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A classification framework for woody vegetation on farms 

Retention and restoration of on-farm forest is a critical tool for sustaining native biodiversity in our agricultural landscape.
 
While the area and distribution of remaining native vegetation can be quantified using GIS data, it is also important to understand the function of the different types of native vegetation present.


Within NZ farms, some native vegetation occurs as remnants of the original forests, some has regenerated following earlier clearance and subsequent abandonment of agriculture, while restoration continues to establish new areas of native vegetation.
 

Remnant native forest (left) creates a different functional ecosystem to forest that has been grazed and is now regenerating (right).

The degree of intactness of native woody vegetation is important. In many agroecosystems the presence of grazing and other agricultural practices mean that native woody species might occur as scattered trees, or groups of trees, within a predominantly pasture-dominated matrix.

 

Farms also contain significant areas of non-native woody species that can be important for biodiversity conservation, erosion control and carbon sequestration.
 

Different areas of Aotearoa support different species, but we wanted to come up with a framework that can compare the type and function of the vegetation, regardless of species composition. 

 

This would enable us to compare woody vegetation patches on farms across the country.

 

A functional framework like this is important for planning how to implement new restoration initiatives, as well as for deciding which vegetation to retain in the landscape. 

What we did

We mapped all of the woody vegetation on our three study farms onto satellite imagery of the areaWe then used this, and remote sensing data, to develop farm-scale maps of woody vegetation.
 
Based on these surveys and more general knowledge of New Zealand woody vegetation, we identified key functional attributes for the classification:
 
1) The history of the vegetation (remnant/regenerating/planted)

2) The origins of the dominant woody species (native/exotic)

3) The amount of canopy cover (low-100%)
 
Each class can be further refined by how modified the vegetation has been by anthropogenic factors (timber extraction, grazing etc). 

An excerpt of the vegetation map for our Ruapehu farm

Continuous (>70% canopy cover)

Diffuse (<70% canopy cover)

Remnant 

Native

Patches that have always been present 

Containing old-growth canopy trees

Could have been modified (eg. historical logging)

More open version of continuous

Includes grassy clearings

Old growth canopy trees still present

Regen.

Native

Established on sites that were previously pasture  

Fast-growing canopy trees (eg. tōtara, kahikatea) or seral species (eg. kānuka, mānuka) are dominant Widespread in rural NZ

Same as continuous but with lower cover and lots of grassy clearings

Regen.

Exotic

Unplanted weedy forest

Dominated by wild conifers, willows, sycamore, etc

Same as continuous, but with grassy clearings

Planted 

Native

Native forest restoration sites  

Forest trees (as opposed to shrubs) have been planted

Discontinuous native forest restoration sites  

Usually a result of being at an early stage of growth or having partially successful establishment

Planted 

Exotic

Plantation forests and farm woodlots

Pine, Douglas fir, eucalypts etc. 

Erosion plantings (eg. poplars, willows) and shelterbelts Classical agroforestry