My comments refer to numbered locations marked on Appendix 4 (attached - see rhs column), continuing at Section 3 before returning to the Summary & Recommendations (Section 1) at the end.
7.0 Beech tree harvesting rates and mitigating effects on wildlife
7.1 The importance of cavity-bearing trees
24. This misrepresents the key point. There is no dispute that some of these species are obligate tree cavity nesters and roosters. What matters is whether these holes are in limited supply and influence abundance of birds or bats in anyway (sic) ( = any way?)
25. These citations cover a huge range of species and habitats, and without exception are from overseas. The DoC Critique is inconsistent in that it earlier argued that overseas studies are unlikely to be relevant to local circumstances. It is logical and expected that preferences for particular sorts of holes and limitation of numbers could result, especially in diverse faunal assemblages crowded into thin marginal strips around clearfelled areas (like the tree dwelling marsupials studied by Australian ecologists). A review on the impacts of feral honeybees (tree cavity nesters) on wildlife in New Zealand (Moller & Butz Huryn 1996) and overseas (Butz Huryn 1997) could find no evidence of tree cavities being in such short supply as to cause competition with other wildlife. As always, lack of evidence does not prove that such an effect does not occur.
7.2 Availability of wildlife trees in the Eglinton Valley
26. The 95% binomial confidence intervals on a sample of 1 tree (with holes suitable for bats) out of 78 trees are 0.033% to 6.77% (Mainland et al. 1956) i.e. the proportion of trees with bat holes may have been 5 times higher than the average used by the DoC Critique, or 39 times lower. These wide limits emphasise the uncertainty in the preliminary calculations presented here by the DoC Critique and the value of further modelling and research. No error bounds were presented on the extrapolations in the DoC report. The expected outcome could therefore be very much safer or riskier for the bats than indicated by mean value extrapolations. The value of a more rigorous and detailed risk assessment is clearly indicated. The DoC Critique is at first quite clear that it signals a potential approach rather than using the models as a firm prediction of outcomes. Unfortunately it nevertheless uses the predictions of the model to assert that logging impacts on bats and birds will occur and are even likely. Planning for a more detailed risk assessment is underway by TWC.
27. The use of such a large number of different holes by each social group is an exciting and remarkable finding of Colin O'Donnell's and Jane Sedgeley's work. Several bats shifted roosts regularly, often at almost daily intervals. This behaviour is markedly different from most overseas bats studied, perhaps in part because tree cavity dwelling bats have received little study until the New Zealand effort. The crucial issue for our present risk analysis is whether or not they need to shift so often amongst such a large number of different holes. Does the continuous mixing reflect ecological or behavioural needs, or simply preference? Does it reflect a superabundance of holes available? It may be that the bats move regularly so that they can gain information about one another for social organisation. If this hypothesis is true, then movement may be necessitated simply because a superabundance of holes exists, forcing the bats to shift more often to stay in contact. It is not known for sure what effect reduction in number of holes in the roosting zone might have on the bats.
28. Merchantable trees exclude the very large hollowed trees that will be left for birds and bats. The upper size limit of > 80 cm is claimed by the DoC Critique to be a better compromise. A formal model can test a variety of such trade-offs and consider whether the 110 cm limit proposed by TWC will be adequate to safe-guard tree-cavity availability. Twenty-two percent of bat roosts in the Eglinton Valley were in standing dead trees. These were favoured roosting sites. The calculations in the DoC Critique excluded consideration of these standing trees that will be left in situ. The calculation in the DoC Critique therefore underestimated the number of holes that will be present at Maruia, assuming that the use of Eglinton data to predict outcomes in TWC forests is valid. The larger trees undoubtedly have more holes (Elliott et al. 1996b). These authors also demonstrated that the birds added use of larger trees was not a reflection of preference per se. They used those trees more often simply because they had more holes in them, not because the quality of the holes was different in some way. This is important when predicting logging impacts because it suggests that holes in all tree sizes are equally likely to be useable (sic).
29. Allowance should indeed be made for loss of roost trees for long-term projections, but so too must there be allowance for growth of new roost trees. The calculations presented in the O'Donnell & Dilks (1987), O'Donnell (1991) and this DoC Critique are all static. The fundamental extrapolation has been that degree of tree removal in particular size classes represents degree of habitat removal - there has been no allowance for subsequent regrowth of the trees (or compensatory mortality, growth, regeneration rates triggered by tree removal), of retention of the very largest live stems and all standing dead spars, nor TWC's proposed rotational removal of ca 15% of stems every 15 years. The models are simplistic extrapolations from which exact predictions should not be attempted, in my opinion. This same caveat was mentioned at the outset by the DoC Critique, but then it nevertheless went on to conclude that the logging impacts were likely.
30. The logic for why the Eglinton availability figure is a "prudent upper limit" for Maruia is not spelled out. If this is a target for management or conservation safety (as urged by the environmental precautionary principle), then is the DoC Critique really argueing (sic) that over double the predicted existing number of holes in Maruia will be needed to safeguard bats? How could this be when bats are obligate tree-cavity dwellers? Where then are half the existing bats roosting if only half the necessary holes are available?
31. Again only one side of the coin has been emphasised. Those same processes are making new holes available for the bats.
32. The same underestimates and problems noted 28 - 31 apply to the calculations for kaka and yellow-crowned parakeets.
7.2 Predicting harvesting rates of wildlife trees
33. This sentence and Table 1 (at the end of this paragraph) capture my fundamental concern with the whole approach taken in the DoC Critique. The logic of the prediction is not made explicit in the DoC Critique, but it implies that all the holes expected to exist in the Maruia Working Circle now are all needed by the bats and birds. Colin O'Donnell (pers. comm. 6 October 1998) confirms that this is the assumption implicit in the DoC Critique. Further overestimation of the risk comes from the way the totals for each species are added together in Table 1. In reality the species are likely to be able to share many of the holes. For example, in the Eglinton mohua and parakeets used many holes with similar dimensions (Elliott et al. 1996b), although 30% of mohua sites were too small for parakeets. Amongst the unthreatened species mentioned, only the rifleman and short-tailed bats are obligate hole users, so it is not clear whether these add risk in the way inferred in the DoC Critique. The prediction of 14.2 cavity-bearing trees as the minimum needed for birds and bats is not scientifically defensible. The flawed nature of the calculation can be illustrated for the instance of kaka. Assuming that kaka need two holes per breeding pair, the predicted minimum density of kaka would be 3.5 kaka per hectare ! Exact estimates of the absolute density of kaka are not available even for closely studied populations in high density mainland situations, but (unfortunately for conservation) the density is likely to be two orders of magnitude below this level.
34. Compensatory changes are expected of increased tree growth rates and increased survival as a result of live-tree removals. Bigger trees have more tree-cavities. The proposed model should explore the outcomes predicted for different assumptions in compensatory changes.
35. There has been no demonstration that these numbers of holes are required.