3). When the intensive land-use practices cease and sediment production returns to background levels, channels usually incise, leaving large buy U0126 deposits on the former floodplain as terrace deposits. Following relatively rapid channel down-cutting, lateral erosion of channels takes a much longer time to widen floodplains and erode the stored LS (Simon and Hupp, 1986). Thus, the initial return of channels to their pre-disturbance base levels and gradients occurs long before the erosion and reworking of LS is complete. Such a sequence can be described as an aggradation–degradation episode (ADE) ( James and Lecce, 2013) and represents the passage of a bed wave and a sediment wave ( James, 2010). Protracted

sediment production from this long term reworking represents a form of temporal connectivity in which Selleckchem PF2341066 the system memory of past sedimentation events is propagated into the future. If the floodplain had been relatively stable prior to the event, a distinct soil may have formed on it. In many cases, the LS deposits left behind by the ADE may be distinguished from the earlier alluvium by an abrupt contact of recent alluvium overlying a buried soil that can

be seen in bank exposures and cores ( Fig. 4). The post-settlement period in North America provides many widespread examples of ADEs. Accelerated sediment production began with land clearance, hillslope erosion, and sediment deliveries in small catchments early in the sequence. Later, post-settlement alluvium arrived down-valley, channels aggraded, and floodplains were buried by overbank deposition. As land-use pressures decreased in the mid-twentieth century—possibly in response to cessation of farming or mining or to initiation of soil conservation measures, and possibly aided by dam construction upstream—sediment deliveries decreased, channels incised, and former aggraded floodplains were abandoned as terraces. In many places

channel beds have returned to pre-settlement base levels and are slowly widening their floodplains. LS may continue to be reworked by Adenosine triphosphate this process and delivered to lower positions in large basins for many centuries. Recognition of these protracted responses to LS is essential to an understanding of watershed sediment dynamics. The production of LS comes from a variety of sources and deposits are located in a variety of geomorphic positions on the landscape. LS may occur on hillslopes as colluvium, as alluvium on floodplains and wetlands, or slack-water or deltaic deposits in lakes and estuaries (Table 2). Production of most LS begins on uplands and much of the sediment does not travel far, so colluvial deposits can be very important. This may not be widely recognized because deep and widespread colluvial deposits are largely unexposed and may not be mapped. Colluvial deposits of LS include midslope drapes, aprons, and fans.

, 2002a, DeLuca et al., 2002b and Zackrisson et al., 2004). Assuming C59 cost wildfires

consume approximately 30–60% of the total N in the O horizon ( Neary et al., 2005) (which in this case would be about 200 kg N ha−1), the annual contribution of N by feathermosses could have replenished this N loss in about 200 years (100 years of forest succession followed by 100 years of N2 fixation). Regular burning would have consumed the moss bottom layer ( Payette and Delwaide, 2003) and greatly reduced the presence of juniper ( Diotte and Bergeron, 1989 and Thomas et al., 2007) resulting in an un-surmountable loss of N, the loss of the predominant N source, and ultimately the loss of the capacity to support stand N demands (approximately 30 kg available N ha−1 yr−1) of a mature Scots pine, Norway spruce forest of ( Mälkönen, 1974). Reindeer do Trichostatin A not eat feathermosses, thus their presence on the forest floor was likely of no value to reindeer herders and may have

been looked upon as a nuisance. Consequently, the use of fire to transform dwarf-shrub/moss dominated forests into lichen dominated heaths to provide reindeers with winter grazing land would rather be essential for, and not be in conflict with, the traditional way of living for reindeer herders. The findings of these studies build upon the thesis put forth by Hörnberg et al. (1999) which suggested that the spruce-Cladina forests were altered by past land management and specifically repeated use of fire. The recurrent fires led to the loss of nutrient capital on these sites and thereby reducing the potential for pines to regenerate and recolonize these otherwise open forest stands.

This is further Rolziracetam supported by previous findings on the black spruce-Cladina forests within the permafrost zone of North America which suggest that repeated disturbance, predominantly fire, induced a change in structure, composition and function of boreal coniferous stands ( Girard et al., 2009, Payette et al., 2000 and Payette and Delwaide, 2003). Natural fire frequency due to lightning strikes in this region in northern Sweden is relatively low ( Granström, 1993) and historical fire intervals mainly driven by climate were likely 300 or more years ( Carcaillet et al., 2007). Human use of fire as a management tool apparently altered historical vegetative communities, reduced nutrient capital, and ultimately created conditions that have perpetuated the vegetative communities present in this region today. Even in subarctic areas of Fennoscandia, that are often considered to be the last wilderness of northern Europe, impact by low technology societies has consequently lead to profound changes in some ecosystems that were carefully selected due to some specific condition that made them manageable by simple means to serve a specific purpose; e.g. use of fire to provide winter grazing land.