Vegetation surveys for restoration and conservation success
A vegetation survey is the collection of spatial data about a species or habitat. It provides a snapshot in time of species presence/absence, abundance and distribution.
Why undertake vegetation surveys?
Vegetation surveys are undertaken for a wide range of objectives such as measuring plant species abundance, evaluating the ecological resource on a site, assessing vegetation trends, or for legal reporting obligations (e.g. funding agreements or resource consent conditions).
Vegetation monitoring is a specific type of vegetation survey that involves the collection of repeated observations to detect trends over time e.g. trends in the composition and structure of plant communities as the results of environmental changes.
Vegetation monitoring is a way of measuring change over time to measure the success of restoration or conservation efforts and make informed management decisions.
The type of vegetation survey or monitoring carried out depends on the objectives of an ecological restoration project but some examples of vegetation survey types and their application are described here.
Kahikatea green wheel (KGW) assessment
Waikato Regional Council developed the Kahikatea Green Wheel (KGW) in 2021 which measures 32 ecological condition sub-attributes within lowland forest patches in the Waikato, dominated by kahikatea (Dacrycarpus dacridioides).
The KGW is based on the five-star system developed by the Society for Ecological Restoration Australasia (SERA) for measuring ecological improvement in kahikatea forest on private land.
The 32 condition sub-attributes are divided into landscape-based indicators and site-based indicators. With respect to vegetation, the sub-attributes consider:
- Native and exotic canopy, mid-storey and ground cover
- Native canopy condition
- Native plant species richness
- Native plant recruitment
- Pest plant species presence and abundance.
The KGW vegetation survey consists of a site walkover and a qualitative assessment of these attributes. Attributes are given a score from 1-5 stars creating a wheel chart showing how well a site is doing.
Long term permanent 20 x 20 m Recce plots
Permanent 20 x 20 m vegetation monitoring plots are used by the Department of Conservation and regional councils to measure long-term vegetation change over time. These plots involve:
- Tagging and identifying plants to species
- Measuring height and diameter at breast height of all stems larger than 2.5 cm at breast height.
- Completing a standard permanent plot reconnaissance (Recce) plot sheet which includes information on the relative abundance of each plant species present in seven vegetation tiers.
- Measuring 24 permanently marked understory plots within the larger plot to track seedling recruitment over time.
- Counting all saplings.
This data is then analysed and extrapolated to the wider environment to monitor changes in species composition over time, to determine the effects of exotic animals on the forest, and to calculate carbon sequestration rates.
Pest plant vegetation surveys
Pest plant surveys involve identifying, recording and marking the GPS location of weed species.
Weed distributions and densities can then be mapped and changes in weed species numbers and/or weed densities can be monitored over time.
Wetland delineation surveys are used to determine the presence and extent of wetlands based on the distribution of hydrophytic vegetation using wetland delineation protocols developed by the Ministry for the Environment and Landcare Research.
This type of vegetation survey involves identifying species within an impermanent plot and assigning a cover score to each species. Plot sizes vary depending on the structure of the vegetation:
- Trees in a prospective wetland are surveyed across 10 m radius plots
- Shrubs are surveyed across 5 m radius plots
- Herbaceous plants are surveyed in 2 x 2 m plots.
Each plant species is assigned a pre-determined wetland indicator status ranging from obligate wetland plants to upland plants. Plant presence and abundance combined with the indicator status of each plant species is then used to calculate a dominance and prevalence score of wetland plants within each plot to determine whether the vegetation within the plot is considered wetland vegetation.
If the vegetation results are inconclusive, soil cores can show the presence of hydric soils, which are indicative of wetlands. Other hydrological characteristics can also be used such as the depth of the water table, water staining on leaves, and position within the landscape.
Photopoints are a useful tool for tracking qualitative changes in vegetation over time, particularly within small restoration projects.
Photopoints are fixed locations within your site where photos are taken repeatedly over time to provide visual evidence of the change in the site.
This method does not provide quantitative data, but the images can be used to show the broad changes occurring at a site over time.
Feel free to get in touch to talk to us about how we can help you with your ecological restoration needs.