Aspectos relevantes en una vivienda sostenible

Background

Three studies were conducted to observe patterns of survival and resprouting position (crown or below) in tuart, peppermint and co-occurring tree species following fires. Study 1 focused on the survival rates for seedlings and small saplings (that is, individuals ≤ 1 cm dbhob), Study 2 examined the survival rates of saplings and trees (that is, individuals > 1 cm dbhob) and Study 3 compared the ability of the species to resprout from crown branches.

General Sites

Six burnt sites covering four separate fires were examined. These sites were Y1, Ya1, Ya2, Ya3, Ya4 and GB (Table 4.1). Plots established prior to planned burns (Y1 and Ya1) were on the whole subjected to only low-intensity fire which resulted in minor canopy scorch. Some measurements were therefore taken opportunistically following unplanned fires (GB, Ya2, Ya3 and Ya4). At GB and Ya2, sampling occurred in plots (see section 3.2.3 in Chapter 3) whereas at sites Ya3 and Ya4 trees were sampled along transect belts that were approximately 20 m wide (locations specified in Appendix 5). In addition, further trees and saplings were selected in two small areas (< 0.5 ha) in zones of higher fire intensity (as indicated by greater scorch heights) outside the main plots within site Y1 (locations specified in Appendix 5).

Control sites (unburnt sites) were monitored during the study period at site Y2 and Y3 (adjacent to Y1) only. A control site (Ya2) was established for the cluster of sites at Yanchep, but was burnt in a subsequent unplanned fire (back-burn for wildfire control).

For site GB, there were no nearby unburnt areas that could have acted as controls. Some control-like comparisons were achieved by comparing trees with fully-burnt canopies against trees with partially scorched or unburnt canopies within burnt areas. Arguably, the interspersion of these “controls” within the “treatment” area was preferable to having controls segregated at different sites.

Table 4.1: Fire and burn description for sites burnt during the study period.

Site Date Ave. est. intensity (kW m-1₎1. Max. scorch ht (m)2. Burnt area (%) 3. _Comments Y1 12/2004 < 350 10 60 Prescribed fire

Ya1 10 - 11/2004 < 350 12 50 Prescribed fire. Lit several times

Ya2 01/2005 < 350 6.5 90 Back burn at night for wildfire control4.

Ya3 01/2005 2000 - 4000 > 20 100 Wildfire

Ya4 01/2005 3000 - 7000 > 20 100 Wildfire

GB 02/2003 350 - 1000 < 15 95 Back burn for wildfire control5.

1. Estimated according to scorch height or observation in the case of Y1 and Ya2 and with reference to Burrows (1984) and Cheney (1981).

2. Measured within plots at Y1, Ya1 and Ya2, estimated at GB, Ya3 and Ya4.

3. Based on visual estimations. At sites Ya1, Ya2 and Y1, multiple estimates were made across plots to derive a mean.

4. J. Wheeler, Department of Conservation and Land Management, pers. comm. 5. G. Napier, Department of Conservation and Land Management, pers. comm.

Sampling

Across all the sites, the species monitored were tuart, peppermint, Allocasuarina fraseriana, Banksia grandis, Banksia attenuata and Melaleuca raphiophylla. Site and

species details are summarized in Table 4.2. All individuals (except germinants) of tree species present within plots at sites Y1, Y2, Y3 and GB were selected for assessment and monitoring. At site Y1, Ya1, Ya2 (burnt sites), Y2 and Y3 (unburnt sites) individuals were tagged prior to the most recent fire. At Ya1 and Ya2 (burnt sites), not all individuals were tagged within plots when densities were high. In these instances, an individual from each species closest to the northwestern corner of a 5 x 5 m sector of the main plot, was selected, tagged and remonitored after the fire. Assessments at sites GB, Ya3 and Ya4 began from immediately after the most recent fire. The additional sampling of tuarts at site Y1 also commenced following the 2004 fire. The primary aim of this additional sampling at sites Y1, Ya3 and Ya4, was to examine the response of large tuart trees to 100 % canopy scorch. There was little difficulty in identifying the

species for scorched or defoliated stem structures. It was assumed that all stems standing after the fires were living prior to the fires. However, at site GB where individuals across all sizes were sampled, seedlings that were incinerated would not have been included.

Measurements

The proportion of foliage scorched in the canopy was estimated for individual trees, seedlings and saplings at all burnt sites. An emphasis on instances of 100 % scorch was given to the presentation of results on survival and resprouting patterns. This was because 100 % scorch is recommended as the standard minimum condition for assessing plant species response to fire (Gill 1981c). In some cases, particularly for seedlings, foliage was not only scorched, but also incinerated, sometimes completely. Therefore, technically the 100 % scorch category refered to the minimum level of plant damage. Survival was recorded as the presence of living resprouts at the final assessment times (7 to 12 months after the fire event). A minority of tagged plants (mostly seedlings) could not be located after the fires. While in most cases the role of fire in the loss of individuals could be deduced, on some occasions this could not be determined with certainty. Where there was uncertainty the data were excluded. The patchy nature of prescribed burns together with the necessity to be opportunistic in the event of unplanned fires meant that there were some inconsistencies in methodology and sampling times between sites. Details of the measurements taken during the surveys are summarised in Table 4.2.

Analyses

Statistical analyses comparing species responses were not conducted as there were small sample sizes for some species at some sites, differences in the size distributions of individuals between species, variations in fire severity within sites and as most species (except tuart) were found at some sites but not others.

Table 4.2: Summary of measurements (trees, saplings and seedlings) by site and species (Spp) for survey of the impact of fire on survival and recovery. dbhob = diameter at breast height over bark. CA = canopy area rating, CH = canopy health rating, n/a = not applicable or not available.

Pre-fire measurements

Date of canopy scorch assessment

and other post-fire measurements Final measurements

Site _Spp1. _n2. _{Date Date Other measurements Date Comments} Y1 Eg Af Alf 105 105 46

03-05/04 dbhob, CA, CH, height3. dbhob, height3.

Estimated height/dbhob

12/04 Burn severity at base4. Burn severity at base4. n/a

01/06 Survival, CA, resprout origins Survival, resprout origins Survival

Plants tagged pre-fire

Y1 Eg 22 n/a n/a 01/05 dbhob, CA, CH 01/06 Survival, CA, resprout origins 100% scorch plants selected post-fire Y2 & Y3 Eg Af Alf 28 138 21

03-05/04 dbhob, CA, CH, height3. dbhob, height3. Estimated height/dbhob n/a n/a n/a n/a 01/06 Survival, CA Survival Survival

Data from these two unburnt sites were pooled GB Eg Alf Ba Bg Mr 430 10 160 55 81 n/a n/a n/a n/a n/a n/a 02/03 dbhob Estimated height/dbhob dbhob dbhob dbhob

09/03 Survival, resprout origins Survival

Survival, resprout origins Survival, resprout origins Survival, resprout origins

Plants tagged post-fire

Ya1 Eg Bg 63 34 04/03 & 09/04

dbhob, CA, CH, height3. dbhob

11/04 Burn severity at base4. Burn severity at base4.

01/06 Survival, CA, resprout origins Survival, resprout origins

Plants tagged pre-fire Ya2 Eg Bg 33 19 04/03 & 09/04

dbhob CA, CH, height3. dbhob

01/05 Burn severity at base4. Burn severity at base4.

01/06 Survival, CA, resprout origins Survival, resprout origins

Plants tagged pre-fire

Ya3 Eg 18 n/a n/a 02/05 dhob, CA, CH 01/06 Survival, CA, resprout origins 100% scorch plants selected post-fire Ya4 Eg 18 n/a n/a 02/05 dhob, CA, CH 01/06 Survival, CA, resprout origins 100% scorch plants selected post-fire

1. Agonis flexuosa (Af), Allocasuarina fraseriana (Alf), Banksia attenuata (Ba), Bg = Banksia grandis (Bg), Eucalyptus gomphocephala (Eg) Melaleuca

2. This number represents all plants that were assessed. For burnt sites, not all plants were necessarily scorched completely or at all. 3. Height was only measured for individuals < 5 m tall.

4. Within 0.5 m radius of the base of tuarts and peppermints < 5 m tall. Severity was rated as unburnt, partially burnt, completely burnt (little or no ash) or burnt with ash formation.

Study 1: survival of seedlings and small saplings Hypothesis:

• When subjected to 100 % canopy scorch, the majority of seedlings and small saplings of tuart and co-occurring tree species survive.

Methods

Survival of all individuals ≤ 1 cm dbhob with 100 % canopy scorch across the various sites was assessed. Sample sizes were 77 (tuart), 33 (peppermint), 2 (A. fraseriana), 9

(B. grandis), 65 (B. attenuata) and 66 (Melaleuca raphiophylla). For tuart ≤ 1 cm dbhob

at sites Y1, Ya1 and Ya2 and peppermint at site Y1, survival rates were compared on the basis of local fire severity and seedling height. Heights were measured either prior to the fire or immediately after the fire. Fire severity around the base of the stem (approximately 0.5 m radius) was rated immediately after the fire as unburnt, partially burnt, completely burnt with little or no ash, or completely burnt with ash formation. There were 17 tuart and 33 peppermint seedlings examined in this way. The growth rings on cut stems of a small sample of tuart (n = 4) and peppermint seedlings (n = 5) at site Y1 and Y3, and tuart seedlings and saplings (n = 14) at site GB, were also counted at the final measurement time in order to estimate stem age (see Table 4.2 for sampling dates and species-site combinations).

Study 2: survival of saplings and trees Hypothesis

• When subjected to 100 % canopy scorch, the majority of saplings and trees of tuart and co-occurring tree species survive.

Methods

Survival of all individuals > 1 cm dbhob that were subjected to at least 100 % foliage scorch was assessed for all sites listed in Table 4.2. Survival rates were calculated for each species by dbhob class. However, A. fraseriana saplings and trees were not

categorized into dbhob classes because of the great irregularities in stem shape arising from previous fire damage. Sample sizes by species for individuals > 1cm dbhob were 377 (tuart), 18 (peppermint), 78 (B. attenuata), 51 (B. grandis), 15 (M. raphiophylla)

and 29 (A. fraseriana). A further number of incompletely-scorched tuarts (n = 125

unscorched tuarts (n = 107 across sites Y1, Y2, Y3, Ya1 and Ya2) and peppermints (n = 162 across sites Y1, Y2 and Y3) were monitored for comparative purposes.

Study 3: ability to resprout from the crown following 100 % canopy scorch Hypothesis:

• When subjected to 100 % canopy scorch, surviving saplings and trees of tuart and co-occurring tree species resprout from the crown.

Methods

The presence or absence of crown-branch resprouts was noted for all completely scorched, surviving saplings and trees (dbhob > 1 cm) at the final post-fire assessment time (Table 4.2). Sample sizes were 349 (tuart), 18 (peppermint), 70 (B. attenuata), 29

(B. grandis) and 7 (M. raphiophylla). A. fraseriana were not assessed. Data were

presented for each species on the basis of dbhob class.

4.2.5 Comparative early canopy recovery of tuart and peppermint seedlings