Effect of Hydrologic Restoration and Lonicera maackii Removal on Herbaceous Understory Vegetation in a Bottomland Hardwood Forest

Amur honeysuckle (Lonicera maackii (Rupr.) Herder), a large deciduous shrub from China, has invaded many forests in eastern/central United States. The species was removed by cutting and herbicide application from a recently hydrologically restored section of a bottomland hardwood forest in central Ohio, and the response of understory plants, especially herbaceous species, was measured. Plots were established in uncleared and cleared sections, and percent cover of each herbaceous understory species was estimated monthly. One season after several years of Lonicera removal efforts, no significant association was discovered between percentage of Lonicera cover and total understory species abundance. There was, however, a direct correlation between elevation and honeysuckle abundance; L. maackii abundance was negatively associated with low elevations, likely due to hydrologic factors. Plant species diversity (H) and richness (s) increased with elevation but were not significantly different on plots with honeysuckle removal (H = 0.86 ± 0.08 vs. 0.78 ± 0.09 and s = 4.4 ± 0.19 vs. 4.2 ± 0.2 species/m², respectively) despite the fact that understory light levels measured by densiometer were significantly higher (α= 0.003) in cleared versus uncleared sections. Native and invasive species were found in similar proportions in the two sections, and significant sprouting and regrowth of L. maackii were observed throughout the cleared section. Although the removal of L. maackii altered the characteristics of the plant species assemblage, the value of this management remains questionable in the years immediately following treatment.     

Acorn and aquatic invertebrate biomass in Mississippi Alluvial Valley hardwood bottomlands

The Mississippi Alluvial Valley (MAV) is an internationally important migration and wintering region for Nearctic waterfowl. Most of the MAV is a lowland forested floodplain that contains vast stands of red oaks (Quercus spp.). These trees produce acorns and, when forests flood, diverse communities of aquatic invertebrates emerge, providing diverse nutritious foods for wintering ducks. The MAV is within the Lower Mississippi Valley Joint Venture (LMV JV) region of the North American Waterfowl Management Plan, but no combined MAV-wide estimates of acorn and invertebrate biomass exist to determine foraging carrying capacity for conservation planning or actions by the LMV JV or other partners in regions containing southern red oaks. We sampled acorns that fell to the ground or were submersed under shallow water deemed accessible to foraging ducks and aquatic invertebrates in the MAV of Louisiana, Mississippi, Missouri, and Tennessee, USA, during fall-winter 2009–2011. In good and poor masting years, acorn abundance was non-linearly related to the percentage of the forest canopy made up of red oaks and peaked in late autumn or winter when most other waterfowl resources are depleted or decomposed. This finding is novel and represents a deviation from how the LMV JV has traditionally assumed food resources exist for waterfowl in hardwood bottomlands. We used a daily ration model to estimate energy use days (EUDs) from combined acorn and invertebrate biomasses relative to red oak canopy coverage. For good and poor acorn masting years at the mean MAV-wide red oak canopy coverage of 45%, EUD = 2,273.1 days/ha and 161.2 days/ha, respectively. The LMV JV currently uses EUD = 385–502 days/ha for forests with 40–50% red oak canopy coverage. Because acorns and aquatic macro-invertebrates are a food resource that persists through winter and reaches peak abundance later in winter, we contend conservation planners have undervalued the potential of bottomland hardwoods to provide energy for wintering ducks.     

Succession of Exotic and Native Species Assemblages within Restored Floodplain Forests: A Test of the Parallel Dynamics Hypothesis

Exotic plants pose a threat to restoration success in post‐agricultural bottomlands, but little information exists on their dynamics during succession of actively restored sites. We hypothesized that exotic assemblages would establish during succession and that their compositional trends during succession time would mirror those published for native species in other systems, with an early peak in herbaceous richness followed by a decline as woody species establish. In the summer of 2008, we sampled 16 sites across an 18‐year chronosequence of restored forests, with an additional four mature forest stands for comparison, within the Cypress Creek NWR, Illinois, U.S.A. We identified all vascular plant species and quantified canopy openness at three canopy strata, and soil texture and chemistry. Trends in exotic assemblages were significantly correlated with canopy openness at all strata. Richness of exotic and native herbaceous species was related to stand age and consistent with a Weibull regression model. Native and exotic herbaceous cover followed an exponential decay model. Woody native richness over time conformed to a logistic model; woody exotics exhibited no relationship with stand age and were present in sites of all ages. Our results indicate that although their rates of decline differ, herbaceous exotics and natives exhibit similar successional dynamics; therefore, herbaceous exotics may not pose a lasting threat to restoration success in reforested floodplains. Woody exotics can establish across a range of successional stages and persist under closed canopy conditions. Bottomland restorations are vulnerable to the invasion and expansion of exotic plant species even after canopy closure.     

Nuclear DNA amounts in 112 species of tropical hardwoods -- new estimates

The 4C DNA values of 112 species, belonging to 37 families have a range from 0.83 pg (Bixa orellana) to 15.54 pg (Thryallis angustifolia), showing a 18.72-fold variation. The genome size varies from 0.21 pg (Bixa orellana) to 3.32 (Thespesia populnea), with a 15.8-fold difference. The Bombacaceae has the minimum range (1.08-fold) of variation, while the maximum (5.0-fold) is shown by the Fabaceae. The Boraginaceae, Lauraceae, Malpighiaceae, and Malvaceae generally have higher 4C DNA values of > 10 pg, while the Bixaceae, Caricaceae, Oxalidaceae, and Santalaceae have lower values of < 2.0 pg. These data add further to our knowledge on variation in DNA amount in tropical hardwoods.     

Bioenergy production and forest landscape change in the southeastern United States

Production of woody biomass for bioenergy, whether wood pellets or liquid biofuels, has the potential to cause substantial landscape change and concomitant effects on forest ecosystems, but the landscape effects of alternative production scenarios have not been fully assessed. We simulated landscape change from 2010 to 2050 under five scenarios of woody biomass production for wood pellets and liquid biofuels in North Carolina, in the southeastern United States, a region that is a substantial producer of wood biomass for bioenergy and contains high biodiversity. Modeled scenarios varied biomass feedstocks, incorporating harvest of ‘conventional’ forests, which include naturally regenerating as well as planted forests that exist on the landscape even without bioenergy production, as well as purpose‐grown woody crops grown on marginal lands. Results reveal trade‐offs among scenarios in terms of overall forest area and the characteristics of the remaining forest in 2050. Meeting demand for biomass from conventional forests resulted in more total forest land compared with a baseline, business‐as‐usual scenario. However, the remaining forest was composed of more intensively managed forest and less of the bottomland hardwood and longleaf pine habitats that support biodiversity. Converting marginal forest to purpose‐grown crops reduced forest area, but the remaining forest contained more of the critical habitats for biodiversity. Conversion of marginal agricultural lands to purpose‐grown crops resulted in smaller differences from the baseline scenario in terms of forest area and the characteristics of remaining forest habitats. Each scenario affected the dominant type of land‐use change in some regions, especially in the coastal plain that harbors high levels of biodiversity. Our results demonstrate the complex landscape effects of alternative bioenergy scenarios, highlight that the regions most likely to be affected by bioenergy production are also critical for biodiversity, and point to the challenges associated with evaluating bioenergy sustainability.     

A cyclical but asynchronous pattern of fine root and woody biomass production in a hardwood forest of southern Quebec and its relationships with annual variation of temperature and nutrient availability

In contrast to the well-documented seasonal variation in growth of below- and above-ground components of trees, the annual variation in below- and aboveground production is not well understood. In this study, we report on the monitoring of an unmanaged hardwood forest ecosystem in a small watershed of southern Quebec between 1993 and 1999. Below- and above-ground biomass production, leaf and soil solution chemistry, and air temperature were measured at different regular intervals and are reported on an annual basis. The objective of the study was to describe the annual dynamics of carbon partitioning between below- and above-ground tree components and to gain a better understanding of the soil and climatic factors that govern it. Fine root production peaked one year earlier than woody biomass production and years with high production of fine roots had low woody biomass production. All models that included May temperature in the calculation of the predicting/independent variables were significant predictors of total tree biomass production (r > 0.87). Fine root production was associated negatively with the previous year average growing season temperature (r < -0.84). Soil solution NO₃ ^–, NH₄ ⁺ and NO₃ ^– + NH₄ ⁺ concentrations were positively correlated with fine root production (r > 0.72) and negatively correlated with woody biomass production (r < -0.84). Leaf N and P concentrations were negatively correlated (r = -0.99 and r = -0.98, respectively) with fine root production for the period of 1994–1998. Our results suggest that a cool growing season, and in particular a cool month of October, is likely to result in low fine root production and nutrient uptake the following year and, therefore, to increase soil N availability and decrease leaf N. This initial response is thought to be the first step of a feedback loop involving plant N nutrition, soil N availability, fine root growth and aboveground biomass production that led to a cyclical (3–4 years) but asynchronous production of fine roots and aboveground biomass production.     

Stand history is more important than climate in controlling red maple (Acer rubrum L.) growth at its northern distribution limit in western Quebec,Canada

Aims We examined growth of red maple (Acer rubrum L.) to evaluate environmental controls of its northern distributional limit in Eastern North America and its potential response to future climate change.Methods We collected growth data from nine sites located along a 300-km transect (47–49°N), which included frontier population of red maple and covered three bioclimatic domains in western Quebec. We analyzed three growth variables: growth rates during the first 30 years of maple lifespan, cumulative basal area increment (BAI) over the most recent decade (2000–2009) and annual growth rate over the whole tree lifespan ranging from 58 to 112 years. We also examined growth sensitivity to climate by using response function analysis.Important findings Three different proxies of maple absolute growth (initial growth rate, BAI during 2000–09 and mean diameter growth rate) indicated a better growth with an increase in latitude. We speculate that stand history effectively overrode the direct effects of colder climate on maple growth along the S-N gradient. Regeneration of maple in the southern sites likely occurred in canopy gaps, whereas in the north it was contingent upon large disturbances such as stand-replacing fires, which apparently provided more favorable light environment for maple growth than canopy gaps. The annual growth variability, which reflects effects of annual weather on growth and is largely independent from the absolute growth rate, was significantly affected by monthly climate, suggesting a positive effect of higher summer temperature in the northern part of the transect (48–49°N) and a negative effect of summer drought in the south (47–48°N). In the future, the natural and human disturbance regimes will be dominant controls of the actual biomass productivity of red maple at the northern limit of its present distribution range. Direct effects of climate on maple growth would likely be less important in this context, and will likely entail negative effect of increased summer drought in the southern part of the study area and positive effects of increased temperatures in the north.     

Gap-scale disturbance processes in secondary hardwood stands on the Cumberland Plateau,Tennessee, USA

Disturbance regimes in many temperate, old growth forests are characterized by gap-scale events. However, prior to a complex stage of development, canopy gaps may still serve as mechanisms for canopy tree replacement and stand structural changes associated with older forests. We investigated 40 canopy gaps in secondary hardwood stands on the Cumberland Plateau in Tennessee to analyze gap-scale disturbance processes in developing forests. Gap origin, age, land fraction, size, shape, orientation, and gap maker characteristics were documented to investigate gap formation mechanisms and physical gap attributes. We also quantified density and diversity within gaps, gap closure, and gap-phase replacement to examine the influence of localized disturbances on forest development. The majority of canopy gaps were single-treefall events caused by uprooted or snapped stems. The fraction of the forest in canopy gaps was within the range reported from old growth remnants throughout the region. However, gap size was smaller in the developing stands, indicating that secondary forests contain a higher density of smaller gaps. The majority of canopy gaps were projected to close by lateral crown expansion rather than height growth of subcanopy individuals. However, canopy gaps still provided a means for understory trees to recruit to larger size classes. This process may allow overtopped trees to reach intermediate positions, and eventually the canopy, after future disturbance events. Over half of the trees located in true gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendron tulipifera. Because the gaps were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. Half of the gap maker trees removed from the canopy were Quercus; however, Acer species are the most probable replacement trees. These data indicate that canopy gaps are important drivers of forest change prior to a complex stage of development. Even in relatively young forests, gaps provide the mechanisms for stands to develop a complex structure, and may be used to explain patterns of shifting species composition in secondary forests of eastern North America.     

毛乌素湖盆滩地土壤温度对寸草苔生长的影响

土壤水热状况影响植物的生长发育、分布以及群落稳定性.选择毛乌素湖盆滩地优势植物寸草苔(Carex duriuscula)进行温控实验,设置对照、升温Ⅰ、升温Ⅱ、降温处理4种土壤温度控温条件,定期测定寸草苔株高、穗数、叶绿素、丙二醛、可溶性糖.结果表明:(1)寸草苔生长指标中,株高与8月之前的土壤温度呈正相关,与8月之后的土壤温度呈负相关;(2)寸草苔生理指标中,丙二醛、可溶性糖在8月底到9月初与土壤温度呈正相关,9月中旬至10月份呈负相关;土壤升温或降温都不利于叶绿素合成.丙二醛、可溶性糖可作为寸草苔植物生长受土壤温度影响的指示参数;(3)构建以土壤温度为自变量、植物生长参数或植物生理参数为因变量的回归模型;土壤温度与穗数的指数模型因其拟合度高,可以预测土壤温度对寸草苔生长的影响.