Forest expansion and grassland contraction within a Eucalyptus savanna matrix between 1941 and 1994 at Litchfield National Park in the Australian monsoon tropics

Abstract

Analysis of digitized aerial photographs taken in 1941 and 1994, using image processing and geographical information system technology, enabled the quantification of change in the coverage of forest and grassland patches that occur within a Eucalyptus savanna matrix in a subcoastal region of the Australian monsoon tropics. The 3058 ha study area was orientated along a low escarpment that separated a sandstone plateau from lowlands that comprised 58% and 42% of the area, respectively. In the 53‐year period, humans modified less than 1% of the study area, primarily for road building, and primarily in savanna areas. More than 85% of the study area at both sample times was covered by savanna. However, over the same period, the forest coverage increased from 5.03% to 9.91% of the study area and coverage of grassland decreased from 6.70% to 2.47%. The aerial photography also showed that tree density in the savanna had increased, although this was not assessed quantitatively. There was an increase in the number of forest patches from 116 to 142. The number of grassland patches decreased (particularly those > 1 ha) from 87 to 59, although the size class distribution of forest and grassland patches was statistically similar for both sample times. A 50‐m GIS buffer was used to distinguish creek‐lines environments from surrounding catchments. Using this criterion, 14% of the study area was classified as plateau creek‐lines and 9% lowland creek‐lines. Although the expansion of forest and loss of grassland varied significantly amongst catchment and creek‐lines on the plateau and lowlands, the 1941 rank order of coverage of each vegetation type was maintained in these four landscape categories in 1994. In both years the greatest extent of forest and grassland occurred on the lowland catchments, despite their accounting for only one‐third of the study area. Transition matrices for vegetation change among the four landscape categories demonstrated that, unlike the other vegetation types, grasslands, particularly on the plateau, had a low probability of remaining unchanged during the study period. The cause(s) of the overall increase of woody biomass across the topographic and edaphic gradient remains unclear but may be related to a period of increased rainfall since the 1970s, as well as to the cessation of Aboriginal landscape burning at the beginning of the study period.

Dinâmica espaço-temporal (1962-2006) das fitofisionomias em unidade de conservação do Cerrado no sudeste do Brasil

“…Além das fi sionomias mencionadas, que puderam ser enquadradas na classifi cação de Ribeiro & Walter (1998) 1, tabela 1). Outras pesquisas sobre dinâmica da cobertura vegetal com dados de sensoriamento remoto, em zonas de interface entre fl orestas e savanas ou campos, mostram resultados semelhantes aos obtidos neste estudo (Archer et al 1988, Carmel & Kadmon 1999, Bowman et al 2001, Oliveira & Pillar 2004, Pinheiro 2006, Durigan & Ratter 2006e Marimon et al 2006. Nessas pesquisas há um consenso de que o avanço das fi sionomias fl orestais sobre formações campestres é explicado pela situação climática favorável às primeiras, e que a eliminação do pastejo e queimadas são fatores importantes para a expansão de formações fl orestais.…”

“…ser explicados os processos ecológicos que estão condicionando a reversão da invasão por esta espécie. Embora sejam relevantes as evidências de que a ação antrópica e os incêndios sejam fatores limitantes para a expansão de tipos vegetacionais fl orestais sobre vegetações campestres ou savânicas (Archer et al 1988, Carmel & Kadmon 1999, Bowman et al 2001, Moreira 2000, Oliveira-Filho & Ratter 2002, Pinheiro 2006, Durigan & Ratter 2006, as explicações para tais alterações não estão esgotadas, devendo ser analisados outros possíveis fatores, tais como tipo de solo, microclima e disponibilidade de luz, como condicionantes desse 6 7 8 9…”

Large-Herbivore Distribution and Abundance: Intra- And Interspecific Niche Variation in the Tropics

“…First, increased temperature and rainfall may result in habitat thickening due to increased numbers and/or growth of woody plants (Hughes 2003), and these plants may be favored by elevated levels of CO 2 (which is thought to favor C3 over C4 plants, and also to simply provide more carbon for plants to engineer structural tissue). A number of studies provide evidence that this may already be occurring (Archer et al 1995, Bowman et al 2001b. Second, under these conditions, rain forest may invade woodlands (Bowman et al 2001b), leading to a reduction of habitat for large macropods.…”

“…A number of studies provide evidence that this may already be occurring (Archer et al 1995, Bowman et al 2001b. Second, under these conditions, rain forest may invade woodlands (Bowman et al 2001b), leading to a reduction of habitat for large macropods. Third, due to possible increased fuel loads associated with longer, hotter dry seasons, the risk and frequency of fire are expected to increase (Howden et al 1999).…”

The Nature of Northern Australia: its natural values, ecological processes and future prospects

“…In response to this change, or perhaps to a combination of factors including increased atmospheric CO 2 , or changed fire regimes, there have been substantial directional changes in vegetation patterning in Northern Australia. This includes in some areas expansion of rainforest and other denser vegetation, and 'vegetation thickening' (Crowley and Garnett 2000;Lewis 2002;Bowman et al 2001a;Fensham and Fairfax 2003;Banfai and Bowman 2006). In parts of north-eastern Australia, where the …”