Fire and the persistence of tuart woodlands

摘要: Tall tuart (Eucalyptus gomphocephala) trees are a defining element of the landscape Perth and coastal plain to north south. However, with health some stands deteriorating, most notably at Yalgorup south Perth, concerns heightening that already fragmented ecosystem will continue contract, leaving cultural ecological scar in landscape. Like many other eucalypt ecosystems, woodlands have had long association fire believed been frequently burnt by Aborigines prior European settlement. Today, fragmentation land management practices led lower frequency across remaining woodlands, but also episodes intense shorter intervals areas. Individual events as well regimes potential shape structure, composition extent ecosystems no different. Thus, impact on regeneration was investigated this study. A survey revealed decline present range sites contrasting histories. Tuart poorest longest unburnt site (35 years) frequent wildfire (three fires 13 years), suggesting these extreme played role decline. Nevertheless, low ratings tree approximately once per decade, point factors than playing Yalgorup. The populations were dominated individuals larger size-classes there significant negative relationship between size probability mortality. In one stand National Park, 38 % saplings/trees died. It follows development seedlings into adults need occur within next two decades if persist. Seedling counts confirmed virtually absent areas, is common species. Interpretations size-class distributions suggested controlled burning contributed little recruitment, whereas areas subject outside Yalgorup, regenerated abundance such skewed towards smaller size-classes. A repeat plots established 1976 supported anecdotal reports mid-storey peppermint (Agonis flexuosa) increasing density height skew smallest presence ( > 200 ha-1) not recently (at least four years since fire) brought focus differing mode for species comparison tuart. further contrast tuart, mature peppermints good dead reported population surveys. possible competition highlighted correlation health. Together, results suggest general drift from woodland forest appears entrenched. Comparative studies bark thickness, response resprouting behaviour illustrated capacity both persist recurrent fire. As or juveniles, resprouted following complete canopy scorch, often crown branches: an ability uncommon co-occurring shrubs environment. Survival 75 100 fully-scorched tuarts ranging small saplings six sites. From sample available comparison, appeared be more vulnerable mortality fire; only 45 diameter breast less-equal 1 cm survived scorch burn. With thicker bark, reliance stem epicormic buds rather lignotuber greater growth, resistance post-fire recovery would expected differ peppermint. Opportunities managers exploit differences their prescriptions so address dominance outlined. addition, indicating positive condition < 10 burn imply vigour may benefit immediately But, observations spikes intensity burns can damage large unhealthy thereby accelerate process. application declining needs conducted skillfully. Patterns growth survival linked establish purported importance ashbeds establishment demonstrated; end summer (February) (Golden Bay), mean three times those off ashbeds, rate 35 15 %, respectively. Therefore, while important, dependent instance. hardy nature when compared planted area tuart-peppermint Yalgorup; nine months after planting, 9 survived. Most summer-drought period it suspected drought tolerant. complementary glasshouse experiment showed shoot:root ratio peppermint, which factor sensitivity drought. Further, increase nutrient supply, proportional increment rooting depth (1.6 times) significantly (0.3 times). An increased availability nutrients fire, particularly phosphorous, measured woodland. inferred critical consequently ashbeds. Overall, concluded share Competitor strategy (after Grime) eucalypts: rapid attainment size. On hand, exhibits traits Stress Tolerator Grime): minimum resource requirements survival. The consequence cover explored field experiments seedlings. No seedling observed. There trend rates under high treatments second approached, although statistical difference could shown. Peppermint influence insect attack foliar pathogen Mycosphaerella cryptica. insects M. cryptica incidental seedlings: level affected 50 soil 18 planting restorative plantings fires. Tuart decline, altered complex avenues research emphasized. findings sufficient enable purposeful actions conserve restore woodlands; recommendations regarding view goals presented final discussion.