Changes in the understory during 14 years following catastrophic windthrow in two Minnesota forests

Abstract

Abstract. We studied the effects of windthrow on the understory plant species composition of a pine forest (dominated by Pinus strobus) and an oak forest (dominated by Quercus ellipsoidalis). We recorded the presence of vascular plant species in randomly located quadrats in the two forests, and in three microsite types associated with tipup mounds (pit, old soil and new soil) in the pine forest at irregular intervals over the course of 14 years. The understories of the two forests remained distinct throughout the study. The frequency of occurrence of a number of forest floor species considerably increased; few species decreased. The disturbance specialists Rubus idaeus and Polygonum cilinode increased in frequency throughout the study in the pine forest, but are beginning to decline in the less disturbed oak forest. Annuals and biennials preferentially colonized the disturbed soil of microsites on tipups, and declined in frequency after about 7 yr. Both forests have increased in understory species richness, but have not changed substantially in the distribution of growth forms. Despite early differences in species composition, microsite types associated with tipup mounds became more similar through time. Although small in magnitude, there was a directional change in understory composition at both forests, with no apparent sign of a return to pre‐disturbance conditions.

Windthrow and salvage logging in an old-growth hemlock-northern hardwoods forest

“…Lasting up to 500 years after formation (Tyrrell and Crow, 1994), tip-up microtopography forms a structural legacy in windthrown forests important to the regeneration of some tree and understory species (Carlton and Bazzaz, 1998;Palmer et al, 2000;Ulanova, 2000). As we expected, salvage logging diminished these legacies of windthrow in our forest.…”

“…Yellow birch is known to be a prolific seeder following windthrow (Burns and Honkala, 1990), and its persistence in the region may be linked to severe windthrow events as experienced on the Flambeau in 1977 (Schulte and Mladenoff, 2005). Two legacies of windthrow -downed tree boles and tree tip-ups -are known to provide conditions important to the successful seed germination and establishment of yellow birch as well as other tree and herb species (Beatty, 1984;Carlton and Bazzaz, 1998;Palmer et al, 2000;Ulanova, 2000;Marx and Walters, 2006). Similar to other studies (van Nieuwstadt et al, 2001;Donato et al, 2006), we found no seedlings and few trees and saplings that survived salvage logging (Fig.…”

“…By definition, severe windthrow in forest systems causes abundant treefalls, especially within large tree size classes, and thereby alters the size structure of the forest (Peterson, 2000). Environmental conditions, including the spatial distribution of light, microrelief of the forest floor through tree tip-ups, and spatial heterogeneity of dead wood and soil resources are also altered as canopy trees are blown over and up-rooted (Carlton and Bazzaz, 1998;Elliott et al, 2002;Palmer et al, 2000;Ulanova, 2000). In turn, these changes result in high variability of microhabitat conditions, which include fine-scale patterning of light, temperature, soil water, and soil nutrients.…”

“…Expanding on their effort, we evaluated the long-term forest response to windthrow and salvage logging. We expected to find that the combined disturbances of windthrow and salvage logging to substantially set back succession and alter (1) forest composition and structure, (2) microrelief and soil characteristics, and (3) relationships between the understory herb community and microrelief in comparison to forests only disturbed by windthrow (Palmer et al, 2000;Ulanova, 2000;Foster and Orwig, 2006;Lindenmayer and Noss, 2006). Specifically, we expected the salvaged areas to have a higher proportion of early successional species represented in all layers of the forest, a less well-developed forest canopy, less microtopographic variation, more compact soils, and less pronounced relationships between the understory herbs community and microrelief.…”

Site quality influence over understory plant diversity in old-growth and harvested Nothofagus pumilio forests

“…Facilitation of introductions with time since disturbance could be related to rapid invasion of early successional species (Arnott and Beese, 1997), which are favored by differences in soil texture and chemistry due to less litter incorporation 34 E. A. Gallo et al / Forest Systems (2013) 22 (1), 25-38 into the forest floor (Økland et al, 1999), which derived in lesser organic matter decomposition. Also, presence of newly exposed soil by litter removal generated by skidders or log movement during harvesting, could favor ruderal (defined as species that are first to colonize disturbed lands) introduction, as was observed in tips and mounds that show a high proportion of annual/biennal plants (Palmer et al, 2000). Ruderal species could affect recruitment of N. pumilio regeneration by competitions by niches and resources, which is more problematic in OH than in RH.…”