Vegetation Changes In Areas Research Articles

Fire Recurrence and Normalized Difference Vegetation Index (NDVI) Dynamics in Brazilian Savanna

Fire is one of the main modeling agents of savanna ecosystems, affecting their distribution, physiognomy and species diversity. Changes in the natural fire regime on savannas cause disturbances in the structural characteristics of vegetation. Theses disturbances can be effectively monitored by time series of remote sensing data in different terrestrial ecosystems such as savannas. This study used trend analysis in NDVI (Normalized Difference Vegetation Index)–MODIS (Moderate Resolution Imaging Spectroradiometer) time series to evaluate the influence of different fire recurrences on vegetation phenology of the Brazilian savanna in the period from 2001 to 2016. The trend analysis indicated several factors responsible for changes in vegetation: (a) The absence of fire in savanna phytophysiognomies causes a constant increase in MODIS–NDVI, ranging from 0.001 to 0.002 per year, the moderate presence of fire in these areas does not cause significant changes, while the high recurrence results in decreases of MODIS–NDVI, ranging from −0.002 to −0.008 per year; (b) Forest areas showed a high decrease in NDVI, reaching up to −0.009 MODIS–NDVI per year, but not related to fire recurrence, indicating the high degradation of these phytophysiognomies; (c) Changes in vegetation are highly connected to the protection status of the area, such as areas of integral protection or sustainable use, and consequently their conservation status. Areas with greater vegetation conservation had more than 70% of positive changes in pixels with significant tendencies. Absence or presence of fire are the main agents of vegetation change in areas with lower anthropic influence. These results reinforce the need for a suitable fire management policy for the different types of Cerrado phytophysiognomies, in addition to highlighting the efficiency of remote sensing time series for evaluation of vegetation phenology.

Signatures of human impact on self-organized vegetation in the Horn of Africa

In many dryland environments, vegetation self-organizes into bands that can be clearly identified in remotely-sensed imagery. The status of individual bands can be tracked over time, allowing for a detailed remote analysis of how human populations affect the vital balance of dryland ecosystems. In this study, we characterize vegetation change in areas of the Horn of Africa where imagery taken in the early 1950s is available. We find that substantial change is associated with steep increases in human activity, which we infer primarily through the extent of road and dirt track development. A seemingly paradoxical signature of human impact appears as an increase in the widths of the vegetation bands, which effectively increases the extent of vegetation cover in many areas. We show that this widening occurs due to altered rates of vegetation colonization and mortality at the edges of the bands, and conjecture that such changes are driven by human-induced shifts in plant species composition. Our findings suggest signatures of human impact that may aid in identifying and monitoring vulnerable drylands in the Horn of Africa.

Neolithic woodland management and land-use in south-eastern Europe: The anthracological evidence from Northern Greece and Bulgaria

Wood charcoal (anthracological) remains accumulated in archaeological deposits provide a valuable tool for reconstruction of past local vegetation and its use. They can offer evidence complementary to pollen analysis or be the main source on past vegetation change in areas where no pollen preservation is available. The current study assembles the anthracological evidence from 18 Neolithic sites situated in the zone spanning between the Lower Danube plain and the Aegean coast. This evidence is presented within the broader archaeological and paleoecological context of the region and in cal. years BC and/or BP. The data is interpreted in terms of land-use related to woodland management and exploitation of woodland resources during three chronological phases which could be distinguished within the Neolithic of south-eastern Europe: a) 6500-5800 cal. BC, b) 5800-5500 cal. BC, and c) 5500-4900 cal BC). The main vegetation type targeted by the Neolithic population were the thermophilous, mixed deciduous oak communities, which contained a rich and diverse undergrowth of light-demanding and fruit/nut bearing trees, shrubs and herbs. Those plant communities were the major source of fuel wood, forest pasture, fodder, gathered fruits, etc. The analyses indicate stability and sustainability of the firewood procurement and woodland management practices for the whole considered period and further suggest that the Neolithic land-use strategies favoured the rich and often fruit-bearing undergrowth of the oak forests and woodland.

Landscape‐scale vegetation dynamics inferred from spatial patterns of soil δ13C in a subtropical savanna parkland

Grasslands and savannas around the world have experienced woody plant encroachment during the past 100 years, but we know little regarding the manner in which woody plants spread across the landscape. We used soil δ13C, aerial photography, and geostatistics to quantify patterns of woody encroachment in a 160 × 100 m georeferenced grid subdivided into 10 × 10 m cells in a savanna parkland landscape in southern Texas. δ13C contour maps revealed that centers of closed contours coincided with centers of woody patches, and that larger woody patches developed from smaller woody plant clusters that spread laterally and coalesced. Areas where woody patches were expanding into grassland were characterized by low densities of soil δ13C contour lines, and indicated the direction and extent of woody encroachment. Conversely, areas with high contour densities represented grassland‐woodland boundaries that were temporally stable. Indeed, aerial photos from 1930, 1941, 1982, and 2003 confirmed that woody patches with low spatial variability in δ13C corresponded to areas where woody plants had encroached during the past 30–75 years. While aerial photos can only record vegetation cover at the photo acquisition time, kriged maps of soil δ13C allowed us to accurately reconstruct long‐term temporal dynamics of woody plant encroachment into grassland. This approach can reliably reconstruct landscape‐scale vegetation changes in areas where historical aerial photography or satellite imagery are unavailable and provides a strong spatial context for studies aimed at understanding the functional consequences of vegetation change.

Post-burn vegetation development of rehabilitated bauxite mines in western Australia

Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah ( Eucalyptus marginata) forest of Western Australia for more than 35 years. Mines rehabilitated in the early 1980s contain some eastern Australian eucalypts and have built up substantial fuel loads (23–35 t/ha) that may be reduced through prescribed burning. The aim of this study was to document vegetation changes in areas rehabilitated in the early 1980s for 6 years following prescribed burning and ascertain the most appropriate fire regime to apply in these areas to achieve identified rehabilitation completion criteria. Following both autumn and spring burning, rehabilitated areas rapidly re-accumulated fuel in the first year after burning, but fuel loads have remained relatively constant since then at a level of 8–9 t/ha. Burning was successful in removing dead aerated fuel that dominated the midstorey of the vegetation and stimulating plant growth in the understorey, making the burnt rehabilitated areas more like the unmined forest. Plant density, live plant cover, Acacia density and Acacia cover were generally higher following autumn than spring burning, although differences were reduced over time. Weed density did not differ significantly between autumn and spring burning, peaking 2 years after burning and then declining back to pre-burn levels. Similarly, species richness peaked in the first few years following burning and then declined, consistent with the predictions of the initial floristic composition model of succession. Tree growth was lower in burnt than unburnt areas for the first 2 years, but 4 and 6 years after burning tree growth was not significantly different between autumn, spring and no burn areas. Alcoa is required to integrate rehabilitated areas into the fire management regime of the surrounding jarrah forest to meet completion criteria. The results suggest that this can be achieved by burning rehabilitated areas containing non-native eucalypt species in spring under low to moderate intensity. This fire regime will lead to reduced fuel accumulation, a less prominent midstorey layer resulting from reduced recruitment of Acacia spp., lower densities of eastern Australian eucalypt species, and greater similarity in the composition and abundance of the understorey to the unmined forest.