Effects of Interacting Disturbances on Landscape Patterns: Budworm Defoliation and Salvage Logging

Abstract

Prior to European settlement, the 450000‐ha Pine Barrens region in northwestern Wisconsin, USA, was characterized by a landscape mosaic of large, open patches, savannas, and closed forest stands of jack pine (Pinus banksiana). Crown‐fires created large open patches that persisted on the droughty soils, providing important habitat for a number of area‐sensitive, open‐habitat species. Insect outbreaks may have contributed to periodic fires by increasing the fuel load. Today, fires are suppressed in the managed landscape, but insect defoliation remains a major disturbance. Salvage logging commonly follows insect outbreaks. Our objective was to evaluate landscape pattern changes caused by this interaction of natural disturbances and forest management. We examined changes in landscape pattern during the most recent (1990–1995) outbreak of jack pine budworm (Choristoneura pinus pinus) in northwestern Wisconsin using four Landsat TM satellite images (1987, 1991, 1993, and 1995). The 1987 image provided the basis for a species‐level forest classification identifying mature jack pine and open habitat prior to the budworm outbreak. Each subsequent image was used to identify clearcuts in mature jack pine. The 1995 image was also used to classify stand development in the open habitat of the 1987 image so that the overall availability of open habitat in 1995 could be assessed. GIS data layers were used to analyze logging rates and clearcut sizes separately for different classes of land ownership and soils. Approximately 12500 ha were salvage logged during the 1990–1995 outbreak. Logging rates were highest on the most infertile soils, and on private, industrial forest land. Annual logging rates of different landowners were 3–6 times higher during the outbreak than previous to it. Salvage cut sizes were larger than clearcuts prior to the outbreak. New cuts were mostly located next to previous cuts, thus increasing the size of openings on the landscape. Initial survey results by N. Niemuth show that populations of one area‐sensitive open‐habitat species (Sharp‐tailed Grouse, Tympanuchus phasianellus) thrive on the salvage cuts. Insect defoliation and subsequent salvage logging did create new habitat for open‐habitat species that were declining. Landscape pattern changes due to multiple interacting disturbances have rarely been studied. The interaction of jack pine budworm defoliation and salvage logging substantially changed landscape pattern in the Pine Barrens. We speculate that interaction between insect defoliation and fire may have significantly shaped the presettlement landscape.

Potential Impacts of Climate Change on Western Hemlock Looper Outbreaks

“…Edmonds et al (1999) suggest many insect outbreaks may be increasing in frequency and becoming more widespread than historically recorded because of increases in the abundance of suitable habitat. Indeed, landscapes with a greater abundance and homogeneity of host tree species tend to sustain larger populations of Lepidoptera due to increases in the likelihood of successful dispersal (Radeloff et al 2000). For western hemlock looper, late-successional western hemlock-dominated forests traditionally were considered most susceptible to western hemlock outbreaks (Koot 1994) and the large-scale cutting of these forests during the 20th century may have reduced the abundance of suitable habitat over the short term.…”

Post-Socialist Forest Disturbance in the Carpathian Border Region of Poland, Slovakia, and Ukraine

“…Moreover, illegal forest harvesting may be common (Nijnik and Van Kooten 2000), but is not included in official forestry statistics, thus limiting the use of such statistics. An alternative is to map forest disturbances using satellite images (Coppin and Bauer 1996, Radeloff et al 2000, Broadbent et al 2006) because it provides current and retrospective land cover information, independent from country borders and in an efficient manner for large areas. The forest disturbance index (Healey et al 2005) has recently been developed, but was so far only tested in the northwestern United States and in northern Russia.…”

Salvage logging in the world’s forests: Interactions between natural disturbance and logging need recognition

“…In fact, immediate, large‐scale salvage logging after major disturbances is so common that reductions in the price of wood due to the flooding of the market are a well‐known sequel of large natural disturbances (Peter & Bogdanski, ). Salvage clearcuts are also often much larger than traditional, green‐tree clearcuts (Hebblewhite, Munro, & Merrill, ; Radeloff et al, ; Sullivan, Sullivan, Lindgren, & Ransome, ). For example, mean clearcut size increased fourfold after a mountain pine beetle outbreak in the southern Rocky Mountains of Colorado (Collins, Rhoades, Underhill, & Hubbard, ).…”