Understory Composition Research Articles

Fine‐Scale Habitat Associations of Red‐Backed Voles in Boreal Mixedwood Stands

Abstract: To provide habitat for late‐successional wildlife species, new ecosystem‐based forest management practices aim to retain elements of complex stand structure, including live residual trees, dead wood legacies, and advanced regeneration, within managed stands. Predicting the effectiveness of these strategies is a challenge for species whose habitat relationships may involve multiple factors and can vary among sites. For 2 years, we live‐trapped a common, late‐successional microtine rodent, the southern red‐backed vole (Myodes [formerly Clethrionomys] gapperi), in 40 1.4‐ha boreal mixedwood sites in Ontario, Canada. Using a neighborhood‐scale modeling approach, we related red‐backed vole capture locations to spatially referenced measures of overstory trees, shrubs and saplings, downed woody debris (DWD), and forest floor substrate. We further assessed how associations with these features varied with availability of the features within a site and as a function of stand management history. In spring, red‐backed voles were associated with trap stations that had, within a 26‐m radius, a dense shrub layer, abundant late‐decay DWD, coniferous understory and litter, and possibly, understory vegetation associated with moist conditions. Positive associations with shrub cover, late‐decay DWD, and a moisture‐associated understory were most apparent in sites in which these elements were scarce (e.g., <1,500 stems/ha of hardwood saplings and short shrubs; <0.8% projected ground cover of late‐decay DWD). The importance of late‐decay DWD; shade‐tolerant, coniferous understory composition; and substrate varied depending on a site's management history, with each feature having a strong positive effect in 47–64‐year‐old stands that were harvested using horse skidding and weaker effects in both 31–40‐year‐old stands that were clearcut with mechanical skidding and >80‐year‐old fire‐origin stands. Our models of fine‐scale habitat relationships for red‐backed voles may be useful in establishing structural retention guidelines suitable for wildlife species dependent on late‐successional habitat structure. In this regard, retaining abundant DWD and 10–30% live trees at harvest may be effective management strategies for providing favorable habitat conditions at localized scales.

Positive association between understory species richness and a dominant shrub species ( Corylus avellana) in a boreonemoral spruce forest

Old growth stands of boreonemoral spruce ( Picea abies) forests frequently have a shrub layer dominated by hazel ( Corylus avellana) – a species which is generally excluded in intensively managed forests due to clearcutting activities. We sampled understory species composition, richness and biomass, as well as environmental variables beneath these two species and also within forest ‘gaps’ in order to determine the effect of overstory species on understory vegetation. Species richness and biomass of herbaceous plants was significantly greater under Corylus compared with plots under Picea and in forest gaps. Indicator species analysis found that many species were significantly associated with Corylus. We found 45% of the total species found under woody plants occurred exclusively under Corylus. Light availability in spring and summer was higher in gaps than under forest cover but no difference was found between plots under Corylus and Picea. Hence, reductions in light availability cannot explain the differences in species composition. However, Ellenberg indicator values showed that more light demanding species were found under Corylus compared to Picea, but most light demanding species were found in gaps. The litter layer under Picea was three times thicker than under Corylus and this may be an important mechanism determining differences in understory composition and richness between the woody species. The presence of Corylus is an important factor enhancing local diversity and small-scale species variation within coniferous stands. Hence, management should maintain areas of Corylus shrubs to maintain understory species diversity in boreal forests.

Land-use history, historical connectivity, and land management interact to determine longleaf pine woodland understory richness and composition

Restoration and management activities targeted at recovering biodiversity can lead to unexpected results. In part, this is due to a lack of understanding of how site-level characteristics, landscape factors, and land-use history interact with restoration and management practices to determine patterns of diversity. For plants, such factors may be particularly important since plant populations often exhibit lagged responses to habitat loss and degradation. Here, we assess the importance of site-level, landscape, and historical effects for understory plant species richness and composition across a set of 40 longleaf pine Pinus palustris woodlands undergoing restoration for the federally endangered red-cockaded woodpecker in the southeastern United States. Land-use history had an overarching effect on richness and composition. Relative to historically forested sites, sites with agricultural histories (i.e. former pastures or cultivated fields) supported lower species richness and an altered species composition due to fewer upland longleaf pine woodland community members. Landscape effects did not influence the total number of species in either historically forested or post-agricultural sites; however, understory species composition was affected by historical connectivity, but only for post-agricultural sites. The influences of management and restoration activities were only apparent once land-use history was accounted for. Prescribed burning and mechanical overstory thinning were key drivers of understory composition and promoted understory richness in post-agricultural sites. In historically forested sites these activities had no impact on richness and only prescribed fire influenced composition. Our findings reveal complex interplays between site-level, landscape, and historical effects, suggest fundamentally different controls over plant communities in longleaf pine woodlands with varying land-use history, and underscore the importance of considering land-use history and landscape effects during restoration.

The understory bird communities in monsoon evergreen broadleaved forest of Mengyang, Xishuangbanna, Yunnan during the dry season.

Understory birds were sampled by mist nets in monsoon evergreen broadleaved forest of Mengyang, Xishuangbanna, Yunnan from October 2008 to March 2009. A total of 1423 individuals of 90 species representing 28 families and 7 orders were captured. The dominant birds were Sliver-breasted Broadbill (Serilophus lunatus), Brown-cheeked Fulvatta (Alcippe poioicephala), White-throated Bulbul (Alophoixus pallidus), Golden-spectacled Warbler (Seicercus burkii), White-tailed Robin (Cinclidium leucurum), Black-breasted Thrush (Turdus dissimilis), Streak-Breasted Jungle Babbler (Pellorneum ruficeps), and Buff-breasted Jungle Babbler (Trichastoma tickelli). Resident birds, the major species of the understory, accounted for 89.3 percent of total captures. The mean capture rate was 9.0 individuals/(100 net-hours). The capture rate differed significantly between months, highest in December 2008 (12.5±1.3）individuals/(100 net·hours), lowest in February 2009 (5.2±0.6 )individuals/(100 net·hours). One important characteristic is more species richness and lower density of birds in Xishuangbanna compared to understory bird composition of South China. Another characteristic is lower babblers' abundance. Sliver-breasted Broadbill, National Key Protection Bird, is one of dominant birds. Thus its habitate conservation needs further concern in Xishuangbanna.

The Effects of Cropping Systems on Avian Communities in Cacao and Banana Agro-Forestry Systems of Talamanca, Costa Rica

Multispecies agro-forestry is generally lauded for providing ecosystem services, especially in tropical environments. Avian communities contribute to services such as biodiversity and pest management. Characterizing and evaluating avian community composition in similar cropping systems will help optimize management for ecosystem services. We examined the relationship between cropping system vegetation and avian communities in four shaded agro-forestry systems common to the Limprovince of Costa Rica: abandoned and managed systems of cacao, cacao with banana, and banana. During two field seasons, we detected 2605 birds from 106 species and identified 2791 trees and shrubs from 62 morphospecies. We compared vegetation and avian species richness across systems with mixed-effects linear models. Canopy, understory, and groundcover vegetation differed among agro-forestry systems. More ground- and understory-foraging forest species were detected in agro-forestry systems lacking banana, whereas richness of agricultural generalist species was highest in systems with banana. Richness of understory- and ground- foraging species correlated with understory tree species richness and leaf litter. Our results indicate that shaded cacao and banana systems can have similar canopy- foraging species richness that includes both agricultural and woodland generalist species, but that interspersing banana with cacao can adversely influence understory forest bird community composition. Agro-forests with diverse understory vegetation support more understory-foraging bird species that have proven valuable in pest management. Abstract in Spanish is available at http: //www.blackwell-synergy.com/loi/btp.

Understory vegetation in reclaimed and unreclaimed post-mining forest stands

In the Sokolov coal mining district of the Czech Republic, spoil heaps are reclaimed by forest plantations, which are planted directly into the rough substrate (alkaline tertiary clay). We compared the understory that spontaneously developed in seven types of forest stands: one type was unreclaimed stands (spontaneously overgrown by Betula pendula and Salix caprea) and six were plantations, each dominated by one tree genus ( Alnus, Larix, Picea, Pinus, Quercus, and Tilia). The age of the stands ranged from 22 to 33 years. The cover of understory plant species in each stand was estimated, and 16 other environmental and community variables were quantified. The number of plant species was highest in Quercus, Larix, and unreclaimed stands, and was negatively correlated with forest canopy cover and with the cover of the understory dominant, the grass Calamagrostis epigejos. Understory composition differed considerably among the types of forest stands and was significantly explained by the measured environmental variables. Forward selection in redundancy analysis indicated that the most important variable driving understory composition was thickness of the fermentation layer, which is clearly connected with soil development. Environmental variables, including fermentation layer, were also affected by the type of forest stand. Therefore, all of the explained variability in understory composition could be attributed to the type of forest stand, which apparently affected the understory by its impact on soil formation. However, the most favorable soil conditions were not favorable for understory development, as they supported mainly C. epigejos, which suppressed other species. Our study also showed that even in the absence of reclamation measures, mining sites can be successfully restored due to spontaneous succession.

Structure and composition changes following restoration treatments of longleaf pine forests on the Gulf Coastal Plain of Alabama

Longleaf pine ( Pinus palustris Mill.) forests of the Gulf Coastal Plain historically burned every 2–4 years with low intensity fires, which maintained open stands with herbaceous dominated understories. During the early and mid 20th century however, reduced fire frequency allowed fuel to accumulate and hardwoods to increase in the midstory and overstory layers, while woody shrubs gained understory dominance. In 2001, a research study was installed in southern Alabama to develop management options that could be used to reduce fuel loads and restore the ecosystem. As part of a nationwide fire and fire surrogates study, treatments included a control (no fire or other disturbance), prescribed burning only, thinning of selected trees, thinning plus prescribed burning, and herbicide plus prescribed burning. After two cycles of prescribed burning, applied biennially during the growing season, there were positive changes in ecosystem composition. Although thinning treatments produced revenue, while reducing midstory hardwoods and encouraging growth of a grassy understory, burning was needed to discourage regrowth of the hardwood midstory and woody understory. Herbicide application followed by burning gave the quickest changes in understory composition, but repeated applications of fire eventually produced the same results at the end of this 8-year study. Burning was found to be a critical component of any restoration treatment for longleaf communities of this region with positive changes in overstory, midstory and understory layers after just three or four burns applied every 2 or 3 years.

Understory vegetation indicates historic fire regimes in ponderosa pine-dominated ecosystems in the Colorado Front Range

Question: Can current understory vegetation composition across an elevation gradient of Pinus ponderosa-dominated forests be used to identify areas that, prior to 20th century fire suppression, were characterized by different fire frequencies and severities (i.e., historic fire regimes)? Location: P. ponderosa-dominated forests in the montane zone of the northern Colorado Front Range, Boulder and Larimer Counties, Colorado, USA. Methods: Understory species composition and stand characteristics were sampled at 43 sites with previously determined fire histories. Indicator species analyses and indirect ordination were used to determine: (1) if stands within a particular historic fire regime had similar understory compositions, and (2) if understory vegetation was associated with the same environmental gradients that influence fire regime. Classification and regression tree analysis was used to ascertain which species could predict fire regimes. Results: Indicator species analysis identified 34 understory species as significant indicators of three distinct historic fire regimes along an elevation gradient from low- to high-elevation P. ponderosa forests. A predictive model derived from a classification tree identified five species as reliable predictors of fire regime. Conclusions: P. ponderosa-dominated forests shaped by three distinct historic fire regimes have significantly different floristic composition, and current understory compositions can be used as reliable indicators of historical differences in past fire frequency and severity. The feasibility demonstrated in the current study using current understory vegetation properties to detect different historic fire regimes, should be examined in other fire-prone forest ecosystems.

The influence of canopy patch mosaics on understory plant community composition in boreal mixedwood forest

We assessed the composition of understory vascular plant communities in relation to the mosaic of canopy patch types, and their associated structure and environment, within unmanaged, mature boreal mixedwood forests in western Canada. Within a 30 km 2 area, we sampled patches of four different canopy types: conifer-dominated, broadleaf-dominated, mixed conifer-broadleaf, and canopy gaps (total n = 98). There were significant differences in understory composition among the four patch types (based on multi-response permutation procedure (MRPP)) and these were mainly due to differences in relative abundances of understory species. The understory communities of conifer patches were characterized by low abundances of shade intolerant species while shade-tolerant and evergreen species were indicators (based on an indicator species analysis (ISA)). Understory communities under gap and broadleaf patches were characterized by higher abundances of grasses and shade intolerant species. Gap, broadleaf, and mixed patches had higher abundances of certain shrub species than did conifer patches. The patch types also differed in terms of their environmental conditions. Conifer patches had drier, cooler soils and the lowest understory light. Broadleaf patches had the warmest soils while understory light during the leaf-off period was similar to that of canopy gaps. Gap patches had the lowest litter cover and PO 4 − availability and the highest light. Seven environmental variables (soil moisture, soil temperature, total light during the leaf-off period, cover of coarse and fine downed woody material, and availability of NH 4 + and Ca 2+) were significantly related to understory species composition (in a constrained ordination by means of a distance-based redundancy analysis (db-RDA); 16.5% of variation in understory community data explained). Even within a single patch type, there was substantial environmental variation that was related to understory species composition. Our study suggests that the mosaic of canopy patches within mixedwood forests supports coexistence of both early and late successional understory plant species in mixedwood stands. Maintaining the mixture of canopy patch types within mixedwood stands will be important for conserving the natural patterns of understory plant composition in boreal mixedwood forests.

Effects of a Prescribed Fire on Understory Vegetation, Carbon Pools, and Soil Nutrients in a Longleaf Pine-Slash Pine Forest in Florida

We quantified fire-driven loss and post-fire recovery of understory and soil carbon (C) and nutrient pools for one to three years following a single prescribed fire in a naturally regenerated longleaf (Pinus palustris Mill.) and slash pine (Pinus elliottii Engelm. var. elliottii) forest located in north central Florida. Fire immediately reduced total aboveground understory C and nitrogen (N) pools, but these pools recovered to pre-fire levels after three years. Our results also showed that the effect of fire on the understory composition and structure was only short-lived. Prescribed fire significantly reduced total C and N pools in the forest floor (F and H horizons), and this effect persisted for at least one year postfire. Available NH4 , PO43-, Ca2 , Mg2, and K concentrations in the forest floor decreased immediately after fire, but increased in the surface mineral soil (O to 5 cm depth); Ca2 , Mg2 , and K remained elevated for the first year after fire. Fire immediately reduced total ecosystem C and N pools by 40% and 27%, respectively, emitting 3860 g C m-2 and 170 g N m-2 to the atmosphere. The pools recovered to 67% and 76% of pre-fire C and N pools, respectively, after one year. Of the pools measured, C and N recovery in forest floor materials was the slowest, and projections of initial recovery rates suggest that it will take more than six years, the previous fire interval, to reach pre-fire levels. This slow recovery may indicate variation in past rates of forest floor accumulation due to management practices as well as effects of the severity of this or previous fires.

Paying the Extinction Debt in Southern Wisconsin Forest Understories

The lack of long-term baseline data restricts the ability to measure changes in biological diversity directly and to determine its cause. This hampers conservation efforts and limits testing of basic tenets of ecology and conservation biology. We used a historical baseline survey to track shifts in the abundance and distribution of 296 native understory species across 82 sites over 55 years in the fragmented forests of southern Wisconsin. We resurveyed stands first surveyed in the early 1950s to evaluate the influence of patch size and surrounding land cover on shifts in native plant richness and heterogeneity and to evaluate changes in the relative importance of local site conditions versus the surrounding landscape context as drivers of community composition and structure. Larger forests and those with more surrounding forest cover lost fewer species, were more likely to recruit new species, and had lower rates of homogenization than smaller forests in more fragmented landscapes. Nearby urbanization further reduced both alpha and beta understory diversity. Similarly, understory composition depended strongly on local site conditions in the original survey but only weakly reflected the surrounding landscape composition. By 2005, however, the relative importance of these factors had reversed such that the surrounding landscape structure is now a much better predictor of understory composition than are local site conditions. Collectively, these results strongly support the idea that larger intact habitat patches and landscapes better sustain native species diversity and demonstrate that humans play an increasingly important role in driving patterns of native species diversity and community composition.

Introduced deer reduce native plant cover and facilitate invasion of non-native tree species: evidence for invasional meltdown

Invasive species are a major threat to native communities and ecosystems worldwide. One factor frequently invoked to explain the invasiveness of exotic species is their release in the new habitat from control by natural enemies (enemy-release hypothesis). More recently, interactions between exotic species have been proposed as a potential mechanism to facilitate invasions (invasional melt- down hypothesis). We studied the effects of intro- duced deer on native plant communities and exotic plant species on an island in Patagonia, Argentina using five 400 m 2 exclosures paired with control areas in an Austrocedrus chilensis native forest stand. We hypothesized that introduced deer modify native understory composition and abundance and facilitate invasion of introduced tree species that have been widely planted in the region. After 4 years of deer exclusion, native Austrocedrus and exotic Pseudots- uga menziesii tree sapling abundances are not differ- ent inside and outside exclosures. However, deer browsing has strongly inhibited growth of native tree saplings (relative height growth is 77% lower with deer present), while exotic tree sapling growth is less affected (relative height growth is 3.3% lower). Deer significantly change abundance and composition of native understory plants. Cover of native plants in exclosures increased while cover in controls remained constant. Understory composition in exclosures after only 4 years differs greatly from that in controls, mainly owing to the abundance of highly-browsed native species. This study shows that introduced deer can aid the invasion of non-native tree species through negatively affecting native plant species.

Floristic and ecological differences between recent and ancient forests growing on non-acidic soils

The aim of this work was to investigate differences in soil chemistry and understory composition between recent forests (sites afforested in the last 170 years) and ancient forests growing on non-acidic soils. The study was carried out on hardwood forests at moderate elevation (400–600m asl) in the Jura Mountains (N.E. France) on four main pedological substrates with different characteristics. The floristic composition of 127 stands from recent forests (n=65) or ancient forests (n=62) was surveyed. Some functional traits and the Ellenberg indicator values of the surveyed species were recorded. In addition, the topsoil from 30 stands was analysed. The composition of the flora was analysed by Detrended Correspondence Analysis and the species which were typical of one class of forest age were identified using a chi-square (χ2) test. The difference between forest classes for plant traits, their indicator values, or soil chemistry was tested using the generalized linear model and Bonferroni t-tests (or Kruskall–Wallis tests). The floristic composition of the ancient forests was significantly different from that of the recent forests and was characterized by a high occurrence of shrub species in recent forests. These differences were associated with higher specific leaf area, low-range seeds dispersal, and some life forms like geophytes. There was no clear difference in soil chemistry between the two classes of forests, except for δ15N values. The weakness of the difference in the soil between ancient and recent forests suggested that changes in soil chemistry caused by a former agricultural land use were not responsible for the differences in understory composition recorded. The differences in functional traits between the two forest classes supported this conclusion. We finally concluded that (i) past land use modifies the vegetation composition of current forests, even on neutral soils and that (ii) in our context, biological filters were probably responsible for these changes.

Impacts of woodchip amendments and soil nutrient availability on understory vegetation establishment following thinning of a ponderosa pine forest

Mechanical thinning for fire mitigation has become increasingly widespread in recent years throughout the western United States. A common practice in fire-mitigation procedures is the conversion of slash into chipped mulch (referred to as “woodchips”) that is spread on-site. Here, we investigated: (1) the effect of woodchip amendments on soil nitrogen availability, and (2) the influence of potential interactions between woodchip amendments and soil nitrogen availability on patterns of understory plant establishment in a thinned montane forest in the Front Range of Colorado. We created a gradient of soil nitrogen availability among experimental plots by applying sugar to reduce plant-available nitrogen and applying ammonium nitrate to increase plant-available nitrogen. Soil and resin bag analyses confirmed the effectiveness of the nitrogen manipulations. Nitrogen manipulations did not affect understory species richness or diversity, but increased nitrogen availability promoted a disproportionate increase in the cover of non-native forbs over the three-year post-treatment interval. Woodchips did not alter inorganic nitrogen availability at ambient levels of soil fertility during the first two years of the study, but were associated with increased soil N availability in the third growing season. Woodchip additions were associated with significantly lower species richness, diversity, and overall plant cover than found in unchipped plots. The observed reduction in plant cover affected native and non-native species similarly, although certain species had distinctive responses to woodchip amendments. On the whole, woodchips excluded more species than they promoted, and the physical effects of woodchips appeared to be more important than soil nitrogen status in influencing the understory composition of this area following thinning. At this site, approximately 60% of the plant cover in the three years following thinning operations was comprised of non-native plant species. Thus, the thinning activity, itself, promoted non-native understory plant species cover, but the application of woodchip mulch reduced vegetation cover and native species richness relative to the thinned areas that did not receive woodchips. This effect was largely independent of soil nitrogen availability during the first three years following thinning.

Fine-Scale Patchiness in Fuel Load Can Influence Initial Post-Fire Understory Composition in a Mixed Conifer Forest, Sequoia National Park, California

ABSTRACT: Many forests, including the mixed-conifer forest of the Sierra Nevada, California, historically experienced a fire regime that generated considerable within- and among-fire environmental variability. Fire suppression has resulted in a heavier, more continuous fuel bed, which can cause today's prescribed fires to be considerably more homogeneous. To evaluate the potential importance of variability in fire severity on post-fire plant communities, I conducted an experiment to test whether understory species respond differently to sites burned under a heavy fuel load versus sites that burned under a light fuel load. Woody fuel was added or removed from small forest plots in order to manipulate the fire severity during prescribed fire. The fuel load manipulations affected which species survived fire as well as which species germinated after fire. Seven species (Chimaphila menziesii, Chrysolepis sempervirens, Osmorhiza chilensis, Pyrola picta, Phacelia hydrophylloides, Rubus parviflorus, and Smilacina...

Floristic Diversity in Managed Forests: Demography and Physiology of Understory Plants Following Disturbance in Southern New England Forests

Current interest in the conservation of biodiversity is generating a need for forest management and silvicultural techniques designed to maintain the integrity of ecosystems while satisfying society's need for timber resources. The conservation of forest understory plant communities should be a major emphasis of this effort as they contain the majority of plant diversity in most U.S. forests and play a significant role in many ecosystem functions. This article reviews the literature regarding plant responses to disturbance—most importantly changes in light environments—and applies that information to forest management. A comparison of developmental plasticity and rapid acclimation as response pathways is used to discuss plant level responses. At the landscape level, diversity models, silviculture treatments, and site characteristics are used to discuss changes in understory community composition following disturbance. Results of ongoing research on the effects of forest management on floristic patterns for southern New England forests are summarized.

Effects of introduced ungulates on forest understory communities in northern Patagonia are modified by timing and severity of stand mortality

Natural disturbances such as fires, windstorms, floods, and herbivory often act on plant communities, affecting their structure and the abundance and composition of their species. Most research has focused on the effects of single disturbances on plant communities whereas the synergistic effects of several disturbances have received less attention. In this study, we evaluated how timing and severity of tree mortality modified plant use by introduced deer and early post-mortality successional trajectories in northern Patagonian conifer forests. We sampled understory composition and deer use in Austrocedrus chilensis (cipres de la cordillera) forest stands undergoing varying timing and severity of forest mortality as reconstructed using dendroecological techniques. In addition, we evaluated the effect of fallen logs on plant composition and deer use of plants by monitoring areas of massive dieback where fallen logs had been removed for fire hazard reduction, and nearby control areas not subjected to such removal. Stepwise regression analyses showed that history and severity of tree mortality strongly influence plant composition and deer use of plants. For deer use (with pellet counts and browsing index as response variables), results showed a positive relationship with degree of stand mortality and a negative relationship with cover of fallen logs. Similarly, cover of unpalatable shrub species was explained by canopy mortality history, whereas cover of palatable shrub species was positively associated with severity of canopy mortality. In areas where fallen logs had been removed, pellet counts were six times higher than those in control areas. Though total shrub species cover was similar between log removal and control areas, proportion of unpalatable shrubs increased in areas where fallen logs had been removed. In conclusion, deer use of plants was strongly limited by tall fallen logs, allowing palatable species to establish and grow. Fallen log removal accelerated deer entrance and changed understory composition toward more browse-resistant and unpalatable species. These results underscore the importance of considering the dynamics (timing, severity, and extent) of fallen woody debris influencing understory herbivory and post-disturbance succession. In addition, experimental results underpin the importance of maintaining snags and large woody debris in disturbed landscapes where salvage logging is a routine procedure.

Comparison of potential non-timber forest products in intensively managed young stands and mature/old-growth forests in south-central British Columbia

Development of understory vegetation has been influenced by the many densely stocked second-growth forest stands in North America, which have an extended stem exclusion successional stage. Understory composition and structure is important for ecosystem functioning, while also having social and economic value through the harvest of certain herb and shrub species. The potential for co-management of young and mature, managed and unmanaged stands for timber and non-timber forest products (NTFPs) was assessed in two separate replicated experiments. Experiment A examined pole-sized lodgepole pine ( Pinus contorta) stands that had been pre-commercially thinned (PCT) to target densities of 250, 500, 1000, and 2000 stems/ha. Half of each of these four thinning units was repeatedly fertilized, resulting in eight experimental units. Experiment B examined six different stand types: young plantations, pole-sized lodgepole pine stands either PCT, PCT plus repeated fertilization, or unthinned, mature, and old growth. Fifty-four herb and shrub species were identified as potential NTFPs, with the responses of individual species, as well as mean total herb, shrub, berry-producing and overall total NTFPs being assessed. In Experiment A, mean total abundance (crown volume index) of NTFPs, as well as mean total herb NTFPs were significantly greater in fertilized than in unfertilized stands. Thinning treatments did not significantly affect NTFP volume, however, fertilization treatments produced five significant responses by individual species ( Achillea millefolium, Epilobium angustifolium, Taraxacum officinale, Arctostaphylos uva-ursi, Rubus idaeus). In Experiment B, four of the six species responses that were significant had greater abundance in young, managed stands (young plantation, thinned, or thinned-fertilized) than in the unmanaged stands. Mean total NTFP volume and mean total herb NTFP volume also followed this pattern. A. uva-ursi, E. angustifolium, Lonicera involucrata, Sorbus sitchensis and Thalictrum occidentale all had significantly higher abundance in young, managed stands than in all other treatments. Results suggest that co-management for timber and NTFPs is possible in this ecosystem, with further research needed to evaluate livelihood values of these crops.

SHIFTS IN SOUTHERN WISCONSIN FOREST CANOPY AND UNDERSTORY RICHNESS, COMPOSITION, AND HETEROGENEITY

We resurveyed the under- and overstory species composition of 94 upland forest stands in southern Wisconsin in 2002-2004 to assess shifts in canopy and understory richness, composition, and heterogeneity relative to the original surveys in 1949-1950. The canopy has shifted from mostly oaks (Quercus spp.) toward more mesic and shade-tolerant trees (primarily Acer spp.). Oak-dominated early-successional stands and those on coarse, nutrient-poor soils changed the most in canopy composition. Understories at most sites (80%) lost native species, with mean species density declining 25% at the 1-m2 scale and 23.1% at the 20-m2 scale. Woody species have increased 15% relative to herbaceous species in the understory despite declining in absolute abundance. Initial canopy composition, particularly the abundance of red oaks (Quercus rubra and Q. velutina), predicted understory changes better than the changes observed in the overstory. Overall rates of native species loss were greater in later-successional stands, a pattern driven by differential immigration rather than differential extirpation. However, understory species initially found in early-successional habitats declined the most, particularly remnant savanna taxa with narrow or thick leaves. These losses have yet to be offset by compensating increases in native shade-adapted species. Exotic species have proliferated in prevalence (from 13 to 76 stands) and relative abundance (from 1.2% to 8.4%), but these increases appear unrelated to the declines in native species richness and heterogeneity observed. Although canopy succession has clearly influenced shifts in understory composition and diversity, the magnitude of native species declines and failure to recruit more shade-adapted species suggest that other factors now act to limit the richness, heterogeneity, and composition of these communities.

Slow understory redevelopment after clearcutting in high mountain forests

Besides natural tree regeneration itself, the development of the forest understory community is highly indicative of the ecological recovery of forest stands post-harvesting, and therefore of the sustainability of forest management. High mountain forests might show particularly slow recovery of the understory plant community because of harsh environmental conditions. We compared understory community richness and composition among three age classes of forest stands in the subalpine Engelmann Spruce–Subalpine Fir zone in the interior of British Columbia, Canada. Species composition was found to differ significantly between mature stands (>110 years old and never harvested) and both recent clearcuts (5–8 years old) and the oldest clearcuts present in the study area (second growth: 24–28 years old). A non-metric multidimensional scaling (NMDS) ordination revealed no unidirectional return of species composition in harvested stands towards that of mature forest; indeed, plots in recent clearcuts and second growth stands were similar to one another and clearly separated from the mature stands. Indicator Species Analysis revealed that moss species were particularly indicative of mature forest, with four moss species being common in mature stands but absent from both younger stages. Compared to what has been reported for lower elevation coniferous forests, e.g. in the U.S. Pacific Northwest, redevelopment of the understory appears to be slow after harvesting in these high elevation mountain forests. Rotation intervals that consider the natural temporal pattern of species turnover and the occurrence interval of major natural disturbances (here: fire) should provide effective approaches to sustainable forest management of these forests.