Chapter 8. Trends in Vegetation Dynamics and Impacts on Berry Productivity
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Chapter 8. Trends in vegetation dynamics and impacts on berry productivity Lead authors Esther Lévesque 1, Luise Hermanutz2, José Gérin-Lajoie 1 1Département de chimie-biologie, Université du Québec à Trois-Rivière, Trois-Rivière, QC; 2Department of Biology, Memorial University, St. John’s, NF Contributing authors T. Bell, S. Boudreau, A. Cuerrier, J. Jacobs, C. Laroque, C. Lavallée, L. Siegwart Collier and B. Tremblay Abstract The vegetation of Nunavik and Nunatsiavut changes from treeline to arctic/alpine tundra moving north- ward and upwards in elevation. Current and predicted environmental changes promote shrub growth as well as treeline expansion, but not in a uniform way. Research has documented an increasing trend in birch and willow cover, as well as an altitudinal expansion of larch. With the improved growing condi- tions (such as increased summer temperatures and Growing Degree Days (GDD)) favouring increased viable seed production and seedling recruitment, trees are expected to gradually expand beyond current boundaries; however, given the highly variable nature of abiotic and biotic factors across the region, the extent and rate of treeline change is currently unknown. Changes in the distribution of shrubs are expected to alter snow distribution and its persistence on the land, affecting permafrost, feedback to the atmosphere (e.g. altered albedo), vegetation, wildlife and human transportation routes. Warmer and longer growing seasons may not benefit the growth and productivity of all berry producing plants. Berry shrubs that have a prostrate or dwarf growth form will face increasing competition from taller erect shrubs such as birch and willow. The potential lack of moisture if summers become drier will also compromise their ability to produce large berry crops. Changes in precipitation across the region are uncertain, and berry productivity is sensitive to amount and timing of precipitation, as well as wind and extreme events (e.g. late frost events in the spring). Berry species that have highest productivity in full sun (especially partridgeberry/redberry and bog bilberry/blueberry) will most likely decline under an increased shrub cover, yet the patchy nature of arctic vegetation should enable other species more tolerant to partial shade such as black crowberry/blackberry and cloudberry/bakeapple to take advantage of the changing conditions. Further research is necessary to understand feedbacks of treeline and shrubline changes on ecosystems and to evaluate how the disturbance regimes will vary in response to climate change, including if and how insect outbreaks and fires will increase. Major uncertainties exist regarding how environmental changes will impact biotic interactions between vegetation and animals, herbivores (both insects and vertebrates) and pollinators. Northerners have observed changes in their environment both in the past and present and have adjusted their berry-picking activities to the high spatial and inter-annual variability in berry productivity. Com- munity-based monitoring is an important tool to enable the collection of long-term data, crucial to under- standing current uncertainties about berry productivity. Such long-term, sustained monitoring will enable Northerners to track environmental changes in their communities and tailor appropriate adaptation strat- egies for their region. Longer time series from a wide range of sites will benefit researchers and commun- ities and greatly enhance scientific predictive abilities. This will in turn help to select areas to be protected from development, to ensure easy access to high quality sites for this culturally important activity. 223 VEGETATION COVER AND BERRY PRODUCTIVITY Chapter 8 8.1 Introduction 80° 70° 60° 0 100km The vegetation of Nunavik and Nunatsiavut ranges from the northern limit of the boreal forest to the arctic tundra. 60° 60° The transition zone between forest and tundra moves Tundra from more abundant closed canopy forest to sparse forest patches then to isolated tree islands, and finally to Labrador Sea Hudson krummholz, which are stunted shrub-like trees (Payette Bay 1983). This complex transition zone is called the forest- Forest-Tundra 55° 55° tundra ecotone, and can either be sharp with an abrupt transition from forest to tundra, or gradual with forests changing to shrub tundra over long distances (Payette et al. Boreal Forest 2001, Harsh et al. 2009). Climate controls on the position and character of the treeline increase in complexity nearer Figure 1. Vegetation zones for Québec and Labrador the coast, as exemplified by the treeline in Nunatsiavut (modified from Payette 1983). (Payette 2007, Hallinger et al. 2010, Kennedy et al. 2010) (Figure 1). cover, other shade-intolerant ground cover species, such as lichens, will also be lost which may have negative ef- The forest-tundra ecotone is highly sensitive to changes fects on caribou food supply. Besides shrub encroachment in environmental conditions (Payette and Lavoie 1994), and expansion, other competitive species may change the with examples of trees and shrubs moving northward and vegetation dynamics. In open areas, tall grasses may in- upwards into the tundra zone across Canada in response vade in areas and displace less competitive species such to climate changes (Payette et al. 2001, Danby and Hik as Rhodiola rosea or cushion plants, like Lapland pin- 2007, Harper et al. 2011). In the Arctic zones, shrubs in- cushion plant (Diapensia lapponica) and moss campion crease in growth and density and are moving into herb (Silene acaulis). tundra areas. Changes in the distribution of shrubs are expected to alter the way snow is distributed on the land In Nunavik, Inuit have already noticed that tall shrubs are and how long it stays, affecting permafrost, vegetation, now invading some of their usual berry-picking spots, wildlife and human transportation routes as well as hav- mostly where they used to find blueberries and black ing feedbacks to the atmosphere, for instance through the crowberry/blackberry (Empetrum nigrum) (Gérin-Lajoie exchange of greenhouse gases. et al. In Prep.). However, other species may become more abundant such as cloudberry/bakeapple (Rubus Shrubs could act as “nurse” plants for trees, accelerating chamaemorus), reported in Kangiqsualujjuaq to have their spread into the tundra (Cranston 2009). However, been mostly found among birches in the mountains in shrubs can form dense thickets that may not be suitable for tree seedling establishment and survival. Taller shrubs the past and now found growing everywhere. In addition, such as dwarf birch (Betula glandulosa), alder (Alnus Elders from Umiujaq, Kangiqsujuaq and Kangiqsualuj- spp.) and willow (Salix spp.), can also shade out shorter juaq, are saying the permafrost is retaining less water (as shrubs such as berry plants, causing localised loss of spe- discussed in chapter 6), resulting in lower water levels cies such as bog bilberry/blueberry (Vaccinium uligino- and plants invading dried up streams and lakes. This in sum) and partridgeberry/redberry (Vaccinium vitis-idaea), turn has an impact on insect emergence and abundance as or affecting the berry productivity. Under thicker shrub well as on fishing and travel on land. 224 Chapter 8 VEGETATION COVER AND BERRY PRODUCTIVITY In Nain, Nunatsiavut, community members have ob- 8.2 Trees and erect shrub served that trees and shrubs are more abundant now and expansion are rapidly growing around their community and up the coast. Some individuals highlighted the difficulty in locat- 8.2.1 Historical trends and current rate of ing and using traveling routes because of their rapid infill- change ing by shrubs. Community members have also indicated changes in berry crops, such as berries being less abun- Vegetation changes observed at treeline interface dant, smaller and changing in taste. However, changes in berry crops were not linked explicitly with shrub expan- Vegetation has always adapted to past climate variations over short and long time periods. The vegetation of Nuna- sion (L. Siegwart Collier, unpubl. data). vik and Nunatsiavut was established following glacier retreat and soil development at the end of the last ice age Influenced by climatic factors, vegetation changes like (approx. 7000-8000 years ago) (Dyke and Prest 1987). treeline patterns affect animal distribution and, con- Tree expansion reached its maximum during the warm sequently, Inuit and Innu people have had to modify their interval known as the hypsithermal (Lamb 1985, Payette travel routes to follow migration of animals (Fitzhugh 2007, Bell et al. 2008). For instance, abundant subfossil 1977, 1997, Fitzhugh and Lamb 1985). Today, Inuit de- tree remains (spruce, fir, larch) were found around the pend less on hunting, fishing and gathering activities margins of shallow ponds above the treeline on the up- for their survival, but going on the land remains a very lands of central Labrador (Photo 1); a random sampling of important part of their activities and a way to obtain a several of these trees provided C-14 dates of 3000-5000 supply of fresh and healthy country food, including ber- years ago illustrating that trees grew higher during this period (Bell et al. 2008). The fragmented pattern of to- ries which are a significant part of country food for Inuit day’s forest-tundra ecotone in Nunavik is a consequence and Northerners (see Chapter 5). Berries are a valuable of forest fires that opened the landscape and the failure of source of vitamins and antioxidants and a natural