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

Kirk M Stueve,Dale D Gormanson,Gretchen G Moisen,Sean P Healey,Charles H (Hobie) Perry,Mark D Nelson,Warren B Cohen,Andrew D Hill,Chengquan Huang

doi:10.1890/es10-00062.1

Abstract

Exogenous disturbances are critical agents of change in temperate forests capable of damaging trees and influencing forest structure, composition, demography, and ecosystem processes. Forest disturbances of intermediate magnitude and intensity receive relatively sparse attention, particularly at landscape scales, despite influencing most forests at least once per generation. Contextualizing the spatial extent and heterogeneity of such damage is of paramount importance to increasing our understanding of forested ecosystems. We investigated patterns of intermediate wind disturbance across a forested landscape in the northern Great Lakes, USA. A vegetation change tracker (VCT) algorithm was utilized for processing near-biennial Landsat data stacks (1984–2009) spanning forests sustaining damage from four recent windstorms. VCT predominantly maps stand-clearing disturbance and regrowth patterns, which were used to identify forest boundaries, young stands, and disturbance patterns across space and time. To map wind damage severity, we compared satellite-derived normalized difference vegetation index (NDVI) values calculated from pre- and post-storm Landsat imagery. A geographic information system (GIS) was used to derive wind damage predictor variables from VCT, digital terrain, soils/landform, land cover, and storm tracking data. Hierarchical and random forests regressions were applied to rank the relative importance of predictor variables in influencing wind damage. A conservative estimate of aggregate damage from the intermediate windstorms (extrapolated to ∼150,000 ha, ∼25,500 severe) rivaled individual large, infrequent disturbances in the region. Damage patterns were relatively congruent among storms and became more spatially heterogeneous with increasing disturbance intensity. Proximity to forest-nonforest edge, stand age, and soils/landform were consistently important damage predictors. The spatial extent and distribution of the first two damage predictors are extremely sensitive to anthropogenic modifications of forested landscapes, the most important disturbance agent in the northern Great Lakes. This provides circumstantial evidence suggesting anthropogenic activities are augmenting and/or diminishing the ecological effects of the natural wind disturbance regime. Natural disturbances of intermediate size and intensity are significant agents of change in this region, and likely in other regions, deserving more attention from ecologists and biogeographers.

Highlights

Temperate forest ecosystems are inherently dynamic, continually responding to exogenous disturbances at a range of spatial and temporal scales (Foster et al 1998, Boose et al 2004, Woods 2004, Millward et al 2010; Flatley et al, in press) and seldom achieving equilibrium (Foster 1988)
The proportion of severe damage displayed a positive relationship with disturbance intensity; the highest percent severe damage occurred during the 1999 Wisconsin storm (;160 km/h wind gusts) and the lowest was in the 2002 Wisconsin and Michigan storm (;115 km/h wind gusts) (Table 1)
The spatiotemporal aggregate of forest damage sustained from the four intermediate windstorms is of considerable size and certainly rivals individual LIDs in the region

Summary

Introduction

Temperate forest ecosystems are inherently dynamic, continually responding to exogenous disturbances at a range of spatial and temporal scales (Foster et al 1998, Boose et al 2004, Woods 2004, Millward et al 2010; Flatley et al, in press) and seldom achieving equilibrium (Foster 1988). Ecologists and biogeographers have studied disturbances since the early 20th century, but our appreciation and understanding of disturbances has increased dramatically over the last several decades (cf White and Jentsch 2001). An enhanced comprehension of landscape-scale disturbances coincides with the rapid development of landscape ecology and the growing appreciation for the influences large, infrequent disturbances (LIDs) exert on species composition, structure, demography, and ecosystem processes (Foster et al 1998, Turner et al 1998, Turner 2005). Fires (Schulte and Mladenoff 2005), hurricanes (Boose et al 1994), and blowdowns (Canham and Loucks 1984, Foster and Boose 1992, Rich et al 2007) have garnered widespread attention, but ice storms, floods, volcanic eruptions, tornados, and insects are stimulating increased interest (cf. Foster et al 1998, Bebi et al 2003, Stueve et al 2007)

Methods

Results

Conclusion