Salvage Logging After Windthrow Alters Microsite Diversity, Abundance And
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Salvage logging after windthrow alters microsite diversity, abundance and environment, but not vegetation Downloaded from https://academic.oup.com/forestry/article/81/3/361/655733 by guest on 30 September 2021 1 2 CHRIS J. PETERSON * and ANDREA D. LEACH 1 Department of Plant Biology, University of Georgia, 2502 Plant Science Building, Athens, GA 30602, USA 2 Department of Cellular and Molecular Biology, University of Georgia, Athens, GA 30602, USA * Corresponding author. [email protected] Summary An increasing number of researchers propose that disturbance effects in forests are mediated through ‘ legacies ’ , which are organisms or organically derived structures that persist after a disturbance. Much controversy currently surrounds the potential impact of post-disturbance salvage logging, in part, because of the potential for such actions to alter post-disturbance legacies and thus forest regeneration. Microsites (e.g. downed tree crowns, boles, stumps, treefall pits and mounds) created by natural disturbances are a subset of the broader concept of legacies, but the effect of windthrow + salvage logging on microsites and their environment and vegetation has not been previously examined. In a wind-damaged forest in western Tennessee, USA, we documented microsite diversity and abundance, environmental conditions, and initial vegetation regeneration in salvaged and unsalvaged areas. We found that salvaged areas had signifi cantly greater variety of microsites, altered microsite abundance, higher soil temperature and greater canopy openness relative to unsalvaged areas. However, 2 years after the storm, herbaceous cover and species richness and tree seedling density and species richness did not differ between salvaged and unsalvaged areas. Soil moisture also was unaffected by salvaging. In contrast, environmental conditions and vegetation characteristics differed signifi cantly among microsite types, with treefall mounds being warmer and drier than other microsites. This intermediate- severity wind disturbance, followed by moderate intensity of salvaging, created microsites that differed in environment and vegetation, and although the salvaging altered microsite diversity, abundances and conditions, the initial vegetation did not show detrimental effects of the salvage operations. We suggest that primary determinants of the consequences of salvaging after natural disturbance are the severity of the natural disturbance, and intensity of salvage operations. Detrimental effects of salvaging may accrue only if some combined severity threshold is exceeded. Introduction 2006 ; Newton et al. , 2006 ; Baird, 2006 ) have brought the discussion of post-disturbance sal- Recent natural disturbances (e.g. extremely large vage logging to a heated intensity ( Floyd, 2006 ). wildfi res in numerous locations worldwide) and Currently, most forest areas subject to large natu- controversial research fi ndings ( Donato et al. , ral disturbances (e.g. fi re or wind) subsequently © Institute of Chartered Foresters, 2008. All rights reserved. Forestry, Vol. 81, No. 3, 2008. doi:10.1093/forestry/cpn007 For Permissions, please email: [email protected] Advance Access publication date 19 March 2008 362 FORESTRY have salvage harvesting activities that aim to re- reduced in salvaged areas. To our knowledge, coup fi nancial losses from the natural disturbance Elliott et al. (2002) and Rumbaitis Del Rio (2006) ( Lindenmayer et al. , 2004). These salvage logging represent the only studies available on the effect operations are widespread and common, but we of windthrow + salvaging on regeneration. Con- know very little about how such management ac- sequently, there is yet exceedingly little informa- tions infl uence forest regeneration, biodiversity tion about forest response to salvaging after wind and risk of later disturbance. disturbance, particularly in eastern North Amer- One of the potential infl uences of salvage log- ica. Therefore, we report here on the microsite ging on forest recovery and diversity might occur abundances and very early regeneration follow- Downloaded from https://academic.oup.com/forestry/article/81/3/361/655733 by guest on 30 September 2021 via alterations in the variety and abundance of ing moderate windthrow in hardwood forests of microsites ( Beatty, 1984 ; Peterson et al. , 1990 ; central Tennessee, USA. Following Lindenmayer Kuuluvainen and Juntunen, 1998), which are et al. (2004) , we hypothesized that salvaging one component of the broader concept of biotic might destroy treefall mounds and remove tree legacies ( Franklin et al. , 2000 ; Lindenmayer, trunks and crowns in addition to exposing bare 2006 ). Lindenmayer et al. (2004 , see also Foster soil in skid trails and depositing pruned branches and Orwig, 2006 ; Lindenmayer and Noss, 2006 ) in slash piles. Therefore we expected that sal- suggested that one way disturbances maintain vaging reduces microsite diversity and alters ecosystem diversity and function is through the microsite abundance (hypothesis 1). We further variety of legacies resulting from disturbances, expected that since salvaging removes downed and that salvaging reduces legacy diversity. It is stems and crowns potentially capable of sprout- indeed well known that differing microsites in ing and surviving, it would increase canopy open- wind-disturbed forests have distinct environ- ness at ground level (hypothesis 2). Finally, we ments ( Beatty, 1984 ; Beatty and Sholes, 1988 ; expected that microsites with exposed mineral Carlton and Bazzaz, 1998a ), and differentially soil (pits, mounds, bare soil patches) and more infl uence tree seedling germination, growth and open conditions (salvaged areas) would contain vulnerability to herbivores (Long et al. , 1998 ; a higher proportion of shade-intolerant, early- Peterson and Pickett, 1995, 2000 ; Krueger and successional species (hypothesis 3) and higher Peterson, 2006 ). These effects often result in species richness (hypothesis 4). vegetation variation among microsites, often with greater abundance of pioneer species in the more severely disrupted microsites (e.g. Peter- Materials and methods son et al. , 1990 ; Peterson and Campbell, 1993 ), Study site although such among-microsite variation is not always found ( Webb and Scanga, 2001 ). Thus, This research was conducted at Natchez Trace decreases in the variety or abundance of micro- State Park and Forest (NTSF), an 18 245-ha sites might decrease forest regeneration poten- natural area located in west-central Tennessee tial or species diversity in the regenerating area. (35º N 88º W). The area lies within the East Gulf However, we know of no studies of microsite Coastal Plain section of the Coastal Plain phys- abundances, composition or diversity after natu- iographic province ( Braun, 1950 ). Braun (1950) ral disturbance and salvaging. classifi ed the vegetation of western Tennessee as The existing information about consequences belonging to the Mississippi Embayment section of post-fi re or post-windthrow salvaging in North of the Western Mesophytic Forest Region. The America are mostly restricted to the north-west topography consists of gently rolling uplands (e.g. Donato et al. , 2006 ) or boreal sites in Canada separated by broad fl oodplains; elevation aver- ( Greene et al. , 2006; Macdonald, 2007 ). Donato ages 165 m above sea level, ranging from 137 to et al. (2006) found reduced tree seedling density 182 m ( Smalley, 1991 ). Soils are derived from the and diversity in salvaged areas of the 2002 Biscuit McNairy sands geologic formation and consist of Fire in Oregon, and Greene et al. (2006) report well-drained fi ne sandy loams and silt loams with that although asexual reproduction by Populus occasional fragipans and a discontinuous loess was unaffected by salvaging in central Quebec, cap ( Kupfer and Franklin, 2000 ). The climate is the regeneration from seed by conifers was much humid continental, with short, mild, wet winters SALVAGING AFTER WIND DISTURBANCE 363 and long, hot, dry summers and an average grow- hectares), perfect randomization and replication ing season of 202 days. Mean annual precipita- would be diffi cult to achieve. tion is 1240 mm, mostly rain falling in the late To quantify relative abundances of microsite winter and early spring ( Flowers et al. , 1960 ). types, we sampled along four parallel 30-m lines Much of the park was settled and cleared for 10 m apart in each large plot. At 0.5-m inter- agriculture in the 1800s and early 1900s, but the vals along these lines, we dropped a pin and re- land was abandoned in 1935 and was deeded to corded microsite information, yielding a total of the state of Tennessee in 1955 (Smalley, 1991 ). 244 points per plot (244 points × 32 plots; n = The second-growth forests consist of Quercus 7,808 sampling points). We classifi ed points into Downloaded from https://academic.oup.com/forestry/article/81/3/361/655733 by guest on 30 September 2021 species (oaks), Carya species (hickories) and other 13 microsite categories on the basis of the sub- mixed mesophytic species, including Pinus taeda strate conditions and the nature of overlying ma- L. (loblolly pine), in the uplands. The understory terials; this classifi cation is the basis for Figure consists primarily of Cornus fl orida L. (fl owering 2 , but does not utilize vegetation in the microsite dogwood), Nyssa sylvatica Marsh. (blackgum) defi nition (see ‘ focal microsites’ below). Substrate and Sassafras albidum (Nutt.) Nees. (sassafras). was recorded as organic or mineral,