Epsilon Archive for Student Projects

Abstract

Riparian zones in boreal forests are known to support high biodiversity and provide important ecological functions. In Sweden’s forests nearly one million kilometers of man-made ditches and modified waterways exist in the landscape, yet they are sometimes difficult to distinguish from natural streams. Understanding the differences and similarities is critical for identifying which modified waterways support unique ecological functions in order to guide more effective biodiversity conservation and management strategies. Invertebrate communities are known to be good bioindicators that respond to changes in microclimates and habitat structure. Thus, this study investigated differences in abundances of three types of invertebrates: ants, spiders and beetles. The invertebrates were collected all across Sweden, from north to south, covering eight sites and over 300 pitfall traps next to both ditches and natural streams. Environmental and structural variables such as distance to waterway, catchment area, understory species richness, forest type and non-vegetative ground cover were also recorded on the sites. The data was analyzed using a general linear mixed model (GLMM) with a negative binomial distribution to evaluate abundance patterns and interactions with the other variables.

The total abundance of all invertebrates was similar across both waterways, but all invertebrates responded differently to various variables. Spider abundance declined with distance to ditches but remained stable with distance to streams. Ant abundance was positively correlated with understory species richness in streams but negatively in ditch environments. Finally, beetle abundance was positively correlated with catchment area for both ditches and streams, slightly more for streams. These results suggest that ditches and streams can support similar abundances of these three groups of invertebrates, but that the underlying ecological processes driving them are different.

This study highlights the need for tailored riparian buffer design as natural stream riparian zones may provide more stable microclimates whereas riparian zones in ditches (if protected) might require different strategies tailored to their specific ecological function and different ecological processes.