Ground-dwelling arthropod response to fire and clearcutting in jack pine: implications for ecosystem management

We tested the response of species composition of three dominant litter-dwelling arthropod taxa (carabid beetles, spiders, and rove beetles) to wildfire and harvest. This study was conducted in north-central Ontario (47°42′N, 83°36′W) in jack pine (Pinus banksiana Lamb.) dominated stands in 2013 using pitfall trapping. Using 222 species (12 015 individuals), we compared the effects of disturbance using recently burned (3 years since fire) and clearcut sites (3 years since harvest; tree length, full tree, stump removal, and blading), as well as older, closed-canopy stands that have regenerated following clearcutting (51 years since harvest) and fire (92 years since fire), with multivariate regression trees. Taxa were more similar in the three controls (including recent fire) than between controls and harvest treatments, with increased forest floor disturbance in harvested plots being a likely explanation. In addition, taxa were different in the younger (51 years) harvest-origin plots than in the older (92 years) fire-origin plots, suggesting that communities had not yet recovered from the harvest disturbance possibly due to insufficient coarse woody debris in the younger stand. These results indicate that forest management practices that match natural forest floor disturbance could ameliorate short-term effects, whereas the maintenance of more coarse woody debris could reduce the recovery time of epigaeic communities.

Changes in forest floor bryophyte (moss and liverwort) communities 4 years after forest harvest

Forest harvest presents a potential threat to forest floor bryophyte communities primarily through alteration of the microclimate and disturbance of substrates on the forest floor. Management, including harvest, applied at the landscape scale creates patches of disturbance of differing severities at the spatial scale experienced by bryophytes. Presumably, bryophyte diversity in managed landscapes is best conserved by forest harvest techniques that minimize community change, thereby allowing disturbed communities to reassemble to approach predisturbance composition. We monitored bryophyte community reassembly by sampling quadrats established in a 54-ha management block of Acadian forest in New Brunswick, before and after harvest. Quadrats were either in unharvested areas, or experienced a range of disturbance severities from removal of some or all canopy, to forest floor disturbance with complete canopy removal. Bryophyte communities showed compositional change over 4 years, even in areas that were not harvested. Although species richness was maintained or recovered 4 years after harvest, changes in species composition were significant in all disturbance classes with greatest change related to forest floor disturbance. In particular, liverworts were lost in areas with forest floor disturbance. We suggest that the simplest method to reduce immediate species loss, and presumably promote conservation of bryophyte communities within managed forest landscapes, is to utilize techniques that reduce the area of forest floor and associated substrates that are physically disrupted.Key words: bryophyte, community change, disturbance, forest harvest, monitoring.

The influence of partial harvesting and forest floor disturbance on nutrient availability and understory vegetation in boreal mixedwoods

The impacts of partial cut systems on nutrient availability and understory vegetation are poorly understood. To examine these responses, white spruce dominated stands in the boreal mixedwood of Alberta were clear-cut or partial-cut and the forest floor treated by slash burning, mixing, mounding, or scalping in a split-plot design. Soil nutrient availability (ion exchange resin), net N mineralization (in situ incubations), and vegetation (density and cover) responses were assessed. With the exception of higher Mg availability in the clearcuts, differences in nutrient availability were driven by forest floor disturbance and not harvest method. Relative to controls, burning increased availability of NH4+, NO3–, and P, and scalping increased Ca and Mg but diminished K. Controls had low levels of NO3–. The mixing treatment substantially reduced net N mineralization. In terms of vegetation, partial cuts reduced root suckering by Populus spp. (Populus tremuloides Michx., Populus balsamifera L.) relative to clearcuts. Burning and mounding stimulated fireweed (Epilobium angustifolium L.) cover, while scalping increased Populus spp. sucker density. In contrast, mixing largely reduced vegetation establishment, likely because of the destruction of roots and rhizomes and reduced N supply. Nutrient availability and vegetation establishment were more strongly controlled by forest floor disturbance than by partial canopy retention.

The importance of forest floor disturbance in the early regeneration patterns of the boreal forest of western and central Quebec: a wildfire versus logging comparison

The nonvascular and vascular plant composition of the early regenerating vegetation present following wildfires and clear-cut logging has been compared separately in three areas of the black spruce (Picea mariana (Mill.) BSP) - feathermoss (Pleurozium schreberi (Brid.) Mitt.)) forest of western and central Quebec. In each area, a detrended correspondence analysis successfully differentiated the burned and logged stands along the first ordination axis. This separation mainly resulted from the greater abundance of pioneer species or lichens after fire and the greater abundance of residual species after clear-cutting. Spearman's correlation coefficients were calculated to relate variables characterizing physical disturbance of the forest floor and general site conditions to the two first differentiating axes. Variables characterizing forest floor disturbance severity were strongly associated with the first ordination axis in two of the study areas but not in the third one. The interpretation of compositional differences in the light of plant reproductive strategies led to the identification of regeneration patterns that illustrated the influence of disturbance type and severity on post-disturbance vegetation composition. These results suggest that certain forestry practices such as careful logging with the protection of regeneration and soil, scarification, and prescribed burning may differ in their capability to address sustainable forest management issues.

Uprooting in boreal spruce forests: long-term variation in disturbance rate

Uprooted trees provide many kinds of exposed and colonizable substrates and may mediate coexistence of plant species. Here we present, for the first time, the temporal forest floor disturbance pattern caused by uprooted trees over a long period of time (120 years). There was a significant correlation between the frequency of high winds and number of uprooted trees, and the fall direction was closely related to the main direction of high winds. The temporal distribution was strongly aggregated, with many uprootings in the 1890s and the 1970s, resulting in large variations in disturbance rate between different decades. This implies periods with low availability of exposed soil. To interpret traits among species dependent on the disturbance as adaptations to some mean rate may thus be strongly misleading. However, the occurrence and importance of such bottleneck periods is hard to evaluate, as studies of the process of uprooting have only documented numbers and rates of uprooted trees and not the availability of exposed soil. We recommend more retrospective studies to evaluate long-term variation in disturbance regime parameters and studies on the temporal availability of exposed and colonizable soil.

Ecology of and control strategies for Calamagrostiscanadensis in boreal forest sites

Calamagrostiscanadensis (Michx.) Beauv. is a widely distributed rhizomatous grass that can seriously inhibit growth of white spruce (Piceaglauca (Moench) Voss) seedlings in the boreal forests of North America. We review the dynamics of this grass during four successional stages: the colonization of disturbed sites; dominance of the site by the grass a few years after disturbance; gradual loss of dominance with overstory development; and maintenance of the grass at low levels in the understory of the mature forest. We also describe C. canadensis in relation to recruitment from clonal growth and seed, environmental conditions for growth, the effects of grass litter buildup on conifer seedling microclimate, and overall competitive abilities. Control strategies for C. canadensis are as follows. If the grass is found in nearly every square metre in the understory prior to logging, there will be rapid spread when the stand is clear-cut unless clones are killed using herbicides or a deep burn. Large spruce seedlings, planted on large soil scalps or mounds, coupled with release by way of herbicides or sheep grazing, may be necessary for plantation establishment under conditions of encroachment by C. canadensis. Alternatively, the shade provided by a partial canopy may inhibit the grass sufficiently to allow spruce seedlings to establish. If grass is not abundant in the understory, we recommend (i) minimizing forest floor disturbance to reduce sites for grass seedling colonization or (ii) a slash burn with the hope of encouraging colonization by herbaceous species that have less impact on conifer seedlings.

Control of Grass and Sedge in Allegheny Hardwood Stands with Roundup-Residual Herbicide Tank Mixes

A small plot experiment was carried out to investigate the effect of forest floor disturbance on establishment of grasses and sedges and to test whether addition of a residual herbicide in tank mix with Roundup could reduce grass and sedge reinvasion. Seven residual herbicides, each at three rates of application, were tested against a Roundup control. Herbicides were Hyvar X (bromacil), Karmex (diuron), Racer (fluorochloridone) (R-40244)), Devrinol (napropamide), Surflan (oryzalin), Oust (sulfometuron methyl), and Sinbar (terbacil). Herbicides were applied on three dates of application at two northwestern Pennsylvania sites. Half of each plot was mechanically disturbed to simulate logging disturbance. Response data were collected for 2 or 3 years after treatment application. Soil disturbance was a significant factor in promoting emergence of grass and sedge; most germination occurred during the growing season immediately following treatment. Little grass or sedge emerged on undisturbed areas. In the second growing season following treatment, plants that did emerge grew to full size. Two of the tank mixes, Roundup plus Hyvar X and Roundup plus Karmex, gave less control of vegetation on the plot at the time of treatment than Roundup alone. Most Round-up-residual herbicide tank mixes reduced emergence and growth of new grass and sedge plants, regardless of application date; however, the amount and duration of control differed among herbicides. Roundup (1 # ai/ac) plus Surflan (2-4 # ai/ac) and Roundup plus Oust (0.09-0.19 # ai/ac) produced the best results reducing grass and sedge ground cover for at least 3 and 2 years, respectively. By use of Roundup-residual herbicide tank mixes and manipulation of cutting techniques, forest land managers can minimize the impact of grass and sedge on the forest regeneration process in Allegheny hardwood stands. North. J. Appl. For. 7:124-129, September 1990.

Effects of forest-floor disturbance on soil-solution nutrient composition in a black spruce ecosystem

This study summarizes the effects of forest-floor disturbance on soil-solution chemistry. For comparative purposes chemical analyses are also presented of soil solution collected beneath undisturbed black spruce (Piceamariana (Mill.) B.S.P.) stands, stream water, and precipitation in the same area. The disturbance treatments were superimposed on the forest floor following removal of the black spruce overstory. These included burning of the forest floor, and mechanical removal of one-half and all of the forest floor. Conductivity, pH, and the concentrations of [Formula: see text], [Formula: see text], phosphates, K, Ca, and Mg were determined in the various water samples. Only in the case of the most severe treatments, one-half and all of the forest floor removed, was there substantial changes in conductivity, pH, and the concentrations of Ca and Mg. Potassium and P showed no consistent treatment effects. Lack of significant change in solution N concentration may reflect increased microbial activity and N immobilization in the forest floor in response to disturbance.

Effect of forest floor disturbance on seedling establishment of Chamaecyparislawsoniana

Native seeds of Chamaecyparislawsoniana (A. Murr.) Parl. (Port-Orford-cedar) were sown on treated 1-m2 plots in four natural stands in southwestern Oregon, U.S.A. Treatments, replicated four times per stand, were (1) control, with natural litter undis-turbed, (2) litter removed, (3) litter removed and burned with ash replaced on plot, and (4) spaded after litter removal. Eighty-nine percent of germination occurred in early to mid-June. The spading treatment had the most germinants and the most survivors. Litter removal and burning treatments supported many fewer germinants, had the smallest seedlings, and had no survival after two growing seasons. Percentage survival of the few germinants in the control was as good as for the spading treatment, 5–6% after three summers. Although much natural seedling establishment may occur on natural litter, soil disturbance appears to greatly increase the rate of establishment. Litter removal alone does not increase establishment.