Understory Diversity Research Articles

Dominant plant species influence nematode richness by moderating understory diversity and microbial assemblages

Belowground assemblages are tightly linked to the aboveground vegetation, and often differ between plant species and vegetation types due to direct and indirect influences. However, the relative contribution of these direct and indirect influences of plants on belowground organisms differs among taxa and remains poorly understood. We established a plant removal experiment to better understand the effects of dominant plant species on nematode assemblages in an alpine meadow on the Tibetan plateau. We quantified plant community diversity, soil microbial assemblage richness and edaphic properties to explore how a dominant shrub and graminoids affect nematode assemblage structure and community-weighted mean (CWM) biomass using structural equation modelling (SEM). We found contrasting responses of nematode richness and CWM biomass of nematodes to the removal of shrubs and graminoids, including an intriguing interaction between them. The latter indicates that interactions between shrubs and graminoids modify nematode communities rather than their independent effects. Our results further suggest that dominant plants predominantly indirectly influence nematode richness through changes in biotic variables, specifically understory diversity, and bacterial and fungal richness. However, the dominant plants had no direct and limited indirect effects on CWM nematode biomass, which instead increased with soil nitrogen content, and decreased with soil pH, carbon and ammonium content. Our results provide insight into the relative role of direct and indirect influences on belowground assemblages and highlight the importance of dominant plants in maintaining belowground diversity. By contrast, edaphic properties appear more important to belowground biomass, likely reflecting longer term influences of the plant community on resource availability and quality. Vegetation changes in grassland, such as reduced dominance of shrubs and graminoids, might therefore reduce soil biodiversity relatively rapidly but contribute to longer term impacts through changes in biogeochemical cycles.

Resilience of Oregon white oak to reintroduction of fire

BackgroundPacific Northwest USA oak woodlands and savannas are fire-resilient communities dependent on frequent, low-severity fire to maintain their structure and understory species diversity, and to prevent encroachment by fire-sensitive competitors. The re-introduction of fire into degraded ecosystems is viewed as essential to their restoration, yet can be fraught with unintended negative consequences. We examined the response of mature Oregon white oak (Quercus garryana Douglas ex Hook.; Garry oak) to “first entry” woodland restoration burns following long fire-free periods.ResultsThirteen to twenty-five months post burn, topkill of oaks was minimal (3%) and mortality was rare in three prescribed burns, despite high levels (mean = 92%) of crown scorching, and irrespective of proportional duff consumption around oak bases (mean = 21%). Percentage of crown scorch volume was the strongest predictor of oak crown dieback, but response was highly variable, especially when canopy scorch was ≥80%. Comparison of our results with FOFEM (First Order Fire Effects Model), a common fire effects model, revealed high model inaccuracy, likely due to lack of a species-specific equation for prediction of Oregon white oak mortality.ConclusionsThe results of this study indicate that Oregon white oak is highly resistant to mortality in restoration burns, even following long fire-free intervals. Prescribed fire is not contraindicated in areas with extant mature oaks, and may promote oak regeneration via basal sprouting.

Recovery of understory assemblage along 50 years after shelterwood cut harvesting in Nothofagus pumilio Southern Patagonian forests

Harvesting modifies the understory due to changes in the overstory structure, microclimate and soil properties. The impact is directly related to the harvesting intensity, although studies are usually developed in logged areas (low impact) avoiding stockpiled areas (high impact). Understory resilience is quite variable, and recovery time remains unknown for different management practices and different temperate forests. The objectives of this work were: (i) to evaluate recovery of understory vascular plants and forest structure in Nothofagus pumilio forests of South Patagonia (Argentina) along a chronosequence of years-after-harvesting (YAH) (1–5, 6–10, 20–30, >50) in shelterwood cuts compared to unharvested forests (UF), and (ii) to analyze differences in the understory recovery in areas with different impact intensity due to the harvesting: low impact harvesting (LIH) in logged areas vs. high impact harvesting (HIH) in stockpiled areas. We selected 12 harvested areas with different YAH, and in each area we sampled three forest treatments (LIH, HIH, UF) with 5 replicas (N = 12 × 3 × 5 = 180). In each sampling unit we analyzed the forest structure (primary or remnant overstory and secondary forests), environmental (soil moisture) and understory variables (richness, cover and species assemblage patterns) through univariate and multivariate statistical analyses. Remnant forest structures presented significant decay in the dominant height along the chronosequence, and an increasing in the secondary forest variables, as well as in the crown cover (remnant + secondary forests). Lower values of forest structure variables were observed in HIH than LIH, but without significant differences between them. Most of treatment levels presented significant differences with UF, and values become similar with time. Understory presented significant differences in richness and cover along the chronosequence, with values become more similar to UF on time. Harvesting impact levels also presented differences, e.g. 104% and 144% more exotic species cover in LIH and HIH compared with 20% in UF. However, greater significant differences were found among treatments for their species assemblage patterns, mainly in the first stages of the chronosequence (e.g., between UF and LIH at 6–10 YAH); meanwhile in the last stage (>50 YAH), species assemblage patterns become similar with UF, both for LIH and HIH. We conclude that understory vascular plant assemblage of N. pumilio forests recovers patterns after 50 YAH, being more similar to original ones as the crown cover reaches similar values to unharvested forests, showing N. pumilio forests as highly resilient to shelterwood cut harvesting, even in high impacted areas.

Does burn severity affect plant community diversity and composition in mixed conifer forests of the United States Intermountain West one decade post fire?

BackgroundWildfire is an important ecological process in mixed conifer forests of the Intermountain West region of the USA. However, researchers and managers are concerned because climate warming has led to increased fire activity in recent decades. More area burned will result in larger land areas in early successional stages and will potentially limit tree establishment; therefore, evaluating long-term forest understory response to fire is important. We evaluate the impact of burn severity, overstory canopy cover, topography, and climate on understory plant community diversity and composition in seven wildfires, 9 to 12 years post fire, along a broad climate gradient from dry to moist mixed conifer forests in Idaho, Montana, and Washington, USA.ResultsClimate was the most important driver for species diversity and composition, but a burn severity gradient was detectable in the species data one decade post fire. A strong overlap in species composition between burn severity levels was documented, but dispersion was lower for high burn severity sites, indicating that those sites are still recovering. Local species richness and diversity had a nonlinear relationship with the burn severity index dNBR, with a maximum at low to moderate burn severity; the relationship was stronger in moist climates. Functional trait analysis revealed higher grass and forb cover in high-severity burns, higher cover of tree seedlings, residual and off-site colonizers in burned areas, and more shade-tolerant species in unburned areas. Of the 270 species recorded, 10% were introduced; however, only three were of noxious status and two were invasive annual grasses, generally occurring on dry sites.ConclusionsThe understory plant community was not fundamentally altered by these fires and fire contributed to increased species diversity both locally and regionally, suggesting that low to moderate burn severity fire is a treatment that contributes to long-term maintenance of a diverse and productive understory. Individual species traits were significant drivers of understory species assemblages and, as future change in climate and fire regimes leads to shifts in species composition, anticipation of consequences will be important. Although invasive species occurred at low cover levels, noxious weeds and invasive annual grasses will continue to be management challenges, particularly in dry regions of mixed conifer forests.

Assessing the effects of shrubs on ecosystem functions in arid sand dune ecosystems

Shrub species play an important role in providing ecosystem functions and these functions may vary based on dominant shrubs and their facilitation roles in the arid ecosystems. This study was done to assess the potential of three shrubs (Tamarix macatensis, Calligonum polygonoides, and Haloxylon ammodendron) for providing three functions i.e. soil fertility, soil stability, and habitat provision in sand dune ecosystems of Iran. Two ecological indicators were selected to measure each function (soil organic matter content and litter mass for soil fertility; mound height and clay content for soil stability; understory plants and macrofauna diversity for habitat provision). As well, some shrub traits were measured for each shrub to assess their relationships with ecological indicators. Results showed that shrubs can significantly change ecological indicators (p < 0.05), except H. ammodendron which had no significant effect on habitat provision (p < 0.05). There were some relationships between shrub traits and provision of ecosystem functions. Stem density and litter production were the most important functional traits affecting regulating and habitat functions. Also, there was a significant positive relationship between soil fertility, soil stability and habitat provision (p < 0.05). It can be recommended that planting spherical shrubs with high potential for litter production will enhance functions and can sustainably maintain sand dunes in arid ecosystems.

Tree species impact on understory vegetation: Vascular plant communities of Scots pine and Norway spruce managed stands in northern Europe

The tree species used in production forests can have direct implications for the understory vegetation, due to species-specific differences in the environmental conditions provided, and silviculture applied. In southern Sweden, there is an ongoing shift from even-aged managed stands of Scots pine (Pinus sylvestris) to even-aged Norway spruce (Picea abies). Here we evaluate the potential ecological consequences of these conversions by surveying the understory vascular plants, stand structural characteristics, and associated understory light levels in three age categories of Scots pine and Norway spruce stands. We quantify the extent of difference in light transmittance between the two stand types, and find large differences in understory abundance, especially among the dwarf shrubs species. Whereas bilberry (Vaccinium myrtillus) generally dominated Scots pine stand understory, the understory of Norway spruce stands was comparably sparse. Differences in vascular plant community composition indicate associated differences between the two stand types in the conditions prior to stand establishment, and subsequent understory development. In Scots pine stands the high abundance of dwarf shrubs may be outcompeting other species of vascular plants, causing a decline in species richness. In Norway spruce stands, species richness and abundance was instead apparently inhibited by limited light transmittance. In these stands generalist ruderal species and remnants from previous land use constituted a considerable part of plant species composition. Our findings suggest that the regional replacement of Scots pine with Norway spruce will lead to a noticeable loss of understory diversity, for which the decline in Vaccinium species will be the most prominent. We discuss the associated implications of our results for forest ecosystem services, and how shortened rotation lengths in Norway spruce stands would compound these impacts.

Diversity of understorey at Singkil Swamp Wildlife Reserve

Singkil Swamp Wildlife Reserve (SSWR) is the only conservation area in the coastal lowlands of Aceh as well as habitat of protected large mammals and migratory birds. Many publications related to Singkil swamp biodiversity have been published; however the understory communities were not studied. Understory communities are important part of peat swamp ecosystem. This study aimed to calculate the understory diversity and distribution using quadrat method. Nine sites were selected and 25 2m by 2m plots were established in each sites. All understorey species within plot were identified and measured their coverage. Overall, 134 species in 42 families were recorded which the community diversity in each site was categorized as moderate and high. Araceae was recorded as richest family (14 species), followed by Orchidaceae (10 species) and Annonaceae (8 species). Subsequently, there are 17 families (40.5%) categorized as very scare family which each family only contains 1 species. It means the vulnerability of the last family group is very high due to the ecosystem disturbance. Some invasive alien species were found at disturbed areas. Therefore, the pristine peatswamp ecosystem is needed to conserve as well as the disturbed area is needed to restore based on scientific approaches.

Understory Vegetation Responses to 15 Years of Repeated Fuel Reduction Treatments in the Southern Appalachian Mountains, USA

Decades of fire exclusion in the Southern Appalachian Mountains led to fuel accumulation and conversion from open oak-pine woodlands to closed-canopy mesic forests dominated by shade-tolerant hardwoods and shrubs that often do not support a diverse understory. Southern Appalachian forest managers and scientists recognize this and are implementing silvicultural treatments such as prescribed burning, mechanical treatments or a combination of these to restore forest structure. In this study, conducted at the Southern Appalachian Fire and Fire Surrogate Study site in Green River Game Land, North Carolina, we assessed the effects of four fuel reduction methods: burned 4x (B), mechanical treatment 2x (M), mechanical treatment 2x + burned 4x (MB), and control (C) on the changes in understory vegetation guilds from pretreatment to post-treatment years (2001–2016). The MB treatment was most effective at meeting the restoration objectives, as it resulted in increases in oak (ΔMB = 23,400 stems/ha) and pine (ΔMB = 900 stems/ha) stem density, importance value - calculated as the sum of relative cover and frequency - for graminoids (ΔMB = 26.0), and density of oak stems &gt;50 cm in height (ΔMB = 7133 stems/ha). The B and M treatments were generally less effective, but nonetheless met a subset of the restoration objectives. The B treatment reduced ericaceous shrub cover (ΔB = −1.2%) and increased oak stems 10–50 cm in height (ΔB = 10,017 stems/ha), while the M treatment resulted in only modest increases of mesic hardwoods, specifically for yellow-poplar (ΔM = 200 stems/ha) and blackgum (ΔM = 200 stems/ha) as compared with other treatments, but significantly increased mountain laurel and rhododendron cover (ΔM = 10.0%). Overall, these fire and fire surrogate treatments had some success in restoring understory structure, but our findings suggest a slow response in understory herbaceous vegetation.

The Diversity of Understory (Shrubs And Herbs) in Mount of Nglanggeran

Mount of Nglanggeran is areas that have diversity of unique flora. This area is uninhabited, so many diversity flora that not identified and have not experienced exploration. Therefore, further exploration of plant diversity is needed. The research is aim to inventory, documentation, and find out the diversity of understory (shrubs and herbs) on Mount Nglanggeran. This research used survey and exploration methods. The researchers documented shrubs and herbs species. Based on result, found 44 family consist of 144 species shrubs and herbs. Those species are flora that has specifically characteristics.

Long‐term understory vegetation dynamics of mixed aspen forests in Rocky Mountain National Park, USA

AbstractAimsForests worldwide are subjected to increasing pressures from altered disturbance regimes, climate change, and their interactions. We resampled previously established vegetation plots to directly assess long‐term vegetation dynamics in the forest understory of mixed aspen forests, including species diversity, distribution, and composition.Study siteRocky Mountain National Park, Colorado, USA.MethodsWe resampled 89 vegetation plots that contained aspen (Populus tremuloides) in the original sampling in 1972/1973 in Rocky Mountain National Park to assess changes in understory diversity, non‐native species abundance, community composition, and elevation ranges. Analyses were performed at three spatial scales: landscape (all plots), ecotone (montane vs. subalpine), and seven forest “series” according to the classification presented in the original publication.ResultsUnderstory vegetation diversity did not significantly change at the landscape scale but increased in forests of the mesic montane series. Changes in diversity varied with elevation, with predominantly increases at lower elevations and decreases at higher elevations. Furthermore, species turnover and upward shifts were more pronounced at lower elevations. The proportion of plots containing non‐native species was similar between data sets, with 48% in 2012/2013 and 46% in 1972/1973. However, the number of non‐native species per plot increased considerably, especially in Pinus contorta forests. Significant shifts in understory community composition occurred in mesic montane forests and Pinus flexilis forests. Generally, higher floristic overlap was evident between forest types, indicating homogenization between 1972/1973 and 2012/2013 understory plant communities.ConclusionsAlthough our results indicate overall little change in understory communities between 1972/1973 and 2012/2013 in Rocky Mountain National Park, they also suggest that observed changes differ by elevation, possibly due to the interactions between elevation and changes in local climate. Our study underscores the importance of analyzing long‐term vegetation dynamics at different spatial scales and provides data from direct observations to improve the predictive power of vegetation models.

Effect of environmental factors on understory species diversity in Southwest Guangxi &lt;i&gt;Excentrodendron tonkinense&lt;/i&gt; forests

Effect of environmental factors on understory species diversity in Southwest Guangxi &lt;i&gt;Excentrodendron tonkinense&lt;/i&gt; forests

林分密度对云顶山柏木人工林林下物种多样性和土壤理化性质的影响

林分密度对云顶山柏木人工林林下物种多样性和土壤理化性质的影响

Site Factors Influence on Herbaceous Understory Diversity in East Texas Pinus palustris savannas

Longleaf pine (Pinus palustris) savannas were once dominant across the southeastern U.S., including East Texas and parts of western and central Louisiana. The diverse understory associated with these historical savannas may occasionally be seen today, but not often in longleaf pine ecosystems. This project aimed to define east Texas site characteristics that are necessary to support these ecosystems with a dense and diverse herbaceous understory with little to no midstory cover. Fifty-nine plots across three study sites were established to evaluate the influence of overstory cover, basal area, aspect, elevation, and slope on the number of plant genera present. Forest structure and site characteristics had significant effects on the number of plant genera found. The number of genera increased with higher elevation and slope; as elevation increased, there was a decline in basal area and overstory cover, leading to a more diverse, understory layer. In order to re-establish and maintain a diverse, herbaceous understory in longleaf pine savannas, sites with more open canopies and on slopes with the most solar exposure should be given priority, particularly when planting desired understory species.

Hurricane disturbances, tree diversity, and succession in North Carolina Piedmont forests, USA

Windthrow plays a critical role in maintaining species diversity in temperate forests. Do large-scale strong wind events (i.e., tropical cyclones, including hurricanes, typhoons and severe cyclonic storms) increase tree diversity in severely damaged forest areas? Do hurricanes (tropical cyclones that occurs in the Atlantic Ocean and northeastern Pacific Ocean) lead to altered relative abundance of shade-tolerant and shade-intolerant species? Did historic hurricanes alter the succession trajectory of the damaged forests? We used nearly 70-year tree demographic data to assess the effects of two major hurricanes on woody species diversity in Piedmont forests, North Carolina, USA. Species richness (S) and Shannon–Wiener’s diversity index (H′) were used to evaluate the changes in tree diversity. The changes in composition were assessed with Nonmetric Multidimensional Scaling. The pre-hurricane successional phase can strongly influence both the damage severity and subsequent responses. Although there is often an immediate drop in diversity following a hurricane, understory tree diversity quickly increases to levels that exceed those prior to the disturbance. This leads to an increase in diversity in stands that were substantially damaged. Hurricanes significantly decrease the dominance of shade-intolerant canopy species while increasing pre-established, more shade-tolerant species. We conclude that large, and infrequent hurricanes help to maintain local tree diversity, but also accelerate the increase in dominance of understory species such as red maple and beech.

UAV Remote Sensing for Biodiversity Monitoring: Are Forest Canopy Gaps Good Covariates?

Forest canopy gaps are important to ecosystem dynamics. Depending on tree species, small canopy openings may be associated with intra-crown porosity and with space among crowns. Yet, literature on the relationships between very fine-scaled patterns of canopy openings and biodiversity features is limited. This research explores the possibility of: (1) mapping forest canopy gaps from a very high spatial resolution orthomosaic (10 cm), processed from a versatile unmanned aerial vehicle (UAV) imaging platform, and (2) deriving patch metrics that can be tested as covariates of variables of interest for forest biodiversity monitoring. The orthomosaic was imaged from a test area of 240 ha of temperate deciduous forest types in Central Italy, containing 50 forest inventory plots each of 529 m2 in size. Correlation and linear regression techniques were used to explore relationships between patch metrics and understory (density, development, and species diversity) or forest habitat biodiversity variables (density of micro-habitat bearing trees, vertical species profile, and tree species diversity). The results revealed that small openings in the canopy cover (75% smaller than 7 m2) can be faithfully extracted from UAV red, green, and blue bands (RGB) imagery, using the red band and contrast split segmentation. The strongest correlations were observed in the mixed forests (beech and turkey oak) followed by intermediate correlations in turkey oak forests, followed by the weakest correlations in beech forests. Moderate to strong linear relationships were found between gap metrics and understory variables in mixed forest types, with adjusted R2 from linear regression ranging from 0.52 to 0.87. Equally strong correlations in the same forest types were observed for forest habitat biodiversity variables (with adjusted R2 ranging from 0.52 to 0.79), with highest values found for density of trees with microhabitats and vertical species profile. In conclusion, this research highlights that UAV remote sensing can potentially provide covariate surfaces of variables of interest for forest biodiversity monitoring, conventionally collected in forest inventory plots. By integrating the two sources of data, these variables can be mapped over small forest areas with satisfactory levels of accuracy, at a much higher spatial resolution than would be possible by field-based forest inventory solely.

Characterization and Conservation Status of Evergreen Rainforest Understory: Case of Campo Ma'an National Park (Cameroon)

The Campo Ma'an National Park is located in the evergreen rainforest area rich in biological diversity. This biological diversity remains poorly known, especially those of the understory. The objective of the present study is to characterize undersotory tree and to determine their IUCN conservation status. To know the floristic diversity of understory (5 cm ≤ dbh <10 cm) of this forest, a tree inventory using the plots method of 25 m x 25 m, in which 36 plots were placed out on 6 transects of 4 km each. The IUCN Red List was used to determine the status of inventoried species. The result showed a total richness of 256 species belonging to 148 genera and 50 families for the entire site has been identified. The Shannon diversity index is 4.90 and 4.02 for Old secondary forest (OSF) and Secondary forest (SFO), respectively. The floristic background belongs to the field of Guinean-Congolese endemism, with 6 endemic species in Cameroon. The conservation status analysis shows that 22 species are listed as endangered in the red list of the International Union for the Conservation of Nature. This study provides a base for reflection on the integration of understory trees species in inventories and in the development of conservation strategies.

Do repeated wildfires promote restoration of oak woodlands in mixed-conifer landscapes?

Oak woodlands are dependent on frequent fire to maintain the low stem density and diverse understories that typify these ecosystems. Without this recurrent disturbance, fire-sensitive conifer competitors encroach on oaks, reducing their vigor, and diminishing habitat quality. In fire-excluded oak woodlands, stand-replacing wildfire can trigger shifts in canopy dominance from seed-generated conifers to oaks, which are capable of vigorous sprouting following topkill. We examined the occurrence and sprouting dynamics of California black oak (Quercus kelloggii Newb.) following repeated wildfires in the Lassen National Forest, California. We found that following reburn, changes in oak relative stand dominance, as well as oak sprout basal area and height, were each positively related to fire severity (P < 0.0001 for each analysis). While conifer regeneration suffered complete mortality at moderate and high reburn severities, 97% of topkilled oaks resprouted from surviving rootstocks, reinforcing oak dominance. Black oak resprouts that originated following topkill in the first wildfire were frequently topkilled in the second fire, including at lower burn severities survived by advance conifer regeneration. The results of this study indicate that while as individuals, black oaks are resilient to recurring wildfire, restoration of historic woodland structure and function is an unlikely outcome of these repeated disturbances. Management of post-wildfire regenerating oak stands in this region will require supplemental fuel reduction treatments, including prescribed burning.

Effects of the overstory on the diversity of the herb and shrub layers of Anatolian black pine forests

Understory plants are important components of forests because they are responsible for the majority of the vascular plant diversity of forest ecosystems. The richness and composition of understory communities are closely related to the tree layer diversity, structure and composition. The aim of this study was to examine the understory diversity of Anatolian black pine (Pinus nigra Arnold subsp. pallasiana (Lamb.) Holmboe)-dominated forests on the Kazdagi Mountains of West Turkey. To describe the overstory structure and composition in a numerically and quantitatively well-defined manner, cumulative abundance profiles (CAPs) of the tree species were used. The resemblance of the sampling plots was classified into five stand types assessing the CAP through the Fuzzy C-Means clustering method. A permutational multivariate analysis of variance (PERMANOVA) was performed to test the variance of the community ecological distance between the five stand types, and the results showed significant differences in these clusters. Many shade-tolerant plants were associated with the mixed stands of Anatolian black pine–Kazdagi fir. The composition of the herb and shrub layer could not be explained by the environmental variables but by differences in the overstory structure of the stands. Pure or nearly pure Anatolian Black pine stands were more diverse than mixed oak–Anatolian black pine and Kazdagi fir–Anatolian black pine stands. However, although dense and young pure Anatolian black pine stands had the most diverse plant species in the shrub layer, they were ranked third in terms of the herb layer diversity. The Anatolian black pine–Kazdagi fir mixed stands had the lowest herb and shrub layer diversity. These results allow us to comprehend the relationship between the overstory structure and composition, and the understory diversity. Understanding this relationship is important for the conservation of understory plant diversity in the management of forest ecosystems.

Benefits of thinning and burning for understory diversity vary with spatial scale and time since treatment

Fuel-reduction treatments have been used effectively in dry, fire-adapted forests to reduce risk of high-severity crown fire, but it is less certain whether they achieve ecological objectives such as promoting understory diversity. Using long-term data from a fuel-reduction experiment, we tested how conclusions about treatment effectiveness are related to the spatial and temporal scales over which ecological responses are evaluated. We modeled the richness of herbs and shrubs at smaller (1–50 m2) and larger (1000 m2) spatial scales as functions of pre-treatment richness, thinning intensity, burning, and time since treatment (2–3 vs. 10–13 years). Pre-treatment richness was the strongest predictor of post-treatment richness, reflecting high rates of species survival, irrespective of treatment. Richness was enhanced by burning and, to a lesser extent, by thinning, although the timing and strengths of these effects varied with spatial scale. Among herbs, annuals showed an early and persistent increase after burning at the larger scale, but a lagged response at the smaller scale—the latter enabled by limited competition from perennial herbs and shrubs. In contrast, perennials showed lagged responses to thinning at smaller scales and to burning at larger scales, suggesting slow recruitment via seed or vegetative spread. Non-natives were unresponsive to treatments but were also uncommon before treatment, suggesting limited propagule pressure from the surrounding landscape. Rates of colonization were unrelated to pre-treatment richness; thus, the potential for understory enrichment was not constrained by initial diversity. The low cover and lagged responses of woody and herbaceous perennials suggest that further enrichment is possible, particularly at smaller spatial scales. Our results illustrate that uncertainty about the ecological effectiveness of fuels treatments can relate to the spatial and temporal scales over which responses are measured. They underscore the value of long-term, multi-scale assessments in defining the spatial and temporal contexts of ecological outcomes, and in evaluating the necessity for, or timing of, further intervention.

Is Competition for Soil Resources by Carex pensylvanica Restricting Tree Seedling Growth in a Temperate Northern Hardwood Forest?

In response to ecological disturbances, sedge species like Carex pensylvanica form dense monocultures on the forest floor. These “sedge mats” have been shown to severely inhibit plant growth, and limit understory species diversity. In recent years, concern has grown that they may also be restricting the regeneration of economically valuable tree species like sugar maple through belowground competition. To determine if and how Carex pensylvanica may be impacting tree seedling growth through belowground competition I located and exclosed 44 tree seedlings in areas of representatively dense sedge at two forest sites at the Queen’s University Biological Station. I removed sedge from half the plots, and measured soil resource availability and seedling growth response at all plots throughout the growing season. I predicted that sedge would negatively impact the growth of tree seedlings by decreasing the availability of soil resources. I found that the presence of sedge did not affect seedling growth over one growing season, but that it did impact soil resource availability by increasing the availability of surface soil moisture and decreasing the availability of soil nitrate, changes which may have implications for seedling growth beyond the single growing season studied. My results were also site specific, indicating that location is important when managing sedge impact on tree regeneration. Understanding the impact of sedge on tree seedling regeneration is important for predicting changes in the trajectory of forest communities and for informing the management of economically valuable species like sugar maple.