Lea Wittenberg

Runoff and erosion processes after a forest fire in Mount Carmel, a Mediterranean area

In the Mediterranean forest area of Israel, fires increase runoff and sediment yield rates relative to undisturbed forested land. The September 1989 fire covered an area of 4 km2 in the main recreation area of Mount Carmel, a typical Mediterranean forest area. The lithology is chalk and limestone, and about 40% of the burnt area has steep slopes, exceeding 30%. Three study plots were established in burnt and unburnt areas. Plots were located on 100–300 m2 areas with different slope exposures. Runoff and sediments were collected after each storm by a collector system. A hydrometric station was established, draining an area of 1 km2 in the burnt zone. Rainfall was measured by two recorders and several rain gauges at the experimental sites. In the first rainfall season after the fire, runoff and sediment yield were 500 and 100,000 times higher respectively in the burnt areas. Rainfall intensity is a dominant factor in runoff and sediment yield rates. In the measured basin, total runoff in the first year was 1.6%. Revegetation recovery of the area was rapid, as shown by the results from the second season: runoff decreased by one order of magnitude, from an average of 10 mm to 1.5 mm; sediment yield decreased by two orders of magnitude, from 1200 g m−2 to 10 g m−2. The third season 1991/1992, was an exceptionally rainy year and therefore runoff and sediment yield increased, but to less than in the first year. Runoff and sediment yield are related to vegetation cover, rainfall intensity, soil properties, slope steepness and exposure and fire intensity. Logging activities after fire increase sediment yields. Through its effects on vegetation cover and soil, fire severity increases the potential for erosion.

Monitoring post-wildfire vegetation response with remotely sensed time-series data in Spain, USA and Israel

Due to the challenges faced by resource managers in maintaining post-fire ecosystem health, there is a need for methods to assess the ecological consequences of disturbances. This research examines an approach for assessing changes in post-fire vegetation dynamics for sites in Spain, Israel and the USA that burned in 1998, 1999 and 2002 respectively. Moderate Resolution Imaging Spectroradiometer satellite Normalized Difference Vegetation Index (NDVI) time-series data (2000-07) are used for all sites to characterise and track the seasonal and spatial changes in vegetation response. Post-fire trends and metrics for burned areas are evaluated and compared with unburned reference sites to account for the influence of local environmental conditions. Time-series data interpretation provides insights into climatic influences on the post-fire vegetation. Although only two sites show increases in post-fire vegetation, all sites show declines in heterogeneity across the site. The evaluation of land surface phenological metrics, including the start and end of the season, the base and peak NDVI, and the integrated seasonal NDVI, show promising results, indicating trends in some measures of post-fire phenology. Results indicate that this monitoring approach, based on readily available satellite-based time-series vegetation data, provides a valuable tool for assessing post-fire vegetation response.

Soil erosion and forestry management after wildfire in a Mediterranean woodland, Mt. Carmel, Israel.

Forestry management is crucial in mitigating erosion processes after extensive fires in Mediterranean woodlands. Fire alters forest ecosystems, causing an increase in rates of geomorphic processes. The September 1989 fire in Mt. Carmel covered an area of 4 km2 in the main recreation area of a typical Mediterranean forest area. Six experimental plots, covering an area of 300-500 m(2) each, were established in order to determine the effect of forestry management practice on soil erosion after the fire; runoff and sediments were collected during and after each rainstorm. Rainfall was measured by two recorders and several rain gauges at the study site. During the first year following the fire, sediment yield was 100-500 times higher than on vegetated slopes. Sediment movement was increased mainly by the lack of vegetation. Results show that there is a clear trend of decrease in sediment yield between the first year and the next five. After this period the burnt areas recovered to similar rates of erosion as in the unburnt areas. The clearings of burnt logs by machine and cable sliding increased the sediment yield in the experimental plots. After vegetation development in the second season following the fire, no significant differences were found among the types of management practice plots.

Structural patterns in coarse gravelriver beds: typology, survey and assessment of the roles of grain size and river regime

The concept of river‐bed stability as indexed by the occurrence of stable bed forms was examined in humid‐temperate perennial streams and in Mediterranean ephemeral streams. The study examined the structural patterns of bed forms and their spatial distribution between temperate‐humid and Mediterranean streams. Study sites in Northumberland, UK, and Mt. Carmel, Israel, were selected for their morphometric similarity, despite the contrast in climate, vegetation and hydrological regime. Fieldwork was based on a large number of Wolman grain size distributions and structure measurements along cross‐sections at seven sites; Differences in mean grain size of bed structures were estimated using the general linear model (GLM) procedure and Duncans multiple range test. Based on field evidence, river‐bed configurations were divided into structural categories, according to the depositional setting of each measured particle on the river bed. Statistical analysis confirmed former qualitative descriptions of small‐scale bed forms. The study identified spatial segregation in bed form distribution. In general, 30–40%of the bed material in the surveyed perennial streams was clustered, in contrast to approximately 10%in the ephemeral counterparts. The sorting index revealed higher values for the perennial streams, namely 2.39–3.59 compared with 1.73–2.07 for the ephemeral counterparts. It is suggested that the degree of sediment sorting and the proportion of clusters are strongly related. Sediment sorting, sediment supply and the hydrological regime explain the mechanism of cluster formation. It is assumed that climate shifts or human interference within river basins might affect the regional characteristic flood hydrograph, and consequently alter the sedimentary character of the river bed. In the case where river bed stability is reduced owing to changes in cluster bed form distribution, rivers that normally do not yield a significant amount of sediment might be subject to notable sedimentation problems.

Spatio-temporal perspectives of forest fires regimes in a maturing Mediterranean mixed pine landscape

It has been suggested that during the past several decades, the frequency and the intensity of wildfires have markedly increased in the Mediterranean basin. We came to assess this postulation in the forested region of Mount Carmel, Israel. This region is characterized by Quercus spp. and Pistacia spp. maquis and has been intensely afforested with Pinus spp. stands since the 1920s. We compiled a GIS-based database of the fires recorded in the region since 1983, in addition to archiving data beginning from the 1940s. The data were collected from land stewardship agencies’ archives, fire departments and aerial photographs. Prior to the early 1980s, no systematic documentation of the fires was available, rather just sporadic qualitative documentation of the large forest fires that occurred. Between 1944 and 1982, only 6 large fires were documented, while after that 11 large fires occurred. Analysis indicated that the spatial distribution of the fires does not occur at random, and their locations are significantly closer to roadsides compared to an expected random distribution. The annual number of fires and the areas burned during the last two decades were not correlated with annual precipitation in any manner. Accordingly, we suggest that the increased number of large forest fires during the last decades is associated with the maturation and senescence of the planted forest coupled with increased human activities.

Effects of Repeated Fires on the Structure, Composition, and Dynamics of Mediterranean Maquis: Short- and Long-Term Perspectives

Wildfires are an important agent in driving ecosystem function by altering vegetation structure and geomorphic processes. In recent decades, the number of wildfires and the total area burned has increased around the world, causing changes to natural regimes. In this study, we compared south- and north-facing slopes, their vegetation structure and dynamics, and the sediment yield generated in areas burned a number of times at the Carmel Mountain ridge in northern Israel. Our underlying hypothesis was that repeated and frequent fires significantly alter eco-geomorphic processes, including prolonged periods of soil erosion and delayed recovery of tree species. We tested whether these phenomenon are characterized by different rates on opposing aspects. To study the long-term changes of the vegetation we analyzed a 21-year (1985–2006) chrono-sequence of satellite images, in areas burned once, twice, or three times. Additionally, we estimated vegetation structure and cover at high resolutions in monitoring plots following a fire in 2005 in areas burned once or twice during the last two decades. To evaluate the long-term dynamics of the system, specific transition probabilities among the vegetation types, as a function of the number of times each site was burned, were used to construct Markov-based transition matrices. Additionally, runoff and sediment have been collected after precipitation events from the plots. The satellite image classifications revealed changes in the composition of tree, shrub, and herbaceous vegetation cover following wildfire events. Satellite image analyses suggest that recurring fires within short-time intervals may significantly alter the long-term structure of the vegetation communities, and may eliminate woody vegetation from the landscape (both trees and shrubs). Consequently, this results in the establishment and dominance of herbaceous vegetation communities. Similar trends were observed in the high-resolution monitoring plots. Sediment yields differed significantly in areas burned twice on south-facing slopes, compared to lower values obtained in areas burned once, or located on north-facing slopes. Thus, we demonstrate that repeated fires may dramatically alter long-term trajectories of Mediterranean-type vegetation communities and ecosystems. This pattern, in turn, may have significant implications for the associated geo-morphological processes, especially runoff and erosion, and should be of particular concern given recent changes of fire regimes.

Soil water repellency persistence after recurrent forest fires on Mount Carmel, Israel

Variations in forest fires regime affect: (1) the natural patterns of community structure and vegetation; (2) the physico-chemical properties of soils and consequently (3) runoff, erosion and sediment yield. In recent decades the Mediterranean ecosystem of Mount Carmel, north-western Israel, is subjected to an increasing number of forest fires, thus, the objectives of the study were to evaluate the long-term effects of single and recurrent fires on soil water repellency (WR) and organic matter (OM) content. Water repellency was studied by applying water drop penetration time (WDPT) tests at sites burnt by single-fire, two fires, three fires and unburnt control sites. Water repellency in the burnt sites was significantly lower than in the unburnt control sites, and the soil maintained its wettability for more than 2 decades, whereas after recurrent fires, the rehabilitation was more complicated and protracted. The OM content was significantly lower after recurrent than after a single fire, causing a clear proportional decrease in WR. The rehabilitation of WR to natural values is highly dependent on restoration of organic matter and revegetation. Recurrent fires may cause a delay in recovery and reduced productivity of the soil for a long period.

Urban Sprawl and Ecosystems — Can Nature Survive?

Contrary to the popular notion that the advancing frontier of urban development has been swallowing and destroying natural ecosystems we present evidence that the sprawl of cities creates ample open space in peri-urban areas. Traditional view of city–nature dichotomy and clear spatial separation should be substituted by a vision that reflects the complex spatial dynamics of city–rural–natural fabric with extended areas of overlap among them. We present a survey of the relevant research concerning urban and ecological systems spatial dynamics and conclude that nonregular, leapfrogging spatial expansion, characteristic of the majority of the modern western cities, may buffer between urban and intensively cultivated agricultural areas and counter their impacts on natural ecosystems. The wealthy sprawling suburbs provide essential habitats for native species and ensure their survival.

Vegetation cover and species richness after recurrent forest fires in the Eastern Mediterranean ecosystem of Mount Carmel, Israel

Fire is a common disturbance in Mediterranean ecosystems, and can have a destructive, influential, and even essential, effect on vegetation and wildlife. In recent decades there has been a general increase in the number of fires in the Mediterranean Basin, including in Mount Carmel, Israel. The effects of recurrent forest fires on vegetation cover and species richness were determined in the spring of 2009 and 2010 by field surveys. The results of this study showed that the vegetation cover changes after recurrent forest fires, and can serve as a good indicator of the influence of fire and the resulting ecosystem rehabilitation. The dominant cover in most fire-damaged areas was composed of shrubs and dwarf-shrubs, especially Cistus salviifolius and Calicotome villosa. Tree cover was severely damaged after recurrent fires, and in those areas there was a drastic decrease of the total plant cover. Species richness increased mainly in the first decade after the recurrent fires, and decreased when the forest canopy began to close. Fire recurrence with short intervals (4-6years) between fires may lower the rehabilitated processes of the ecosystem and change its equilibrium.

Ash-soil interface: Mineralogical composition and physical structure

Fires exert many changes on the physical, chemical, morphological, mineralogical, and biological properties of soil that, in turn, affect the soils hydrology and nutrient flux, modifying its ability to support vegetation and resist erosion. The ash produced by forest fires is a complex mixture composed of organic and inorganic particles with varied properties. This research was conducted to study and characterized ash properties produced at different temperatures and with different soil organic matter combinations. The samples, which included two treatments of soils with underlying mixed leaves and branches composed mainly by Pinus halepensis, Pistacia lentiscus, Cistus salviifolius and typical herbaceous vegetation, versus samples of mixed leaves and branches alone. Both were exposed to 400°C and 600°C heat in a muffle furnace for 2h. The residue ash was generally grayish, consisting of mixed-sized particles that preserved almost none of the original characteristics of the fuel, and was deposited in ash layers with diverse physicochemical and textural properties. The results of this study highlight the differences between all examined samples and strongly support the assumption that ash produced from a complex vegetation-soil system is a new substance with unique structural, textural, and mineralogical properties. Moreover, the ash produced at different temperatures appeared in distinct layering patterns.