Natural disturbance in an old‐growth landscape of northern Maine, USA

Abstract

Summary 1.Disturbance histories derived from old-growth forest remnants in Europe and eastern North America have shaped many of our current theories of forest dynamics and succession. Yet the small size typical of these remnants suggests they might not capture the full range of variability that may emerge at larger scales. 2. We investigated the frequency and severity of natural disturbance in a 2000-ha old-growth landscape (Big Reed Forest Reserve) in northern Maine, USA. Given its size, the Reserve provides an ideal opportunity to study, at multiple scales, natural forest processes in a region that has otherwise been dramatically altered by human activities. Using dendrochronological methods, we reconstructed disturbance histories for 37 randomly located plots stratified by five forest types (hardwood forests, mixed woods forests, red spruce forests, northern white-cedar seepage forests and northern white-cedar swamps). 3. We found no evidence of stand replacing disturbance on any plot during the last 120-280 years (depending on plot). The overall mean disturbance rate was 9.6% canopy loss per decade (median 6.5%, maximum 55%, plots pooled), yet the distribution was strongly skewed toward the lower rates. 4. We found little differences in disturbance rates between forest types, save a slightly lower rate in the northern white-cedar swamps. However, if we ignore forest-type classifications, we see that disturbance rates are clearly influenced by gradients in the relative abundance of component tree species, owing to species' relative susceptibilities to particular disturbance agents. 5. Synthesis. Relatively low rates of canopy disturbance allow the accrual of shade-tolerant saplings. The abundance of this advance regeneration, coupled with the absence of stand-replacing disturbance, has maintained canopy dominance by shade-tolerant species in all plots, all forest types and throughout the entire landscape. Disturbance histories from individual plots coalesce to form a picture of a landscape in which pulses of moderate-severity disturbance are interposed upon a background of scattered small-scale canopy gaps. The landscape-level mosaic resulting from this disturbance regime consists of patches in various stages of structural development, not various stages of compositional succession.

Disturbances can control fine-scale pedodiversity in old-growth forests: is the soil evolution theory disturbed as well?

“…This indicates that the traditional sum of disturbance history (e.g. D'Amato and Orwig, 2008;Fraver et al, 2009) can mask significant differences in the pattern of weaker events and encumber the ecological interpretation of results. At the same time, weak disturbances are known to be of key importance in the dynamics of beech-dominated temperate forests (Splechtna et al, 2005;Šamonil et al, 2013a).…”

“…Typical publications include overviews of canopy disturbances in individual decades as far into the past as possible (e.g. D' Amato and Orwig, 2008;Fraver et al, 2009). In European areas settled since prehistory, much recent research has dealt with the disturbance history of old-growth forests of a few to hundreds of hectares.…”

“…Spatial relationships are usually studied only in the search for synergy in the occurrence of individual disturbance events and in the evaluation of disturbance area and severity (e.g. Fraver et al, 2009).…”

“…As a measure of disturbance intensity, we used the proportion of disturbed tree canopy (e.g. Fraver et al 2009). For that purpose, we modelled the relation between the area of exposed crown and DBH for particular woody species (Šamonil et al 2013a).…”

Ecological importance of intermediate windstorms rivals large, infrequent disturbances in the northern Great Lakes

“…Compared to LIDs, damage from intermediate disturbances tends to be patchier, less catastrophic, and usually occurs over tens of thousands of hectares or less. Damage typically removes 30-60% of the canopy, but patchy areas of catastrophic damage (.70% canopy loss) are common (Dyer and Baird 1997, Hanson and Lorimer 2007, Fraver et al 2009). Criteria for identifying intermediate disturbances are inevitably subjective, but the critical elements appear to be an event markedly less severe (in terms of storm intensity and area impacted) and more frequent than rare benchmark LIDs, yet strong enough to inflict patchy catastrophic damage and not considered a gap disturbance.…”