Alien Invasive Species Management

ENVASS has a holistic approach to all matters pertaining to the environment and consequently, we ensure that every aspect impacting on the environment is taken into account. As part of our scientific approach to alien invasive species identification, mapping, control, and eradication – we include a biodiversity assessment on indigenous vegetation. Our clients are not charged extra for this as it can be done simultaneously with alien invasive surveying. Biodiversity assessments are important as part of an alien invasive management plan due to the threat posed by aliens to biodiversity. By knowing how species-diverse a particular site is, one can determine the significance of the threat by aliens and act accordingly.


Invasive alien plants are described as species which are ‘non-indigenous’ to an area and which have been introduced through anthropogenic activities from other countries either intentionally (for domestic or commercial use) or accidentally; furthermore, they have the ability to reproduce and spread without the direct assistance of people into natural or semi-natural habitats and are destructive to indigenous biodiversity and human interests (WESSA-KZN, 2008).


The National Environmental Management: Biodiversity Act 2004 (Act No, 10 of 2004) together with Notice 3 of the 2016 updated NEM:BA Alien and Invasive Species List, lists 379 plant species that are legally declared invasive species. Each species is assigned to one of three categories based on the level of threat posed by the species and the legal status assigned to each:

  • Category 1a – Plant species that must be immediately controlled and eradicated.
  • Category 1b – Plant species that must be contained and controlled.
  • Category 2 – Plant species that requires a permit for a restricted activity and should be contained, the species must be contained and treated as a Category 1b species if no permit is issued.
  • Category 3 – Invasive species regulated by activity, individual plant requires a permit for the listed activities (import, possess, grow, breed, move, sell, buy or accept as a gift). If identified in a riparian zone it must be considered a Category 1b species.

Invasive Species and must be managed according to regulations prescribed in NEM:BA, 2014 and the 2016 updated NEM:BA Alien and Invasive Species Lists. The management plans and biodiversity protocols should be generated by utilizing the protocols and guidelines as indicated in the Draft Species Environmental Assessment Guideline (SANBI, 2020).

River Health Assessments (SASS5)

The SASS method is based on the British Biological Monitoring Working Party (BMWP) method and has been adapted for South African conditions by Dr. F. M. Chutter (1998). It must be noted that this method has been specifically designed to be used in low to medium flow hydrology and is not applicable for wetlands, impoundments, estuaries and other lentic habitats (Dickens & Graham 2002); furthermore, it should be noted that this method should be used with caution in ephemeral rivers as it has not been sufficiently tested in these environments.
The SASS method works on the principle that some macro-invertebrates are more sensitive than others, therefore if an abundance of pollutant tolerable species are found, but no sensitive taxa, it would be an indication that the water is polluted. It works well as aquatic macro-invertebrates are not prone to migrate over large distances and are rather sedentary thus proving a reasonably accurate representation of a localised area. The SASS5 method works best when there are a variety of biotopes including riffles or rapids, but it is not limited to this type of  environment; it can produce valuable data from poor habitats (Dickens & Graham, 2002). Of crucial importance for this method of bio- assessment is the interpretation of data in relation to the habitat quality, availability of different biotopes and ultimately in relation to the ecoregion of the subject area. Other factors to take into consideration are seasonality – it is necessary to interpret the data based on the season of the assessment as well as the overall climatic conditions, especially in areas prone to droughts.

Wetland Delineations

Wide variation exists within wetland ecosystems, but it is considered feasible to have a general set of criteria to guide and standardise delineation. Wetland delineation is a very well established practice, with a strong scientific and legally-defended base, especially in the USA (USACOE, 1987; National Review, 1995). There is evidence from within South Africa that the current national wetland delineation method (DWAF, 2005) allows for identification and delineation of most wetlands, in most landscape settings, nationally. The method relates to the existing wetland definition in the NWA (Act 36 of 1998).

Wetland delineation includes:

  • confirmation of the presence (and size) of wetland; and
  • an approximate determination of the outermost edge (boundary) of the wetland.
  • Wetland delineation should result in three things:
  • a wetland boundary indicated on a map, and where necessary, in the field;
  • a map that clearly identifies data collection points and the boundaries of the delineated wetland (topographic and aerial site maps); and
  • a report that explains how the boundary was determined.

Ecological Studies

Environmental Assurance (Pty) Ltd has an in-house Ecology Unit that serves to conduct ecological assessments and other specialist studies pertaining to biodiversity impact assessments and ecosystem disturbances.

The study of environmental systems or economy of nature (ecology) is used to connote some sort of normative or evaluative issues regarding the environmental status. As part of ecology, biodiversity measures the health of the ecosystem. Analysing how the environment functions is an empirical tool used to understand the biodiversity that sustains the ecosystem that drives the ecology of the area.

Rapid environmental changes and human impact have caused a significant environmental impact that affects species on many levels. Therefore, ecology can be very useful to help understand what these impacts are, their implications on various ecosystems, and interventions that might influence socio-economic or nature and to try to mitigate or otherwise alter these changes/impacts.

Visual Impact Assessments

People`s sense of place and perception can easily be influenced by the development of the landscape and environment where they are located. The scenic and visual components of the environment is a valuable resource to people and developers alike of which the personal value and enjoyment can be compromised by existing and potential future uses. ENVASS provides a Visual Impact Assessment (VIA) service for personal and public developments to assess the significance of the visual impacts caused by or potentially caused by new developments. VIA`s are often required as part of a Basic Assessment (BA), Scoping or an Environmental Impact Assessment (EIA).

A significance assessment is performed by defining the closest zone to the development activities of most significant impact, along with an extensive survey of the site and surrounding areas to determine the visibility of the proposed development from various viewpoints and in the receiving environment. The result is a report stating the impact and provides mitigation measures which can be implemented to ensure that the impact is minimal.

Visual Impact Assessments aim to describe the current and potentially affected environments through using a range of objective and subjective assessment points. Inclusive to the development and modelling of viewpoints and high sites in GIS maps. The result is a substantiated report detailing the impact and potential mitigation measures that can be applied to the development to minimise the visual impact. Visual Impact Assessments can be combined with remote sensing technology to provide current and up to date information related to aerial imagery, contours, heights and sizing of structures to create a holistic assessment.

Noise Studies

Noise can easily become a nuisance and is therefore defined as an “unwanted sound” or an audible acoustic energy that adversely affects the physical and/or psychological well-being of people. Noise leads to the disturbance of peace, personal wellbeing and various other impacts. Sound is the results of pressure changes in the air, caused by vibration of turbulence. The ENVASS team measures these changes in the air by the using a calibrated Type 1 sound level meter in accordance with the South African National Standard (10328:2008 methods for environmental noise impact assessments), to evaluate the noise impact. Measurements are further evaluated against the Department of Environmental Affairs and Tourism Government Notice Regulation (GNR) 154: Noise Control Regulations in Terms of Section 25 of the environmental Conservation Act, 1989 (Act No. 73 of 1989), together with SANS 10103:2008. It is important to control noise both pro-actively and reactively before it becomes a nuisance. ENVASS provides a report on the measured noise and possible exceedances of health and environmental noise limits and includes mitigation measures that can be implemented to reduce, prevent and manage the noise impact. These noise assessments reflect the current state of ambient and generated noise in terms of their environmental impact and is assessed in terms of the set maximum noise level allowed per assessment area. These assessments can be undertaken before any development occurs to detail ambient conditions or repeated depending on the need of the assessment. Results provide a clear and concise result of exceedances of noise limits should it occur.

Odour Assessments

Unwanted odour emissions are a problem for many industrial processes such Landfills, Waste Water Treatment Works, Slaughterhouses, etc. Odour itself is a combination of many different compounds and gases. Many of the compounds that combine to produce odours are the result of anaerobic bacterial decomposition of organic materials during storage or natural desertion. Decomposition rate is affected by temperature, pH, and moisture. ENVASS assists in identifying odour emissions that can adversely impact on the well-being of the surrounding land users and the receiving environment. A Report is compiled on the possibility of odours impacting on the land users and includes precautionary actions and management measures that can be taken to minimise the effect of the odours on the receiving environment.

Odour assessments are undertaken by a panel of assessors who through a subjective assessment determine and rate the impact of the observable odours. These assessments can be further supplemented with characterisation of the actual emissions generated and modelled by using dispersion modelling of the odour constituents to provide an expected area of influence and potential mitigation and management measures.

Waste Classification

Waste has to be classified in accordance with the National Environmental Management: Waste Act (Act 59 of 2008) [as amended] (NEMWA) Waste Classification and Management Regulations (Government Notice 634 – 635 of 2013) to determine the necessary liner requirements and related disposal mechanisms and methods for an identified waste type, for waste facilities. ENVASS collects samples of waste and contracts a registered laboratory to conduct tests on the waste samples in order to obtain concentrations of parameters, which can be used to classify waste.

Land Capability and Soil Remediation

Taking a variety of variables in consideration after analysing various samples from an area for which a land capability and/or Soil Remediation Plan is required, ENVASS can determine the current state of the soil, its fertility, levels of erosion, causes of erosion, levels of pollutants, nutrient deficiencies and more. In addition to this, a team of dedicated scientists can make recommendations as to minimise impacts on the soil and land as a whole, remediate the area and/or restore it to a state close to the original. This may either be to prevent further damage or to increase the value of a property by creating a sense of place or restoring the land to be agriculturally viable.

FRAI (Fish Response Assessment Index)

The purpose of the Fish Response Assessment (FRAI) is to provide a habitat-based, cause-and-effect underpinning fish communities and habitats to interpret the deviation of the fish assemblage from a Fish Reference Frequency of Occurrence (FROC) database in accordance with the SQR fish data from DWS (2013) and is implemented by the National River Health Programme (Kleynhans et al., 2007). The FRAI methodology was implemented to evaluate the existing state of the fish communities. This community metric measure allows for the evaluation of a range of metrics (flows, cover feature availability, migration impacts, water quality impacts and alien invasive fish’s impacts) that are known to affect fish community conditions (Kleynhans et al., 2007).

Effective fish sampling included an electro-fishing apparatus (SAMUS 1000®) for 45 minutes per site. Stunned fish is then collected, photographed, identified and released. All fish sampled were identified using Skelton (2001). Fish data was collected using the protocol prescribed for velocity/depth-categorised habitats (Kleynhans et al., 2007). Undercut banks and riparian vegetation were identified, their coverage estimated and scored. The fish and environmental data collected during this study was used to determine the ecological integrity of the fish communities. The reference frequency of occurrence developed by Kleynhans et al. (2007) was used in conjunction with the fish species list per quaternary reach in the SQR data provided by DWS to determine the reference fish species list in order to calculate the FRAI.

The FRAI was used to address specific information requirements regarding the response of fish assemblages to changes in the environment (Kleynhans et al, 2007). These ecosystem variables usually include physical and chemical variables, which are referred to as “ecological driver components”.

An assessment of the responses of the species metrics to changing environmental conditions may be done either through direct measurement (surveys) or are concluded from the change in environmental conditions (habitat) (Kleynhans et al., 2007). Evaluation of the derived response of species metrics to habitat changes is based on knowledge of the ecological requirements of species. Changes in environmental conditions are related to fish stress and form the basis of ecological response interpretation (Kleynhans et al., 2007). These metric groups include: the available habitats or velocity and depth; a cover metric which considers the preferences of overhanging vegetation, aquatic vegetation, water column, substrata as well as undercut banks and root wads; flow modifications in terms of volume, timing and the duration of flows; migration and introduced species. As a result, expected and actual patterns can be evaluated to achieve an Ecological Category (EC) rating as seen in the table below.

VEGRAI (Vegetation Response Assessment Index)

Riparian vegetation areas are divided into two sub-zones, marginal and non-marginal zones. This is important given that riparian vegetation distribution and species composition varies in different sub-zones, which has implications for flow-related impacts. The EC of the riparian zone is then assessed using the Riparian Vegetation Response Assessment Index (VEGRAI) level 3 (Kleynhans et al., 2007).

Since all VEGRAI assessments are relative to the natural unmodified conditions (reference state) it is necessary and important to define and describe the reference state for the study area. This is done (in part) before going into the field, using historic aerial imagery, present and historic species distributions, general vegetation descriptions of the study area, any anecdotal data available and knowledge of the area and comparison of the study area characteristics to other comparable sections of the stream that might be in a better state. With this information, the reference (and present state) is quantified on site; the assessor reconstructs and quantifies the reference state from the present state by understanding how visible impacts have caused the vegetation to change and respond. Impacts on riparian vegetation at the site are then described and rated. It is important to distinguish between a visible / known impact (such as flow manipulation) and the response of riparian vegetation to other impacts such as erosion and sedimentation, alien invasive species and pollution. If there is no response to riparian vegetation, the impact is noted but not rated since it has no visible / known effect. These impacts are then rated according to a scale from 0 (No Impact) to 5 (Critical Impact). Once the riparian zone and sub- zones have been delineated, the reference and present states have been described and quantified (basal cover is used) and species description for the study area has been compiled, the VEGRAI metrics are rated and qualified (Kleynhans et al., 2007).

The riparian ecological integrity was assessed using the spreadsheet tool that is composed of a series of metrics and metric groups, each of which is rated in the field with the guidance of data collection sheets. The metrics in VEGRAI describe the following attributes associated with both the woody and non-woody components of the lower and upper zones of the riparian zone:

  • Removal of the riparian vegetation;
  • Invasion by alien invasive species;
  • Flow modification; and
  • Impacts on water quality.

Results from the lower and upper zones of the riparian vegetation are then combined and weighted with a value that reflects the perceived importance of that particular criterion in determining habitat integrity, allowing this to be numerically expressed in relation to the perceived benchmark. The score is then placed into one of six classes, namely A to F (Kleynhans et al., 2007).

Other services

Request a proposal

To request a proposal, please fill in and submit the form below: