Forest fragmentation and impacts of intensive agriculture: Responses from different tree functional groups

Forest cover controls the nitrogen and carbon stable isotopes of rivers

Deforestation affects the ecological integrity of rivers and streams, threatening biodiversity and ecosystem services worldwide. However, few studies have strictly analyzed the effect of the functional responses of tropical streams to changes in forest cover since deforested basins are usually also influenced by confounding anthropogenic inputs. Here we address tropical streams and test whether the stable isotopic ratios of nitrogen (N, δ¹⁵N) and carbon (C, δ¹³C) and the ratio of C:N of ecosystem components vary along a forest cover gradient. We also assess the ecological integrity of streams by in situ measurements using physical features commonly used in stream quality assessments. The results showed that the δ¹⁵N of most aquatic components, δ¹³C of particulate matter and omnivorous fish, and C:N of particulate matter and algae vary significantly with forest cover, indicating the role of terrestrial vegetation in regulating stream biogeochemistry. The dual stable isotope analysis satisfactorily indicated the changes in terrestrial-aquatic connections regarding both N and C cycles, thus showing the role of algae and particulate matter in influencing stream fauna through food web transfers. Our results support the use of stable isotopes to monitor watershed deforestation and highlight the need for reassessment of the effects of anthropogenic inputs on δ¹⁵N increase in globally distributed inland waters since the loss of forest is a significant cause in itself.

Linking Ecosystem Services to Social Well-Being: An Approach to Assess Land Degradation

Land degradation usually leads to the loss of ecosystem services, which may threaten social well-being. There is no approach to identify and manage all ecosystem services based on their importance in degradation processes and social systems. This study aimed to link ecosystem services to social well-being in order to assess rangeland degradation. Eleven ecosystem services (forage production, water yield, edible plants, fuel, medicinal plants, pollination, gas regulation, soil resistivity to erosion, soil fertility, scenic beauty, and recreation) were assessed in a semiarid rangeland near Bardsir city, Kerman Province, southeast Iran. There were significant differences between the rangeland types in providing ecosystem services (p < 0.05). Four criteria and 17 indices of social well-being were weighed according to their importance for local stakeholders. Rangeland degradation was estimated using the weight of the indices for social well-being and ecosystem services. Discriminant analysis indicated that supporting services (soil fertility) and provisioning services (water yield and forage production) had the greatest impact on rangeland degradation, which is related to food security in social well-being. Ecosystem services and social well-being declined in medium and severe degradation due to plant composition change and overgrazing based on principal component analysis (PCA). More than 70% of the watershed has been highly and severely degraded. There was a trade-off relationship between ecosystem services and social well-being in very severe degraded areas because of social well-being promotion due to agriculture expansion. Based on our approach, the loss rate of the ecosystem services and social well-being indices in each degradation category is a good guide for management programs and decision-makers to meet both the needs of the people and the preservation of ecosystems.

Short-Term Responses of Aquatic and Terrestrial Biodiversity to Riparian Restoration Measures Designed to Control the Invasive Arundo donax L

Invasive species are among the top five causes of biodiversity loss worldwide. Arundo donax has progressively colonized the riparian zones of Mediterranean rivers with detrimental effects on terrestrial and aquatic biodiversity, being catalogued as one of the 100 worst invasive species. In order to control this invasive species and restore native riparian vegetation, different methods have been traditionally used, depending on the environmental, economic and social context. Here, the effect of repeated above-ground removal of A. donax on aquatic and terrestrial communities was assessed by testing two different frequencies of mowing (monthly-intensive and quarterly-extensive), combined with the plantation of native species. Specifically, it was evaluated if riparian vegetation, birds and aquatic macroinvertebrates showed significant responses throughout time and between restoration treatments based on 4-year annual biomonitoring data (2015–2018). Changes in taxonomic diversity and ecological quality indices for the different biological communities were tested using mixed-effect models (LMEs). Similarly, comparisons between restored and reference sites were also performed. LMEs were also applied to assess how riparian variables were related to bird and aquatic macroinvertebrate indices. NMDS and MGLM-Mvabund analyses were performed to detect significant post-treatment differences in taxa composition compared to the initial state and reference sites. During this short-term assessment, increases in riparian and aquatic macroinvertebrate richness and quality indices were found, as well as significant decreases in A. donax height, density and cover, without significant differences between restoration treatments. However, differential effects between extensive (positive-neutral effect) and intensive treatments (neutral-negative effect) were detected for bird richness, density and abundance. After three years of restoration actions, restored sites are still far from reference values in terms of taxa composition, species richness and ecological quality, especially for riparian vegetation and birds. Given the high cost and the great efforts required for restoration, extensive repeated mowing, together with native species plantation, are only recommended on river reaches not fully invaded by A. donax and with a high ecological interest.