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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan Kevin Bonham Report to Forest Practices Authority November 2013
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Kevin Bonham
Report to Forest Practices Authority
November 2013
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Summary
The keeled snail (Tasmaphena lamproides) occurs only in far north-western Tasmania and southern Victoria, and is listed as Rare on the schedules of the Tasmanian Threatened Species Protection Act 1995. Management of the species on State Forest and forested private land has been largely based on information obtained from a survey of the Togari Block and Bond Tier in 1992, plus a range of smaller surveys and informal sampling in other areas. Many coupes within Togari Block have since been converted to eucalypt plantation or clearfelled and silviculturally regenerated. The species is managed primarily by ensuring a contiguous network of native forest over 30 years old, and by ensuring retention in harvested areas.
In October 2013 a resampling of the original areas surveyed was undertaken to help assess the effectiveness of existing management and to establish some additional long-term monitoring sites. The survey found broadly comparable levels of presence and abundance in mature forest and older first-rotation plantations, but greatly reduced levels of presence and abundance in young native forest regrowth. It is likely that numbers of T. lamproides within Togari Block have declined within the last 20 years, but by less than prior modelling of the impacts of logging within the Block would have predicted.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Background
The keeled snail (Tasmaphena lamproides (Cox, 1868)) is a large carnivorous land snail endemic to far north-western Tasmania and southern Victoria. The Tasmanian population is listed as Rare on the schedules of the Threatened Species Protection Act 1995, primarily because of its restricted range and low population density. The species has an estimated extent of occurrence in Tasmania of 770 km2 and an estimated area of occupancy of 42, 000 hectares (Fauna Strategic Group, 2006).
Very little was known about the status of Tasmanian populations prior to a survey of the Togari Block (plus two sites in Bond Tier) undertaken in 1992 (Bonham and Taylor, 1997). The survey established that the species occurred quite consistently in a range of wet forest habitats in the block, including rainforests, but was most common at the northern end of the block and in forests that were 60 years old or older. In other surveys it has sometimes been found in regrowth as young as 20 years (Bonham, 1999b), in 12-13 year old plantations near forest edges (Bonham, 2006) and rarely in unusual habitat types such as eucalypt scrub in the north-western corner of Woolnorth (Bonham, 2000) and coastal shrubbery at The Nut (Bonham, 1999a). The species appears to occur much less frequently at sites with very sandy soils (Bonham, 2000).
Keeled snails can be found under and sometimes inside logs, and in deep leaf litter. They are carnivorous and their known diet includes other land snail species and worms. They are noted for occurring at very low population densities, although some derived estimates have been miscalculated. Assuming an average undercount of 20% by the methods used in the 1992 survey, population density in most of Togari Block was around 10 live adults/hectare, rising to around 20 live adults/hectare in the north of the block, and to 60 live adults/hectare in some areas of unusually high density. However, surveying that uses smaller search sites has produced higher density estimates and it is probable that the undercounting rate (and hence the population density) is therefore higher. The total population in Tasmania is likely to be several hundred thousand live adults (TSU, 2012).
Keeled snails are locally eliminated by land clearance for conversion to pasture. The lack of records in young silvicultural regrowth suggested they might be locally eliminated by logging, with a slow recovery time. A management plan for this species was developed for State forest in 2000 (FT and DPIPWE 2000). This plan was developed from the modelling work of Regan et al. (1999; 2001; 2000) and delivered through the Threatened Fauna Adviser. The primary objectives of the plan were:
To provide for the long term survival of Tasmaphena lamproides on State forest in northwest Tasmania, by minimising impacts from threatening processes.
To provide a strategic planning framework for the long-term protection and management of T. lamproides habitat within its known range on State forest.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
To limit the degree of plantation development within the range of the species such that a substantial network of native forest habitat is maintained throughout the species’ range.
To maintain or improve the conservation status of T. lamproides in an area subject to production forestry.
To provide, for T. lamproides, a more strategic alternative to the current coupe-by-coupe based approach to threatened species management within production forests.
These objectives were to be achieved by retaining a contiguous network of native forest (including forest greater than 30 years of age) throughout the range of the species, ensuring adequate retention and contiguity of native forest especially in areas of intensive plantation development.
The plan area has been subject to intensive native forest harvesting and conversion to plantation since the plan was developed, but reporting by Forestry Tasmania indicates the management plan for this species has largely been complied with (Forestry Tasmania 2013).
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Methods
1. Site Selection
Site selection in the 1992 survey had been conducted subjectively based on the following criteria:* Coverage of a wide range of habitat types within the survey area* Extensive coverage of common habitat types* Coverage of areas intended for conversion to plantation and wildlife corridor status* Geographic coverage of the whole of Togari Block* Accessibility
However, as shown in Table 1, some sites originally designated for conversion to plantation had not been converted, or were logged for silvicultural regeneration instead.
Twenty-eight sites approximately matching the locations of the original Togari Block and Bond Tier sites were searched. Of the original thirty-one sites, a group of three in the north-east of the block (12, 13, 14) could not be resurveyed because of the presence of a wedge-tailed eagle nest. In any case, access to these sites on foot is now difficult because of the damming of creeks since the original survey. Three new monitoring sites were surveyed; two in Togari Block and one at Grunter Road, Seventeen Mile Plain. Previous data exist for two of these three new sites, which were both considered to be high abundance areas that would be useful for demonstrating any long-term decline in the species' numbers. (One is adjacent to recent logging while the other is well inside a large reserve.) The third new site was a small streamside reserve surrounded by recent logging, as a result of which understorey windthrow into the reserve had greatly opened up the site.
Relocation of the exact original survey sites proved challenging. The original survey report (Bonham 1992) contained only six-figure grid references for sites to an intended accuracy of 100 metres. Slightly more accurate estimates were obtained by remeasuring point estimates on the author's original 1:25,000 survey map for sites 1-26. Sites were navigated to by GPS and the following principles were followed in determining site selection:* If the original site could be recognised exactly from memory then it was used and a more accurate grid reference obtained. This rarely happened. One example was site 10, recognised on the basis of distinctive landforms at the site.
* If the original site had been logged or converted to plantation, or was unrecognisable from memory because of subsequent regrowth, then the grid reference estimated from the original survey map was used exactly.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
* If the area corresponding to the grid reference estimate for the original site was clearly not the original site (based either on the author's memory of the original site or on serious mismatches with the author's notes on the vegetation and aspect) then a replacement site that was the best possible match and was near to the original grid reference was selected.
* If the original site was not recognised from memory but the area matching the original grid reference was not clearly wrong then the original grid reference was used.
Some minor errors were made in the site relocation process, meaning that some sites are replicated in the sense of being in the same area and with similar vegetation, but were not in exactly the same location. Sites 8 and 9 were incorrectly relocated (albeit by less than 200 m and in similar habitat types in each case) because a road junction that was not mapped was confused for another. Site 27 was surveyed at the target grid reference, but it was realised long after it was surveyed that the original site had been on the other side of the road.
Grid references for sites provided here are considered accurate to within 30 metres, although those in open recently logged sites are typically accurate to within 10 metres. When using a GPS device to find sites in dense forest, it was often noted that once the distance remaining dropped below 30 metres, the device's estimate of the distance to go to the site started varying unreliably. This is probably because tree cover was affecting the reliability of the device.
Table 1 provides the grid references of sampled sites together with notes on their forest type and relocation issues.
2. Sampling
All sites were hand-sampled by Kevin Bonham and Nora Ohlsen. This meant that as in the original survey, the survey was conducted by one person experienced in searching for land snails and one person without prior experience. The percentage of keeled snails found by the searcher without prior experience was similar (between 20-30% of the total) in both surveys.
All sites were surveyed by hand-searching within a 15 metre radius of a designated central point, as in the original survey. Available shelters were searched including the undersides of logs and rocks, piles of deep leaf litter (especially around the bases of trees and stumps or in deep ditches), and logs were broken apart. One significant departure from the original survey was that a time limit of one hour was imposed for searching at each site to standardise search effort. In the original survey sites were searched until there was confidence that all suitable and movable shelter had been searched, which took from 70 to 120 minutes (on average, probably around 90 minutes). While there was some dropoff in the rate at which specimens were being found towards the end of searches in the original survey, this difference would nonetheless (all else being equal) have reduced the average number of specimens found by around 25%, and caused the species to sometimes be not recorded during the available search time.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
The order of resurveying of sites was determined mainly by convenience but there was also a significant safety issue with strong winds during the first week. This caused most of the logged, young regrowth and plantation sites to be surveyed in the first week (which was also the wettest week) and most of the mature forest sites to be surveyed in the second.
As with the original survey, numbers of all land snail species (including both native and exotic slugs) were recorded. These were relevant because some native snails (mainly Stenacapha and Helicarion spp) are known prey for Tasmaphena lamproides, and one species (Victaphanta milligani) is another carnivorous species that displayed a negative correlation with T. lamproides numbers in the original survey. Numbers of other land snail species should not be assumed to accurately indicate population densities as some species have different microhabitat preferences, and some species are very small and less likely to be found while targeting T. lamproides.
Sites were surveyed on the following dates:21 Oct – 7; 22 Oct – 9, 8, 10, 6; 23 Oct – 20, 21, 19, 27, 29; 24 Oct – 24, 22, 17, 16, 2; 25 Oct – 15, 5; 28 Oct – 3, 23; 29 Oct – 31, 30, 28, 1, 4; 30 Oct – 25, 18, 26, 32; 31 Oct – 11, 33, 34
When additional personnel wanted to search for the species they were permitted to do so outside the 15 metre radius only. Such additional searching occurred near some sites and not others and with varying searchers, methods and time spent searching. Results of searching outside sites were also noted.
Vegetative characteristics of sites are presented in Appendix 1.
Specimens of T. lamproides were recorded as alive or dead and as adult or juvenile. As in the initial survey specimens over 14 mm wide were deemed adult, although the size at which the snail becomes reproductively mature has not been determined. The species was deemed to be present at a site if either living or freshly dead T. lamproides were recorded. If only old long-dead T. lamproides (typically whitened or badly damaged shells or fragments) were found then the species was considered absent. Both live and dead shell numbers can be unreliable as an indicator of habitat quality: live snail numbers because of weather-related variations in how cryptic a given species is, and dead snail numbers because preservation conditions can vary from site to site.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Table 1. Legend on next page.
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Easting Northing 1992 type 2013 type Basis for change
1 327460 5470820 mature (60 yo) informal reserve mature Yes Approx location2 327013 5471664 regen (1986) regen regen (1986) No (not applicable)
3 327518 5473584 mature informal reserve mature Yes Approx location 4 328651 5472423 mature informal reserve mature Yes Approx location
5 329813 5472834 mature (40 yo) intended plantation freshly logged No (not applicable)
6 330579 5472837 mature (60 yo) intended plantation Yes Approx location
7 331313 5472084 mature (60 yo) intended plantation No (not applicable)
8 331572 5473180 mature intended plantation regen (2005) Yes Relocation error9 331473 5473205 mature intended plantation mature Yes Relocation error
10 332657 5474712 mature (40 yo) other mature Yes Exact location
11 333263 5474865 mature (60 yo) other Yes Approx location
12 333863 5477634 mature (60 yo) intended plantation (not applicable)
13 333863 5477934 mature other (not applicable)
14 333583 5477884 mature informal reserve assumed regen (not applicable)15 328313 5470334 regen (30 yo) other regen (50 yo) No (not applicable)
16327013 5471984
mature intended plantation No (not applicable)
17327563 5472224
mature (60 yo) intended plantation No (not applicable)18 327491 5478845 mature other mature Yes Approx location19 327563 5477734 mature other regen (2000) No (not applicable)20 327146 5477486 mature (60 yo) informal reserve mature Yes Approx location21 327113 5477114 mature other regen (2002) No (not applicable)
22 327413 5472884 mature (60 yo) intended plantation regen (2012) No (not applicable)
23 328073 5474484 mature intended plantation mature No (not applicable)
24 327313 5474754 mature intended plantation No (not applicable)25 329813 5479284 mature (60 yo) other regen (2009) No (not applicable)
26 325197 5471302 mature other mature Yes27 324813 5463984 mature (60 yo) other mature (80 yo) No (not applicable)28 326913 5467984 regen (30 yo) other regen (50 yo) No (not applicable)
29 328051 5463864 mature (60 yo) other mature Yes
30 318484 5454419 mature formal reserve mature Yes Approx location
31 318513 5464284 mature (60 yo) formal reserve mature (80 yo) No (not applicable)
32 329979 5479648 N/A N/A mature (80 yo) New site (not applicable)33 323232 5474508 N/A N/A mature New site (not applicable)34 331507 5473923 N/A N/A mature (*) New site (not applicable)
Site No
reason for inclusion
GR changed?
plantation (2nd rot, 3 yr)freshly logged (*)
mature (see note)assumed mature
Not resurveyed
assumed mature
Not resurveyedNot resurveyed
plantation (est 14 yr)plantation (est 12 yr)
plantation (est 14 yr)
Nearby and similar
Nearby and similar
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Table 1 Legend (from previous page): In “1992 type” and “2013 type” columns figures followed by “yo” are estimated age. Years such as (1986) in brackets are known actual years of clearing. The “reason for inclusion” column gives the basis for the site's selection in the 1992 survey.
Notes for specific sites: 7 – site partly logged with about 40% in streamside reserve; 11 and 34 – site very close to edge of logged area
Results
Results of searching for Tasmaphena lamproides are presented in Table 3. Results of searching for all snail species are presented in Appendix 2. A breakdown of Tasmaphena lamproides results by microhabitat at each site is presented in Appendix 3.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
As with the original survey, Tasmaphena lamproides was considered to be present at a site if either live or freshly dead specimens were found. There was only one site (34) at which the species was recorded as absent despite a dead shell being found within the site. The dead shell in this case was a long-dead adult that was mostly buried in the soil.
Summary results by treatment for sites surveyed in both 1992 and 2013 are presented in Table 2:
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1992 20131992 2013 # Pres Live At LA LJ DA DJ sum Pres Live At LA LJ DA DJ sumMature (TB) Mature (TB) 12 7 5 7 3 10 2 22 8 2 4 1 5 13 23Regen (30) Regen (50) 2 1 1 1 0 2 0 3 1 0 0 0 0 2 2Regen (7) Regen (28) 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0Mature Plantation (<5) 1 1 1 1 0 0 0 1 0 0 0 0 0 0 0Mature Plantation (>5) 3 3 1 0 1 7 1 9 2 2 2 4 0 1 7Mature Freshly logged 2 2 1 3 1 2 1 7 2 2 2 0 2 1 5Mature Regen 5 5 3 5 4 7 8 24 1 1 1 0 0 0 1(Total TB) (Total TB) 26 19 12 17 9 28 12 66 14 7 9 5 7 17 38Mature (BT) Mature (BT) 2 1 0 0 0 1 0 1 2 1 0 1 2 2 5
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Table 2 Summary results for matched sites. Numbers in brackets are estimated ages. TB = Togari Block, BT = Bond Tier.
Table 3 Site by site results for Tasmaphena lamproides. Results for matching sites in 1992 are shown in italics on right. Note that sites where only very old dead shells are found are marked as non-presence records. A case could be made for including sites 20 and 16 in 1992 in this category.
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2013 1992site treatment Pres LA LJ DA DJ Sum Pres LA LJ DA DJ Sum
1 mature Yes 0 0 1 5 6 No 0 0 0 0 02 regen (1986) No 0 0 0 0 0 No 0 0 1 0 13 mature Yes 0 0 0 1 1 Yes 2 1 1 0 44 mature Yes 0 0 1 2 3 Yes 1 2 1 1 55 freshly logged Yes 1 0 2 1 4 Yes 0 0 2 0 26 plantation (2nd rot, est 3 yr) No 0 0 0 0 0 Yes 1 0 0 0 17 freshly logged (see note) Yes 1 0 0 0 1 Yes 3 1 0 1 58 regen (2005) Yes 1 0 0 0 1 Yes 0 0 1 0 19 mature No 0 0 0 0 0 Yes 1 0 0 0 1
10 mature Yes 2 1 1 1 5 Yes 1 0 0 0 111 mature (see note) Yes 0 0 0 2 2 No 0 0 0 0 015 regen (50 yo) No 0 0 0 0 0 Yes 1 0 2 0 316 plantation (est 14 yr) No 0 0 0 0 0 Yes 0 0 5 0 517 plantation (est 12 yr) Yes 1 1 0 0 2 Yes 0 0 1 1 218 mature Yes 0 0 1 1 2 No 0 0 0 0 019 regen (2000) No 0 0 0 0 0 Yes 1 3 0 2 620 mature No 0 0 0 0 0 Yes 0 0 6 0 621 regen (2002) No 0 0 0 0 0 Yes 1 0 0 4 522 regen (2012) No 0 0 0 0 0 Yes 0 0 1 1 223 mature No 0 0 0 0 0 No 0 0 0 0 024 plantation (est 14 yr) Yes 1 3 0 1 5 Yes 0 1 1 0 225 regen (2009) No 0 0 0 0 0 Yes 3 1 5 1 1026 mature Yes 2 0 0 0 2 No 0 0 0 0 027 mature (80 yo) Yes 0 0 1 1 2 Yes 0 0 1 1 228 regen (50 yo) Yes 0 0 0 2 2 No 0 0 0 0 029 mature No 0 0 0 0 0 Yes 2 0 1 0 330 mature Yes 0 0 1 0 1 No 0 0 0 0 031 mature (80 yo) Yes 0 1 1 2 4 Yes 0 0 1 0 132 mature (80 yo) Yes 2 1 1 4 8 N/A33 mature Yes 2 1 3 2 8 N/A34 mature (see note) No 0 0 1 0 1 N/A
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
A total of sixty Tasmaphena lamproides (alive and dead) were recorded at the sites searched. However, seventeen were recorded at the three new sites that were not matched to the 1992 sites. At the matched sites within the Togari Block, 38 specimens were recorded compared to 66 in 1992. The difference is partly explained by the shorter search time in the 2013 survey. Beyond that the one treatment type that showed a strong difference between 1992 and 2013 is young silvicultural regeneration. Of five mature forest sites that were clearfelled and burnt between 2000 and 2012 then regenerated to native forest, only one had a single live adult T. lamproides, compared with 24 specimens including nine live specimens at these five sites prior to harvesting.
Overall, at matched sites within Togari Block, live adult numbers were 53% of the 2013 level, or about 66% of that level accounting for shorter searching time. Total specimen numbers were 58% of the 2013 level, or about 72% accounting for shorter searching time. In sites that were not young regrowth or plantations under 5 years old, these figures were 54% (68% adjusted) and 90% (113% adjusted) respectively. However the number of live adults sampled at the remaining matched sites (11 in 1992, six in 2013) are too small for meaningful conclusions to be drawn about population change at those sites.
Some other notable aspects of the results are as follows:
* At 12 resampled Togari Block sites that were mature forest in both surveys, there was no relationship between recorded presence in 1992 and recorded presence in 2013. The species was recorded in both surveys at four sites and not recorded in either survey at one. There were four sites at which the species was not recorded in 1992 but was recorded in 2013, and three at which the species was not recorded in 2013 but had been recorded in 1992.
* However, of the sites where the species was recorded in 1992 but not in 2013, in two cases (sites 9 and 29) the site was not exactly relocated, and in one case (site 20) the site had been modified by the removal (or decay) of large stacks of logs observed in the 1992 survey.
* Of the sites where the species was not recorded in 1992 but was recorded in 2013, one (site 26) is known not to have been exactly relocated.
* At matched sites in Togari Block, the proportion of live specimens found that were adult was effectively identical to the 1992 survey (37% compared to 39% in 1992) and the proportion of all specimens found that were alive was also effectively identical (65% compared to 64%). However, while 70% of dead specimens at these sites were adults in 1992, in 2013 71% of dead specimens were juvenile.
* Although T. lamproides was recorded at more matched mature forest sites than in 1992, and the number of total specimens recorded at those sites was higher (in both cases despite the shorter search time), the number of live specimens recorded at these sites (5 at 2 out of 12 sites) was lower than in 1992 (10 at 5 out of 12 sites).
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
* Two live adult specimens were found together in bark at the base of a very large eucalypt at site 26. Eight snail eggs were found 15-20 cm away. It is likely that these were eggs of Tasmaphena lamproides, as had they been eggs of any other snail the two T. lamproides would probably have eaten them. If so, this is the first known record of the species with eggs.
* At site 26, one T. lamproides was in the process of eating a Stenacapha ducani, and another dead S. ducani at the same site appeared to have also been eaten by T. lamproides. At site 10, a juvenile T. lamproides was observed eating Prolesphanta dyeri, a smaller member of the family Rhytididae. This is the first time T. lamproides has been observed eating another rhytidid, or that any other rhytidid has been observed eating P. dyeri.
* Some differences in microhabitat preference for recorded T. lamproides specimens were found compared to the 1992 survey. No specimens were recorded at the base of Dicksonia in this survey (compared to seven in the 1992 survey, six of them at matched mature forest sites). Ten specimens were recorded at the base of eucalypts compared to only two in 1992. This was mainly because bark at the base of eucalypts was the main microhabitat at plantation sites, at which a reduced range of microhabitats were available. The numbers of specimens recorded under logs (8 compared to 22) and at the base of Pomaderris/Olearia (7 compared to 17) were both down. However the first change is largely explained by shorter survey time and by seven of the specimens under logs from the 1992 survey having been at non-resurveyed sites. The second change is probably because many sites with older Pomaderris/Olearia no longer had that microhabitat type following logging.
* Numbers of other native snails showed a dramatic difference in the number of Stenacapha spp, a known T. lamproides diet item. At matched sites in Togari Block only 117 were found, compared to 436 in the original survey. This difference applied across the full range of treatment types (including matched mature forest) and numbers were less than half the 1992 total at 17 of 26 matched Togari Block sites, and higher than the 1992 total at only two (one of which was 30 year old regenerating forest at the time of the 1992 survey).
* The carnivorous snail Victaphanta milligani was also less common at matched sites in Togari Block (71 specimens at 11 sites compared to 173 at 17). However in this case, once adjustment is made for reduced searching time, the near-complete absence of the species at logged sites was the major cause. Only one dead specimen (a long dead one at that) was found at the 11 sites logged since 1992, compared to 48 specimens from six of those sites in 1992.
* Helicarion sp. (also a diet item of Tasmaphena lamproides) occurred in similar numbers in the 2013 survey to the 1992 survey. It was generally eliminated or nearly so in recently logged and young silvicultural regen sites, but was common at two of the three older plantation sites. However, the older plantation site where it was absent (24) was the one where T. lamproides was most common.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
* Few live specimens of any of the above large snails were found. Only 16 of 136 Stenacapha spp, 15 of 97 Victaphanta milligani and 10 of 117 Helicarion sp were alive across all sites. In the latter case, this is more than the 3 of 142 Helicarion sp alive in the 1992 survey, but proportions alive for the other two species were much higher in 1992 (although not recorded). It appears that Helicarion sp has an annual dieoff in spring as several freshly dead and some obviously dying adult specimens were observed. However, live sub-adults, when seen, were always vigorous. The species may have a two-year life cycle.
* The exotic slug Arion intermedius was among the most common land molluscs recorded. This is in contrast to the 1992 survey, in which only 10 specimens were seen and the species was present at just three sites. The species was especially common at some recently logged sites but was also more common in mature forest sites than in 1992.
* The above excepted, results for other snail species were broadly similar to the 1992 survey, given differences in forest treatment and the addition of the Seventeen Mile Plain site (which has some species that have not been recorded at Togari Block). Some very small snail species were more numerous. Three native and one exotic species that were found once only at matched sites in the original survey were not re-recorded, but two native and two exotic species not found at matched sites in the original survey were recorded in small numbers.
Informal searching outside the site by extra searchers was conducted to some degree at the following sites: 2, 7, 10, 11, 16, 17, 19, 20, 21, 22, 24, 27, 29. Generally this was unsuccessful but one dead juvenile was found by an extra searcher at each of the following sites: 2, 11, 16, 17. Of these, site 2 was the only site at which the species was not recorded within the 15-metre radius. A dead adult was also found outside site 34 by the author while walking to the site.
Relatively few of the surveyed sites were suitable for assessing persistence in small areas of retained forest adjacent to logging The species was found alive in retained forest on the edge of a freshly logged (unburnt) area at site 7, but it was also found alive at a freshly logged unburnt site with no retained forest at site 5. At site 34, windthrow caused by adjacent logging had felled the understorey at the site, and no live native snails were found at all (though this is not necessarily significant given the low proportion of live native snails generally). At site 32, high densities of T. lamproides were found in intact forest within 20 metres of a logged and burned forest edge (but in a known high-density area).
Discussion
The survey provides some results that slightly alter previous understanding of the species:
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
1. Following the original survey (Bonham 1992, Bonham and Taylor 1997) some types of mature forest site such as extremely swampy or sandy sites, or sites with poor litter quality, were considered unsuitable because the species had not been found at them. However, in this survey the species was found at most matched mixed forest sites at which it had not been found in 1992. Inexact site matching (site 26) and changes in litter quality (site 18) probably contributed to this result but for sites 1 and 11 it may be that the negative results in the original survey were false negatives. The find of the species at site 26 also demonstrates that very small rises around the bases of large eucalypts are sufficient for the species to occur in swamp environments. It should be considered that the species occurs more or less universally in wet forest over 50 years old in the Togari Block, even if it might not be found in a targeted 15 m radius search at a given site in such forests.
2. While the presence of the species was already confirmed in older plantations, this survey confirms the species can occur in older plantations well away from native forest edges. Also, the species was common at one of the three plantation sites surveyed. The species should therefore be assumed to be substantially present in plantations over 12 years old. While broadscale plantation conversion on public land has ceased, incorporating this result in past modelling relating to the species could lead to different outcomes. More surveying in age-matched plantation and silvicultural regeneration sites would be needed to confirm this, but the species appears to recover more rapidly in at least first generation eucalypt plantations than regenerated forest of the same age.
3. Although the survey supports the previous view that recovery in young regenerating forest is slow, there was a single find of a live adult in 8 year old forest near a forest edge.
4. The immediate response of the species to logging has not been surveyed before. In this survey it was found alive at two freshly logged sites that had not yet been burnt, although in one case the live specimen was within a retained area on the edge of the logged area. It is possible on this basis that regeneration without burning would retain T. lamproides, but this would need to be tested by experiment, as the persistence of the species after logging in such cases might be short-term and unviable (eg if food supply or shelter conditions were not adequate for long-term survival).
5. The 1992 survey found that the species' numbers were strongly correlated with those of combined prey species Helicarion sp and Stenacapha spp, and inversely correlated with those of Victaphanta milligani. In this survey, this result was not repeated. Numbers of T. lamproides were not even close to correlated with those of the other large common snails, and this applied whether all sites are considered or just mature forest sites.
The survey provides evidence that T. lamproides remains fairly common within Togari Block. However, given the increased proportion of the block that is now either young regrowth or young (second-rotation) plantations, it is very likely that the species' population within the Block as a whole is substantially lower now than in 1992.
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Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Assessing changes in the species' population in those parts of the Block that are not now young regrowth or very young plantations is difficult. Live adult numbers at these sites declined but were too low in either survey to provide meaningful evidence that numbers had actually decreased. Total specimen numbers at these sites increased insignificantly once adjusted for reduced survey time, but mainly because of an increase in the number of dead juveniles. This could be the result of one or more breeding seasons in which there was a higher breeding success rate than available prey levels could sustain, for example. It is possible on this basis that T. lamproides numbers in unharvested areas are actually lower than in 1992, but much more data would be needed to demonstrate this. Furthermore if numbers are indeed lower, it is likely to be because of temporary factors unrelated to forest management (such as fluctuations in prey availability.)
The data collected are not suitable for BACI (Before/After Control/Impact) statistical methods or other complex statistical before-and-after analysis. Difficulties in applying such tests include the lack of a single impact type (rather, there are many impact types, which seem to have different impacts on the species and which occurred at different times and in different ways at different sites), the time between samples, weather-related bias in site selection, the use of a standardised one-hour search in the 2013 samples, varying accuracies of replication of site location and the possible influence of natural fluctuations in snail numbers.
It is surprising that live specimens were found at so few of the matched mature forest sites (just two such sites in Togari Block – one of them not exactly matched - and another at Bond Tier). There was no difficulty in finding live specimens at two of the three new monitoring sites (sites 32 and 33, both in known high-density population areas.) It is unclear whether the low proportion of live specimens found at matched mature forest sites represents stochastic sampling noise, weather, short-term fluctuations (eg in prey availability), something else, or some combination of these factors.
Management
The findings of this survey are consistent with the general modelling finding of Regan et al (1999, 2000, 2001): that while various logging scenarios would lead to various levels of population decline in Togari Block, there was no risk of logging alone (including plantation establishment) causing the complete extinction of the snail from the Togari Block. Indeed, this survey shows that some of the modelling assumptions (especially, concerning occurrence in plantations) were pessimistic and that overall population changes caused by logging are likely to be less dramatic than expected, mainly because the species lives in older plantations and can occur to some degree (although this was only demonstrated once) in young native regrowth.
16
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Despite this, the results are consistent with clearfell, burn and sow methods causing near-total population loss within logged coupes, from which recovery is slow. Although older plantations are very suitable habitat for the species (apparently, much more so than native regrowth of equivalent age), they are likely to reach that stage only in their last few years of their harvesting cycle. It has also yet to be confirmed that the species will live in older plantations past the first rotation, although there is no evident reason why it should not.
One aspect of the species' management that was not directly addressed in this survey is the effectiveness of small retained areas within coupes in encouraging reinvasion of regrowth habitats. It is likely that the species' reoccupation of regrowth is determined by a combination of the age of the regrowth and the distance from the native forest edge, although more detailed surveying would be required to test this. Assuming that this is the case, it would be expected that the snail would be retained in areas of retained habitat (such as streamside reserves and retained habitat clumps) and that it would reinvade regrowing coupes faster if they had a larger total edge distance of retained native forest within them. However, this may not be the case if retained areas are burned or become degraded. It is likely (but would require detailed study) that important influences on the rate of reinvasion in regrowth habitats will include the shape of the coupe and the condition of retained areas of native forest within the coupe.
Acknowledgements
I thank Nora Ohlsen for field assistance and specimen photography, Sarah Munks and Amy Koch (FPA) for project coordination, and Amy Koch, Dydee Mann, Anne Chuter (FPA), Marie Yee (FT) and Smithton district staff for transport and field assistance.
References
Bonham K. (1992) Tasmaphena lamproides (Cox 1868) in the Togari Forest Block. Unpublished report to Forestry Commission of Tasmania. 19 pp.
Bonham, K (1999a) Distribution, habitat and conservation status of the land snail Miselaoma weldii (Pulmonata: Punctidae) Tas. Nat. 121: 2-12
Bonham, K (1999b) Range boundary survey for the keeled snail Tasmaphena lamproides Unpublished report to Forestry Tasmania.
Bonham, K. (2000) Distribution and habitat characteristics of Tasmaphena lamproides (keeled snail) on private land. Unpublished report to Forest Practices Board and Threatened Species Section, DPIWE. 6 pp.
Bonham K. (2006) Keeled Snail Coupe And Plantation Surveys December 2006. Unpublished report to Forestry Tasmania, Smithton. 4 pp.
17
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Bonham K. & Taylor R. (1997) Distribution and habitat of the land snail Tasmaphena lamproides (Pulmonata: Rhytididae). Tasmania. Molluscan Research 18, 1-10.
Fauna Strategic Group (2006) Strategic plan for Tasmaphena lamproides (Keeled Snail) in areas subject to a Forest Practices Plan in North West Tasmania. Forest Practices Authority, Hobart 39 pp.
Forestry Tasmania. (2013) Implementation of strategic recommendations for threatened fauna - State forest in Togari block. Report for the Forest Practices Authority prepared by FT Sustainability Branch and Murchison District, Hobart.
Forestry Tasmania & DPIPWE. (2000) Management plan for Tasmaphena lamproides (keeled snail) on State forest in north west Tasmania. A Public Authority Management Agreement between Forestry Tasmania and the Department of Primary Industries, Water and Environment, Hobart.
Regan T., Bonham K., Regan H., Taylor R., Tuson D. & Burgman M. (1999) Forest Management and Conservation of Tasmaphena lamproides in North-west Tasmania: Use of Population Viability Analysis to Evaluate Management Options. Forestry Tasmania, Hobart.
Regan T. J., Regan H. M., Bonham K. J., Taylor R. J. & Burgman M. A. (2001) Modelling the impact of timber harvesting on a rare carnivorous land snail (Tasmaphena lamproides) in northwest Tasmania, Australia. Ecological Modelling 139, 253-64.
Regan T. J., Taylor R. J. & Burgman M. A. (2000) Investigation of Harvest Scheduling Options for Forest Management: Implications for the Carnivorous Land Snail, Tasmaphena lamproides in Northwest Tasmania. Forestry Tasmania, Tasmania.
Threatened Species Unit (2012). Fauna Recovery Plan: Threatened Tasmanian Land Snails 2013-2017. Department of Primary Industries, Water and Environment, Hobart (Draft)
18
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Appendix 1 Vegetation characteristics of sites.
19
Site
Euc
alyp
tus
spp
Pom
ader
ris
Ole
aria
arg
ophy
llaN
otho
fagu
s cu
nnin
gham
iiA
caci
a m
elan
oxyl
onD
icks
onia
ant
arct
ica
Lept
ospe
rmum
Ath
eros
perm
a m
osch
atum
Mel
aleu
caP
ittos
poru
mZi
eria
Cop
rosm
aG
roun
d fe
rns
(Pte
ridiu
m, B
lech
num
)S
edge
s (G
ahni
a/Le
pido
sper
ma)
Notes1 y y y y2 y y y3 y y y y y4 y y y y some rocks at site5 y y y Recently logged, logpiles, regrow th f rom stumps, some cover
6 y Second rotation eucalypt plantation7 y y y About 60% short regrow th, rest unlogged but some trees fallen8 y y y y Dense regrow th, many logs, poor litter quality9 y y y y y Parts of site sw ampy
10 y y y y y y11 y y y y y y Near logged edge12 Not resurveyed13 Not resurveyed14 Not resurveyed15 y y y y y16 y y y Plantation, excellent litter around trees17 y y y y y Plantation, excellent litter around trees18 y y y19 y y y y y Regrow th, dense litter20 y y y y y y21 y y y Dense regrow th. Old manfern remnants present. Poor litter
22 y y Recently burned, eucalypts < 1m, very little cover23 y y y y y24 y y y y Plantation, excellent litter around trees25 y y y y y Dense regrow th, many logs, very tall bracken26 y y y y Partly f looded. Tw o very large eucs w ith bark around bases27 y y y y y y28 y y y29 y y y y30 y y y y y y31 y y y y y32 y y y y y y Near logged edge33 y y y34 y y y Very steep site, surrounds logged and w ith w indthrow
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Appendix 2 Specimen numbers for all recorded land snails (including exotic slugs) by site.
20
Nat
ive
spec
imen
s
1 6 8 2 1 1 1 1 2 9 9 31
2 1 1 13 3 15
3 1 9 1 2 9 4 13
4 3 1 1 3 1 1 6 4 8 20
5 4 1 2 1 1 5 9
6 1 1 9 40 2 3 11
7 1 9 1 3 11
8 1 3 1 2 3 5
9 13 5 1 3 19
10 5 18 1 7 11 3 5 42
11 2 1 1 1 3 3 7 7 18
15 11 5 2 16
16 2 13 2 15
17 2 4 15 3 21
18 2 1 1 1 3 1 8 6 9
19 1 1 7 3 9
20 1 2 3 3 6
21 3 2 1 3
22 1 15 1 1
23 16 3 10 3 4 32
24 5 14 4 2 19
25 1 3 6 1 4 2 4 11
26 2 1 1 1 5 1 1 7 12
27 2 1 10 1 3 13
28 2 2 1 2 1 1 6 2 2 1 4 10 20
29 2 4 1 3 7
30 1 3 1 1 1 3 9 7 19
31 4 8 1 1 1 1 6 16
32 8 1 1 4 5 3 6 22
33 8 1 1 1 1 2 1 2 1 9 18
34 1 13 4 1 28 4 19
Total 60 97 7 1 6 1 4 1 2 3 2 1 10 4 19 7 3 133 117 4 119 4 1
Sites 19 16 6 1 5 1 4 1 2 3 1 1 5 2 10 4 3 28 23 4 11 2 1
Tasm
aphe
na la
mpr
oide
s
Vic
taph
anta
mill
igan
i
Pro
leso
phan
ta d
yeri
Pro
leso
phan
ta s
p “T
ogar
i”
Par
alao
ma
halli
Par
alao
ma
sp “K
nock
lofty
” (?)
Pun
ctid
ae s
p. “M
icro
Crip
ps”
Laom
avix
col
lisi
Ped
icam
ista
sp
“Chi
shol
m”
Troc
hola
oma
parv
issi
ma
Mag
ilaom
a pe
nole
nsis
Pla
nila
oma
luck
man
ii
Allo
char
opa
tarr
avill
ensi
s
Per
nage
ra k
ings
tone
nsis
Ore
omav
a jo
hnst
oni
Thry
ason
a di
emen
ensi
s
Ste
naca
pha
ham
ilton
i
Ste
naca
pha
duca
ni
Hel
icar
ion
sp
Cys
tope
lta b
icol
or
Ario
n in
term
ediu
s (e
xotic
)
Lehm
anni
a ny
ctel
ia/v
alen
tiana
(e
xotic
)
Lim
ax m
axim
us (e
xotic
)
Nat
ive
spp
Monitoring the effectiveness of the keeled snail (Tasmaphena lamproides) management plan
Appendix 3 Microhabitats for specimens of Tasmaphena lamproidesTotals (LA/LJ/DA/DJ) Under logs 8 (1/0/2/5), Litter around edge of logs and stumps 8 (2/0/4/2), Exposed on open ground 3 (0/0/3/0), Litter in the open 11 (2/1/1/7), Litter under sedges 3 (0/1/0/2), Litter in ditches and depressions 10 (2/0/3/5), Bark and litter around eucalypt bases 10 (4/5/1/0), Litter around bases of Pomaderris/Olearia 7 (2/1/0/4)
21
Live
adu
lts
Live
adu
lts
Live
adu
lts
Live
adu
lts
Live
adu
lts
Live
adu
lts
Live
adu
lts
Live
adu
lts
Live
juve
nile
s
Live
juve
nile
s
Live
juve
nile
s
Live
juve
nile
s
Live
juve
nile
s
Live
juve
nile
s
Live
juve
nile
s
Live
juve
nile
s
Dea
d ad
ults
Dea
d ad
ults
Dea
d ad
ults
Dea
d ad
ults
Dea
d ad
ults
Dea
d ad
ults
Dea
d ad
ults
Dea
d ad
ults
Dea
d ju
veni
les
Dea
d ju
veni
les
Dea
d ju
veni
les
Dea
d ju
veni
les
Dea
d ju
veni
les
Dea
d ju
veni
les
Dea
d ju
veni
les
Dea
d ju
veni
les
site
Und
er lo
gs
Litte
r ar
ound
edg
e of
logs
or
stum
ps
Exp
osed
on
open
gro
und
Litte
r in
the
open
Litte
r un
der
sedg
es
Litte
r in
ditc
hes
and
depr
essi
ons
Bar
k an
d lit
ter
arou
nd b
ase
of e
ucal
ypts
Litte
r or
mos
s ba
se o
f Pom
ader
ris/O
lear
ia
Und
er lo
gs
Litte
r ar
ound
edg
e of
logs
or
stum
ps
Exp
osed
on
open
gro
und
Litte
r in
the
open
Litte
r un
der
sedg
es
Litte
r in
ditc
hes
and
depr
essi
ons
Bar
k an
d lit
ter
arou
nd b
ase
of e
ucal
ypts
Litte
r or
mos
s ba
se o
f Pom
ader
ris/O
lear
ia
Und
er lo
gs
Litte
r ar
ound
edg
e of
logs
or
stum
ps
Exp
osed
on
open
gro
und
Litte
r in
the
open
Litte
r un
der
sedg
es
Litte
r in
ditc
hes
and
depr
essi
ons
Bar
k an
d lit
ter
arou
nd b
ase
of e
ucal
ypts
Litte
r or
mos
s ba
se o
f Pom
ader
ris/O
lear
ia
Und
er lo
gs
Litte
r ar
ound
edg
e of
logs
or
stum
ps
Exp
osed
on
open
gro
und
Litte
r in
the
open
Litte
r un
der
sedg
es
Litte
r in
ditc
hes
and
depr
essi
ons
Bar
k an
d lit
ter
arou
nd b
ase
of e
ucal
ypts
Litte
r or
mos
s ba
se o
f Pom
ader
ris/O
lear
ia
1 1 3 23 14 1 1 15 1 2 17 18 1
10 2 1 1 111 1 117 1 118 1 124 1 3 126 227 1 128 1 130 131 1 1 1 132 2 1 1 1 333 2 1 2 1 234 1all 1 2 0 2 0 2 4 2 0 0 0 1 1 0 5 1 2 4 3 1 0 3 1 0 5 2 0 7 2 5 0 4
