Tree dieback, woody plant diversity, and ecosystem driven by topography in semi-arid mountain forests: Implication for ecosystem management.

Mountain landscapes are highly heterogeneous due to topography, notably positions along slope and slope shapes, which control ecosystem mechanisms. We hypothesized that tree dieback is controlled by topography, selecting productive and less diverse communities in lower slopes, and stress-resistant and more diverse communities on upper slopes. Understanding how this heterogeneity drives vegetation patterns should provide benchmarks for ecosystem management of mountain forest dominated by Quercus brantii. Woody communities were sampled along convex vs concave topography (i.e., ridge vs talweg), and with measurements of tree dieback severity, environmental variables (litter depth, soil quality, rock outcrop), stand structure (canopy cover, mistletoe infestation, tree diameter and height, diameter and height differentiations, oaks' number from sprout-clumps or seed-origin), and biodiversity. Slope position was the most significant driver that affected all variables, excepted evenness. Dieback severity was higher on slope shoulders and summits, and lower in lower slopes where trees were the most productive: taller, larger, more homogeneous, and mostly seed-origin. Catena shape affected the diversity and dieback severity, both higher in talwegs, but had no effect on environmental variables and little on stand structure. Outputs indicate that the higher diversity of woody plants is on upper slopes supporting stress-resistant community associated with more severe dieback and mistletoe infection probably because frugivore birds attracted by the shrubs' fruits. Semi-arid forest management must consider the shaped-slope ecosystem heterogeneity by preserving ridges that are more susceptible to tree dieback, and naturally support biodiversity. Restoration measures on lower fertile slopes could be carried out by oak planting or seedlings under the cover of shrubs to counter dieback effects and environmental stresses. In addition, forestry measures can be taken in lower positions for the conversion of coppice to high oak forest to potentially consider a moderate forestry.

Decrease in Soil Functionalities and Herbs' Diversity, but Not That of Arbuscular Mycorrhizal Fungi, Linked to Short Fire Interval in Semi-Arid Oak Forest Ecosystem, West Iran.

The semi-arid forest ecosystems of western Iran dominated by Quercus brantii are often disturbed by wildfires. Here, we assessed the effects of short fire intervals on the soil properties and community diversity of herbaceous plants and arbuscular mycorrhizal fungi (AMF), as well as the interactions between these ecosystem features. Plots burned once or twice within 10 years were compared to unburned plots over a long time period (control sites). Soil physical properties were not affected by the short fire interval, except bulk density, which increased. Soil geochemical and biological properties were affected by the fires. Soil organic matter and nitrogen concentrations were depleted by two fires. Short intervals impaired microbial respiration, microbial biomass carbon, substrate-induced respiration, and urease enzyme activity. The successive fires affected the AMF's Shannon diversity. The diversity of the herb community increased after one fire and dropped after two, indicating that the whole community structure was altered. Two fires had greater direct than indirect effects on plant and fungal diversity, as well as soil properties. Short-interval fires depleted soil functional properties and reduced herb diversity. With short-interval fires probably fostered by anthropogenic climate change, the functionalities of this semi-arid oak forest could collapse, necessitating fire mitigation.

Fire disturbance effects on plant taxonomic and functional ß-diversity mediated by topographic exposure.

Although the diversity-disturbance relationship has been extensively studied, the differences in responses of taxonomic vs. functional diversity to natural disturbances (i.e., fire) call for an improved understanding of this relationship. Here, we investigated how fire disturbance influenced plant taxonomic and functional diversity in Golestan National Park, in northeastern Iran. We evaluated the response of α- and ß-plant diversity considering both taxonomic and functional diversity and different ß-diversity components (i.e., turnover and nestedness) as a function of fire regime, topographic exposure, and their interactive effect. We considered different indices of functional diversity including functional richness, functional evenness, functional divergence, functional dispersion, Rao's quadratic entropy, and community-weighted mean (CWM). Functional diversity indices were computed using four leaf traits related to species growth strategy and fire response including leaf thickness and leaf length, specific leaf area (SLA) and leaf dry matter content (LDMC). Taxonomic and functional diversity had contrasting response to fire disturbance. Fire significantly decreased taxonomic α-diversity similarly in both north and south exposures. ß-diversity increased in south exposures but decreased in north exposures. Fire decreased functional richness, increased CWM of SLA, and decreased CWM of LDMC. In contrast, abundance-weighted metrics of functional diversity (functional evenness, functional divergence, functional dispersion, Rao's quadratic entropy) were not impacted by fire disturbance. Finally, the main contributors to heterogeneity were driven by a fire × exposure interaction, suggesting that fire disturbance interacts with topographic exposure. Our results suggest that taxonomic and functional α- and ß-diversity have contrasting responses to fire illustrating the need to consider both dimensions to understand how disturbance impacts plant communities. At large spatial scale, species turnover and nestedness appear as essential parameters to maintain species-rich communities in response to fire disturbance.

A GIS-expert-based approach for groundwater quality monitoring network design in an alluvial aquifer: a case study and a practical guide.

Groundwater quality monitoring is a critical part of water management in all groundwater basins. In order to be effective and to meet the required needs, groundwater quality monitoring networks (GQMNs) must be designed to be able to operate long-term and economically without minimal disruption. The analytical hierarchical process (AHP), a multi-criteria decision-making program, was used to design a GQMN for an alluvial aquifer located in the Islam Abad plain west of Kermanshah province, Iran. This semi-arid area is subject to groundwater depletion and water quality changes. The model used 8 primary criteria sub-divided with 5 sub-criteria based on a combination of empirical data and expert opinion. The primary criteria included density of wells, well discharge, well depth, water quality (conductivity), flow direction, annual groundwater extraction, water level declines, and accessibility. The model showed that 59 of 254 production wells in the basin could provide optimal monitoring locations. When a second screening of the wells was used to determine constraints (physical conditions of the wells and pumps, owner permission of use, type of the pump, etc.), the number of wells was reduced to 13 wells. An initial round of water sampling and chemical analysis demonstrated that the design of the GQMN met the goals of the water management agency of the region.

Linkage between plant species diversity and soil-based functions along a post-agricultural succession is influenced by the vegetative forms.

There is a growing body of knowledge that ecosystem functions, in particular, soil-based ecosystem functions, are related to biodiversity. However, how plant species diversity influences soil-based functions along post-agricultural secondary succession is still a largely ignored question in Mediterranean semi-arid conditions. Therefore, we used the plant functional group approach to investigate the relationships between plant species diversity indices and soil-based functions including microbial biomass carbon (MBC), basal respiration (BR), and carbon sequestration (CS) across three different stages of the vegetation succession corresponding to ~ 5 years after agricultural abandonment, ~ 15 years after abandonment, and oak forests which represent the terminal stage. We also tested if these relationships are supported by the niche complementarity and selection effect hypotheses. The results showed that soil-based functions significantly increased with time since abandonment as BR, MBC, and CS increased respectively by 1.7, 1.5, and 2.7 times across the three successional stages. We also found strong correlations between the diversity indices and the soil-based functions BR, MBC, and CS which were positive for richness (R2 values 0.75, 0.74, and 0.75) and Shannon diversity (R2 values 0.61, 0.58, and 0.61) but negative for evenness (R2 values 0.38, 0.38, and 0.36 for, respectively). Similarly, richness and Shannon diversity of the different plant functional groups positively correlated with soil-based functions. However, contrasting results were found for evenness which positively correlated with soil-based functions for perennial grass only. We suggested that increasing the diversity of plant species and facilitating dominant species would be needed to improve the soil-based ecosystem functions after abandonment of degraded soils. This study also revealed that the mechanisms behind the relationships between biodiversity and ecosystem functions were influenced by the vegetative forms.