Invasive Alien Plant Species as a Revenue-Generating Resource for Conservation Efforts: The Case of Nyanga National Park,Zimbabwe

Introduction

Invasive alien species (IAS) represent one of the five major direct drivers of global biodiversity loss, alongside land-use change, direct exploitation of organisms, climate change, and pollution (Kapitza et al., 2019; Richardson et al., 2023). The 2023 Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) Thematic Assessment Report on invasive alien species and their control, the most comprehensive global synthesis to date, revealed that over 37,000 alien species have been introduced by human activities worldwide, with approximately 3,500 having demonstrable negative impacts on nature and people (Roy et al., 2023). The economic burden is staggering, with invasive alien species costing the global economy more than $423 billion annually, with costs quadrupling every decade since 1970. Despite this overwhelming evidence of harm, invasive alien species continue to spread at unprecedented rates, with 200 new introductions recorded annually and a projected increase under business as usual scenarios (Seebens et al., 2017). The IPBES assessment further identified critical gaps in current management approaches, noting that while 80% of countries include invasive alien species targets in their national biodiversity plans, only 17% have specific national laws addressing these challenges. This implementation deficit is particularly pronounced in Africa, where invasive alien species affect livelihoods in 70% of countries, yet coordinated, cross-sectoral approaches remain limited. The IPBES report emphasized that prevention, early detection, and rapid response are the most cost-effective strategies, but acknowledged that for established invasions, innovative management approaches are essential (Roy et al., 2023).

Recent scientific discourse has begun to recognize the complex economic dimensions of invasive alien species management, moving beyond simple cost accounting to acknowledge potential benefits and trade-offs (Carter et al., 2024; Epanchin-Niell, 2017; Fantle-Lepczyk et al., 2022; Hanley & Roberts, 2019, 2019, 2019; Kourantidou et al., 2022; Lambertucci & Speziale, 2011; Meadows & Sims, 2023; Robuchon et al., 2025). This nuanced perspective is particularly relevant for economically valuable invasive alien species, particularly invasive alien plants such as Eucalyptus and Pinus species, which simultaneously provide significant economic benefits through timber production while imposing substantial ecological costs. In Africa, Eucalyptus plantations contribute approximately 25% of farmers’ income in Ethiopia (Belachew & Minale, 2025), while in South Africa, invasive Eucalyptus species are responsible for 16% of the 1.44 million cubic meters of water resources lost annually to invasive plants (Coles, 2020). Similarly, Pinus plantations contribute approximately $300 million annually to South Africa’s economy while simultaneously threatening native fynbos ecosystems and reducing water flow in catchments (Martin et al., 2025; Moran et al., 2000).

The challenge of managing economically valuable invasive alien species has prompted innovative approaches that can balance economic realities with conservation imperatives. South Africa’s pioneering work through programs like Working for Water demonstrates how large-scale invasive alien plant control can be integrated with employment creation and ecosystem service protection (van Wilgen & Wannenburgh, 2016). More recently, innovative financial mechanisms, such as invasive plant bonds, are emerging. These mechanisms quantify ecosystem service recovery and attract private sector investment in the management of invasive alien plants. These developments align with the growing recognition that protected areas must adopt business-oriented approaches to generate sustainable financing for conservation (Thomas et al., 2003).

In Zimbabwe, invasive alien plants pose significant threats to biodiversity and ecosystem integrity, with the government spending approximately $50 million annually on control efforts (Ziana, 2023). Nyanga National Park (NNP) exemplifies these challenges, where invasive alien plants of the Pinus, Eucalyptus, and Acacia genera have extensively invaded mountainous habitats (Maroyi, 2012; Matongo, 2016). Traditional chemical and mechanical control methods have proven costly and often ineffective, creating an urgent need for alternative management strategies that can simultaneously address conservation objectives and financial sustainability.

Responding to these challenges, the Zimbabwe Parks and Wildlife Management Authority (ZPWMA) initiated an innovative community-based management approach in 2014, engaging small-scale timber operators from the surrounding communities through a permit system to harvest economically valuable invasive alien plants. Management was of the opinion that this approach transforms the invasive species problem into a potential solution by creating economic incentives for removal while generating revenue for park management.

This study presents the first comprehensive evaluation of the management model for revenue-generating invasive alien plants at Nyanga National Park (NNP), focusing on Pinus and Eucalyptus trees as case studies, as these species were deemed of economic importance by the saw millers. We assess the financial viability and conservation effectiveness of this approach after a decade of implementation, examining both achievements and challenges. Our findings contribute to the growing body of literature on innovative approaches to managing invasive alien plant species and provide insights for similar protected areas facing resource constraints and pressures from invasive alien plants. Through documenting this experience, we aim to inform the development of scalable models that can balance conservation imperatives with economic realities, addressing the implementation gaps, while advancing Target 6 of the Kunming-Montreal Global Biodiversity Framework. We also reflect on the achievements and potential challenges to consider if such a strategy is applied to other areas similar to NNP. We believe that ensuring accessibility and the widespread availability of information, as revealed in this study, can unite various groups interested and capable of contributing to the management of IAS, particularly in protected areas like NNP.

Materials and Methods

Study Area

The study was carried out in Nyanga National Park (NNP). It is located in the high altitude (>1500 m) region in the Eastern Highlands of Zimbabwe (Figure 1). Within the park, altitude ranges from 600m in the Honde valley to 2953m at the peak of Mount Nyangani (ZPWMA, 2023). The Park falls in Zimbabwe’s natural region 1, with rainfall of more than 1,000 mm/year (most of which falls throughout the year), low temperatures, high altitude, and steep slopes. The region’s mean annual temperature of 20–25°C prevails, with winter temperatures ranging from 9 to 12°C (Meteorological Services Zimbabwe, 2024). The Park covers approximately 470 km² and is a crucial conservation area for flora and fauna. It is characterized by scenic grassland areas interspersed with fynbos-like vegetation on the plateau summit, moist montane forest, and patches of medium to low-altitude rainforest in the Honde and Pungwe valleys. NNP contains Zimbabwe’s most extensive undisturbed montane grasslands and many montane forests, particularly on Nyangani Mountain. The high humidity and low evaporation rates provide suitable conditions for continuous plant growth throughout the year. A complex assemblage of native plant communities characterizes NNP’s montane forest-grassland mosaic (Clark et al., 2017). The park’s elevation gradient supports distinct vegetation zones, with extensive high-altitude Afromontane grasslands (1,800–2,400 m a.s.l.) dominated by microphyllous shrubland and herbaceous species (Clark et al., 2017). At mid-altitudes, Afromontane rainforests occur on windward slopes and in protected ravines, with Syzygium guineense (Willd.) DC.subsp. afromontanum F. White as the dominant canopy species. Lower slopes support miombo woodland dominated by the unique dwarf Brachystegia spiciformis Benth. woodland and Julbernardia globiflora (Benth.) Troupin, while patches of Widdringtonia nodiflora (L.) Powrie (Mountain cypress) coniferous forest persists in fire-protected gullies.

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Figure 1.

Location of Nyanga National Park, Zimbabwe

Invasive alien plants, which were introduced for forestry in the early 20^th century in Zimbabwe, have transformed significant portions of this native vegetation mosaic. For instance, in 1988, approximately 40% of the park had been invaded by invasive alien plants, with the situation deteriorating substantially since (Matongo, 2016; Mukwashi & Matsvimbo, 2008). Spatial analysis reveals that Acacia species have become the most extensive invader, occupying approximately 68% of invaded areas by 2010, representing a continuous increase over three decades. The Pinus genus, primarily Pinus patula Schldl. et Cham. (Pine) and its hybrids, showed peak invasion extent of approximately 26% in 1995, though their spatial coverage has since declined due to control efforts and natural mortality (Matongo, 2016). Other abundant species include Acacia dealbata Link (Silver wattle), A. mearnsii De Wild (Black Wattle), Acacia melanoxylon R.Br. (Blackwood), and Eucalyptus grandis W.Hill ex Maiden(Flooded Gum). These invasions have resulted in a corresponding decrease in montane grassland and natural woodland extent. All invasive alien plants of the Pinus, Acacia, and Eucalyptus genera present have fire-adapted reproductive strategies that suggest substantial regeneration potential, though the actual harvestable biomass and sustainable yield rates remain poorly quantified within the park. Much of the park has been transformed from open montane grasslands to thick monotypic vegetation of invasive alien plants (Muvengwi et al., 2018). The area’s microclimate is favourable for forestry species that have become invasive in the Pinus, Acacia and Eucalpytus genus (Maroyi, 2012; Richardson et al., 2011; Wilson et al., 2007). Introduced during the early 20^th century, these species have established feral populations and have since become problematic. The increase of the species has generally caused the deterioration of the Park from a “moderate” to a poor state between 2001 and 2008 (Mukwashi & Matsvimbo, 2008) due to invasive alien plant species.

Data Collection

Data on station revenue and volumes harvested were obtained from the Nyanga National Park finance department database, and additional financial and historical information was obtained from archived board packs from the Registry department. All revenue stream categories for analysis were sourced from financial records and board-packs and recorded as shown in these records. Data was cross-checked with timber tally sheets from Wildlife officers and Senior Rangers who captured volumes and invoices for saw millers. The total volumes were extracted from timber tally sheets and finance department records over the years (Figure 2). The finance department captured the totals in their database through copies of receipts and invoices issued to contracted saw millers. Data were collected from 2014 to 2024 as harvesting timber for commercial purposes was initiated in October 2014; however, to eliminate bias in the data, full years (12 months) were considered for analysis, thus omitting entries of 2014 and 2024 as they did not complete a 12-month cycle (January to December). Due to this omission, data from nine years of 2015–2023 was considered for analysis. All payments in the local Zimbabwean currency were converted to USD using the prevailing exchange rate for each payment period to unify revenue due to multiple local currency changes within the study period.

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Figure 2.

An extract showing timber sharing invoice between NNP and timber operator. Note that the sharing ratio differs depending on the type of timber used

Results

Revenue

Timber from invasive alien plants contributed significantly to overall revenue during the assessment period, with a mean contribution of USD$150,000 per annum. Each category has some variability, with categories like Accommodation and Tourist activities showing notable year-to-year changes (Figure 3).

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Figure 3.

A plot showing a more focused view of the revenue distribution for each revenue(USD) stream/category per annum over nine years

However, a weak relationship exists between the revenue generated and the volume extracted during the assessed period (r = 0.185, p-value = .633) (Figure 4).

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Figure 4.

Showing the relationship between the volume of timber extracted and revenue collected.

The revenue distribution varies significantly across the years, with some categories showing more stability than others. However, timber appears to be a significant contributor to revenue, especially in the earlier years, but its share seems to decrease in later years. Accommodation has shown an increasing trend over the years, becoming a more significant portion of the revenue in recent years (Figure 5).

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Figure 5.

Stacks showing the percentage contribution of each category to revenue. The total revenue contribution of all categories over the study period (2015–2023) is shown

Resource Availability

Timber volumes from invasive alien plants sharply increased between the inception year 2014 and 2016. From there, the volume harvested gradually increased, reaching its peak in 2018. Post-2018, the volumes sharply decreased, with an average of approximately 1500 cubic meters harvested per annum (Figure 6).

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Figure 6.

Trend in volumes of timber harvested over nine years (2015–2023)

Discussion

Our study indicates that timber from invasive alien plants plays a crucial role in overall revenue, primarily sourced from Pinus spp, which has the highest market value in Zimbabwe. Invasive alien plants’ harvest declined after 2018 due to the progressive depletion of large-diameter trees, as sawmillers selectively removed the most commercially valuable size classes. No management interventions were implemented to maintain or regenerate trees of desirable dimensions, since the primary conservation objective is invasive alien plants control rather than sustainable timber production, eliminating the rationale for silvicultural maintenance practices. Notably, there is a weak correlation between the volume harvested and timber revenue (r = 0.185, p-value = .6333), possibly due to the varying values for different species and types of timber, including both processed and unprocessed. Revenue from consolidated payments reflects a mix of species with different values. The management of timber from invasive alien plants did not adhere to standard forestry practices, emphasizing quality over quantity. In 2021, a flat annual lease was granted to a contractor for timber harvesting on the park’s eastern side, independent of the volume extracted.

Timber from invasive alien plants has been a significant revenue contributor, particularly in earlier years, but its share has decreased over time. The decline in income after 2018 may be attributed to the depletion of preferred species like Pinus, which previously had higher prices. Although Eucalyptus remained available, it generated less income and was less favored by operators due to the challenges of felling larger gum trees compared to pine (personal observation). Consequently, annual permits declined as preferred resources became scarce [Supplemental 1]. The success of the practice hinges on species preference, which influences saw miller choices. While the timber saw millers remove invasive alien plants, they prefer larger trees to ensure profitability, leading to selective harvesting that may compromise conservation goals, which ideally would include clearing small-diameter stems. The COVID-19 pandemic also impacted operations from 2019 to 2020. Overall, the revenue structure has evolved over the nine years, reflecting shifts in the significance of various revenue streams. However, the practice has still significantly contributed to income generation for the station and shows potential for funding conservation efforts.

While income generation from timber operations in protected areas is feasible, several factors can hinder the effectiveness of invasive alien plants clearing. Small-scale operators often do not fully comply with environmental standards outlined in permits, citing increased operational costs. This non-compliance can lead to selective tree felling to maximize profits, compromising the objective of clear-felling designated areas. The resulting debris from processing adds fuel load, increasing the frequency and severity of fire incidents, which can disrupt fire regimes. Additionally, unauthorized access routes developed by bush millers can fragment habitats, degrade grasses, and facilitate erosion, while unintentionally improving access for poachers [Supplemental 2]. Noise pollution from chainsaw operators may also negatively impact tourism and the surrounding environment.

A critical issue is that market creation can pressure the sustainability of problematic species. For instance, small-scale timber operators often suggest planting invasive alien plants for profit, prioritising immediate economic gains over less visible conservation benefits. This is counterproductive; in addition to controlling invasive alien plants in protected areas, it is crucial to raise community awareness about these species and their unchecked spread. The program has various pros and cons (Nuñez et al., 2012). Based on our experience with economically valuable invasive alien plants, we propose additional considerations for practitioners aiming to generate revenue for conservation efforts:

Monitoring and Management: Effective monitoring is essential to ensure timber operations don’t disrupt ecosystem services, such as water filtration and soil protection. Assessing whether harvesting reduces target populations is crucial, as mortality may not always translate into decreased overall growth. Implementing targeted removal strategies at suitable life stages can significantly reduce invasive alien plant populations. However, this is challenging in forestry, especially with smallholder stakeholders prioritizing economic gain over ecological considerations (de Carvalho-Souza et al., 2024). Unmanaged mixed-age stands complicate identifying life stages, and careless management can lead to negative outcomes and poor returns.

Implications for Conservation

This study underscores the dual reality faced by protected areas as they confront the challenges of invasive alien plants. While the harvest and utilization of invasive alien plants’ timber can generate short-term financial returns, it does not inherently solve underlying ecological problems (Hanley & Roberts, 2019). Our findings show that the valuable timber resource from invasive alien plants declines over time due to repeated harvesting, offering ecological benefits by gradually reducing their dominance. Although the decline of invasive alien plant species is beneficial for conservation, it brings new challenges. Economic operators, mainly small-scale sawmillers, may increase their demand for harvests, potentially leading them to ignore sustainable practices aimed at removing these invasive plants. Instead of supporting efforts to eradicate or control these species, they might continue to perpetuate their existence. If this situation is not regulated correctly, it could conflict with restoration goals (Boltovskoy et al., 2022; Hanley & Roberts, 2019; Robuchon et al., 2025).

Empirical evidence and the latest IPBES assessment highlight that selective felling targeting only the most commercially valuable invasive alien plants has mainly proven ineffective in suppressing populations (Roy et al., 2023). Residual individuals rapidly resprout, maintain propagule banks, and perpetuate invasion dynamics, impeding native ecosystem recovery (Ricciardi, 2013; van Wilgen, 2018). This is evident in the recent adaptive shift of the Nyanga National Park towards clear-felling. The recent decision to clear-fell invasive alien plants, including the least economically desirable Acacia species, on a large scale, in partnership with a tobacco curing company, Sustainable Afforestation Association (SAA), reveals adaptive management (NNP Records). Removing all invasive alien plants, regardless of diameter or market value, demonstrates improved efficacy for species control and restoration outcomes, aligning with global best practices for established invasions. However, clear-felling alone is not a panacea; long-term restoration requires monitoring and, where feasible, integration with biological control, ecosystem rehabilitation, active restoration efforts, and prevention of re-invasion (Chikowore et al., 2025).

The economic incentive to harvest invasive alien plants can provide essential funding for conservation efforts in resource-constrained settings, as shown in this study. However, this should not be the sole driver of management decisions. Without clear conservation objectives, robust monitoring, and policy safeguards, economic motivations may overshadow ecological priorities, potentially leading to exploitation rather than restoration. Effective management requires transparent frameworks that prioritize ecosystem health, supported by adaptive policies responsive to changing pressures and ecological feedback.

Sustainable solutions for managing invasive alien plants rely on several key elements that enhance effectiveness. A rigorous monitoring and adaptive management approach is essential for successful restoration. Regular assessments of invasive populations and the impacts of resource extraction, alongside integrated control methods such as clear-felling, biological control, and fire management, can improve long-term outcomes. Innovative financing mechanisms, such as conservation funds supported by the forestry industry that utilize invasive alien plants and carbon credits, can aid ongoing control and restoration efforts, thereby reducing the heavy reliance on revenue from these invasive species in protected areas. Additionally, strong policy support and stakeholder engagement are crucial for aligning economic interests with conservation goals. Focusing on these interconnected strategies can effectively address the challenges posed by invasive alien plants.

Ultimately, while exploiting invasive alien plants for revenue may offer a significant solution to finance protected areas affected by them, it must be part of a comprehensive, evidence-based management plan where conservation outcomes take precedence. As supported by global literature, the long-term sustainability of biodiversity and ecosystem services depends on prioritizing eradication or control strategies, rigorous ecological monitoring, and sound policy frameworks, rather than relying solely on the economic benefits generated by invasive alien species.

Conclusion

Harvesting invasive alien plants can provide quick but temporary financial gains and should be viewed as a transitional strategy rather than a long-term solution. On its own, especially when based on selective felling, it is insufficient and does not ensure ecological restoration unless explicitly embedded within robust, integrated, and science-based management that prioritizes clear conservation objectives and uses short-term revenue to finance lasting biodiversity protection.

Supplemental Material