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Forest growth is commonly used to explore tree vitality and ability to resist to environmental changes or climatic fluctuations. This paper illustrates and examines how regional climatic conditions can be related to the decline of tree growth, which were found to be more distinct in Quercus frainetto Ten. (Hungarian oak) and Fagus sylvatica L. (European beech) and less pronounced in Abies borissi-regis Matt f. (Bulgarian fir) on three long-term intensive monitoring plots (ICP Forests-Level II) in Greece during the period 1996–2009. Relative basal area increment and volume increment were calculated, expressing tree growth in terms of mean relative annual periodic increment. A decline in the growth of basal area and volume was observed after hot and dry periods, where annual temperatures and precipitation were far from the mean of the analyzed period. This observation was statistically confirmed in oak and beech plots regarding summer precipitation only and are in agreement with the findings of previous studies in Europe. The representativeness of the results at a national scale needs further investigation, although our results provide a good basis for further and more intensive monitoring programs to address various forest management scenarios against the background of potential climatic changes in the Mediterranean area.

A significant challenge in community ecology is the establishment of ecological baselines, which permit the evaluation of the variations in ecological dynamics at different temporal and spatial scales. To our best knowledge, few studies have been conducted in the forest openings of Mt. Parnon to establish a baseline for future monitoring. Hence, a floristic study of the herbaceous plant species composition, diversity, cover, and biomass was conducted in the forest openings of the Mt. Parnon-Natura 2000 Site in Greece to develop an ecological baseline that could be utilized in decision making for conservation and the sustainable use of forest biodiversity and ecosystem services in the forest ecosystem of Mt. Parnon. In the spring season, a thorough floristic survey was performed on Mt. Parnon for two consecutive years, 2021 and 2022. Herbaceous plant composition, diversity, cover, biomass, and plant indicator species (indicator value analysis) in the forest openings of Mt. Parnon were assessed. In the studied area, 63 plant species belonging to 58 genera from 20 families were recorded. The most numerous families were Asteraceae and Poaceae, followed by Fabaceae. Variable plant diversity, herbaceous plant cover, and produced biomass were recorded in different sites. It is noteworthy that some plant species could be regarded as indicators of the sites in the study area [Geranium molle L., Cerastium candidissimum Correns, Vicia villosa Roth, Euphorbia myrsinites L., Odontarrhena muralis (Waldst. & Kit.) Endl., Medicago lupulina L., Lotus corniculatus L., Crepis fraasii Sch. Bip., Bellis sylvestris Cirillo, and Trifolium stellatum L.], and information about these indicators, including Ellenberg type indicator values, is also provided. This study contributes to the understanding of the relevant ecological topics and provides key elements that could be utilized in decision making for the conservation and sustainable use of forest biodiversity and ecosystem services on Mt. Parnon. [ABSTRACT FROM AUTHOR]

Juniperus drupacea Labill. (Cupressaceae) is a species with ecological and medicinal value. In Europe, it is native only in southern Greece, and is listed as endangered. Due to its uniqueness, this study attempted, for the first time, an in vitro propagation effort of Syrian juniper. Explants of the lateral shoot tips were surface-sterilized and cultured on Murashige and Skoog (MS) medium. The cultures were subcultured on MS, woody plant medium (WPM), and Driver and Kuniyaki Walnut (DKW) supplemented with different concentrations of 6-benzylaminopurine (BA), thidiazuron (TDZ), or meta-topolin [6-(3-hy-droxybenzylamino)purine] for shoot induction. Explants derived from female trees exhibited 54.17% bud proliferation on DKW medium with 4 μM meta-topolin or 4 μM TDZ and on WPM with 4 μM meta-topolin or 4 μM BA. A total of 62.50% of the male tree derived explants produced multiple shoots on DKW with 4 μM BA. The maximum average number of shoots per explant were 1.17 per explant in both cases. The length of the shoot derived from explants of female origin was 2.94 mm compared to 2.69 mm of the in vitro shoots from the explants of male trees. Overall, the best medium and plant growth regulator combination for the explants derived from both female and male trees, for the traits under study, was proven to be DKW + 4 µM TDZ. Our experiments show that Juniperus drupacea, under in vitro conditions, shows recalcitrance in rooting, as the applications of IBA, NAA, and IAA concentrations were proven to be ineffective treatments. Although the results show low values, this avant-garde study provides a foundation for further research on the in vitro regeneration of Juniperus drupacea. [ABSTRACT FROM AUTHOR]

Seed germination traits were assessed on Pinus heldreichii H. Christ, a Tertiary relict, high-elevation Mediterranean pine, endemic in the western Balkan Peninsula and southern Italy; it is naturally grown at the northern Greece mountains, but also found in shrubby form above the timberline. Closed and mature cones were collected (October) for three consecutive years from Pindos Range and Mt. Olympus populations. Cone and seed morphological traits were recorded along with the seedling cotyledon number. Seed germination tests were performed under various ecologically meaningful temperatures and light regimes; climate change effects on seed germination and seedling development were assessed based on two climate scenarios. Final seed germination was moderate (~55%) on both, untreated seed lots at most favourable conditions (15 and 20 °C). Although cold stratification is not an absolute requirement, seed germination rate and final percentage are promoted by both a month of cold stratification (at least 30 or 45 days) and white light. The predicted climate change suggests that a prolonged drought period (>3 months) might turn out by the end of the century in the populations studied. Although the temperature increase might not have significant effects in the germination window of the species. The rainfall decrease will inevitably expose the young seedlings to the summer drought, thus increasing the potential mortality rate. Both ex situ (e.g., germplasm conservation) and in situ measures of conservation are recommended for the species survival in Greece, with a particular focus on the populations established at lower altitudes. [ABSTRACT FROM AUTHOR]

Lack of tree fecundity data across climatic gradients precludes the analysis of how seed supply contributes to global variation in forest regeneration and biotic interactions responsible for biodiversity. A global synthesis of raw seedproduction data shows a 250‐fold increase in seed abundance from cold‐dry to warm‐wet climates, driven primarily by a 100‐fold increase in seed production for a given tree size. The modest (threefold) increase in forest productivity across the same climate gradient cannot explain the magnitudes of these trends. The increase in seeds per tree can arise from adaptive evolution driven by intense species interactions or from the direct effects of a warm, moist climate on tree fecundity. Either way, the massive differences in seed supply ramify through food webs potentially explaining a disproportionate role for species interactions in the wet tropics. [ABSTRACT FROM AUTHOR]

Masting and regeneration dynamics were investigated in a long-term perspective using Abies cephalonica as a study tree species. Extensive fieldwork was implemented in Parnitha National Park, Greece, following a large-scale wildfire. Annual cone production was monitored for a 5-year period in 130 tagged trees, in 13 plots with 10 individuals each, established both within the unburned part of the forest and in surviving fragments of the burned area. In the most recent masting year, a high percentage (88%) of cone-bearing trees was recorded, along with a sizeable, average cone production (40.8 cones per tree). In the intermediate, non-masting years, the corresponding values ranged from 2% to 55% and 0.08 to 5.9 cones per tree, respectively. The reproduction process is affected by both tree density and regional climatic conditions, in particular temperature during spring of the maturation year and precipitation during spring and summer of the previous year. For the first time according to our knowledge, natural regeneration was recorded for a 4-year period, in 13 permanent transects within the monitoring plots, in relation with a masting event and the additional implications of a preceding wildfire. Highest mean density of seedlings and saplings (11.4 per m2) was observed during the first spring after masting. In the non-masting years, the corresponding value ranged from 2.1 to 2.9 per m2. Seedling survival during their first summer was considerable (30–76%) but stabilized afterwards (1–3 years) at a lower level (10–20%). The particular post-masting seedling flush was followed by an extremely high mortality rate (88.6%) and cannot represent a major recruitment event. [ABSTRACT FROM AUTHOR]

Abies cephalonica cone and seed morphometric characteristics as well as seed germination behaviour were investigated during an 8-year-long diachronic study (2007–2015). The research was carried out in Parnitha National Park, in the part of this Greek endemic, silver fir population that was spared from an unprecedented wildfire (2007). A statistically significant interannual and among-tree variation of cone traits has been identified, except for cone diameter. Cone length is correlated to the number of seeds per cone, while the percentage of empty seeds has been consistently high, with extreme values of 29.3 and 81.8% in a masting (2015) and lean crop (2009) year, respectively. There is also a considerable proportion of dead (including infected) and non-germinated seeds, and the eventual germinable fraction is well below 25% with spikes in masting years (39.4 and 60.9% in 2010 and 2015, respectively). Untreated seeds have been tested at a wide range of constant and alternating temperatures and germination is completed within 4–5 weeks at T ≥ 15°C and ca 15 weeks at 5–10°C. A chilling pretreatment of 4–8 weeks (at 2–4°C) concludes germination at 15–20°C within 2 weeks. A significant white light requirement has been observed for untreated seeds at 15–20°C, while germination was light indifferent at lower or higher temperatures. Data obtained in this study confirm the present, field seed germination during springtime; we may also predict an earlier germination (late autumn to mid-winter) in forest gaps, under the predicted, warmer conditions in the future. [ABSTRACT FROM AUTHOR]

The risk of N saturation was assessed in a mountainous fir stand in central Greece. The motivation of the research was the high content of N in soils as well as the low ratio of C/N in the FH soil horizon. Specifically, the stocks of N in both organic and mineral soil layers at a total depth of 80 cm were found 10,864 kg ha-1 and the ratio of C/N in the FH soil horizon 19. The ecological parameters measured to assess the N saturation status were the N fluxes in throughfall deposition, the concentrations of nitrate N in soil solution and the N content in current and second year needles over time. The time series statistical analysis showed that the fluxes of inorganic N in bulk and throughfall deposition did not have a significant trend and did not exceed the limit set in literature. It was also found that the average concentrations of nitrate N in soil solution were low although the values varied a great deal. Also the content of N in current and second year needles did not change significantly over time. It can be concluded that the fir stand is not saturated with N. The low concentrations of inorganic N in throughfall deposition, the dense ground vegetation and the stability of organic compounds may have contributed to the N retention in soil. [ABSTRACT FROM AUTHOR]

Due to climate changes, the interest in the post-fire recovery of forest communities not adapted to wildfires, such as Greek fir (Abies cephalonica) forests, has increased. In this study, the post-fire recovery of the burned A. cephalonica forest of Parnitha National Park (central Greece) was investigated after a stand-replacing fire occurred in summer 2007, as well as the performance of A. cephalonica plantings in the post-fire conditions. The research focused on the estimation of the A. cephalonica stand reproductive capacity without fire, the evaluation of the post-fire regeneration of the burned stands, and the monitoring of the plantations performance after the fire in the area. Then, based on the field and laboratory data, the post-fire recovery process of A. cephalonica was evaluated by application of a simplified form of the comprehensive causal framework for ecological succession estimation in open site, developed by Pickett et al. (1987), adapted to the study conditions. According to the findings of the study, stand seed crop without fire was high, while seed quality was found extremely low. In the burned area, no A. cephalonica seedling recruitment was observed during the three years after the fire. A. cephalonica plantings exhibited a medium overall survival rate (65.3%), while seedlings growth was very slow. Thus, we can suppose that an ecological succession process may occur in the burned area, if no human interventions applied, and species adapted to wildfires (mainly shrubs and herbaceous) will dominate in the area. However, planting of A. cephalonica seedlings could contribute to the species participation in the post-fire communities. [ABSTRACT FROM AUTHOR]

Beech forests play an important role in temperate and north Mediterranean ecosystems in Greece since they occupy infertile montane soils. In the last glacial maximum, Fagus sylvatica (beech) was confined to Southern Europe where it was dominant and in the last thousand years has expanded its range to dominate central Europe. We sampled four different beech forest types. We found 298 insect species associated with beech trees and dead beech wood. While F. sylvatica and Quercus (oak) are confamilial, there are great differences in richness of the associated entomofauna. Insect species that inhabit beech forests are less than one fifth of those species living in oak dominated forests despite the fact that beech is the most abundant central and north European tree. There is a distinct paucity of monophagous species on beech trees and most insect species are shared between co-occurring deciduous tree species and beech. This lack of species is attributed to the vegetation history and secondary plant chemistry. Bark and leaf biophenols from beech indicate that differences in plant secondary metabolites may be responsible for the differences in the richness of entomofauna in communities dominated by beech and other deciduous trees. [ABSTRACT FROM AUTHOR]

We estimated differences, five years after a wildfire, in soil and vegetation between Pinus halepensis stands that were once burnt (1998) and stands that were burnt twice in a short time interval (1995 and 1998), in the area of Penteli, central Greece. The parameters monitored were the physical and chemical attributes of upper soil layer and the vegetation composition, density and height. The results showed that five years after the wildfire, soil pH did not differ between areas burnt once and twice, while the organic matter was higher in the once-burnt areas. The vegetation composition was similar in the two areas and the dominant species were those pre-existing the fire. On the contrary, vegetation density was considerably lower in the twice-burnt areas. The height of woody species oscillated in the same levels in the two areas. The plant community was composed mainly by resprouting species, like Quercus coccifera, Pistacia lentiscus, or Phillyrea latifolia, and less individuals from seed-regenerated species, like Pinus halepensis, Cistus monspeliensis, and C. creticus. It is suggested that the recurrence of wildfire affected negatively the ecosystem attributes, and contributed to the increased risk of degradation. [ABSTRACT FROM AUTHOR]

Reforestation constitutes a challenge in post-fire ecosystem restoration, although there are limitations such as species and genotype selection, planting and management design, and environmental conditions. In the present study, the basic issue is the longevity of Abies cephalonica Loudon—the Greek fir seedlings planted extensively in Parnitha National Park (Central Greece), located near the metropolitan city of Athens, following the large-scale wildfire of 2007. Seedling performance was assessed for a 3-year monitoring period (2013–2015) through the establishment of 8 permanent transects, including 400 seedlings at the burned, reforested sites. According to the long-term reforestation project, two seedling provenances were used: (a) from Mt. Mainalon (South Greece, Vytina provenance) and (b) the local one from Mt. Parnitha. Both provenances showed a relatively successful survival rate reaching, in average, 73.8%, with the first summer after planting being crucial for seedling survival. The overall mean seedling height was 39.2 ± 1.1 cm, with a mean crown diameter of 47.3 ± 1.4 cm in the last monitoring survey. Although Parnitha seedlings seem to perform better in terms of growth, seedling performance in both provenances was affected by reforestation site characteristics, mainly altitude and aspect. Approximately one third of seedlings exhibited damage in their crown architecture (29.8%), while apical bud damage was less extensive (12.2%) in the final field measurement. Data indicate that seedling performance has proved to be quite promising for post-fire restoration, although long-term monitoring data should be considered. [ABSTRACT FROM AUTHOR]

The fundamental trade-off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade-off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non-proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change., (© 2024 John Wiley & Sons Ltd.)