Seed losses can occur due to various factors, such as climatic conditions, inadequate pollination, failed seed development, and infestation by fungi and seed-feeding insects (Owens et al., 1991; Owens, 1995). Biological factors, including irregular flowering, lack of synchronous development and flowering, failed flower or embryo development, and immature seeds and fruits, can also impact seed formation. For example, newly formed conelets may be prematurely shed if fertilization is absent or insufficient. Research on stone pine pollen viability has shown that early conelet shedding is unrelated to pollination and fertilization. Insect damage can also contribute to seed losses and low germination rates. Insects feeding on seeds can consume nutritional stores and embryos, preventing germination (Boivin et al., 2019). L. occidentalis damages seeds by sucking the embryo and endosperm, leading to the discarding of young cones (Bracalini et al., 2013; Farinha et al., 2021). Damage to larger cones can result in empty or pathogen-infected seeds (Tamburini et al., 2012). Feeding by L. occidentalis on developing cones can result in the formation of visually undamaged yet empty or damaged seeds (Lesieur et al., 2014a; Bates et al., 2001). Therefore, insect damage can be detected through cone expulsion, presence of empty seeds in mature cones, and wrinkled or spongy seed endosperm. Cone set can be affected by various stresses, including climate changes, rainfall patterns, pollination, cone diseases, and abiotic factors. However, the recent decline in cone set and germination rates in Turkiye has coincided with the spread of L. occidentalis. Previous investigations into seed formation decline in coniferous species have not identified any abiotic factors that could explain abnormal seed decline in all species. These findings, along with logical inferences, support the thesis that L. occidentalis is the primary factor contributing to the formation of empty seeds. In fact, studies by İpekdal et al. (2019)d uzoğlu and Avcı (2020) have highlighted the widespread presence of this insect in Turkiye and the significant decrease in germination rates compared to previous years. The feedback received from the General Directorate of Forestry management and nursery directorates further supports these findings.
3.1. Statistical results on germination rates in coniferous species
The germination of seeds can be influenced by the amount of protein and oil consumed by the seed. This consumption is affected by damage caused by L. occidentalis during cone development. Even with the same degree of damage, the germination of the seeds may vary (Bates, 1997). The one-way analysis of variance was conducted to compare germination rates among different species. The results indicated a statistically significant difference in the formation of empty seeds based on species (Table 2). It can be inferred that the insect's feeding preferences vary across species when it is assume that the presence of empty seeds is due to damage caused by L. occidentalis. Duncan tests were performed to determine the differences in germination rates. The tests revealed that fir, stone pine, and Turkish red pine had the lowest rates, while black pine and Scots pine had higher rates (Table 3). The severity of damage caused by L. occidentalis varies among coniferous species. The rate of damage varies depending on the developmental stage of the seed (Krugman and Koerber, 1969). It has been noted that Pinus engelmannii experiences a high rate of empty seed formation due to damage caused by L. occidentalis during the embryo stage (Bermudes, 2012). The insect's damage to young cones increases cone drop by five times, and when it damages mature cones, it significantly reduces the percentage of viable seeds. Specific temperature thresholds are required for egg-laying and hatching, making temperature the most crucial climatic factor influencing the number of offspring. Higher numbers of offspring are produced at lower elevations (Jung et al., 2023). The extremely low germination rates observed in Turkish red pine and stone pine may be attributed to their ecological adaptation to lower elevations, where the higher number of offspring of the insect could have increased the damage.
L. occidentalis is an insect that feeds on the cones of conifers, particularly pines, and causes significant damage to pine forests. It has also been known to cause damage to other species such as Pseudotsuga menziesii, Juniperus, Tsuga, Picea, Cedrus, and Calocedrus. Studies on Pseudotsuga menziesii have shown that a two-week feeding period by female L. occidentalis during the late season can reduce seed production by 70% (Koerber, 1963; Cambell and Shea, 1990; Bates et al., 2000a, b; Lait et al., 2001; Bates, 2002; Mjøs et al., 2010). The damage rate of Pinus echinata in seed orchards has been reported to reach as high as 83% (EPPO, 2010), and it causes 41% damage to Douglas trees (Koerber, 1963). Controlled studies have shown that nymphs of L. occidentalis can reduce seed production in Pinus strobus by 75% (Bates et al., 2002a). Second instar nymphs have been found to feed on Pinus echinata cones for only four weeks, resulting in 100% cone shedding due to the destruction of the ovary. Similar damage occurs at the end of summer when the nymphs are feeding (DeBarr and Kormanik, 1975). L. occidentalis has been reported to cause up to 75% seed loss in annual cones of Pinus contorta and Pinus monticola Dougl. (Bates et al., 2000; Strong et al., 2001; Bates et al., 2002b). It has also been observed to reduce seed and seedling formation by 50% in some coniferous species (Blatt, 1994; Bates et al., 2000; Bates et al., 2001). It has been found in various coniferous species such as Pinus halepensis, Pinus laricio, P. pinea, P. nigra, Pseudotsuga menziesii in Sicily, and Pinus strobus, P. sylvestris in northern Italy (Rice et al., 1985; Hellrigl, 2006; Maltese et al., 2009). Damage percentages reported include 26% for Pinus monticola, 41% for Pseudotsuga species, and 30% for P. cembroides (Mitchell, 2000; Bustamante-García et al., 2012; Gapon, 2013). Additionally, it has been found to cause 55% damage to Pinus ponderosa (Krugman and Koerber, 1969; Pasek and Dix, 1988). In laboratory studies, it has been reported to cause a 50% decrease in empty seed formation in Douglas and a 90% decrease in seed formation in Pinus contorta (Schowalter and Sexton, 1990; Strong et al., 1998). Seed loss is generally less in coniferous species such as spruce and larix compared to others (Hedlin et al., 1981; Strong et al., 2001).
3.1.1. Aspect and germination
The results indicate that there is no statistically significant difference in germination rates between the slopes (Table 4). However, according to the Tukey tests germination rate of 12.3% was observed in flat areas, while a germination rate of 25% occurred on the southern slope (Table 5). The reason for the lack of statistical difference is thought to be the wide variation in germination exhibited by seeds collected from the same slope. Further studies are necessary to uncover the reasons for the insect's preference for certain appearances.
Table 4
Anova analysis of variance for germination rates according to aspect
|
Sum of Squares
|
df
|
Mean Square
|
F
|
Sig.
|
Between Groups
|
2878.68
|
8
|
359.84
|
1.473
|
.167
|
Within Groups
|
64011.68
|
262
|
244.32
|
|
|
Total
|
66890.36
|
270
|
|
|
|
Table 5
Tukey tests for germination rates according to aspects
Aspect
|
N
|
Subset for alpha = 0.05
|
Flat
|
9
|
12.294
|
East
|
27
|
15.410
|
Southeast
|
25
|
18.832
|
Northwest
|
33
|
18.930
|
North
|
33
|
19.182
|
West
|
32
|
19.212
|
Southwest
|
28
|
22.941
|
Northeast
|
43
|
23.202
|
South
|
41
|
25.006
|
Sig.
|
|
0.103
|
3.1.2. Slope and germination
The study analyzed the correlation between slope and germination rates, considering the potential impact of slope and sun angle on insect spread and damage (Fig. 2). The correlation analysis revealed a correlation coefficient of R² = 0.9336 for slopes ranging from 10–50%, and R² = 0.7455 for slopes ranging from 50–100% (Fig. 3). Due to the significant relationship between slope and germination, further research is necessary to investigate the feeding behavior of insects and the influence of microclimate. In a similar study conducted by Lee et al. (2023), it was discovered that slope had a strong positive effect (R2 (??) > 0.5; p < 0.05) on insect dispersal.
The body temperature of insects is crucial because they are poikilotherms and highly influenced by external conditions. When temperatures are low, their activity is restricted, and they are unable to fly. It has been observed that male flowers have a higher temperature and greater heat reflection ability. Objects with higher temperatures emit more infrared radiation, which can be detected by L. occidentalis. Furthermore, higher temperatures lead to an increased release of volatile compounds like monoterpenes. Therefore, male flowers, with their high reflectance, high temperature, and high concentration of volatile compounds, may be more appealing to L. occidentalis (Kitajima et al., 2022). Previous research has shown that first-stage nymphs feed on male flowers during the spring season (Schaefer and Panizzi, 2000). Sloping areas allow both male and female flowers to receive more light and solar radiation compared to flat areas. This may help explain why sloping areas have a greater impact on insect density in terms of feeding the first nymphs and adults, rather than flat areas. Additionally, since eggs require a certain temperature for hatching (Jung et al., 2023), the slope of the area may influence the insect's preference for warmer spots on the tree for egg-laying.
3.2. Germination rates and weights of 1000 seeds of the species.
Germination rates and 1000 seed weights of different tree species were compared using the data collected prior to the insect's arrival in Turkiye. Among the species, fir seeds had the lowest germination rate at 0.4%, followed by Scots pine seeds at 37.9% and black pine seeds at 25.1%. Stone pine, which has been experiencing empty seed formation for many years, had a germination rate of 2.6%, while Turkish red pine had a rate of 3.7%. The germination rate for maritime pine, commonly used in fast-growing afforestation, was found to be 22.1%, and, it was 16.5% for spruce. These results highlight the significant variation in germination rates across different tree species (Table 6). This difference suggests that insect damage may vary depending on factors such as seed size, reproductive cycle, sensitivity of the host tree, and tree species (Bates, 1999). Studies have shown that insects are capable of distinguishing between different conifers and selecting hosts in a versatile manner. They first choose the tree, then the cone, and finally their feeding place. Robust insects tend to select trees with dense crowns and long needles. Nutritional status and cone size may also play a role in the selection process, particularly for polyphagous species like L. occidentalis. Additionally, irrigated and fertilized trees are more likely to be preferred by these insects (Blatt, 1997; Lesieur et al., 2014; Farinha et al., 2018a).
Table 6
Comparison of germination rates found in this study and at literature by species
|
Average germination rate at (%)
|
|
Species
|
literature
|
in this study
|
Decrease rate (%)
|
Scots pine (Pinus sylvestris)
|
Giray (1993)
|
96.8
|
37.9
|
61
|
Black pine (Pinus nigra)
|
Varol (1968)
|
82.0
|
25.1
|
69
|
Maritime pine (Pinus pinaster)
|
Marques et al. (2012);
Alía et al. (1996)
|
80.0
|
22.1
|
72
|
Cedar (Cedrus libani)
|
Eler et al. (1992)
|
76.4
|
17.9
|
77
|
Spruce (Picea orientalis)
|
Erkuloğlu (1989)
|
66.7
|
16.5
|
75
|
Turkish red pine (Pinus brutia)
|
Öktem (1992)
|
81.6
|
3.7
|
95
|
Stone pine (Pinus pinea)
|
Saatçioğlu (1967)
|
85.0
|
2.6
|
97
|
Fir (Abies spp.)
|
Saatçioğlu (1967)
|
82.0
|
0.4
|
99
|
L. occidentalis not only causes damage during seed formation and development but also affects mature seeds, resulting in decreased seed germination. Research shows that seed loss due to L. occidentalis can exceed 70% in natural regeneration studies. It has been found that when more than one-third of the seed content is consumed, its ability to germinate is lost (Lesieur et al., 2014). Only 18% of the seeds consumed by L. occidentalis in a germination experiment were able to sprout (Blatt and Borden, 1998). Certain clones of the species are preferred by L. occidentalis (Blatt and Borden, 1996). In a study on Pinus contorta, 86% of the insects were found in only 10% of the clones, indicating that certain clones were more attractive to the insects. Among conifers in the same plantation, certain species were found to be more preferred. Factors such as cone weight and temperature influence the insect's choice (Strong, 2010; Richardson, 2013; Loewe-Muñoz et al., 2019), and the insect uses infrared sensors to locate the cones (Takács et al., 2009). Comparing the results of the study with previous studies revealed significant decreases in germination rates. While Scots pine had the lowest decrease at 61%, fir species experienced up to a 99% reduction. Turkish red pine (95%) and stone pine (97%) had the highest germination losses (Table 6). A study on pine species reported that if one-third of the seed was damaged by L. occidentalis, germination dropped below 30%. Moderate damage resulted in germination rates below 5% (Bates et al., 2001; Lesieur et al., 2014). Even slight damage to the seed leads to failed germination (Mitchell, 2000).
The effect of elevation on 1000 seed weight and germination was determined by grouping based on elevation stage. The data revealed that seed weight and germination rates were concentrated at specific elevation levels, particularly in Turkish red pine and Scots pine (see Fig. 4). It is necessary to investigate in detail whether this difference in germination is due to insect damage or inadequate seed development depending on elevation. No significant difference in germination was observed depending on elevation in other species (Additional Table 1). The study reported that damage in high elevation species like Pinus albicaulis was as low as 2.1%. While the insect tends to prefer species growing at lower elevations in their natural distribution areas, it may choose species residing at higher elevations in forced conditions such as food competition or lack of sufficient cones (Anderton and Jenkins, 2001). Elevation has a strong positive effect (r > 0.5p < 0.05) on insect spread, and modeling indicates that the probability of spread increases when elevation is below 345 m or slope is less than 200% (Lee et al., 2023).
The study compared the weights of 1000 seeds with previous studies conducted before the insect first detected in Turkiye. It was found that, except for Scots pine, the 1000 seed weights of other species were lower than in the previous studies (Fig. 5). Only the 1000 seed weights of Scots pine were consistent with the literature data. However, the 1000 seed weights of other species showed decreases ranging from 15–75%. Turkish red pine had the smallest decrease (12%), while fir seeds had the largest decrease (75%) (Table 8). This decrease in seed weight can be attributed to damage to the endosperm and embryo. Previous studies have demonstrated that coniferous species, which serve as hosts for L. occidentalis, not only experience a decrease in seed germination but also a decrease in seed weight depending on the amount consumed (Lesieur et al., 2014). These studies highlight that the severity of damage varies between locations (Bustamante-García et al., 2012) and that local climatic conditions may influence the population and, consequently, the damage (Schowalter et al., 1985; Tamburini et al., 2012).
Table 8. Comparison of seed weights of different species between literature and present study
3.2.1. Formation of empty seeds in stone pine (Pinus pinea)
In stone pine, the average weight of 1000 seeds in cones collected from 87 localities was determined to be 529.4 g. The lowest recorded weight for 1000 seeds was 88.1 g, while the highest was 847.4 g. Interestingly, there is a noticeable increase in seed weight as elevation increases. For instance, the weight of 1000 seeds was found to be 466.1 g in the 0-250 m range, but it increased to 644.4 g in the 1000–1250 m range. This represents a 29.4% decrease in average seed weight compared to previous studies where the average weight was 750 g (Saatçioğlu, 1967; Kılcı et al., 2011). Although stone pine is known to have high germination rates, this study revealed low germination rates, suggesting that the seeds may have lost their germination feature. The highest germination rate observed in stone pine trees was 14.7%, while the average germination rate was 2.6%. In contrast, Ganatsas et al. (2008) reported an average germination rate of 88% in stone pine. Interestingly, the varying elevations did not show a clear correlation with germination rates. The lowest germination rate was recorded at 2.3% in the 750–1000 m elevation stage, whereas the highest germination rate was observed in the 0-250 m elevation range, reaching 3.3%. The statistical analysis revealed a low correlation (R² = 0.1227) (Fig. 6).
The feeding behavior of insects, larger size, and higher nutrient content of stone pine seeds contribute to increased damage. Germination rates for stone pine seeds are lower compared to those of other species, likely due to the seed insect L. occidentalis. Suction holes caused by L. occidentalis were observed on the seed shells. Farinha et al. (2021) found a strong positive correlation (R2 = 0.98) between high insect densities and seed loss in stone pine trees, providing evidence for the impact of L. occidentialis on seed loss. It is still unknown if L. occidentalis is the cause of empty seeds in stone pine trees (Strong, 2006). Cone shedding in the Mediterranean Basin significantly impacts pine nut production (Bracalini et al., 2013). Major crop losses due to L. occidentalis were observed in stone pine trees in the Mediterranean basin. From 2011 to 2014, the rate of empty seeds increased to 50% in countries such as Portugal, Spain, Italy, and Turkiye (Mutke et al., 2014). In Italy alone, pine nut production decreased by 95% (Bates et al., 2002b). Prior to the damage caused by L. occidentalis, the rate of healthy seeds was 70%. However, three years after the insect was detected, this rate dropped to 6% (Innocenti and Tiberi, 2002).
Calama et al. (2020) found that the rate of damage in cones exposed to L. occidentalis varied between 67% and 100%. It caused a 70% loss of stone pines in the Iberian peninsula (Farinha et al., 2017). It was reported that if L. occidentalis damages one-year-old cones, it leads to 86% cone shedding, and if it damages two-year-old cones, it causes 100% cone shedding (Ponce-Herrero et al., 2017). Feeding during the first cone period and completed cone development can still result in a 47% decrease in seed amount (Bates et al., 2002b). Low damage severity significantly reduces seed germination (Sanchez et al., 2013).
Stone pine seeds are larger than those of other host trees (Sorensen and Miles, 1978), making them more attractive for feeding by L. occidentalis. Bigger seeds result in shorter feeding times for the insect, making stone pine seeds more advantageous in terms of benefit/cost (Farinha et al., 2018b). Regardless of natural stand, plantation, elevation, and aspect, Parlak (2017) found that empty seed rates in cones collected from 42 localities in stone pine areas in Turkiye varied between 14% and 98%. In Farinha et al.'s study (2018b), it was determined that the damage rate of L. occidentalis adults on stone pine trees was 0.014 seeds/day per individual. Examination of damaged seeds revealed that multiple insects feed from the same hole, suggesting cooperation among the insects to feed and benefit from the same feeding hole instead of drilling new holes. This feeding tactic reduces feeding time in stone pine trees and intensifies the damage severity.
In Mediterranean countries, particularly in Europe, damage from L. occidentalis significantly reduces the yield in natural stone pine areas by approximately 95%. In Italy, the annual production of stone pine seeds was 40 thousand tons; however, production sharply declined by 95% in 2009 due to insect damage (Bates et al., 2002b; Roversi et al., 2011). Damaged seeds wither inside and cones are discarded (Brambila, 2007). The invasive insect in Europe is considered the main factor contributing to the significant decrease in stone pine production in the Mediterranean Basin (Roversi et al., 2011; Bracalini et al., 2014). It has been observed that L. occidentalis consumes approximately 1/5 of mature stone pine cones every month (Farinha et al., 2017). Early sowing leads to the shedding of conalets, while late period feeding causes the formation of empty seeds and destruction of the endosperm (Mutke et al., 2015). Many of the cones damaged by L. occidentalis exhibit resin exudates (Bracalini et al., 2013).
3.2.2. Formation of Empty Seeds in Cedar (Cedrus libani)
According to Saatiçioğlu (1967) the average weight of 1000 cedar seeds to be 76.4g. Another study found the weight of 1000 seeds to be 88.0 g in seeds taken from two elevations and 10 dominant trees (Özdemir et al., 1986). In this study, the weight of 1000 seeds was found to be 15% lower compared to previous studies. The damage rate in cedar seeds was lower compared to other species. Besides, there was no significant difference in the germination rates of cedar seeds based on elevation. A low correlation was observed between elevation and germination rate, and the correlation was calculated to be very low for 1000 grain weight (Fig. 7).
The germination rates of cedar seeds have shown a significant decrease. In this study, the average germination rate was 17.9%, with the highest rate recorded at 41.7%. Previous studies on the germination percentages of cedar seeds have reported higher rates. For instance, Odabaşı (1967) found a germination rate of 75.9% in seeds collected from 15 different sources. Eler et al. (1992) determined an average germination rate of 76.4%. In this study, the germination rate recorded in this study was 76% lower compared to the average rates reported in previous studies. Furthermore, although there are limited studies, it has been determined that L. occidentalis also causes damage to cedar (Nemer et al., 2019).
3.2.3. Formation of empty seeds in Turkish red pine (Pinus brutia)
The study analyzed seeds collected from cones at 259 locations in Turkish red pine within an elevation range of 0-1500 m. The average weight of 1000 seeds in Turkish red pine was found to be 45.8 g. Previous studies reported average seed weights 51.9 g. In the current study, a seed weight loss of 12% was observed. To assess the impact of elevation on empty seed formation, germination rates were analyzed based on elevation levels. It was observed that as elevation increased, there was a corresponding increase in 1000 seed weights, but germination rates decreased by approximately half. The average germination rate from the study was determined to be 3.7%. In this study, a germination loss of 95% was observed. There was no correlation found between 1000 seed weight and elevation in Turkish red pine seeds, and a low correlation was observed between elevation and germination rate.
3.2.4. Formation of empty seeds in black pine (Pinus nigra)
Studies on black pine were conducted using seeds from 104 different locations. The average weight of 1000 seeds ranged from 6.4 g to 59.6 g, with an overall average of 17 g. Deligöz and Gezer (2005) found that the weight of 1000 seeds was 21.8 g in their study. Comparing these results to previous studies, a 75% reduction in seed weight was observed. In black pine, a weak correlation (R² = 0.0241) was found between 1000 seed weights and elevation (Fig. 9). The average germination rate was 25.1%. Germination rates varied depending on altitude, with rates of 19.6% and 16.1% at 0-500 m and 1500–2000 m, respectively. Rates of 24.4% and 25.4% were observed at 500–1000 m and 1000–1500 m, respectively. Kalkan et al. (2021) reported a germination rate of 13.9% for seeds damaged by L. occidentalis. In terms of altitude, there was no statistically significant relationship (R² = 0.0401) between germination rates. Previous studies have indicated that 25% of P. nigra seeds, of which more than half are consumed by L. occidentalis, have the potential to germinate (Lesieur et al., 2014). It has been reported that adults of L. occidentalis can consume between 0.7 and 1.7 seeds per day in P. nigra, with another study reporting a rate of 0.7 seeds per day (Lesieur et al., 2014; Farinha et al., 2018b). The insect is responsible for a 25% seed loss in black pine seed orchards and up to 70% in natural stands, with damage reaching as high as 77.4%. In P. nigra and P. sylvestris, the potential for natural regeneration is reduced by over 70%, resulting in seed yield reductions ranging from 24.2–44.2% in subsequent years. Seeds exposed to slight damage by L. occidentalis in black pine trees had a germination rate seven times lower than intact seeds (Lesieur et al., 2014).
3.2.5. Formation of empty seeds in Scots pine (Pinus sylvestris)
Sample cones were collected from 64 different locations in Scots pine to obtain seeds. The weight of 1000 seeds ranges from 2.6 g to 20.1 g, with an average weight of 10.6 g. Previous studies conducted by Giray (1993), Eliçin (1970), and Saatiçioğlu (1967) reported the weight of 1000 seeds as 9.2 g, 9.7 g, and 10.3 g, respectively. Gezer and Yücedağ (2006) found the average weight of 1000 seeds to be 9.6 g in their study. A noteworthy finding of this study was that the weight of 1000 seeds was discovered to be 10% higher than the average weight observed in previous studies. The correlation coefficient between 1000 seed weight and altitude in Scots pine seeds was very low (R² = 0.0095). However, there was a slight decrease in germination rates associated with higher elevations. This relationship was also observed in the correlation tests (Fig. 10), with an R² value of 0.1578.
In this study, the average germination rate for Scots pine was found to be 37.9%, which is higher than that of other species. Giray (1993) reported the average germination rate for Scots pine as 96.8%. The higher germination rates in Scots pine compared to other species suggest that it experiences lower insect damage. Lesieur et al. (2014) found that P. sylvestris seeds, with more than half of their content consumed, did not germinate at all. The damage rate of L. occidentalis adults in P. sylvestris ranged from 0.8 to 1.7 seeds per day per insect, while another study reported it as 0.8 seeds per day (Lesieur et al., 2014; Farinha et al., 2018b). In Scots pine natural areas, insect damage causes a seed loss of 70%, and sometimes up to 54% in seed orchard (Lesieur et al., 2014). Additionally, the insects cause further damage to the seeds by feeding on adult females (Bates et al., 2002b). The damage rate in P. sylvestris seeds provided to mating females reached 99% (Lesieur et al., 2014). In the natural distribution areas of Scots pine, it can be inferred that low winter temperatures affect the vitality of seed insects and reduce their damage, thereby contributing to higher germination rates. Another factor may be the shorter vegetation period in Scots pine growing environments due to higher altitudes, as insects prefer lower altitudes for wintering. Several studies have identified temperature, humidity, precipitation, and wind speed as the most important environmental factors influencing the survival and development of insects (Stanton, 1983; Berryman, 1986; Córdoba-Aguilar et al., 2018; Dent, 2000). Temperature plays a crucial role in the wintering site selection of many insects, while photoperiod promotes overwintering (Leather et al., 1995). A study on this subject suggests that low temperatures, especially in high-altitude mountainous regions, limit the spread of insects (Jung et al., 2023).
3.2.6. Formation of empty seeds in maritime pine (Pinus pinaster)
Seeds were collected from cones at 27 different locations in maritime pine trees. The average weight of 1000 seeds was determined to be 59.2 g. When compared to existing literature data, it was found that the weight of 1000 seeds decreased by an average of 26%. Additionally, there was no correlation (R² = 0.0001) between elevation and 1000 seed weight (Fig. 11).
The average germination rate was measured to be 22.1%. When compared to existing literature data, it was found that germination rates decreased by an average of 72%. The average germination rate in maritime pine varies between 82.5% (Marques et al., 2012) and 77.5% (Alía et al., 1996). Similarly, there was no correlation (R² = 0.0046) between elevation and germination rates. Some studies have reported that seed germination in maritime pine is hindered by L. occidentalis (Ribeiro et al., 2022).
3.2.7. Formation of empty seeds in spruce (Picea orientalis) and fir (Abies spp.).
The number of cones collected from areas where spruce and fir trees are found is lower compared to other species. Cones were collected from 5 locations in these areas and the seeds were removed. The average weight of 1000 spruce seeds was found to be 2.9 g. Erkuloğlu (1989) reported that the weight of 1000 seeds of eastern spruce ranged from 7.2 g to 8.9 g. Compared to previous studies, there was a 64% decrease in the weight of 1000 seeds determined in present study, while the average germination rate of spruce was 16.5%. When compared to previous studies, it was found that there was a 75% decrease in germination rates. Göktürk et al. (2019) reported in their study on spruce that the highest germination percentages ranged from 57.0–62.7%, while the lowest germination percentage was 14.1%. According to Erkuloğlu (1989), the germination percentage of spruce seeds was generally over 80%.
The weight of 1000 fir seeds was found to be 15.0 g, which was lower than the average values reported in previous studies. For example, Yüksel and Dirik (2021) found the weight of 1000 seeds of Kazdağı fir (Abies nordmanniana subsp. equi-trojani) to be 82.7 g. In other studies conducted on Kazdağı fir, Aslan (1982) found the weight of 1000 seeds to be 63.2 g, Velioğlu et al. (2012) reported an average of 71.8 g, and Yılmaz et al. (2011) found it to be 94.9 g. In studies on seeds of other native fir species, the weight was determined as 82.9 g in Uludağ fir (Abies bornmulleriana) (Turna et al., 2010). Altun (2011) reported an average 1000-seed weight of 79.0 g for three origins of Eastern Black Sea fir (Abies nordmanniana), while Sevik et al. (2012) found it to be 81.6 g. In present study, the weight of 1000 seeds was found to be 75% lower than that of found in previous studies. It was found that the average germination rate in fir was 0.4% in present study. When compared to data obtained from previous studies, it was determined that germination decreased by 99%. For example, in the study conducted by Yılmaz et al. (2011), germination rates in seeds taken from different origins ranged from 30–65%. The highest germination rate was 79.2% in Taurus fir. Varsamis et al. (2014) also found the highest germination rate of 91.8% in fir. Velioğlu and Arslan (2000) reported an average germination rate of 42.4% in the Eastern Black Sea fir (Abies nordmanniana), while Schopmeyer (1974) found average germination rates of 83% in the fir species of Abies bornmulleriana and Abies nordmanniana, respectively.