Responses to specific points raised by Colin O'Donnell Page 5.
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
7.3 Problems with TWCL harvesting rates
35. There has been no demonstration that these numbers of holes are required.
36. A formal simulation model is now planned to test these hypotheses.
37. The DoC Critique has emphasised and added assumptions that all work to increase perceived potential risk. No error limits are presented and these are likely to be wide (see point 26 for the effect of error limits on just one part of the extrapolation). Calculations are presented only for tree removals > 80 cm DBH rather than running two scenarios (in which all trees > 80 are left c.f. all trees > 110 are left). There has been no demonstration that a significant risk exists, let alone that retention of trees > 110 cm DBH "seems likely to be inadequate".
38. The model now proposed could simulate a series of trade-offs between leaving different sized trees for biodiversity risk simulation c.f income from timber extraction. Estimates of the proportion of defective trees in each size class after single tree selection criteria have been applied can then be predicted.
39. There is no evidence for such competition in New Zealand forests so far. This does not necessarily mean that it does not exist, just that we do not know one way or the other. It is another example of useful follow-up research for consideration by TWC and/or DoC.
40. The vast majority of common wasp nests are in the ground (Moller et al. 1991), and rats and starlings nests are not always in tree holes. It is unknown whether these other introduced species significantly reduce tree cavity availability.
41. The simulation model now proposed will separate out these two classes of trees to track their fates.
42. Research in search of a reliable technique for detecting cavities would be valuable so that foresters can avoid felling defective trees and risks to biodiversity are minimised.
43. The logic for this assertion is not spelled out, but Colin O'Donnell informs me in litt., 5 October 1998) that he is concerned that the foresters will compensate for felling defective trees by taking more than the allotted cut.
44. Again, this figure has been used from a putative compensatory increase in number of trees felled if many are found defective (Colin O'Donnell in litt., 5 October 1998).
45. The model now proposed should be able to formalise this expectation.
46. Such areas are likely to be relatively very small because the use of helicopters obviates the need for much new roading. The exact amount could presumably be estimated by TWC to remove all doubt.
47. Use of a sensitivity analysis in a model to set likely limits from current best knowledge, follow-up monitoring, and an active adaptive management approach (Walters & Holling 1990, Parma 1998) all safe-guard environmental values. TWC have recognised these risks and plan all these approaches to safeguard against them. The formal hypotheses for test in an adaptive management framework need to be spelled out and formalised as part of the process and audit cycles. Adaptive management represents best professional practice and risk management, and is equally needed for interventions from DoC managers (Several risks apply to conservation management interventions on reserved land as well).
48. The philosophical approach taken by TWC is to accept current ecological processes and productivity levels occurring naturally in the forest (rather than to force the system for maximum timber production), including leaving of slash and rotting hollows etc for pinhole borer and other hole-generating microbes and invertebrates in the forest.
49. Natural gap formation will indeed continue, but not necessarily at the previous rate if compensatory processes are triggered by live-tree extraction. These aspects should be modelled and monitored for long-term predictions, and their impacts on tree cavity availability.
50. In most instances ca 3 to 5 trees will be felled in one gap. The only instances of 10 trees will be when many small trees are grouped together (Kit Richards, pers. comm.). Such small trees rarely have trees cavities (Elliott et al. 1996b). Where very large trees are logged usually only one or two trees are removed (Kit Richards, pers. comm.). This expectation needs to further emphasised (sic) in TWC plans because Colin O'Donnell was not assured that 10 very large trees might be felled in the one gap (Colin O'Donnell, in litt. 5 October 1998). If he was unaware, so too will other readers be unaware. On average ca 3 gaps will be created per hectare of forest in each logging event (every 15 years). Most passerines have territories in the order of a hectare, and bats in the order of 10s of square km, so localised effects are unlikely to be significant. The assertion that up to 70% of the cavities could be felled in "one patch" is alarmist.
51. This statement is unproved and relies on several assumptions; speculative scenarios could easily be built to negate the concern altogether (see points 20 & 27 above).
52. See point 20 for the assumptions behind this assertion.
53. The whole importance of food limitation for forest bird populations is unproved, and even more difficult to evaluate than the hypothesis that tree hole availability limits the population. Again from first principles, if predation has depressed the populations it seems most unlikely that they could now be limited by food levels. Evidence for the mechanisms for the effects of past logging methods on bird numbers is almost completely lacking - removal of foods and nesting hollows are mentioned but we do not know which, if any, of these are important. Indirect mechanisms such as the effects of logging on predation have not even been considered. Without this knowledge of mechanisms it is much harder to guess at the likely impact of small group tree removals when the bigger/older trees are left in place. However, the same general argument about the likely impacts of predation apply to the food limitation hypothesis i.e. when severe predation occurs, especially of adults as in the kaka case, food is most unlikely to be a limiting factor. Just as assumption can not rule food limitation in, so too it can not rule it out. The monitoring and adaptive management approach promised by TWC act as an overall safeguard for these risks, however remote they might seem. Similarly, the same large trees left in situ by the group-tree selection protocols to safeguard availability of cavities will also help ameliorate potential food impacts because the largest trees are also the favoured feeding trees for many species of bird (O'Donnell & Dilks 1994).
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