Introduction

Invasive alien plants (IAPs) have been described as environmental nuisance or pollutants due to their roles in threatening biodiversity, natural ecosystems, human wellbeing and livelihoods1,2,3. Their impacts on the ecosystems have led to biodiversity loss, endangering native plants and altering the structure of the plant communities where they invade4,5,6. Recently, ecologists have been assessing the invasive ability of plants through their functional traits7. Functional traits are described as those attributes of plants (i.e. morphological, biochemical and physiological) which are related to changes in the environment8, Marteinsdóttir and Eriksson 2014). Generally, they are those features that are influenced by the environment (Shipley 2010).

Functional traits have been used to assess the impacts of invasion on ecosystems and for understanding the drivers of invasion success of IAPs9,10. This could be achieved through comparing the functional traits between native and IAPs which would reveal distinct traits differences between them. Although, in some circumstances, there may not be clear differences between the functional traits of native and IAPs11, particularly due to the growing conditions. The ability of IAPs to compete better, adapt to disturbances and varying environmental conditions has been linked to some growth and reproduction-related traits such as heights, leaf area, size and photosynthetic rates, seed production and germination12,13. However, these invasion-promoting traits are habitat-dependent and diverse traits are responsible for invasions14.

Plant functional traits are very important in helping us understand how plants respond and adapt to varying site conditions and land use types, due to their direct influence on growth, reproduction, and establishment under different environments. Plants’ strategic response to disturbances and resource availability is demonstrated by the influence of soil abiotic factors such as moisture availability, organic matter and nutrients on some plant traits including leaf thickness (LT), specific leaf area (SLA), leaf water content (LWC) and wood density (WD)15,16. For instance, lower WD and higher SLA are described to be closely associated with plants that are fast-growing and having high acquisitive strategies in nutrient-rich environments, whereas LT and high WD are associated with plants ability to conserve resources in nutrient-poor or stressful conditions17. Studies have also shown that some soil conditions such as organic matter and nitrogen have strong impact on the community-weighted mean traits, which eventually drive ecosystem functions including carbon storage and productivity17. Intra and interspecific trait variability enhance plant communities to adapt to different land use changes, by adjusting community composition in line with the traits that are well suited to the new conditions15.

Hyptis suaveolens, an annual herb and a prolific seed producer, can yield up to 3000 seeds/m2 in dense vegetations. This enables it to form persistent propagule banks within a short period of time and usually reaching up to 3 m in height18,19. Taxonomically, H. suaveolens belongs to the family Lamiaceae which comprises about 300 species20. Although this species originated from the neotropics (particularly Central America), it has since been introduced to other tropical and sub-tropical regions. It is spreading rapidly in India21, and was first recorded in Zhejiang, China in 201322. However, the time of its introduction to Nigeria was not documented until recently when it began to spread profusely across different disturbed landscapes in northern part of the country23. In terms of habitat, this species is common in wetter tropical regions, but it can also occur in sub-tropical and semiarid environments. It is a weed of roadside and cultivation field, pasture, rangeland, grassland, open woodlands, riverbanks, flood plains, coastal regions, disturbed sites, and wasted areas21.

Padalia et al.21 modeled the potential distribution of H. suaveolens and suggested that some areas in the tropics are climatically suitable for this species with West and Central Africa, tropical Southeast Asia and Northern Australia at high risk of invasion. In Nigeria, it has been predicted that the highest percentage of the land (47.5%) likely to be invaded by H. suaveolens is in Nasarawa State, followed by Rivers state and Abuja and the least affected state is Adamawa state24. Hyptis suaveolens exhibits a high level of genetic polymorphism and plasticity, a quality that enhances its adaptability to diverse environmental conditions and that results in inter and intra-population variability of its chemical components25, as well as seeds polymorphism26.

Consequently, this species competes with some crops such as Arachis hypogaea for nutrients and space27. Its allelopathic properties against other crops in controlled trials has been reported28. In disturbed habitats, Hyptis suaveolens form dense thickets and could limit native vegetation19. This species spread rapidly in new habitats and affects biodiversity and productivity of the invaded ecosystem. There is a need for understanding the functional traits variability across its distributional range as part of unravelling its mechanisms of invasion. This is vital in the management of the plant. Assessing and isolating the functional traits that enable it to become invasive across its distributional range will also help in ensuring the implementation of trait-targeted management and control measures at the affected sites in Nasarawa State, Nigeria. Hence, this study aimed at examining the intraspecific functional traits variability of H. suaveolens across its distributional range in Nasarawa State. Our research question was whether the functional traits (FTs) of H. suaveolens would differ with respect to the land use types at the different study sites.

Materials and methods

Study area

The samplings were carried out in three Local Government Areas (LGAs) of Nasarawa State, Nigeria namely Lafia, Doma and Akwanga (Fig. 1). Doma occupies an area of 3656 Km2 with a population of 139,607 in the 2006 census The predominant people in Doma have farming as their major occupation. Climate in Doma is described as having an average annual temperature and rainfall of 300C and 1750 mm respectively. Akwanga occupies an area of 996 Km2 with a population of 513,930 in the 2006 census. The major occupation is mining and farming29. Lafia, being the largest city of Nasarawa State is also the capital which has an area of 2,827 km2 and a population of 330,712 in the 2006 census. Lafia has a hot, humid climate, partly cloudy dry seasons, with an annual precipitation range of 1000 to 1500 mm and mean annual temperature range of 24 °C to 33 °C30. The prominent land use in the three study areas include farmlands, built-up areas, wastelands (abandoned land), forested areas, roadside, and wetlands. However, the study sites were chosen to be the land use types that were heavily invaded by Hyptis suaveolens.

Fig. 1
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Map of Nasarawa state showing Lafia, Doma and Akwanga Local government areas.

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Sampling techniques

The geographical coordinates data for this plant at each site was collected using a GPS device and digital camera was used to capture notable features during study. Within each site, an area of 100 × 100 m2 was demarcated for the study. Each site was located at each different land use types (i.e. roadsides, farmland, and abandoned land). This gives rise to a total of nine sites for the whole study (i.e. three sites per each local government area). At each site, the traits of H. suaveolens were determined using ten 1.5 × 1.5 m2 quadrants placed at 2 m intervals on a 100 m transect31. This study was done towards the end of the growing season (i.e. between July and December) in the year 2023. The FTs, which include whole plant, foliar,regenerative; stem; and below ground traits were determined31. Apart from the functional traits, the abundance data for all the plant species encountered in each quadrant was also documented. The identities of the plant species were established on the field through the help of a taxonomist who was part of the sampling team. Those with difficult identification were taken to the herbarium of Department of Plant Science and Biotechnology, Federal University of Lafia, Nigeria for proper identification. The data collected was used to estimate the diversity indices of the plant community of each site.

Functional traits measurements

All the selected FTs for H. suaveolens represent its potential for using and storing resources in the habitat32. The FTs were assessed at the quadrant level at each site, and they include the following:

Whole plant functional traits

The whole plant traits that were determined include the growth form, life form, clonality and plant height. The growth form, life form and clonality were visually observed in the field being categorical traits33,34,35. The underground organs of the plant were classified following the descriptions by Klimeš and Klimešová36. As for the plant height, at least ten healthy and mature individuals of H. suaveolens were measured per quadrant at each site.

Foliar and stem traits

The same individual plants used for plant height determination were also used for the foliar and stem traits determination. The specific leaf area (SLA) was determined on each plant by dividing the leaf area by its dry weight. The leaf area was determined following traditional method of measuring the leaf length and width and then multiplying both together with a correction factor 2.32537. The fresh and dry weights were used to calculate the leaf dry matter content (LDMC) and stem dry matter content (SDMC) following standard methods32. The thickness of the bark was also measured.

Below-ground and regenerative traits

Specific root length (SRL), fine root diameter (FRD), and root depth distribution (RDD) were measured following methods described by Akomolafe and Rahmad31. The resprouting ability of H. suaveolens was determined by studying parts of the sites where removal of aerial parts (the shoots) of the plant had occurred (Plate 1). This was determined by the ability of the plant to produce new shoots after removal of the older ones38. At the point of the disturbance, plots of 20 m × 20 m were marked and the numbers of new shoots resprouted after four to five months were documented.

Plate 1
figure 2

Resprouted plant from the destroyed shoots of the plant.

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Statistical analyses

Principal component analysis (PCA) was used to isolate the FTs regarded as the axes of specialization of the plant at each site31,39. The VARIMAX rotation method was employed to maximize the correlations between the PCA components and the quantitative FTs considered. Through this, at least one trait on each PCA component with Eigen value greater than 1 was chosen as a functional marker representing each axis of specialization31. These extracted traits are regarded as independent variables driving the species niche and are the most important traits enabling the invasion of H. suaveolens at the invaded sites40. The differences in each FT between the sites were determined using a one-way analysis of variance (ANOVA). All analyses were carried out using IBM SPSS statistics version 26.

A rarefaction and extrapolation analysis which estimates the diversity indices between different plant communities without bias was used to estimate and compare the diversity indices at the invaded sites. The diversity indices include the Shannon-Weiner index, Simpson index and species richness. This was done using the abundance data of the plant species with 500 bootstrap replicates at each sampling site. The significant difference between the sites was revealed by the non-overlap in the confidence intervals of the curves41. This analysis was done using iNEXT online software62.

Results

Qualitativefunctional traitsof H. suaveolens

At all the study sites at the three locations, no difference was observed in the qualitative FTs of H. suaveolens. The growth form of H. suaveolensis is herbaceous (erect leaf) whereby it is essentially erect with leaves concentrated at the top parts. The life form of H. suaveolens is phanerophytes whereby it grows taller than 0.5 m and its shoots do not die back periodically to that height limits. H. suaveolens can be described as having clonal above ground where vegetative bud can produce new plant (including axilary buds, bulbils and turion). It is also described as plants which do not have spines, thorns or prickles but have smooth and sometimes hairy back texture. At all the sites, H. suaveolens was mostly observed to form multiple shoots from root tips after surviving major disturbance for about four months, which was mainly by clearing of the site for building and sanitation purposes. The leaves are simple and arranged in opposite direction on the root tips.

Determination of axis of specialization of H. suaveolens in Doma

The results revealed significant differences (P < 0.05) in leaf area and leave dry matter content (LDMC) across the three sites while there were no significant differences (P > 0.05) in the remaining seven quantitative FT of H. suaveolens between the invaded sites (Table 1). Eleven (11) quantitative FTs were deployed in the PCA. At the farmland site, PCA extracted four components with eigen values of not less than 1 (Table 2). The four components of the PCA explain 87.09% of the total variation in the FTs of H. suaveolens. Varimax rotation method extracted three FTs including leaf area, specific leaf area and root depth distribution which were strongly loaded on component 1. Leaf area was the most strongly correlated (r = 0.98) trait with component 1. On component 2, fine root diameter and stem specific density are the most strongly loaded (r = 0.93 and 0.65 respectively). Also, stem bark thickness, rooting depth are the strongly loaded traits (r = 0.92 and 0.77 respectively) on component 3 while plant height is strongly loaded (r = 0.69) on component 4. Therefore, the main axes of specialization of H. suaveolens at the Doma farmland are leaf area, stem back thickness, rooting depth, fine root diameter and plant height based on their loadings to the four components.

Table 1 Functional traits of H. suaveolens at different sites in Doma.
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Table 2 Rotated component matrix of PCA for Hyptis suaveolens in Doma.
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At Doma abandoned land, the PCA showed that four components explain 81.12% of the total variation in the FTs of H. suaveolens. Fine root diameter and rooting depth were loaded strongly (r = 0.96 and 0.60 respectively) on component 1 (Table 2). Plant height and stem bark thickness were loaded strongly (r = 0.95 and 0.86 respectively) on component 2 while stem specific density and stem dry matter content were strongly loaded (r = 0.91 and 0.62 respectively) on component 3. Specific leaf area and leaf area were loaded strongly (r = 0.84 and 0.68 respectively) on component 4. Out of all these FTs, the main axes of specialization of H. suaveolens at the Doma abandoned land are fine root diameter, plant height, stem specific density, stem bark thickness and specific leaf area (Table 2).

At Doma roadside, the PCA showed that four components explain 81.34% of the total variation in the FTs of H. suaveolens. Fine root diameter and stem bark thickness were strongly loaded (r = 0.94 and 0.87 respectively) on component 1 while rooting depth and specific leaf area were loaded strongly (r = 0.86 and 0.84 respectively) on component 2. Also, Leaf dry matter content and leaf area were strongly loaded (r = 0.89 and 0.77 respectively) on component 3 while stem dry matter content was loaded strongly (r = 0.82) on component 4. Therefore, the main axes of specialization of H. suaveolens at the roadside in Doma are fine root diameter; stem bark thickness, rooting depth, leaf dry matter content, specific leaf area and stem dry matter content (Table 2).

Determination of axis of specialization of H. suaveolens in Akwanga

The results revealed significant differences (P < 0.05) in only the leaf area across the three sites while no significant differences (P > 0.05) in the remaining ten quantitative FTs of H. suaveolens between the sites (Table 3). At the farmland site, PCA extracted three components with eigen values of not less than 1 (Table 4). The three PCA components explain 77.36% of the total variation in the FTs of H. suaveolens. Varimax rotation method isolated three FTs including leaf dry matter content, leaf area and plant height which were loaded strongly (r = 0.93, 0.90 and 0.88 respectively) on component 1. Leaf dry matter content was the most strongly loaded trait on component 1 (r = 0.93). In component 2, fine root diameter, specific leaf area and stem specific density were the most strongly correlated (r = 0.89, 0.66 and 0.58 respectively). Also, stem dry matter content was strongly correlated (r = 0.88) with component 3. Therefore, the main axes of specialization of H. suaveolens at Akwanga farmland are leaf dry matter content, leaf area, fine root diameter, stem dry matter content and plant height based on their loadings to the three components (Table 4).

Table 3 Functional traits of H. suaveolens at different sites in Akwanga.
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Table 4 Rotated component matrix of PCA for Hyptis suaveolens in Akwanga.
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At Akwanga abandoned land, the PCA showed that four components explain 86.68% of the total variation in the FTs of H. suaveolens. Fine root diameter, plant height, stem dry matter content, rooting depth, stem bark thickness and specific leaf area were loaded strongly (r = 0.86, 0.76, 0.75, 0.70, 0.59 and 0.52 respectively) on component 1. Leaf area and stem bark thickness were loaded strongly (r = 0.82 and 0.60 respectively) on component 2 while stem specific density is strongly loaded (r = 0.91) on component 3. Root depth distribution is loaded strongly (r = 0.95) on component 4. Out of all these functional traits, the main axes of specialization of H. suaveolens at the Akwanga abandoned land are root depth distribution, stem specific density, fine root diameter, and leaf area (Table 4).

At Akwanga roadside, the PCA showed that four components explain 87.72% of the total variation in the FTs of H. suaveolens. Stem specific density, specific root length, and stem dry matter content were strongly loaded (r = 0.97, 0.90 and 0.82 respectively) on component 1 while root depth distribution and leaf dry matter content were loaded strongly (r = 0.94 and 0.81 respectively) on component 2. Also, plant height and rooting depth were strongly loaded (r = 0.91 and 0.80 respectively) on component 3 while specific leaf area and leaf area were strongly loaded (r = 0.90 and 0.84 respectively) on component 4. Therefore, the main axes of specialization of H. suaveolens at the roadside in Akwanga are stem specific density, root depth distribution, plant height, specific root length and specific leaf area (Table 4).

Determination of axis of specialization of H. suaveolens in Lafia

The results revealed significant differences (P < 0.05) in leaf area, specific leave area, specific root length, fine root diameter, root depth distribution, stem specific density, stem bark thickness, Stem dry matter content and plant height across the three sites while no significant differences (P > 0.05) existed in the remaining of the quantitative FTs of H. suaveolens between the three sites (Table 5). At the farmland site, PCA extracted five components with eigen values of not less than 1 (Table 6). The five components explain 92.93% of the total variation in the FTs of H. suaveolens. Fine root diameter, stem specific density and stem dry matter content were strongly loaded (r = 0.83, 0.79 and 0.73 respectively) on component 1. Rooting depth and specific root length were loaded strongly (r = 0.96 and 0.95 respectively) on component 2. While root depth distribution and leaf area were strongly loaded (r = 0.97 and 0.89 respectively) on component 3. Also, stem bark thickness and plant height were loaded strongly (r = 0.97 and 0.75 respectively) on component 4. While specific leaf area was loaded strongly (r = 0.88) on component 5. Therefore, the main axes of specialization of H. suaveolens at the farmland in Lafia are root depth distribution, stem bark thickness, rooting depth, specific root length, leaf area, specific leaf area and fine root length (Table 6).

Table 5 functional traits of H. suaveolensat different sites in Lafia.
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Table 6 Rotated component matrix of PCA for Hyptis suaveolens in Lafia.
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At Lafia abandoned land, four PCA components explain 89.78% of the total variation in the FTs of H. suaveolens. Leaf area and leaf dry matter content were loaded strongly (r = 0.95 and 0.78 respectively) on component 1. Root depth distribution and fine root diameter were loaded strongly (r = 0.95 and 0.89 respectively) on component 2 while plant height, rooting depth and stem bark thickness were strongly loaded (r = 0.88, 0.79 and 0.74 respectively) on component 3. Stem specific density and stem dry matter content were loaded strongly (r = 0.87 and 0.78 respectively) on component 4. Out of all these FTs, the axes of specialization of H. suaveolens at the Lafia abandoned land are leaf area, root depth distribution, fine root diameter, plant height and stem specific density (Table 6).

At Lafia roadside, PCA extracted three components with eigen values of not less than 1. Three PCA components explain 74.66% of the total variation in the FTs of H. suaveolens. Varimax rotation method extracted three FTs including leaf dry matter content, stem specific density and stem dry matter content which were loaded strongly (r = 0.68, 0.65 and 5.1 respectively) on component 1. Fine root diameter, rooting depth and stem specific density were strongly loaded (r = 0.95, 0.76 and 0.56 respectively) on component 2. Root depth distribution, plant height and stem bark thickness were loaded strongly (r = 0.81, 0.73 and 0.56 respectively) on component 3. Therefore, the axes of specialization of H. suaveolens at the Lafia roadside are fine root diameter, root depth distribution, rooting depth, plant height and leaf dry matter content based on their loadings to the three components (Table 6).

Comparison of species diversity between the invaded sites

The results show that all the species accumulation curves reached asymptote which is an indication of the adequacy of the sampling. The highest species richness (6) was observed at the roadside land use in Doma, but not significantly different from those of the abandoned land and farmland due to the overlap in their confidence intervals (Fig. 2A). Also, roadside was observed to have the highest Shannon index (Hi = 3.7) and Simpson index (3.26) and are significantly different from the other land use types in Doma (Fig. 2B and C respectively).

Fig. 2
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Sample-sized based rarefaction and extrapolation curve for (A) species richness (B) Shannon index (C) Simpson index of the land use sites of Doma. Reference samples are indicated by solid shapes, rarefaction by solid lines, and extrapolation by dashed lines.

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In Akwanga, the highest species richness (6) was observed at the farmland land use and it is significantly different from those of the roadside and abandoned land due to the non-overlap in their confidence intervals (Fig. 3A). However, abandoned land was observed to have the highest Shannon index (Hi = 3.5) and Simpson index (2.75) and are significantly different from the other land use types (Fig. 3B and C).

Fig. 3
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Sample-sized based rarefaction and extrapolation curve for (A) species richness (B) Shannon index (C) Simpson index of the land use sites of Akwanga. Reference samples are indicated by solid shapes, rarefaction by solid lines, and extrapolation by dashed lines.

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In Lafia, the highest species richness (8) was observed at the roadside land use and it is significantly different from those of the farmland and abandoned land due to the non-overlap in their confidence intervals (Fig. 4A). Also, roadside land was observed to have the highest Shannon index (Hi = 4.52) which is not significantly different from that of abandoned land (Hi = 4.00, Fig. 4B). The highest Simpson index (3.40) was observed at the abandoned land and is not significantly different from that of roadside (Fig. 4C).

Fig. 4
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Sample-sized based rarefaction and extrapolation curve for (A) species richness (B) Shannon index (C) Simpson index of the land use sites of Lafia. Reference samples are indicated by solid shapes, rarefaction by solid lines, and extrapolation by dashed lines.

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Discussions

In Nigeria, it was predicted that about 47.5% of the land is likely to be invaded by H. suaveolens and the higher portion of it is in Nasarawa state24. This plant could have become truly invasive through evolving invasion-promoting traits over the years. Some newly introduced plants are better exploiters of unused resources in their new locations, thereby becoming invasive in the future8. Hyptis suaveolens could be described as an abundant resprouting plant due to the number of new leaves formed after the destruction of its shoots. From our study, it was observed that H. suaveolens possessed different functional traits that enabled them to colonize different habitats. This supports the report that IAPs exhibit diverse mechanisms of colonizing different habitats with respect to the habitat-specific conditions31. The similarity in the drivers of H. suaveolens observed across the different land use types study sites in the three locations could be a pointer to some shared peculiarities of the sites.

The high stem bark thickness observed in Doma farmland and roadside could be an indication of the resistance of the plant to external attacks. According to Wainhouse and Ashburner42, high stem bark thickness of plants tends to insulate meristem and bud primordial from lethally high temperatures associated with fire and protect the vital tissues in the plant against herbivores, pathogen and drought. Not only that, but it could also be possible that the plant developed high stem bark thickness as a strategy for resisting physical hazards from farm practices such as tilling and trampling. Leaf area plays a significant role in leaf energy and water balance. It has been related to climatic variation, nutrient stress, disturbance stress and high radiation stress43. The higher leaf area possessed by H. suaveolens at Doma (farmland and roadside), Akwanga (farmland and abandoned land) and Lafia (abandoned land) may indicate a high nutrient availability and utility at the sites as compared to the low leaf area at the abandoned land which may be having a high rate of radiation, heat stress, and nutrient stress43. Also, possession of high leaf area by H. suaveolens at the land uses mentioned earlier is an indication that the plant was able to compete better for sunlight than the other plants, hence photosynthesize efficiently15. The smaller fine root diameter observed across the three sites in Doma, Akwanga (farmland and abandoned land) and Lafia (farmland and roadside) may indicate greater root absorption performance of the plant in denser soils (for acquisition of soil nutrient and resources) through increase in the surface area. Also, there are high rooting depths in Doma (farmland and roadside), Akwanga (abandoned land and roadside) and Lafia (farmland and abandoned land) which show the ability to take up more nutrients and absorb water from the soil44. It makes the plants penetrate soil to absorb resources, thereby enhancing their performance in drought or nutrient-deficient soil, particularly at roadsides and abandoned lands45. Moreso, H. suaveolens needed this high rooting depth to acquire more water and nutrients than the other plants at the farmlands.

Specific leaf area explains the resource acquisition ability of plants in their habitats46. Plants with high SLA are regarded as efficient in resource acquisition and usage47. There are high SLAs at Doma (abandoned land and roadside) and Akwanga (roadside), which could be a pointer to status of resources at the sites since species with higher SLA are related with resource-rich habitats33. Many studies have also correlated SLA of plants positively with their corresponding relative growth rates43,48,49,50. Considering this, H. suaveolens could possibly be possessing a high relative growth rate in Doma abandoned land and roadside. This could be possible because in abandoned land, where nutrient levels might recover after farming activities have ceased, a high SLA could help H. suaveolens to quickly utilize the available nutrients for rapid growth. Similarly, plants species with high SLA could be well adapted to water stress than other neighbouring plants through increasing their water-use efficiency12,51,52.

Plant height is one of the drivers of H. suaveolens at Doma (farmland and abandoned land), Akwanga (farmland and roadside) and Lafia (abandoned land) which best describes its ability to adequately compete for available resources (mainly light) and tolerates disturbances in the presence of other plants40,53. The height exhibited by H. suaveolens could have enhanced its ability to outcompete for resources in the habitats54,55. Stem dry matter content and LDMC are the some of the FTs that describe the flammability and the resilience of plant species in the face of disturbances56. From our results in Doma roadside, H. suaveolens could be classified as a species which appeared to be relatively tough and are thus assumed to be highly resistant to physical hazards (for instance wind, hail, and herbivore) at that site. Since roadsides are typically disturbed environments with potentially poor soil quality and exposure to stress. Hence, a higher LDMC and SDMC could provide H. suaveolens with a greater ability to withstand these stressful conditions. However, low LDMC and SDMC of H. suaveolens in Doma (farmland and abandoned land), Akwanga (abandoned land and roadside) and Lafia (farmland and abandoned land) also explain its plasticity to adapt to prevailing conditions in different land use types57. There is a high stem specific density (SSD) in Akwanga (abandoned land and roadside) and Lafia (abandoned land) which provides structural strength that the plant needs to stand upright and the duration it needs to live sufficiently long. It could also be an indication of defense against pathogens, herbivores or physical damage by abiotic factors33.

All these identified functional traits of H. suaveolens in this study perfectly agreed with previous studies on the functional traits of invasive plants, particularly in sub-Saharan Africa. For instance, Akomolafe and Rahmad31 also reported the functional traits of an invasive fern, Pneumatopteris afra in Nigeria and discovered that these similar traits that drive its invasion differ with respect to the different study sites. Other studies have also confirmed that invasive plants are known to grow faster and taller with high specific leaf area which indicate their high resource acquisitive ability58,59. High LDMC coupled with other traits that were not assessed in this study, were also identified as drivers of invasions in other related studies5,60,61.

Conclusion

This study has identified the possible functional traits of H. suaveolens in Doma, Akwanga and Lafia local government areas of Nasarawa state, Nigeria. These include plant height, leaf area, fine root diameter, specific stem diameter, root depth distribution, stem bark thickness, specific root length, specific leaf area, leaf dry matter content and stem dry matter content as drivers of its invasion success in the three local government areas of Nasarawa state. These are combinations of traits that were possibly triggered by the prevailing conditions related to the different land use types. The identified functional traits appeared to support the invasion success of H. suaveolens by enhancing competitive ability, resource acquisition, and resistance to stress and hazardous conditions such as herbivores, pathogen, and drought stress at each land use type. Also, due to the regenerative capacity after destruction, this plant was able to persist in the studied areas.

This understanding of the mechanism of invasion of H. suaveolens in the study areas through isolating and assessing its functional traits might be useful in the implementation of trait-targeted management and controlled measures at the affected sites. Some of the suggested control measures could be by: planting of crops that can germinate, grow and mature before H. suaveolens seed set while cutting down the roots of its small infestation; and plugging before crop planting that help in reducing germination only if the seeds can be controlled (that is complete removal of the invasive plant before seed set.