Partial Canopy Removal Research Articles

Managing climate change microrefugia for vascular plants in forested karst landscapes

Microrefugia are small areas that support favourable climate and allow species to persist during regional and global climate changes. Dolines in karst landscapes may provide such areas for many climate change-vulnerable species. Here we provide a better understanding on how plant species indicate changes in their environment (temperature, soil moisture and light availability) after a few years of partial canopy removal from dolines and their close surroundings (logged areas: >1 ha). We place our results in the context of the most widely used forest management practices within the study area (Mecsek Mts, Hungary), in addition to presenting a general framework for the maintenance of doline microrefugia in forested karst landscapes. Three types of habitats were investigated: dolines before logging, dolines after logging, and the forested plateau. Three large dolines and three sites on the plateau were selected for vegetation sampling. All dolines were sampled before logging and 5–10 years after partial canopy removal. Logging resulted in a 50–80% reduction of canopy cover in the dolines and their close surroundings. We established a transect across each doline from north to south passing through doline bottoms, and across each plateau site. We estimated the percentage cover of vascular plant species (tree saplings – up to 1 m in height, shrubs and herbs) along the transects using 1 m × 1 m vegetation plots, determined the diagnostic species of the doline and plateau habitats, and used multivariate methods and linear mixed-effects models during analyses. Plant species indicated clear gradients of the main microclimatic factors within the dolines and that significant changes took place after logging. Canopy removal caused substantial changes in the main microclimatic factors of most doline microhabitats (e.g., south-facing slopes). The vegetation of the dolines before logging indicated moister conditions than that of the plateau and cooler and shadier conditions than that of the dolines after logging. These and our previous results suggest that logging may directly and indirectly influence dolines to be microrefugia under global warming. By applying our framework to refugia conservation and management for the karst landscape in the Mecsek Mts, we can conclude that the protection of old forests and natural forest dynamics in as many large dolines as possible and the implementation of close-to-nature forestry practices may be essential to maintain regional biodiversity in the long run.

Restoring native forests from Pinus radiata plantations: Effects of different harvesting treatments on the performance of planted seedlings of temperate tree species in central Chile

Extensive areas of native vegetation have been cleared to establish commercial exotic tree plantations in south-central Chile, a region known as a world biodiversity hotspot. Despite increasing societal demands to restore native forests in parts of the landscape, documented experiences for this form of restoration are lacking. We conducted a landscape-replicated experiment to test the influence of different harvesting treatments (clearcut, strip-cutting and unharvested control) on the early establishment of native tree species in 20-year-old Pinus radiata plantations. Group plantings of shade-intolerant (Nothofagus dombeyi; Nothofagus obliqua), semi-tolerant (Nothofagus alpina; Laurelia sempervirens) and shade–tolerant species (Aextoxicon punctatum; Cryptocarya alba) were established across the treatments, and seedling performance and water status were monitored during the first two growing seasons. Mean survival was significantly higher in the strip-cuttings (77%) and control (70%) than in the clearcuts (38%), while mean height and root collar diameter growth were significantly higher in the strip-cuttings (16 cm year−1; 0.2 cm year−1) and clearcuts (16 cm year−1; 0.2 cm year−1) than in the control (5 cm year−1; 0.1 cm year−1). Shade-intolerant and semi-tolerant species showed the highest growth responses to openings. Leaf water potential was significantly higher in seedlings in the strip-cuttings than those in the control and clearcuts, and stomatal conductance was significantly higher in the strip-cuttings and clearcuts than in the control. Higher seedling performances and lower water stress in the strip-cutting treatment suggest that partial canopy removal is a suitable method for artificial regeneration of native tree species with different shade tolerances for native forest restoration from P. radiata plantations.

A field experimental study on the impact of Acer platanoides, an urban tree invader, on forest ecosystem processes in North America

BackgroundInvasive species affect community dynamics and ecosystem functions, but the mechanisms of their impacts are poorly understood. Hypotheses on invasion impact range from Superior Competitor to Novel Function, from Enemy Escape to Microbial Mediation. In this study, we examined the effects of an urban tree invader, Acer platanoides (Norway maple, NM), on a mesic deciduous forest in contrast to its native congener Acer rubrum (red maple, RM) with a split-plot design experiment. A total of 720 maple seedlings were transplanted to 72 plots under 24 trees of three canopy types. The three experimental treatments were removal of resource competition at above- and belowground and removal of leaf-litter effect. Soil moisture and nitrogen-related microbial activities were followed for each plot.ResultsWe found that partial canopy removal increased canopy openness and light transmission to the forest floor, but to a greater extent under NM than under RM trees. NM seedlings were more shade tolerant than RM seedlings in height growth. During the reciprocal transplantation in the mixed forest, biomass accumulation of NM seedlings under RM trees were twice as much as under NM, while that of RM seedlings under NM trees was 23.5% less than under RM. Soil net nitrification and relative nitrification were significantly higher, but mineralization rate was much lower under NM than under RM trees, which would lead to faster N leaching and lower N availability in the soil. Plots with litter removal had significantly higher seedling mortality due to herbivory by the end of 2 years, especially for NM seedlings under NM trees. Trenching enhanced soil water availability but there was no difference among canopy types.ConclusionsOur results demonstrated that invasion of NM not only altered forest canopy structure but also changed herbivory rate for seedlings and N dynamics in the soils. NM seedlings were more shade tolerant under NM canopies than RM seedlings and were more protected by NM litter under NM canopies than under RM canopies. These altered biotic and abiotic environments will likely facilitate further invasion of NM in the forests, hence positive feedbacks, and make it an increasingly serious tree invader in North America.

Trajectories and resilience of stand structure in response to variable disturbance severities in northern hardwoods

In late successional forests, stand development processes are often more easily monitored and are more closely related to key ecological parameters when using structural criteria rather than stand age or time since stand-replacing disturbance. In this paper, the effects of various disturbance regimes on long-term structural change and resilience in 70 primary northern hardwood stands were analyzed using the CANOPY individual-tree model. Compared to a ‘dichotomous’ disturbance regime of small gap dynamics with infrequent severe disturbance, the historic natural disturbance regime of periodic low- and moderate-severity disturbances produced a more complex landscape mosaic similar to the current landscape. Under the natural disturbance regime, mean residence time in each of 8 structural stages was short (8–35years) and followed descending monotonic distributions. Mean residence time in old growth was 87years. Old-growth stands with stable size distributions were much more frequent when defined by relevant structural criteria than when defined by their past history (timing and severity of disturbances). Repeated mild and moderate disturbances often caused stand structure to retrogress to mature or earlier old-growth stages without undergoing stand replacement. However, simulation experiments often demonstrated structural resilience to repeated mild disturbance, even at the 0.5ha scale. In some cases, disturbances accelerated the development of more complex structure typical of late transition or steady-state stands. Recovery from heavy partial canopy removal was markedly faster than recovery after stand-replacing disturbance. Stands recovered to an old-growth condition with a stable size distribution (‘quasi-steady state’) 175years after disturbances removing 60% of the aggregate crown area, compared to 280years after a disturbance with no residual trees. High dominance of these landscapes by old-growth forest (78% of total area) is due not only to the low frequency of stand-replacing disturbance, but also to the structural resilience of old growth to periodic episodes of low- and moderate-severity disturbance.

Meta-analysis of the effects of canopy removal on terrestrial salamander populations in North America

Terrestrial salamander abundance in North American forests is closely associated with forest characteristics, and salamander populations typically decline following timber removal. However, salamander responses to timber harvest vary considerably from one study to the next – some studies have shown limited or no effects whereas others have found harvest-related declines of up to 95%. To estimate overall effect sizes of timber harvest on salamander populations and to examine factors that contribute to variation in salamander responses to harvest, we carried out a meta-analysis of published studies of the effects of timber harvesting on terrestrial salamander abundance. Based on 108 salamander species/treatment combinations from 24 studies, we found mean harvest-related declines ranged from 29% (95% CI=−2% to 51%) for long-term responses to partial canopy removal to 62% (95% CI=29% to 80%) for short-term responses to clearcutting. Multivariate mixed models suggested that clearcutting had a modestly greater impact on salamander populations than partial harvest and that decreases following harvest were more pronounced at sites with warmer summer high temperatures. In addition, active sampling of salamanders (e.g., surface counts) led to greater apparent effects of timber harvest than passive sampling (e.g., cover boards or pitfall traps), suggesting that sampling methodology influenced the perceived effects of harvest. In the studies evaluated, salamander numbers almost always declined following timber removal, but salamanders were never extirpated and populations typically increased as forests regenerated.

Litter decomposition and nutrient dynamics following forest tending (Soopkakkugi) works in a Pinus densiflora stand

This study was conducted to determine mass loss rates and nutrient dynamics from decomposing litter following forest-tending (Soopkakkugi) works (FTW) which are one of the most important forest management activities in Korea. We measured litter decomposition rates for 2 years in FTW and non-FTW (control) stands of approximately 40-year-old red pine (Pinus densiflora S. et Z.) forests in the Hwangmaesan Soopkakkugi model forest in Sancheonggun Gyeongsangnam-do, Korea. Mass loss rates from decomposing needle litter were significantly lower (P < 0.05) in the FTW than in the control stands for three of the six sampling dates during the study period. Nutrient concentrations and nutrients remaining such as carbon, nitrogen, phosphorus, potassium, and magnesium from decomposing litter were significantly different (P < 0.05) between the FTW and control stands because of decreased mass loss rates by increased gaps following FTW. The results indicate that FTW clearly influence litter decomposition and nutrient dynamics from decomposing needle litter because of the change of environmental factors caused by partial canopy removal such as FTW.

Tree species and environment associations within hemlock-silverbell stands treated for hemlock woolly adelgid in Great Smoky Mountains National Park1

The hemlock-silverbell (Tsuga canadensis-Halesia tetraptera) association is endemic to several small stands in federally protected lands in the southern Appalachian Mountains and is currently threatened by the hemlock woolly adelgid (Adelges tsugae). Pre-infestation stand structure was still evident at the time of the study but hemlock mortality and associated vegetation responses portend rapid changes in this system. In order to guide potential future restoration efforts and impact assessments, a study was implemented to determine the structure of hemlock-silverbell stands and to identify environmental variables associated with differences in stand composition in areas of Great Smoky Mountains National Park treated to control hemlock woolly adelgid. Halesia tetraptera and T. canadensis exhibited even-aged and uneven-aged stand structures, respectively. Forest composition varied as a function of environmental variables within the hemlock-silverbell association with overstory H. tetraptera relative density positively correlated with higher water availability (Beers aspect and slope) and overstory T. canadensis was negatively correlated with Beers aspect. Relative density of H. tetraptera and T. canadensis in the understory were similarly associated with higher and lower productivity conditions, respectively. In the understory, Acer pensylvanicum relative density was negatively associated with that of understory T. canadensis. The results suggest that partial canopy removal resulting from the loss of T. canadensis due to hemlock woolly adelgid may benefit aggressive tree species such as A. pensylvanicum. The United States Park Service vegetation management policies, here and in other natural areas where non-native invasive species are controlled (but native species responses are unaccounted for), will need to address this phenomenon if T. canadensis restoration is to be accomplished in the event adelgid control can be achieved.

Comparative physiological responses of Rhododendron groenlandicum and regenerating Picea mariana following partial canopy removal in northeastern Quebec, Canada

In boreal black spruce ( Picea mariana (Mill.) BSP) dominated stands, careful logging around advance regeneration contributes to protect the shrub layer while increasing light availability. Therefore, it may promote expansion of bog Labrador tea ( Rhododendron groenlandicum (Oeder) Kron &amp; Judd), which can impair black spruce growth by direct competition for nutrients and by alteration of soil biochemical conditions. Such harvesting approaches may not be suited for irregular, uneven-aged black spruce stands in the context of ecosystem-based management. Our objectives were to evaluate the effects of different intensities of partial harvest on critical resource availability and to compare the physiological and morphological responses of black spruce and Rhododendron to different intensities of partial harvest treatments. Two years after harvest, photosynthesis rate of black spruce was unchanged and was lower than that of Rhododendron, which was 63% higher after harvest. Nitrogen and water use efficiency were, respectively, 171% and 42% higher in Rhododendron than in black spruce after logging. Following harvest, black spruce physiology appeared to be regulated by the atmospheric humidity deficit, but for Rhododendron, physiology was regulated by light availability. The high plasticity of Rhododendron leaf traits could be indicative of the future advantage of this species in these stands following canopy removal associated with harvest.

Long-term response of planted conifers, natural regeneration, and vegetation to harvesting, scalping, and weeding on a boreal mixedwood site

This study reports 14th-year response of a boreal mixedwood stand to different harvest intensities (uncut, 50% partial cut with and without removal of residuals after 3 years, and clearcut), spot site preparation treatments (none and scalped), and chemical weeding frequencies (none, single, and multiple) in northeastern Ontario. The response variables include the survival and growth of planted white spruce ( Picea glauca [Moench] Voss) and jack pine ( Pinus banksiana Lamb.), height and density of natural regeneration and shrubs, and cover of shrubs and non-woody vegetation. Harvesting and weeding generally improved survival and growth of planted trees, although white spruce survival did not significantly differ among the three weeding frequencies. Harvesting tended to increase heights of hardwood (mostly trembling aspen ( Populus tremuloides Michx.)) and conifer (largely balsam fir ( Abies balsamea (L.) Mill.).) natural regeneration, cover and density of shrubs, and cover of herbs, lichens, and ferns. Chemical weeding reduced height, density and cover of shrubs, height and density of hardwood regeneration, and fern cover, but increased moss and lichen cover. Spot scalping did not significantly affect planted seedling, natural regeneration, or the vegetation. Maximum survival and growth of planted white spruce and jack pine were achieved using a combination of clearcutting and multiple weeding. However, partial cutting followed by a single weeding produced acceptable survival and reasonable growth of planted trees, particularly for white spruce. Partial canopy removal alone substantially reduced the amount of hardwood regeneration, relative to clearcutting, but did not adequately suppress understory shrubs. Significant improvement in seedling growth following multiple weedings was evident primarily in the complete canopy removal treatments: 50% partial cut with removal of residuals after 3 years and clearcut. While the effects of harvesting and weeding on planted crop trees found in the 5th-year assessments generally persisted at year 14, survival decreased, likely due to light competition from developing hardwood and shrubs.

Influence of fire and mountain pine beetle on the dynamics of lodgepole pine stands in British Columbia, Canada

An outbreak of the mountain pine beetle ( Dendroctonus ponderosae Hopkins; MPB), currently affecting over 10.1 million hectares of lodgepole pine forests ( Pinus contorta Dougl.) in British Columbia, Canada, is the largest in recorded history. We examined the dynamics of even-aged lodgepole pine forests in southern British Columbia, which were undergoing this MPB outbreak. Using dendroecology and forest measurements we reconstructed the stand processes of stand initiation, stand disturbances, tree mortality, and regeneration, and explained the current stand structure and the potential MPB impacts in selected stands. Our results indicate that stand-replacing fires initiated even-aged seral lodgepole pine stands in this region. In the absence of fire in the 20th century, multiple MPB disturbances, which each resulted in partial canopy removal, modified the simple one-layer structure of the fire-origin stands by the initiation of post-MPB disturbance regeneration layers, transforming the stands into complex, multi-aged stands. Despite high overstory mortality due to the current MPB outbreak, regeneration layers, which are likely to survive the current outbreak, will provide important ecological legacies and will contribute to mid-term timber supply.

Open woodland and savanna decline in a mixed-disturbance landscape (1938 to 1998) in the Northwest Wisconsin (USA) Sand Plain

Our research illustrates how a landscape mosaic changes in association with a mixed natural-anthropogenic disturbance history. Our study area is the Northwest Wisconsin (USA) Sand Plain (NWSP), a region with a rich disturbance history including fire, insects and clearcut forestry. We integrated historic airphotos from 1938, 1960, 1980 and 1998 within a GIS to describe change among four landcover classes describing a canopy-closure gradient: closed forests, woodlands, savannas and “open barrens”. Our work addresses two literature needs: empirical studies of mixed-disturbance landscapes, and nonforest habitats within a forest matrix. Our analysis shows that: the area of open barrens fluctuated, woodlands and savannas declined severely and closed forests increased through time. Falling median patch sizes and other landscape metrics suggest that the woodlands are becoming more fragmented. The landcover transitions driving this change vary according to time and place. The dominant transitions are toward closed forests from all classes, and transitions toward open barrens are also consistently important. The woodlands, savannas and open barrens habitats are mostly comprised of transient patches, persisting for less than 20 years. This contrasts with closed forests that often persist for 40 plus years. These changes are consistent with the disturbance regime that is shifting from fire- to forestry-dominance. Our results show a trend towards landscape simplification, manifest as losses of intermediate-density habitats (woodland and savanna) and shrinking patch sizes. The transient nature of the nonforest habitats shows that disturbance resulting in total or partial canopy removal will be vital for their conservation at a landscape scale.

Influence of Species on Site Selection and Timber Removal: A Case Study for West Virginia

Abstract Over the last 40 years the composition of West Virginia forests has been changing as selective cutting practices have removed larger-diameter timber of specific species and partial canopy removal has fostered the regeneration of shade-tolerant species such as red maple. However, since the mid-1990s there has been considerable change in the number of markets accepting lower-quality and smaller-diameter roundwood, especially yellow-poplar. These changes have increased the number of roundwood markets and thus have increased the potential for harvesting based on silvicultural objectives or clearcuts. An examination of harvesting and merchandising practices for 28 harvest sites in West Virginia found an average of four merchandising separations or markets per site. Although the presence of new markets may have increased the section of sites containing yellow-poplar and the removal of this species from these sites, the continuation of diameter-limit cutting seems to have the greatest effect on which trees are removed. This pattern of partial harvests continues to favor the regeneration of shade-tolerant species such as red and sugar maple.

Effects of experimental forestry treatments on a Maine amphibian community

Predicting how timber harvesting will influence sensitive taxa such as amphibians is of critical importance for sustainable management of forests. In 2004 and 2005, we studied the effects of four forestry treatments (clearcut with coarse woody debris [CWD] removed, clearcut with CWD retained, partial-cut of 50% of canopy cover, and an uncut control) on movement, habitat selection, and abundance of amphibians in Maine. Four landscape-scale replicates of these four forestry treatments were created with each replicate centered on a breeding pool. A total of 8632 emerging juvenile wood frogs were captured and marked at drift fences encircling breeding pools, with 1166 marked wood frogs ( Rana sylvatica), and 13,727 unmarked amphibians captured in drift fence/pitfall arrays at 16, 50, 100, and 150 m from the pools. Our capture results in the different treatments were consistent with previous studies in showing that adult abundance and habitat use differed among species, with wood frogs, spotted salamanders ( Ambystoma maculatum), and eastern red-backed salamanders ( Plethodon cinereus) preferring uncut and partial-cut habitat, and adult green frogs ( Rana clamitans) and American bullfrogs ( Rana catesbeiana) being more tolerant of clearcutting. Spotted salamanders also showed reduced captures with partial canopy removal and increased captures with the retention of CWD. Our results for juvenile amphibians differed from previous research, with lower captures of all study species (statistically significant for seven of nine species) in clearcuts compared to uncut and partial-cut treatments. Clearcuts did not reduce habitat permeability for the low number of marked wood frogs that entered these treatments. Data from marked wood frogs also suggest that both density of conspecifics and habitat quality can influence habitat selection, and potentially dispersal of juvenile amphibians. The avoidance of clearcuts by juveniles of all study species suggests that this silvicultural technique may reduce both abundance and dispersal of many species, rather than just species where adults are known to be forest-dependent. Species may also be affected by partial as well as full canopy removal, and the retention of CWD may play a role in mitigating some of the effects of clearcutting.

Aspen canopy removal and root trenching effects on understory vegetation

Effects of aspen ( Populus tremuloides Michx.) canopy removal and root trenching on understory vegetation were examined at Parkland and Boreal sites in Alberta, Canada to provide a better understanding of the ecological basis of agroforestry systems suitable for north temperate and boreal areas. The greatest changes in understory production (ANPP) were in response to canopy removal with less consistent changes from reduction of root effects. Root trenching did not influence ANPP at the parkland site, but did at the boreal site where it interacted with canopy removal. During severe drought, ANPP under a full canopy at the parkland site increased and may relate to paradoxical understory resource increases during drought. At the parkland site there was a shift away from forb and shrub production under a full canopy towards a greater proportion of graminoids with complete or partial canopy removal. At the boreal site, partial canopy removal resulted in more shrubs and greater production from graminoid species relative to complete overstory removal but only with root trenching using a barrier. Trends in the relative yields of understory species and the cover of plant groups generally followed the patterns observed in ANPP. Leaf litter decreased with the level of canopy removal and may have factored in greater moisture conservation under aspen. Understory production gains with a partial canopy may be attributed to favourable microclimatic conditions of a closed forest retained by the partial aspen cover, while simultaneously increasing PAR penetration. Soil resources were important to ANPP and cover, particularly among forbs, however, when root trenching was significant, it generally coincided with increases in PAR.

Trophic linkages between headwater forests and downstream fish habitats: implications for forest and fish management

This study examined the fluvial transport of invertebrates (aquatic and terrestrial) and coarse organic detritus from forested headwaters in alternatives-to-clearcutting (ATC) harvest units to aquatic habitats downstream in the coastal mountains of southeastern Alaska. Fifty small streams (mean discharge 2.7 L s −1, range 0.1–128.1 L s −1) representing three geographic areas (ATC installations) throughout southeastern Alaska were sampled with 250 μm nets three times per year (April, July, September). Samples were used to assess the subsidy of energy from fishless headwaters to downstream systems containing or potentially containing fish, and to obtain preharvest data on streams for the ATC study. Invertebrates of both aquatic and terrestrial origin were captured, with aquatic taxa averaging roughly 3/4 of the total individuals sampled. Invertebrates and detritus were transported from headwaters during all sampling periods, averaging 163 mg invertebrate dry mass stream −1 day −1 (1.7 mg m −3 water) and 10 g detritus stream −1 day −1 (0.05 g m −3 water), respectively. Based on the frequency of headwater streams in the watersheds studied, and the average amount of food delivered to downstream habitats by these streams, every kilometer of salmonid-bearing stream could receive enough energy from fishless headwaters to support 100–2000 young-of-the-year salmonids. These results illustrate that headwaters are source areas of aquatic and terrestrial invertebrates and detritus, linking upland ecosystems with habitats lower in the catchment. ATC activities are predicted to have variable effects on headwater stream productivity, and subsequent food resources for downstream salmonids. Partial canopy removal is expected to increase solar penetration to the stream and primary and secondary production within these partially harvested sites, and full canopy removal will likely reduce allochthonous inputs of leaf litter into the streams, and reduce stream invertebrate abundance.

Canopy cover effects on nitrogen and phosphorus status in understory vegetation in oak and pine stands

The rate of change of leaf mass, N and P levels in understory vegetation at various levels of canopy cover were measured for 2 years following canopy cover manipulations in northern red oak (Quercus rubra L.) and red pine (Pinus resinosa Ait.) stands in northern Lower Michigan, USA. Canopy cover treatments consisted of clearcut, 25% (50% during first sampling year), 75%, and uncut. Leaf mass, and N and P contents were significantly higher in the clearcut treatment than in other canopy cover treatments, except for the 25% treatment in red pine stands. Leaf N concentrations in understory vegetation were also significantly higher in the clearcut (1991, 20.8mgg−1; 1992, 22.4mgg−1) than in the uncut treatment (1991, 16.5mgg−1; 1992, 16.9mgg−1). Canopy type (northern red oak and red pine) had little influence on understory nutrient status and leaf mass. In addition, fronds of bracken ferns in all canopy cover treatments in both northern red oak and pine stands were a major sink of nutrients in the understory. The results of this study showed that partial canopy removal generally had only a minor impact on understory leaf production and nutrient status compared with clearcuts during the 2-year period following canopy removal.

Responses of available soil nitrogen and litter decomposition to openings of different sizes in dry interior Douglas-fir forests in British Columbia

Selection of an appropriate silvicultural system that maintains productivity requires an understanding of the effects of harvest type on post-harvest changes in nitrogen availability. The effects on inorganic nitrogen availability and litter decomposition of various harvesting systems, including partial canopy removal and a range of clearcut opening sizes, were investigated in a dry Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) forest in southern British Columbia. We measured concentrations of ammonium and nitrate after 6-week buried bag incubations of forest floor and mineral soil samples in replicated plots within uncut forest, within partially harvested forest, and in openings of 1.7, 0.4, and 0.1 ha, from two to seven growing seasons after harvest. Post-incubation nitrate and the proportion of inorganic N as nitrate in forest floor and mineral soil were elevated from 2 to 7 years after harvesting in the 1.7 ha openings. There was no consistent trend of higher ammonium concentration in either uncut forest or 1.7 ha openings. The proportion of inorganic N as nitrate was consistently the lowest in the uncut forest, and often significantly different from any opening treatment, including partial cutting. The increased proportion of inorganic N as nitrate occurred within 11 m of the uncut forest edge. At very low moisture contents, nitrate concentrations tended to zero only in the uncut forest. Leaching of the increased available nitrate is unlikely because of the large increase in grass biomass that occurs after harvesting, and the dry soil moisture conditions during the growing season. Decomposition of Douglas-fir, lodgepole pine and trembling aspen litters, or forest floor was inconsistently, or not affected by any harvest treatment or by distance from, or aspect of, the edge of the forest. The post-harvest increases in nitrate concentrations cannot be attributed to faster decomposition.

Effects of nitrogen availability on northern red oak seedling growth in oak and pine stands in northern Lower Michigan

The nitrogen (N) status and dry weight increment of northern red oak (Quercusrubra L.) seedlings in relation to N availability were examined at various levels of canopy cover and understory removal treatments under field conditions in red oak and red pine (Pinusresinosa Ait.) stands. Net N mineralization rates over two growing seasons following canopy cover treatments were determined by the in situ buried bag technique. Canopy removal increased N mineralization in both oak and pine stands. Net N mineralization rates were ≈1.2–2.2 times higher in the clearcut and the other partial canopy cover treatments than in the uncut stands. Net N mineralization in the same canopy cover treatments was ≈2–3 times higher in red oak stands than in red pine stands. However, red oak seedlings from the same canopy cover treatments in both stand types had similar dry weight, N concentrations, N content, and N-use efficiency despite differences in soil N availability. The only exception was ≈2 times greater seedling dry weight and N content in the red oak clearcuts compared with the red pine clearcuts. The similarity in seedling performance within partial canopy removal or uncut stands may have been due to limiting factors other than N in the red oak stands. Red oak seedlings from litter removal treatments within the clearcuts had significantly higher N-use efficiency than those from the herb and shrub removal treatments. These results suggest that (i) canopy manipulation increases soil N availability; (ii) increases in dry weight and N uptake by red oak seedlings when forest canopies are completely removed are due, in part, to increased available soil N; (iii) red oak seedling response to soil N availability resulting from no or only partial canopy removal may be the same in different stand types (e.g., red oak vs. red pine) because factors other than N, such as light, are limiting.

Density-dependent regulation of ramet recruitment by the red:far-red ratio of solar radiation: a field evaluation with the bunchgrass Schizachyrium scoparium

Depressions in the red to far-red ratio (R:FR) of solar radiation arising from the selective absorption of R (600-700 nm) and scattering of FR (700-800 nm) by chlorophyll within plant canopies may function as an environmental signal directly regulating axillary bud growth and subsequent ramet recruitment in clonal plants. We tested this hypothesis in the field within a single cohort of parental ramets in established clones of the perennial bunchgrass, Schizachyrium scoparium. The R:FR was modified near leaf sheaths and axillary buds at the bases of individual ramets throughout the photoperiod without increasing photosynthetic photon flux density (PPFD) by either (1) supplementing R beneath canopies to raise the naturally low R:FR or (2) supplementing FR beneath partially defoliated canopies to suppress the natural R:FR increase following defoliation. Treatment responses were assessed by simultaneously monitoring ramet recruitment, PPFD and the R:FR beneath individual clone canopies at biweekly intervals over a 12-week period. Neither supplemental R nor FR influenced the rate or magnitude of ramet recruitment despite the occurrence of ramet recruitment in all experimental clones. In contrast, defoliation with or without supplemental FR beneath clone canopies reduced ramet recruitment 88% by the end of the experiment. The hypothesis stating that the R:FR signal directly regulates ramet recruitment is further weakened by evidence demonstrating that (1) the low R:FR-induced suppression of ramet recruitment is only one component of several architectural modifications exhibited by ramets in response to the R:FR signal (2) immature leaf blades, rather than leaf sheaths or buds, function as sites of R:FR perception on individual ramets, and (3) increases in the R:FR at clone bases following partial canopy removal are relatively transient and do not override the associated constraints on ramet recruitment resulting from defoliation. A depressed R:FR is probably of greater ecological significance as a signal of competition for light in vegetation canopies than as a density-dependent signal which directly regulates bud growth and ramet recruitment.

Value of selectively cut deciduous forest for understory herb conservation: An experimental assessment

Deciduous forest stands managed for timber production by selective cutting could also be valuable for conservation of herbaceous plants, if herbs are not negatively affected by partial canopy removal. The short-term effect of partial canopy removal on forest herbs was assessed by recording how many species either disappeared or occurred less frequently 2 years after selective tree cutting (33% or 66% removal of tree basal area) in experimental plots of three sizes (0.01, 0.05, 0.20 ha). A similar percentage of herbaceous species disappeared from permanent quadrats within cut plots (3–12% of herbs) as within adjacent uncut plots (9–13%). The percentage of herbaceous species that occurred less frequently 2 years after cutting was significantly smaller in cut plots (13–36%) than in uncut plots (34–37%). The short-term to longer effect of partial canopy removal on forest herbs was assessed by comparing their frequency in canopy openings and under adjacent intact canopy in stands selectively cut 2, 5 and 9 years earlier. The percentage of herbaceous species occurring less frequently in canopy openings than under intact canopy did not differ significantly among 2-, 5-, and 9-year-old stands (i.e. 29%, 17% and 25%, respectively). Nor did the percentage of herbaceous species absent from canopy openings differ significantly among 2-, 5- and 9-year-old stands (i.e. 14%, 28% and 19%, respectively). These results indicate that selectively cut forest may be valuable for species conservation as well as timber production.