I live in the town ofWanganui, on the banks of the Whanganui River. This is on the West Coast of the lower part of the North Island. The Whanganui River starts on the shoulders of the volcanoes on the central plateau. Volcanoes called Ruapehu, Ngauruhoe and Tongariro. There is a lovely Maori legend of how the Whanganui came to be.

The entire length of the river, from mountain stream to tidal mouth, is 290 km, and 200 kilometers of that is navigable by boat (see all the canoe trips listed below). Steam and paddle boats used to provide passenger services as far up the river as Taumarunui. These days only jet boats and canoes ply the upper river. Canoes are especially prominent because the Whanganui river is part of the Great Walks of New Zealand, and has the distinction to be the only river journey.

However, the Whanganui does draw from a large catchment and if excessive rains fall, as they did about 3 months ago, then it floods. At the mouth, where I live, the flooding wasn't too bad. The river crept over its banks in some places and left a 30 - 50 cm deposit of silt as a calling card. The amount of trees and debris, including whole rafts of floating pumice from the volcanic plateau, hurtling down the otherwise placid river was phenomenal. But all that material had to come from somewhere, somewhere upstream.

The purpose of the jet-boat ride on this fine, slightly overcast day, was for the DoC journalist JP to see and record the damage caused by the floods. DoC maintains camping sites (with a toilet and water catcher) at approximately one day (canoe paddling time going downstream) intervals along the river. My task was to observe the damage, if any, caused by possums and goats. We drove up to Pipiriki, at the downstream end of what is known as the river gorge. Here we hopped into one of the Doc jet-boats ably skippered and trailer maneuvered by DM.

The river on this day was smooth and calm and the rapids mere ripples because the river is still in winter mode, and 2 m higher than in summer. The banks on either side rapidly closed in, until we were hurtling up a canyon some 30 - 40 m wide and up to 70 m deep in places. In most places the forest, with a fringe of tree ferns, comes down to about 3 m above the water level. Below that level are smaller hardy plants that can regrow quickly after floods.

Flood damage and evidence became obvious quite early on, paper and debris stuck in the branches of trees a good 7 m above our heads. GOODNESS, THE RIVER ROSE 7 M !!!! where did all that water go? The force must have been phenomenal! (Infact I discovered later that in some places the river was 16m above normal flow!!!! ) You could also easily tell that many of the banks had very recently eroded, some to quite a degree. A couple of months later we had another even bigger flood which washed even more of the repairs out. On that occasion the river rose by 18 m in the canyon, and gently flooded low lying parts of Wanganui.

Our first stop was the Upper Mangapurua campsite opposite the end of the track to the Bridge to Nowhere. Conservation Corps teenagers were doing a great job digging new tent sites, steps up to the relocated toilets and a new home for the undermined water-catcher. All this work was badly needed because the front 10 m or so, where the level camping area used to be, is now a sloping layer of silt that starts only a few metres from the bush edge. The new tent sites are precariously perched on the interface between two habitats, the river and the bush, with nowhere else to go because cliffs form the backdrop.

All the camping sites we looked at were similar, the camping areas, mainly old silt build ups from previous eras, were reduced to sloping silt deposits, soft and crumbly underfoot. The amount of work to restore some of these sites to usability is enormous, and some might never be able to be opened again because there is just not enough land left in front of the cliffs or the bush edge. That is going to make canoeing trips a lot harder for people floating down the river.

As if that wasn't depressing enough, I had been keeping an eye on the bush. We spotted at least a dozen goats, mostly jet-boat shy after the recent cull by hunters from boats. To see that number after all the effort spend on hunting them down showed me just how many of those fleetfooted ground-harvesting machines (called goats) are wrecking Whanganui National Park. Goats just about vacuum the forest floor for tasty tit-bits, they especially like the seedlings of the canopy trees. Unfortunately this means that if a canopy tree dies there are no seedlings to replace it and fill the gap.

Sure, the understorey of the forest still looks relatively green and healthy, but those are the species that the goats don't like, and most of them are short scrubby species that never make it to good canopy height. So, eventually, the canopy of the forest gets lower and lower as the tall trees die, and only the short scrubby species are left. It won't be a forest anymore at that point, but a shrubland. That is why we are hammering the goats, deer, and pigs where and whenever we can.

I have some more bad news however, it is not only the forest floor that is getting a beating, we have aerial vacuum-cleaners too, the possum (Trichosurus vulpecula - quite a different beastie from the American Opossum). Not much in the way of ripe fruit ever gets to the ground to germinate because the possums eat the unripe fruits and flowers and most of the leaves too.

The possum was introduced from Australia as a fur species. Indeed, it has a lovely pelt, and was introduced throughout the country and extensively hunted for that reason. Minor problem, the New Zealand forest has done without mammalian browsers for millions of years. In fact, until the arrival of man the only land mammals were a couple of species of small bat (more about bats). What this means is that the trees of the New Zealand forest are not used to and can not cope with being constantly eaten to bare branches.

For possums NZ must really be Godzone, because in Australia the trees have developed sophisticated chemical defenses to reduce the amount of foliage and fruit eaten by this fury marsupial. New Zealand trees don't have such defenses and the possum is probably in heaven eating desert flavoured trees morning, noon and night (well, mostly night, seeing that they are nocturnal). I'm just glad for small mercies. We use a naturally occurring, chemical called 1080 to reduce possum numbers. In Western Australia the levels of 1080 in the leaves of plants can be higher than the effective dose to kill possums here in NZ. Luckily the early settlers grabbed possums from Tasmania and Queensland where 1080 levels are much lower and the possums much more susceptible to the stuff.

It is estimated that New Zealand has about 70 million possums and that between them they eat about 21 000 tonnes of leaves, shoots, fruits and flowers every 24 hours, that is a large container ship full every day. To put that in perspective there are about 50 million sheep, for which New Zealand is famous, and 3.5 million people living here. So we are severely outnumbered by the Aussie import.

The New Zealand forests just can't cope with that amount of foliage browse and it shows. Everywhere that I looked along the Whanganui river trench I saw bare branches, dead and dying trees and very little in the way of fruits or flowers. The damage occurs in patches, you might see one bit and think "that's not too bad" but around the next bend, or over the next spur, you are faced with a grey forest, mostly dead and dying branched sticking up. And, DM mock cheerfully told me, "the bush on the river trench is actually in comparatively good nick, it gets worse further in". As if it could get any worse.

Whanganui National Park is 74 231 hectares of forest under siege. And it is my job to monitor the changes in this forest, hopefully for the better. The task is totally daunting, the terrain consists of steep hills and impenetrable gullies, real remote experience area and nearly impossible to monitor properly. What makes it even worse is that Whanganui National Park is only one of many forests I and others in my office have to look after. Don't think I'm going to get bored in a hurry, plenty to do here.

Just to leave you on a positive note, one side along part of the Whanganui River trench has had a possum control operation through it. And I could definitely pick it even before I was told. If you happen to go down the river one of these days see if you can too. Here is what to look for, the forest looks greener (or not so grey) with fewer dead trees poking up, the canopy is more closed and individual trees are harder to pick out, you might notice more flowers on one side than the other too. When I went through the Clematis paniculata was in flower, much more obviously so on the side with possum control. Locals in the area say that they hear more birds than before along that stretch too.

Mind you, I hope that the difference is going to get more difficult to pick as time goes by, because hopefully we can do the scheduled possum control on the other bank sometime soon.

Ps, I really did enjoy the jet-boat ride, only my second time in a jet-boat :-)

Some additional reading, in case you want it.