Kalliopi Radoglou

Forests of the Mediterranean region: gaps in knowledge and research needs

Mediterranean forests are characterised by a remarkable set of features that make them naturally and aesthetically attractive, on the one hand, but also quite fragile, on the other, therefore calling for careful strategies for their conservation and management. An exceptionally large variation of environmental conditions characterises the Mediterranean countries, where the environment can limit forest growth and succession but can also give rise, more often than it is supposed, to lush, mesic forest ecosystems, similar to those of central Europe. Moreover, Mediterranean forests contain an ample, plant and animal biological diversity, exemplified by the large number of tree species as compared to Nordic forests, and by their relatively high genetic variability due to the survival of many conifer and broadleaf species in southern European refuges, during the glacial periods. Another peculiar aspect of this region is the long-lasting manipulation of trees, forests and landscapes, since ancient times, with the diffusion all over the Mediterranean basin of such species as Pinus pinea, Cupressus sempervirens, Castanea sativa, and Quercus suber. The harsh and unpredictable climate, the difficult socio-economic conditions and the history of over-exploitation of the Mediterranean forests require that a scientifically sound conservation strategy and a locally-tailored sustainable management should be implemented. In particular, the need for identifying those silvicultural and management strategies appropriate for southern European forests should be stressed. Obviously, this consideration will have important effects on the definition of criteria for sustainability and eco-certification. Also, social issues should be considered key factors for effective forest conservation in the Mediterranean region, otherwise it will be impossible to control forest fires and landscape degradation. Based on these considerations a number of research priorities are discussed, with special consideration to possible impacts that global change may have on Mediterranean forest ecosystems.

Appraisal of root leakage as a method for estimation of root viability

Abstract We review the applications of REL test as a technique for detecting injury and thereby forecasting survivability of transplanted seedlings. The objectives of the present review are to present the fundamentals of this method, assess the relevant literature, present evidence of seasonal variations of REL, describe how REL responds to different stress conditions, suggest priorities for future research as well as practical recommendations for REL testing, and assess leakage of organic compounds as an indicator of root damage. Seasonal changes in REL may be connected with root freezing tolerance that varies among plants of different seed sources and species and thus does not always indicate health state of seedlings. REL technique can be used for assessing frost hardiness of roots under certain conditions (e.g. roots should be sampled into the test tubes prior to the freezing test). It can be used for studying heat stress with certain prerequisites (e.g. series of high temperatures or different exposure times should be used to find a threshold for heat tolerance). In desiccation tolerance assessment, REL presents high variation depending on species. In case of rough handling or hypoxic conditions, the effect depends on certain developmental stages. Additionally, though REL may be useful in quantifying damage caused by cold storage, it should be considered as a relative index of plant quality only since the relationship between REL and survivability could vary depending on cultural and handling practices prior to planting as well as on post-planting environmental conditions. In some cases, REL is correlated with field performance of seedlings, but in other cases the correlation is weak. Factors as species, seed lots, developmental stage of root tissue, season, and bud dormancy intensity may affect REL. Thus, REL must first be calibrated to these factors before it can be reliably used to predict the field performance of all types of seedling stock. Ambient storage, ageing and amino acids and protein leakage are also discussed. Limitations and questions for future research are suggested (e.g. species-dependence and decreasing variation). In general, REL is casually and statistically related with root damage and survivability of seedling. However, it depends on many other factors apart from root damages, and thus it remains a great challenge to improve its reliability.

Biodiversity and ecosystem functioning relations in European forests depend on environmental context

The importance of biodiversity in supporting ecosystem functioning is generally well accepted. However, most evidence comes from small-scale studies, and scaling-up patterns of biodiversity-ecosystem functioning (B-EF) remains challenging, in part because the importance of environmental factors in shaping B-EF relations is poorly understood. Using a forest research platform in which 26 ecosystem functions were measured along gradients of tree species richness in six regions across Europe, we investigated the extent and the potential drivers of context dependency of B-EF relations. Despite considerable variation in species richness effects across the continent, we found a tendency for stronger B-EF relations in drier climates as well as in areas with longer growing seasons and more functionally diverse tree species. The importance of water availability in driving context dependency suggests that as water limitation increases under climate change, biodiversity may become even more important to support high levels of functioning in European forests.

The decline of Greek fir (Abies cephalonica Loudon): Relationships with root condition

Abstract The decline of Greek fir (Abies cephalonica Loudon) has been reported throughout Greece during the last three decades. The symptoms include crown dieback, needle discoloration and loss, death of twigs, branches or whole tree death. A number of causes for the fir decline have been proposed such as drought, climatic change, air pollution and pathogens or insects. Our studies have focused on the relationship between fir decline symptoms and root growth and condition. The crown and root condition of fir trees, at different stages of decline, were assessed and the results showed that root condition was related to needle loss and crown discoloration. Declining trees were characterized by a decreased portion of fine root biomass. No significant differences in total root length and number of roots for each root order were found. In conclusion, our studies showed that the crown condition of Greek firs is reflected on root condition.

Ecophysiology and Survival of Acer pseudoplatanus L., Castanea sativa Miller. and Quercus frainetto Ten. Seedlings on a Reforestation Site in Northern Greece

Seedlings of three tree species (Acer pseudoplatanus L., Castanea sativa Miller. and Quercus frainetto Ten.) were planted on a field site in Northern Greece to investigate factors connected to planting failures. On several dates, for the first two growing seasons after planting (1997 and 1998), leaf water potential, chlorophyll fluorescence, gas exchange variables and seedling survival were determined. Q. frainetto seedlings exhibited the lowest values of leaf water potential (Ψ) for most of the season in both studied years. Seedlings of all species showed large reductions in Ψ the mid-summer in both years, with particularly low values in 1998. In both years, a sharp reduction in Ψ was observed at the beginning of July when all three species exhibited their lowest net CO2 assimilation (A) rate by the end of July. In 1997, A recovered after the July depression to values even higher than those recorded in June. However, in 1998, only Q. frainetto and to a lesser degree C. sativa recovered from a similar July depression in physiological values. Species reached their highest A rates by the end of August in 1997 and in June during 1998. In general, stomatal conductance and transpiration rates paralleled the A patterns. In 1997, the seasonal course of effective quantum yield (ΔF/Fm), for all plant species followed a rise-and-fall pattern with a peak at the beginning of July. In 1998, ΔF/Fm values were relatively high in June, showed a deep depression during July and while Q. frainetto and C. sativa recovered afterwards, A. pseudoplatanus continued to exhibit very low values. This study showed that differences in mortality between species were due to differences in tolerance to water stress and the superiority of Q. frainetto was probably related to the fact that it was the only species native and adapted to the planting site

Vegetation biomass estimation with remote sensing: focus on forest and other wooded land over the Mediterranean ecosystem

ABSTRACT Carbon sequestration service of Mediterranean forest and other wooded land is threatened by their fragile, complex, and highly evolving nature, due to both human disturbances and climate change. Remote-sensing methods for forest biomass estimation have gained increased attention, and substantial research has been conducted worldwide over the past four decades. Yet, the literature body focused on Mediterranean forests is rather limited as a result of their small extent compared to other biomes. We discuss the remote-sensing studies over the Mediterranean forest and other wooded land, discriminating research based on the primary data source used, such as optical imagery, datasets from active sensors, and combination of multisource data. The review indicates that there is a significant research gap in terms of the studies, as well as a need for a reduction of the errors and uncertainty of estimates, which are associated with both the sensors’ characteristics and the Mediterranean forest and other wooded land structure. Biomass estimates based on optical data were generally less accurate (R2 close to 0.70, where R2 is the coefficient of determination), however, when data from active sensors were involved, accuracy of estimations was considerably greater (usually R2 greater than 0.80). With respect to scale, most of the local scale studies established relationships with R2 over 0.70 and as high as 0.98, while the few regional scale studies exhibited R2 close to 0.80. Further, in-depth analysis can provide more efficient data fusion, classification methods, and procedures for operational regional and national assessment of forest biomass over such Mediterranean areas.

The physiological and morphological quality of Pinus brutia container seedlings produced from mini-plug transplants

Abstract The use of the mini-plug system for the production of container seedlings is relatively new, so there is little information on the potential impact of method on the quality of planting stock. The objective in this study was to evaluate the impact of mini-plug growing method on quality of Pinus brutia seedlings, and compare the performance of this stock type with that of standard container nursery stock. Seedling survival, growth and physiological status (root growth potential, shoot electrolyte leakage) were measured after pre-cultivation in mini-plugs, at the end of the first growing season in standard containers and after field transplanting. Our results showed that mini-plug transplants of P. brutia seedlings performed as well as the standard planting stock currently used in nursery operation in Greece. For the pre-cultivation of P. brutia seedlings in mini-plugs, the use of peat and a density of 2000 mini-plugs m−2 are recommended.

Continuous Spectrum LEDs Promote Seedling Quality Traits and Performance of Quercus ithaburensis var. macrolepis

Regulation of the growth, development, and quality of plants by the control of light quality has attracted extensive attention worldwide. The aim of this study was to examine the effects of continuous LED spectrum for indoor plant pre-cultivation and to investigate the morphological and physiological responses of a common broadleaved tree species in Mediterranean environment, Quercus ithaburensis var. macrolepis at seedling developmental stage. Thus, the seedlings were pre-cultivated for 28 days, under five different LED light qualities: (1) Fluorescent (FL) as control light (2) L20AP67 (high in green and moderate in far-red), (3) AP673L (high in green and red), (4) G2 (highest in red and far-red), AP67 (high in blue, red, and far-red), and (5) NS1 (highest in blue and green and lowest in far-red) LEDs. Further examination was held at the nursery for 1 year, on several seedling quality traits. Indeed, AP67 and AP673L triggered higher leaf formation, while L20AP67 positively affected seedling shoot development. NS1 and AP67 LED pre-cultivated seedlings showed significantly higher root fibrosity than those of FL light. Furthermore, NS1 and AP673L LEDs induced fourfold increase on seedling root dry weight than FL light. Hence, evaluating the seedling nursery performance attributes, most of those photomorphogenetic responses previously obtained were still detectable. Even more so, LED pre-cultivated seedlings showed higher survival and faster growth indicating better adaptation even under natural light conditions, a fact further reinforced by the significantly higher Dickson’s quality index acquired. In conclusion, the goal of each nursery management program is the production of high quality seedlings with those desirable traits, which in turn satisfy the specific needs for a particular reforestation site. Thus, the enhanced oak seedling quality traits formed under continuous LEDs spectrum especially of NS1 and AP673L pre-cultivation may potentially fulfill this goal.

Density and substrate effects on morphological and physiological parameters of plant stock material of four forest species grown in mini-plugs

Abstract The aim of this study was to measure a number of morphological and physiological parameters of planting stock material of forest species grown in mini-plugs and to evaluate them as indicators of planting stock quality under different density and substrate treatments. The studied species were black locust (Robinia pseudoacacia L.), Italian cypress (Cupressus sempervirens L.), brutia (Pinus brutia Ten.) and black pine (Pinus nigra Arnold). Seeds were sown in two growing substrates (peat and stabilized medium), using two mini-plug densities (3500 and 975 mini-plugs m−2). After a 4–5 week growth period under controlled conditions, both morphological (root length, shoot height, leaf area, root and shoot dry weight) and physiological (shoot electrolyte leakage, root growth potential) parameters were assessed. The use of stabilized growing medium and lower densities resulted in higher quality seedlings of black locust, black and brutia pine, in terms of growth and physiological status. In the case of Italian cypress, the use of low density improved seedling morphological characters, but negatively affected its root growth potential. Moreover, this species performed better when peat was used. Correlation analysis showed that for brutia and black pine, seedling morphological traits reliably reflect seedling quality during the precultivation phase in mini-plugs.

Use of innovative technology for the production of high-quality forest regeneration materials

Abstract The aim of this paper is to introduce the innovative technology created within the framework of PRE-FOREST project, funded by the European Commission under the CRAFT 6th Framework Research Programme. PRE-FOREST was an innovative research project in the field of forest planting stock material, enhancing co-operation between research foundations and small and medium-sized enterprises. Among the projects objectives were the introduction of a new technology based on precultivation (in mini-plugs) of forest regeneration material in a cost-efficient and environmental friendly production unit, not affected by outdoor climate; the development of a new, adapted to mini-plugs, grading technology and replug robot; the integration of these technologies into a functional prototype unit capable of large-scale forest regeneration material production; and the introduction of this production system at strategic locations in Europe. The system has been developed for year-round production and function in the same way, independently of climatic variations in different parts of Europe. To obtain these objectives the study focused on the interaction among production technology, mini-plug container design and rooting media, to develop cultivation protocols for forest reproductive materials of special economic and ecological importance for each participating country. One of the main benefits of the new technology was the environmentally friendly production of a large number of seedlings per square metre, leading to a cost-efficient result.