Vegetation Monitoring

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At Malilangwe, we view vegetation as the natural capital that sustains the entire ecosystem. Just as financial capital underpins a business, healthy vegetation supports wildlife, ecological processes, and ecosystem resilience. When vegetation degrades, the ecological consequences can be far-reaching. For this reason, monitoring changes in plant composition and structure is one of the cornerstones of our management programme.

History of Vegetation Monitoring at Malilangwe

Our first comprehensive vegetation survey was conducted in 1994, when 18 plant communities were identified and 32 permanently marked monitoring sites were established across the reserve. A detailed assessment of range condition followed in 1997, and comparison with historical records revealed substantial changes in the herbaceous layer over the preceding 50 years.

Much of the grassland had shifted from a diverse community dominated by long-lived perennial grasses, particularly Cenchrus ciliaris, to one dominated by Urochloa mossambicensis. This transition was accompanied by a decline in carrying capacity. The severe drought of 1992 was identified as the primary driver of this change, although historical cattle overgrazing and the long-term exclusion of fire had also contributed. As a result, the vegetation composition recorded during the 1970s, when Cenchrus ciliaris was abundant, was adopted as a medium-term management target.

To provide a more detailed baseline for future monitoring, a reserve-wide vegetation survey was undertaken between 2000 and 2003. This work identified 38 vegetation types, and the herbaceous, shrub, and tree layers were sampled at 201 sites. These data now serve as an important benchmark against which long-term ecological change can be measured.

Monitoring Elephant Impacts

Long-term monitoring has shown that elephants are the primary drivers of woody vegetation change at Malilangwe. While elephants are a natural and important component of the ecosystem, bull elephants can cause substantial damage to trees through debarking, branch-breaking, and toppling.

To better understand their impacts, monitoring plots within the most heavily affected vegetation types were resampled in 2004 and again in 2014. The results indicated that tree damage was occurring at unsustainable levels. If left unmanaged, elephant activity had the potential to transform large areas of woodland into shrubland. In response, Malilangwe translocated 53 elephants to another conservation area in 2008 to reduce pressure on vulnerable vegetation communities.

Because detailed vegetation surveys require considerable time and resources, they can only be conducted at relatively long intervals. To provide more regular information on elephant impacts, a rapid assessment method was developed in 2008. Earlier research had identified four highly preferred tree species that could serve as indicators of elephant impact:

Marula (Sclerocarya birrea)
False marula (Lannea schweinfurthii var. stuhlmannii)
Wing pod (Xeroderris stuhlmannii)
Tall firethorn corkwood (Commiphora glandulosa)

These species are particularly attractive to elephants and therefore represent a worst-case scenario for tree damage within the ecosystem. To monitor change over time, 50 trees of each indicator species were permanently marked and assessed annually between 2008 and 2026. The following variables were recorded for every tree:

Status (alive, dying, or dead)
Percentage canopy biomass removed
Percentage trunk circumference debarked
Whether roots had been excavated

This monitoring system produced several important insights, most notably regarding tall firethorn corkwood (Commiphora glandulosa): the data suggest that corkwood is gradually being eliminated from large parts of the reserve. Elephants frequently push these trees over to access nutritious shoots in the canopy. Unlike many other tree species, corkwoods are poor re-sprouters and seldom recover once toppled. Corkwoods’ vulnerability is further increased by fire. Because these trees lack a thick protective bark layer, they are highly susceptible to fire damage and often die following burning. As a result, corkwoods persist most successfully in rocky or sparsely vegetated areas where grass production, and therefore fire intensity, is limited. Evidence suggests that corkwoods expanded beyond their historical range during the period when both elephants and fire were absent from the landscape. Prior to Malilangwe’s establishment, these ecological processes had been excluded for approximately 50 years. Since their return in 1994, corkwood distribution appears to be contracting toward historical refuge areas where the species is naturally protected from these pressures.

By 2014, the early stages of woodland conversion outside of just corkwood damage were already evident. Researchers documented a reduction in standing trees, a decline in trees less than 10 metres tall, an approximately four-fold increase in pollarded stems, and a decrease in shrub density. At that stage, however, the largest trees were still largely being retained. Much of this change was linked to the arrival of approximately 70 bull elephants from neighbouring Gonarezhou before 2014. Their impact highlighted an important lesson: significant vegetation change can occur through the actions of a relatively small number of bulls, even when overall elephant numbers remain moderate.

Understanding the Drivers of Tree Damage

More recent research has focused on understanding why elephants damage trees and identifying factors that may reduce this impact.

Studies have shown that the most destructive feeding behaviour occurs when palatable grass becomes scarce. Although elephants use both grasses and woody plants as food sources, severe tree damage – such as debarking, branch-breaking, and toppling – typically increases when elephants are forced to rely more heavily on browse.

The availability of grass is influenced by rainfall, soil moisture, soil texture, and fire history. Consequently, elephant impacts on woodlands fluctuate over time in response to these underlying environmental drivers.

Perhaps the most important finding has been that the bulls responsible for the heaviest tree damage derive particularly large nutritional benefits from green grass and are therefore expected to preferentially seek it out when available. This has significant management implications. By maintaining productive grasslands and extending the availability of green grass later into the dry season, it may be possible to reduce pressure on woody vegetation.

This reinforces one of Malilangwe’s long-standing management objectives: restoring and maintaining a productive perennial grass layer. Achieving this goal benefits not only grazing animals, but also helps safeguard the reserve’s woodlands and the many ecological processes they support. Through continued monitoring and research, we are steadily refining our understanding of these complex interactions to ensure that Malilangwe’s vegetation remains healthy and resilient into the future.