Gerhard Gerold

The surface fractal dimension of the soil–pore interface as measured by image analysis

Abstract There is general interest in quantifying soil structure in order to obtain physically based parameters relevant to transport processes. To measure the surface fractal dimension of the pore–solid interface we use approaches known from fractal geometry. The characteristics of this interface, expressed by its fractal dimension, are descriptors of the heterogeneity and complexity of soil structure. Samples of the Bt horizon of a Luvisol in loess were taken near Gottingen, Germany. To prepare thin sections, the material was dehydrated and embedded in resin. We obtained digital images at different magnifications from a field emission scanning electron microscope. Automatic image analysis was used to determine the corresponding surface fractal dimension by using the box counting and dilation methods, respectively. As the fractal dimension of a line ( D L ) within a plain has been measured, the surface fractal dimension D S is obtained by D S = D L +1 assuming isotropy. We strongly focussed the calculation of the fractal dimension from the measured data files. The decision as to which data should be included between the lower and upper cutoffs is of fundamental significance to the final result. For the upper cutoff, we followed the convention that the scale range should not exceed 30% of the characteristic length (object or image size). Data derived from outside both cutoffs reflect structural properties, either of pixels (lower cutoff) or of structuring elements (upper cutoff). Different methods were used to derive a mean surface fractal dimension for one magnification for (i) single images and (ii) each measurement step. Within the same range of scale, differences between the two methods (box counting and dilation) were smaller than the standard deviation of D S . In contrast to our expectations for a mathematical fractal, we found decreasing values for D S with increasing magnification. The values drift from D S =2.91 for a resolution of 2.44 μm/pixel to D S =2.58 for a resolution of 0.05 μm/pixel. By fitting two straight lines to the log–log plot, we found a crossover-point at a scale of about 14 μm, forming the border between textural and structural fractality. In addition, we will discuss further results obtained as well as possible sources of error.

Proximate causes of deforestation in the Bolivian lowlands: an analysis of spatial dynamics

Forests in lowland Bolivia suffer from severe deforestation caused by different types of agents and land use activities. We identify three major proximate causes of deforestation. The largest share of deforestation is attributable to the expansion of mechanized agriculture, followed by cattle ranching and small-scale agriculture. We utilize a spatially explicit multinomial logit model to analyze the determinants of each of these proximate causes of deforestation between 1992 and 2004. We substantiate the quantitative insights with a qualitative analysis of historical processes that have shaped land use patterns in the Bolivian lowlands to date. Our results suggest that the expansion of mechanized agriculture occurs mainly in response to good access to export markets, fertile soil, and intermediate rainfall conditions. Increases in small-scale agriculture are mainly associated with a humid climate, fertile soil, and proximity to local markets. Forest conversion into pastures for cattle ranching occurs mostly irrespective of environmental determinants and can mainly be explained by access to local markets. Land use restrictions, such as protected areas, seem to prevent the expansion of mechanized agriculture but have little impact on the expansion of small-scale agriculture and cattle ranching. The analysis of future deforestation trends reveals possible hotspots of future expansion for each proximate cause and specifically highlights the possible opening of new frontiers for deforestation due to mechanized agriculture. Whereas the quantitative analysis effectively elucidates the spatial patterns of recent agricultural expansion, the interpretation of long-term historic drivers reveals that the timing and quantity of forest conversion are often triggered by political interventions and historical legacies.

Can joint carbon and biodiversity management in tropical agroforestry landscapes be optimized

Managing ecosystems for carbon storage may also benefit biodiversity conservation, but such a potential ‘win-win’ scenario has not yet been assessed for tropical agroforestry landscapes. We measured above- and below-ground carbon stocks as well as the species richness of four groups of plants and eight of animals on 14 representative plots in Sulawesi, Indonesia, ranging from natural rainforest to cacao agroforests that have replaced former natural forest. The conversion of natural forests with carbon stocks of 227–362 Mg C ha−1 to agroforests with 82–211 Mg C ha−1 showed no relationships to overall biodiversity but led to a significant loss of forest-related species richness. We conclude that the conservation of the forest-related biodiversity, and to a lesser degree of carbon stocks, mainly depends on the preservation of natural forest habitats. In the three most carbon-rich agroforestry systems, carbon stocks were about 60% of those of natural forest, suggesting that 1.6 ha of optimally managed agroforest can contribute to the conservation of carbon stocks as much as 1 ha of natural forest. However, agroforestry systems had comparatively low biodiversity, and we found no evidence for a tight link between carbon storage and biodiversity. Yet, potential win-win agroforestry management solutions include combining high shade-tree quality which favours biodiversity with cacao-yield adapted shade levels.

Effects of lianas and Hurricane Wilma on tree damage in the Yucatan Peninsula, Mexico

Climate change may increase the intensity of hurricanes (Emanuel 1987, 2003), and thus the size of disturbance in tropical forests. As a consequence, disturbance-specialist plants, such as lianas, may increase in abundance there (Phillips & Gentry 1994). Putz (1984) hypothesized that lianas create larger treefall gaps by connecting trees together and pulling down multiple trees during storms. This positive-feedback cycle may increase the prevalence of lianas in disturbed tropical forests (Schnitzer & Bongers 2002, Schnitzer & Carson 2001). Alternatively, Putz (1984) proposed that lianas tie and stabilize canopies together, resulting in less disturbance. Forest age may determine the role of lianas during disturbance because liana abundance and composition vary through secondary succession (De Walt et al . 2000, Schnitzer et al . 2000). To test the two hypotheses of Putz (1984), we evaluated the effect of liana cutting between forests of different successional ages on tree damage by hurricane Wilma.

Hydrology and Biogeochemistry of Tropical Montane Cloud Forests

Tropical montane cloud forests (TMCFs) are differentiated from other forest types by their frequent immersion in fog. This characteristic implies that TMCFs are unique in their hydrological functioning, as they receive a substantial amount of water input via direct deposition of cloud droplets. Because it is generally associated with reduced solar radiation and increased humidity, frequent fog occurrence can lower evapotranspiration (ET). Many TMCFs also have certain characteristic structural and floristic features, which have further hydrological effects. Cloud water is often chemically different from rain water (Heath 2001; Liang et al. 2009); hence, fog deposition can alter inputs of nutrients and other chemicals into the ecosystem. The hydrological, biological, and chemical characteristics of cloud forests give rise to differences in biogeochemical processes as well.

Modelling potential habitats for Artemisia sieberi and Artemisia aucheri in Poshtkouh area, central Iran using the maximum entropy model and geostatistics

Abstract Predicting potential habitats of endemic species is a suitable method for biodiversity conservation and rehabilitation of rangeland ecosystems. The present study was conducted to estimate the geographic distribution of Artemisia sieberi ( A. sieberi ) and Artemisia aucheri ( A. aucheri ), find the most important environmental predictor variables and seek for similarities and differences in habitat preferences between the two species for Poshtkouh rangelands in Central Iran. Maps of environmental variables were created by means of geographic information system (GIS) and geostatistics. Then predictive distribution maps of both species were produced using the maximum entropy modeling technique (Maxent) and presence-only data. Model accuracy is evaluated by using the area under the curve (AUC). Lime1, gravel1, lime 2 and elevation most significantly affect habitat distribution of A. aucheri , while habitat distribution of A. sieberi is affected by elevation, lime1, am1, lime2, and om2. For both species, elevation has an influence on their potential distributions. However, A. aucheri depends more on elevation, and consequently climate in comparison to A. sieberi . Finally, it is revealed that the potential distribution of A. aucheri is limited mostly to mountainous landscapes while A. sieberi is present in wide ranges of environmental conditions.

Structure and management of cocoa agroforestry systems in Central Sulawesi across an intensification gradient

Central Sulawesi is a major cocoa producing region in Indonesia. Nevertheless, very little is known about the basic socio-economic and pedological properties of cocoa agroforestry systems in the region. In the vicinity of Lore Lindu National Park (LLNP), 144 cocoa plots covering an intensification gradient were selected for an intensive 1-year cocoa management study including a subset of 48 plots for extended soil analyses.

Greenhouse gas emission peaks following natural rewetting of two wetlands in the southern Ukhahlamba-Drakensberg Park, South Africa

The global importance of wetlands in the carbon and nitrogen cycles is well documented, but the specific greenhouse gas characteristics of South African wetlands are less well known. These wetlands most likely differ from more prominent wetlands from continuously humid climate zone (boreal, temperate and tropics). Particular wetlands in the southern Drakensberg are adapted to the seasonal drying during the winter months. Greenhouse gas emissions were measured during natural rewetting at two wetlands. A rapid reaction and significant positive correlation between greenhouse gas fluxes and ground water level were determined. Methane emissions were observed after two days of rewetting at one of the wetlands, and nitrous oxide emissions started within a day of rewetting at the other wetland. The high nitrous oxide emissions may be caused by the recent winter burning of vegetation, which most likely resulted in a greater availability of nitrogen in the soil. High nitrous oxide emissions following natural rewetting (the annual cyclical process in these wetlands) could contribute significantly to the local greenhouse gas budget. Hence, besides the methane emissions, the nitrous oxide emissions of wetlands in southern Africa should be taken into account.

Effects of conversion of native cerrado vegetation to pasture on soil hydro-physical properties, evapotranspiration and streamflow on the Amazonian Agricultural Frontier

Understanding the impacts of land-use change on landscape-hydrological dynamics is one of the main challenges in the Northern Brazilian Cerrado biome, where the Amazon agricultural frontier is located. Motivated by the gap in literature assessing these impacts, we characterized the soil hydro-physical properties and quantified surface water fluxes from catchments under contrasting land-use in this region. We used data from field measurements in two headwater micro-catchments with similar physical characteristics and different land use, i.e. cerrado sensu stricto vegetation and pasture for extensive cattle ranching. We determined hydraulic and physical properties of the soils, applied ground-based remote sensing techniques to estimate evapotranspiration, and monitored streamflow from October 2012 to September 2014. Our results show significant differences in soil hydro-physical properties between the catchments, with greater bulk density and smaller total porosity in the pasture catchment. We found that evapotranspiration is smaller in the pasture (639 ± 31% mm yr-1) than in the cerrado catchment (1,004 ± 24% mm yr-1), and that streamflow from the pasture catchment is greater with runoff coefficients of 0.40 for the pasture and 0.27 for the cerrado catchment. Overall, our results confirm that conversion of cerrado vegetation to pasture causes soil hydro-physical properties deterioration, reduction in evapotranspiration reduction, and increased streamflow.

Effects of Insect Mass Outbreaks on Throughfall Composition in Even Aged European Pine Stands - Implications for the C and N Cycling

In this paper we report on the herbivore-affected C and N concentrations in the throughfall and altered canopy to soil transfer during a Pine Lappet (Dendrolimus pini L) mass infestation in 60-year-old Scots Pine (Pinus sylvestris L) forests. Our investigations covered a period of 7 months and could show, that herbivore defoliation significantly altered C and N concentrations in the throughfall solution and enhanced organic matter input situation to the forest floor. Compared to the uninfested site mean concentrations of the throughfall solution at the infested site under strong frass activity contained 80% more C and 61% more N. Additionally, C and N inputs were with 131 kg C ha-1 time-1 and 9.6 kg N ha-1 time-1 higher under strong frass activity during 3 months compared to the input at the uninfested site. We assume that outbreaks of phytophagous insects play an important key role in monoculture forest by influencing the nutrient turnover.