PlantLife Volume 57.4 July 2024. The status of Calanthe sylvatica within Dlinza Forest Nature Reserve and Rutledge Park Swamp Forests.

 

The status of Calanthe sylvatica (Thouars) Lindl. within Dlinza Forest Nature Reserve and Rutledge Park Swamp Forests.

Text and photos by Sharon Louw

Ezemvelo KwaZulu-Natal Wildlife, P.O. Box 13053, Cascades, 3202, South Africa.

Calanthe sylvatica (as synonym Calanthe natalensis) plate 6844 in: Curtis's Bot. Magazine (Orchidaceae), vol. 111, 1885

Introduction

The robust terrestrial orchid, Calanthe sylvatica, is widespread in deep shade in temperate or submontane forests, often growing near streams or seepages, occasionally on tree trunks, from near sea level to 1 700 m a.s.l.

Calanthe is a genus of 209 species and is centred in Asia. It is also native to tropical and southern Africa from Sierra Leone to Tanzania to South Africa, as well as Madagascar, Comoros, Mauritius and Réunion. Three species occur in Africa and one in South Africa. Calanthe sylvatica, according to Johnson & Bytebier (2015), displays a rosette of broad pleated leaves, with a short, leafy stem, from which a slender stalk arises, to display a terminal inflorescence, with 10–20 dense to laxly arranged, hairy flowers. Flowers are often large and showy, white to pink or pale mauve, fading to apricot. Peak flowering is between December and March.

 

Figures 1a, b & c: Typical Calanthe Sylvatica growth form and inflorescence

 

Figure 2: Calanthe sylvatica pseudobulbs are shallow rooted, often forming vegetative clumps, which are easily undermined and uprooted during flooding events. 

Figure 3 a & b: Calanthe sylvatica inflorescence (a) and flowers white to pink or pale mauve, fading to apricot (b).

Figure 4: Calanthe sylvatica ‘clump’ growing within the Swamp Forest. 

Background

Calanthe sylvatica occurs in colonies within Dlinza Forest Nature Reserve and Rutledge Park Swamp Forests, Eshowe. The orchids were first observed in the late 1990’s when Sharon Louw, Prof Dai Herbert, and the late Honorary Officer Denis Eckard, were conducting field surveys in search of the endemic, Critically Endangered Chilocystis clifdeni Dhlinza Pinwheel (a snail) in Dlinza Forest Nature Reserve. 

According to Prof. Herbert, the stands of Calanthe sylvatica were of the largest he had ever seen. Chilocystis clifdeni were observed feeding on the leaves of C. sylvatica on the edge of the Swamp Forest in Dlinza Forest Nature Reserve. Monitoring the C. sylvatica colony took place randomly and a suspected decline in C. sylvatica abundance in the Swamp Forest formalised the development of the five-year C. sylvatica Monitoring Plan. The monitoring plan has guided the annual C. sylvatica monitoring in the Swamp Forest at Dlinza Forest Nature Reserve and Rutledge Park since 2020. Prior to the development of Eshowe, the Rutledge Park Swamp Forest would have formed part of the greater Dlinza Forest area. Monitoring C. sylvatica in a protected area managed by Ezemvelo KZN Wildlife (Dlinza Forest Nature Reserve) and on uMlalazi municipal land (Rutledge Park) was beneficial to understand the effects of management and the impact on orchid colonies.

The Swamp Forest environment

Swamp Forests are dependent on water. The characteristic vegetation component is adapted to withstand waterlogged soils, with Voacanga thouarsii a dominant canopy species, with emergent breathing roots exposed in the shallow water. The epiphytic cactus Rhipsalis baccifera, and ferns (Asplenium rutifolium, Microsorum punctatum) as well as orchids (Aerangis mystacidii, Bulbophyllum scaberulum and Bolusiella maudiae) grow in abundance. The herb layer is dominated by Impatiens hochstetteri, Clivia miniata, Plectranthus saccatus, Calanthe sylvatica and Todea barbara.

Mature Calanthe sylvatica orchids are pedestaled in this wet environment, resulting in vegetative ‘’orchid clumps.’’ They grow vigorously during the peak flowering period between the end of January through to March. 

Figure 5: The tropical like Swamp Forest habitat favoured by Calanthe sylvatica in Dlinza Forest Nature Reserve.

Figure 6: The open, dappled sunlight forest canopy in the Rutledge Park Swamp Forest.

Figure 7 (left) Platylepis glandulosa,and Figure 8 (right) Bolusiella maudiea

Figure 9: Aerangis mystacidii

Tree falls within the Swamp Forest environment are dynamic and gaps in the canopy are quickly colonised by a dense herb understory, however the threat of alien invasive species taking hold can present a challenge. Several alien invasive plant species are established within the Swamp Forests and threaten the natural dynamics of this wetland system. Stands of Psidium cattleianum (Strawberry guava) dominate the understory. Other species include Hedychium gardnerianum (Kahili ginger lily), Hedychium coronarium (White ginger lily), Ardisia crenata (Coralberry tree), Nephrolepis cordifolia (Sword fern), Livistona chinensis (Chinese Fan Palm), Cyathea cooperi (Australian tree fern), Syngonium podophyllum (Goose foot), Litsea glutinosa (Indian laurel) and Cinnamomum camphora (Camphor tree).

Figure 10 (left): Psidium cattleianum and Figure 11 (right): Hedychium gardnerianum

Calanthe sylvatica monitoring

The objectives of the five-year monitoring programme were to acquire information to evaluate the status of the Calanthe sylvatica populations at the two sites. In addition, the collection of basic ancillary data could explain the temporal dynamics of the populations expressed through its flowering activity, orchid abundance, and distribution. Monitoring took place in February during the peak C. sylvatica flowering period. The tall flowering spikes and the spectacular mauve flowers make this orchid easy to identify in the Swamp Forest. Transects were carefully walked through the Swamp Forest, to ensure that all orchids were recorded. GPS locations were recorded for all individual C. sylvatica orchids. In certain instances, a point could record an ‘orchid clump,’ when vegetative reproduction had occurred, and the record reflected the number of individual plants counted. The following data were collected: number of orchids, plant phenology and vigour, number of inflorescences and fruit/seed development. Information on the general condition of the Swamp Forest was also recorded, including threats and species of interest.

Figure 12: Calanthe sylvatica monitoring results compare the trends between the colonies within the Dlinza Forest Nature Reserve and Rutledge Park Swamp Forests.

Monitoring trends indicated substantial differences between the two Calanthe sylvatica colonies. The C. sylvatica population in Dlinza Forest Reserve was stable but the population at Rutledge Park had to contend with anthropogenic impacts that threaten its existence. Ancillary data collected showed a strong correlation with climatic conditions, and although the sites are 1.5 km apart, differences in microclimates influenced orchid growth. The C. sylvatica colonies responded directly to habitat conditions within the Swamp Forest. At Rutledge Park in 2023, most C. sylvatica inflorescences suffered from black rot that killed the inflorescence spikes. This could have been in response to wet conditions and a cold spell within this lower lying drainage line. 

Figure 13 a (left): Noxolo Nzama and Anele Gumede collecting data. Figure 13 b (right): Calanthe sylvatica inflorescence rot at Rutledge Park in 2023.

In recent years, the Calanthe sylvatica colony at Rutledge Park has declined owing to anthropogenic impacts. The expansion of residential erf boundaries, stream canalisation, tree felling, chemical spraying, vegetable gardens, concentrated stormwater runoff and invasive alien plant establishment within the Swamp Forest have had a negative impact on the C. sylvatica colony. The increase in non-compliant activities have impacted on the natural functioning of the Swamp Forest, contributing to the decline in the C. sylvatica population. The density of alien invasive plant species and the lack of an alien plant control programme at Rutledge Park add to the threats faced by the orchid population.

Figure 14 a & b: Erf expansion, tree felling, stream canalisation, chemical spraying and drainage trenches at Rutledge Park have had a negative impact on the Swamp Forest and Calanthe sylvatica population.

Calanthe sylvatica translocation and re-establishment

Failure to address non-compliant activities at Rutledge Park led to the identification of similar, secure Swamp Forest habitat within the Eshowe Hills Golf Estate, where the species was absent. Calanthe sylvatica orchids at Rutledge Park that were exposed through tree felling and chemical spraying were translocated in 2023 and 2024 and established at the Golf Estate to secure a third C. sylvatica colony. Monitoring this small colony has yielded positive results, with three C. sylvatica orchids which were translocated in 2023 flowering this season.

Conservation threats and mitigation

The management and natural functioning of Swamp Forests will secure C. sylvatica populations and the rich biodiversity contained within this sensitive ecosystem.

A systematic approach to controlling alien invasive species in the forest understorey is critical to allow indigenous species to colonise the gaps while simultaneously managing dappled sunlight levels. The total clearing of alien invasive species in this sensitive environment will cause considerable damage, through trampling and increased light levels, which will negatively impact the C. sylvatica populations, including other plant and animal species reliant on the natural functioning of the Swamp Forest. Chemical control is not recommended due to the sensitivities associated with aquatic environments.

Anthropogenic disturbances require management to re-instate natural base water flows, including the rehabilitation of local hydro-geological processes. Municipal entities need to apply by-laws and environmental legislation to protect natural assets. The importance of environmental awareness, including the results of the C. sylvatica monitoring needs to be shared with the community. Ezemvelo’s continued engagement with uMlalazi Municipality officials, including the KwaZulu-Natal Department of Economic Development, Tourism and Environmental Affairs, to address non-compliance, manage concentrated stormwater outflows and initiate alien invasive plant control within the catchment will mitigate key threats posed by suburban change at Rutledge Park. Updating the five-year C. sylvatica Monitoring Plan will allow for continued monitoring, threat identification and implementation of appropriate mitigation measures. 

Figure 15 a (top left), b (top right) & c (bottom):  The endemic, Critically Endangered Chilocystis clifdeni (Dhlinza Pinwheel) are routinely observed feeding on detritus and algae on Calanthe sylvatica leaves in the Dlinza Forest Nature Reserve Swamp Forest.

During the C. sylvatica surveys, the abundance of the Critically Endangered Chilocystis clifdeni observed on C. sylvatica orchids in the Dlinza Forest Nature Reserve Swamp Forest could be used as an ecological indicator of Swamp Forest health.

It is evident that the management and maintenance of the Swamp Forests will secure habitat for the long-term survival of Calanthe sylvatica populations. Swamp Forests that can withstand extreme stochastic weather conditions and climate change will secure the survival of associated fauna and flora reliant on the natural functioning of these sensitive ecological systems.

 

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Acknowledgements

Ezemvelo KZN Wildlife Field Rangers and General Assistants based at Dlinza Forest Nature Reserve, including Interns and Cadets who have assisted with C. sylvatica monitoring over the years, without whose assistance, the success of the project would not have been realised.

References

BOON, R. (2010) Pooley’s Trees of Eastern South Africa, A Complete Guide. Flora and Fauna Publications Trust, Durban, South Africa.

HERBERT, D.G. 2004. Trachycystis clifdeni. The IUCN Red List of Threatened Species 2004: e.T44710A10938455. http://dx.doi.org/10.2305/IUCN.UK.2004.RLTS.T44710A10938455.en

JOHNSON, S. & BYTEBIER, B. (2015) Orchids of South Africa, A Field Guide. Struik Nature, Cape Town, South Africa.

About the author: Sharon is Ezemvelo KZN Wildlife’s District Ecologist Central East, based in Mtunzini and is responsible for the King Cetshwayo and iLembe Municipal Districts. Part of the Ecological Advice East Division, Sharon provides ecological advice support to Protected Area and District Conservation Managers, co-ordinates and manages several monitoring programmes and is an Environmental Management Inspector (EMI-Level 2). Sharon is enthusiastic about her work, has a wide range of interests, including plants and animals, photography, and a supporter of iNaturalist.