Fire regimes in Alaskan coastal herbaceous communities and active inland dunes


Table of Contents:

 
Figure 1. Coastal salt marshes at Lake Clark National Park and Preserve, Alaska. Photo courtesy of K. Jalone, National Park Service.
 
Figure 2. An active inland dune in Kobuk Valley National Park, Kotzebue, Alaska. Photo courtesy of the National Park Service.

INTRODUCTION
This Fire Regime Synthesis brings together information from 2 sources: the scientific literature as of 2013, and the Biophysical Settings (BpS) models and associated Fire Regime Data Products developed by LANDFIRE, which are based on literature, local data, and/or expert estimates. This synthesis is intended to:
  1. provide consistent, up-to-date information to the management community on historical fire regimes and contemporary changes in fuels and fire regimes,
  2. supplement information on individual species’ adaptations and responses to fire provided by FEIS species reviews, and
  3. enable LANDFIRE to incorporate the latest science on historical fire regimes into data revisions and identify regions and plant community types lacking fire history data.

The primary geographic focus of this synthesis is Alaska; however, information from Canadian communities is included to provide a wider perspective. No information is included on fire regimes in communities outside North America. Common names are used throughout this synthesis. For a complete list of common and scientific names of species discussed in this synthesis and links to FEIS species reviews, see Appendix B.

Citation for this synthesis:
Innes, Robin J. 2013. Fire regimes of Alaskan coastal herbaceous communities and active inland dunes. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].
SUMMARY
This section summarizes fire regime information available in the scientific literature as of 2013. Details and documentation of source materials follow this summary.

Coastal herbaceous communities and active inland dune communities (Appendix A) were combined in this review because of similarities in landform, geomorphic processes, and parent material. An extensive search of published literature on fire regimes and fire history in these communities yielded few results. Although this review focuses on active dunes, vegetated dunes are also discussed because they may become activated after fire. In general, however, vegetated dunes have fire regime characteristics of their dominant plant communities (boreal forest, trundra, etc.). See the Fire Regime Table for more information on these communities.

The fire season in Alaska primarily goes from May to August. Because of the maritime climate, fewer lightning-caused fires occur in coastal areas than in interior Alaska. In the communities covered by this review, fire is likely to be very infrequent due to scarce or poorly distributed fuels and/or because of frequent spray or inundation by water. No studies reported fire records in these communities in contemporary times. Although active coastal and inland dunes have little vegetation and thus few fuels to carry a fire, vegetated dunes often have abundant fuels. Vegetated dunes may be activated when burned or otherwise disturbed. Fire triggers eolian activity (wind-caused movement of sand) in dunes because it removes humus layers and exposes sand. Paleoecological studies indicated that fire appeared to play a greater role in initiating eolian activity in dunes in the boreal forest region than in regions to the north or south. Climate appears to be the most important driver of eolian activity in dunes in tundra and boreal-deciduous transitional zones. Fire severity likely determines whether a fire initiates eolian activity on vegetated dunes, but no published information was available on this topic.

Appendix A summarizes data generated by LANDFIRE succession modeling for the Biophysical Settings (BpSs) covered in this review. Fire was not considered an important disturbance in these communities, where the main disturbance processes are wave and wind action and the transport and deposition of sand and silt. Thus, LANDFIRE models generated no values for fire regime characteristics in these communities (fire regime group="NA"):

Fire interval¹ (years)
Fire severity² (% of fires)
Number of Biophysical Setting (BpS) groups in each fire regime group
Replacement Mixed Low
I
II
III
IV
V
NA³
NA
 
 
 
0
0
0
0
0
13
¹Average historical fire-return interval derived from LANDFIRE succession modeling (labeled "MFRI" in LANDFIRE).
²Percentage of fires in 3 fire severity classes, derived from LANDFIRE succession modeling. Replacement-severity fires cause >75% kill or top-kill of the upper canopy layer; mixed-severity fires cause 26%-75%; low-severity fires cause <26%.
³NA (not applicable) refers to BpS models that did not include fire in simulations.

DISTRIBUTION AND COMMUNITY COMPOSITION

Figure 3. Distribution of coastal herbaceous communities and active inland dunes within Alaska based on the LANDFIRE Biophysical Settings (BpS) data layer [19]. Numbers indicate LANDFIRE map zones (http://www.landfire.gov/NationalProductDescriptions20.php). Click on the map for a larger image and zoom in to see details.

Coastal herbaceous communities and active inland dunes are both derived from wind, wave, or long-shore transport of sand and silt [2]. Although this review focuses on active dunes, vegetated dunes are discussed in portions of this review because they may become activated by fire. Appendix A shows the Biophysical Settings (BpSs) covered by this review.

Distinct landform and vegetation patterns are common to Alaskan coastal communities. Landforms on the seaward side include low gradient beaches, sparse to unvegetated dunes, interdune areas dominated by low herbaceous communities, and sea cliffs or back dunes dominated by tall herbaceous, shrub, or forested communities. On coastal dunes, dune crests grade into mainland landscapes or uplands. Behind the dune line on the estuary side are uplifted marshes (marshes that have been uplifted by tectonic activity), tidal marshes, and tidal flats [3]. With thousands of kilometers of Arctic shoreline, one might assume that tidal and brackish marshes, coastal dune complexes, and other coastal herbaceous communities would be common. Bliss [2] explains that this is not the case because favorable habitats are limited. Figure 3 illustrates the scarcity of such habitats. Factors that restrict the distribution of coastal herbaceous communities are the few areas of fine sands and silts, the annual reworking of shorelines by sea ice, a limited tidal amplitude, low salinity of coastal waters, a very short growing season, and low soil temperatures [2].

Figure 4. Eolian deposits of Alaska, Yukon, and Northwest Territories. Image courtesy of Wolfe and others [26].

In contrast, vegetated dunes are common throughout coastal and interior Alaska (Figure 4). Vegetated dunes are also widespread at high latitudes in Canada, Europe, and Russia ([17], Wolfe 2006 cited in [26]). Many vegetated dunes reside along former margins of continental ice sheets [26]. Small blowouts and other areas of active transport and deposition exist in Alaska, but are relatively uncommon [17,26].

On active dunes in coastal Alaska, American dunegrass is often the first species to establish. As American dunegrass and other pioneer vegetation establish, the input of fresh sand decreases, and species diversity increases. Shrubs and trees, such as Sitka alder, salmonberry, and black cottonwood then establish and pioneer species decrease [3]. Species from adjacent tundra communities such as sedges, cottongrass, cloudberry, black crowberry, and lichens (e.g., snow lichen and whiteworm lichen) are also common on vegetated coastal dunes [23].

Many types of communities occur on vegetated inland dunes in Alaska. Inland dunes in the Arctic are commonly dominated by low and tall willows such as grayleaf, Alaska, Richardson, and barrenground willows; mesic herbaceous communities such as American dunegrass, arctic brome, and dwarf fireweed; and wet sedge communities (in and around ponds and wet depressions) dominated by water sedge and pendantgrass [17]. Boreal inland dunes support many kinds of communities, including grasslands, shrublands, woodlands, and forests. Common species include white spruce, dwarf birch, alder, blueberry, and crowberry [18]. Boreal inland dunes occur at Dune Lake in interior Alaska near Fairbanks and occupy about 4,800 miles² (12,000 km²). The dunes are completely vegetated, except for one small blowout near the lake. Well-drained dune crests support birch, quaking aspen, white spruce, herbs, shrubs, and lichens, whereas wetter interdune areas commonly support black spruce muskegs with permafrost at or near the surface [5]. The Great Kobuk Sand Dunes are among the largest active inland dunes in Alaska. They are located just north of the Arctic Circle (Figure 4) [20] and are surrounded by boreal forest [21]. Although most coastal dune plant species are rare on the Great Kobuk Sand Dunes, American dunegrass, which is mostly restricted to a narrow strip along the coast, is common there [22]. Plant distribution on inland dunes is strongly controlled by moisture gradients [3]. In Saskatchewan, the depth of the water table was important in determining the type of vegetation occurring in different locations on dunes in the Great Sand Hills [6,15].

Removal of vegetation from vegetated dunes typically leads to destabilization, blowouts, and erosion. Trigger mechanisms for blowout initiation include wind abrasion, water erosion, desiccation, grazing, trampling, and disturbance by vehicles [3]. Paleoecological studies suggest that fire may have been a trigger mechanism [4,9,12,16,20]. Blowouts are a primary method of dune movement and elongation and an initiator of primary succession [3]. A blowout occurs when wind exposes bare sand, forming a small depression on the windward side of a vegetated dune [3,14]. The blowout continues to expand, the shape becoming concave with a steep back slope. Much of the wind-transported sand is deposited on the downwind side of the back slope and forms "deltalike" or "plumelike" formations. In time, sand avalanches and wind erosion reduce the steepness of the back slope, and vegetation colonizes and stabilizes the blowout [3].
HISTORICAL FIRE REGIMES
In June of 2013 an extensive search was done to locate information on fire regimes in Alaskan coastal herbaceous communities and active inland dunes, with few results. The lack of contemporary fire records suggests that fire in these communities is rare, as is indicated in the Biophysical Settings models (Appendix A). Wind and wave action are the most important disturbance factors in these communities. The following paragraphs provide details of the available information.

Fire ignition: Because of the maritime climate, fewer lightning-caused fires occur in coastal areas than in interior Alaska. Alaskan coastal areas have a relatively mild climate, with more stable air masses, less surface heating, and warmer air aloft than other regions of Alaska. These conditions inhibit extensive convective activity. Thus, there is less potential for fire ignitions in coastal herbaceous communities than in inland dunes. Interior areas experience large annual temperature extremes, with relatively hot summers and sufficient moisture to fuel thunderstorms [7].

Fire season: The typical fire season in Alaska starts in May after melting of winter snows and lasts until August. During each of these months there is commonly a period of a week or more with little or no rainfall [13].

Fire frequency: No studies reported contemporary fire records in the communities covered in this review. Records of fires occurring in dunes are limited to a few paleoecological studies of fire on vegetated dunes. In general, fires in many coastal herbaceous communities are likely to be very infrequent due to scarce or poorly distributed fuels (e.g., Aleutian rocky headland and sea cliff and Aleutian American dunegrass grassland) and/or because of frequent spray or inundation by water (e.g., Aleutian and Arctic marine beach and beach meadow, Aleutian and Arctic tidal marsh, Alaska Arctic coastal brackish meadow, Alaskan Pacific Maritime coastal meadow and slough-levee, North Pacific Maritime eelgrass bed, and temperate Pacific tidal salt and brackish marsh). Active coastal and inland dunes have little vegetation and thus few fuels to carry a fire. However, vegetated dunes may have abundant fuels. For example, along the high terraces of the Kuskokwim River, stabilized sand dunes were covered by black spruce-lichen woodland and quaking aspen communities with birch and white spruce [8]. In western Quebec along the eastern coast of Hudson Bay, vegetated dunes in boreal forest and shrub tundra were considered to be relatively "fire prone" because they were dry sites [12].

Vegetated dunes may be activated by fire and other disturbances that result in blowouts [3,20]. For example, active blowouts occur on ridges of older stabilized dunes north of Champagne, Yukon, and in dune fields to the south near the Dezadeash River. These blowouts probably resulted from the loss of forest cover from fires in the 1940s and 1950s [26]. Fire triggers eolian activity in dunes because it removes humus layers and exposes mineral soil to wind action [4]. Vegetation succession from active sand dunes to white spruce-star reindeer lichen woodlands on stabilized dunes appears to take 150 to 200 years in northwestern Quebec [11].

In boreal, tundra, and boreal-tundra transitional zones of North America, charcoal layers are frequently embedded in dune sediment profiles, indicating past fires (e.g., [4,9,12,16,20]). In northwestern, subarctic Quebec along the eastern coast of Hudson Bay, all study sites from the boreal zone to the shrub tundra zone had buried organic horizons containing charcoal. The presence of many buried organic horizons in dune sediment profiles suggested that stable stages, when dunes are covered by vegetation, alternate with erosional stages triggered by wildfire. Radiocarbon dating indicated that the time between peaks of eolian activity during the past 5,000 years varied from 250 to 450 years (with the exception of one 600-year interval between 1,175 and 575 years BP). Peak fire-initiated eolian activity intervals occurred between 3,125 and 2,875 years BP, 1,475 and 1,175 years BP, and 575 to 175 years BP [9]. A subsequent study supplemented the radiocarbon dates of Filion [9] with data from the past 4,000 years in shrub tundra and the past 6,000 years in boreal forest; this study reported peak dune activity between 3,650 and 2,700 years BP, 1,650 and 950 years BP, and 700 and 100 years BP [12]. The peaks in dune activity were interpreted as a response to increased fire occurrences under cold and dry climates that inhibited tree regeneration and favored erosion of sand dunes [9,12]. Filion [9] summarized the periglacial eolian cycle in the boreal forest and forest-tundra ecotone as follows:

Figure 5. Periglacial eolian cycle in the boreal forest and forest-tundra in western Quebec [9].

The author stated, however, that this model does not apply to the tundra zone, where climatic cooling after 3,000 years BP was so important that dune stabilization did not occur even during brief warm periods. The author concluded that

Studies of dune profiles in the Great Lakes-St Lawrence region indicated that fire was a relatively frequent process in setting back dune succession and exposing sand in blowouts during the late Holocene [4,10,24]. A study in western Quebec examined fire frequency using profiles of 2 dunes: the dune of Villemontel and the dune of Lac Lunette. Both dunes were covered with jack pine/sheep-laurel forest. The study found a slow rate of charcoal accumulation from approximately 7,000 to 3,000 years BP, then a gentle rise until 2,500 years BP, rapidly followed by a strong rise until 2006 when the study ended. The close relationship between fire and eolian processes was attributed to the dry and thin humus layers on the vegetated dunes [4].

However, some researchers found that fire did not appear to play a major role in initiating eolian activity in vegetated dunes. Wiles and others [25] examined dune profiles in the subboreal Tana Dune region of southeastern Alaska and considered the role of fire in dune mobilization to be minor during the late Holocene compared with the effects of climate cooling. Fire appeared to play a minor role in the St Lawrence Lowland in southern Quebec, where Filion [10] found only one minor eolian phase following a single fire episode about 1,230 years BP in 1 of 3 dune profiles examined. The author stated that early Holocene dune formation and eolian activity in the region were less affected by fires than dune formation and eolian activity in northern, subarctic Quebec. In the St Lawrence Lowland, dune formation and eolian activity were most affected by the retreating Laurentide Ice Sheet about 10,000 years ago and the dry, temperate climate during that period [10].

Fire type: No information is available on this topic.

Fire severity: No information is available on fire severity in Alaskan coastal herbaceous communities. Whether dune activity is initiated by fire in vegetated dunes probably depends on fire severity and the amount of mineral soil exposed by fire. The number of past fires indicated by dune sediment profiles in western Quebec along the eastern coast of Hudson Bay was considered a minimum estimate of fires occurring in the area, because some fires presumably were not "catastrophic" enough to be followed by eolian activity [12].

Fire intensity: No information is available on this topic.

Fire pattern: No information is available on this topic for Alaskan coastal herbaceous communities. According to Filion and Payette [11], complex interactions between fire and wind disturbances, most likely with a variable periodicity, have produced patchy dune systems with different successional stages in Quebec.

Fire size: No information is available on this topic.
CONTEMPORARY CHANGES IN FUELS AND FIRE REGIMES
Little was reported in the literature regarding historical or contemporary changes in fuels or fire regimes in Alaskan coastal herbaceous communities and active inland dunes as of this writing (2013). Research on the response of dune activity in northern North America to climate changes during the Holocene [1,20,25,26] indicates that decadal- and century-scale climate changes have played a major role in dune formation, stabilization, and activation. Climate appears to have a major influence on eolian activity resulting from fire, particularly in the boreal forest and boreal-tundra zones [4,9,12] (see Fire frequency). Evidence presented by Filion [9,12] indicated that fires occurring during cold and dry periods of the past 6,000 years were more likely to result in deforestation and eolian activity than those occurring during warm and humid periods and that warm and humid periods were associated with dune stabilization. Parker and Mann (2000 cited in [18]) said that given the remote location of most inland dunes, changes in climate are more likely than changes in human activity to affect these communities in the future.
LIMITATIONS OF INFORMATION
Biophysical Settings models lack fire regime information because modelers did not consider fire an important disturbance in Alaskan coastal herbaceous communities and active inland dunes; the main disturbance processes are wave and wind action that transport and deposit sand and silt. Very little information has been published on fire in these communities, and a lack of fire records suggests that fire has been very infrequent in contemporary times, except on some vegetated dunes. Vegetated dunes have the fire regime characteristics of their dominant plant communities; see the Fire Regime Table for more information on these communities.
APPENDIX A: Summary of fire regime information for Biophysical Settings covered in this synthesis

APPENDIX B: Plant species included in this synthesis

REFERENCES:


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