PlantLife Volume 50.10 December 2020. The future of coastal forests in KwaZulu-Natal

 

THE FUTURE OF COASTAL FORESTS IN KWAZULU-NATAL

By Astika Bhugeloo, Syd Ramdhani and Sershen

 

Indigenous forests in South Africa

Worldwide, indigenous forests occupy approximately 36% of global land area and are important key biodiversity areas, supporting more than half of the world’s faunal and floral species (Anderson-Teixeira et al., 2015). Forests also provide several economic and social goods and ecosystem services, including the provision of food, timber, medicine and firewood, improved water quality and carbon sequestration. Despite their value, forests are under increasing threats worldwide mainly due to climate change, land use change, unsustainable deforestation and the spread of invasive alien plant species (Anderson-Teixeira et al., 2015; Food and Agriculture Organisation (FAO), 2016).

In South Africa (SA), indigenous forests are the country’s smallest biome, existing mostly as highly fragmented patches, covering approximately 0.5% of the total land area (Department of Agriculture, Forestry and Fisheries (DAFF), 2020). A substantial proportion of the country’s forest biome exists within urban landscapes and many urban, peri-urban and rural citizens rely on forests for their wellbeing and livelihood. Combined with increased clearing of forests for urbanisation, current levels of indigenous forest loss are high, according to global standards, at approximately 0.2% per annum (FAO, 2015).

KwaZulu-Natal (KZN) is particularly important in terms of conserving the country’s forest biodiversity as three types are found there, namelyAfromontane, Mist belt and Indian Ocean Coastal Belt (IOCB) forests that differ in species composition, recruitment patterns, regeneration patterns and evolutionary history. KwaZulu-Natal is also nested in the Maputaland-Pondoland-Albany Biodiversity Hotspot – one of 35 globally recognised biodiversity hotspots, making the biodiversity within it of global importance (Rouget et al., 2016). Indigenous forests in coastal KZN are diverse and comprise various forest types, most notably dune, swamp, riverine, coastal lowland, coastal scarp and sand forests (Image 1). Despite KZN forests types being recognised as critically endangered and ecologically valuable (Scott-Shaw and Escott, 2011; Govender, 2013; Jewitt, 2018), recent studies have shown that they are being transformed and lost at unprecedented rates, especially due to urbanisation and land use change (Bhugeloo et al., 2019).

 

Image 1: Coastal forest north of Durban

Land use changes and forests

Anthropogenic pressures, particularly land use change (the conversion of indigenous forest for agriculture, commercial forestry, sand and heavy metal mining, tourism infrastructure development and urbanisation) are the most significant impacts threatening indigenous coastal forests in KZN (Image 2). Besides the direct transformation of forests into other land use types, the subsequent loss of endemic biodiversity and proliferation of invasive alien plants (IAPs) leads to a decline in ecological structure, functioning, integrity and services (Vitousek et al., 1996). Due to the ever-growing human population and the associated land use changes, the pressures on forests are only expected to increase in the near future. The importance of informed land use planning and conservation management strategies and an increased understanding of the extent of changes in current and future forest distribution cannot be understated. Understanding past and present forest distribution can enable conservation managers to make better-informed conservation management decisions and priorities. 

Image 2: Urbanisation encroaching onto forest systems

 

Mapping forests from above

Forest cover in the developing world is generally mapped and monitored using traditional field-based methods. This is a resource-intensive undertaking in terms of human resources, cost and time, that is not always feasible in resource-limited countries such as SA. Furthermore, ground surveys are limited in terms of spatial and temporal extent resulting in data gaps, especially for large areas of land and land with inaccessible terrain — common in remote tropical and subtropical forest systems. This can be circumvented via the use of remote sensing spatial technologies, when financial and human resources are limited (Image 3).

Aerial imagery of the Hawaan Forest for 1971 (Image 3 A)  captures the forest surrounded by a larger mosaic of sugar cane plantations, informal roads and a small patch of urban housing. By the year 2016, as seen in the Google Earth image (Image 3 B), most of the sugar cane plantations have been replaced by urbanisation (housing and roads) that is directly encroaching onto the forest (indicated by arrows). This encroachment has resulted in a decrease in forest area. This is shown in a much higher resolution, resulting in clearer visualisation in the remote sensed SPOT7 image, thereby allowing finer mapping and more accurate analyses to be conducted (Image 3 C).

Remote sensing imagery has successfully been used to identify disturbances in coastal forests with high levels of accuracy (>80%) (Bhugeloo et al., 2018). Given the financial constraints in running forest monitoring programmes and limited success in developed countries, the use of geospatial technologies as a monitoring tool are considered the way forward.

 

A. Aerial image (1971)

B. Google Earth image (2016)

 

C. Satellite image (SPOT7) (2016)

 

Image 3: The contrasting (A) aerial image, (B) Google Earth image and (C)
SPOT7 Satellite image of Hawaan Forest (Durban) (Yellow arrows indicate
urbanisation)

Forest disturbance and decline

Natural and anthropogenic disturbances occur regularly in forest systems. Natural disturbances are disturbances that occur without human intervention, e.g. fires, droughts, tree fall and insect outbreaks. Anthropogenic disturbances are disturbance events caused by humans that directly affect forests. These include but are not limited to clearing and logging, exploitation of forest species (e.g. Adenia gummifera (Harv.) Harms, Albizia adianthifolia (Schumach.) W.Wight, Apodytes dimidiata E.Mey. ex Arn.), introduction of alien plants, hunting and mining, creation of pathways, placement of benches and other artificial structures and the indirect impacts of surrounding land use activities.

Spatial and temporal studies are urgently required in order to gain a holistic understanding of the effect of disturbance on small and fragmented forest systems. Although time-series assessments are regularly used to map and quantify disturbance events (such as deforestation) for long-term monitoring programs in other regions of the world, surprisingly no such continuous monitoring program exists for KZN. In light of this, past and future indigenous forest cover in the eThekwini Metropolitan Area (EMA), one of the fastest growing municipalities in SA, was recently examined by Bhugeloo et al. (2019). The use of satellite imagery to assess the historic impact of land use changes, determine important drivers of forest loss and predict the future impacts of land use changes on indigenous forests can assist with the development of valuable spatial and temporal conservation frameworks. The study referred to above showed that indigenous forest cover decreased by c. 53% between the years 2000 and 2014, mainly due to urban development and agriculture. Investigating past trends in forest loss can be used to make accurate predictions about future forest loss, should the status quo of rate of loss and conservation strategies remain unchanged. Modelling carried out by the authors also revealed a worrying, continued, sustained loss in forest cover for the future with the majority of forest patches, particularly along the coastline, declining by the year 2035.

Monitoring disturbance

Given the implications of climate and land use changes on local coastal forests, monitoring disturbance events in forests in real time (or as closely as possible) is therefore vital. As mentioned above, this has proven tricky, especially in developing countries with limited resources. High resolution satellite imagery (e.g. IKONOS) is expensive to acquire but what about freely available multi-spectral imagery as a solution? Freely available multi-spectral imagery (SPOT7) acquired to track canopy gaps and in turn disturbance events did show high accuracy levels at 5 m and 1.5 m resolutions (Bhugeloo et al., 2018). This proved that the lack of high resolution images should not hamper developing countries’ efforts to effectively use remote monitoring programmes since multi-spectral imagery can be used to accurately identify canopy gaps making it a cost-effective spatial approach for monitoring and managing natural forests.

Regeneration of forests following disturbance events

While the cover of forests can be tracked remotely, the science has not progressed enough to assess the integrity of the diversity housed within remnant forest patches or individual species, especially taxa other than large trees. Tracking the diversity housed within forest still needs a fair amount of good old-fashioned field work and dirty-hand work. Walking through remnant forest patches in KZN, canopy gaps are one of the most obvious signs of disturbance. Both natural and anthropogenic disturbances help shape the structural and spatial pattern of forests by creating these large breaks or gaps in canopy cover (Image 4). A closer look at these gaps reveals an abundance of seedlings and saplings, as well as alien vegetation, something that is not widely evident in imagery.

Despite their importance, data on regeneration strategies in coastal KZN forests are lacking. The importance of trees to the forest structure and functioning is pivotal. Some key species in KZN coastal forests include Brachylaena discolor DC., Albizia adianthifolia (Schumach.) W.Wight, Baphia racemosa (Hochst.) Baker,  Cola natalensis Oliv and Ziziphus mucronata Willd (Personal observations). Regeneration within canopy gaps mainly consists of grasses and shrub species, highlighting the need to focus on tree species to fill and maintain forest integrity. An investigation of gap floristics through classical vegetation surveys, has proved to be a useful indicator of regeneration in disturbed forests. Data retrieved from these surveys can provide critical information and insights (e.g. species re-introductions) that can be used to inform forest management and recovery strategies. Examination of seed banks (the regeneration potential of seed species stored in soil) can also provide critical insights into species that can be used for reintroduction and regeneration.

Case study: Canopy gaps of the Hawaan, uMdoni and uMdloti forests

Forests with varying disturbance levels along the KZN coast (e.g. least disturbed Hawaan Forest situated in uMhlanga, highly disturbed uMdoni Forest situated in uMdoni and highly disturbed and transformed uMdloti Forest situated in uMdloti), revealed that disturbance levels directly affected species richness with forests that display higher disturbance having lower species richness. Not only did canopy gaps (Image 4) in all forests have lower species richness than intact canopy but the species composition differed significantly between intact canopy and canopy gaps. One of our observations was the high levels of alien species present in the gaps compared to the intact canopy. It is possible that alien species act as ‘transient gap occupiers’ that facilitate gap infilling but do not necessarily persist and increase species richness in intact forest. Many indigenous species that emerge in canopy gaps are shade-dependant seedlings and saplings that grow and persist under the faster growing alien plants. Once alien plants mature, they are outcompeted for resources by indigenous species, explaining their low occurrence in intact canopy. Another interesting finding was that species richness was positively correlated with gap size and soil moisture content and negatively correlated with air temperature, i.e. higher temperatures result in lower species richness and species richness was higher in larger gaps with higher soil moisture content. High temperatures and low soil moisture contents have important implications as these are limiting factors to plant growth in coastal KZN. Warmer conditions, as predicted for the KZN region in recent climate change studies, could therefore have a negative effect on the recovery of forests post disturbance and possibly influence forest edges negatively.  

 

Image 4: Canopy gap surrounded by the enclosing canopy at Hawaan Forest

 Concluding remarks

It is clear that current levels of urbanisation and deforestation are unsustainable and if current trends persist, most KZN coastal forests will decline in cover and integrity. While it is the responsibility of botanists and conservationists to develop practical, affordable and adaptable frameworks for the management of urban forests (Image 5), the success of these frameworks is not solely dependent on the land use planners and policy-makers who oversee their implementation. Land owners and local citizens have an important role to play in helping to ensure the conservation of our forests by our everyday choices and actions and steps should be taken that would allow governments and citizens to work closely together. Local citizens with the knowledge and resources can have a profound impact on the conservation of our forests. Some of the steps that citizens can take to help the successful conservation of our forests are, for example, clearing invasive alien vegetation on weekly walks, photographing and documenting indigenous species in local forest patches to help contribute to species lists, documenting flowering and fruiting times of species and growing indigenous seedlings, especially trees, for reintroduction into forest systems. By choosing conservation of natural vegetation over development, and compassion over cost, we are ensuring the integrity of our ecosystems and their continued existence for future generations to enjoy. 

 

Image 5: Hawaan Forest situated in uMhlanga, KwaZulu-Natal

 

Acknowledgements

The authors would like to thank Joceyln Sutherland (Hawaan Forest Management), Rynardt Crous (uMdoni Trust), Steve Untiedt (Wildlife and Environment Society of Southern Africa [WESSA], Twinstreams) and the uMdloti Improvement Project (UIP) for allowing us access to the study sites. This work was supported by the University of KwaZulu-Natal and the National Research Foundation of South Africa.

Suggested reading and work used

Anderson‐Teixeira, K.J., Davies, S.J., Bennett, A.C., Gonzalez‐Akre, E.B., Muller‐Landau, H.C., Joseph Wright, S., Abu Salim, K., Almeyda Zambrano, A.M., Alonso, A., Baltzer, J.L., Basset, Y., et al., 2015. CTFS‐Forest GEO: a worldwide network monitoring forests in an era of global change. Global Change Biology, 21(2), 528-549. https://doi.org/10.1111/gcb.12712

Bhugeloo, A., Peerbhay, K. Ramdhani, S., and Sershen, 2018. Assessing the trade-Offs of SPOT7 imagery for monitoring natural forest canopy intactness. Forests, 9(12), 781. https://doi.org/10.3390/f9120781

Bhugeloo, A., Peerbhay, K. Ramdhani, S., and Sershen, 2019. Tracking indigenous forest cover within an urban matrix through land use analysis: the case of a rapidly developing African city. Remote Sensing Applications: Society and Environment, 13, 328-336. https://doi.org/10.1016/j.rsase.2018.12.003

Department of Agricultural Affairs, Forestry and Fisheries (DAFF), 2020. South African Government: Forestry. Available from: https://www.gov.za/about-sa/forestry [Accessed October 2020].

Food and Agriculture Organization of the United Nations (FAO), 2015. Southern Africa’s forests and people: Investing in a sustainable future. Durban, South Africa.

Food and Agriculture Organization of the United Nations (FAO), 2016. Global forest resources assessment 2015: How are the world‘s forests changing, second edition. Rome, Italy.

Govender, N., 2013. Durban Climate Change Strategy Introductory Report Theme Biodiversity. Environmental Planning and Climate Protection Department, eThekwini Municipality. Durban.

Jewitt, D., 2018. Vegetation type conservation targets, status and level of protection in KwaZulu-Natal in 2016. Bothalia-African Biodiversity & Conservation, 48(1), 1-10. http://dx.doi.org/10.4102/abc.v48i1.2294

Rouget, M., O’Donoghue, S, Taylor, C., Roberts, D., Slowtow, R., 2016. Improving the management of threatened ecosystems in an urban biodiversity hotspot through the Durban Research Action Partnership. Bothalia - African Biodiversity and Conservation, 46 (2), 1-3. http://dx.doi.org/10.4102/abc.v46i2.2199

Scott-Shaw, C.R. and Escott, B.J., eds, 2011. KwaZulu-Natal Provincial Pre-Transformation Vegetation Type Map-2011. Pietermaritzburg: Biodiversity Conservation Planning Division, Ezemvelo KZN Wildlife.

Vitousek, P.M., D'Antonio, C.M., Loope, L.L. and Westbrooks, R., 1996. Biological invasions as global environmental change. American Scientist, 84 (5), 468-478.

About the authors:

Astika Bhugeloo is a PhD graduate from the University of KwaZulu-Natal. Her PhD focused on understanding the dynamics of indigenous coastal forests of KZN within an urban landscape. She is currently a post-doctoral research fellow at the University of the Western Cape.

Syd Ramdhani is a senior lecturer in the School of Life Sciences, University of KwaZulu-Natal. He is interested in systematics, evolution and biogeography.

Sershen (aka Sershen Naidoo) is the executive director of the Institute of Natural Resources and Honorary Research Fellow at the University of the Western Cape. He is interested in multiple fields that span the biological, environmental and social sciences.