduced in Portugal and commonly called Cypress, with two particularly notable and significant stands located in the Bussaco Mountains and Reboredo Mountains (Central and Northwest Portugal, respectively), valued for their landscape importance, ecological, and historical value.

Despite its name suggesting Iberian origins, C. lusitanica was introduced to Europe from Mexico and Guatemala [3,4,5]. Today, it is cultivated across various regions, including Central America (Mexico, Guatemala, El Salvador, and Honduras), parts of Africa (Kenya, Ethiopia, Sudan, and South Africa), India, Brazil, New Zealand, and Portugal. In its native range—mountainous tropical regions of Central America—it typically grows at altitudes between 1200 and 3000 m, with annual precipitation ranging from 2000 to 3000 mm [3,4,6,7,8].

In Africa and New Zealand, it is also found at elevations near 3000 m, although under lower rainfall conditions, generally exceeding 1000–1500 mm/year [8,9,10]. Some studies indicate that the species prefers deep, moist, well-aerated soils with a neutral pH [7,8,11]. According to [12], C. lusitanica demonstrates high adaptability to degraded soils, particularly shallow and erosion-prone substrates, and exhibits satisfactory growth performance in sloped terrains. Given its vigor and ecological resilience, the species presents considerable potential for integration into watershed management and soil restoration initiatives within agricultural areas. In a study on C. lusitanica conducted in New Zealand, ref. [13] concluded that the species exhibits higher productivity in warm regions characterized by moderate rainfall intensity, deep soils, and elevated levels of available phosphorus.

When considering ecological indicators such as understory biodiversity and soil ecological properties, plantations of C. lusitanica have proven to be as effective as various Pinus species in high-altitude, high-biodiversity regions of Colombia. Moreover, they were found to be more effective than pastures or abandoned degraded lands, although they still exhibited lower indicator values than native vegetation. Nonetheless, these indicators hold potential for improvement under appropriate silvicultural management [14].

Also in Colombia, it was observed that, when compared with native forest areas and Eucalyptus globulus plantations, indicators reflecting saturated soil hydraulic conductivity did not differ significantly among treatments. This suggests that C. lusitanica preserves key soil properties, contributing to its stability [15].

Carbon accumulation in C. lusitanica and Pseudotsuga menziesii was compared under varying climatic conditions. While carbon accumulation in P. menziesii was more strongly correlated with winter precipitation from the previous year, C. lusitanica was more sensitive to autumn temperatures during the current year [16], an effect also supported by findings from [17].

In the highlands of central Ethiopia, C. lusitanica demonstrated higher biomass values in plantations aged 25 to 30 years compared with those observed in Eucalyptus saligna and Pinus patula plots [18].

In addition to the species’ intrinsic potential, C. lusitanica may also respond positively to silvicultural treatments that enhance its suitability for degraded land restoration and climate change mitigation, particularly when integrated within bioeconomy strategies. For instance, ref. [13] reported a positive correlation between carbon stocks and gradients of stand density and age for C. lusitanica in New Zealand.

In Portugal, C. lusitanica has demonstrated excellent adaptability and growth in regions with environmental conditions that differ markedly from its native habitat. One such region is Northeast Trás-os-Montes, characterized by significantly lower altitudes (100–800 m), hot and dry summers, and low annual precipitation—factors that induce high water stress, potentially affecting both tree growth and wood properties. Despite these challenges, C. lusitanica was used to afforest approximately 15,000 hectares in this region, largely due to its rapid initial growth, adaptability to diverse environmental conditions, versatile applications, and favorable wood quality.

However, no known studies have evaluated or compared the performance of this species under these specific conditions or the quality of the wood produced. To fill this gap, a young stand of C. lusitanica, 14 years old, located in northeastern Portugal, was selected for analysis.

C. lusitanica wood is typically yellowish, occasionally exhibiting pale brown or slightly pinkish hues. It has a straight grain and a fine, uniform texture. The wood is moderately dimensionally stable, exhibiting minimal warping and drying rapidly under ambient conditions, with little to no surface or end checking. Due to its moderate mechanical properties, it is suitable for applications not requiring high structural strength, such as fence posts, rural constructions, crates, and certain types of [12,19,20].

The wood analyzed in this work is predominantly juvenile wood, whose characteristics differ from mature wood formed in later stages of tree development. Juvenile wood is typically defined as the wood produced during the early stages of tree development, under the influence of hormones such as auxins from the apical meristem [21]. As a result, juvenile wood typically presents growth rates higher, leading to wider growth rings, a greater proportion of earlywood, lower wood density, and inferior physical and mechanical properties [21,22,23,24].

The aim was to assess the species’ adaptability to the Mediterranean climate through analysis of biomass production and distribution, as well as to evaluate the quality of the produced wood. Comparisons will be made primarily with juvenile wood of other softwoods based on scientific literature.

2. Materials and Methods

2.1. Study Area

This study was conducted in a 14-year-old C. lusitanica stand, approximately 15 hectares in size, located in Vila Boa (41°23′ N, 7°20′ W; altitude 400 m), in the interior of northeastern Portugal. The stand was established from nursery-grown seedlings, with a 2.5 m × 2.5 m planting spacing, corresponding to a planting density of 1600 trees per hectare.

To establish the stand, the site was prepared by harrowing to remove shrub vegetation, followed by continuous deep scarification, heavy plowing, and fertilization. Fertilizers were applied in the planting holes at the following rates: 70 units of P₂O₂, 50 units of 42% superphosphate, and 20 units of K₂O using the compound fertilizer Foskapa 0-21-21, per hectare. Five years after planting, a second surface fertilization was applied within the canopy projection area, consisting of 100 units of P₂O₂, 50 units of K₂O, 15 units of nitrogen (nitric + ammoniacal), and 15 units of boron plus molybdenum.

The region has a typical Mediterranean climate, characterized by hot, dry summers and cold, wet winters, with an average annual temperature between 13 °C and 15 °C and annual precipitation ranging from 500 to 800 mm. According to the Köppen climate classification, it is classified as “Csa” [25]. As reported by [26], the soil moisture regime is xeric, and the soil temperature regime is thermal.

In Figure 1a, the climatological normal shows that the minimum temperature is relatively constant and stable, averaging around 7 °C, while the maximum temperature is approximately 17 °C. However, its curve reveals an upward trend in recent decades, whereas the mean temperature remains between 12 and 14 °C. In Figure 1b, it can be observed that total precipitation exhibits a highly variable pattern, alternating between years exceeding 1200 mm and others barely reaching 500 mm. Climatological normal curve of temperature (1991–2020) (c) and climatological normal curve of precipitation (1991–2020) (d) to the Bragança region.

The original soils in the area belong primarily to the District Leptosols unit, with some inclusions of District Cambisols, both derived from schists. These soils are typically shallow, with low water retention capacity, deep rooting potential, and high susceptibility to erosion, particularly under soil stress. They are also acidic, with low chemical fertility, and have low contents of organic matter and fine particles. Mechanical tillage and fertilization prior to planting improved the soil profile by increasing rooting depth and the availability of water and nutrients. As a result of these interventions, the soils evolved into Dystrophic Aric Surríbic Anthrosols, as described by [26].

The study was carried out in four sample plots with 25 trees each, distributed by the area according to the topographic (shape, slope, and exposure) and soil conditions, in order to capture the widest possible range of edaphoclimatic conditions within the study. Topographic conditions include terrain shape, related to local relief (flat, undulating, or steep), slope, indicating the average degree of inclination, and exposure, referring to the terrain’s orientation relative to solar radiation. The use of four plots was implemented to ensure representation of varying site conditions, including differences in solar exposure, relative elevation, and slope. This design ensures that, if these factors influence the results, the average across plots captures their combined effect, allowing for the determination of mean values representative of the diverse site conditions.

2.2. Biomass Quantification

Each tree was individually numbered from 1 to 100, and the diameter at breast height (DBH) was measured in order to select 24 trees with a proportional distribution of DBH values for felling. In these selected trees, the base diameter (bd) and total height (h) were also measured. The sampling was considered adequate since the stand originated from a plantation of uniform seedlings and its general characteristics were highly homogeneous (coefficients of variation of 0.30 and 0.19 for DBH and height, respectively). Therefore, we consider the sample size sufficiently large to encompass the full dendrometric variability within the stand.

Biomass was quantified by component, including the stem, branches (wood + bark, cut into logs), small branches (supporting the leaves and cones), needles, and fruits. All components were individually weighed in their fresh state. Two samples from each component were collected for laboratory analysis and used to determine dry weight by oven-drying at 100 °C until constant weight.

For each tree, the proportion of biomass allocated to each component (logs, branches that derive directly from the main trunk, small branches, needles, and fruits) was calculated based on the fresh weight of each component relative to the total fresh biomass of the tree.

2.3. Physical Properties

Three wood discs were collected from each tree at the base, at breast height (DBH), and in the upper third of the stem. The following physical properties were analyzed: basic density, oven-dry density, air-dry density (12% MC), actual moisture content, total shrinkage, shrinkage coefficients (tangential, radial, axial, and volumetric), fiber saturation point, air-drying stability coefficients, drying differentials (tangential, radial, and volumetric), and the anisotropy coefficient (tangential/radial).

Densities were determined according to Portuguese Standard NP 616:1973, regularly employed by the Forest Products Laboratory of the University of Trás-os-Montes and Alto Douro, as it has proven to be a simple, reliable, and reproducible standard. Basic density was calculated using saturated volume obtained via the hydrostatic balance method, based on Archimedes’ principle.

Shrinkage, shrinkage coefficients, air-drying stability coefficients, drying differentials (calculated as shrinkage between the fiber saturation point and the equilibrium moisture content at 20 °C and 65% relative humidity), and moisture content were assessed in accordance with Portuguese Standards NP 614:1973 (Moisture Content) and NP 615:1973 (Shrinkage). These properties were determined by measuring the stabilized weight and volume of the test specimens subjected to a stepwise desorption process under the following controlled conditions:

20 °C at 98% RH, 81% RH, 53% RH, 42% RH, oven-dry at 103 ± 2 °C, and fully saturated (immersion in water).

2.4. Anatomical Properties

In the same samples used for determining physical properties, the following anatomical characteristics were also assessed: ring width, grain orientation, and fiber (tracheid) length.

Ring widths were measured on radial samples taken from wood discs collected from each tree. The transverse surfaces of the samples were scanned at 600 dpi resolution, and ring widths were analyzed using the Image Pro-Plus 6.2 software.

Tracheid length was measured by analyzing 20 tracheids per annual ring, at two-year intervals, after maceration using Franklin’s method, following the methodology described by [28].

Spiral grain orientation was determined following the methodology of [29]. In each disc collected at breast height (DBH), the tracheid inclination angle was measured in the most recently formed latewood of the outermost growth ring. Measurements were performed using a grain slope detector, with the pith serving as the reference point relative to the tree’s vertical axis. Spirality direction was indicated by assigning a positive sign to the left-handed angles. Measurements in each disc were taken in two opposite radii, and the mean grain angle was calculated

2.5. Chemical Properties—Extractives Content

From three trees at each site, a radial wedge was extracted at breast height (DBH). The samples were then milled and passed through a 1 mm mesh sieve.

To determine the extractives content, aliquots of the milled wood were sequentially Soxhlet-extracted with dichloromethane, ethanol, and water, according to the methodology described by [30].

2.6. Mechanical Properties

From the 24 sampled trees, two logs of approximately 1 m in length were collected per tree—one from the lower part of the stem (with fewer knots) and one from the upper part (with more knots). In each log, the annual ring width and knot characteristics were recorded.

A test specimen with nominal dimensions of 20 × 20 × 340 mm (Tangential × Radial × Longitudinal) was prepared from the outermost portion of each log, amounting to a total of 48 test specimens, to assess mechanical performance using three-point bending tests. The following mechanical properties were assessed in accordance with Portuguese Standard NP 619:1973: Modulus of Elasticity (MOE or Young’s Modulus); Modulus of Rupture (MOR); Ultimate Load; Deflection at failure.

Regarding knot characterization, both the number and size of knots were evaluated in each log. Two types of knots were distinguished: outer knots, visible on the external surface and associated with living branches, and inner knots, not visible on the surface, resulting from dead or previously pruned branches. The standard for classifying internal and external knots was visual: knots visible on the trunk exterior were classified as external, while those visible only inside the trunk (already enclosed by subsequent growth after branch death) were classified as internal. For each knot, both minimum and maximum diameters were measured using a caliper.

3. Results

3.1. Evaluation of the Productive Capacity

To further investigate the productive capacity of C. lusitanica in Mediterranean environments, dendrometric characteristics were measured, and biomass was estimated for all sampled trees.

The 100 sampled trees exhibited a mean diameter at breast height (DBH) of 12.1 cm, with a standard deviation of 4.0 cm and a coefficient of variation of 32.8%. The distribution of DBH across diameter classes is presented in

Table 1. Distribution of the 100 trees measured by DBH class.

DBH Class (cm)	Frequency (%)
[3.0–6.0[	6
[6.0–9.0[	17
[9.0–12.0[	29
[12.0–15.0[	25
[15.0–18.0[	15
[18.0–21.0[	7
[>21.0[	1
Total	100

The majority of trees (54%) fall within the 9 to 15 cm diameter classes, followed by 17% in the 6 to 9 cm class, 15% in the 15 to 18 cm class, 8% in the class above 18 cm, and only 6% in the 3 to 6 cm class.

Based on the diameter distribution of the 100 trees, a subset of 24 trees was selected for felling, with an average DBH of 11.6 cm, an average base diameter of 16.6 cm, and an average height of 6.1 m (Appendix A).

The mean values of DBH, base diameter, and height by diameter class for the 24 sampled trees are shown in

Table 2. Dendrometric characterization of the trees according to class of diameter.

DBH Class (cm)	DBH (cm)	D Base (cm)	Height (m)
[3.0–6.0[	5.30	8.70	4.25
[6.0–9.0[	8.26	12.96	5.24
[9.0–12.0[	10.80	16.03	5.91
[12.0–15.0[	14.02	18.36	6.88
[15.0–18.0[	17.07	23.10	7.87
[18.0–21.0[	19.1	28.00	6.90
[>21.0[	21.30	28.20	7.30

.

The average DBH per diameter class ranges from 5.30 cm to 19.10 cm, while the base diameter varies between 8.70 cm and 28.00 cm. Regarding heights, generally, the thicker trees are also taller, except for the [18.0–21.0[ class, which has an average height lower than the previous class, at 6.90 m compared with 7.87 m, respectively.

3.2. Biomass Production

Regarding the quantification of biomass production, the results obtained from the weights of the different diameter classes, distributed by tree crown components, and the relative contribution of these components to the total tree weight are presented in

Table 3. Biomass weights by tree components distributed by DBH class.

DBH Class (cm)	Components	Average Weight (kg)	Weight Distribution (%)
[3.0–6.0[	Logs	4.05	49.9
	Branches	0.86	10.6
	Small branches	0.28	3.4
	Needles	2.63	32.5
	Fruits	0.29	3.6
	Total	8.11	100.0
[6.0–9.0[	Logs	9.68	37.8
	Branches	4.88	19.1
	Small branches	1.11	4.4
	Needles	8.46	33.0
	Fruits	1.47	5.7
	Total	25.61	100.0
[9.0–12.0[	Logs	15.11	42.8
	Branches	6.82	19.3
	Small branches	1.85	5.2
	Needles	9.71	27.5
	Fruits	1.86	5.3
	Total	35.34	100.0
[12.0–15.0[	Logs	26.15	43.2
	Branches	12.66	20.9
	Small branches	2.96	4.9
	Needles	15.28	25.3
	Fruits	3.44	5.7
	Total	60.49	100.0
[15.0–18.0[	Logs	34.40	39.4
	Branches	25.39	29.1
	Small branches	4.68	5.4
	Needles	21.84	25.0
	Fruits	1.06	1.2
	Total	87.37	100.0
[18.0–21.0[	Logs	34.48	39.9
	Branches	27.00	31.2
	Small branches	5.46	6.3
	Needles	17.84	20.6
	Fruits	1.67	1.9
	Total	86.44	100.0

.

Total weights range from 8.11 kg in the smallest diameter class to 87.4 kg in the largest class. The slightly lower weight in the largest class compared with the immediately smaller class is likely due to the shorter height of these trees (Table 2).

The distribution of weights among biomass components shows a significantly higher proportion in the logs, which range from 37.8% to 49.9%. This is followed by needles and branches, accounting for 20.6% to 33.0% and 10.6% to 31.2%, respectively. The weight of the needle component decreases in larger diameter classes, whereas the branch component increases.

When conducting the same analysis at the stand level, calculating the average weight of each component weighted by the representativeness of each diameter class within the stand (

Table 4. Biomass weights by component and DBH class proportion in the stand.

Components	Average Weight (kg)	Weight Distribution (%)
Logs	20.73	41.3
Branches	11.99	23.9
Small branches	2.62	5.2
Needles	12.93	25.7
Fruits	1.96	3.9
Total	50.23	100.0

), we find that the log is the largest biomass component in the tree, averaging 20.73 kg. It is followed by needles and branches, which have similar mean weights of 12.93 kg and 11.99 kg, respectively. The small branches and fruits contribute less than 10% to the total biomass, with an average weight of approximately 50.23 kg per tree.

A summary of the biomass productivity for C. lusitanica, compared with other species growing under similar conditions, is presented in

Table 5. Biomass productivity of C. lusitanica in northeastern Trás-os-Montes compared with other softwood species.

		Cupressus lusitanica	Pseudot. menziesii 1	Pinus pinaster 2
Region		Northeast (Portugal)	Northeast (Portugal)	Tâmega (Portugal)
Latitude		41°23′ N	41°24′ N	41°20′ to 41°47′ N
Longitude		7°20’ W	7°06′ W	7°38′ to 8°02′ W
Altitude	(m)	400	710	350 to 900
Aver. Ann. Precip.	(mm)	500 to 800	690	>1200
Aver. Ann. Temp.	(°C)	13 to 15	12,5	10 to 16
Stand age		14	15	16
Nº trees/ha		1600	1250	1650
Dbh
Average	(cm)	11.6	11.0	9.0
Aver. domin. tree	(cm)	-	-	15.8
Height
Average	(m)	6.1	6.0	-
Aver. domin. tree	(m)	-	-	9.5
Weight	(% component)	20.7 (41%)	29.6 (82%)	11.0 (67%)
Logs	(kg)	12.0 (24%)	3.4 (9%)	-
Branches	(kg)	2.6 (5%)	0.1 (0%)	-
Small branches	(kg)	12.9 (26%)	2.8 (8%)	-
Needles/leaves	(kg)	2.0 (4%)	-	-
Fruits	(kg)	29.5 (59%)	6.3 (18%)	5.3 (33%)
Crown	(kg)	50.2	35.9	16.3
Total biomass	(kg)	20.7 (41%)	29.6 (82%)	11.0 (67%)

¹ Source: [31]. ² Source: [32].

.

3.3. Characterization of the Wood Quality

The descriptive statistics of the anatomical, physical, chemical, and mechanical properties of C. lusitanica from two stands in northeastern Portugal are presented in

Table 6. General characterization of the anatomical, physical, chemical, and mechanical properties of the C. lusitanica wood.

Properties		Average	CV * (%)
Anatomical
Ring width	(mm)	5.9	31.3
Tracheids length	(mm)	1.6	9.9
Grain orientation	(°)	3.0	61.0
Physical
Anhydrous density	(kg/m3)	457	8.3
Basic density	(kg/m3)	404	9.7
12% density	(kg/m3)	488	9.2
Total Shrinkage Tang.	(%)	6.6	30.2
″        ″    Radial	(%)	5.1	26.7
″        ″    Axial	(%)	1.4	42.9
″        ″    Volumetric	(%)	13.1	25.7
Coef. Shrinkage Tang.	(%)	0.23	20.4
″       ″    Radial	(%)	0.15	29.5
″       ″    Axial	(%)	0.04	109.9
″       ″    Volumetric	(%)	0.43	27.6
Coef. Air Stability Tang.	(%)	0.05	0.8
″      ″      ″    Radial	(%)	0.03	0.5
Drying Differential Tang.	(%)	4.19	1.8
″             ″    Radial	(%)	2.99	1.7
Fiber Saturat. Point Tang.	(%)	29.8	31.0
″      ″      ″    Radial	(%)	39.5	46.1
″      ″      ″    Axial	(%)	61.1	67.4
″      ″      ″    Volum.	(%)	32.6	32.6
Chemical
Extractives content:
Dichloromethane	(%)	0.4	57.0
Ethanol	(%)	3.6	20.8
Water	(%)	1.1	43.1
Total	(%)	5.1	24.6
Mechanical
Lower Logs
MOE	(MPa)	3617.1	23.2
MOR	(MPa)	68.9	17.2
Ultimate Load	(N)	1156.2	17.0
Deflection	(mm)	5.1	31.5
Upper Logs
MOE	(MPa)	3592.5	20.7
MOR	(MPa)	57.7	32.1
Ultimate Load	(N)	956.5	32.1
Deflection	(mm)	5.2	54.9
Knots Lower Logs
Number		28.8	24.1
Dimension	(cm)	2.8	19.9
Knots Upper Logs
Number		19.5	47.1
Dimension	(cm)	1.9	33.4

* Coefficient of Variation.

.

3.3.1. Anatomical Properties

The most important characteristic of C. lusitanica wood is its high average radial growth (5.9 mm), especially considering the edaphoclimatic conditions of the region, which are characterized by low precipitation, high summer temperatures (leading to significant water stress), and low soil fertility.

The wood exhibits a typical radial variation pattern, with fiber length gradually increasing from the pith (1.3 mm) to the bark (1.8 mm) (Figure 2).

Regarding grain orientation, it was observed that 18 out of the 24 C. lusitanica trees analyzed exhibited a left-handed spiral grain, with an average inclination of 3.0º relative to the tree’s longitudinal axis.

3.3.2. Physical Properties

Wood density is considered one of its most important physical properties, as it not only reflects the productive potential of woody biomass per unit volume but also correlates strongly with other properties such as mechanical strength, dimensional stability, and calorific value. As such, it serves as a key index for assessing the general characteristics of wood, regardless of its intended application.

In this study, the average density values obtained for C. lusitanica wood were 457 kg/m³ (anhydrous), 404 kg/m³ (basic), and 488 kg/m³ (at 12% moisture content) (Table 6), classifying it as a light wood according to [33]. The high productivity of C. lusitanica, and consequently its generally lightweight wood, makes it suitable for industrial applications with short-life-cycle products, which paradoxically conflicts with its potential for carbon sequestration. However, alternative applications, such as in plywood when combined with other species [34], may mitigate this trade-off observed for the species.

3.3.3. Chemical Properties-Extractives Content

In this study, C. lusitanica wood exhibited an average extractives content of 5.14%. The ethanol-soluble fraction accounted for the majority of the extractives (3.6%), followed by the water-soluble fraction (1.1%).

3.3.4. Mechanical Properties

Regarding mechanical properties, the average MOE (Modulus of Elasticity) values obtained for the lower and upper portions of the trunk were 3617.1 MPa and 3592.5 MPa, respectively, whereas the corresponding MOR (Modulus of Rupture) values were 68.9 MPa and 57.7 MPa. These results indicate that the lowest values of MOE (Modulus of Elasticity) and MOR (Modulus of Rupture) were recorded in the upper portions of the trunk, which can be attributed to the higher proportion of juvenile wood in these areas. Juvenile wood is known to exhibit lower mechanical strength and greater variability (Table 6).

As observed in Figure 2, the growth of tracheids follows a pattern consistent with an upward linear trend, which is characteristic of juvenile wood and, in turn, indicates that the transition to mature wood has likely not yet occurred.

4. Discussion

These results confirm the remarkable productive capacity of C. lusitanica under the challenging environmental conditions of northeastern Portugal.

If mean diameter at breast height (DBH) is taken as an indicator of productivity, the present study reports a value of 12.1 cm at 14 years of age. For comparison with other regions, previous studies have reported mean DBH values of 12.6 cm for 10-year-old stands in Ethiopia [35], 15.5 cm for 10-year-old stands in Costa Rica [36], and 12.6 cm for 13-year-old stands in southern Brazil [37]. Nevertheless, the most reliable indicator of productivity is stand volume or biomass production, which should always be compared against appropriate criteria due to differences in climate, soil conditions, and silvicultural practices across regions.

In fact, when compared with other species (Table 5), the total biomass of 50.2 kg achieved at 14 years of age surpasses that of any other species under comparable conditions. The closest value, 35.9 kg, was recorded for P. menziesii (Mirb.) Franco, a species widely recognized for its high biomass productivity, is in a stand with a lower planting density (1250 trees/ha) compared with C. lusitanica (1600 trees/ha).

As for Pinus pinaster Ait., a pioneer species well adapted to poor soils, low rainfall, and high summer temperatures, even under the more favorable growing conditions of the Tâmega Valley, the recorded biomass values remain lower, ranging between 16 and 17 kg.

When compared with E. globulus in Mexico, a region native to the latter species, C. lusitanica accumulated a lower amount of aboveground carbon—312 tC/ha versus 358 tC/ha, respectively. However, C. lusitanica exhibited higher values of litter accumulation on the forest floor, underscoring once again its potential ecosystem service role in soil protection [38].

It is also noteworthy that in both P. menziesii and P. pinaster, the trunk accounts for the majority of biomass accumulation, 82% and 67%, respectively, while the crown contributes only 18% to 33%. In contrast, C. lusitanica allocates a greater proportion of biomass to the crown, which represents 59% of the total, due to its numerous branches and limited natural pruning. Therefore, systematic pruning, particularly during the early stages of development and as long as technically feasible, is essential to encourage the formation of knot-free wood, thereby enhancing timber quality.

A study on C. lusitanica in southern Brazil reported that maximum productivity (6–31 m³ ha⁻¹ year⁻¹) occurs between 16 and 18 years of age, depending on site quality. The trees used in the present study are 14 years old, suggesting that peak productivity may not yet have been reached [39]. Studies conducted in Costa Rica provide even clearer evidence of biomass accumulation in the stem. The author indicates that the majority of the biomass is concentrated in the stem, with values of up to 61% found in this compartment, while the remaining 39% was distributed across the other aboveground components of the plant [40].

Regarding anatomical proprieties, in comparison with other species growing under similar conditions in northeastern Portugal, ref. [41] reported lower average ring widths for Pinus pinaster, ranging between 2.4 mm and 2.7 mm. These values were later confirmed by [42], who found an average ring width of 2.6 mm for the same species in the same region.

Comparable values have been reported for other species adapted to similar conditions. Refs. [43,44] found average ring widths of 2.4 mm and 2.5 mm, respectively, for Quercus faginea Lam. wood grown near the same region. There was reported ring widths ranging from 3.3 mm on the coast to 2.8 mm in the interior of Alentejo for P. pinea [45]. Additionally, ref. [46] observed ring widths between 1.3 mm and 3.3 mm in P. pinea stands in Tuscany (Italy), while [47] reported values ranging from 1.7 mm to 3.3 mm for the same species across various sites in central Italy.

These findings demonstrate the high productive potential and adaptability of C. lusitanica to the harsh environmental conditions of northeastern Portugal.

Tracheid length is one of the key indicators of wood quality for use in the production of pulp, particleboard, and fiberboard. A characteristic feature of softwoods, such as C. lusitanica, is the presence of significantly longer cellular elements (tracheids) compared with hardwoods, which is why they are commonly referred to as long-fiber species. However, in this study, the average tracheid length obtained for C. lusitanica was only 1.6 mm—a value considerably lower than that of most softwood species—and identical values (1.51 mm) were found by [48]. The subtropical region of China possesses abundant broad-leaf tree species resources; however, the anatomical properties and microstructure of the wood are still unclear, which restricts the processing and utilization of wood. In this study, 14 broad-leaf trees and four coniferous trees were selected. Wood anatomical indices and wood microanatomy were used to evaluate the wood properties using a comprehensive index method. The results show that Dalbergia assamica exhibited the highest wood basic density among the 14 broad-leaved tree species, accompanied by a significant fiber proportion and vessel lumen diameter, but a small vessel proportion and a high number of wood rays. Conversely, Parakmeria lotungensis and Michelia chapensis had relatively low wood basic densities, rendering them less suitable as valuable broad-leaved wood sources. Altingia chinensis, Castanopsis kawakamii, and the remaining 11 tree species exhibited medium-level wood basic densities. The 14 broad-leaved tree species had medium-length fibers. Phoebe bournei, D. assamica, and C. kawakamii demonstrated relatively high fiber proportion. A. chinensis, D. assamica, and C.kawakamii exhibited a large number of wood rays, making their wood more susceptible to cracking, whereas other broad-leaved tree species possessed fewer wood rays. The findings have provided a scientific basis for the exploration of precious broad-leaved tree resources and wood use [22,49].

Regarding the radial variation in tracheid length, ref. [50] found identical radial variation patterns for 19-year-old trees, but with longer tracheid lengths, with values of 4.79 mm near the pith and 6.85 mm at the outermost part.

When comparing the anatomical properties of C. lusitanica with other species from the same genus—namely Chamaecyparis pisifera, Fokienia hodginsii, and Taiwania cryptomerioides—in mature trees aged between 34 and 40 years in China, C. lusitanica exhibited the lowest basic density, at 0.3554 g·cm⁻³. This value was lower than that reported in studies conducted in Portugal, even though those involved older trees. C. lusitanica had the thickest cell wall (13.61 µm), but it also showed the shortest (1519 µm) and narrowest (24.8 µm) tracheids, as well as the largest lumen area of vessels and tracheids (19.54 µm²). These characteristics help explain its relatively low wood density compared with the other species. In addition, C. lusitanica exhibited the largest microfibril angle (32.74°) [48].

Compared with other softwood species also growing in northeastern Portugal, ref. [42] reported average tracheid lengths of 4.6 mm and 4.1 mm, respectively, for P. pinaster wood at 14 years of age. Similarly, ref. [51] recorded a value of 4.0 mm for P. menziesii at 15 years of age.

It is worth noting that the tracheid lengths observed in the present study for C. lusitanica are closer to the fiber lengths typically found in hardwood species. The characteristic of C. lusitanica wood to exhibit tracheids significantly shorter than those of most softwoods has been reported by several authors across different regions. The highest recorded value (2.9 mm) was reported by [12] in a study of this species in the state of Paraná, Brazil. However, it is important to note that the trees in that study were 56 years old, and given the typical radial pattern of tracheid length variation, it is expected that younger trees will present substantially lower values. When studying 11-year-old C. lusitanica trees from Minas Gerais, Brazil, ref. [52] reported an average fiber length of only 2.12 mm. They emphasized that, “Although C. lusitanica is a softwood species, the length of its fibers is much shorter than that of Pinus and Araucaria, and these inferior fiber morphology characteristics may negatively affect pulp strength, particularly tearing resistance.” Similar findings were reported by [53], who observed reduced fiber length in C. lusitanica wood grown in Sudan. They noted that pulp produced from this wood exhibited low tearing strength, rendering it unsuitable for manufacturing strong materials such as packaging paper and fibreboards.

A higher average inclination of 4.2° to the left was reported in 17-year-old Pinus pinaster trees in Portugal [29]. Slightly lower values were recorded by [54] in Sweden for 25-year-old Picea abies (L.) Karst. trees, with an average left-handed grain angle of 2.1°; however, the same trees showed an average of 4.5° at 15 years of age. Some authors have highlighted the propensity for the C. lusitanica to develop spiral grain [7], a characteristic that can limit the wood’s suitability for high-value applications. The implementation of selection and genetic improvement programs targeting this trait represents a viable strategy to enhance wood quality and expand its potential for industrial applications.

These values of wood density obtained are consistent with those reported by [20] for C. lusitanica in India (D_basic = 415 kg/m³; D_12 = 440 kg/m³), by [12,55] in Brazil (D_basic = 415 kg/m³ and 410 kg/m³, respectively), and by ref. [19] for C. lusitanica in Western Sudan, India, and Costa Rica (D_basic = 446 kg/m³, 434 kg/m³ and 430 kg/m³ respectively). They are also slightly higher than those presented by [56] in India (D_basic = 389 kg/m³; D_12 = 434 kg/m³), [3] in New Zealand (D_basic = 370 kg/m³), [52] in Brazil (D_basic = 389 kg/m³), [49] Also in Brazil (D_basic = 0.375 kg/m³) and [48] in Subtropical Region of China (D_basic = 0.355 kg/m³).

Conversely, slightly higher density values have been reported for this species by [19] in Sudan (D_basic = 446 kg/m³), ref. [17] in New Zealand (D_basic = 457 kg/m³) and by [55] in Brazil (D_basic = 515 kg/m³). These variations in density can be attributed to multiple factors, including tree age, regional edaphoclimatic conditions, and genetic differences among provenances.

Wood strength is directly related to the density of wood, and as density increases, the strength of the wood and wood quality also increase [57]. Regarding shrinkage, the values obtained, tangential (T) = 6.6%, radial (R) = 5.1%, longitudinal (L) = 1.4%, and volumetric (V) = 13.1%, fall within the ranges proposed by [58] for softwoods: 4.4–9.1% for tangential shrinkage, 2.1–5.1% for radial shrinkage, and 5.8–14% for volumetric shrinkage. However, these values are generally higher than those reported by several authors for C. lusitanica. For example, ref. [20] reported T = 2.93% and R = 1.89%; ref. [55] recorded T = 5.5%, R = 3.6%, and V = 9.2%; ref. [12] reported T = 5.6%, R = 3.5%, L = 0.5%, and V = 9.5%; and ref. [3] noted T = 5.9%, R = 2.8%, and V = 8.0%.

As for the fiber saturation point, while the average value obtained in the tangential dimension (29.8%) aligns with typical softwood values, the markedly higher values in the radial (39.5%) and longitudinal (61.1%) directions indicate a strong tendency for this wood to exhibit deformation, such as warping, during the drying process.

The air-drying stability coefficient and drying differential values fall within the normal range for softwoods, as reported by [42].

Regarding chemical characteristics, similar results of extractive contents have been reported for this species by [12,55,59,60]. There are, however, studies that report lower extractive content values, such as [55] with 1.1% or [61] with 3.9%.

Wood extractives play a critical role in the forestry sector, particularly in the pulp and paper industry, where their presence can negatively affect processing efficiency. High levels of extractives are associated with increased chemical consumption, inhibition of delignification, equipment corrosion, reduced pulp quality, and complications in black liquor recovery [62]. For this reason, species intended for pulp and paper production should contain low levels of extractives. In this context, C. lusitanica shows extractive contents within acceptable limits when compared with commonly used Pinus species. On the other hand, extractives are fundamental to the natural durability of wood, as they contribute to its resistance against fungal decay and insect attack [62], which is essential for the use of solid wood in various applications.

The use of C. lusitanica wood for pulp production should be considered due to its rapid growth and favorable anatomical fiber characteristics compatible with cellulose production [50]. However, investment in genetic improvement is required to reduce the high extractive content, which constitutes a limiting factor for this process [49].

Regarding mechanical properties, the lowest values of MOE (Modulus of Elasticity) and MOR (Modulus of Rupture) were recorded in the upper portions of the trunk, which can be attributed to the higher proportion of juvenile wood in these areas. Juvenile wood is known to exhibit lower mechanical strength and greater variability, as reflected by higher coefficients of variation, compared with mature wood [21,23].

In general, the transition from juvenile to mature wood in conifers occurs between 5 and 20 years of age [21]. However, it is possible that, due to the weakly expressed natural pruning in C. lusitanica and the relatively young age of 14 years, the sampled trees have not yet undergone a representative transition to mature wood. Therefore, the study focused exclusively on juvenile wood.

Comparable values have been reported by [55] for C. lusitanica wood in Brazil (MOE = 3587 MPa; MOR = 66 MPa) and by [20] in India (MOE = 4300 MPa; MOR = 53.9 MPa). Lower values were reported by [17] in New Zealand (MOE = 3300 MPa), while significantly higher values were observed by [56] in India (MOE = 8600 MPa; MOR = 74.8 MPa). These discrepancies are likely due to differences in tree age, which strongly influences the mechanical performance of the wood.

Compared with other softwoods, C. lusitanica wood from Portugal exhibits significantly lower MOE values than those reported for other species. For instance, ref. [63] reported an MOE of 7677.4 MPa for Pinus pinaster in Portugal, while ref. [64] recorded 4520 MPa for P. menziesii, and ref. [65] found 5705.9 MPa for Cryptomeria japonica D. Don grown in the Azores. In contrast, the MOR values for C. lusitanica are more comparable to those observed in these species.

Beyond species and geographical origin, the presence of knots plays a critical role in determining wood mechanical properties [66,67,68,69,70] . This trend was confirmed in the present study, which found that the lower logs, characterized by fewer and smaller knots, exhibited higher mechanical performance, with a Modulus of Elasticity (MOE) of 4060.9 MPa and a Modulus of Rupture (MOR) of 75.4 MPa. In contrast, the upper logs, which had a higher frequency and larger size of knots, showed reduced values, with an MOE of 3173.3 MPa and an MOR of 62.4 MPa.

Given the negative impact of knots on mechanical behavior, compounded by C. lusitanica’s pronounced branching habit and poor natural pruning capacity, artificial pruning during the juvenile growth phase is essential [71]. This silvicultural practice is particularly important if the objective is to produce high-quality timber for value-added applications such as sawmilling, carpentry, or furniture manufacturing.

Before drawing any conclusions regarding the potential of C. lusitanica for biomass production and as an agent of sustainability within the Portuguese territory, it is necessary to highlight the species’ susceptibility to certain pests and diseases. Among those most frequently reported in the literature and considered to pose the greatest potential damage are the mite Oligonychus ununguis, described as a cause of foliage deterioration in hedgerows and productive stands [72], and the cypress aphid (Cinara cupressi), recognized as one of the most destructive invasive pests of the Cupressaceae family, capable of inducing high mortality rates, significant economic losses, and marked ecological impacts in C. lusitanica plantations [73]. Furthermore, fungi of the genus Seiridium are responsible for cypress canker, a disease that produces lesions on stems and branches, ultimately reducing both productivity and tree longevity [74].

The cypress aphid affects tree growth and can lead to high mortality rates, while cypress canker compromises wood structure, undermining its effective utilization. For this reason, it is crucial—particularly for forest managers and silviculturists—to consider integrated strategies such as genetic improvement programs, which have already demonstrated effectiveness, as well as the use of chemical and biological control agents that enhance stand resilience to these pathogens. These measures are essential to ensure the sustainable and economically viable large-scale utilization of C. lusitanica [72,73,74].

The results of this study provide support for the discussion regarding the potential incompatibility between high biomass production and relatively low wood quality, representing a trade-off in terms of high productivity but lightweight wood. Due to its low density, such wood would indicate a reduced carbon retention capacity and, when processed, would predominantly yield short-life-cycle products. Therefore, research aimed at validating this species as a viable alternative for large-scale silviculture in Portugal should consider strategies to mitigate this paradox. Such approaches may include, for instance, the high resistance to biological deterioration [59], its utilization in densified bioenergy products that allow the use of young wood and shorter cycles [75], and genetic improvement programs to enhance wood quality, productivity, and tree form [76].

5. Conclusions

C. lusitanica wood displays inferior quality in terms of its physical, anatomical, and mechanical properties when compared with most softwood species. Nevertheless, it demonstrates an exceptional growth rate and remarkable adaptability to the harsh edaphoclimatic conditions found in Northeast Portugal. Indeed, under identical site conditions, the productivity of C. lusitanica typically exceeds that of Pinus pinaster, P. menziesii, Castanea sativa, and Quercus faginea by more than twofold. These results highlight the species’ high potential for biomass production and carbon sequestration in regions with strong Mediterranean influence, where many forest species face significant limitations.

In terms of the low density of C. lusitanica, it is recommended that further studies be conducted to evaluate its suitability for use in reconstituted wood panels (particleboard and MDF), for which low-density species are preferable, as they allow for a higher compaction ratio, resulting in improved physical and mechanical properties.

If the primary objective of establishing C. lusitanica stands in these areas is the production of high-quality timber, special attention must be paid to wood-forming characteristics. Given the adverse impact of knots on mechanical performance—exacerbated by the species’ vigorous branching habit and poor natural pruning ability—it is crucial to implement artificial pruning during the juvenile phase. Without such silvicultural intervention, wood quality will be substantially reduced, rendering it unsuitable for higher-value applications such as sawmilling, carpentry, or furniture production.

As a continuation of this study, further analyses using the available data can be conducted, particularly growth modeling based on ring width and on current and mean annual biomass increments, thereby enabling the development of models to determine, for example, the optimal harvest age. To complement and advance the understanding of the species’ potential for large-scale use, further studies are recommended to identify optimal silvicultural practices, for maximum sustainability, to conduct genetic improvement research aimed at enhancing growth performance and wood quality, to perform production cash flow analyses and financial assessments, and to expand the study to different sites and edaphoclimatic conditions in order to determine the most suitable geographic areas for its cultivation.