Recent Forest Encroachment into Subalpine Grasslands near Mount Hotham, Victoria, Australia

Wearne, Lynise J.; Morgan, John

doi:10.1080/15230430.2001.12003441

Cited by 33 publications

(29 citation statements)

References 34 publications

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“…Like the Bunya Mountains, change in Valles Caldera has also primarily been around ecotones, by expansion of the forest margin, suggesting seed limitation. Similar spatial limitations have been noted for tree recruitment into alpine grasslands in southern Australia (Wearne & Morgan, ) and for expansion of monsoon thickets in north Australian savannas (Bowman et al ., ) and tropical rain forests (Tng et al ., ). However, margin expansion is not the only common process of vegetation change.…”

Section: Discussionsupporting

confidence: 73%

Aborigine‐managed forest, savanna and grassland: biome switching in montane eastern Australia

Butler¹,

Fensham

Murphy

et al. 2014

Journal of Biogeography

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Aim To assess hypotheses about the role of anthropogenic fire in the maintenance and origin of a fine‐scale vegetation mosaic of rain forest, eucalypt savanna and grassland. Location Bunya Mountains, subtropical eastern Australia. Methods A time series of vegetation maps was compiled from historical and recent aerial photography and field surveys. Geospatial models were constructed of environmental domains for rain forest, savanna and grassland, and for areas of biome change. Grassland soils were analysed for carbon isotope ratios (δ13C), and radiocarbon (14C) dates were acquired for bulk samples from a range of depths. Results Analysis revealed weak associations between topography and the distribution of rain forest, savanna and grassland, and their patterns of recent change. Grassland occupied an environmental domain intermediate between rain forest and savanna and was more than four times as likely to occur within a matrix of rain forest rather than savanna. There was a large proportional reduction in the area of both grassland (−35%) and savanna (−19%) between 1961 and 2006 because of the expansion of rain forest. However, the greater initial extent of savanna meant that the areal loss of savanna was an order of magnitude greater than for grassland (1433 vs. 146 ha). There was no evidence of abrupt changes in δ13C in grassland soil profiles, indicating stability of the vegetation over the last 2000 years. Main conclusions There is no simple gradient in ‘tree suitability’ from rain forest, through savanna, to treeless grassland on the Bunya Mountains. A general absence of fire since the 19th century has greatly reduced the extent of grassy savanna and grassland formations, to the advantage of rain forest. These results support the hypothesis that the vegetation mosaic on the Bunya Mountains is a cultural artefact and testament to millennia of skilful and persistent burning. We could not conclusively reject the hypothesis that the grasslands are Pleistocene relicts that have declined throughout the Holocene; nonetheless, an explanation more consistent with the evidence overall is that the grasslands must have had periods of expansion during the Holocene, probably as a consequence of severe fires that have destroyed patches of rain forest.

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Section: Discussionsupporting

confidence: 73%

Aborigine‐managed forest, savanna and grassland: biome switching in montane eastern Australia

Butler¹,

Fensham

Murphy

et al. 2014

Journal of Biogeography

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“…). Indeed, E. pauciflora forests are known to expand into non‐tree alpine areas under long fire‐free intervals (ca > 40 yr) in favourable environmental conditions (Wearne & Morgan ; McDougall ). Our study illustrates the possibility that climate change‐associated changes in large‐scale disturbance regimes (such as fire) could override the putative effects of increased CO 2 and temperature on vegetation composition in alpine and sub‐alpine environments (Jarrad et al.…”

Section: Discussionmentioning

confidence: 99%

Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

Fairman

Bennett

Tupper

et al. 2017

J Vegetation Science

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Question Frequent severe wildfires have the potential to alter the structure and composition of forests in temperate biomes. While temperate forests dominated by resprouting trees are thought to be largely invulnerable to more frequent wildfires, empirical data to support this assumption are lacking. Does frequent fire erode tree persistence by increasing mortality and reducing regeneration, and what are the broader impacts on forest structure and understorey composition? Location Sub‐alpine open Eucalyptus pauciflora forests, Australian Alps, Victoria, Australia. Methods We examined tree persistence and understorey composition of E. pauciflora open forests that were unburned, burned once, twice or three times by high‐severity wildfires between 2003 and 2013. At each of 20 sites (five per fire frequency class) we assessed extent of top‐kill and mortality of eucalypt clumps, spatial configuration of surviving and dead clumps, densities of new and lignotuberous eucalypt seedlings, and shrub and grass cover. Results At least 2 yr after the last wildfire, proportions of top‐killed E. pauciflora stems were significantly higher, and densities of live basal resprouts significantly lower, at sites burned two or three times compared to once burned or unburned sites. Clump death increased to 50% of individuals at sites burned by three short‐interval wildfires, which led to changes in live tree patchiness, as indicated by nearest‐neighbour indices. Increased tree mortality was not offset by seedling recruitment, which was significantly lower at the twice‐ and thrice‐burned sites relative to single‐burn sites – although seedling recruitment was also influenced by topography and coarse woody debris. In addition to changes in the tree layer, the prominence of understorey shrubs was substantially reduced, and the frequency of grasses markedly increased, after two, and particularly three wildfires. Conclusions Our study provides strong empirical evidence of ecologically significant change in E. pauciflora forests after short‐interval severe wildfires, namely, erosion of the persistence niche of resprouting trees, and a shift in understorey dominance from shrubs to grasses. Our findings highlight the need to consider the impacts of compounded perturbation on forests under changing climates, including testing assumptions of long‐term persistence of resprouter‐dominated communities.

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“…Across the globe, nighttime temperatures have been warming much more rapidly than daytime temperatures [ Karl et al , 1993]. Many biological organisms, such as bark beetles, crickets, piñon mice, and pine trees, are limited by nighttime mean temperatures or extreme minima [ Beatley , 1975; Tenow and Nilssen , 1990; Virtanen et al , 1998; Wearne and Morgan , 2001], leading to inverted tree lines and colonies of more cold‐tolerant species, such as pikas, being found in CAP‐prone locations. Thus regions with frequent cold‐air pools may prove to be biological refuges in a warmer world.…”

Section: Discussionmentioning

confidence: 99%

“… Whiteman et al [2001] define a cold‐air pool as a “topographically‐confined, stagnant layer of air that is colder than the air above.” The American Meteorological Society Glossary of Meteorology [ Glickman et al , 1999] (available at http://amsglossary.allenpress.com/glossary) adds, “This air can remain stagnant, trapped by the surrounding higher terrain, resulting in long periods of poor air quality and fog.” Cold pools can cause localized icing or freezing precipitation, and can delay the melting of snow and ice, thus having a large impact on basin hydrology. They are associated with regions of permafrost and provide unique microclimates that influence species distributions and diversity [ Tenow and Nilssen , 1990; Blennow and Lindkvist , 2000; Wearne and Morgan , 2001]. Because of decoupling from the free atmosphere, these cold pool areas may respond differently to climate change than surrounding regions.…”

Section: Introductionmentioning

confidence: 99%

Automated algorithm for mapping regions of cold‐air pooling in complex terrain

Lundquist¹,

Pepin²,

Rochford³

2008

J. Geophys. Res.

129

158

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[1] In complex terrain, air in contact with the ground becomes cooled from radiative energy loss on a calm clear night and, being denser than the free atmosphere at the same elevation, sinks to valley bottoms. Cold-air pooling (CAP) occurs where this cooled air collects on the landscape. This article focuses on identifying locations on a landscape subject to considerably lower minimum temperatures than the regional average during conditions of clear skies and weak synoptic-scale winds, providing a simple automated method to map locations where cold air is likely to pool. Digital elevation models of regions of complex terrain were used to derive surfaces of local slope, curvature, and percentile elevation relative to surrounding terrain. Each pixel was classified as prone to CAP, not prone to CAP, or exhibiting no signal, based on the criterion that CAP occurs in regions with flat slopes in local depressions or valleys (negative curvature and low percentile). Along-valley changes in the topographic amplification factor (TAF) were then calculated to determine whether the cold air in the valley was likely to drain or pool. Results were checked against distributed temperature measurements in Loch Vale, Rocky Mountain National Park, Colorado; in the Eastern Pyrenees, France; and in Yosemite National Park, Sierra Nevada, California. Using CAP classification to interpolate temperatures across complex terrain resulted in improvements in root-mean-square errors compared to more basic interpolation techniques at most sites within the three areas examined, with average error reductions of up to 3°C at individual sites and about 1°C averaged over all sites in the study areas.

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Recent Forest Encroachment into Subalpine Grasslands near Mount Hotham, Victoria, Australia

Cited by 33 publications

References 34 publications

Aborigine‐managed forest, savanna and grassland: biome switching in montane eastern Australia

Aborigine‐managed forest, savanna and grassland: biome switching in montane eastern Australia

Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

Automated algorithm for mapping regions of cold‐air pooling in complex terrain

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