Background information and definitions
Soil compaction affects soil microclimatic conditions and nutrient availability. This can affect species composition by giving an advantage to early successional understory species.
Supporting evidence from individual studies
A replicated, randomized, controlled study in 1995-2000 in boreal forest in British Columbia, Canada (Kabzems & Haeussler 2005) found that soil compaction treatments decreased the height of trembling aspen Populus tremuloides saplings but not their density. Height of dominant aspen saplings was lower in medium and heavy compaction plots (175 and 170 cm respectively) than in control plots (230 cm). Sapling density was similar between treatments (38,000-39,000 stems/ha). The height of at least 12 dominant aspen saplings and total sapling density were monitored in nine control (no deliberate compaction), nine medium compaction (2 cm impression in soil) and nine heavy compaction (5 cm impression in soil) treatment plots (40×70 m). Treatments were applied in 1995, data were collected in 2000.Study and other actions tested
A replicated, randomized, controlled study in 1998-2002 in boreal forest in British Columbia, Canada (Tan, Kabzems & Chang 2006) found that soil compaction increased understory plant cover in debris-removed plots but decreased plant species richness and the height of trembling aspen Populus tremuloides saplings in debris remaining plots. Total cover of shrubs, herbaceous species and mosses was higher in compaction plots with woody debris removal (compaction: 115%; control: 81%). With debris remaining species richness was lower in compaction (17 species/subplot) than control plots (21), as was the maximum height of aspen (compaction: 225 cm; control: 345 cm). There was no difference between compaction treatments and controls for: understory plant cover in debris remaining plots (compaction: 75%; control: 77%); plant species richness in debris removal plots (compaction: 23; control: 22); understory or the maximum height of aspen in debris removal plots (compaction: 110 cm; control: 120 cm). Six compaction (soil depressed by 4–5 cm; 40×70 m) and six control treatment plots were established in 1998-1999. Three of each treatment were assigned as woody debris removal (whole tree harvested, forest floor stripped to expose the soil) and three as debris remaining (trunk only harvested, woody debris left) plots. Under-canopy plants were monitored in 2001 in two subplots (4 m radius). Aspen saplings were measured in 2002 in three subplots within each treatment plot.Study and other actions tested
A replicated, controlled study in 1994-2003 in temperate broadleaf forest in Missouri, USA (Ponder 2008) found that soil compaction decreased tree and woody-vine density and increased annual plant density but had no effect on the density of shrubs, perennial herbaceous species and grasses, or on the height of trees or all other plants. Density of trees was lower in severe compaction than in control plots (control: 5.5; medium compaction: 4.2; severe compaction: 3.2/m2). Density of woody vines was lower in severe compaction (2.6/m2) than in medium compaction (4.6) and control plots (4.9). Density of annual herbaceous plants was lower in control (2/m2) than medium (4.1) and severe compaction plots (3.7). There was no difference between treatments for the density of shrubs (control: 2.5; medium compaction: 3.1; severe compaction: 3.5/m2), perennial herbaceous species (control: 2.5; medium compaction: 3.1; severe compaction: 2.5/m2) and grasses (control: 1.2; medium compaction: 1.5; severe compaction: 2.4/m2), or for the height of trees (control: 2.7; medium compaction: 2.5; severe compaction: 2.3 m) or all other plants (control: 0.6; medium compaction: 0.5; severe compaction: 0.5 m). Data were collected in 2003 in three plots (8 m2) in each of three replicates of: control (average soil bulk density 1.3 g/cm3), medium compaction (to 1.7 g/cm3) and severe compaction (to 1.8 g/cm3) treatment plots (0.4 ha). Treatments were applied in 1994.Study and other actions tested