Relationships Between Forest-Floor Invertebrate Distribution, Movement, and Microclimate Under Alternative Riparian Management Practices Redacted for Privacy
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AN ABSTRACT OF THE DISSERTATION OF Jessica J. Rykken for the degree of Doctor of Philosophy in Entomology presentedon June 9, 2004. Title: Relationships Between Forest-floor Invertebrate Distribution, Movement, and Microclimate Under Alternative Riparian Management Practices Redacted for Privacy Andrew R. Moldenke Headwater streams and their riparian zones are a common, yet poorly understood, component of Pacific Northwest landscapes. I sought to describe the ecological significance of headwater stream riparian zones as habitat for forest-floor invertebrate communities,and to assess how alternative management strategies for riparian zones may impact these communities. I compared community composition of forest-floor invertebratesat five distances along 70 m trans-riparian (stream edge to upsiope) gradients in three treatments:mature forests; clearcuts; and across riparian buffers of 30 m width. In the buffer treatments, I looked forevidence of microclimatic edge effects, and also biological edge effects,as characterized by species distribution and movement patterns across the forest-clearcut boundary. Invertebrateswere collected in pitfall traps, in five replicate blocks of three treatments each, in theWillamette National Forest, OR. Air and soil temperature, and relative humiditywere measured at a subset of pitfall locations at each site. A pitfall grid was installed atone riparian buffer site for a mark- release-recapture study to record carabid beetle and lycosid spidermovements across the buffer edge. Ordination revealed a distinct "riparian" invertebrate community within 1m of the stream edge in mature forest treatments, which was strongly relatedto a cool, humid microclimate. The stream appeared to influence microclimate at least 20 m up slope in the mature foresttreatments. Invertebrate community composition in buffer treatmentswas far more similar to that of mature forests than was that of clearcuts, a pattern mirrored by microclimate.Microclimatic edge effects were not evident in the buffer, suggesting that the stream's cool, humid influenceon microclimate may be modifying any warm, drying effects coming in from the forest-clearcut edge. While biological edge effects were not clear for invertebrate communities,individual species showed various responses to the buffer edge, dependingon their habitat affinities and mobility. These results suggest that invertebrate distributionsare strongly associated with microclimate, and that riparian buffers of -30 m width provide suitable habitat formany forest species. However, buffer edges may serve as barriers to dispersal for some forest interior species,or be permeable to invasion by open-habitat species, with possible consequences for long-term populationand community dynamics within the buffer. ©Copyright by Jessica J. Rykken June 9, 2004 All Rights Reserved Relationships Between Forest-floor Invertebrate Distribution, Movement, and Microclimate Under Alternative Riparian Management Practices by Jessica J. Rykken A DISSERTATION submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented June 9, 2004 Commencement June 2005 Doctor of Philosophy dissertation of Jessica J. Rykken presented on June 9. 2004. Redacted for Privacy Major Professor, representing Redacted for Privacy Head of the Entomology Program Redacted for Privacy Dean of the lrduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. Redacted for Privacy Jessica J. Rykken. Author ACKNOWLEDGEMENTS Many people contributed to the success, and ultimate completion, of this dissertation. Andy Moldenke, my advisor, was willing to take to the field, or clear off a chair in his office, whenever the need arose. Carolyn VerLinden always lent her chair, a ready ear, or her computer skills at a moment's notice. The rest of my committee, Paul Jepson, Dede Olson, Sandy DeBano, and Tom Chastain guided me through the process with sound advice, and helpful comments on the dissertation itself. Sam Chan generously shared his enthusiasm and knowledge about forest and riparian microclimate, and, importantly, provided me with all the equipment that I needed to measure it. Bill Porter, at the Sweet Home Ranger District, made a variety of resources available to us for selecting field sites. Tim Schowalter supported me at the start of my program. Jack Lattin always gave encouraging words from the hall when he saw me hunched at the microscope. Several taxonomists gave freely and generously of their time and expertise to verify my invertebrate identifications: James LaBonte (Carabidae); Don Chandler (Pselaphinae); Sean O'Keefe (Scydmaenidae); Bob Anderson (Curculionidae); Paul Marek (all millipedes); Paul Hohenlohe (all gastropods); and James Cokendoipher (all spiders). Leif Gunderson, Jason Barker, Nancy Baumeister, Hoonbok Yi, and the indomitable Willey provided company and help out in the headwaters; Therese Bagnell and Nick Baisley managed to keep me, and themselves, amused while sorting through untold stacks of pitfall contents in the lab. Joan Hagar, Sid, Lava, Chilko, Rocky, and Rogue doggedly tracked my progress and provided infinite amounts of advice and encouragement along the muddy trails of Mac Forest. And finally, I owe my sanity and a great deal of thanks to Sheila Halpin, who left her garden and ski trails in Vermont to endure these few years in Oregon with me. Without her day to day support and encouragement, this endeavor might have been just another ordeal, rather than a true learning experience. Financial support for this project was generously provided, in part, by the Oregon Headwaters Research Cooperative. Additional support came from an Oregon Sports Lottery fellowship. TABLE OF CONTENTS Page CHAPTER 1. INTRODUCTION ................................................................................................... 1 CHAPTER 2. FOREST-FLOOR INVERTEBRATE DISTRIBUTIONS ACROSS HEADWATER STREAM RIPARIAN ECOTONES AND THEIR RESPONSE TO ALTERNATIVE FOREST MANAGEMENT PRACTICES..........................................................4 INTRODUCTION.......................................................................................................................4 METHODS LIST OF FIGURES Figure 2.1 Location of study area (Sweet Home Ranger District) in the Willamette National Forest on the western slopes of the Cascade Range of Oregon, USA... 7 2.2 Pitfall trapping design on three riparian management treatments................... 10 2.3 NMS ordination of forested sample units (trap zones; n=25) in species space, only two dimensions of the 3-dimensional solution are shown...................... 19 2.4 Average invertebrate species richness (5) and Shannon-Wiener diversity (H) at increasing distances from the stream in forest sites ± 95% confidence interval(n = 5)........................................................................ 25 2.5 NMS ordination of 75 sample units (trap zones) from buffer, clearcut, and forest treatments in species space, only two dimensions of the 3-D solution are shown........................................................................................ 26 2.6 Mean values for invertebrate species richness (S) and Shannon-Wiener diversity (H) at increasing distances from the stream across three treatments (B=buffer, C=clearcut, F=forest; n=5................................................... 31 2.7 Proportional abundances of four major invertebrate groups in three management treatments (between 1 and 20 m from the stream)..................... 31 2.8 NMS ordination of 20 buffer and 20 forested sample units (trap zones) in species space, only two dimensions of the 3-D solution are shown................. 33 2.9 Mean abundance per trap zone of selected species at increasing distances from the stream, across buffer, clearcut, and forest treatments............................. 35 2.10 Characteristic distribution patterns (represented spatially by lines) of species groups across a nparian forest-clearcut edge ........................................... 42 3.1 A hypothetical model of opposing daytime "effects" on microclimate exerted by the stream (i.e., cooler air and soil temperatures, higher relative humidity extending away from the stream) and by the clearcut adjacent to the riparian buffer edge (i.e., warmer air and soil temperatures, lower relative humidity extending towards the stream)............................................................ 49 3.2 Sampling design for collecting microclimate data in three riparian management treatments.................................................................................... 52 3.3 Mean minimum air temperature (at 6AM) and maximum air temperature (at 3PM) in buffer, clearcut and forest treatments, between 1 and 70 m from the stream(n = 5)............................................................................... 58 LIST OF FIGURES (Continued) Figure 3.4 Mean minimum soil temperature (at 6AM) and maximum soil temperature (at 3PM) in buffer, clearcut and forest treatments, between 1 and 70 m from the stream(n=5)................................................................................. 59 3.5 Mean maximum relative humidity (at 6AM) and minimum relative humidity (at 3PM) in buffer, clearcut and forest treatments, between 1 and 70 m from the stream(n=5).............................................................................