Mean Stem Height Research Articles

How the scrub height of dwarf pine Pinus pumila decreases at the treeline

AbstractPlant height decreases much within narrow altitudinal spans near treelines. We compared the stem age, stem inclination and shoot elongation rates of alpine dwarf pine Pinus pumila between the upper distribution limit (treeline, 2,850 m a.s.l.) and the lower distribution limit (2,500 m a.s.l.) on Mount Norikura in central Japan, to examine how the growth traits of P. pumila change with altitude. The mean stem height at the upper distribution limit (49 cm) was about a quarter of that at the lower distribution limit (187 cm). The mean ratio of stem height to length was lower at the upper distribution limit than at the lower distribution limit, indicating that P. pumila stems inclined more at the higher altitude. The mean stem age at the upper distribution limit (48 years) was less than a half of that at the lower distribution limit (109 years). Although the shoot elongation rate positively correlated with stem length at the two altitudes, the shoot elongation rate at a given stem length was lower at the upper distribution limit than at the lower distribution limit. Thus, less developed scrub at the upper distribution limit than at the lower distribution limit was due to shorter stem age, more creeping stems and lower shoot elongation rates. Generally, wind velocity is greater in higher altitudes. Probably, strong wind reduces the growth and mean stem age of P. pumila stems at the upper distribution limit. Therefore, this study concludes that the scrub height of P. pumila is controlled not only by temperature, but also by strong wind.

Phytotoxicity assessment

Phytotoxicity assessment

Frost hollows of the boreal forest as extreme environments for black spruce tree growth

An extensive survey of spruce growth forms was conducted in frost hollows of the Parc national des Grands-Jardins located in the highlands of the Charlevoix region (Quebec). Frost hollows studied were situated within lichen woodlands, which are a favourable environment for the formation of cold air masses. The mean number of frosts recorded 1 m aboveground during the growing seasons of 1997–2002 indicates that there is no frost-free period in frost hollows. Based on the records of minimum temperature in two frost hollows, the critical threshold for frost-ring formation is a nocturnal temperature below 0 °C for 6.4 h with a climax at around –5.7 °C, i.e., at a cooling rate of 1.78 °C/h under the freezing point for at least 3.2 h. Frequent and severe nocturnal frosts slow down the colonization of black spruce in frost hollows, and are at the origin of the inverted tree line that surrounds frost hollows. Mean stem height of black spruce in frost hollows is 1.97 m ± 2.15. A comparative analysis of aerial photographs between 1950 and 1996 showed a 34% reduction in frost hollow area due to the progressive colonization of black spruce. Massive tree establishment occurred in frost hollows between 1970 and 1980 because of the reduced frequency of freezing temperatures during the growing season.

Assessing fine beam RADARSAT-1 backscatter from a white mangrove (Laguncularia racemosa (Gaertner)) canopy

To determine whether spaceborne Synthetic Aperture Radar (SAR), specifically fine beam RADARSAT-1 C-band, could be used to provide quantitative data on white mangrove (Laguncularia racemosa (Gaertner)) forests, backscatter coefficients (σ°) were examined in relation to structural parameter data collected from plots located in a mangrove forest of the Mexican Pacific. Significant coefficients of determination were recorded between the backscatter coefficients and the logarithms of both Leaf Area Index (LAI) and mean stem height at two incident angles for both the dry and wet seasons. The highest coefficients of determination for LAI (r 2 = 0.60) and mean stem height (r 2 = 0.72) were observed using the shallower (~40°) and steeper (~47°) incident angles, respectively. No significant relationships were recorded between the backscatter coefficients and either stem density, basal area or mean DBH. Given the results of this investigation, it is recommended that for cloud covered regions, fine beam RADARSAT-1 data could be used by resource managers when they require a quick method for surveying structural damage to mangroves resulting from both natural and anthropogenic causes.

An integrated management strategy for the control of purple loosestrife Lythrum salicaria L. (Lythraceae) in the Netley-Libau Marsh, southern Manitoba

We evaluated the eVectiveness of an integrated vegetation management strategy (IVM) for the management of purple loosestrife (Lythrum salicaria) by comparing the performance of herbicides alone (glyphosate and triclopyr amine), a biological control agent (Galerucella calmariensis) alone, and herbicides integrated with the biological control agent. The study was conducted from 1996 to 1998 within Weld-cages placed in a 2-ha stand of purple loosestrife located in southern Manitoba. Using a randomized complete block design, each treatment was replicated three times. Herbicides were applied in the summer of 1996 while G. calmariensis were released at either low-densities (12 adults) or high-densities (24 adults) in 1997. We measured performance using data on Wnal stem heights, terminal spike length, the number of Xowering spikes, and the number of seed capsules in each year and the total number of all stems at the end of each year. Integrated treatments were found to cause signiWcant reductions in the mean number of purple loosestrife stems. The G. calmariensis alone treatments resulted in no signiWcant change in mean stem densities; however, herbivory reduced mean stem heights by almost 70%. Mean stem densities of purple loosestrife increased in the herbicide alone treatments when compared to pretreatment levels. Results indicated that an IVM strategy using herbicides integrated with G. calmariensis outperformed herbicide alone treatments and G. calmariensis alone. While further open-Weld investigations are required, these results have important management implications.  2004 Elsevier Inc. All rights reserved.

Using 1-min scans and stem height data in a post-release monitoring strategy for Galerucella calmariensis (L.) (Coleoptera: Chrysomelidae) on purple loosestrife, Lythrum salicaria L. (Lythraceae), in Manitoba

Abstract The emergence of a North American classical biological control program against purple loosestrife has offered opportunities to develop post-release monitoring strategies providing objectively measurable results. The biological control agent Galerucella calmariensis, a leaf-feeding beetle, was released into a purple loosestrife (Lythrum salicaria) population in the Netley-Libau Marsh in southern Manitoba. A total of 578 adult beetles were released into a fixed monitoring station (FMS) between 1994 and 1995. The FMS was 10-m long by 5-m wide and divided into 1-m2 sampling quadrats. A 1-min visual scan was used to estimate the number of egg masses, adults, and larvae present in randomly selected 1-m2 sampling units. Similar data were also collected from 30 (3 in each of 10 quadrats) randomly selected stems. Data were collected about every 10 days from late May to September from 1996 to 2001. Heights of all stems in each 1-m2 sampling unit were measured in the fall of each year. Mean stem-height data derived from 30-tagged stems indicated that G. calmariensis had suppressed mean stem heights by 30%, while 56% of the all tagged stems were dead by late July by 1998 [4-years post-release (YRPR)]. By the fall of 2000 (6-YRPR), G. calmariensis herbivory resulted in eradication of all purple loosestrife stems. The results of this study indicated that: (1) simple 1-min visual scans employed every 10-days can be used for post-release monitoring to provide objective measures of G. calmariensis establishment and phenology, (2) using three randomly selected stems per quadrat or all stems in a quadrat can be used to measure plant performance, and (3) G. calmariensis can be used in a single-species release strategy against purple loosestrife.

Defining deer overabundance and threats to forest communities: From individual plants to landscape structure

Changes in habitat and reduction in predation and hunting pressure are two primary causes of high-density populations of white-tailed deer (Odocoileus virginianus) in many areas of eastern North America. Despite increasing recognition of the major effects deer exert on forest communities, deciding when deer are overabundant remains a major challenge to managers charged with conserving native plant communities. In this context, we define overabundance as a condition where deer are causing the local extinction of a native plant species. Because this definition is difficult to apply from a management perspective, we outline an approach using native understory forbs. Indicator species are selected based on combined criteria of palatability to deer, leaf and flower morphology, and demographic characteristics. Four indices related to plant population viability are derived from understory survey data: flowering rate, mean stem height, stage-class distribution, and deer browsing pressure. We apply this analysis to Trillium populations from forests in Minnesota (highly fragmented agricultural landscape with varying deer densities), Pennsylvania (forested and fragmented landscape with long-term high deer densities), and New York (forested and fragmented landscape with long-term low deer densities). We observed two distinct types of deer-affected plant populations. In sites with moderate or recent increases in deer density, Trillium populations were characterized by low mean plant size, high browsing rates, intermediate flowering rates, and a size class distribution lacking large, reproductive plants. Sites affected by long-term high deer densities exhibited low browsing rates on Trillium, low Trillium flowering rates, a population structure lacking both large and small plants, and high summer browsing pressure on woody saplings. We suggest these combined indices be used to assess deer browsing impact, and we discuss the role of landscape structure and deer density in defining deer overabundance.

Biological constraints on the growth of hardwood regeneration in upland Piedmont forests

The effects of aboveground fungi, insects, browsing mammals and weeds on the growth (height, diameter and volume index) and density of hardwood stems were studied on three upland sites in the Piedmont of North Carolina, USA during the first two growing seasons following clearcutting. Competition from weeds was the most detrimental to hardwood growth. Pesticide treatments alone (broad-spectrum insecticide, fungicide and mammal repellent) did not significantly increase growth. Compared to the control (no weeding or pesticides), stems receiving the pesticide+weeded treatment increased in height 1.6–4.5 times, diameter 1.7–5.3 times and volume index 3.4–5.1 times by the end of second growing season, across all sites. Stem density did not exhibit clear treatment effects, although individual tree mortality and recruitment in the plots were not recorded. Exclosures, with weeding, to eliminate the browsing impact of white-tailed deer ( Odocoileus virginianus Zimmermann), installed only during the second year of study, yielded a 1.9, 1.6 and 3.2 times increase in mean stem height, diameter and stem volume index, respectively, as compared to weeded only plots. Results indicate that very young hardwood regeneration can respond quickly to release from biological constraints and the rate of stand establishment and development may be enhanced with stand manipulations in the first two growing seasons.

Interaction of vegetation control and fertilization on conifer species across the Pacific Northwest

An experiment evaluating three levels of vegetation competition control (no control, 1.5 m2of vegetation control, and 3.3 m2of vegetation control), each with two fertilization treatments (fertilization at the time of planting with complete slow-release fertilizer (Woodace®IBDU), or no fertilization), was installed at five sites. Two of these sites were planted with Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in the Oregon Coast Range, one with ponderosa pine (Pinus ponderosa Dougl. ex P. Laws. & C. Laws.) in eastern Washington, one with western hemlock (Tsuga heterophylla (Raf.) Sarg.) in the coastal hemlock zone in Oregon, and one with coastal redwood (Sequoia sempervirens (D. Don) Endl.) in northern California. At four of the five sites, mean stem volume, basal diameter, and height of seedlings increased significantly with increasing area of weed control, and the magnitude of difference between treatments increased with time. Fertilization significantly increased seedling size only at the two sites with adequate soil moisture; increases were marginally significant at a third. Response to fertilization was less than from weed control and impacted growth for only the first year, whereas the influence of weed control continued to influence growth the entire length of the study (4 years). Area of vegetation control and fertilization did not interact significantly at any site.

Growth Responses of Carya ovata (Juglandaceae) Seedlings to Experimental Sun Patches

The heterogenous structure of eastern deciduous forest canopies creates an understory light continuum ranging from deep shade to extended periods of direct solar irradiance below large canopy gaps. We designed an experiment to explore how shagbark hickory (Carya ovata (Mill.) K. Koch; Juglandaceae) seedlings respond to changes in both the total amount of available light and the durations of experimental sun patches. Seedlings were grown in a common garden under shadehouses where they experienced one of two light levels (high vs. low light), one of two sun patch durations (short vs. long duration) and 100% light (control). Over the growing season, seedlings responded morphologically to the amount of available light by changes in mean stem height, weight, basal diameter, specific leaf mass, chlorophyll content, taproot length, primary and secondary root weight and root ash weight. Chlorophyll content and stem height were negatively related to the amount of available light whereas the other morphological characters were positively related to increased amounts of light. Changes in the duration of experimental sun patches significantly affected stem biomass, basal diameter, secondary root dry weight and root ash weight independent of total light amount. Though the effects of sun patch duration were not as pronounced as those found for amount of light, our results demonstrate the importance of including periods of direct light in experimental designs involving responses of seedlings to varying light regimes. The ecological responses of many hardwoods, especially those of midshade tolerance, to the middle portion of the gap-understory continuum remain poorly studied.

Mortality and growth of cut pieces of viviparous mangrove ( Rhizophora apiculata and R. mucronata) seedlings in the field condition

Viviparous seedlings of the mangrove species Rhizophora apiculata and R. mucronata were divided into even lengths of the top, middle, and bottom parts, and these cut pieces were planted in the field. The mortality and growth were monitored for 38 months after transplantation, and compared with intact seedlings planted in the same place. Both mean diameter and stem height of R. mucronata cut pieces were largest for the bottom parts, intermediate for the middle parts, and the smallest for the top parts. Among cut pieces of R. apiculata, the pattern for diameter was the same, but the mean stem height showed no differences among treatments. For both species, the mortality was associated with the initial volume of individual cut pieces. The bottom cut pieces with large volumes showed lowest mortality. Almost all cut pieces of R. apiculata formed prop roots above ground, but only 30% of R. mucronata cut pieces formed them. In the 38-month-old plantation, the mean diameters of the various cut-piece treatments of R. apiculata and R. mucronata were, respectively, 0.78–1.37 and 0.56–0.89 times as large as those for the intact seedlings; corresponding values for mean stem heights were 0.81–0.85 and 0.50–1.00. These results suggest a possibility that cut pieces can be a useful plantation material.

Topographic variations of soil properties and stand structure in a Pinus thunbergii plantation

AbstractSoil properties and above‐and belowground forest structure were studied across various topographies in a 20‐year‐old Pinus thunbergii Parl. plantation on Mt Tanakami, Japan. The soil properties and stand structure varied greatly with slope position fromridge top to valley floor. Soil thickness, fine soil content and soil moisture content were greater in lower slope positions. The amount of organic carbon in the forest floor was greater in upper slope positions. The organic carbon content in the mineral soil was slightly greater in lower slope positions. These changes in soil properties suggested an upslope decrease in decomposition rate and water and/or nutrient availability. The aboveground structure of P. thunbergii was more developed at lower slope positions. The mean stem diameter, height and volume of P. thunbergii increased downslope with decreasing tree density. However, fine root biomass increased greatly upslope. This inverse relationship between tree height and fine root biomass indicated morphological plasticity of P. thunbergii in exploiting environmental heterogeneity. Variations in soil‐plant interactions in the stand along various topographies caused spatial heterogeneity in the accumulation pattern of organic matter in plants and the soil.

Effects of waves on helophyte stands: mechanical characteristics of stems of Phragmites australis and Scirpus lacustris

The effects of wave attack on stands of the two species Scirpus lacustris L. and Phragmites australis (Cav.) Trin. ex Steudel were studied in a wave tank, and related to bending and breaking characteristics of the stems. Stands of the two species, growing at a water depth of 0.5 m, were exposed to uniform waves with a height of 0.23 m high and a wave period of 1.9 s. Mean stem height and density were reduced strongly in the S. lacustris stands after wave attack. The effects of wave attack on mean stem height and density of P. australis stands were much less pronounced. In both species, critical breaking force and flexural stiffness of stems increased with individual stem height. Bending stiffness was much lower in S. lacustris stems (mean E = 0.25 GPa) than in P. australis stems (mean E = 4.93 GPa). Seasonal variation in stiffness was observed in P. australis stems but not in S. lacustris; for P. australis, E was lower in February (dead standing stalks) and June (young shoots), than in August. Stands of P. australis withstand exposure to waves better than S. lacustris stands as the result of a higher bending stiffness of the stems and a lower susceptibility to breaking under mechanical stress. Therefore, S. lacustris can grow in waterside helophyte fringes when wave exposure is moderate or absent, but cannot survive at highly wave-exposed shores.

Effects of shallow flooding on newly established purple loosestrife seedlings

Purple loosestrife (Lythrum salicaria) is a nuisance exotic species that displaces native plants and has little value as food or habitat for wildlife. Attempts to control adult plants have had limited success. We investigated the effects of shallow flooding ( 0.05). The flooding treatments significantly affected mean stem heights, but there were no identifiable trends within size classifications. All seedlings continued to grow during the experiment. The survival of any purple loosestrife plants can have serious implications in wetlands. The results from this study indicate that shallow flooding is not an effective approach to limiting or preventing establishment of purple loosestrife seedlings.

Growth in controlled water regimes of three grasses common in freshwater wetlands of the southeastern USA

Growth and drought tolerances of three common freshwater wetland grasses, Panicum hemitomon Schult., Manisuris rugosa (Nutt.) Kuntze, and Leersia hexandra Sw., were compared in experimental manipulations. Additionally, the effect of fire on the growth of P. hemitomon was examined. Rhizomes of these three perennial species were grown in small plastic pools under the following water treatments: (1) moist soil; (2) saturated soil (0 cm water depth); (3) inundated (13 cm water depth all year); (4) inundated-moist (13 cm water depth part of the year, followed by moist soil). Inundated plants of all species grew twice as tall as those in the moist soil treatment. This difference was interpreted as an elongation response to partial submergence. Under inundated conditions, stem elongation in M. rugosa was the same regardless of the water duration or depth. In P. hemitomon, stem heights varied with duration and depth of flooding: inundated > inundated-moist > saturated. For L. hexandra, mean stem height did not differ between inundated-moist and saturated water regimes. Mean above-ground to below-ground biomass ratio for L. hexandra was greater than that of either P. hemitomon or M. rugosa regardless of treatment. Panicum hemitomon produced no flowering stems under any of the treatments. For M. rugosa and L. hexandra, most flowering stems were produced under the inundated or saturated treatments. Winter fire, followed by the inundated or inundated-moist treatments, had a negative effect on emergence and overall growth of P. hemitomon, suggesting that winter stems are important for survival of this species. Relative drought tolerances, as measured by stomatal conductance and predawn xylem pressure potential, indicated least stomatal control by L. hexandra, followed by P. hemitomon and M. rugosa. Results suggest greater drought tolerance by M. rugosa and greater flood tolerance by P. hemitomon and L. hexandra.

Interactions between Apion species (Coleoptera: Curculionidae) and Polygonaceae. II. Apion violaceum Kirby and Rumex obtusifolius L.

Abstract. The biology of Apion violaceum is described, particularly with respect to its primary host, Rumex obtusifolius. Oviposition in Rumex acetosa is directly into the stem, but in R. obtusifolius it takes place through the sheath enclosing developing flowers, stem leaves and stem. Larvae cannot complete development in the leaf petioles and must migrate downwards to the stem or die before pupation. Mortality of A. violaceum in the stems was highest in eggs and first instar larvae and in third instar larvae. The latter mortality was caused almost entirely by parasitoids. Stems of R. obtusifolius on the study site increased in number up to August and reached the maximum height in late June. Over the 4 year study period there was a parallel decline in stem numbers and mean stem height at two of the sites studied. At these sites there was also a decline in A. violaceum numbers and density per stem. The quality of sites for A. violaceum, as defined by the product of stem numbers and stem height, showed a significant correlation with A. violaceum numbers.

The Paradox of Plant Height in an Andean Giant Rosette Species

(1) Espeletia schultzii (Compositae), a perennial rosette species common above the treeline in the Venezuelan Andes, increases in mean stem height and maximum stem height with increasing altitude, whereas, in general, species occurring above tropical and temperate treelines decrease in size with increasing elevation. (2) Greater height in E. schultzii is the result of greater longevity, which may be caused by reduced interspecific competition, and by reduced intraspecific competition between pre-reproductive and adult plants. (3) In addition, selection at high altitudes may favour genotypes which produce longer-lived plants.