Page 4 of the DoC Critique written by Colin O'Donnell.

7.0   Beech Tree Harvesting Rates and Mitigating Effects on Wildlife


The most effective way to predict whether the harvest rates proposed (sic) is to compare those rates with the specific requirements of wildlife (in terms of sizes and ages of trees required for breeding and foraging) and then determine if sufficient trees remain through the harvesting cycle to allow for maintenance of critical wildlife populations in perpetuity.

While tree density estimates and proposed harvesting rates have been provided for the Maruia working circle, unfortunately there have been no surveys by TWCL to determine the frequency of availability of wildlife trees in the area.

I use research findings from mixed beech forest in the Eglinton Valley, Fiordland to illustrate:
(a) how the specific effects of the logging regimes proposed might be predicted;

(b) show that proposed harvesting rates in the Maruia working circle may remove significant amounts of wildlife habitat, particularly for threatened species (long-tailed bat, kaka, yellow-crowned parakeet).

7.1   The importance of cavity-bearing trees

One of the main predicted impacts of the harvesting regimes proposed would be the reduction in the number of older cavity-bearing trees (see below).

(See comment 24) TWCL dispute that availability of cavities is in fact a limiting factor (BSM, p. 69). Their assumption is wrong. If trees which contain the cavities which hole-breeding and roosting species require are removed there are simply no alternatives available. It is extremely unlikely that threatened species such as kaka and parakeets would be able to nest on the ground or in the open.
Bats would not be able to thrive outside of cavities or in cavities which did not provide suitable microclimates because of their highly specialised thermoregulatory needs ( e.g Racey 1973, Trune & Slobodchikoff 1976, McNab 1982, Kunz 1987, Roverud & Chappell 1991, Hamilton & Barclay 1994).

(See comment 25) There is a huge literature available on how the limitation cavity of availability (sic) influences the viability of wildlife populations ( a few examples: Saunders et al. 1982, DeLotelle & Epting 1983, Nilsson 1984, Raphael & White 1984, Rendell & Robertson 1989, Lindenmayer et al 1991 Rudolph & Conner 1991, Bennett et al 1994, Newton 1994, Lindenmayer et al 1995, Rieger 1996, Vonhof & Barclay 1996, Smith 1997).

7.2   Availability of wildlife trees in the Eglinton Valley

7.1.1 (sic) Long-tailed bats: Using information from Sedgeley & O'Donnell (unpublished manuscript) and an earlier study of roost trees availability ( Sedgeley & O'Donnell, in press), it is possible to estimate how abundant suitable roost cavities may be. Firstly, 95% of roosts are found in only at (sic) lower altitudes. Of 78 random trees assessed in this study, only 17 had cavities. These 17 trees contained a total of 51 cavities which conformed to the basic assumptions of being available to bats (i.e. the entrance and internal dimensions exceeded the minimum dimensions required by a single roosting bats). However, most of the measured available cavity characteristics fell outside of the range of bat roost cavity characteristics (i.e. were hollows, were damp inside, were below 5 m from the ground, entrance and internal volume were less than minimum dimensions of roost cavities, and cavities were completely surrounded by vegetation at less than 2 m away). Only six cavities had characteristics which were within the range characteristics of cavities used by bats and these were all located on one tree.
(See comment 26) Thus only 1.3% of random trees contained cavities of a type which bats select to roost in.
With available trees density at 298/ha in the Eglinton Valley this extrapolates to 3.8 cavity bearing trees/ha.
(See comment 27) Bats have used a minimum of 304 roost cavities in the spring-autumn months during this four year study.
The majority of bat roosts were in red beech trees and 80% percent (sic) of red beech roost trees had stem diameters of 80 cm DBH, but only 34% of available red beech trees were in this size class.

These figures give us a range of estimates for the availability of bat roost trees in the Maruia working circle. Table 3.6 (p. 32, MSMP) indicates a
(See comment 28) merchantable tree density
of 111 trees/ha.
(See comment 28) If bat roosts occur at a similar frequency to the Eglinton (1.3%)
then we expect 1.4 bat roost trees/ha of which the majority would be in trees > 80 cm DBH.
(See comment 29)Allowance must also be made for natural death of bat roost trees. A prudent upper estimate might be 3.8 trees/ha
(See comment 30)(the availability figure for the Eglinton).

We do not know how many additional cavities are used in the winter months and this model of abundance does not include estimates for cavity turnover. Little is known about the ongoing processes of wood decay and cavity formation. Most species of bat are not known to manipulate the structural environment of their roosts,
(See comment 31) so natural structural changes and degradation can frequently exclude or cause bats to abandon their roost sites (e.g. Rieger, 1996a, 1996b).

(See comment 32)7.1.2 (sic) Kaka: Using similar extrapolation procedures we estimated that 6.4% of trees in the Eglinton Valley contained cavities suitable for nesting (19.1 trees/ha). All kaka nests in the Eglinton (and elsewhere) were in trees > 80 cm DBH.

These figures give us a range estimates (sic) for the availability of kaka nesting trees in the Maruia working circle. Table 3.6 (p. 32, MSMP) indicates a merchantable tree density of 111 trees /ha. If kaka cavities occur at a similar frequency to the Eglinton (6.4%) then we expect 7.1 nest trees/ha of which all would be in trees > 80 cm DBH. A prudent upper (See comment 30 again) estimate might be higher than this. It is realistic to expect that greater densities of cavity-bearing trees will be required for birds because they breed as pairs rather than in colonies, as bats do.

7.1.3. (sic) Yellow-crowned parakeet: Using similar extrapolation procedures (based on cavity sizes from Elliott et al. (1996a) we estimated that 5.1% of trees in the Eglinton Valley contained cavities suitable for nesting (15.2 trees/ha). Eighty-five percent of nests in the Eglinton were in trees > 80 cm DBH.

These figures give us a range estimates (sic) for the availability of parakeet nesting trees in the Maruia working circle. Table 3.6 (p. 32, MSMP) indicates a merchantible (sic) tree density of 111 trees.ha. If parakeet cavities occur at a similar frequency to the Eglinton (5.1%) then we expect 5.7 nest trees/ha of which 85% would be in trees > 80 cm DBH. A prudent upper estimate would be higher than this.

7.2 Predicting harvesting rates of wildlife trees

By combining these estimates from the Eglinton Valley (Table 1) it is possible to gauge the potential impact of harvesting on threatened hole-using species in Maruia forests. For a more definitive model, data should be collected specifically from the North Westland forests.

Harvesting rates have been set at 1.009 trees/ha/year, of which 0.392 trees will be red beech. Harvesting rates for red beech trees > 80 cm DBH have been set at 0.105 trees/ha/yr (Table 5.5, p. 80, MSMP). Red beech trees in this category occur at a rate of 17/ha in the Maruia (Table 5.1, p. 73, MSMP). Thus 1.575 trees from a pool of 17 would be felled every 15 years.

(See comment 33) We predict that a minimum of 14.2 cavity-bearing trees/ha are required for threatened species
(long-tailed bat, kaka and yellow-crowned parakeet) for breeding and roosting (i.e. 83.5% of the 17 trees > 80 cm DBH/ha present in the Maruia Working Circle). Thus the rate of felling these trees at 0.105 trees/ha/yr indicates a high probability of removing 9.3% of preferred breeding trees/ha per 15 year rotation.
(See comment 34) Over 120 years (allowing for 15 year resting between each cycle), 37% of preferred trees would be removed. This is unlikely to be sustainable for wildlife in the long term given that trees take a minimum of 450 - 600 years to reach a size whereby they are used for breeding by threatened species (see Ogden 1978, Wardle 1984) ( or ca. 320 years to reach 80 cm DBH according to Table 5.2, p. 75, MSMP)

Table 1. Examples of predicting minimum number of cavity-bearing trees/ha
(See comment 35) required by threatened species in the Maruia Working Circle.


Percent roost trees in trees > 80 cm DBH Percent of available trees per ha with suitable cavities * Minimum trees/ha (See comment 35) required
Threatened species
Long-tailed bat
80
1.3
1.4
Kaka
100
6.4
7.1
Yellow-crowned parakeet
85
5.1
5.7
Total
14.2
Other species
morepork
?
?
?
rifleman
?
?
?
robin
?
?
?
tomtit
?
?
?
paradise shelduck
?
?
?
short-tailed bat
?
?
?
* Extrapolated from Eglinton Valley data.