Topicalities in the Forest Ecology of Seeds

The main task of forest seed farming is to ensure that there is a sufficient number of fruit/seeds of high genetic value from all required tree species for annual management. Current trends are based on an environmental approach to forest management and work with natural forest regeneration. To map some partial biological, ecological, and technological aspects of the current state of research and anticipated developments in the field of fruit/seeds is the main aim of this Special Issue entitled “Topicalities in Forest Ecology of Seeds”.

This Special Issue focuses primarily on fruit/seed research in forestry, which is based on practical burning situations arising from forest management. In the last few years, there have been numerous climatic and meteorological abnormalities, the impact of which can be negative on ensuring the necessary composition of the reproductive material of forest trees. Furthermore, it can stem from the great irregularity of seed years, from the lack of preparation of the seed in time and the correct harvesting, storage, and protection against pathogens, etc. To improve the situation, it would help to know the issue of seed dormancy, the stimulation of seed germination, and the possibilities of seedling protection. An integral part is also the maintenance of species biodiversity, which also includes the special protection of rare tree species. The articles presented in this Special Issue can be divided into the following four topics, which are directly related to seed ecology (Figure 1).

1. Seed Dormancy

Two articles are devoted to the knowledge of physiological dormancy and methods in which to break it. Seed dormancy causes the poor germination of planting material and leads to economic losses. Physiological dormancy can be broken by the standard procedure of cold stratification [1] or by new high technology using non-thermal plasma [2].

An et al. [1] were focused on Fraxinus chinensis subsp. rhynchophylla (Oleaceae), a forest tree growing in northeastern China. This tree has great production potential. However, little is known about its dormancy and seed germination, which prevents the regeneration of this species from seed. The aim of this work was to determine the type of seed dormancy and how to break it. It was found that non-dormant seeds germinated very well (63%). For dormant seeds, cold stratification at 5 °C for 8 weeks was effective in breaking dormancy, and when cold stratification time was prolonged, the ability of seeds to germinate at low temperatures (e.g., 10 °C and 15 °C) increased. From these findings, it emerged that the seeds of F. chinensis subsp. rhynchophylla have a physiological dormancy type 2 nondeep PD. For seedling production in practice, 8 weeks of cold stratification at 5 °C and subsequent seed cultivation at temperatures ranging from 15 °C to 30 °C were recommended.

In the other article, Šerá et al. [1] investigate the disruption of the physical dormancy of black locust (Robinia pseudoacacia, Fabaceae) seeds using non-thermal plasma (NTP, treatment time: 5, 10 and 20 min). These seeds have a hard testa that is impermeable to water and air. All treatment times caused seed surface degradation (5000× magnification). The 20 min NTP treatment proved to be the best for stimulation as the O/C ratio increased from 0.28 ± 0.03 (control set) to 1.4 ± 0.3, the highest seed water absorption and hydrophilicity were recorded, and seed germination increased to 44% (control 6%). Scarified seeds had a germination rate of 93%. The detected changes on the seed surface and changes in germination showed that NTP can partially disrupt physical dormancy in black locust seeds.

2. Desiccation Tolerance

The excessive drying of seeds after ripening is an increasingly common problem that can be associated with the global warming of the planet and landscape aridiation. Values lower than optimal seed moisture lead to a decrease in seed vitality and germination. How to keep seeds with the right moisture is, therefore, another topic addressed.

Peng et al. [3] studied the deciduous species Sassafras tzumu (Hemsl.) Hemsl. (Lauraceae), which is an important economic tree with ecological value in China. However, its seeds show poor storage tolerance and rapid decline in seed vitality. This comprehensive study investigated the desiccation tolerance of S. tzumu. The results indicate that dehydration to 15% seed water content is a key turning point in the seed drying process, and CAT is the key enzyme to maintain the viability of these seeds. During storage, it is essential to maintain a safe water content above 23.58% to maintain seed viability above 70%. Storage below 50% water content is not recommended for S.tzumu seeds [3] as this leads to a rapid drop in viability.

3. Complex Bioecological Study

Endemic populations of woody species are part of species biodiversity and are under the scrutiny of nature conservation. Maintaining the size and vitality of populations depends on a comprehensive knowledge of the biological and ecological requirements of a given species. Only then can specialized protection come into play together with targeted management. The following articles [4,5] provide essential information for the complex bioecological study of the reproduction of two endemic tree species in China.

Abies beshanzuensis M. H. Wu (Pinaceae) is a rare species occurring in a small population in China (3 adults, Zhejiang Province) studied by Hu et al. [4]. The seeds of this fir germinate very poorly, and their regeneration is, thus, almost impossible. The aim of this work was to find a temperature regime to improve seed germination and to determine if the roots have ectomycorrhizal (ECM) mutualism. The experiments conducted in this study showed that the rate of seed germination A. beshanzuensis can be increased to 4.5% (originally 1%–2%) after 14 days of cold stratification and a temperature regime of 20/25 °C. In addition, A. beshanzuensis was identified as an ECM tree, and suitable ECM fungi were identified in the root tips of parental trees. The authors envision a future integration of molecular tools with physiological experiments to select suitable ECM fungi and then inoculate them into seedlings. This study [4] sheds more light on the population dynamics of this species.

The team of Liu et al. [5] focused on Hopea chinensis (Merr.) Hand.-Mazz. (Dipterocarpaceae). It is a deciduous tree with extremely small populations (endemic in China and Vietnam). The biological characteristics of the fruit/seeds and the ambient environment of the habitat caused a significant loss of viable seeds and gravely impacted population regeneration and maintenance. The goal of this work was to examine in detail the bioecological requirements of fruits/seeds in relation to generative reproduction. Significant differences in fruit phenotypic characters and seed germination characters among four investigated populations were found. The H. chinensis seed germination rate is high, there is no dormancy, no significant effect of calyx lobes and seed coat on germination percentage, and the seed germination effect and seedling growth of large seeds within the population are better. H. chinensis seeds are sensitive to dehydration and intolerant to drought, salinity, flooding, and low temperatures, being typical recalcitrant seeds. The seeds are suitable for germination on a moist substrate surface with good water retention and breathability at 30 °C. This study [5] contributed to the knowledge of fruits/seeds and to the subsequent development of their possible strategic protection.

4. Reproductive Capacity

Reproductive capacity indicates the number of seeds produced per plant in one year. Determining reproductive capacity is, therefore, key information for population biologists. The following article [6] deals with aging trees and the number of seeds produced.

Pardos et al. [6] assessed how the age of Scotch pine mother trees (Pinus sylvestris, Pinaceae, Sierra de Guadarrama, Spain) affects seed size, seed viability, seed germination, and the survival of seedlings growing under greenhouse conditions. The age of the parent tree had a significant effect on cone size, seed size, and seed weight, but there was no effect on seed germination and seed viability. Seedling survival was primarily affected by reduced water availability. The presented results show the ability of over-aged Scotch pine trees to maintain a relatively high reproductive capacity, which is important for maintaining the tree population.

5. Conclusions

This Special Issue presents a valuable collection of studies on seed ecology in forestry. The collected articles serve to better understand the complex mechanisms of biological and ecological problems in fruits, seeds, and seedlings. The results of these articles provide a scientific basis for application in forestry and nature conservation. The content of this Special Issue will facilitate the development of more effective strategies to promote the health and resilience of forest ecosystems and the maintenance of biodiversity in the context of ongoing environmental challenges.