PlantLife Volume 58.7, December 2024. Exploring Maputaland’s Grasslands: How Topography, Soil, and Disturbance Shape a Resilient Multi-Functional Ecosystem

Exploring Maputaland’s Grasslands: How Topography, Soil, and Disturbance Shape a Resilient Multi-Functional Ecosystem

Allister Starke (PhD)

Introduction

South Africa’s Maputaland coastal plain is a fascinating landscape where dunes, wetlands, and grasslands meet to form a mosaic of biodiversity, shaped by subtle shifts in soil type, fire, elevation, and water availability. With the pressures of agriculture and forestry growing, understanding how this ecosystem responds to disturbance is vital for sustainable land management. Our research, conducted through the Water Research Commission of South Africa, examined which species thrive across these environments, allowing us to explore how vegetation communities respond to plantation forestry disturbances—and thus we leveraged a natural filter for identifying plants suited to semi-natural and agro-ecological systems. In the broader picture, understanding which species are resilient to plantation and other agricultural land uses provides a framework for making informed choices about plants that will thrive in managed landscapes.

Figure 1. A landscape perspective of a relatively untransformed area of Maputaland, showing the differences in vegetation communities across topographic gradients.

Maputaland’s Diverse Grasslands: A Dynamic Landscape of Soil, Water, and Resilient Plant Forms

Maputaland’s grasslands are shaped by variations in topography and soil, where even slight changes in elevation lead to distinct vegetation communities. Within these communities, certain species have evolved unique adaptations, including a plant-group known as geoxylic suffrutices—often called “underground trees.” Plants like Syzygium cordatum, Parinari capensis, and Salacia kraussiana keep most of their biomass below ground, enabling them to withstand fires, drought, flooding, and heavy grazing. Typically low-growing shrubs, these geoxylic suffrutices allow smaller forbs and grasses to grow among them without being outcompeted for light, supporting a diverse herbaceous layer in the vegetation community.

In the higher, sandy areas of dune-ridge grassland, nutrient-poor soils limit vegetation to drought-tolerant plants. Grasses like Hyperthelia dissoluta and Andropogon gayanus are large thatching grasses that thrive among hardy shrubs such as Strychnos madagascariensis, Strychnos spinosa, and Ozoroa obovata.

In hygrophilous grassland, where the soil retains more moisture, we find a more productive environment. In these low-lying areas, species such as Themeda triandra and Eragrostis lappula thrive alongside other geoxylic suffrutices like Elephantorrhiza elephantina and Eugenia albanensis. Periodic fires and grazing maintain these spaces as open “grazing lawns” essential for local wildlife, including herbivores that rely on these high-nutrition grasses during the drier winter months.

At the lowest points, wetland-depression grasslands with soils high in clay and proximity to the water table support hydrophilic grasses like Acroceras macrum and Hemarthria altissima. These clay-rich depressions are nutrient-dense, supporting high biomass and lush vegetation that also sustain grazing animals during dry spells.

Figure 2. One beautiful plant to be expected in wetland and peatlands is Coleus reticulata.

Figure 3. Acroceras macrum is a characteristic and beautiful lawn grass in depression-grasslands.

Figure 4. A well- known geoxylic suffrutex, Parinari capensis sub.sp incohata

Figure 5. Another well- known geoxylic suffrutex, Salacia kraussii (Photos fire Figures 3a and 3b by Geoff Nichols). 

Secondary Grasslands: A Natural Filter for Agro-Ecological Suitability

Maputaland’s landscape also includes secondary grasslands—once forestry sites that have since been abandoned. The vegetation in these areas, which has developed after land disturbances, provides a unique opportunity to observe which plants are resilient to typical agricultural disturbances and therefore suitable for semi-natural and agro-ecological systems. Studying these sites allows ecologists to identify plants with a proven tolerance to modified environments; in essence, they are species that can thrive in managed landscapes while contributing to ecological stability.

Grasses like Cynodon dactylon, Digitaria swazilandensis, Dactyloctenium geminatum, and Brachiaria brizantha are among the most disturbance-tolerant species in these secondary grasslands. These species form dense grazing lawns that not only stabilise the soil but also provide forage that remains available even in tougher seasons. Alongside these, resilient geoxylic suffrutices such as Parinari capensis and Salacia kraussiana occur, offering biodiversity, cultural, and production benefits in agro-ecological systems like silvopasture systems, where maintaining ecological functionality is essential. These species are more than just survivors; they form the foundation of potential agro-ecological systems and offer insights into the future floristic composition of the landscape.

Figure 6. At Mazengwenya plantation, after 20 years of abandonment, the composition vegetation within secondary grasslands represented a fraction of what was sampled in untransformed grasslands, but there was still some goodness to be found, including geoxylic suffrutices and the local Maputaland restio, Restio zuluensis.

Figure 7.  While naturalising pines and local grasses ( Digitaria diversinervis, Digitaria debilis, and Sacciolepis curvata) had spontaneously developed into a ‘silvopasture.

How Ecologists Classify and Interpret Vegetation Communities

To classify natural and semi-natural vegetation communities, ecologists use statistical tools that reveal underlying patterns of species occurrence. Classifying or grouping plant communities based on the composition of species highlights distinct communities where the differences can be measured, for example the difference between dune-ridge and wetland-depression grasslands. Part of this approach lays the platform for identifying ecological indicators, for example, our study found that species like Andropogon eucomus indicated secondary grassland, while Themeda triandra indicated hygrophilous grassland. Finally, multivariate analysis reveals how environmental factors such as soil variables (e.g., carbon and nitrogen) correspond with plant distribution across topographies, showing that certain plant communities associate with fertile lowlands whereas drought-tolerant plants associate with sandy ridges. These insights help guide sustainable land-use by identifying resilient species for managed ecosystems.

Figure 8.  Se the text box below which provides a detailed explanation of the ordination used to describe the patterns of variation.

Key Findings: The Power of Disturbance as a Selection Tool

Our research underscored how topography and soil shape plant composition across Maputaland’s grasslands, while revealing that historical disturbance plays a role by selecting for and against certain key plant species which may be suitable for agro-ecological systems. Low-lying grasslands, rich in organic matter, support productive grazing lawns with forage grasses like Acroceras macrum (in undisturbed low-lying areas), while in secondary grasslands Cynodon dactylon would be available alongside resilient geoxylic suffrutices. In contrast, dune-ridge grasslands support robust thatching grasses and multi-purpose shrubs adapted to less fertile soils. Secondary grasslands in abandoned forestry sites offered a measurable insight into disturbance-tolerant species, showcasing a selection of forage and disturbance-capable grasses, while disturbance-sensitive species like Themeda triandra were notably absent. The resilience of geoxylic suffrutices in secondary grasslands also underscored their potential for agro-ecological integration, where they could contribute to biodiversity, cultural products, forage, and soil health.

Conclusion: Using Ecological Insights to Guide Sustainable Land-Use

Examining the patterns across Maputaland’s intact and disturbed grasslands, from their native ecosystems to secondary semi-natural areas, present valuable lessons for sustainable agriculture and land use. By observing which species withstand disturbances associated with plantation forestry, we gain a practical toolkit of plants suited for semi-natural systems that balance productivity with ecological health. Integrating resilient species, particularly geoxylic suffrutices and disturbance-tolerant grasses, into agroforestry systems would support biodiversity while enhancing soil stability and forage availability. Thanks so much to the communities of Mvelabusha, KwaZibi, and Manzengwenya plantation for providing access to their lands, and to my fellow team members on the project.

About the author: Allister Starke (PhD, Forest Science) is a conservation horticulturist and applied ecologist passionate about designing and managing spaces that connect people with nature. He has extensive experience in integrating ecological restoration into urban, agricultural, and natural landscapes across East and Southern Africa. Allister has collaborated with conservation organisations and local governments, focusing on applying ecological theory to practical management. He finds great fulfilment in creating environments that support both human needs and ecological resilience.