Drought- and Salt-Tolerant Plants of the Mediterranean and Their Diverse Applications: The Case of Crete

: Drought and salinity are two of the most urgent challenges faced in Mediterranean ecosys-tems, equally impacting natural systems, agricultural crops, and urban green. While many technical and soft approaches have been proposed to anticipate, mitigate, and remediate these impacts, a class of solutions has possibly been in front of us all along. Native Mediterranean fauna is well adapted, and when properly established still has unexploited conservation, restoration, and production diver-siﬁcation potential. Here, we outline the results of a long-term experiment taking place on the island of Crete, Greece that started in 1996 and involves over 70 native Mediterranean plants planted and monitored in various green spaces (private, shared, public) and a university campus under a diversity of adverse topographies (e.g., coastal, steep slopes), soils (e.g., disturbed, nutrient-deﬁcient), and microclimatic conditions, taking various plant formations and serving various functions. After plant establishment, drought and salinity resistance were evaluated by gradually exposing plants (n = 5249) to deﬁcit irrigation and saline environmental conditions, and plants were followed up for at least 5 years to empirically assess their ability to cope with abiotic stress. From the Mediterranean plants that were planted and tested, 52 were singled out because of their resistance and additional favorable traits. Motivated by this long-term assessment, a systematic literature review was conducted using the protocol Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) to validate empirical results, determine which were still unexplored, and bring to light additional uses. Results showed that 41 of the plants included in this research have signiﬁcant medicinal properties, 26 have nutritional uses, 17 industrial uses, and 18 have evidence of cosmetology uses. Additionally, the empirical assessment gave new evidence of at least 40 new species–trait combinations. By formally documenting the characteristics of these native Mediterranean plants, this work highlights their versatile traits, and the prospect of creating new uses and value chains enables, for the ﬁrst time their inclusion in planting-decision support systems and aims to increase demand and facilitate the scaling up of native greening in the context of sustainable land and water management within and beyond the Mediterranean basin.


Introduction
Climate change is expected to have a significant impact on global hydroclimatic patterns [1,2]. The Mediterranean coast and islands will be at the epicenter of these changes [3,4], with climate-model projections indicating a strong susceptibility to water stress [5,6] and a corresponding increase in the frequency and intensity of droughts [7]. It is characteristic that for the climatic scenario Representative Concentration Pathway (RCP) 8.5, the end of the 21st century finds most of the Mediterranean regions drier by at least one category on the aridity index scale [8]. Increasing irrigation to cover vegetation evapotranspiration requirements under the low natural leaching frequency experienced in arid zones will inadvertently lead to salinity accumulation in the soil [9]. In the Mediterranean regions, this is already a harsh reality [10], with 25% of irrigated Land 2022, 11, 2038 3 of 21 or NW direction), which are hot and dry. In addition, southern regions of the island are affected in the winter by southern dry and warm winds originating from Africa [40]. The island receives an average of 7.7 billion m 3 of rainfall, of which only 10-15% ends up in surface runoff, while 68-76% evapotranspires and 14-17% infiltrates [41]. Crete, like other Mediterranean islands, is highly dependent on groundwater resources, a problem that is already exacerbated by rising temperatures due to climate change [41]. The soils of Crete are mainly of limestone origin, deep, moderate, shallow, rocky, and well drained [42,43]. The main sources of soil salinity in Crete include coastal alluvium soils and proximity to the sea. In addition, the extremely rugged nature, dissolution, and erosion of limestone rock have created a wide variety of karst features [44] that often control the inflow of seawater into the coastal aquifer and pose challenges to hydrogeological modeling [45].

Empirical Assessment
In October 1996, research began to evaluate the tolerance of several native plants and the ornamental value and uses in landscape architecture, which continues until today. The plantings took place in coastal areas, lowland and mountainous, with various microclimatic peculiarities across Crete ( Figure 1). The plants were planted in urban, semiurban, and rural areas, in hotels, gardens, private and public spaces, school and church yards, squares, archeological sites, parks, sections of Motorway 90 (known as Northern Road Axis of Crete), shared, public-private open spaces of apartment buildings, terraces, verandas, tree planting of community roads, etc. Among the green spaces documented here, 17 are private green spaces planted exclusively with native plants of Crete, 32 are private green spaces planted with mixed native (majority) and imported plants, and 26 are public green spaces planted mainly with native plants of Crete, all covering an area over 500 m 2 each. Of these green spaces, 20% are located in urban, 75% in semiurban, and 5% in natural areas (e.g., rural roadside tree lines). Documented green areas (private and public) with a total area of more than 0.2 ha are shown in Figure 1. In all cases, introduced native plants were at least one year old, depending on the requirements of the respective landscape architecture design, and planting was avoided during summer. Plants were introduced individually, in groups, clusters, tree lines, hedges, borders, rock gardens, flower beds, in free planting, or in combination with structural elements, etc., which allowed later determination of optimal configurations for each species. Irrigation in all green spaces was carried out using micro-irrigation techniques with emitters and driplines.
Drought resistance evaluation was carried out by gradually reducing the frequency of irrigation with irrigation extent depending on local soil conditions. Irrigation frequency started from once every second day for the first three months after planting, reduced to 2 to 3 times per week depending on seasonal climatic conditions until year 3 of establishment, further reduced to 1 to 2 times per week until year 5 of establishment, and eventually culminated in irrigation only in the summer months or complete cessation of irrigation in drought-resistant plants such as Nerium oleander L., Ceratonia siliqua L., and others. This gradual reduction of irrigation was intended to force plants to stimulate the development of a stronger root system [22,46]. During the experiment, it was unnecessary and exceedingly rare to give additional irrigation (except of the irrigation model mentioned) during the summer months after prolonged high temperatures (heatwaves). Supplementary irrigation was applied mainly to plants smaller than the fifth year of planting and in regions with difficult soil and microclimatic conditions. For the purposes of this study, plants that could withstand irrigation only in the summer months or less after the 5th year of establishment were considered drought-tolerant. Salinity tolerance was assessed at the green spaces located on the coastal front, which is directly exposed to various types of salt loading, such as sea salt aerosol, saline groundwater, sedimentary brines, etc. [11]. For the purposes of this study, plants that could withstand direct exposure to this environment for over 5 years were considered salinity-tolerant. Drought resistance evaluation was carried out by gradually reducing the frequency of irrigation with irrigation extent depending on local soil conditions. Irrigation frequency started from once every second day for the first three months after planting, reduced to 2 to 3 times per week depending on seasonal climatic conditions until year 3 of establishment, further reduced to 1 to 2 times per week until year 5 of establishment, and eventually culminated in irrigation only in the summer months or complete cessation of irrigation in drought-resistant plants such as Nerium oleander L., Ceratonia siliqua L., and others. This gradual reduction of irrigation was intended to force plants to stimulate the development of a stronger root system [22,46]. During the experiment, it was unnecessary and exceedingly rare to give additional irrigation (except of the irrigation model mentioned) during the summer months after prolonged high temperatures (heatwaves). Supplementary irrigation was applied mainly to plants smaller than the fifth year of planting and in regions with difficult soil and microclimatic conditions. For the purposes of this study, plants that could withstand irrigation only in the summer months or less after the 5th year of establishment were considered drought-tolerant. Salinity tolerance was assessed at the green spaces located on the coastal front, which is directly exposed to various types of salt loading, such as sea salt aerosol, saline groundwater, sedimentary brines, etc. [11]. For the purposes of this study, plants that could withstand direct exposure to this environment for over 5 years were considered salinity-tolerant.
The scope of this work was to use native plants with reduced requirements, surviving under adverse conditions, without evaluating the growth rate. While imported species were also assessed, their evaluation is beyond the scope of this research. Nevertheless, for the sake of providing a comprehensive picture some of the problems experienced with nonnative plants are also discussed. Eventually, evaluation took place by checking the fulfilment of the requirements of the landscape architecture plan and with qualitative re- The scope of this work was to use native plants with reduced requirements, surviving under adverse conditions, without evaluating the growth rate. While imported species were also assessed, their evaluation is beyond the scope of this research. Nevertheless, for the sake of providing a comprehensive picture some of the problems experienced with nonnative plants are also discussed. Eventually, evaluation took place by checking the fulfilment of the requirements of the landscape architecture plan and with qualitative results based on interviews of owners of private green spaces and visitors of public and common-use green spaces.

Systematic Review
A systematic review was conducted following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) method consisting of a checklist and a four-step process with key elements for a transparent and reproducible reporting of a systematic review [47]. The steps of PRISMA are: (1) search (the search string and database types are defined), (2) evaluation (inclusion and exclusion of literature items as well as quality assessment criteria are predetermined), (3) synthesis (data are extracted and categorized), (4) analysis (results and conclusions are presented) [48].

Empirical Assessment
From 1996 until today, 52 native Cretan plants were investigated, planted, and tested for their tolerance and uses. The private and public landowners were very positive about the use of native plants in their areas of ownership or responsibility, as they were informed about the advantages of native plants and witnessed good aesthetic results. Native plants were assessed for shapes and forms not typically practiced and not documented in previous research. The pruning method determined the dimensions of the crown of a plant, influencing its use depending on the desired aesthetic and functional result. Native plants with small foliage and slow growth rates gave impressive results, such as the Querqus ilex L. tree, which was formed into a spherical bush ( Figure 2).
for their tolerance and uses. The private and public landowners were very positive about the use of native plants in their areas of ownership or responsibility, as they were informed about the advantages of native plants and witnessed good aesthetic results. Native plants were assessed for shapes and forms not typically practiced and not documented in previous research. The pruning method determined the dimensions of the crown of a plant, influencing its use depending on the desired aesthetic and functional result. Native plants with small foliage and slow growth rates gave impressive results, such as the Querqus ilex L. tree, which was formed into a spherical bush ( Figure 2).
Based on this assessment, Table 1 provides an overview of the possible shapes, forms, and functions of 52 native plants that are relevant to landscape architecture applications. From the list presented in Table 1, the most common forms were group or cluster planting, and pot planting (possible for all 52 plants, and for 45 out of 52 plants, respectively), and the rarest form that of high hedges (only seen in 15 out of 52 plants). The rarest function was that of providing shade (13 plants), since it is also limited to trees. The plants with the highest diversity in shapes, forms, and functions where Tamarix parviflora DC., Rosmarinus officinalis L., Quercus coccifera L., Pistacia lentiscus L., Nerium oleander L., Limoniastrum monopetalum (L.) Boiss., Ebenus cretica L., and Crithmum maritimum L. The least versatile was Petromarula pinnata (L.) A. DC. (suggested only for group or cluster planting in flower beds, and rock gardens) and Rhamnus alaternus L. (suggested only for group or cluster planting, pot planting, and high hedges).  Based on this assessment, Table 1 provides an overview of the possible shapes, forms, and functions of 52 native plants that are relevant to landscape architecture applications. From the list presented in Table 1, the most common forms were group or cluster planting, and pot planting (possible for all 52 plants, and for 45 out of 52 plants, respectively), and the rarest form that of high hedges (only seen in 15 out of 52 plants). The rarest function was that of providing shade (13 plants), since it is also limited to trees. The plants with the highest diversity in shapes, forms, and functions where Tamarix parviflora DC., Rosmarinus officinalis L., Quercus coccifera L., Pistacia lentiscus L., Nerium oleander L., Limoniastrum monopetalum (L.) Boiss., Ebenus cretica L., and Crithmum maritimum L. The least versatile was Petromarula pinnata (L.) A. DC. (suggested only for group or cluster planting in flower beds, and rock gardens) and Rhamnus alaternus L. (suggested only for group or cluster planting, pot planting, and high hedges).

Systematic Review
Using the above empirical assessment as a starting point, information was collected from published literature databases accessible online (Science Direct, PubMed, Springer, and Google Scholar) and books (Greek and English) using keywords based on the genera and species of the 52 native Mediterranean plants. From the search results (6750) and 17 books and from those selected from publications in peer-reviewed scientific journals and plant databases (1120), duplicate entries were found (24). After reviewing the scientific publications, only the relevant publications were included (313), of which 38 concerned adverse soil and climatic condition tolerance, 62 of nutritional value, 161 medicinal use, 25 industrial application, and 27 cosmetology and dyeing application ( Figure 3).

Abiotic Stress Tolerance
From the 52 plant species of this study, 29 plants were selected for long-term assessment and systematic literature review and were evaluated for abiotic stress tolerance. From these 29 Mediterranean plants, evidence has been documented ( Table 2) of their tolerance to salinity (17 cases from the literature and 23 cases from the empirical assessment), tolerance to drought (21 cases from the literature and 27 cases from the empirical assessment), tolerance to nutrient-deficient soils (15 cases from the literature and 24 cases from the empirical assessment), and frugality (9 cases from the literature and 29 cases from the empirical assessment). In limited cases (6 for salinity, e.g., Borago officinalis L., 9 for drought, e.g., Cichorium spinosum L., and 5 for nutrient-deficiency, e.g., Hypericum perforatum L.), they were neither tested in this study nor found in the literature (column NT marked in Table 2), which means that potential properties of these pants still need to be investigated. According to the systematic review and assessment, the most tolerant trees in all salinity, drought, nutrientdeficient soils and with few maintenance requirements were the native Mediterranean Tamarix parviflora DC., Ceratonia siliqua L., Pinus pinea L., Cercis siliquastrum L., Cupressus sempervirens L. and Juniperus oxycedrus L., Examples of native Mediterranean bushes and shrubs tolerant in all salinity, drought, nutrient-deficient soils and with few requirements were Nerium oleander L., Limoniastrum monopetalum (L.) Boiss., Spartium junceum L., and Rhamnus alaternus L. (Table 2). Figure 4 shows an example of a cut-and-fill restoration project that took place on high-limestone soils in HMU, where 566 individual plants from 15 native Mediterranean species (mostly Tamarix parviflora DC., Nerium oleander L., Cercis siliquastrum L., Viburnum tinus L., Ceratonia siliqua L., Pistacia lentiscus L., Rosmarinus officinalis L., and Hedera helix L.) and 5 alien species (mostly Elaeagnus pungens C. P. Thunb. Ex A. Murray, Lantana camara L., and Metrosideros excelsa Soland. Ex Gaertn.). After five years, native plants have survived and are resistant to arid, nutrition-deficient soils, reducing soil erosion. In addition, some alien species have also survived, but the results are not shown in the present study.

Systematic Review
Using the above empirical assessment as a starting point, information was collected from published literature databases accessible online (Science Direct, PubMed, Springer, and Google Scholar) and books (Greek and English) using keywords based on the genera and species of the 52 native Mediterranean plants. From the search results (6,750) and 17 books and from those selected from publications in peer-reviewed scientific journals and plant databases (1,120), duplicate entries were found (24). After reviewing the scientific publications, only the relevant publications were included (313), of which 38 concerned adverse soil and climatic condition tolerance, 62 of nutritional value, 161 medicinal use, 25 industrial application, and 27 cosmetology and dyeing application (Figure 3).

Abiotic Stress Tolerance
From the 52 plant species of this study, 29 plants were selected for long-term assessment and systematic literature review and were evaluated for abiotic stress tolerance. From these 29 Mediterranean plants, evidence has been documented ( Table 2) of their tolerance to salinity (17 cases from the literature and 23 cases from the empirical assessment), tolerance to drought (21 cases from the literature and 27 cases from the empirical

Nutrition
International gastronomy is often associated with the ethnobotanical background and especially the use of plants that combine beneficial properties (such as medicinal herbs) while reducing the use of salt in the preparation of dishes and increasing consumer acceptance and appreciation [30,94]. In this sense, Mediterranean plants are of great interest because of their important nutritional value and central role in the Mediterranean diet and its many health benefits [95]. Edible parts from native plants are usually leaves (e.g., Crithmum maritimum L., Rosmarinus officinalis L., Borago officinalis L., Thymbra capitata (L.) Cav.) flowers (e.g., Borago officinalis L., Origanum onites L.), fruits (e.g., Arbutus unedo L., Myrtus communis L., Capparis spinosa L.), and bulbs (e.g., Muscari comosum (L.) Parl.). Many ways exist for using or cooking these plants, which can be dried, boiled, cooked in pies, used for tea, salads, and cooked with meat, fish, snails, etc. ( Figure 5). Many of the edible native Mediterranean plants can also be grown in private gardens, flower beds, pots or planters, green roofs that produce food, and even in semiurban or urban areas in public or private spaces [96,97]. In addition, the food industry and many new diet trends use native Mediterranean plants for their antioxidant properties for immediate consumption or consumption after food processing [26][27][28]98]. According to the literature, in some native Mediterranean plants, e.g., Daucus carota L., the whole plant is edible [99] or can also be used for beverage, e.g., Arbutus unedo L. and Myrtus communis L. [100][101][102][103][104][105]. To the authors' knowledge, 26 of the plants included in this research have nutritional uses (Table 3), but it is possible that more are used and not published. assessment), tolerance to nutrient-deficient soils (15 cases from the literature and 24 cases from the empirical assessment), and frugality (9 cases from the literature and 29 cases from the empirical assessment). In limited cases (6 for salinity, e.g., Borago officinalis L., 9 for drought, e.g., Cichorium spinosum L., and 5 for nutrient-deficiency, e.g., Hypericum perforatum L.), they were neither tested in this study nor found in the literature (column NT marked in Table 2), which means that potential properties of these pants still need to be investigated. According to the systematic review and assessment, the most tolerant trees in all salinity, drought, nutrient-deficient soils and with few maintenance requirements were the native Mediterranean Tamarix parviflora DC., Ceratonia siliqua L., Pinus pinea L., Cercis siliquastrum L., Cupressus sempervirens L. and Juniperus oxycedrus L., Examples of native Mediterranean bushes and shrubs tolerant in all salinity, drought, nutrient-deficient soils and with few requirements were Nerium oleander L., Limoniastrum monopetalum (L.) Boiss., Spartium junceum L., and Rhamnus alaternus L. (Table 2). Figure 4 shows     [96,97]. In addition, the food industry and many new diet trends use native Mediterranean plants for their antioxidant properties for immediate consumption or consumption after food processing [26][27][28]98]. According to the literature, in some native Mediterranean plants, e.g., Daucus carota L., the whole plant is edible [99] or can also be used for beverage, e.g., Arbutus unedo L. and Myrtus communis L. [100][101][102][103][104][105]. To the authors' knowledge, 26 of the plants included in this research have nutritional uses (Table  3), but it is possible that more are used and not published.

Medicine
Native plants of the Mediterranean region are used for nutrition in Mediterranean diet and contribute significantly to maintaining good health and preventing serious chronic diseases [26][27][28]106]. Free radicals hinder many biological processes, and are the source of damage to lipids, proteins, membranes, and nucleic acids, thus causing a variety of diseases such as atherosclerosis, inflammation, cancer, cardiovascular disease, etc. [107]. A variety of plant products have important antiviral and anti-inflammatory effects against diseases that relate to free radicals, due to their contents in phenolic compounds, such as flavonoids, phenolic acids, tannins, and phenolic diterpenes [107]. In the last 2 decades, special emphasis has been placed on the natural antioxidant activity offered by the consumption of several native plants, which are rich in omega 3 fatty acids and antioxidants [108].
People in ancient times used plant parts for therapeutic purposes. The parts of the plants used in traditional medicine are mainly leaves, stems with leaves or upper part, seeds, flowers, buds, bark, bulbs, roots etc. with the leaves being usually the most widely used [109]. In addition, essential oils, produced from a variety of Mediterranean plants are secondary metabolites of plants that have various pharmacological properties, mainly antioxidants, antimicrobials or immunomodulators [110]. In our research, we worked on searching literature references for the 41 native Mediterranean plants for their significant medicinal properties (Table S1) and therapeutic activity in a variety of diseases, contributing significantly to human health and well-being. Table S1 lists the medicinal properties of these native plants, but it is possible that there are more and not published.

Industry
Besides nutritional value, the food industry takes advantage of the important antimicrobial activity of many native Mediterranean plants. For example, Borago officinalis L. has been used as a natural preservative in fresh pasta [111] and sausage production [112], and Rosmarinus officinalis L. as a preservative in various types of processed meat (pork, beef, lamb, and poultry), and fish [113,114]. Beyond the food industry, the gum that is produced from the carob seeds after peeling and grinding has been used in the production of photographic film, matches, paints, inks, and adhesives [115]. Also, generally, plant colors can come from different parts, for example the leaves (Rubia tinctorum L.), roots (Berberis cretica L.), bark (Quercus ilex L.), and petals (Dittrichia viscose (L.) Greuter), and contribute various colours such as blue (Olea europaea L.), red (Rubia tinctorum L.), yellow (Berberis cretica L.), green (Ditrichia viscose (L.) Greuter), brown (Quercus ilex L.), etc. [116], and have been traditionally used (and in some cases still are) for dyeing fibres or fabrics of animal and plant origin (e.g., Hypericum perforatum L. [117], Phillyrea latifolia L. [118], Quercus ilex L. [116], Spartium junceum L. [119]). In our research, we worked on searching literature references for the 52 native Mediterranean plants and we found evidence for industrial use for 17 plants shown on Table 4, but it is possible that there are more and not published. The plants with the most industrial uses and better documentation in the literature are Borago officinalis L., Ceratonia siliqua L., Myrtus communis L., and Rosmarinus officinalis L.

Cosmetology
In cosmetic production from plants leaves, flowers, essential oils, plant extracts and other selected ingredients of natural origin are used. They are used for many cosmetic productions that are used in face, hair, and body care products, such as soaps, shower gels, face, body creams, waxes, perfumes, sunscreens, shampoos, hair conditioners, hair masks, moisturizing lotions, soothing massage oils, etc. Natural cosmetics are products whose effectiveness is attributed to their herbal ingredients and the native plants of the Mediterranean offer proven uses or perspectives of innovation at various levels. A variety of products have now been marketed, utilizing, and highlighting the uses of Mediterranean plants (e.g., BioSelect, Athens, GR; Agrecofarms, Rethymno, GR; Cretanbee, Agios Nikolaos, GR). Evidence of cosmetology use of 18 native Mediterranean plants is shown in Table 5, but it is possible that there are more which have not been published. [169] Satureja thymbra L.

Discussion
Nowadays, many of the native plants used in the past have gained the interest of the wider scientific community by presenting a variety of uses, which can be a very interesting cultivation proposal for an innovative and sustainable economy. Current trends in the food science industry and consumers' preferences for diversified diets suggest the consumption of many native Mediterranean plants not only as diet complements but also as healthy medicinal foods for targeted conditions. The current movement in the industry of food science, as well as consumer preference for higher dietary diversification, point to the consumption of many native Mediterranean plants not just as dietary supplements, but also as healthy "prescription" diets for targeted conditions. These plants with limited needs for irrigation and high resistance to adverse conditions are considered as commercial cultivation of major importance. The increased consumption of insufficient water in many arid regions of the planet, can function as a deterrent to many inadequate or demanding imported plant species. In the Mediterranean region, with the forthcoming climate change and increase of temperature and drought, there is growing interest in native Mediterranean plants, which have already been tested in extreme temperature and dry conditions. In addition, the native plants are offered for several profitable business crops and also plantings in the urban environment with significant, positive ESSs.
In the empirical assessment part of this work, 52 native Mediterranean plants were evaluated for use primarily in landscape architecture. According to interviews of owners of private green spaces and visitors of public and common use green spaces where this vegetation was established, it was notable that native Mediterranean plants fulfil the aesthetic purpose and can be used in private and public green spaces. The adequate aesthetic value of Mediterranean plants for public and private green spaces has been previously demonstrated in the literature [17,18,190], and can be attributed to their full harmonization with the natural landscape and the capacity to blend in, update and preserve cultural heritage, thus appealing to non-material criteria. For example, trees such as Cercis siliquastrum L., Sambucus nigra L., Styrax officinalis L., and shrubs such as Nerium oleander L., Calicotome villosa (Poir.) Link, Limoniastrum monopetalum (L.) Boiss., Vitex agnuscastus L., and herbaceous plants such as Daucus carota ssp maximus (Desf.) Ball, Borago officinalis L. and Campanula cretica (A.DC.) D.Dietr. combine an impressive flowering and ornamental foliage suitable for a variety of uses in landscape architecture. Apart from their aesthetic value, adaptation to adverse soil and climatic conditions and irrigation limitations, frugal plant protection and maintenance, significantly reduce maintenance costs and make native Mediterranean plants ideal for use in UGSs. For these plants, deficit irrigation may inhibit growth and result to a stable compact plant form, and facilitate easier landscape management [191].
Furthermore, according to our systematic review and assessment, 29 of the discussed native Mediterranean plants were evaluated as tolerant to abiotic stress. Despite the different microclimatic conditions in every region in the Mediterranean basin, plants tolerant in abiotic stress, are preferable and more effective for farmers and landscapers. In Mediterranean regions, drought stress limits plant growth, and survival is threatened due to lack of rainfall and high temperatures in summer that impose extreme stress conditions [8,191] and a critical threat to world food security in the future. Also, coastal alluvium soils and proximity to the sea, increase salinity and stress to the plants. In our research, many of the Mediterranean plants that have been studied show significant resistance to drought, sea water spray, salinity, planting near the sea and strong winds. The continuing trend of global warming is predicted to cause significant changes in the climatic characteristics of several regions and in particular, the Mediterranean region it is expected to undergo a significant reduction in rainfall with more extremely dry and hot periods [192]. In Mediterranean areas, agriculture and green spaces will have to suffer drier, hotter, and longer summers, and therefore more attention should be given to water use and plant selection.
Alien flora and imported plant species were also assessed and compared with native plants. Some of the problems experienced with nonnative plants were in terms of increased maintenance costs (irrigation, nutrition, plant protection, cultivation requirements) and resistance to current microclimatic conditions (drought, poor soils, salinity, planting near the sea, strong winds, etc.). Moreover, many plants dried up completely from the first year (or second summer if planting took place late with lower temperatures), like Leptospermum sp., which gradually stopped being used in Crete, especially in some costal arias. Nonnative plants that survived faced increased problems with calcareous soil (e.g., Callistemon sp. Camellia sp.) or entomological infestations (e.g., Pittosporum sp.) or problems with their extensive root system and the unsuitable planting sites (e.g., Ficus sp.) or maintenance problems (e.g., Yucca sp.). In addition, some imported plants have caused extent entomological problems by invasive alien pests, such as Rhynchophorus ferrugineus, which has caused enormous damages to cultivated palms across the Mediterranean [193]. Furthermore, some nonnative plants such as Eucalyptus sp. and Ailanthus altissima (Miller) Swingle, have become weeds [194,195], and pose threats to the local ecosystem because of their efficiency in abstracting water (to the extent that they are a known threat to infrastructure and monuments), as well as allelopathic effects due their high concentration in terpenes [196] and quassinoids [197], respectively. For this reason, before planting it is always advisable to consult the most recent alien species list [198], and also consider which native species can substitute this alien counterpart in terms of functions and aesthetic result, as shown in Table 6. Nevertheless, substitution of such species is not always straightforward as they now also carry some cultural value, and a landscape architecture study is required on a case-by-case basis.
The establishment of native Mediterranean plants in the Mediterranean biome for cultivation or landscaping of UGSs can significantly contribute to biodiversity conservation [199] and the restoration of ecological balance. Their proven tolerance to conditions of increased salinity and drought, renders them imperative for the success and sustainability of ecosystem restoration actions, and the exploitation of low-productivity or marginal land, now as well as under future climate induced stresses. This way the employment of native Mediterranean plants offers superior, long-term, and cost-effective regulatory ecosystem services (ESSs) [200] and ecological benefits [201], and leads to healthier local communities and positive effects on their well-being [202][203][204].  [195] and [203] for Crete and Greece, respectively.
X X X X X Acacia saligna (Labill.) H. Wendl X X X X X Ailanthus altissima (Miller) Swingle X X X X Eucalyptus sp. X X X X Lantana camara L. X X X Robinia pseudoacacia L. X X X Solanum elaeagnifolium Cav. X X X Tamarix arborea (Ehrenb.) Bunge X Finally, the need of natural capital protection and ESSs is crucial achieving the goals of sustainable development. At the same time, there is a global need for solutions based on nature to significantly alleviate pressures on environmental, economic, and social challenges. Native Mediterranean plants offer superior nature-based solutions, ranging from UGSs, applications to reforestation programs, and community forestry, and expanding their applications is well aligned with European Union (EU) actions focused on a smart, sustainable, and inclusive economy, with strategies for biodiversity and green infrastructure in the context of the Europe 2020 development strategy [205].

Conclusions
This work provides a framework for organizing native Mediterranean vegetation properties and functions that can be used as a basis for prioritizing and selecting native plants for various land-management purposes, such as landscaping, agriculture, and ecosystem restoration in the Mediterranean. Through the application of this framework on the island of Crete, we highlight the multiple positive properties and diverse functions of native Mediterranean plants, both for agriculture and UGSs, and in the context of ecosystem preservation, ecosystem restoration, and crop production for diverse applications and markets (nutrition, medicine, industry, and cosmetology). For these prospects to flourish, a better understanding of a significant number of species still needs to be investigated for their tolerance to abiotic factors and possibly for other alternative uses. For native Mediterranean plants to be widely adopted, besides the need for wider dissemination, several barriers still need to be overcome, such as the availability of plants that are trade-licensed and compliant with cultivation protocols, the capacity of local communities to implement sustainable plant establishment and appreciate the upgraded ESSs, the availability of financial and policy tools for the implementation, and eventually access to postharvest and market solutions.