Habitat Selection to Reintroduce Iris bismarckiana in Semi-Arid Environments

Abstract

Conservation of endangered plant species in their indigenous regions is of crucial importance, especially for those grown in semi-arid regions. The objectives of this study were to explore the Nazareth iris’s (Iris bismarckiana) natural habitat and identify new suitable sites to initiate a reintroduction program of this endangered plant species in a semi-arid environment. The study was conducted in Dibbeen Forest Reserve, Jordan, where six zones inside the reserve [A–F] were assessed in addition to zone G outside the reserve borders that represents the area where I. bismarckiana still exists. Habitat selection variables (topography, soil physical and chemical properties, climatic data, and potential risks and benefits) from all zones within the reserve were cross matched with that of zone G. The results showed that climatic data of all selected sites were suitable for reintroduction; all sites are open to direct sunlight most of the day. The minimum soil depth was greater than 40 cm in all zones, while soil respiration level revealed that zone A (a recreation site) was below the recommended thresholds. The percentage of stone volume (>2 mm) in the soil profile was high in zones D and F. Zones E, C, and F were extremely steep (>40 degrees), which undermined their potential to be suitable habitats. All sites are susceptible to high human disturbance risk except zone B, which is protected and under continuous surveillance by the Reserve Botanist. Considering all measured suitability indicators, including slope degree suitability (<25), soil respiration (57–77 mg kg⁻¹), soil stone percentage value (8.3%), tree canopy cover (open area), and human disturbance potential (low risk), zone B holds promise as a suitable site for a I. bismarckiana reintroduction program. Therefore, the initiation of long-term reintroduction programs within this site with timely surveillance is urgently needed to conserve and support such valuable species self-regeneration.

1. Introduction

Climate change and anthropogenic activities are continuously changing the environment and increasing the risk of species shift or extinction. Therefore, several species are considered rare, endangered, or extinct plant species [1], while on the other hand, these phenomena encourage the appearance and probably dominance of other species through microclimate changes and the speciation process [2]. In the Mediterranean region, it is being observed more frequently that the populations of forest species are being reduced to levels that threaten their sustainability potential and limit their original habitat coverage [3]. Global plant species were categorized into different levels according to their conservation needs. Globally, 5475 vascular plant species on Earth are known as critically endangered (CR) species; 10,377 are endangered (EN); 9790 are vulnerable (VU); 3903 are near threatened (NT); and 30,049 are in the least concern category (LC) [4,5]. Similarly, in Jordan, around 1820 plant species were studied, among which are 221 plants that have been recorded as CR, 275 as EN, 96 as VU, 39 as NT, and 1189 as LC [6,7]. About 27.1% of the wild plant species in Jordan are identified as CR or EN species, which is a little higher than the global mean (26.6%) of at-risk plant species [4,6,7].

It has been reported that indigenous plants around residential areas are being eliminated for the benefit of alien plant species [8,9]. The abundance of native plant species is becoming more limited due to climate change and collection of such plants by humans for the benefits they expect from these plants, including decorative value in home gardens or utilitarian value [9]. Therefore, people work to collect seeds and dig out seedlings of plants of interest from the wild and, consequently, deplete their wild populations [4]. However, basic information about the taxonomy, distribution, ecology, and threats are still missing for many plant species, especially in the Mediterranean region [3], within the same genus as Iris pseudopumila Tineo [10], or genera with taxonomic problems [11].

Plant conservation protocols can be in situ, ex situ conservation, or reintroduction of species of interest [1,12]. Plant conservation involves two essential strategies: translocation or introduction [13]. Translocation conservation refers to the purposeful relocation of plant species from one location to another aiming to generate conservation advantages at population, species, or ecosystem levels [14]. This conservation strategy encompasses two key strategies: reinforcement and reintroduction within the species’ native range. However, the introduction conservation strategy involves facilitating colonization and ecological replacement outside the species’ native range [14]. The introduction activities can be implemented away from the current range, or in an adjacent area near the existing range [13]. The main principles of reintroduction are (1) augmentation or enhancement (e.g., of plant species) by increasing the population size, and (2) restitution or restoration of a species by releasing the individuals of a species into an area it was formerly inhabiting [1]. The new area should have sufficient carrying capacity to sustain growth of the reintroduced population and can support a viable (self-sustaining) population in the long run [15]. In fact, the reintroduction’s success depends on several components, including the propagation method of the endangered species, site properties, soil health, human disturbance, and the surveillance and management of the introduced plant after reintroduction to the site [1,15].

The Center for Plant Conservation in the United States suggested a framework for best reintroduction practices [16]. The framework is composed of six components: justification, preparation, public involvement, implementation, aftercare, and monitoring. A reintroduction can be justified if the species is extinct from the wild, its distribution is limited, or the species population is small and continuously declining [16]. The selected sites for reintroduction have similar biological and physical features (topography, climate, community composition, soil edaphic properties, etc.) to those of extant populations. It is also encouraged to select protected sites within the species’ historic range, if they exist [16]. Several studies have executed reintroduction programs of rare plants (including bulbous and rhizomatous ones) to new sites that share similar levels of different variables. These variables included soil edaphic factors (pH, electrical conductivity, depth, percent of rock fragment by volume of soil, texture, respiration rate), soil microbial abundance and activity (e.g., mycorrhizae), site topography (slope degree), vegetation cover, climatic conditions (e.g., rainfall, radiation, and temperatures), reproductive biology, pollinators, protection status, and land use/cover information [13,17,18,19].

Iris is a perennial herbaceous flowering plant that includes about 300 species [20]. The Nazareth iris (Iris bismarckiana Damm. and Spreng. ex Regel) has been listed as an EN species according to the 2016 IUCN Red List of Threatened Species [21]. The species’ geographical range is Jordan, Lebanon, Palestine, and the Syrian Arab Republic [21]. In Jordan, this species exists in the northern part of Jaresh city. The plant numbers are projected to decline due to multiple threats including construction, infrastructure development, and tourist pressure in the city [6]. I. bismarckiana plants are being collected by locals or visitors due to its nicely showy flowers and transferred into inappropriate habitats and subjected to unsuitable management practices. These small populations of Iris are also subjected to grazing and tillage for agricultural purposes [20]. Therefore, conservation of the remnant populations of Iris is urgently needed. One viable solution is to reintroduce those highly threatened Iris individuals to safer and more appropriate sites within the same ecological zone (e.g., Dibbeen Forest Reserve, Jordan). However, the selection criteria for proper habitats within these semi-arid regions is not fully understood, especially the use of climatic conditions, site topography, soil edaphic factors, and tree canopy cover (open area vs. fully shaded) indicators, as well as the human disturbance risk. Thus, the main goal of this study was to identify a suitable restoration habitat for the endangered Nazareth iris (I. bismarckiana) in Mediterranean semi-arid environments. This work is expected to support the local and regional conservation efforts of such valuable plant species and align with the world’s efforts towards the conservation of endangered plant species.

2. Materials and Methods

2.1. Study Site

The study was conducted in Dibbeen Forest Reserve (32°14′31.47″ N, 35°49′45.97″ E, WGS84) (Figure 1), Jerash city, north of Jordan. The Dibbeen Forest Reserve’s total area is 8.5 km², and it has three major habitats. The first is the habitat pine zone where Aleppo pine (Pinus halepensis Mill.) trees are abundant, the second habitat is the mixed trees zone where P. halepensis, Eastern Strawberry-Tree (Arbutus andrachne L.) and Kermes Oak (Quercus coccifera L.) trees are existing, an the third is the “Oak zone” where Q. coccifera trees are existing. Dibbeen Reserve has a predominantly sloping topography, consisting of shallow to steep hills. The soil is terra rossa, a well-drained, silty to silty-clayey soil. The reserve elevation ranges from 600 m to 1100 m. Few I. bismarckiana plants were found in the reserve in the last decade (Figure 1, zone D).

The privately owned lands along the reserve borders showed existence of a small population of I. bismarckiana (around 70 Iris plants). The land use category of this area is residential and thus subjected to daily human activities and disturbances that might lead to the complete elimination of I. bismarckiana individuals from that location. During the study period (February 2022 to May 2023), I. bismarckiana plants were identified in these spots outside the reserve borders by plant taxonomists. Then, six sites (zones) within the reserve were suggested by the Royal Society for the Conservation of Nature (RSCN) to initiate an I. bismarckiana reintroduction program. These selected sites are spatially spaced areas and represent diverse habitats within the reserve limits. Historically, these sites showed the existence of I. bismarckiana before human disturbance and thus were expected to represent suitable habitats for Iris plants. The selected sites inside the reserve included zone A, which is open for recreational purposes and dominated by P. halepensis trees with some scattered A. andrachne and Q. coccifera trees; and zone B, a protected zone that is dominated by P. halepensis. Access to zone B is restricted to the Reserve Team. Zones C, D, E are dominated by Q. coccifera, while zone F is a mixed stand of Q. coccifera, P. halepensis, and A. andrachne trees. Zones C, D, E, and F are open for grazing activities in specific months (controlled grazing practice). The full plant species list in each zone is presented in Table S1.

2.2. A Brief History of Nazareth Iris

I. bismarckiana (Iridaceae, Oncocyclus Siemssen, I. sect. Oncocyclus (Siems.) Baker, Oncocyclus Irises) belongs to one of the most diverse groups in Asparagales that contains at least 23 genera and approximately 250–300 species with high ecological significance and economic impact [22,23]. Iris-related genera are widely distributed in Eurasia, North America, and North Africa [22]. All Oncocyclus irises are mostly found in small populations in rocky hillsides and desert habitats from the Caucasus to the eastern Mediterranean lands [24]. Iris species pollinators (e.g., bumblebees, honeybees, and hover flies) are attracted to bismarckiana flowers that have large, showy colored flowers, release attractive stimuli, and have some aromatic volatile compounds [23]. The major pollinators of I. bismarckiana are solitary male bees of Eucera spp. (Apidae family) [13]. In Dibbeen Forest Reserve, only Apis, Bombus, and Melecta genera were recorded from the Apidae family [25].

I. bismarckiana are herbaceous perennial flowering plants. It is a rhizomatous iris (diameter 1.5 cm) and can grow to between 30 and 40 cm in height (Figure 1). The species is native to southern Lebanon and northern Palestine and can be found at a wide range of altitudes from sea level to 1300 m. Iris species prefer open, unshaded areas. The species requires a chilling period during winter and can tolerate a wide range of temperatures [26]. The species requires a minimum of 100 mm of water annually. Its main propagation method is rhizomes; their flowers are self-incompatible flowers (diameter 6–10 cm) blooming in spring [13,27]. In Jordan, this species was recorded in Jerash and flowers between March and April [27].

2.3. Measurements

Multiple climatic, soil, vegetation, and risk potential measures were assessed for all the selected zones within the study area during the study period. These measures were employed and recommended by several researchers [13,17,18,19] and included a climatic component (long-term temperature and precipitation, 20 years), soil edaphic factors including soil pH, electrical conductivity of soil solution, soil depth, organic matter percentage, respiration rate, percent of rock fragment by volume of soil, and soil texture. Soil texture represents the proportions of sand (0.05 to 2.0 mm), silt (0.002 to 0.05 mm), and clay (<0.002 mm) particles in a soil sample [28]. Site topography (slope degree), tree canopy cover (presence of an open area), and human disturbance risk were also assessed.

2.3.1. Surface Temperature and Precipitation

Thermal data for the selected sites were derived using Landsat sensor data. Satellite sensor data from Landsat 8 (TIRS, Thermal Infrared Sensor) and Landsat 7 (TIR, Thermal Infrared) were downloaded from the United States Geological Survey (USGS) website/earth-explorer portal (http://earthexplorer.usgs.gov, accessed on 25 April 2023). The acquisition time for each image was 10:45 am (Jordanian time). Landsat sensors (TIRS, TIR) series images are available for free from the USGS website [29,30,31,32]. Those images were used to explore land surface temperature (thermal) changes of the selected sites between 2000 and 2021. All images were corrected and georeferenced using Environment for Visualizing Images (ENVI) 5.3 (Research Systems, Boulder, CO, USA). The final thermal maps were clipped to represent the land surface temperature map of the selected sites using ArcGIS tools. Thermal data (°C) were then collected from each site. Rainfall data for the same period were analyzed to determine the long-term precipitation in the reserve.

2.3.2. Human Disturbance

A recent aerial image (2022) was used to assess the human disturbance at each site including the closeness to roads, agricultural activities, etc. ArcGIS software was used to identify the proximity of roads and distances to the proposed reintroduction spots.

2.3.3. Soil Edaphic, Vegetation, and Topographic Variables

The selected sites were visited from April to June of 2022 and 2023 to identify existing vegetation cover and soil edaphic variables. Four surface soil samples were collected from each site (20 cm deep). Samples were air dried overnight and then sieved using a 2 mm sieve. Soil pH and electrical conductivity were measured when soil samples of 100 g were added to 300 mL glass beakers. One hundred ml distilled water (1:1 ratio) was added to each sample. Each sample was stirred for 5 s and sat for 15 min. Each sample was stirred again after 15 min. Then, soil solution pH and electrical conductivity were measured using a pH meter and an electrical conductivity meter. Soil respiration and relative N mineralization potential were measured using the Solvita soil respiration test [33]. The test was conducted on 40 g of sieved (2 mm) air-dried soil. The released CO₂-C from soil samples was measured using a digital color reader (Solvita-DCR, Woods End Laboratories, Inc., Mt. Vernon, ME, USA). Soil depth was determined based on the average depth of 4 randomly selected points in each selected site. The soil stoniness class was determined from four soil samples obtained from the top 30 cm soil layer for each tested zone. The four soil samples (1 L) were then sieved using a 2 mm sieve. Stones and soil clods (diameter > 2 mm) were washed, and their volume was determined. Slope degree was derived using a Digital Elevation Model (resolution: 12.5 m) image. The output slope raster (steepness degree) was calculated using the ArcGIS Spatial Analyst toolbar. The slope tool in ArcGIS identifies the surface steepness at each pixel (cell) within the study area where higher slope values represent steeper terrain and vice [34]. The tree canopy cover within each zone was assessed by delineating the open area (direct sunlight area) using the image-digitizing tool in ArcGIS. The analysis of variance (ANOVA) and variable mean separation among the studied sites were conducted at α = 0.05 level of significance using the Statistical Analysis Software-SAS (Version 9.4 for Windows; SAS Institute, Cary, NC, USA).

3. Results and Discussion

3.1. Climatic Conditions

The mean minimum and maximum surface temperatures at each suggested site in the reserve (sites mean) showed that the minimum surface temperatures were observed in January and February while July-August were the hottest months (Figure 2). Landsat-thermal maps showed slight variation (±3 °C) in surface temperatures among the reserve zones for each month over the study period, 2000–2021 (Figure 2). Zone G, where I. bismarckiana exists outside the reserve, had higher temperatures (3–4 °C) than those inside the reserve in July. This can be attributed to the heating effect from residential area components outside the reserve and the limited cooling effect from the surrounding surface vegetation compared to that within the reserve where vegetation is more abundant. It is believed that residential areas negatively impact the services provided by natural ecosystem [8]. Greenspace cover significantly reduces sun radiation, humidifies the microclimate, and lowers the land surface temperature [35].

I. bismarckiana species require a chilling period during winter and can tolerate a wide range of temperatures [26]. Across the investigated period (2000–2021), the temperatures for all the selected sites inside the reserve in February were low (5–10 °C) while the summer temperatures were never above 40 °C. The low temperatures (<10 °C) of February (winter) are sufficient for breaking rhizome dormancy and inducing flowering in the next spring as an adequate chilling period is achieved. The historical annual precipitation in the six zones along the investigated period was higher than 200 mm. Such precipitation levels (200 mm or more) are adequate to sustain I. bismarckiana growth and productivity as compared to those in Zone G. Overall, the climatic data revealed that all selected sites within the reserve are suitable for reintroduction in terms of climatic parameters.

3.2. Human Disturbance

Successful conservation or reintroduction programs principally consider all threats and disturbance sources that interfere with the conservation goals. A thorough and comprehensive understanding of possible threats should be considered to ensure that these threats do not exist at the suggested sites for reintroduction [16]. I. bismarckiana flowers are attractive to people because of the flowers’ nice colors and large size, and thus being near recreation areas or beside main roads risks these plants’ sustainability and propagation. Unfortunately, firewood cutting, agricultural practices, overgrazing, and uncontrolled harvesting of wild plants have never stopped across native forests [4]. Accordingly, the distance of reintroduced plants from roads and recreation zones is of crucial importance. In this study, the distances between the main roads around or within Dibbeen Forest Reserve and any point inside the selected zones (A, B, C, D, E, F) as well as zone G, do not exceed 0.5 km (Figure 3). Therefore, none of the suggested zones are expected to be away from human disturbance risk (e.g., grazing and recreation) unless protected.

I. bismarckiana is still sustained in zone G that is subjected to multiple disturbances from recreational activities, grazing practices, construction, and agricultural activities. Therefore, I. bismarckiana is expected to disappear from that habitat unless a conservation action is applied. Habitat disturbance continues to be the main threat to varied species. Occasionally, a small population survives and keeps reproducing through inbreeding. Inbreeding in small populations results in inbreeding depression and impacts the survival potential of the species’ offspring. A small population size can be deteriorated and extinct if frugivorous animals exist where no in situ seed germination is expected [4]. In Jordan, human activities have been and continue to be a critical threat to forest biodiversity and plant species abundance [29]. In most Mediterranean forests, including Debeen Forest Reserve, the private properties of locals are scattered within and connected to the forest. This fragments the forest land into pieces that are distributed within a complex mosaic of land use categories. Furthermore, neighboring locals can freely access large areas of the forest and contribute to the continuous human disturbance in that area. Fortunately, one fragment from this forest, zone B (Figure 3), is large and restricted to the reserve staff. A limited number of staff members are allowed to access zone B and they are only permitted to execute nondestructive experimental procedures. Therefore, it is believed that this zone could potentially be selected for reintroduction if other studied factors revealed its suitability as a habitat for I. bismarckiana, especially because it is under Reserve staff surveillance, protected, and under a long-term monitoring plan.

3.3. Soil Edaphic Factors

Soil edaphic factors including soil structure, temperature, pH, and salinity can significantly affect plant diversity, distribution, and soil living organisms’ availability [36]. Soil pH, electrical conductivity, organic matter percentage, and respiration rate in 2022 and 2023 are presented in

Table 1. Soil pH, electrical conductivity (EC), organic matter, and respiration (CO₂-C) of the investigated sites in Dibbeen Forest Reserve in June 2022 and April 2023.

Year	Zone	pH	EC (ds m−1)	Organic Matter (%)	CO2-C (mg kg−1)
2022	A	7.81 a	0.29 a	1.03 c	18.2 d
	B	7.53 a	0.24 a	4.47 a	77.1 a
	C	7.59 a	0.39 a	4.62 a	72.3 a
	D	7.49 a	0.45 a	3.77 ab	48.3 b
	E	7.71 a	0.38 a	1.93 b	24.4 cd
	F	7.76 a	0.29 a	4.11 a	55.1 b
	G	7.44 a	0.47 a	2.49 b	29.1 c
	p-Value	0.44	0.23	0.03	0.02
2023	A	7.73 a	0.25 a	1.24 c	25.7 b
	B	7.57 a	0.30 a	3.33 ab	56.8 a
	C	7.70 a	0.25 a	3.93 ab	63.7 a
	D	7.63 a	0.27 a	2.87 b	61.9 a
	E	7.77 a	0.26 a	4.43 a	55.4 a
	F	7.67 a	0.28 a	3.38 ab	60.0 a
	G	7.63 a	0.34 a	2.90 b	60.8 a
	p-Value	0.96	0.83	0.0037	0.0009

Means in columns followed by different letters are significantly different at p < 0.05.

. The results showed that there were no significant differences among all zones in terms of their soil pH where pH levels were 7–8 indicating that the soils are slightly alkaline. Similarly, the EC of the tested soils in all zones showed that the EC values were low (<0.5 dS m⁻¹), and no significant differences were observed. Thus, no salinity issues are present across the studied zones. Soils that are experiencing salinity problems show EC values above 4.0 dS m⁻¹. In this study, soil respiration (CO₂-C released) analysis in 2022 showed that the values for zones A, E, and G were below the recommended thresholds (30 mg kg⁻¹), which indicates that microbial populations in these sites are limited (Table 1). Zone A had low soil respiration rates in both years, and thus it is not recommended for reintroduction if no additional conservational practices are employed to amend the site because the microbial community’s abundance and activity are critical for plant and ecosystem health [37]. Researchers use soil respiration and organic matter percentage as good indicators of soil health [33]. These measures are efficient and cost-effective tests to evaluate the soil microbial respiration process [37,38] and the relative N mineralization potential [38].

The soil texture types were loamy soil in zones A and B and silt-loam soil in zones C, D, E, F, and G (

Table 2. Soil texture (sand, silt, and clay proportions), percentage of stones by volume, and depth of Dibbeen Forest Reserve zones (A–G) soils in April 2023.

	Soil Texture (Particle Proportion)
Zone	Clay	Silt	Sand	Texture	Stone Diameter > 2 mm (% of Stones by Volume)	Soil Depth (cm)
A	20.7 a	45.7 b	37.0 a	Loam	8.4 b	>40
B	20.0 ab	43.7 b	36.2 a	Loam	8.3 b	>40
C	18.9 ab	69.3 a	15.1 c	Silt-loam	10.7 b	>40
D	17.5 ab	66.1 a	16.4 c	Silt-loam	21.0 ab	>40
E	16.8 ab	53.7 b	29.5 ab	Silt-loam	17.7 ab	>40
F	15.3 ab	53.2 b	28.2 b	Silt-loam	24.5 a	>40
G	13.9 b	68.0 a	18.1 c	Silt-loam	13.0 ab	>40
p-Value	0.037	0.0004	<0.0001	-	0.05	-

Means in columns followed by different letters are significantly different at p < 0.05.

). Loamy soil is a combination of the three types of particles (sand, silt, clay) in relatively equal proportions [28]. Loamy soil is superlative for most plants because it holds an adequate amount of air and moisture around the root rhizosphere [28]. The results showed that stone percentages were significantly different among studied zones (Table 2). Zones A, B, and C had the lowest stone percentage (8.3%–10.7%) while zone F had the highest value (24.5%). In addition, the stone percentage in zone G (Iris location outside the reserve) was 13% (Table 2). Morandage et al. [39] found that a linear increase of stone (>5 mm) percentage from 4% to 50% results in a linear decrease of rooting depth. High values of stones and rock fragments reduce the overall porosity of the soil and consequently, soil aeration [40]. Insufficient soil aeration reduces root respiration and nutrient uptake, leading to reduced growth and overall plant health [39,40,41]. It has been reported that Iris plants prefer deep soils with low stone percentages (few rock fragments) [13]. In addition to the soil’s stone content, soil depth can potentially influence Iris performance. Volis and Blecher [13] attributed the extinction of the Iris atrofusca population in one of the tested sites to the very low soil depth and identified a soil depth of 40 cm as the threshold for I. atrofusca because its root system cannot penetrate deeper into soil layers. In the present study, soil depth in all tested sites was higher than the suggested threshold (40 cm) and consequently, soil depth is not a survivor-limiting factor for Iris across the selected zones. Overall, zones A, B, and C are the best candidates in terms of soil texture, stone percentage, and soil depth.

3.4. Site Topography and Tree Canopy Cover

Slope steepness degrees were different among the studied zones (Figure 4). About 90% of zone C had a slope degree higher than 40 (steep slope). Around 50% of zones E and F had slope degrees between 25 and 40 degrees. Interestingly, more than 80% of zones A, B, D, and G had a flat to slight slope topography (slope degree < 16). Iris plants prefer a slight slope steepness topography [13]. Slope gradient affects the detachment, transport, and deposition of soil layers [42]. As slope degree increases, the detachment of individual particles and water runoff increases and leads to higher soil erosion [42]. When slope degree becomes steeper, the runoff coefficient increases, the detachment of individual particles and the kinetic energy as well as the carrying capacity (transport) of surface water flow become greater, soil stability decreases, and soil sediment loss increases [42,43]. Jourgholami et al. [44] found that runoff increased from 2.45 to 6.43 mm as the slope gradient increased from 5 to 25%, reaching the threshold point of 25%. Runoff mainly carries fine soil particles and transports sediment of soil particles that are smaller than 20 µm diameter [45]. Larger particles and stones tend to settle quickly over short distances, leading to a higher percentage of rock fragments relative to soil volume (stoniness). In addition, higher runoff (e.g., due to steep slope) can lead to higher nutrient translocation (loss) due to a higher chance of sediment transport [45].

I. bismarckiana and other Oncocyclus plants grow in open areas and do not tolerate shade [13]. In this study, I. bismarckiana was found in open fields (zone G) outside the reserve (Figure 5). The plants were fully exposed to direct sunlight. In fact, the distance between I. bismarckiana plants and nearby trees was about 10 m. Therefore, the selected site for reintroduction is preferred to be in an open area and free of woody vegetation (trees and tall shrubs). Similarly, all studied zones (A–F), are considered appropriate sites for reintroduction due to the availability of sufficient open sky area in some spots within the zone area (Figure 5).

3.5. Successful Reintroduction Component

Iris species exhibit exogenous (hard seed coat) and/or endogenous (physiological) dormancy that slows the seed germination process. Dormancy could restrict seed germination for up to 6 years [46,47]. For example, Iris tenax experiences both exogenous and endogenous dormancy, and thus achieves a 63% germination rate after stratification in warm conditions at 20–30 °C followed by 12 weeks of cold stratification at 5 °C to achieve a higher seed germination percentage [46]. The I. bismarckiana species propagates naturally through rhizomes where their seed production is extremely low. In addition, most bulbous and rhizomatous Iris species including I. bismarckiana do not produce more than 5 to 10 daughters annually [48,49]. Somatic embryogenesis techniques that were implemented in embryo culture labs were successful for I. bismarckiana [20] and other iris species [48] regeneration, where acclimatization and reintroduction protocols support such achievement [48].

The successful reintroduction of plant species is a long-term process that requires intensive monitoring. The selected sites for translocation should be designed as an experimental layout and followed by frequent monitoring of those selected habitats and the reintroduced individuals [16] because the responses of I. bismarckiana plants to external factors and their habitat requirements are not fully understood. In fact, the reintroduction process of plant species cannot be judged successful unless the introduced species develop a self-sustaining population for more than four years, especially for long-lived perennials [15,16], keeping in mind that any possible threat including diseases, collection, competition with other species, and grazing should be avoided [15]. Hai et al. [1] reported that short-term criteria for evaluating the success of reintroduction projects initially include the ability of reintroduced individuals to complete their life cycle at the new site, in addition to the ability to reproduce naturally and increase the reintroduced species population. Higher chances of reintroduced species to spread their seeds to a wider extent through wind or insects support the success of the reintroduction process as this amplifies and expands the species population outside the reintroduction location. In the USA, the Center for Plant Conservation at the International Reintroduction Registry that is dedicated to saving rare plant species from extinction reported that out of 49 reintroduction projects in 2009, 76% had reached reproductive maturity, 33% of those produced a second generation, and 16% had reproductive individuals in the next generation [16]. Even though the survival rates of plants in these projects exceeded 90%, the researchers insisted that careful monitoring of these projects’ populations is necessary because they were launched over a short period of time. However, it is highly recommended to implement environmental education and awareness programs targeting local communities (especially children). This is expected to raise their awareness about the intrinsic value of these plants and appreciate the value of rare species in their region. Conservation policies should be implemented for attractive ornamental and decorative wild species and along with encouragement of the initiation of private and governmental breeding programs for such valuable species.

4. Conclusions

Dibben Forest Reserve and the surrounding area can serve as suitable habitat for I. bismarckiana. However, some sites within the reserve can serve as a refuge area for this species that are facing critical environmental (higher microclimate temperatures) and anthropogenic risks including human-made environmental consequences, grazing, and pressures from visitors trespassing. The identified zone within the reserve that shares similar habitat components to that in zone G was zone B. This zone represented a preferable microclimate for the introduced plants under investigation where it is an open flat area with a silty-loamy soil texture and slightly alkaline, non-saline, not shallow soil with a proper organic matter percentage, stone content, and soil respiration rate for healthy soils. Therefore, it can be concluded that zone B potentially corresponds to the proper zone for initiation of an I. bismarckiana reintroduction program in this semi-arid environment. However, restoration or reintroduction programs should be applied scientifically and follow long-term plans that merge an experimental setup with timely monitoring efforts to avoid accidental or unknown limiting factors that interfere with the new population’s sustainability and suppress its normal growth rate and self-regeneration.