With findings that will surprise some, shock others, Hawke’s Bay Regional Council released its report this week on the make-up of the woody debris that washed up post-cyclone against bridges, on beaches and littering flooded areas.
HBRC examined woody debris at 17 sites where damage occurred to bridges or had accumulated on land or on beaches. The aim of the report was to understand the likely origins of large woody debris that washed down the waterways during Cyclone Gabrielle to help inform future land use planning. Was it ‘slash’ (the result of logging) or something else.
The shock and surprise?
Most fingers lately in our region have been pointing at slash. But that not the case according to HBRC.
Regional Council’s Group Manager – Asset Management Chris Dolley says: “At all but one of the surveyed sites, there was little evidence of slash, indicating that the majority of pine came from erosion of hillsides and streambanks.”
Most punters use the term ‘slash’ colloquially to refer to all the wood debris they see littering the countryside. But technically, ‘slash’ is “generated by harvesting, pruning or thinning pine plantations. It can be identified through evidence of machinery marks or the debris having a cut mark at one or both ends,” says HBRC.
Such slash did not constitute the bulk of our woody debris. The site with the most cut pine was Mangaone at Rissington, where 9% of the timber had cut marks.
Overall, “the woody debris assessed in Hawke’s Bay consisted of a mixture pine, willow, poplar and ‘other’ – native timber and debris that could not be identified.” Its composition differed from catchment to catchment and largely was the result of whatever tree species was predominant in the catchment upstream.
The results are summarised here:
| Catchment / Area | Mix of debris |
| CHB* | Willow |
| Ngaruroro | Largely clear of debris |
| Upper Tutaekuri and Mangaone– Dartmoor and Rissington | Predominately pine with the remaining being willow |
| Lower Tutaekuri – Puketapu – Awatoto | Predominately willow / poplar with the remaining being pine |
| Esk River and Beach | Predominantly pine |
| Te Ngarue | Mix of pine and willow |
| Aropaonui (beach) | Predominantly pine |
| Waikare (beach)** | Predominantly pine |
| Mohaka (beach) | Predominantly pine with some ‘other’ |
| Wairoa (rivermouth)** | Predominantly pine |
| Mahia (beach) | Predominantly pine with some ‘other’ |
*Sites in CHB weren’t formally surveyed as it was evident from preliminary assessments that willow/poplar was the dominant timber source.
** Waikare beach and Wairoa River mouth sites were assessed by air as access to a suitable site was not found.
HBRC noted: “Pine plantations and wilding pine are found extensively across Hawke’s Bay. Much of the pine that was found at the sites tested constituted windthrown or previously dislodged pine, pine remaining from community operations or clearance, or general pine pieces that lacked evidential origins but were in the vicinity of flood waters and our river systems.”
HBRC also commented on willow, one of the most effective and commonly used species for both erosion and riparian margin control due to the strength of their rooting systems.
Normally willow do a good job of protecting stream and river banks. However, many trees could not withstand the volume and strength of the flood waters, and were found within the sites tested. Nevertheless, areas of riverbank willow plantings remained in place, “proving they remain one of the best options for erosion control”.
The full post-cyclone large woody debris assessment can be found here: https://hbrc.info/woodydebris2023.
Does this mean commercial foresters are off the hook? Not at all, for reasons that are sure to be evidenced during the East Coast inquiry into forestry practices initiated by then-Forestry Minster Stuart Nash, due to report in June (see BayBuzz coverage here).
We did a quick interview with Jon Kingsford about why we plant in the river banks if anyone is interested: https://fb.watch/jVmgY6i4sk/?mibextid=RUbZ1f
Surely it is splitting hairs to argue whether it is ‘Slash’ or other pine? 8 of the 11 sites surveyed were “predominately pine”. There fore Pine is the problem — it is not suitable for our terrain!
And I wonder if HBRC might come to regret planting willow to stabilise banks when they see the millions of shoots appearing from all the twigs and branches embedded in the silt!
Unsurprised by the HBRC load of coblers!! Just saying!! Be interesting to learn the comments from the “Elected Public Representatives” come the Next HBR Council Meeting? Hello
This finding sounds suspiciously like it’s trying to deflect blame away from pine forestry.
If one considers that a) a huge pine afforestation process followed by recent harvesting has occurred in Nth Hawkes Bay / Tairawhiti over the last 30 or so years; b) when trees are felled, branches, old thinnings and prunings break, so they’re not always going to show chainsaw cuts, and c) ‘wilding’ pine is minimal in the region; then the recent huge deposit of pine debris to be seen stretching from Mahia to vanishing point is logically a result of forestry.
Then there’s the tsunami of silt – on the face of it, likely due to forestry harvesting. The science needs to be reviewed / commissioned.
Not totally surprising actually – especially for the likes of the Tutaekuri and Ngaruroro and those further south. Ask yourselves where are the huge forests on steep and highly erodible land in the headwaters? Sure there are a few investment forests and woodlots on tributaries, and those planted in the 1990’s are beginning to be harvested – but nothing to create the huge volumes of slash seen further north. This doesn’t mean I am an apologist for (a) blanket plantings of Radiata or (b) the cavalier attitude of the corporate foresters and their harvesting methods!
The debris is nothing short of an ecological disaster and should be compared to the damage caused by strip `or open-cast mining. As a response to cyclone Bola, blanket afforestation was simplistic. The findings of the HBRC scientists, that only 8% of the debris was slash, is a very conservative scientific conclusion. That there is a much larger proportion which cannot be categorically defined either way as ‘slash’, because it doesn’t show chainsaw marks etc, is being pedantic.
A vast volume of pine/slash/waste was removed from East Coast streams, rivers and beaches by machinery (i.e. mechanical excavators, skidder’s, tracked loader’s, log handler’s, log stacker’s, etc,.. ) and natural river and beach erosion processes between 13th of February 2023 and 28 February 2023.
The report ‘ Cyclone Gabrielle Woody Debris Species Composition Assessment’ by EcoLogical Solutions, Environmental Consultants, is based on investigations (pertaining to woody debris (consequential to Cyclone Gabrielle 2023) starting on 28 February 2023.
The CCE, ‘Cyclone Disaster – NZ East Coast’ is based on investigations from the 12th of February 2023.
The CCE, ‘Cyclone Disaster – NZ East Coast’ report alleges that 96% of woody debris (in rivers and on beaches pertaining to Cyclone Gabrielle) was pine forest slash/waste material.