Multi-Scale Assessment of Relationships between Fragmentation of Riparian Forests and Biological Conditions in Streams

Yirigui Yirigui,Nejadhashemi Nejadhashemi,Lee Lee

doi:10.3390/su11185060

Yirigui Yirigui, Nejadhashemi Nejadhashemi + Show 1 more

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https://doi.org/10.3390/su11185060

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Journal: Sustainability	Publication Date: Sep 16, 2019
Citations: 9	License type: CC BY 4.0

Affiliation: Konkuk University, Michigan State University

Abstract

Due to anthropogenic activities within watersheds and riparian areas, stream water quality and ecological communities have been significantly affected by degradation of watershed and stream environments. One critical indicator of anthropogenic activities within watersheds and riparian areas is forest fragmentation, which has been directly linked to poor water quality and ecosystem health in streams. However, the true nature of the relationship between forest fragmentation and stream ecosystem health has not been fully elucidated due to its complex underlying mechanism. The purpose of this study was to examine the relationships of riparian fragmented forest with biological indicators including diatoms, macroinvertebrates, and fish. In addition, we investigated variations in these relationships over multiple riparian scales. Fragmentation metrics, including the number of forest patches (NP), proportion of riparian forest (PLAND), largest riparian forest patch ratio (LPI), and spatial proximity of riparian forest patches (DIVISION), were used to quantify the degree of fragmentation of riparian forests, and the trophic diatom index (TDI), benthic macroinvertebrates index (BMI), and fish assessment index (FAI) were used to represent the biological condition of diatoms, macroinvertebrates, and fish in streams. PLAND and LPI showed positive relationships with TDI, BMI, and FAI, whereas NP and DIVISION were negatively associated with biological indicators at multiple scales. Biological conditions in streams were clearly better when riparian forests were less fragmented. The relationships of NP and PLAND with biological indicators were stronger at a larger riparian scale, whereas relationships of LPI and DIVISION with biological indicators were weaker at a large scale. These results suggest that a much larger spatial range of riparian forests should be considered in forest management and restoration to enhance the biological condition of streams.

Highlights

Land use patterns with strongly fragmented forests or no forests located in stream riparian areas have significant negative impacts on water quality and aquatic ecological communities [1,2,3,4] due to alteration of stream environments and sediment run-off mechanisms, pollution, and nutrient loading [5,6,7,8,9]
We investigated the relationships between riparian forest fragmentation and biological condition of diatoms, macroinvertebrates, and fish, and examined the variations in these relationships over multiple scales
We observed that the proportion of riparian forest (i.e., PLAND) and the largest riparian forest patch ratio (i.e., LPI) were positively correlated with biological condition of diatoms (i.e., trophic diatom index (TDI)), macroinvertebrates (i.e., benthic macroinvertebrates index (BMI)), and fish (i.e., fish assessment index (FAI)), whereas the spatial proximity of riparian forest patches (i.e., DIVISION) showed significant negative relationships with biological indicators at multiple scales

Summary

Introduction

Land use patterns with strongly fragmented forests or no forests located in stream riparian areas have significant negative impacts on water quality and aquatic ecological communities [1,2,3,4] due to alteration of stream environments and sediment run-off mechanisms, pollution, and nutrient loading [5,6,7,8,9]. Forest fragmentation within riparian areas has been directly linked with degraded water quality and stream ecosystem health [8,11,20,21,22], and spatiotemporal changes in land use, logging, intensive forest management, and rapid economic development have played significant roles in accelerating forest fragmentation [23,24,25,26,27]. The main characteristics of the relationship between forest fragmentation and stream ecosystems remain poorly understood, because they are associated through complex mechanisms involving numerous other factors (e.g., climate, geology, topography, and hydrological processes) [37,38,39,40]

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