Braided Rivers - Weed Mapping

A map showing weed distributions by species in two different years

Created by: canterburymaps
Last updated: Thursday, January 28, 2021

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Description

Environment Canterbury commissioned weed mapping by species and abundance in and adjacent to riverbeds for selected braided rivers and weed species.  This has been undertaken to help meet the Braided River goals and targets under the Canterbury Water Management Strategy (CWMS).  

The upper Rakaia River was surveyed in 2013 and 2018 (similar areas but see note below), the upper Rangitata in 2019, and the Waiau Toa Clarence River in 2018 and 2019 (note: the data is listed as 2019 for both years).  There are reports available for each survey including weed control recommendations.  Limited weed control work was undertaken at the same time for remote scattered weeds where time and access allowed.  

The surveys and associated maps are being used to inform a strategic approach to weed control for high value braided riverbed habitat (for nesting birds), for outcome monitoring (when repeated), to track changes in distribution and abundance over time, for surveillance of new species incursions, and to control scattered remote plants.

Rakaia River notes

The two maps (2013 and 2018) are not directly comparable due to differences in effort and mapping accuracy between the two surveys.  Additional effort was directed to the upper extent of the weeds in the 2018 survey.  

Summary concerning the differences for the upper Rakaia for 2018: most of the key riverbed weed species (broom, gorse, crack willow, grey willow, and tree lupin) remain widespread, but with no significant increase in their distribution since 2013.  In some places there has been a noticeable reduction in extent and density as a result of recent weed control work.  Conversely there has been a substantial increase in the distribution and abundance of false tamarisk and to a lesser extent stonecrop.  This is based on a variety of information that includes data not in the 2013 maps.

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