Canadian Journal of Zoology Bird communities and vegetation associations across a treeline ecotone in the Mealy Mountains, Labrador, an understudied part of the Boreal forest Journal: Canadian Journal of Zoology Manuscript ID: cjz-2014-0309.R2 Manuscript Type: Article Date Submitted by the Author: 20-Apr-2015 Complete List of Authors: Lewis, Keith; Memorial University Starzomski,Draft Brian; University of Victoria, Environment and Conservation vegetation-habitat concept, tree line, avian species richness, forest-tundra Keyword: ecotone, boreal forest, Labrador https://mc06.manuscriptcentral.com/cjz-pubs Page 1 of 35 Canadian Journal of Zoology 1 1 2 3 4 5 6 7 8 Bird communities and vegetation associations across a treeline ecotone in the Mealy 9 Mountains, Labrador, an understudied part of the Boreal forest 10 11 12 13 Keith P. Lewis 1,2 and Brian M. Starzomski 3,4 14 15 16 17 18 1 Department of Biology 19 Memorial University of Newfoundland 20 St. John’s NL Draft 21 Canada A1C 3X9 22 23 2 Department of Environment and Conservation 24 Government of Newfoundland and Labrador 25 St. John’s NL 26 Canada A1B 4J6 27 28 3 School for Resource and Environmental Studies 29 Dalhousie University 30 6100 University Avenue, 31 Halifax, Nova Scotia 32 Canada, B3H 3J5 33 34 4School of Environmental Studies 35 University of Victoria 36 3800 Finnerty Road. 37 Victoria, British Columbia 38 Canada. V8P 5C2. 39 [email protected] 40 41 42 43 1 Author for correspondence: [email protected] https://mc06.manuscriptcentral.com/cjz-pubs Canadian Journal of Zoology Page 2 of 35 2 44 Abstract 45 46 We examined the factors structuring bird communities across a complex sub-arctic treeline in the 47 Mealy Mountains, Labrador, Canada. Using point counts of bird abundance in 2007 and 2008, 48 we show that changes in vegetation driven by elevation are strongly correlated with avian 49 community structure in this treeline ecotone system. Overall, avian diversity was higher in the 50 forest compared to other habitat classes (krummholz, deciduous shrub, and alpine). There were 51 strong correlations between avian diversity and vegetation richness as well as structure among 52 and within habitat class in 2008. Numerous habitat types (subset of habitat class) were 53 correlated with avian composition although some species were clearly habitat generalists. 54 Contrary to expectation, avian species composition was associated with physiognomy 55 (vegetation structure) in alpine and deciduousDraft shrub, and with neither physiognomy or floristics 56 (vegetation species composition) in krummholz and forest. Given the strong impact of elevation 57 on vegetation and the demonstrated influence on bird communities, we note that for bird species 58 whose near-southernmost populations are found in the Mealy Mountains, climate change is likely 59 to have a strong negative effect if alpine tundra habitat is lost. Further, forest bird species are 60 likely to benefit from the increased tree cover as treeline moves poleward and upward. 61 62 Keywords : treeline, avian species richness, vegetation volume, forest-tundra ecotone, plant 63 community composition, boreal forest, Labrador https://mc06.manuscriptcentral.com/cjz-pubs Page 3 of 35 Canadian Journal of Zoology 3 64 Introduction 65 Ecotones have been extensively studied in large part because of the significant influence they 66 have on biodiversity (Risser 1995; Payette et al. 2001; Harper et al. 2005). This increase in 67 biodiversity is often attributed to the large changes in vegetation structure over short distances or 68 specialization at edges (Ries and Sisk 2004). Changes in vegetation at the forest-tundra ecotone 69 (treeline), an ecotone caused by complex changes at a latitudinal or altitudinal gradient, have 70 been extensively documented, (Payette et al. 2001; Harper et al. 2011), in response to the 71 growing concern that global climate change (GCC) may adversely affect these important areas 72 (Grace et al. 2002). However, the impact of treeline ecotones on other key organisms like 73 passerine songbirds remains relatively unstudied (Terborgh 1985; Archaux 2004; Lloyd et al. 74 2011; Kent et al. 2013), and boreal ecotoneDraft communities are especially understudied. 75 The influence of treelines on biodiversity is of concern in northern regions because the 76 boreal forest is critical for the biodiversity and viability of populations of North American 77 passerine birds (Blancher 2003; 2005). Further, significant impacts of climate change are 78 predicted to occur at boreal latitudes resulting in increased plant growth (infilling, Danby and 79 Hik 2007) or increased recruitment in treeline species, and a subsequent migration of the treeline, 80 latitudinally and altitudinally (Cannone et al. 2007; Rucksuhl et al. 2008; Harsch et al. 2009). 81 The potential for changes in avian distribution in response to a changing climate was suggested 82 by Cumming et al. (2014), who showed that climate variables explained most of the deviance in 83 abundance of boreal songbird distribution. An examination in the boreal region will broaden our 84 understanding of the influence of ecotones on avian diversity and shed light on the influence of 85 GCC on these regions. 86 Relevant to understanding the influence of ecotones and a changing climate on passerine https://mc06.manuscriptcentral.com/cjz-pubs Canadian Journal of Zoology Page 4 of 35 4 87 songbirds is the vegetation-habitat concept, considered a unifying theory in avian biology (Lee 88 and Rotenberry 2005). Vegetation as habitat can influence avian assemblages in terms of 89 structure (physiognomy: MacArthur et al. 1962; James and Wamer 1982; Cody 1985; Bersier 90 and Meyer 1995), and composition (floristics: Rotenberry 1985; Bersier and Meyer 1995). 91 Ecotones, including the treeline, provide an excellent opportunity to examine the vegetation- 92 habitat concept because the changes in physiognomy and floristics across the treeline allow for 93 examination of communities that may differ dramatically over short distances (< 5 km). 94 Therefore, although the debate over the relative roles of physiognomy and floristics on avian 95 assemblages is not new, it should be re-examined in the context of global climate change and 96 expected poleward and upward shifting treeline ecotones. 97 We examined avian community Draftstructure and its relationship to vegetation across a 98 treeline ecotone in the Mealy Mountains (Akamiuapishkua ), a highland area of south-central 99 Labrador, Canada. This region is projected to warm by 2.05-4.32 oC over the next eighty years 100 (Bell et al. 2008) and climate-habitat simulations show that the treeline is expected to move both 101 poleward and upward (Loader 2007). Due to topography and edaphic factors, the treeline 102 ecotone is complex, resulting in a highly variable deciduous shrub-krummholz zone bounded by 103 largely contiguous forest, and capped by a small amount of alpine tundra (currently less than 104 10% of the total area [Loader 2007]). The relatively species-poor avifauna (composed of both 105 habitat specialists and generalists) and high variation in physiognomy and floristics over a small 106 area allowed us to test the following questions: A) how do measures of avian diversity vary with 107 elevation, vegetation richness, and vegetation structure across the ecotone?; and B) to what 108 degree are elevation, floristics, and physiognomy associated with avian composition across the 109 ecotone? Answers to these questions are critical to our ability to predict shifts in avian https://mc06.manuscriptcentral.com/cjz-pubs Page 5 of 35 Canadian Journal of Zoology 5 110 communities due to climate change. Finally, we report the first systematic study on avian 111 diversity in this rarely studied part of North America. 112 113 Methods 114 Study Area 115 The Mealy Mountains are the dominant highlands of southern Labrador, occupying an 116 area of approximately 2000 km 2 directly south of Lake Melville (Fig. 1). Mountain summits are 117 broad and rounded, with an elevation just over 1100 m. The highlands (above 800 m) are 118 dominated by alpine vegetation, are surrounded by boreal forest and wetlands at lower 119 elevations, and have been described as southernmost mountainous outliers of the High Subarctic 120 Tundra Ecoregion (Meades 1990). LocalDraft glacial and glaciofluvial deposits are conspicuous and 121 important components of the landscape, influencing position and structure of the vegetation . 122 The Labrador Highlands Research Group base camp is located approximately 20 km south of 123 Lake Melville, in an eastward trending valley south of an unnamed mountain (Mt. 1057, N 53 o 124 36’ W 58 o 50’, Fig. 1), and west of an unnamed lake forming the headwaters of the Eagle River 125 (N53 o 36’ W58 o 47). Our total study region comprises approximately 64 km 2, between 500 – 126 1000 m in elevation. Following the terminology of Körner (2007), the timberline occurs at ~ 550 127 m, the treeline up to 700 m in sheltered areas, and the tree species limit at ~ 900 m. Conifer 128 species include black spruce (Picea mariana (Mill.) Britton,Sterns & Poggenb.), white spruce 129 (Picea glauca (Moench) Voss), balsam fir ( Abies balsamea (L.) Mill.),) and larch ( Larix laricina 130 (DuRoi) K. Koch) that become increasingly stunted (i.e. krummholz), and occur in smaller, more https://mc06.manuscriptcentral.com/cjz-pubs Canadian Journal of Zoology Page 6 of 35 6 131 isolated, and sheltered patches above 640 m. See Munier et al. (2010) and Trant et al. (in 132 review)1 for a more complete description of the vegetation. 133 134 Bird sampling 135 Birds were surveyed during 2007-2008 using standard point count methods (100 m 136 radius; Bibby et al. 2000). Point counts were placed along transects every 300 m by following a 137 compass bearing from an arbitrary point parallel to the trend of the valley. A total of 76 point 138 counts were surveyed from 4:20-10:00am from 2 July - 13 July, 2007.