Hydric Sites Research Articles

Herbicide trials on Campuloclinium macrocephalum (Asteraceae) during adverse conditions reveal incompatibility with biocontrol and a narrow window of opportunity for chemical control

Herbicide trials on pompom weed Campuloclinium macrocephalum (Less.) DC. (Asteraceae) were carried out in grasslands with xeric and hydric soils, at sites in Gauteng, South Africa, from 2005 to 2008. The rust fungus Puccinia eupatorii Dietel, an established self-perpetuating biocontrol agent on C. macrocephalum, caused significant damage to shoots in late summer and autumn. Herbicide efficacy was significantly better on foliage that did not already present symptoms and that was sprayed in early summer compared with on infected plants treated in autumn, at both the xeric (F = 36.71, p < 0.001) and hydric (F = 3.59, p = 0.031) sites. This pathogen has reduced the time available for effective chemical weed control from six months to three months. However, none of the herbicide treatments achieved commercially acceptable mortality rates of ≥80%, and after three annual applications none succeeded in extirpating C. macrocephalum from the plots. Regression analyses of count data showed that metsulfuron-methyl at 45 g ha−1 (USD 20.05 ha−1), picloram at 252 g ha−1 (USD 25.47 ha−1) and 2,4-D/dicamba/MCPA at 540/360/474 g ha−1 (USD 45.41 ha−1) required five annual treatments in summer to eradicate C. macrocephalum, whereas 2,4-D amine at 1 440 g ha−1 (USD 13.65 ha−1) and MCPA at 1 200 g ha−1 (USD 14.46 ha−1) required six treatments. Hence, there is a trade-off between the use of slightly more effective herbicides against the lower costs of other selective herbicides.

Longleaf pine restoration on hydric sites: Understorey plant community responses to site preparation through 15 years

AbstractQuestionLongleaf pine (Pinus palustris) restoration is an important management objective throughout the southeastern United States. Site preparation prior to planting longleaf pine seedlings is often required to overcome challenges to seedling establishment on hydric sites. We know site preparation improves growth and survival of planted longleaf pine on hydric sites, but what are the impacts of site preparation on the understorey plant community?LocationMarine Corps Base Camp Lejeune in Onslow County, NC, USA.MethodsThis study tested eight site preparation treatments, including an untreated control, six combinations of two vegetation control treatments (chopping or herbicide) with three soil manipulation treatments (mounding, bedding, or flat‐planting [no treatment]), and a chopping–herbicide–bedding treatment. We collected data on understorey plant abundance, diversity, and composition through the first three and at 15 years after plantation establishment. We used ANOVA procedures and multivariate ordination to test for differences in understorey responses among the study treatments and through time.ResultsSite preparation had lasting impacts on the understorey plant community. The chop‐only treatment was the only treatment that resulted in dominance of herbaceous vegetation and was among the treatments with the highest diversity and greatest abundance of Aristida stricta (wiregrass). Herbicide produced lasting reductions in Aristida stricta abundance and apparent shifts in community composition. Reduced graminoid abundance was particularly pronounced when herbicide was combined with soil manipulation treatments.ConclusionsUnderstorey responses to site preparation through 3 years differed from responses observed in year 15, highlighting the importance of long‐term monitoring. For example, herbicides controlled shrubs early, but by year 15, herbicide treatments were dominated by shrubs. Restoration scenarios often must balance ecological objectives (e.g., maintenance of a diverse understorey community) with forestry objectives (e.g., timely establishment of overstorey trees), and our findings can be used as a guide to balance these trade‐offs.

Functional differentiation of invasive and native plants along a leaf efficiency/safety trade-off

Plant invasive alien species (IAS) are a serious threat to biodiversity. Several studies have compared the functional features of IAS and native species to identify the functional traits, or set of traits, favouring the process of invasion. However, most of these studies analysed traits only related to carbon and nutrients, and the inclusion of traits related to water use and acquisition might be useful to describe the functions underlying plant invasion. Here we present an analysis of cost-related, hydraulic and leaf vein traits measured on a large assemblage of woody and herbaceous native and invasive species (93 species in total, 78 natives and 15 IAS), that co-occur in site types in the Mediterranean area with different water availability (i.e. xeric, mesic and hydric sites). IAS shared lower leaf construction costs and drought resistance, but potential higher efficiency in water transport (i.e. higher values of vein length per unit area/mass) than native species. Moreover, IAS and native species separated along the trade-offs drawn by the measured traits, suggesting that hydraulic and vein traits could set an important axis of variation between IAS and native species. At last, IAS tended to occupy the fast-growth region of the functional space, independently of growth form and site type. Hydraulic and vein traits provide stronger mechanistic linkages between construction costs and photosynthetic and growth rates, thus possibly playing a central role in determining the invasive potential of IAS. IAS could reduce costs associated with leaf construction and resistance to drought stress having, at the same time, high efficiency of water transport and photosynthetic rates by developing a denser venation network, translating to higher growth rates than native and more conservative species.

Structural diversity of the longleaf pine ecosystem

Structural diversity is an important attribute of forest ecosystems and is related to ecosystem stability, adaptability and resilience as well as biodiversity and productivity. Structural diversity in the longleaf pine (Pinus palustris Mill.) ecosystem, the most diverse ecosystem of North America, has not been well documented, especially across the longleaf pine’s range of occurrence. We utilized data from 919 Forest Inventory and Analysis (FIA) plots of longleaf pine distributed across 9 states of the southeastern United States and classified these plots on the bases of stand origin (natural or artificial), ownership (public or private), burn condition (burned or not burned in the past 5 years), site conditions (xeric, mesic, or hydric), and number of age classes (one or two). For each plot under a classification category, we calculated Shannon diversity index based on 5-cm diameter classes. The structural diversity estimates, based on Shannon diversity indices, were then analyzed for the entire range of the longleaf pine ecosystem. Our findings indicate that the structural diversity varies between 0.00 and 2.20 across the longleaf pine range, with mean and median structural diversity of 1.35 and 1.42, respectively. Stand origin, site condition, ownership, and number of age classes significantly affected mean structural diversity (α = 0.05). Plots with natural origin, mesic or hydric site conditions, public ownership, and two age classes had higher structural diversity. Using the geographic coordinates of each FIA plot and the corresponding Shannon index value, we created a structural diversity distribution map and a hot spot map of the longleaf pine ecosystem. The maps showed that the longleaf pine ecosystem exhibited variable and heterogeneous distribution of structural diversity in the southeastern United States, with southeastern Mississippi and central Alabama areas as the hotspots. Southcentral Georgia exhibited least structural diversity in longleaf pine forests in the southeastern United States.

Site preparation for longleaf pine restoration on hydric sites: Stand development through 15 years after planting

Longleaf pine (Pinus palustris Mill.) restoration is an important land management goal throughout the southeastern U.S. On hydric sites within the Atlantic Coastal Plain, restoration may involve site preparation prior to planting to overcome challenges to seedling establishment, such as abundant competition and poor soil drainage. Investment in site preparation assumes that treatments will result in long-term benefits to stand development, yet lasting impacts of site preparation on longleaf pine are not well understood. We sampled longleaf pine plantations in Onslow County, North Carolina through three years and at 15 years after site preparation and planting. The eight study treatments we tested include an untreated control, six combinations of two vegetation control treatments (chopping or herbicide) with three soil manipulation treatments (mounding, bedding, or flat-planting [no treatment]), and a chopping-herbicide-bedding treatment. Our findings indicate that site preparation significantly improved survival and growth of longleaf pine through 15 years. Herbicide resulted in greater growth, higher survival, and earlier grass stage emergence than chopping. Similarly, soil manipulation treatments resulted in improved stand establishment outcomes relative to flat-planting (no treatment). Effects of site preparation treatments on diameter growth were observed early and maintained through the end of the study period, while effects on survival were not observed within the first three years. Differences in stand height among treatments were more strongly driven by growth rates following grass stage emergence than timing of emergence. Our results demonstrate that site preparation improves longleaf pine stand establishment on hydric sites, although the intensity of site preparation treatments recommended for restoration depends on management objectives.

Forest Wetland Area and the Forest Sector Economy in the U.S. South

This article reviews current data on forest wetlands and their economic contributions in the South, ranging from Texas to Virginia. Based on USDA Forest Service Forest Inventory and Analysis (FIA) data, the wetland category comprised 17.7% of timber land area on all private and public lands in the South. This included 4.25 million ha of hydric sites; 0.77 million ha mesic wet; 9.55 million ha mesic, with only seasonal access; for a total of 14.57 million ha. The Natural Resource Inventory (NRI) for 2012 on private lands estimated that there were 14.71 million ha forested wetlands, which comprised 17.7% of all forested private forest area. The 2015 National Land Cover Data for the South estimated that there were 17.8 million ha of woody wetlands, which comprised 8% to 12% of the southern land area, and there were also 4.45 million ha of emergent herbaceous sites. About 10% of the southern timber forest sector would be based on harvests from wetland forests economy ($455 million per year), while the 17.7% of wetland land area would provide a proportional share of the annual nontimber forest products ($44 million) and payments for ecosystem services ($134 million). Wetlands also provide important nontimber forest products, and ecosystem services, which are beginning to develop active private and public markets.

Summer activity patterns for mosses and lichens in Maritime Antarctica

AbstractWithin Antarctica there are large gradients both in climate and in vegetation which offer opportunities to investigate links between the two. The activity (% total time active) of lichens and bryophytes in hydric and xeric environments was monitored at Livingston Island (62°39'S). This adds a northern site with a maritime, cloudy climate to previous studies in the southern Antarctic Peninsula and the Dry Valleys (78°S). Annual activity increases northwards from less than 1% to nearly 100%. There is a major and consistent difference between hydric sites which, with snow melt, can be 100% active in summer months even in the Dry Valleys, and xeric sites which, depending on precipitation, rarely exceed 80% activity even at Livingston Island. Mosses dominate hydric sites and lichens the xeric sites all along the gradient. Mean temperatures when active are 2–4°C at all sites, as liquid water is required. Light is a potential major stress reaching 880 µmol m-2s-1when active in continental sites. The lack of extremes in temperatures and light combined with high activity levels means that summer at Livingston Island is one of the better sites for lichen and bryophyte growth in the world.

Physiographic factors underlie rates of biomass production during succession in Great Lakes forest landscapes

Biomass production in living trees is the basis of numerous forest ecosystem functions and services. However, rates of and controls on biomass production vary widely across temperate forests, particularly over successional timescales of decades and centuries. Biomass production in temperate forests is most often interpreted within the context of biotic or top-down controls, such as species composition or disturbance. However, there is need to investigate how bottom-up physiographic factors, such as landform attributes, drainage, and soil properties mediate biomass production. In order to investigate patterns, controls, and potentials for biomass production across spatial levels ranging from individual ecosystems, to landscapes, to entire regions, we synthesized long-term forest inventory datasets from the United States Great Lakes region, placed them in the context of a hierarchical ecological unit classification, and tested the influence of physiographic factors on biomass production rates and temporal trajectories across ecological levels. Key findings include: 1) At nearly all ecological levels, physiographic controls (e.g., soil texture, drainage class, water table depth) on soil moisture status are significant predictors of variation in biomass production rates, with mesic sites accumulating biomass more rapidly than xeric sites, which, in turn accumulate biomass more rapidly than hydric sites. 2) Aboveground live biomass can apparently continue to accumulate through 2–3 centuries of succession, exceeding 300–400Mgha−1 on mesic sites throughout the region. 3) Stand age distributions indicate that hydric sites are harvested least often, while the high production rates of mesic sites suggest they are most appropriate for frequent harvesting. 4) Median, 1st-quartile, and 3rd-quartile growth rates of individual ecosystems, landscapes, and ecoregional subsections and sections reveal ecological units in which forests may vary in their potential for increases or decreases in biomass production, e.g., due to management interventions, climate change, or disturbances. Specifically, some units have tightly constrained distributions, suggesting little capacity for change in production rates relative to observed medians, while other units have wide variation in biomass production rates, indicating the potential for relatively large increases or decreases in production. Altogether, the results of this analysis show that physiography exerts widespread, bottom-up controls on biomass production across the region of study, and can be used in spatially explicit frameworks to understand ecosystem functioning and inform scientific forest management.

Insights into plant water uptake from xylem‐water isotope measurements in two tropical catchments with contrasting moisture conditions

AbstractWater transpired by trees has long been assumed to be sourced from the same subsurface water stocks that contribute to groundwater recharge and streamflow. However, recent investigations using dual water stable isotopes have shown an apparent ecohydrological separation between tree‐transpired water and stream water. Here we present evidence for such ecohydrological separation in two tropical environments in Puerto Rico where precipitation seasonality is relatively low and where precipitation is positively correlated with primary productivity. We determined the stable isotope signature of xylem water of 30 mahogany (Swietenia spp.) trees sampled during two periods with contrasting moisture status. Our results suggest that the separation between transpiration water and groundwater recharge/streamflow water might be related less to the temporal phasing of hydrologic inputs and primary productivity, and more to the fundamental processes that drive evaporative isotopic enrichment of residual soil water within the soil matrix. The lack of an evaporative signature of both groundwater and streams in the study area suggests that these water balance components have a water source that is transported quickly to deeper subsurface storage compared to waters that trees use. A Bayesian mixing model used to partition source water proportions of xylem water showed that groundwater contribution was greater for valley‐bottom, riparian trees than for ridge‐top trees. Groundwater contribution was also greater at the xeric site than at the mesic–hydric site. These model results (1) underline the utility of a simple linear mixing model, implemented in a Bayesian inference framework, in quantifying source water contributions at sites with contrasting physiographic characteristics, and (2) highlight the informed judgement that should be made in interpreting mixing model results, of import particularly in surveying groundwater use patterns by vegetation from regional to global scales. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Permafrost warming and vegetation changes in continental Antarctica

Continental Antarctica represents the last pristine environment on Earth and is one of the most suitable contexts to analyze the relations between climate, active layer and vegetation. In 2000 we started long-term monitoring of the climate, permafrost, active layer and vegetation in Victoria Land, continental Antarctica. Our data confirm the stability of mean annual and summer air temperature, of snow cover, and an increasing trend of summer incoming short wave radiation. The active layer thickness is increasing at a rate of 0.3 cm y−1. The active layer is characterized by large annual and spatial differences. The latter are due to scarce vegetation, a patchy and very thin organic layer and large spatial differences in snow accumulation. The active layer thickening, probably due to the increase of incoming short wave radiation, produced a general decrease of the ground water content due to the better drainage of the ground. The resultant drying may be responsible for the decline of mosses in xeric sites, while it provided better conditions for mosses in hydric sites, following the species-specific water requirements. An increase of lichen vegetation was observed where the climate drying occurred. This evidence emphasizes that the Antarctic continent is experiencing changes that are in total contrast to the changes reported from maritime Antarctica.

Ash (Fraxinus spp.) mortality, regeneration, and seed bank dynamics in mixed hardwood forests following invasion by emerald ash borer (Agrilus planipennis)

Emerald ash borer (EAB; Agrilus planipennis) has killed millions of ash trees and threatens ash throughout North America, and long-term persistence of ash will depend on the potential for regeneration. We quantified ash demography, including mortality and regeneration, of Fraxinus americana (white ash), Fraxinus pennsylvanica (green ash), and Fraxinus nigra (black ash) in mixed hardwood forests near the epicenter of the EAB invasion in southeastern Michigan and throughout Ohio. Plots were established across a gradient of ash densities. Ash was the most important species in hydric sites, and ranked second among all species in mesic and xeric sites. In sites nearest the epicenter in Michigan, ash mortality exceeded 99 % by 2009, and few or no newly germinated ash seedlings were observed, leaving only an “orphaned cohort” of established ash seedlings and saplings. As ash mortality increased, the number of viable ash seeds in soil samples decreased sharply, and no viable seeds were collected in 2007 or 2008. In Ohio sites farther from the epicenter, densities of new ash seedlings were much higher in plots with healthy ash trees compared to plots where trees had died. EAB was still present in low densities in Michigan and Ohio stands in 2012 where average mortality of ash was nearly 100 %. The future of ash at these sites will depend on the outcome of the dynamic interaction between the orphaned cohort of previously established ash seedlings and saplings and low density EAB populations.

Interactions between stand thinning, site quality and host tree species on spruce budworm biological performance and host tree resistance over a 6 year period after thinning

Forest management activities such as thinning have been proposed to reduce defoliation damage incurred by spruce budworm (Choristoneura fumiferana (Clem.)). Yet, information regarding thinning effects on tree and stand vulnerability to spruce budworm is equivocal. A better understanding of thinning with respect to host tree resistance and budworm performance could be useful to reduce its impacts while respecting forest ecological integrity. Our objectives were (1) to evaluate the effects of thinning and site drainage quality on balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and black spruce (P. mariana (Mill.) BSP) resistance to spruce budworm through time (6years) and (2) to produce a resistance classification model that could be used by forest managers to determine when and where to apply this treatment. Field-rearing experiments of spruce budworm were conducted, together with foliar chemical analyses, along a gradient of stand thinning intensity (0%, control; 25%, light; 40%, heavy) and drainage class (rapidly drained, class 2; mesic with seepage, class 3; subhygric, class 4; hydric, class 5). Budworm performance was followed throughout the insect’s life cycle, including its winter biology. Balsam fir resistance, unlike that of white and black spruce, was significantly reduced 1year after thinning. Fir response was related to increased defoliation linked to reduction of certain monoterpenes on mesic sites and to decreased foliage production on subhygric sites. On hydric sites, thinning increased fir resistance by increasing foliage production. We observed an opposite response 3years after treatment. Heavy thinning (40%) positively affected balsam fir and white spruce tolerance and, therefore, tree resistance, by increasing foliage production and the amount remaining after budworm feeding throughout the study, except 6years after thinning in white spruce growing on mesic sites. From the fourth year onward, black spruce resistance was positively affected by thinning. This response was observed despite thinning also having favoured insect performance (high female pupal mass), which resulted in greater foliage destruction in thinned stands. These findings suggest that thinning may be used to increase tree and stand resistance to spruce budworm. Our resistance classification system could be useful to forest managers in planning thinning that would reduce budworm impacts at the stand level.

Differential radial growth patterns between beech (Fagus sylvatica L.) and oak (Quercus robur L.) on periodically waterlogged soils

Climate scenarios for northern Central Europe project rising temperatures and increasing frequency and intensity of droughts but also a shift in precipitation pattern with more humid winters. This in turn may result in soil waterlogging during the following spring, leading to increasing stress for trees growing on hydric sites. The influence of waterlogging on growth of common beech and pedunculate oak has been studied intensively on seedlings under experimental conditions. However, the question remains whether results of these studies can be transferred to mature trees growing under natural conditions. To test this, we investigated general growth patterns and climate-growth relationships in four mature stands of beech and oak growing on hydromorphic soils (Stagnosols) in northeast Germany using dendrochronological methods. Our results confirmed the expected tolerance of oak to strong water-level fluctuations. Neither extremely wet conditions during spring nor summer droughts significantly affected its radial growth. Oak growth responded positively to warmer temperatures during previous year October and March of the current year of ring formation. Contrary to our expectations, also beech showed relatively low sensitivity to periods of high soil water saturation. Instead, summer drought turned out to be the main climatic factor influencing ring width of beech even under the specific periodically wet soil conditions of our study. This became evident from general climate-growth correlations over the last century as well as from discontinuous (pointer year) analysis with summer drought being significantly correlated to the occurrence of growth depressions. As ring width of the two species is affected by differing climate parameters, species-specific chronologies show no coherence in high-frequency variations even for trees growing in close proximity. We assume differences in rooting depth as the main reason for the differing growth patterns and climate correlations of the two species under study. Our results indicate that under the projected future climate scenarios, beech may suffer from increasing drought stress even on hydromorphic soils. Oak might be able to maintain a sufficient hydraulic status during summer droughts by reaching water in deeper soil strata with its root system. Wet phases with waterlogged soil conditions during spring or summer appear to have only a little direct influence on radial growth of both species.

Old-Growth Characteristics of DisjunctThuja occidentalisStands at their Northwestern Distribution Limit, Central Canada

ABSTRACT: Old-growth northern white-cedar (Thuja occidentalis L.) stands were examined in the Mid-Boreal Lowlands of west-central Manitoba. These stands represent the NW distribution limit of the species, which occurs disjunct from its continuous range limit in North America. The objectives involved characterizing the vegetation-environmental relationships, forest structure, and old-growth attributes of these stands. The environmental control exerted on these communities was explored with both cluster analysis and canonical correspondence analysis. Three T. occidentalis stand types were identified: xeric, mesic, and hydric — each representing a specific moisture regime and successional pathway. In the xeric sites, T. occidentalis co-occurred with jack pine (Pinus banksiana Lamb.), whereas in the mesic sites it co-occurred with white spruce (Picea glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.). In the hydric sites, tamarack (Larix lancina (Du Roi) K. Koch) was the companion species. All s...

Floristic diversity of arboreal communities in the high altitude deserts of Ladakh

Analysis of woody components of 4 communities in Nubra valley of Ladakh revealed that Hippophae rhamnoides was the most dominant species sharing 31 per cent of total importance value. Across the communities within landscape relative dominance of this species decreased from 77.76 per cent on most hydric sites (along river bank) to merely 0.27 per cent on most xeric sites (dry rocks). On the other hand, relative dominance of Ephedra gerardiana and Berberis ulicina increased with increasing aridity of sites. Productivity-diversity relationship followed unimodal curve which peaked at sites along streams. Maximum species turnover rate was found across the sites along steams while the most xeric sites were more uniform within.

Effect of midstory and understory removal on the establishment and development of natural and artificial pin oak advance reproduction in bottomland forests

Regenerating oaks (Quercus L.) on mesic and hydric sites has remained a problem largely because of inadequate density and poor distribution of large oak advance reproduction prior to harvesting. We examined the effect of midstory and understory removal on the establishment and 3-year development of natural and artificial sources of pin oak (Q. palustris Muenchh.) advance reproduction in bottomland forests in southeastern Missouri, USA. Midstory and understory removals increased the photosynthetically-active radiation (PAR) reaching the seedling layer from about 3 to 15%. This increased light did not increase the density of natural pin oak advance reproduction compared to control, but it increased the survival and nominally increased the growth of the natural pin oak advance reproduction. Where the midstory and understory had been removed, underplanted RPM® container stock and bareroot pin oak stock maintained high survival, but of the two only the RPM® stock maintained positive height and diameter growth while bareroot stock suffered some growth reductions. Pin oaks originating from the direct seeding of stratified acorns sown in the spring had low germination and survival, but the survivors had growth rates similar to those of natural seedlings in thinned stands. Applying triclopyr to competitors in the ground flora layer only nominally increased PAR but reduced the percent survival and marginally increased the growth of natural and artificial pin oak. We conclude that artificial reproduction may be used to further increase the probability of achieving adequate numbers of the desired species in the future. Bareroot seedlings may not perform as well as RPM® seedlings and natural seedlings already present. However, bareroot and RPM® seedlings remained significantly larger than the natural seedlings after 3 years.

Testing the Effects of Experimental Snow Removal on Soil Moisture and Plant Responses in Montane Meadows

Regional models of global climate change for the northern Rocky Mountains predict warmer temperatures and western states have shown a recent trend towards increases in the fraction of precipitation falling as rain rather than snow. Thus, the amount of soil moisture available to plants during the growing season may already be varying significantly from historical conditions. In order to simulate drier summer soil conditions and test soil moisture and plant responses, we set up a pilot snow removal experiment in Grand Teton National Park, WY in 2008. Because most of the precipitation comes in the form of snow, and spring snowpack is about 50% water by volume, removing all snow present in early May can reduce the annual precipitation by approximately half. Snow was removed from three ~9x15 m experimental plots using a Thiokol in early May. These experimental sites were paired with adjacent control sites and the pairs were established along a hydrological gradient of meadow types representing hydric, mesic, and xeric sites. Dataloggers were installed in June and soil moisture was monitored at 5, 20, and 50 cm depths through August. Water potential was measured in Bromus and Carex during mid-July. Over the summer season, there were differences in soil water between the snow removal and control plots, as well as across the hydrological gradient. Decreases in soil water content and water potential of Carex showed strongest responses in the mesic site, whereas Bromus showed the strongest response in the hydric site. This is the first study to reveal that variability in spring snowpack can lead to measurable impacts on the vegetation community, even into mid-late summer when soil water is fairly scarce throughout the landscape. Furthermore, changes in snow depth are not likely to have equivalent impacts on the different community types within a region; the effects will vary predictably as a function of soil and plant community characteristics.

Purple Loosestrife on the Susquehanna River's West Branch: Distribution and Environmental Correlates

The Eurasian Lythrum salicaria is invading wetlands throughout North America. Our study sought to (1) document the extent of L. salicaria invasion along the lower West Branch of the Susquehanna River in central Pennsylvania and (2) assess the correlates of L. salicaria abundance including associated species and environmental/edaphic characteristics. We documented that L. salicaria is well established on the West Branch of the Susquehanna River, but only in that portion within the Ridge and Valley Province. Multiple analyses indicated that L. salicaria is associated with open-canopied, hydric sites with nutrient-rich, clay and/or silt soils. The vulnerability of a West Branch site to invasion by L. salicaria is best assessed by the presence of plant associates including Eleocharis obtusa, Phalaris arundinacea, and others.

Assessing the patterns and controls of fine root dynamics: an empirical test and methodological review

SummaryElucidation of the patterns and controls of forest net primary production at ecosystem scales has been hindered by a poor understanding of fine root production, due largely to technical limitations.Fine root (≤ 0.5 mm diameter) production was assessed using minirhizotron, soil core, ingrowth core, nitrogen budget and carbon budget techniques in three longleaf pine‐wiregrass forest ecosystem types (hydric, mesic and xeric) forming an edaphic resource availability and above‐ground productivity gradient.Fine root production estimates differed substantially in magnitude, e.g. values ranged from 0 to 4618 kg ha−1 year−1for the soil core and minirhizotron techniques, respectively, in the hydric site.Minirhizotron production estimates in the hydric, mesic and xeric sites were 4618, 1905 and 2295 kg ha−1 year−1, respectively.Soil core and ingrowth core root production estimates were on average 81 and 54% lower, respectively, than corresponding minirhizotron production estimates, and minirhizotron estimates were negatively related to soil core and ingrowth core estimates across the resource gradient.The N budget method yielded unreliable root production estimates, presumably due to the underestimation of N availability for plant assimilation.C budget estimates of total below‐ground C allocation (6773, 5646 and 4647 kg C ha−1year−1) were positively related to minirhizotron production estimates, but negatively related to soil core and ingrowth core production estimates.Critical evaluations of the assumptions, potential errors and results for each method suggest that the minirhizotron technique yielded the most reliable root production estimates, and that the negative relationship between minirhizotron and core‐based estimates may be attributed to the inherent deficiency of the core techniques in assessing root production when mortality and production occur simultaneously.Minirhizotron root production estimates were positively related to foliage production estimates, supporting the hypothesis of constant proportional allocation of production to foliage, wood and fine roots across resource availability gradients in temperate forests.These results suggest that fine root production is not negatively correlated with soil resource availability and foliage production as is commonly perceived in the ecological community and represented in ecosystem computer models.

Testing the ecophysiological basis for the control of monoterpene concentrations in thinned and unthinned balsam fir stands across different drainage classes.

Stand thinning across different soil drainage types was used to test the ecophysiological basis for the control of foliar monoterpenes in current-year foliage of balsam trees [Abies balsamea (L.) P. Mill.] the year following treatment. Photosynthetic capacity (A max) was greater on mesic sites than on sub-hygric and hydric sites (1.81, 1.33 and 0.88 µmol m-2 s-1, respectively) and greater in mid-July than at the end of June (1.86 vs 0.77 µmol m-2 s-1). Foliar N was greater on thinned plots than control plots (2.6 vs 2.2g m-2); starch was greater on mesic control plots than mesic thinned plots (16.3 vs 10.9g m-2); and total soluble sugars (TSS) were higher in mid-July than at the end of June (16.5 vs 12.8g m-2). Total monoterpenes, as well as five individual monoterpenes, showed a complex interaction between site drainage class, thinning treatment and time of sampling (P<0.05). For all sites and dates combined, total monoterpenes were negatively correlated with specific leaf area (r 2=0.46), and positively but weakly correlated with A max (r 2=0.35), foliar N (r 2=0.29) and TSS (r 2=0.24). Total monoterpenes were not correlated with the different measures of carbon to nitrogen ratio as predicted by the carbon-nutrient balance hypothesis. Our results offer partial support to the different hypotheses proposing that foliage having greater resource availability, enzymatic machinery and potential for building storage structures will have greater monoterpene content. However, the strength of the relationships with monoterpenes often varied with sampling date, suggesting that phenological development may play a strong role in determining which factors control monoterpenes at a given time.