Introduction

Orchids belong to the family Orchidaceae is the most valuable group of flowering plants that advanced in the floral variation with visually stunning blooms among the monocotyledons. Orchids are adapting to various types of ecosystems, including dry conditions (Gogoi et al., 2012). Malaysia’s rainforests are considered ‘hot spots’ of orchid diversity with a high conservation priority. At the latest count, Peninsular Malaysia is now having 972 species in 159 genera (Ong et al., 2017) and about 20% of these orchid species are endemic (Ong et al., 2011). Sabah and Sarawak harbour about 3,000 species of wild orchids with Mount Kinabalu, alone owning about 2,000 species, and Sarawak has about 1,000 species (Go & Hamzah, 2008; Go & Pungga, 2018). Orchids are one of the most threatened families yet most challenging one to conserve due to their complex biology and life history strategies (Gale et al., 2018; cited in Fay, 2018).

In general, primary forests or undisturbed forests offer favourable habitats for orchid species because of the diverse canopy structure and undisturbed ground vegetation. Oftentimes, natural forest stands are well-endowed with species in contrast to managed forests (Webb & Sah, 2003; Song et al., 2010). National Parks in Malaysia encompass an ecosystem across five vegetation types: montane forest, lower montane forest, upper dipterocarp forest, hill dipterocarp forest, oak-laurel, and lowland dipterocarp forest (Saw, 2010; JPSM, 2019). The diverse ecosystems of protected forests promise a large number of orchids and presence of the rare species (Ummul-Nazrah et al., 2011; Md Isa et al., 2018). Malaysia is one of the world’s three countries with the highest national deforestation rates. More than 80% of forests in Sarawak and Sabah have been severely affected by logging (Bryan et al., 2013; Yong, 2014). The issue of logging is exigent throughout Peninsular Malaysia, customarily, in the permanent nature forest reserve and in the surrounding areas near the Permanent Reserved Forest (PRF), the National Parks. However, there are also pockets of disturbed forests in the protected area (Usui et al., 2006; Hairul et al., 2016). Malaysian tropical rainforest is very thick, and some fragments are located far off deep into the forest and involve vast areas hidden from the attention of public, monitoring agencies, and media (Gani, 2013). Hence, detection of misconduct is low in some areas (Gani et al., 2013). Unsustainable logging activities and the natural disaster that follows has been a controversy and a threat, not merely to just human but also to the wild orchids. In the logged forests, the orchids are being exposed to the intense heat and dryness which had slowly killed them (Besi et al. 2019a).

Logged forests generally have lower orchid density if compared to disturbed secondary forests but still harbouring a higher diversity of which most are epiphytes on fallen trees (Besi et al. 2019a). However, orchids in logged forests experience extreme ecological conditions with higher surrounding temperature and lower humidity than in canopy-covered secondary forests (Werner & Gradstein, 2009). Likewise, secondary moist tropical forests regenerating after clear-cutting show shrinking species abundance if compared to mature forests (Krömer & Gradstein, 2003). The canopy disruptions affect the temperature, humidity, and light conditions inside forests, making it unfavourable for shade-adapted species (Benítez et al. 2012; Besi et al. 2019a). Species density is correlated with crown closure suggesting strong influence of microclimate on patterns of diversity and floristic composition (Werner & Gradstein, 2009). The more shade-adapted epiphytes that are susceptible to dryness are often substituted by sun-adapted ones. Open canopy forests are generally drier, warmer, and windier compared with closed canopy forests, where moisture content is higher and less variable (Gradstein, 2008; Benίtez et al., 2012; Besi et al. 2019a). Logging pose imminent impacts on the occurrence of epiphyte due to the removal of host plant species (Gradstein, 2008). Host plant characteristics (e.g., size, bark roughness, and bark pH) play an important role in epiphyte colonization (Adhikari et al., 2017; Timsina et al., 2016) and most likely due to greater bark surface available for colonization on large trees that also creates additional microhabitats (Ranius et al., 2008; Fritz et al., 2009). Host position and type, and growth of epiphytic species are influenced by microclimate conditions such as annual precipitation, humidity, and light intensity (Timsina et al., 2016; Adhikari et al., 2016). Degree of host specificity is also significant in conservation because host specialist species are more vulnerable to habitat alterations and climate change (Clavel et al., 2011), and are threatened by co-extinction with their hosts (Colwell et al., 2012).

Rescuing orchids from logging sites gives the opportunity to collect all orchids especially those from the tree canopy that leads to discovery of many new and cryptic species. Cryptic species, product of rapid evolutionary radiations within a single genus, can form suites of morphologically similar taxa or species complexes that are indistinguishable both in the field and the herbarium (Elliott & Davies, 2014). Discovering the potential presence of species complexes and lineages is an important application of DNA barcoding and floral anatomy, and this remains within the domain of taxonomy (Metacalfe & Chalk, 1979; DeSalle et al., 2005). To understand better the overall discriminatory power of the plant barcoding loci, future work on systematics and taxonomy should focus on groups that experienced rapid evolutionary radiations, for example, the closely related species within a single genus (Yan et al., 2015). Most of all, research concerning to the role of symbiotic microbiome in conservation practices are greatly insufficient but of great significance to the protection of rare and endangered orchids. Orchids are highly dependent on the relationship with mycorrhizal fungi (McCormick et al., 2018). However, the IUCN Red List of Threatened Species indicates that the mycorrhizal status of most of the threatened species has not been assessed (Bothe et al., 2010). Interestingly, most of the orchid holobionts investigations have focused on their mycorrhizal associations, overlooking at the potential role of other microbial partners (Alibrandi et al., 2020) including plant growth promoting rhizobacteria and Archaea.

Orchidaceae

Orchids belong to the family Orchidaceae is the most fascinating and valuable group of flowering plants advanced in the floral variation and distinctive form among the monocotyledons (Go et al., 2010). Roughly about 25,000–35,000 orchid species with 800–1,000 genera can be found worldwide (Gogoi et al., 2012; Zotz, 2013). Malaysia is blessed with thousands of marvellous orchids of various sizes, shapes, and colours. It is estimated that as abundant as 1,026 species in 155 genera occur in Peninsular Malaysia, of which about 215 species are endemic and 3,000 species occur in Borneo, which is estimated equal to 15% and 10% of the world’s orchids, respectively. Orchids can thrive in different types of ecosystems, especially in tropical mountainous regions like South and Central America and Andes mountains or isolated islands like Papua New Guinea and Panama (Hassler & Rheinheimer, 2013). Some orchids adapted to the extreme dry conditions such as semi-desert habitats (Pridgeon, 2014). All members of Orchidaceae are considered rare, endangered and one of the global conservation objectives that are afforded protection at local, regional, national, and international scales (Cribb et al., 2003; Fay, 2018).

Important and Uses of Orchids

Orchids are of conservation objectives due to their research and commercial importance, and intrinsic aesthetic value within their habitats (Flores-Palacios & Valencia-Diaz, 2007; Cruz-Fernández et al., 2011). Orchids are a widely known as a very valuable ornamental plant. Enthusiasts cultivate orchids as cut-flowers and ornamental because of their exotic beauty and long-lasting blooming period (Hew et al., 1997; Go et al., 2010). Most wild and hybrid species of orchids are the result of high-value agricultural and horticulture products. Orchid floriculture is a lucrative industry in Malaysia, and in Sarawak in particular. Floriculture industry in Malaysia contributes largest income earner and export value, recorded an export value of RM 417.3 million in 2021 compared to RM 403 million in the previous year. In Sarawak, planting materials, cut flower and foliage contributes RM 551,755 (Source: Department of Agriculture Sarawak). The hybrid orchid is one of the major contributors to the decoration industry in Malaysia because of its beautiful, fragrant, and durable flower. The Malaysian orchids floriculture industry contributed 40% of total value of country’s floriculture production with the annual growth rate 6–9% (Source: Department of Statistics Malaysia). Moreover, orchids are now customary utilized as herbal medicines, food, and flavour (Pant, 2013). For instance, seed pods of Vanilla planifolia, Vanilla × tahitensis, and Vanilla pompona are processed for ‘Vanilla’ essence, and Phalaenopsis equestris is globally domesticated as a perfume in China (Go et al., 2010; Cameron, 2011; Gallage & Møller, 2018). In Malaysia, there are at least twelve species of Vanilla. Unfortunately, so far, no Malaysian species have been grown commercially for fruit or ‘vanillin’ production, although some of the species produce reasonably big pods of up to 20 × 1.2 cm in size and are reportedly sweet scented (Go, 2019). In Malaysia, there are several species of orchids that can be used in traditional medicine. For example, plants of Acriopsis javanica (sakat rawang, sakat ubat kepialu), Corymborkis veratrifolia (hancing Ali, lelumbah paya), and Phalaenopsis amabilis (orkid kupu-kupu or moth orchid) are crushed and used to relieve fever (Go, 2019; Burkill, 1966). Dendrobium crumenatum, also known as orkid merpati or pigeon orchid, is also used for treating ears (Burkill, 1966). Orchids occurrence in every habitat, undisturbed and disturbed forests in Malaysia proves its importance as an ecological indicator of climate change of a forest as their survival and distribution were observed greatly affected by changes in temperature and water availability (Go et al. 2015a; Besi et al. 2019a).

Life Form and Growth Patterns

Orchid species own very attractive trimerous flowers composed of three inner petals and three outer sepals, and a single large gynostemium (Dressler, 1981). Orchids use its flower to draw pollinators for reproduction by scent, mimicry, and stealth, as a driving force in orchid diversification and speciation (Cozzolino & Widmer, 2005; Gaskett, 2011). The life-form of a plant species in a particular ecosystem is the sum of its all-life processes and evolved directly in response to the environment (Cain, 1950) and are said to be the indicators of micro and macroclimate (Shimwell, 1971; Saxena et al., 1982). In nature, Malaysian orchids presented in different sizes and forms that some of them can be so small such as most of the Bulbophyllum species, leafless such as Taeniophyllum species, and some of them can weigh to hundreds of kilograms like Grammatophyllum species, and creeper and climber with several meters long like Galeola and Vanilla. About two-thirds of the total orchid species are predicted to grow on another plant as epiphytes in tree canopies (Gentry & Dodson, 1987; Gravendeel et al., 2004), whereas the remaining are terrestrials grow in the ground, lithophytes grow on exposed rocks, rheophytes grow on rocks in running water and mycoheterotrophs grow in soil rich in decaying matters (Go et al. 2015b). There are two main growth structures: sympodial orchids have base part sends out new leaves and pseudobulb that peaks with a flowering spike (inflorescence) at the end of each growing season, and monopodial orchids have main stems which grow constantly which produce inflorescences, mostly from Aeridinae (Go et al., 2014).

Classification

All pre-DNA era classifications for Orchidaceae were based on a relatively small set of morphological and anatomical features, particularly aspects of the gymnostemium (Gřniak et al., 2010). Dressler (1993) recognized five subfamilies: Apostasioideae, Cypripedioideae, Orchidoideae, Spiranthoideae and Epidendroideae. Chase et al. (2003) presents putative ideas of phylogenetic relationships and character evolution and restructured Dressler’s circumscription. Undeterred by low taxon sampling, the results of this study supported the division of the orchids into five subfamilies: Apostasioideae, Cypripedioideae, Epidendroideae, Orchidoideae, and Vanilloideae (Chase et al., 2003). Also, the later topology of a Xdh-derived tree for these subfamilies sensu clades presented in Gřniak et al. (2010) is mostly congruent with the molecular DNA classification of Chase et al. (2003).

Undisturbed and Disturbed Forests in the Tropics

Primary forests are old-growth forests that have experienced little to no recent anthropogenic disturbance, although, few primary forests are genuinely pristine (Gibson et al., 2011). In general, undisturbed ecosystem is defined as ‘old growth’, ‘natural’, ‘undisturbed’ or ‘pristine’ forest (Spake & Doncaster, 2017). Usage of ‘undisturbed’ term is not always appropriate; however, an exception can be applied for generalizations, and the concept of ‘pristine’ forest may be inappropriate in the current era of prevalent anthropogenic change (Ghazoul et al., 2015). These forests have grown undisturbed for many decades with optimum ecological conditions providing ecosystem services such as water catchment, wildlife habitats, carbon sequestration, and food security (Law, 2021). In these biodiverse tropical forests, many species are rare, and populations of all species may fluctuate considerably over decades (Newbery et al., 1999). Undisturbed forest areas constitute only about 6.8% of the total land area in Peninsular Malaysia. Within the forested areas, the National or State Parks and the Wildlife and Bird Sanctuaries are the best-protected areas with no logging allowed (Saw, 2010). Within National Park, the Terengganu Hills, an undisturbed forest enriched with endemic species as their flora is known to show similarities to the flora of Borneo (Ashton, 1992). In Borneo, besides Kinabalu National Park, Crocker Range National Park (CRNP) emerges as one of the most interesting areas for orchid diversity studies in the northern part of the island. With an area of 1,399.19 km2, this park gazetted as the largest terrestrial and protected area in the state of Sabah (Majit et al., 2014). Native orchids diversity could be associated with forest age (Bergman et al., 2006; Cohen & Ackerman, 2009). As the forests become older, their trend is to reduce in tree density and to increase in both mean tree size and in the density of standing dead trees (Lee et al., 1997; Vanderwel et al., 2006). The old primary forests contain a large amount of standing wood and trees with large mean size (Cruz-Fernández et al., 2011) which often observed as favourable habitats for epiphytes. Apparently, sometimes the damaged standing trees could also harbour epiphytes (Mikhailova et al., 2005; Fritz et al., 2009). Even though the stringent protection of old-growth forests remains a conservation priority globally, the potential for other types of forests to preserve biodiversity should be explored too (Putz et al., 2008). It is now probable for any assessments of biodiversity and ecosystem service to include data pertinent to management decisions covering variable management regimes (Whigham & Willems, 2003; Spake & Doncaster, 2017). Unsustainable human land-use changes are of serious concern in Southeast Asia, particularly timber extraction for expansion of oil palm monoculture and exotic-tree plantations (Koh & Wilcove, 2008; Gibson et al., 2011) that could be damagingly impact the wild orchids wellfare (Cruz-Fernández et al., 2011).

Disturbance is discrete and sudden event in time that disturbs the structure of ecosystems, communities, populations, resources pools, substrate availability, or the physical environment (Pickett & White, 1985; cited in Calderon-Aguilera et al., 2012). Forest disturbance occur with a wide range of temporal and spatial scales, and are characterized by their extent, spatial arrangement, frequency, predictability, and magnitude. Large disturbance is disastrous such as deforestation, hurricanes, extreme floods, volcanic eruptions, and large fires (Turner et al., 1997; Turner & Dale, 1998; cited in Calderon-Aguilera et al., 2012), whereas small disturbance is likely non-destructive such as branch and tree falls in a forest (Martίnez-Ramos et al., 1988; cited in Calderon-Aguilera et al., 2012). The quality and biodiversity of forest ecosystems are experiencing rapid conversion under the influence of a broad range of man-made and natural disturbances (Calderon-Aguilera et al., 2012; Yong, 2014). The effect of deforestation on global and local climate changes has been neglected by the conservationist and authority due to lacking workforces willing to work in risky and fragile logging sites (Besi et al. 2019a). Moreover, forest remnants or fragments in anthropogenically disturbed ecosystems might be essential for biodiversity conservation (Gibson et al., 2011). Forest degraded by repeated logging and fires, as well as secondary and plantation forests, are escalating (Wright, 2005; Chazdon, 2008). In the tropics, frequent forest disturbances of low to moderate intensity, occurring largely at random, continually affect forest growth and composition (Huston, 1979, 1994; Shugart, 1998). The disturbed forests need protection to prevent continual disturbance and further long-term carbon emissions (Maxwell et al., 2019; Reid et al., 2019). In Malaysia, the disturbed lowland forest turns into secondary forest dominated by mainly pioneer species, bamboo, and a variety of small shrubs with big open patches of grass such as Imperata cylindrica (Go et al., 2010). The secondary, disturbed or logged-over forests often dominates the remaining forested land in Southeast Asia (Bryan et al., 2013). The secondary forests or any large area of forest remnants can be a functional complement to primary or undisturbed forests in sustaining biodiversity and should be considered as equally important for conservation (Dent & Wright, 2009). The forests provide supplements for natural regeneration, including a source of seeds, wildings, and cuttings to produce resilient planting stock, and habitat for supporting biodiversity, including seed dispersers and pollinators (Di Sacco et al., 2021).

Primary Legislations for Plant Diversity Conservation in Malaysia

In Malaysia, forest resources utilization and plant species protection are regulated by forestry legislations as per specified under Article 74(2) of the Malaysian Constitution (Gani et al., 2013). Primarily, the National Forestry Act 1984 (amended 1993) and National Forestry Policy of 1978 are followed in safeguarding forest resources from violation (Chiew, 2004; Gani et al., 2013). These acts are accompanied by the Wood-Based Industries Act 1984 which regulates to guarantee the rational development of wood-based industries (Wood-Based Industries 1984, 2020, April). In Peninsular Malaysia, the most important policy-related legislation in terms of forest law and enforcement is the National Forest Policy 1978 (NFP) (National Forestry Policy 1978, 2020, April). The main goal of the National Forestry Policy and the National Forestry Act 1984 is to sustain timber production for perpetuity, make up over 85% of forests in Peninsular Malaysia. The National Forestry Act 1984 provides for the establishment of the Permanent Reserved Forests (PRF) that is further subcategorized into 12 functional classes: Timber Production Forest, Soil Protection Forest, Soil Reclamation Forest, Flood Control Forest, Water Catchment Forest, Forest Sanctuary for Wildlife, Virgin Jungle Reserve, Amenity Forest, Education Forest, Research Forest, Forest for Federal Purposes, and State parks. Under the forestry laws, the PRF are under the jurisdiction of the Forest Departments of Peninsular Malaysia (FDPM), while national parks and wildlife sanctuaries are managed by the Department of Wildlife and National Parks Peninsular Malaysia (PERHILITAN) (Weng, 2002). In Sabah, the State Forest Policy of 1954 and the Forest Enactment policy of 1968 are the dominant state laws (Forest Law of Sarawak 1954, 2020, April). Similarly, Sarawak’s Statement of Forest Policy of 1954 and the Forests Ordinance of 1954 control operations there. Also, under Sarawak Wildlife Protection Ordinance 1998, all orchids are listed as protect plants.

Trend and Overview of Logging in Malaysia

Practical forestry involves harvesting, measuring the large tree, assessing the growth of the next potential coupe, and counting and establishing seedling bank as a predictor of over storey regeneration (Newbery et al., 1999). Tree species with small stems are abundant quantitatively and are densely occupying some forests in Malaysia, for instance like Danum valley (Newbery et al., 1992, 1996). By 1991, Malaysian primary forests were greatly diminished by deforestation. Of the total 132,104 km2 of land area of Peninsular Malaysia, only a total of 57,341 km2 remained as primary forests (World Bank, 1991; Yong, 2014; JPSM, 2019). In 1977, the proposed area for logged-over forests as recommended by the National Forestry Council was 20,000 km2, however, by 1991, it was increased to 24,000 km2, which showed that logging was happening in logged-over forests because most of the primary forests were gone (World Bank, 1991; Yong, 2014). Between 2001 and 2019, forestry departments in Peninsular Malaysia reported total forest loss of 2,456 km2. In contrast, primary forest loss reported by satellite imagery is thrice that at 7,584 km2 (Law, 2021). After logging, logged forest areas were turned into plantations (mostly for oil palm) and industrial trees, for a set period (Yong, 2014; Law, 2021). In 2012, less than 5% of Sarawak’s primary forests remain unlogged (Global Witness, 2012). In Peninsular Malaysia, detection of illegal logging in the PRF and the government land from 2006 to 2011 were 222 cases (FDPM, 2012; cited in Gani et al., 2013). Illegal logging well-defined as logging without a permit and outside a licensed area and construction of infrastructure including unauthorized building of forest roads (FDPM, 2003; cited in Gani et al., 2013). Policies implemented by the state government are incidental to this issue. The high tender price charged for timber harvesting rights caused timber companies to log areas that not agreed to them to recover costs from timber harvesting operations (Rusli, 1999; Gani et al., 2013). In summary of an article written by Law and published in Macaranga in March 2022, forest reserves can be selectively logged but clear-felling was prohibited except for developing limited plots of forest plantations. However, the rules were altered when the National Land Council permitted forest plantation zones of 4,392 km2 within forest reserves (covers 9% of forest reserves) in Peninsular Malaysia in 2012 (Law, 2022). According to the author, from the year 2007 to the year 2020, a total of 2,568 km2 in reserves was cleared (covers 5.2% of reserves in Peninsular Malaysia). By year 2020, there was 1,212 km2 of forest plantations established inside forest reserves in Peninsular Malaysia. The situation deteriorates when planters omit to replant trees.

Identifying Knowledge Gaps and Challenges to Better Protect Orchids in Disturbed Forests

Ideas on the effect of climate change and global warming due to anthropogenic activities are largely driven by studies on those plant species with wind-dispersed pollen, and the response of herbaceous and understory species (Miller & Brubaker, 2006; Liu et al., 2010). As selective logging continues to expand across the tropics, understanding its long-term impacts and contacts with varies forms of forest disturbance (Asner et al., 2009; Gardner et al., 2009) vitals for the conservation of tropical biodiversity. Anthropogenic driven climate changes have been an obstacle for conservation biologists because the projected warming has resulted in a hotter and drier, much beyond tolerable level (Davis and Shaw 2001; Barnosky 2010; Besi et al. 2019a). Under anthropogenic disturbance, species respond primarily by shrinking in population size (Cribb et al., 2003). Migration might not overcome environmental alterations as a result of climate change even with the presence of their adaptive survival strategies (Cribb et al., 2003). Plus, it is critical that habitat fragmentation and resources non-availability may impede natural migration because of the complex terrain and limited area for colonization (Liu et al., 2010). Ecological specificity of terrestrial orchids was still poorly studied in Malaysia. Especially, the orchids-microbiome alliances which are delicate and sensitive to environmental factors (Batty et al., 2001; Tadych et al., 2009). Also, vertical stratification of epiphytic orchids assemblages and its association with the microclimatic gradients within vegetation and occurrence of bryophytes and lichens requires supporting evident. For future studies, it is important to cover key functional differences in order to disentangle the complex diversity-ecology relationships. Although some studies suggest that logged forests could retain a high richness of forest taxa (Edwards et al., 2011), there are a number of important aspects must be considered: (i) if logged forests are adjacent to undisturbed forests, spill-over effects might overstate the species richness of logged forests (Prugh et al., 2008); (ii) the proximity of logged forests to undisturbed forests can be the occasion of species extinction debts that are repaid over lengthy periods of time (Gibson et al., 2011); (iii) repeated logging might further intensify the disturbance impacts on biodiversity (Gibson et al., 2011); and (iv) the networks of forest roads or skid trails created by logging activities ease human immigration to forest interiors and frontiers, trigger fires and forest conversion (Laurance et al. 2009; Besi et al. 2019a).

The Action Plan drafted by IUCN SCC group suggests dual strategies to conserve orchid diversity (IUCN SSC Orchid Specialist Group, 1996; compiled by Alec M. Pridgeon); (i) establishing in-situ protection of natural habitats, and (ii) promoting trade of artificially propagated plants and cut flowers. Shown below are the specific priority actions recommended in the Action Plan and shown in Fig. 1 is the proposed conservation framework for orchids of Malaysia:

  • publications of global checklists of orchid species, including the notes on identification of the high biodiversity areas.

  • legislation and funding to support the protection, research, and management and monitoring of the identified areas.

  • provide resources for propagation material of rare and new species for commercialization, preferably in those countries where the species are native, thereby reducing demand for wild-collected plants.

  • rescuing efforts for orchid plants from areas of deforestation where appropriate, followed by artificial propagation and distribution.

  • inclusion of educational programmes on orchids and their role in biodiversity by orchid societies and botanical gardens to the public.

  • registration and involvement of bona fide herbaria and scientific institutions belonging to CITES party countries to enable freer movement of pressed and liquid-preserved plant materials for scientific purposes.

  • allocations of plants, seeds, and pollen from and among orchid growers and botanical gardens for conservation purposes.

Fig. 1
figure 1

Proposed integrated orchid conservation approach for conservation of orchids in Malaysia. The framework was modified based on a model developed for the conservation and recovery of Caladenia huegelii in Western Australia; Swarts (2007) cited in Swarts & Dixon (2009)

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Flora Diversity Patterns in Malaysia

Four phytogeographical provinces are known in Peninsular Malaysia: Northern Province, Perak Province, Continental Intrusion, and Riau Pocket, based on species assemblages (Wong, 1998). The Riau Pocket covered Southeast Johor to the entire east coast of Peninsular Malaysia, Singapore, Banka, Riau Islands, Southeast Sumatra, and Northwest Borneo. It gives inference that these areas harbour similar flora element (Kiew & Saw, 2019). The Northern Province lies in the northwest of Peninsular Malaysia experiences a monsoon climate (Kiew & Saw, 2019). The province houses a distinctive congregation of species and has a close similarity with the flora of southern Thailand (Ridley, 1922; Van Steenis, 1950; Whitmore, 1984). Peninsular Malaysia has similarity with Borneo in plant species diversity, especially plants species that occur within the Northwest Borneo Province: the eastern sub-province covering from the Crocker Range, Sabah, to the Lupar River, Sarawak; and the western sub-province covering from the Lupar Valley, Sarawak, to the Kapuas Lakes, Kalimantan (Ashton, 1992, 1995). Forest biodiversity research in these phytogeographical provinces typically measure the biodiversity value corresponding to its value in a reference state with attributes of an undisturbed ecosystem (Bullock et al., 2011).

Diversity Assessment for wild Orchids in the Disturbed Forests

Diversity assessment is based on the species richness and species evenness in specific area. As species richness and evenness increase, so diversity increases. Species richness must generally be estimated based on samples as the relative abundance influences the diversity value (Chao, 2004). Collecting evidence such as pH, temperature, light, slope, moisture, and degree of disturbance is important in explaining the index value. Species richness is used in conservation studies to evaluate the sensitivity of ecosystems and the inhabitants. Conducting a full count of the number of species in an ecosystem and a relatively large area is nearly impossible, so sample plots at a variety of sites is important to avoid repetitive counting. However, there is no available guideline for sampling plots design for highly disturbed forests, such logging sites own not just altered vegetation but also altered topography. Also, positions of the orchids in the logging are largely dependent on the position of the fallen trees. Orchids are sensitive to both microclimate conditions and anthropogenic disturbance, because of their intricate biology (Christenson, 2003; Zhang et al., 2018). The uncontrolled logging activities and the aftermath mud floods that occurred in Peninsular Malaysia reduced the quality of the wild orchid habitats and their species diversity. Wild orchids welfare in these extremely disturbed areas is being neglected due to the inaccessibility and harsh environment (Besi et al. 2019a; Go and Besi 2020). The logged forests had a higher ambient temperature and lower moisture level than the mud flood-disturbed and canopy-covered secondary forests. Based on a study on the diversity of orchids in the logging sites in Terengganu, besides the massive ground vegetation clearing, low soil moisture and the absence of leaf litter were majorly caused by the low abundance of terrestrial orchids in the logged forests. High richness of epiphytic orchids and large difference of their densities in the logged forests are strongly associated with the densities of fallen trees hosting orchid(s), disturbance-induced dryness stresses, durations of exposure to disturbance, and altered soil conditions due to vegetation clearance by tractor (Wan Mohd Shukri et al., 2007; Besi et al. 2019a). Also, phorophyte age and existing orchid richness of an area may affect colonization of epiphytic orchids in the disturbed and undisturbed forests (Huda & Wilcock, 2011). However, deforestation in the logged area resulted in major loss of epiphytic orchids (Gradstein, 2008), given a very low number of surviving plants were salvaged from the logging sites in the Terengganu area (Besi et al. 2019a). Besi et al. (2019b) reports on 280 orchid species found and rescued from the disturbed forests in Terengganu, Peninsular Malaysia, including the newly recorded and endemic species. Almost all the epiphytic orchids found were collected from the fallen trees in the logged forests of the Kenyir Lake area. Of these, Bulbophyllum and Dendrobium were the most abundant genera lived in these extremely disturbed forests (Fig. 2). Dendrobium mizanii, a new species to science discovered at the summit region of a disturbed montane forest in Terengganu (Besi et al. 2018a). Another two new Dendrobium species, D. ainiae and D. ruseae were found in a disturbed lowland dipterocarp forest in the same area (Besi et al. 2018b). Also, a new Bromheadia petuangensis rescued from an active logging site in Hulu Terengganu has increased the total of orchid species recorded for Terengganu to 318 species in 92 genera (Besi et al. 2019a, 2020a).

Fig. 2
figure 2

Number of taxa associated with the different genera in the disturbed forests in Peninsular Malaysia

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Forest Ecology and Orchid Structural Adaptations

As most of the central Asia experiences a monsoon climate with a dry season, Peninsular Malaysia located within the equatorial zone, and experiences rain throughout the year (Kiew & Saw, 2019). The different climate profoundly affects the flora composition (Van Steenis, 1950). Data from the analysis of climate by Walsh (1996a, b); Walsh and Newbery (1999) supports the inference that possibly Sabah’s lowland forest is constantly drought-disturbed and recovers. Comparatively, the Bornean rainforest has an equitable aseasonal climate (Brünig, 1969, 1971), in explaining the heath forest formation in northwest Borneo. Sporadic dry periods are part of the decadal and century-scale environmental fluctuations across Borneo’s rainforest (Newbery et al., 1999). Based on studies on epiphytes in dry forests, epiphytes in dry season may receive up to nine times more photo-synthetic photon flux density (PPFD) compared to the wet season (Graham & Andrade, 2004). Under dry conditions, dew and fog formation can be a main source of water or moisture for these plants encourages the vertical distribution of epiphytes (Andrade, 2003; Chesson et al., 2004; Graham & Andrade, 2004; Reyes-García et al., 2008). Upon the projected warming, increase in the precipitation and evaporation rate will eventually result in decrease of soil moisture (Bates et al., 2008). However, too much rainfall occurrence also can accelerate erosion and may wipe out the cliff and lowland terrestrial populations (Besi et al. 2019a). Habitat destruction threatens orchid species to a different degree of severity based on geographical distribution, habitat specificity, and population size. Some species have restricted distributions (endemic and rare species) and require large stands of forest for reproductive success and are now facing extinction due to the loss of vital pollinators and genetic erosion (Cribb et al., 2003). In conjunction to the above, the impact of extreme environmental conditions on plant-pollinator would lead to disruptions and even extinction of both plant and insect species, supported by Memmott et al. (2007). There is limited information about orchids’ physiological responses to habitat and ecology alterations (Cruz-Fernández et al., 2011). Anthropogenic activity limits orchids reproductive success indicating that human-induced disturbance hinders orchid-pollinator mutual relationship (Huang et al., 2009). Some ecological studies suggest that epiphytic orchids can survive in human transformed habitats (Williams-Linera et al., 1995; Solís-Montero et al., 2005; Flores-Palacios & García-Franco, 2008). Also, very few studies reported on the mycorrhizal fungi of leafless epiphytic orchids. Qin et al. (2021) revealed that the leafless epiphytic orchids have a highly specialized association with Ceratobasidiaceae. Apart from mycorrhizal fungi, free-living and symbiotic bacteria (e.g., Rhizobia and Frankia species) associate with orchid roots remain poorly explored (Basu et al., 2017; Herrera et al., 2022). Moreover, there are studies that have made known that terrestrial orchids could not persist in secondary habitats (Williams-Linera et al., 1995; Bergman et al., 2006; cited in Cruz-Fernández et al., 2011). And there are orchid species can thrive in both undisturbed and disturbed forests (Cohen & Ackerman, 2009). Though some studies based on herbarium voucher specimens and historical records report that epiphytic and terrestrial orchids (Espejo-Serna et al., 2005; cited in Cruz-Fernández et al., 2011) can survive in transformed habitats, while other studies report local extinction of orchid species in certain habitats (Olmsted & Juárez, 1996; Sosa & Platas, 1998; Jacquemyn et al., 2005). In the logged forests, epiphytic species are particularly susceptible to local extinction (Turner et al., 1994) due to the removal of their host plants (Go & Besi, 2020). Most of the orchids collected have fleshy and thick stems and leaves which are also presumed to have thick epidermis and cuticles layers (Benzing, 1990; Helbsing et al., 2000), mostly adapted by Bulbophyllum species, and several species of Dendrobium, Eria, Grammatophyylum, Pholidota, Pinalia, and Thrixspermum. Some species were with thin, broad, and plicate leaves such as in the epiphytic Coelogyne species, and terrestrial Calanthe and Corymborkis species (Besi et al. 2019a) (Table 1).

Table 1 General morphologies of orchids found in disturbed forests in Peninsular Malaysia
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Two commonly known adaptive strategies for orchids to water deficit are ‘drought escape’ and ‘drought avoidance’. The epiphytic orchids employed ‘drought escape’ by being deciduous, shedding leaves and roots at dry conditions and leaving dormant pseudobulbs or stems to minimize transpiration (Zhang et al., 2016), which occurred in Acriopsis, Appendicula, Bulbophyllum, Dendrobium, and Pholidota. These orchids adapt their vegetative and reproductive growth according to the water availability, essentially through two different mechanisms: short-cycled phenological development and developmental plasticity (Jones et al., 1981; Basu et al., 2016). Suberized cells (velamen radicum) found on the roots of mostly monopodial orchids provide a barrier to transpirational water loss when the environments are dry (Zotz & Winkler, 2013; Zhang et al., 2016) and protects the roots against sun radiation damage (Chomicki et al., 2015). Meanwhile, the evergreen species demonstrated ‘drought avoidance’ phenology by increasing water uptake and reducing water losses through its broad leaves with denser veins and stomata, and succulent pseudobulbs with thick storage tissues. Both epiphytic and terrestrial orchids employed the ‘drought avoidance’ mechanism by being able to maintain higher tissue water content despite reduced water content in the surrounding (Levitt, 1980; Basu et al., 2016).

Also, orchids survival depends on specialized pollination systems, symbiotic relationship with mycorrhizal fungi, and mass seed production (Ackerman, 1986; Gravendeel et al., 2004). Species with larger peduncles tended to have larger inflorescences and larger flowers indicating inflorescence and peduncle size can be correlated with biomass allocation to reproductive organs (Feng et al., 2021). Flowering orchids could undergo self-pollination due to the extreme environmental conditions signified there was a very rare possibility for a cross-fertilization by insects in these ecological marginal areas to occur. Self-fertilization is an evolution strategy adapted by monoecious (male and female reproductive organs in the same individual) orchid species to increase the chances of producing sterile seeds during unfavourable conditions (Stebbins, 1957; Piper et al., 1984; Liu et al., 2006). This mode of pollination occurs under windless, drought conditions when insects are scarce to ensure the plant’s reproductive success (Wang et al., 2004, Liu et al., 2006). However, this adaptation is not applicable to dioecious (male and female reproductive organs in separate individuals) plants. Besides, these adaptive responses might only lead to the orchids continued survival, but not to their population diversification. Direct exposure to sun radiation cause burn and browning of the plant parts, which would eventually lead to injuries and death (Besi et al. 2019a) (Fig. 3). Higher the temperature and lower the moisture induces lower the turgor pressure in plant cells (Beauzamy et al., 2014) explains the displays of signs of dying such as flowers or buds browning, flowers or buds dropping off and dormant, and pseudobulbs browning and shrivelled in the disturbed forests (Besi et al. 2019a).

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Epiphytic orchids on the fallen trees and ground threatened by direct exposure to the heat, sun irradiation and dryness in the logging sites

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Host Characteristics and Specificity in Vascular Epiphytes Key Factors for Maintaining High Orchid Diversity in Tropical Forests

Learning the degree of host specificity of epiphytes is a significant part of the ‘diversity jigsaw puzzle’ (Kitching, 2006). Strong host specificity by host-dependant species opens the possibility for sympatric speciation and may allow species coexistence by habitat niche balance (Wagner et al., 2015). Learning the degree of host specificity is also accommodating in a conservation context because specialist species are generally more vulnerable to habitat alterations and climate change (Kitching, 2006; Clavel et al., 2011). The orchid abundance per host species positively correlated with the number of host individuals (Timsina et al. 2016; Besi et al. 2019a). Based on the previous studies (Hietz, 1999; Callaway et al., 2002; Partomihardjo et al., 2004; Adhikari et al., 2012; Hsu et al., 2014), epiphyte abundance depends on different host characteristics. Tree architecture, bark stability, bark texture, bark peeling rate, and water-holding capacity is often hypothesized to be the main variables for the suitability of trees as host plants (Castro-Hernández et al., 1999; Callaway et al., 2002; Cardelús & Chazdon, 2005; López-Villalobos et al., 2008; Wagner et al., 2015). Epiphyte occupancy and abundance per tree associate with two variables: tree age (Huda & Wilcock, 2011; Zotz & Vollrath, 2003) and substrate area (Zotz & Vollrath, 2003). Also, it associates with the growth adaptation where abundance is higher on evergreen than on deciduous hosts (Hirata et al., 2008). Epiphytes are abundant on tall trees because tall trees are more exposed to light (Timsina et al., 2016). However, the evidence for host specificity is difficult to obtain due to the complex vegetation structure and the multitude of host traits (Wagner et al., 2015).

Effects of the Method of Tree Extraction on Forest Structure and Potential Host Plants for Orchids in Malaysia

Tree extraction method need to be controlled to reduce damage on forest structure, composition, and regenerating capacity for achieving sustainable forest management to compensate for the loss caused by deforestation (Pinard & Putz, 1996). Reintroduction of locally extinct species into their former habitat is not possible when the intact habitat is no longer present (Schuiteman & Vogel, 2003). Degree of damage is measured by felling intensity (number or volume of trees felled per hectare) that strongly influenced by method of the logging practices (Hendrison, 1990; Webb, 1997; cited in Seng et al., 2004). The regularly utilized methods of tree extraction in Malaysia, include conventional, mechanized, and selective logging (Seng et al., 2004). Selective logging produces disturbances like natural treefall gaps (Webb, 1997) and does not significantly alter forest structure (Matthews, 1989), but stimulates natural regeneration and growth with formation of gaps (Hartshorn, 1989). However, removal of superior adult and old trees drives species loss (Willottf, 1999) and reduces the genetic quality of the remaining and successive regenerating gene pools (Seng et al., 2004; Bergman et al., 2006) that would therefore cause a decline in epiphytic orchid abundance (Huda & Wilcock, 2011). Also, logging in any forms still leads to severe disturbance to the soil and water catchments that upsets the establishment of seedlings and regeneration and can perilously alter the species composition and stand structure (Cannon et al., 1994; Van Gardingen et al., 1998). The most abundant families occurring in the before and after logging plots in forest reserves with an average elevation (~ 300 m a.s.l.) are Dipterocarpaceae, Myrtaceae, Annonaceae, Lauraceae, Myristicaceae, Euphorbiaceae, Burseraceae and Ebenaceae, and of these, the commonest species are Dryobalanops, Shorea and Hopea species (Seng et al., 2004). Forest edge shows greater impoverishment, but similar epiphyte floristic affinity to closed canopy forest types and their assemblages are influenced by the microclimatic changes (Werner & Gradstein, 2009). Because of the high reliability of epiphytes to abiotic factors, especially moisture, changes in the local climate have a substantial impact on their diversity (Lugo & Scatena, 1992; Benzing, 1998).

Complication in Systematics and Diversity Predictions Remains a Conundrum

One of the most pressing issues in modern systematics is the choice of most diagnosable version of species concept in the decision to a species status. Regardless of the species concept adopted by a taxonomist, full range of a species’ biological variation is imperative in consideration of what a species is (Pridgeon, 2003). Correct identification in species-rich or taxonomically challenging groups also needs expert knowledge, which is lacking, especially in tropical areas (Phillips et al., 2003; Webb et al., 2010). The classical method of species determination frequently also warrants expert interpretation. However, most species are studied by only a few specialists, and even specialists frequently encounter specimens that cannot be reliably identified. Most morphological characters represent expression suites of many genes, and, thus, their relationship amongst at intergeneric and infrageneric levels should be mirrored in the phylogeny (Patterson et al., 1993; Gřniak et al., 2010). In the early classification, floral characters, especially the anther and pollinarium structures, were the primary basis for classification of orchids (Dodson, 1962; Romero, 1990). However, gynostemium prones to selective pressure from pollinators, hence, they are likely to display high levels of convergence or parallelism (Dodson, 1962; Atwood, 1986). Therefore, the instability has caused contradictions in systems of orchid classification (Burns-Balogh & Bernhardt, 1985; Dressler, 1981, 1993; Rasmussen, 1985; Szlachetko, 1995). Pending the evaluation of these questions by classical techniques, new technology enables the application of molecular analysis for orchid systematics (Cameron et al., 1999). Genetic-based trees indicate that some floral and vegetative attributes and fungal symbionts have more complex evolutionary histories than previously postulated (Kores et al., 2001). Through phylogenetic analysis, a major generic change has been made to Malaysian orchid genera like Ascocentrum, Aschochilopsis, Biermannia, Chelonistele, Cordiglottis, Dendrobium, Entomophobia, Geesinkorchis, Eria, Malleola, Microtatorchis, Nabaluia, Panisea, Pholidota, Tuberolabium, Ventricularia, and Ornithochilus (Clements, 2003; Cribb & Ng, 2005; Schuiteman, 2011; Gardiner, 2012; Kocyan & Schuiteman, 2014; Chase et al., 2021). The taxonomic revisions may cause changes in the species richness of an area. Therefore, further integrative morphology-molecular genetic (phylogenetic) analyses with greater taxon sampling may be desirable for some groups to establish more robust phylogenetic hypotheses and to ascertain the generic changes.

Molecular Identification of Orchid Complexes Based on the Nuclear and Plastid DNA Barcode Regions and Its Application for Phylogenetic Study

Current molecular DNA analysis in Orchidaceae, at the lower taxonomic levels, involves non-coding plastid markers and nuclear ribosomal internal transcribed spacer (nrITS) marker (Gřniak et al., 2010). At the higher taxonomic levels, family level in particular, plastid protein-coding genes have been the primary focus. Such as ribulose bisphosphate carboxylase large chain (rbcL), maturase K (matK), Photosystem I P700 chlorophyll a apoprotein A2 (psaB), and Yeast Cadmium Factor gene (ycf1) (Chase et al., 1994; Cameron et al., 1999; Cameron, 2004; Freudenstein et al., 2004; Neubig et al., 2009). In addition, phylogenetic analyses using nuclear ribosomal 18 S rDNA and the mitochondrial Nicotiana alata Defensin 1 (nad1b-c intron) (Cameron & Chase, 2000; Freudenstein et al., 2000; Freudenstein & Chase, 2001) have been trendy for Orchidaceae in the present-modern plant systematic era. The use of DNA as a tool for species identification and enhancing the discovery of new species is known as “DNA barcoding” (Floyd et al., 2002; Hebert et al., 2003; Remigio & Hebert, 2003). DNA barcoding is a technique using a short and standardized DNA fragment to discriminate among species (Parveen et al., 2012; Hosseini et al., 2012; Moudi et al., 2013; Moudi & Go, 2016; Hosseini et al., 2016; Rajaram et al., 2019). Regardless of the morphological parts of samples and the professional level of users, the technique should consistently identify a species (Sun & Chen, 2013). DNA barcoding is inefficient for identification in taxa where taxonomic study and morphogical description have not been detailed, and species delimitation is limited to a few traditional morphological character sets, untested by additional studies and tools (Meyer & Paulay, 2005). In plants, several candidate genes of Chloroplast DNA [including matK, rbcL, an intergenic spacer located between the psbA and trnH gene (psbA-trnH), and an intergenic spacer between atpF and atpH encode ATP synthase subunits CFO I and CFO III (atpF-atpH)] and the nuclear internal transcribed spacer (nrITS) region of the nuclear ribosomal DNA have been promoted as plant barcodes (Kress & Erickson, 2007; Lahaye et al., 2008; CBOL Plant Working Group et al., 2009; Chen et al., 2010). The approach for Malaysia has been genus-by-genus (Bulbophyllum – Hosseini et al., 2012, 2016; Dendrobium - Moudi & Go, 2016; Paphiopedilum – Rajaram et al. 2019; Coelogyne – Yoh et al., 2022; Spathoglottis – Nordin et al., 2022) and rare and endemic species due to the tremendous number of species present, and fund constrained.

One disadvantage of using DNA sequences from a plastid or chloroplast gene is the possibility those resulting phylogenetic topologies may not represent the true phylogeny because of hybridization (Smith & Sytsma, 1990). Orchidaceae is well known as a family in which hybridizations are common occurrence. Orchids interspecific and intergeneric hybrids are the foundation for a developing horticulture and cut flowers markets (Cameron et al., 1999). In this day and age, there is a critical need for rigorous species delineation for many theoretical studies and practical applications (Dayrat, 2005). However, using alpha or morphology-based taxonomy is difficult to discover morphologically cryptic or uncertain taxa within species complexes (Hebert et al., 2003). Species that are the product of rapid radiations within a single genus own suite of morphologically similar taxa (a complex) that are difficult to distinguish both in the field and the herbarium (Elliott & Davies, 2014). Although after 10 years’ development of DNA barcoding, large genera with rapid evolutionary radiations still present a significant challenge for a universal barcoding system (Kekkonen & Hebert, 2014; Twyford, 2014).

To test the efficacy of the plant barcodes, DNA barcoding work should focus on discriminating the uncertain taxa or complex groups within a single genus (Yan et al., 2015). One of the good examples for Orchidaceae is genus Dendrobium. Dendrobium is one of the three largest genera in Orchidaceae with approximately 1,450 species and a taxonomic challenging group with many unresolved species delimitations at the infrageneric level (Wood, 2014). The accurate identification of Dendrobium species is essential to their safe utilization and genetic resource conservation (Feng et al. 2015a). Traditional methods to identify Dendrobium species are based on phenotypic (morphology) observations (Jin & Yao, 2006; cited in Feng et al. 2015a), while morphological features are often affected by environmental and developmental factors (Wang et al., 2009; Ding et al., 2009). During the absence of floral structures, the vegetative characteristics of many Dendrobium species are extremely similar, rendering the taxonomic delimitation very difficult (Wang et al. 2009; Xiang et al. 2013; Feng et al. 2014, 2015b). Therefore, a simple and an accurate identification method for not only Dendrobium but other genera too is crucial.

Profiling of Floral-Surface Micromorphology Using SEM for Malaysian Orchid Species

Floral-surface micromorphology study provides diagnostic microcharacters of the species that would help in its morphological and floral anatomical authentication, supported by photographic illustrations. Several studies on the taxonomic usefulness of floral-surface microphology have been conducted for Malaysian orchid species: Corybas holtumii, C. selangorensis (Besi et al., 2019c), Crepidium amplectens, C. lowii, C. micranthum, C. rheedei subsp. rheedei (Besi et al. 2020b), Hymenorchis javanica (Besi et al. 2020c), Paphiopedilum barbatum, P. callosum var. sublaeve, P. niveum (Besi et al. 2021a), Vanda dearei, and V. helvola (Besi et al. 2021b). However, a larger sampling is required to know the level of variation of the analysed characters and to be able to make stronger conclusions. Taxonomic profiling is the study and description of variation in organisms. Electron microscopy is an advanced approach in the profiling of surface features of cells, tissues, and organs of flowering plants (Fowke et al., 1991; Khasim, 2002). Scanning electron microscope (SEM) is used to look at finer details in external features, the micromorphology (Singh, 1999). Micromorphology is formed by the sculpture and shape of epidermal cell. The basic unit of surface sculpture is an epidermal cell, includes the features of anticlinal and periclinal walls. The variable cell shapes and microstructure on the cell surface and formation of multicellular structures contribute to the diversity of plant surfaces (Koch & Barthlott, 2009). SEM allows three dimensional views and internal views of the specimen with higher resolving power than a compound light microscope (Purohit, 2006). Studies using an electron microscope are stable and unaffected by environmental conditions (Singh, 1999). SEM was introduced for pollen studies in the 1970s (Hesse et al., 2009). Pollen is observed in great depth of field and high resolution (Williams & Broome, 1976). The steps involved before the specimen viewed under electron microscope are fixation, post-fixation, dehydration, critical point drying, mounting, and coating (Khasim, 2002; Pathan et al., 2008; Timp & Matsudaira, 2008). Pollen sizes range from 10 μm to more than 100 μm. The size of pollen is affected by hydration and preparation method (Hesse et al., 2009). The pollen wall (sporoderm) consists of two layers: inner intine and outer exine. The inner intine layer is softer in comparison to the outer exine layer (Erdtman, 1971). Pollen grains of Orchidaceae are either single or united in tetrads or pollinia. The longest axis in single grains ranges from 20 μm for Vanilla africana to 50 μm for Cypripedium species (Erdtman, 1971). The type of pollen aggregation in Orchidaceae includes monads, tetrads, massulae and pollinia (Wolter & Schill, 1985).

For orchids, surface of ventral labellum may either be glabrous or covered with hair (Tang, 2007). The papillae that were found in the labellum of Maxillaria species are in various shapes such as viliform, conical, and moniliform, and can either be unicellular or multicellular (Davies & Winters, 1998). Papillae may also occur on multiseriate trichomes that perhaps function as pseudostamens and contain pigment or act as osmophores, thereby attracting insects (Davies & Turner, 2004). This difference may represent different evolutionary lines. Therefore, surface of labellum demands further investigation to provide additional taxonomic characters. Findings based on the photomicrographs using SEM revealed that V. helvola and V. dearei are comparable based branched glandular and biseriate trichomes on the labellum of V. helvola but was absent in V. dearei (Besi et al. 2021b).

In a study by Steinhart et al. (1980), the surface contours of orchid columns were examined. Some of the surfaces of the column were convoluted and others had smooth ridges. Ridge spacing and the presence of papillose surface differ in species (Steinhart et al., 1980). Glandular trichomes and papillae are responsible for generation, storage, and release of fragrance substances (Holman et al., 1981). Several types of stomata are anomocytic, anisocytic, cyclocytic, diacytic, paracytic, and paralelocytic (Perveen et al., 2007). A stoma with their stomatal pore consists of a pair of guard cells which responsible for the opening and close of the stomata, is surrounded by neighbouring cells or subsidiary cells (Fryns-Claessens & Van Cotthem, 1973). More than 25 main types of stomata identified in dicots based on the arrangement of the epidermal cell neighbouring the guard cell (Metacalfe & Chalk, 1979). Presence of stomata, glandular trichomes, and papillae on the dorsal sepal and labellum are the distinguishing characters for Malaysian Corybas (Besi et al., 2019c). Apart from that, epicuticular ornamentation can be distinguishing characters for Malaysian orchids species (Besi et al. 2019a, b, 2021a, b).

DNA Metabarcoding Uncovers Orchid-Associated Microbiota

Arbuscular Mycorrhizal Fungi (AMF) give multiple advantageous effects on plant growth, health, nutrition, productivity, environmental stress relief as well as soil fertility and stability (Fuchs & Haselwandter, 2008). Many endangered orchid species live in symbiosis with AMF (Herrera et al., 2022). However, studies concerning the role of AMF in conservation practices are insufficient, with mechanisms yet to be unravelled (Evelin et al., 2019), especially for Malaysian orchid species. Apart from AMF, orchids need beneficial root-associated bacteria to sustain the plantlet development and completion of its life cycle (Herrera et al., 2022). In orchids occupying different habitats, the spectra of the bacterial genera are proved to be different (Tsavkelova et al., 2001). Also, microbial community of epiphytic plant may differ from that of the terrestrial one (Tsavkelova et al., 2016). Orchid-Archaea relationship is much less known. However, association between archaean communities and plants have been proven (Chelius & Triplett, 2001; Simon et al., 2001). Over the last decade, DNA metabarcoding has rapidly emerged as a powerful and cost-effective method for the description of microbiota in environmental samples (Francioli et al., 2021). Next Generation Sequencing technology (NGS) DNA metabarcoding characterizes species composition of bulk samples (Taberlet et al., 2012; Ji et al., 2013; Bohmann et al., 2014; Yang et al., 2014). The NGS-based DNA metabarcoding uses universal PCR primers to mass-amplify a taxonomically informative gene from mass collections of organisms or from environmental DNA (Korpelainen et al., 2016). Taxonomic and abundance assessments of microbiota using DNA metabarcoding coherent with methods of microscopy (Banchi et al., 2019). Additionally, being DNA metabarcoding a culture-independent approach, it lessens the need for laboratory isolation and culturing of specimens that may not grow well (Knief, 2014; An et al., 2018; Francioli et al., 2021). Although DNA metabarcoding demands multidisciplinary skills and knowledge including field and theoretical knowledge, taxonomy, molecular biology, bioinformatics, and computational statistics for minimizing the possible experimental artifacts and biases that can be introduced at any step of the experimental workflow (Zinger et al., 2019).

Conclusion

Forest destructions induced human themselves undoubtedly could be bring extinction towards orchids community if no effective conservation and restoration efforts are being applied. Forest destruction caused ecosystem fragmentation and loss of orchid diversity. When the forests were logged, orchid species lost their habitat and shelter. When the trees fell, abundant of attached epiphytic orchids were being exposed to the heat-induced stresses. In Malaysia, conservation efforts have been started for quite a while, which led to the implementation of several ruling acts and development of local and international conservation organizations and funds. However, conservation initiative is still simply poor on local scale, especially when the demand caused by overpopulation and economic interest command different priorities. As shown by biodiversity studies of tropical forests on forest fragmentation and clear-felling effects on epiphyte and terrestrial communities, factors including microclimate, host plant characteristics, distance and habitat quality, and symbiotic microbes including plant growth promoting rhizobacteria, mycorrhizal fungi and archaeal microbes could explain the orchid floristic impoverishment in tropical forests. Studies on molecular genetics and microstructures of Malaysian orchid species prior to an accurate species delimitation are lacking documentation. The use of an integrative approach of classical taxonomy, DNA barcoding, and floral anatomy has great potential especially in the identification and taxonomy of plants to clearly elucidate the species and eliminate confusion on very closely related species. For threatened species, whose trade is regulated by the CITES, correct identification is crucial for the enforcement of the regulations and future conservation of the species. As well the application of IUCN Red List Criteria at Regional and National levels is much recommended to re-evaluate the current orchid diversity status in Malaysia.