Impoverishment Of Forests Research Articles

Long-Term Responses of Mediterranean Mountain Forests to Climate Change, Fire and Human Activities in the Northern Apennines (Italy)

Fagus sylvatica (beech) dominates the montane forests of the Apennines and builds old-growth high-conservation value stands. However, recent severe drought-induced diebacks raise concern on the future persistence of these forests and of Southern European mesophilous woodlands overall, growing at their dry edge. To explore the history of Apennine beech-dominated forests, we draw on the multiproxy paleoecological record from Lago Verdarolo, which includes a robust vegetation-independent temperature reconstruction. Numerical techniques are used to investigate the drivers of long-term Mediterranean mountain forest dynamics. Specifically, we focus on disentangling the ecological factors that caused the shift from high-diversity mixed forests to beech-dominated stands and on assessing the occurrence of legacy effects on present-day forests. Abrupt climate change largely drove vegetation dynamics during the Late Glacial and Early Holocene. Species-rich mixed Abies alba (silver fir) forests dominated about 10,500—5500 years ago, under rather dry and warmer-than-today conditions (+ 1—2 °C) and limited fire occurrence. Cooler and moister summers and increasing fire activity caused declines in several fire-sensitive temperate deciduous trees (for example, Ulmus, Tilia, Fraxinus) and favored the establishment of fir-beech forests around 5500 years ago. Further enhancement of fire activity and farming around 2000 years ago led to local Abies alba extinction and forest impoverishment. We conclude that the currently widespread monospecific Apennine beech forests are the result of multi-millennial land-use intensification superimposed on Late Holocene cooling and moistening. Given their higher drought-tolerance compared to beech stands, reviving ancient species-rich mixed fir forests represents a feasible and ‘tested’ possibility to adapt forests to climate change.

Impoverishment of local wild resources in western Amazonia: a large-scale community survey of local ecological knowledge

A growing number of studies point to the depletion of flora and fauna along rivers of the Brazilian Amazon but the status of wild resources over large areas in Western Amazonia remains poorly known. In this paper we report on findings from the Peruvian Amazon based on the first large-scale community survey that uses local ecological knowledge to assess the presence of indicator species and expected harvest yields of game, fish and timber along four major rivers. Our findings from nearly 700 communities suggest that the forest and lakes near riverine communities have been impoverished over the past 50 years, especially of vulnerable species of high commercial value. A zone of species depletion is detected around the two major regional cities of Iquitos and Pucallpa as well as around an important oil town. Local extirpations are common though some recovery is noted for specific fish and timber species. Expected yields are falling and evidence is found for harvesting of previously non-preferred species. Newer communities face lower initial availability of wild resources and forest impoverishment is driven by market demand over subsistence needs. Our findings illustrate the value of drawing on local ecological knowledge and the importance of considering historical baseline conditions in assessments of the fate of wild resources in tropical forests.

Forest Understory Fire in the Brazilian Amazon in ENSO and Non-ENSO Years: Area Burned and Committed Carbon Emissions

Abstract Understory fires, which burn the floor of standing forests, are one of the most important types of forest impoverishment in the Amazon, especially during the severe droughts of El Niño–Southern Oscillation (ENSO) episodes. However, the authors are aware of no estimates of the areal extent of these fires for the Brazilian Amazon and, hence, of their contribution to Amazon carbon fluxes to the atmosphere. In this paper, the area of forest understory fires for the Brazilian Amazon region is calculated during an El Niño (1998) and a non–El Niño (1995) year based on forest fire scars mapped with satellite images for three locations in eastern and southern Amazonia, where deforestation is concentrated. The three study sites represented a gradient of both forest types and dry season severity. The burning scar maps were used to determine how the percentage of forest that burned varied with distance from agricultural clearings. These spatial functions were then applied to similar forest/climate combinations outside of the study sites to derive an initial estimate for the Brazilian Amazon. Ninety-one percent of the forest area that burned in the study sites was within the first kilometer of a clearing for the non-ENSO year and within the first four kilometers for the ENSO year. The area of forest burned by understory forest fire during the severe drought (ENSO) year (3.9 × 106 ha) was 13 times greater than the area burned during the average rainfall year (0.2 × 106 ha), and twice the area of annual deforestation. Dense forest was, proportionally, the forest type most affected by understory fires during the El Niño year, while understory fires were concentrated in transitional forests during the year of average rainfall. The estimate here of aboveground tree biomass killed by fire ranged from 0.049 to 0.329 Pg during the ENSO and from 0.003 to 0.021 Pg during the non-ENSO year.

MODELING FOREST UNDERSTORY FIRES IN AN EASTERN AMAZONIAN LANDSCAPE

Forest understory fires are an increasingly important cause of forest impoverishment in Amazonia, but little is known of the landscape characteristics and climatic phenomena that determine their occurrence. We developed empirical functions relating the occurrence of understory forest fires to landscape features near Paragominas, a 35‐yr‐old ranching and logging center in eastern Amazonia. An historical sequence of maps of forest understory fire was created based on field interviews with local farmers and Landsat TM images. Several landscape features that might explain spatial variation in the occurrence of understory fires were also mapped and co‐registered for each of the sample dates, including: forest fragment size and shape, forest impoverishment through logging and understory fire, sources of ignition (settlements and charcoal pits), roads, forest edges, and others. The spatial relationship between forest understory fire and each landscape characteristic was tested by regression analyses. Fire probability models were then developed for various combinations of landscape characteristics. The analyses were conducted separately for years of the El Niño Southern Oscillation (ENSO), which are associated with severe drought in eastern Amazonia, and non‐ENSO years.Most (91%) of the forest area that burned during the 10‐yr sequence caught fire during ENSO years, when severe drought may have increased both forest flammability and the escape of agricultural management fires. Forest understory fires were associated with forest edges, as reported in previous studies from Amazonia. But the strongest predictor of forest fire was the percentage of the forest fragment that had been previously logged or burned. Forest fragment size, distance to charcoal pits, distance to agricultural settlements, proximity to forest edge, and distance to roads were also correlated with forest understory fire. Logistic regression models using information on fragment degradation and distance to ignition sources accurately predicted the location of >80% of the forest fires observed during the ENSO event of 1997–1998. In this Amazon landscape, forest understory fire is a complex function of several variables that influence both the flammability and ignition exposure of the forest.

Road paving, fire regime feedbacks, and the future of Amazon forests

Fire poses the greatest threat to the forests of Amazônia. The magnitude of this threat is amplified by three positive feedback loops that drive the expansion of forest fire in the region: (1) Fire promotes drought, and therefore more fire, by releasing smoke into the atmosphere, thus reducing rainfall. Fire-assisted conversion of forests to pastures may also promote drought by increasing albedo and decreasing water vapor flux to the atmosphere, further inhibiting rainfall. (2) Fire increases the susceptibility of forests to recurrent burning by killing trees, thereby allowing sunlight to penetrate the forest interior, and increasing the fuel load on the forest floor. (3) Finally, fires also self-perpetuate by burning agricultural and forestry systems, discouraging landholders from making those fire-sensitive investments in their land that would allow them to move beyond their dependence upon fire as a management tool. The long-term reduction of Amazon fire, and its substantial costs to society, is most likely to emerge through investments and policy change that stimulate permanent agricultural and forestry production systems within existing frontiers while slowing the rate of frontier expansion. But the Brazilian government’s plan to pave, recuperate or construct 6245 km of roads in the Amazon may have the opposite effect. We present research findings that the government plan would nearly double the area of forestland that is accessible by paved highways, including 192,000 km 2 of fire-prone forest. Our analysis finds that these roads will stimulate 120,000–270,000 km 2 of additional deforestation, and forest impoverishment through logging and understory fire, if the historical relationship between road paving and forest alteration by humans continues. Infrastructural investments are urgently needed in Amazônia to help integrate isolated urban centers into the market economy, to improve the quality of life for millions of rural Amazonians, and to improve the profitability of agribusiness in Brazil’s agricultural belt. But as currently planned, these investments will have the ancillary effects of accelerating deforestation, logging, forest fire, smoke-related illness, and the displacement of small-scale farmers.

Large-scale impoverishment of Amazonian forests by logging and fire

Amazonian deforestation rates are used to determine human effects on the global carbon cycle1,2,3 and to measure Brazil's progress in curbing forest impoverishment1,4,5. But this widely used measure of tropical land use tells only part of the story. Here we present field surveys of wood mills and forest burning across Brazilian Amazonia which show that logging crews severely damage 10,000 to 15,000 km2 yr−1 of forest that are not included in deforestation mapping programmes. Moreover, we find that surface fires burn additional large areas of standing forest, the destruction of which is normally not documented. Forest impoverishment due to such fires may increase dramatically when severe droughts provoke forest leaf-shedding and greater flammability; our regional water-balance model indicates that an estimated 270,000 km2 of forest became vulnerable to fire in the 1998 dry season. Overall, we find that present estimates of annual deforestation for Brazilian Amazonia capture less than half of the forest area that is impoverished each year, and even less during years of severe drought. Both logging and fire increase forest vulnerability to future burning6,7 and release forest carbon stocks to the atmosphere, potentially doubling net carbon emissions from regional land-use during severe El Nino episodes. If this forest impoverishment is to be controlled, then logging activities need to be restricted or replaced with low-impact timber harvest techniques, and more effective strategies to prevent accidental forest fires need to be implemented.

Forest Structure and Productivity in Puerto Rico's Luquillo Mountains

Net aboveground primary production (NPP) at 725 m in elevation in the colorado forest (montane rain forest, sensu Beard; lower montane wet forest, sensu Holdridge) of the Luquillo Mountains of Puerto Rico averaged 7.60 t/ha yr on two 0.4-ha permanent plots and was determined by summing aboveground biomass accrual (0.59 t/ha yr), litterfall (6.80 t/ha yr), and herbivory (0.21 t/ha yr). The total leaf area index (trees, epiphytes, and ground vegetation) was 4.95 m2/i2, the aboveground woody volume and biomass, 220 m3/ha and 130 t/ha, respectively, and standing herbivory and the herbivory rate, 5.1 and 4.0 percent/yr, respectively. The mean standing crop of litter was 680 g/m2, with a turnover rate of 0.78 times per year. Of the structural features studied over a 600-m elevational gradient in the Luquillo Mountains, the number of trees per hectare, basal area, and soil organic matter increased with elevation; whereas, the specific leaf area, canopy height, range of tree diameters, forest volume and biomass, leaf area index, and species richness declined. Of the dynamic features studied, ingrowth and mortality of trees, tree growth (diameter, volume, and biomass growth), litterfall, loose litter, standing herbivory and herbivory rates, litter turnover, aboveground woody NPP, and total NPP all declined with an increase in aboveground elevation. The structural and floristic impoverishment of forests and changes in forest dynamics with ascent in the Luquillo Mountains reflect cooler temperatures, fog, and heavier rainfalls that interact to produce saturated soils and retard the mineralization of organic matter.