Forest Edge Effects Study

Transcription

1 Forest Edge Effects Study A sub-project of the Ecology as Education Network (EREN) Permanent Forest Plot Project (PFPP) Prepared by Eric Keeling, August 1, 2013 (last updated ) This document articulates the purpose of including edge plots at an EREN PFPP site and provides additional concepts, terminology, procedures, and a data sheet for EREN PFPP participants who would like to include edge plots in their PFPP sites. Why include both edge and interior plots in an EREN PFPP site? 1. Edge plots are easy to add to an existing PFPP site. a. Including both edge and interior plots in a PFPP site is already built into the current PFPP protocols, so adding an edge/interior component to existing PFPP activities does not add significant time or work other than what is needed to add extra plots to an existing site. No new field techniques or new types of data collection are necessary. 2. Edge plots add educational value to EREN PFPP studies. a. Comparing edge and interior plots provides an opportunity for students to test simple hypotheses about differences in community composition and do statistical analyses without the need for additional sites. b. The topic of edge effects is included in standard ecology textbooks in chapters on landscape ecology (eg. Smith & Smith 8th ed., CH 20). So students will be able to relate the EREN field activities to ecological concepts learned in the classroom. 3. Sites with both edge and interior plots will increase publication opportunities. a. The study of forest edge effects is currently an important topic in ecological research. However, there are few studies with multiple sites that use the same protocols. Including edge and interior plots may provide more meaningful data and publication possibilities for the broader EREN PFPP research effort than just interior plots (see research questions and timeline to publication below). Conceptual Background and terminology Forest fragmentation is prevalent in North American landscapes and the ecological effect of forest edges is an active area of research. Basic conceptual frameworks and terminology are covered in standard ecology textbooks (eg. Smith & Smith, 2013) and in the peer-reviewed literature (eg Pickett & Cadenasso, 1995). For the current PFPP edge effects study, we adopt the concepts and terminology used in Smith & Smith, 2013, Chapter 20. This set of terms differs slightly from terminology used in the current (July 2013) PFPP protocols. Below, we clarify these differences and introduce new terminology. A patch is area of habitat or land cover that differs from its surroundings. In our studies, we are dealing with two patches, 1) the forest patch where our plots are located and 2) the adjacent patch that is nonforested land. The edge of a forest patch is the place where the vegetation changes from forest to whatever the adjacent land cover type is. At some sites, the forest edge may be so abrupt that a single edge line could depict the edge between both patches (for example, the edge of a clear-cut ). However, at many sites, the transition from forest to non-forest may be more gradual with a transition zone

2 known as a border or border zone. (The border may also be referred to as edge-zone, boundary, or transition zone.) The border will have a certain border width and be of several border types such as straight, convoluted, or perforated (see figure 1). A border that is relatively wide may be referred to as an ecotone. Fig. 1 From Smith & Smith, 8th ed. Within the border zone there may be a curtain of vegetation known as the sidewall that is intermediate in height between the forest canopy and the adjacent patch. The physical conditions within the border may be influenced by the border aspect, which is the direction (compass bearing) that runs perpendicular to the general contour line of the border, and the border slope which is the slope in the direction of the aspect (Cadenasso et al. 1997). Forest community composition and structure (ie what we are measuring in PFPP plots) within the forest patch is likely influenced by a) distance to the edge (or defined edge line) of the forest, b) width of the border zone, c) border aspect, d) border slope, d) land cover type of the adjacent patch, and e) distance across the adjacent patch to nearest forest patch. For purposes of determining distance to the edge where edges are not abrupt, the edge line within the border zone may have to be defined based on some set of criteria (see "Setting up edge plots", below). Clarification of terms in existing PFPP protocols and datasheets (July 2013) Edge Type refers to the adjacent patch type. For example, "impervious surface", "utility corridor", "old field" are all possible values for "Edge Type" in the PFPP database. Edge Width refers to the distance across the adjacent patch to the next forest patch. Edge Description may include additional information about the edge, border, adjacent patch type, and how edge lines are defined in particular circumstances. Research Questions Within a given site, adding edge plots allows your students to investigate a simple research question without reference to any other EREN sites. A basic, within-site, research question could be phrased as follows:

3 1) Do any of the following forest community response variables (tree species composition, forest structure, tree biodiversity, or number of non-native species) differ between edge and interior at this particular forest site? For a larger set of sites across the EREN PFPP network, we may ask: 2) How do differences between edge and interior in any of the above-mentioned response variables vary with a) forest type, b) border conditions such as border type, border width, aspect, slope, and c) other broader scale landscape variables (including existing PFPP variables, but also see proposed PFPP Landscape sub-project, outlined at 2013 EREN meeting). Experimental Design Ideally, at least three edge vs. three interior plots per site would be best for both within-site and across site (EREN-wide) comparisons. Obviously, a large number of sites across the EREN network with a variety of forest types and replication of similar forest types would be ideal for a wider cross-site analysis. Because it may be difficult to control for many of the independent variables (ie distance to edge, border type, border width, aspect and slope, etc.) across sites, these variables may be treated as covariates for analyses that compare different forest types. Or, with enough sites of a given forest type, analyses could be based on responses in a single forest type to a range of one or more independent variables. Timeline to publication Edge/interior studies should require only one year of data from each participating site. The key element needed for publication will be a high number of participating sites that include both edge and interior plots. Allowing for a year for data analysis and writing, a manuscript could be ready for publication as early as Setting up edge plots For square plots, measure your distance to the forest edge line from the nearest corner of your edge plots. Edge plots must be < 30 m from the nearest forest edge (see existing PFPP protocols, July 2013). However, we suggest edge plots be as close to the edge line as possible, while staying within the forest patch itself. So, edge plots should still contain mostly trees of full canopy height. For square plots along straight edges, set up plots parallel to the edge line. Measure the distance to the edge from the nearest plot corner (or plot perimeter, if circular) so that the maximum distance to edge for edge plots is 30m. If the edge is an abrupt, "hard" edge (eg edge of a recent clear cut), the edge line is easily defined as the place where the trees end. However, defining the location of the edge line may be more difficult where the vegetation changes gradually from forest into a transitional border zone. Arbitrarily, the edge line will be defined as the place along a gradient from the forest to the adjacent non-forested area (within the border zone) where the average tree/shrub stem height is reduced to <20% of the full canopy height. Distance to the edge would measure up to the middle of the stems of trees that were <20% of full canopy height. In some cases, other criteria for defining the edge line may make more sense and should be recorded under "Edge Description".

4 Data Collection Once edge plots are set up and edge plot variables have been recorded (See "Appendix 1 - Supplemental Data Sheet for Edge Plots", below), data collection procedures within edge plots will be identical to procedures for interior plots and will follow normal PFPP protocols. Data Management Guidelines for data management for the Edge Effects sub-group are currently as follows: 1) Collect all of your PFPP data using PFPP protocols. 2) Collect the supplemental data on the Supplemental Data Sheet for Edge Plots below (Appendix 1). 3) Enter all of your PFPP data into the main PFPP database accessed from the EREN website. 4) Obtain access to the shared googledrive file Edge Effects supplemental data (shared). If you do not have access to this file, keelinge@newpaltz.edu to get a link to the file. 5) Alternatively, use the excel file named Edge Effects supplemental data (template). Rename the file, fill in your data, and it to keelinge@newpaltz.edu. The template file is available on the Edge Effects page on the main EREN website, or on the Edge Effects page on the PFPP collaborator s page, or by ing keelinge@newpaltz.edu. 6) Note: There are three short worksheets (tabs) in the data file to fill out: Plot level data, Site level data, and Results Summaries. Useful References Cadenasso, M.L, Traynor M.M., and Pickett, S.T.A Functional location of forest edges: gradients of multiple physical factors. Canadian Journal of Forest Research. 27: Geiger, R The climate near the ground. Harvard University Press, Cambridge, MA. Smith, Thomas M., and Smith, Robert L Elements of Ecology (8th ed.). Benjamin Cummings. Pickett, S.T.A and Cadenasso, M.L Landscape ecology: spatial heterogeneity in ecological systems. Science. 269:

5 Appendix 1 - Supplemental Data Sheet for Edge Plots For each edge plot, fill in all the required data in the standard PFPP data sheet. Note that "Edge Type" refers to adjacent patch type, and "Edge Width" refers to distance across adjacent patch. Under "Edge Description" record the following: a) What you know about the origin, longevity (age), and maintenance of the edge. b) If you selected "other" for any variables, provide an explanation. c) If you defined the edge line differently than specified above, provide an explanation. In addition to the fields already on the PFPP datasheet, record the following information for each edge plot: Distance to Edge: Record the distance (in m) to the forest edge from the plot corner or perimeter closest to the forest edge as defined above. If you are using a different criterion for defining the edge line, please explain under "Edge Description" in your PFPP data.. Border Type: Circle one of the following: Straight Convoluted Perforated Other Border Width: Circle one of the following <1m 1-5m >5m Border Aspect: Use a compass to determine the bearing perpendicular to the general contour line of the edge nearest to this plot. Border Slope: Use a clinometer to determine the slope (in %) perpendicular to the general contour line of the edge nearest to this plot.