Response of the herbaceous layer to natural disturbance in North American forests

Abstract

Most work on the disturbance ecology of North American forests has focused on the tree canopy and woody understory, with little consideration of the herbaceous layer. Understanding how this species-rich and ecologically important layer responds to natural disturbances is needed as a guide for conservation. As a framework for this review, selected natural disturbances common to North American forests are evaluated in terms of a three-axis model of disturbance severity: percentage of tree canopy removed, percentage of understory vegetation removed, and percentage of forest floor and soil removed or disrupted. Eight factors, which control herbaceous-layer response, are linked to the three axes; these factors vary in dominance, depending on disturbance type and severity. The relative importances of different species' regeneration mechanisms also vary along severity gradients. The disturbance-severity model, along with the linked response factors and regeneration mechanisms, provide a framework for evaluating impacts of both natural and anthropogenic disturbances. Long-term studies of herbaceous-layer response to disturbance are needed, particularly mechanistic studies that focus on the relative importance of the eight factors controlling response. The conceptual model proposed herein needs to be tested across the full spectrum of severity levels. Finally, comparisons between natural and anthropogenic disturbances are needed.Key words: disturbance, forests, herbaceous layer, life-history characteristics, succession, understory.

Survivors, not invaders, control forest development following simulated hurricane

“…Similarly, disturbance-associated shrubs and herbs colonized the pulldown plot, but few persisted beyond the first decade. Rather than gap theory (Whitmore 1989, Veblen 1992, these findings better fit multidimensional disturbance models such as that proposed by Roberts (2004), which explicitly include understory and forest floor disturbance intensity in addition to canopy damage. Although 80% of the canopy was removed, the understory and forest floor (8% of the area was covered by pits and mounds; Cooper-Ellis et al 1999) remained mostly intact.…”

What are the Environmental Consequences of Using Silviculturally Effective Forest Vegetation Management Treatments?

“…The reoccupation will depend on the type, severity, and frequency of disturbances (Oswald 1990;Roberts 2004Roberts , 2007Johnstone 2006;Fraterrigo and Rusak 2008;Smirnova et al 2008). Results from field studies across North America suggest that FVM treatments that lead to light to moderate disturbances increase plant diversity.…”

Environmental filtering drives herb community composition and functional trait changes across an elevational gradient

“…Herb species comprise the majority of plant diversity in forest systems and they affect nutrient cycling and energy exchange (Roberts 2004). Recently, forests have experienced climate warming, and it is important to evaluate the responses of herb communities to these changes (Naeem & Wright 2003).…”