Annual Basal Area Increment Research Articles

Long-term response of yellow-poplar to thinning in the southern Appalachian Mountains

As the focus of forest management on many public lands shifts away from timber production and extraction to habitat, restoration, and diversity-related objectives, it is important to understand the long-term effects that previous management activities have on structure and composition to better inform current management decisions. In this paper, we analyzed 40years of growth data to quantify (1) the long-term response of yellow-poplar to thinning across an age and site quality gradient, and (2) the longevity of any growth response yellow-poplar may have to thinning throughout the southern Appalachian Mountains. Between 1960 and 1963, 134–0.1ha plots were established across an age and site quality gradient in yellow-poplar (Liriodendron tulipifera L.) stands throughout the southern Appalachian Mountains. All plots were thinned from below, with post-thinning relative density categorized into three classes: low (relative density <0.25), moderate (relative density ⩾0.25 but <0.35), and high (relative density ⩾0.35 but <0.60). Using plot-level annual basal area increment (BAI; cm2 yr−1) chronologies reconstructed from tree cores, average annual BAI was calculated for 10years prior to thinning (BAIpre) and each following 10year period thereafter (BAIpost).Site index and age at the time of thinning had a positive effect on BAIpost. During the first 10year period following thinning, annual BAI (at a site index=32.3m and age=43) averaged (SE) 33.7 (1.6), 26.3 (1.3), and 21.6 (1.1) cm2 yr−1 in the low, moderate, and high density classes, respectively. Significant differences between low and moderate and low and high density classes remained throughout the duration of the study. During the 10years post-thinning the ratio of BAIpost to BAIpre (RBAI) was >1.0 in 92%, 86%, and 57% of plots in the low, moderate, and high density classes, respectively indicating an overall increase in growth relative to pre-thinning growth rates. By the fourth decade post-thinning the percentage of stands containing trees that possessed RBAI values >1.0 had fallen; however trees in 71% of the plots in the low density class continued to experience growth rates greater than those prior to thinning. We conclude the increase in growth is short-lived when density is reduced to moderate and high levels whereas the response of trees to more intense thinnings is long-lasting.

Plant response to climate change along the forest‐tundra ecotone in northeastern Siberia

Russia's boreal (taiga) biome will likely contract sharply and shift northward in response to 21st century climatic change, yet few studies have examined plant response to climatic variability along the northern margin. We quantified climate dynamics, trends in plant growth, and growth-climate relationships across the tundra shrublands and Cajander larch (Larix cajanderi Mayr.) woodlands of the Kolyma river basin (657000km(2) ) in northeastern Siberia using satellite-derived normalized difference vegetation indices (NDVI), tree ring-width measurements, and climate data. Mean summer temperatures (Ts ) increased 1.0°C from 1938 to 2009, though there was no trend (P>0.05) in growing year precipitation or climate moisture index (CMIgy ). Mean summer NDVI (NDVIs ) increased significantly from 1982 to 2010 across 20% of the watershed, primarily in cold, shrub-dominated areas. NDVIs positively correlated (P<0.05) with Ts across 56% of the watershed (r=0.52±0.09, mean±SD), principally in cold areas, and with CMIgy across 9% of the watershed (r=0.45±0.06), largely in warm areas. Larch ring-width measurements from nine sites revealed that year-to-year (i.e., high-frequency) variation in growth positively correlated (P<0.05) with June temperature (r=0.40) and prior summer CMI (r=0.40) from 1938 to 2007. An unexplained multi-decadal (i.e., low-frequency) decline in annual basal area increment (BAI) occurred following the mid-20th century, but over the NDVI record there was no trend in mean BAI (P>0.05), which significantly correlated with NDVIs (r=0.44, P<0.05, 1982-2007). Both satellite and tree-ring analyses indicated that plant growth was constrained by both low temperatures and limited moisture availability and, furthermore, that warming enhanced growth. Impacts of future climatic change on forests near treeline in Arctic Russia will likely be influenced by shifts in both temperature and moisture, which implies that projections of future forest distribution and productivity in this area should take into account the interactions of energy and moisture limitations.

Herbivory-induced mortality increases with radial growth in an invasive riparian phreatophyte

Under equal conditions, plants that allocate a larger proportion of resources to growth must do so at the expense of investing fewer resources to storage. The critical balance between growth and storage leads to the hypothesis that in high-resource environments, plants that express high growth rates are more susceptible to episodic disturbance than plants that express lower growth rates. This hypothesis was tested by measuring the radial growth, basal area increment (BAI) and carbon isotope ratios (δ(13)C) in tree-ring α-cellulose of 62 mature tamarisk trees (Tamarix spp.) occurring at three sites in the western USA (n = 31 live and 31 killed trees across all sites, respectively). All of the trees had been subjected to periods of complete foliage loss by episodic herbivory over three or more consecutive growing seasons by the tamarisk leaf beetle (Diorhabda carinulata), resulting in approx. 50 % mortality at each site. Mean annual BAI (measured from annual ring widths) in the 10 years prior to the onset of herbivory was on average 45 % higher in killed trees compared with live trees (P < 0·0001). Killed trees that had higher growth rates also expressed higher (less negative) δ(13)C ratios compared with live trees. In fact, at one site near Moab, UT, the mean annual BAI was 100 % higher in killed trees despite having about a 0·5 ‰ higher δ(13)C relative to live trees (P = 0·0008). Patterns of δ(13)C suggest that the intrinsic water-use efficiency was higher in killed than surviving trees, possibly as a consequence of lower whole-canopy stomatal conductance relative to live trees. The results show that a likely trade-off occurs between radial growth and survival from foliage herbivory in Tamarix spp. that currently dominates riparian areas throughout the western USA and northern Mexico. Thus, herbivory by D. carinulata may reduce the overall net primary productivity of surviving Tamarix trees and may result in a reduction in genetic variability in this dominant invasive tree species if these allocation patterns are adaptive.

Effects of stabilized wood ash on nutrient status and growth of Scots pine – Comparison between uplands and peatlands

The effects of granulated and self-hardened wood ash on the nutrient status and stem growth of middle-aged Scots pine (Pinus sylvestris L.) stands were studied at two upland and two peatland sites 13years after ash application. The study sites were located in central Finland and represented different site fertility classes. The treatments consisted of an unfertilized control and two different doses of ash, 3 and 9Mgha−1 (upland sites) or 5 and 15Mgha−1 (peatland sites) on fresh weight basis, with both types of wood ash. All four sites had a similar experimental design following the principles of randomized blocks with four replications.The effect of ash treatments on the stand growth depended on the site type and ash dose. At the nutrient-poor upland site, the ash-induced response in the basal area growth was slightly positive and at the more fertile site slightly negative. However, in all cases the growth response at the upland sites was non-significant. At peatland sites, the ash applications increased stand growth remarkably, and the ash-induced basal area response strengthened with time, especially at the more fertile site. The high application rates resulted in stronger responses than the lower doses at the peatland sites. At the end of the study period, the annual basal area increment on the plots treated with the higher application rate of ash was 1.7–1.8-fold at the nutrient-poor site and 4–5-fold at the more fertile site compared with the control.While the trees in unfertilized control plots of peatland sites had sufficient (Site 3) or even an abundance of (Site 4) available N, they were suffering from severe P and K deficiencies (Site 4) or moderate K deficiency (Site 3). Higher dose of both ash types increased needle K concentrations at both peatland sites and that of P at Site 4 above the deficiency limit. At upland sites no nutrient deficiencies were found. All ash treatments increased needle B concentrations both at upland and peatland sites.

Comparison of growth and wood production of Populus deltoides and Paulownia fortunei in Guilan province (Iran)

An area about 3000 m2 located in Shanderman nursary (Guilan province, North Iran) was selected in order to compare increment and wood production of Paulownia fortunei and Populus deltoides (collected from clone no. 69.77), These species were planted at a 4 m by 4 m spacing in the form of complete randomize block design. After planting, they were measured in terms of diameter of the bright height (dbh) and total height. The given parameters were also measured in the second, third and fourth years for determining increment of whole species. The obtained results revealed that after four years, the increment condition of Paulownia fortunei was better than Populus deltoids. The mean annual increment of the both species has increased in comparison with last year and this increment was significant at the 0.01 confidence interval. Mean annual diameter and height increment for Populus deltoides were 2.65 and 201.84 cm, respectively and for Paulownia fortune, it was obtained 5.23 and 298.03 cm, respectively. Mean annual basal area increment of Paulownia fortunei and Populus deltoides was 7.66 and 27 cm2 and there were significant differences between mean dbh, height and basal area increment of Paulownia fortunei and Populus deltoides at the 0.01 confidence interval in this area. Plantation of both Paulownia fortunei and Populus deltoides as pure plantation or mix plantation together did not show a significant difference on mean dbh and height increment of these species at this study area. Keywords: Fast-growing, Increment, Guilan province, Populus deltoids, Paulownia fortunei

Comparison of Growth and Wood Production of Populus deltoides and Paulownia fortunei in Guilan Province (Iran)

An area about 3000 m 2 located in Shanderman nursary (Guilan province, North Iran) was selected in order to compare increment and wood production of Paulownia fortunei and Populus deltoides (collected from clone no. 69.77), These species were planted at a 4 m by 4 m spacing in the form of complete randomize block design. After planting, they were measured in terms of diameter of the bright height (dbh) and total height. The given parameters were also measured in the second, third and fourth years for determining increment of whole species. The obtained results revealed that after four years, the increment condition of Paulownia fortunei was better than Populus deltoides . The mean annual increment of the both species has increased in comparison with last year and this increment was significant at the 0.01 confidence interval. Mean annual diameter and height increment for Populus deltoides were 2.65 and 201.84 cm, respectively and for Paulownia fortunei , it was obtained 5.23 and 298.03 cm, respectively. Mean annual basal area increment of Paulownia fortunei and Populus deltoides was 7.66 and 27 cm 2 and there were significant differences between mean dbh, height and basal area increment of Paulownia fortunei and Populus deltoides at the 0.01 confidence interval in this area. Plantation of both Paulownia fortunei and Populus deltoides as pure plantation or mix plantation together did not show a significant difference on mean dbh and height increment of these species at this study area.

Interactions of thinning and stem height on the drought response of radial stem growth and isotopic composition of Norway spruce (Picea abies)

Radial stem growth and the isotopic composition of growth rings are commonly used to quantify the effects of droughts on trees. However, often these parameters are quantified only at one stem height, e.g., 1.3 m, and it is not known how representative this is for the whole stem. This study investigated radial growth at four stem heights (1.3, 5.5, 9.8 and 14 m) of 21, and wood Δ(13)C and δ(18)O at two heights (1.3 and 14 m) of 10 (co-)dominant Norway spruce trees from heavily (HT) and moderately thinned (MT) stands to assess whether different thinning intensities influenced the drought response of stems at different tree heights. Annual basal area increments (BAIs) and stable isotopes in earlywood and latewood were compared between thinning treatments and among the different stem heights. For BAIs, linear correlations with climate were analysed as well. The response of radial growth and isotopic composition to drought was similar at different stem heights in HT trees, but varied with height in MT trees, which were also more sensitive to climatic variations. Recovery of radial growth after drought was more rapid in trees from HT compared with MT stands, except for the topmost height. Basal area increments at breast height (1.3 m) provided good estimates of the volume growth response to drought for the whole stem, but not for its recovery. The faster recovery of radial growth at 1.3 m height of HT compared with MT trees after the 2003 drought was not accompanied by differences in recovery of isotopic composition. However, this is likely to be related to differences between treatments in remobilization of stored C and in tree structure (leaf area, root systems).

Growth Sensitivity to Drought of Co-OccurringPinusspp. along an Elevation Gradient in Northern Mexico

Climate change is predicted to increase the frequency of severe drought, yet little information exists on the impacts of drought on dominant trees of Mexican pine forests, which are among the most biologically diverse forests in the world. We conducted the first comparison of growth sensitivity to drought of two co-occurring Pinus species in Mexico to understand whether growth of dominant pines of the Sierra Madre Occidental in northern Mexico is sensitive to drought and temperature variation and to understand how sensitivity differs between tree species and elevations. We sampled and analyzed tree-ring data across a 400-m elevation gradient for the years 1945–2004 for co-occurring Pinus engelmannii and Pinus lumholtzii at Basaseachi National Park, Chihuahua, Mexico. We hypothesized that growth sensitivity to drought would be highest at low elevations, annual basal area increment (BAI) would be lowest at low elevations, and winter precipitation would covary positively with BAI at all elevations. Growth sensitivity to drought, as measured by a wet-dry ring-width index ratio (W:D), was significantly higher for both species at low elevations (W:D range 2.2–2.8) than at intermediate and high elevations (WD range 1.5–1.9). Pinus engelmannii had significantly higher W:D (2.2) than P. lumholtzii (1.8). Annual BAI did not differ between elevations or species. Annual ring—width index was positively and significantly associated with winter (December–April) precipitation. This association was stronger at low elevations than at high elevations. Other seasons of precipitation and other climatic variables were not significantly associated with annual growth. Our results suggest that the increasing frequency and severity of drought predicted for this region in the coming decades will reduce growth of P. engelmannii and P. lumholtzii, with greater impacts on low-elevation populations and on P. engelmannii.

Time course of 13C in poplar wood: genotype ranking remains stable over the life cycle in plantations despite some differences between cellulose and bulk wood

Genetic differences in δ¹³C (isotopic composition of dry matter carbon) have been evidenced among poplar genotypes at juvenile stages. To check whether such differences were maintained with age in trees growing in plantations, we investigated the time course of δ¹³C as recorded in annual tree rings from different genotypes growing at three sites in southwestern France and felled at ∼15-17 years. Wood cores were cut from tree discs to record the time course of annual basal area increment (BAI). The isotopic ratio δ¹³C was recorded in bulk wood and in extracted cellulose from the annual rings corresponding to the period 1996-2005. Discrimination against ¹³C between atmosphere and tissues (Δ¹³C) was computed by taking into account the inter-annual time course of δ¹³C in the atmosphere. Annual BAI increased steadily and stabilized at about 8 years. An offset in δ¹³C of ∼1‰ was recorded between extracted cellulose and bulk wood. It was relatively stable among genotypes within sites but varied among sites and increased slightly with age. Site effects as well as genotype differences were detected in Δ¹³C recorded from the cellulose fraction. Absolute values as well as the genotype ranking of Δ¹³C remained stable with age in the three sites. Genotype means of Δ¹³C were not correlated to annual BAI. We conclude that genotypic differences of Δ¹³C occur in older poplar trees in plantations, and that the differences as well as the genotype ranking remain stable while trees age until harvest.

Density–growth relationships in thinned and unthinned Norway spruce and Scots pine stands in Norway

Drawing on national forest inventory data representing a wide range of stand densities, site qualities, ages, and management practices in Norway, this study (1) analyzed the stand density–growth relationships in Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) dominated stands and (2) evaluated the influence of site index, stand age, and thinning on the density–growth relationships. We developed nonlinear growth models that described the periodic annual basal area or volume increment as a function of initial basal area, site index, and stand age. The results showed that for both species, basal area growth increases with stand density although degressive at higher densities. Volume growth increases nearly linearly with stand density. Nevertheless, as demonstrated by the similar shapes of the growth curves, the pattern of the density–growth relationships did not vary considerably by site index classes, by stand ages, and between thinned and unthinned stands. Thinned stands grew about 10% more than unthinned stands of the same density, site index, and age. Our models showed a much stronger decrease of volume growth with decreasing density than previously published results from thinning experiments for the two species in Fennoscandia. The study also demonstrated the suitability of national forest inventory data for analyzing the density–growth relationship.

EFECTO DEL CONTROL DE MALEZAS Y FERTILIZACIÓN SOBRE EL CRECIMIENTO INICIAL DE Gmelina arborea Roxb. EN EL DEPARTAMENTO DEL TOLIMA, COLOMBIA

La revista Colombia Forestal publica manuscritos originales en temáticas del campo forestal y diversos aspectos de los recursos naturales y del medio ambiente, los cuales se discriminan en las categorías de artículo de investigación, de revisión, de reflexión y notas técnicas de acuerdo con lo estipulado por COLCIENCIAS para las publicaciones científicas. De acuerdo a la clasificación de áreas científicas de la Organización para la Cooperación y el Desarrollo Económico (OCDE), la revista Colombia Forestal pertenece al gran área de Ciencias Agrícolas(4), área de Agricultura, Silvicultura y Pesca(4A) y a la disciplina Forestal (4A02).

Fire-Excluded Relict Forests in the Southeastern Klamath Mountains, California, USA

The rare relict ponderosa pine (Pinus ponderosa C. Lawson) mixed-conifer forests of northern California’s Whiskeytown National Recreation Area (WNRA), USA, present a classic example of fire exclusion. Altered fire regimes in this biologically unique area have been documented, but the resulting changes in forest composition and structure have not previously been described. A fully randomized, park-wide sampling of relict forest structure at WNRA reveals a high degree of topographic variability in tree species composition, but strikingly similar changes in recent structural development. A distinct cohort of encroachment trees initiated approximately 64 yr to 67 yr ago with little age variation (2 yr SE), with distinct strata now distinguishing the relict and encroachment cohorts. Over the past five decades, the average periodic annual basal area growth of relict trees has remained at a virtual constant of 24 cm2 to 27 cm2 per tree. In contrast, the annual basal area increment of encroachment trees has been steadily increasing, from 3 cm2 per tree in 1955 to 16 cm2 per tree in 2005. Whereas relict trees are comprised primarily of pine species (76%), they represent just 17% of encroachment trees. In contrast, white fir, Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco.), and tanoak (Lithocarpus densiflorus [Hook. & Arn.] Rehder) are rare among relicts (16%) but are the most predominant species among encroachment trees (64%). This study’s findings should inform the planning of restoration activities to reduce threats to relict forests at the WNRA as well as similar forests in the southeastern Klamath Mountains.

Stand growth models for more intensive management of Juglans nigra: A case study in Croatia

The study focuses on the development of stand growth models for more intensive management of black walnut (Juglans nigra L.) plantations in Croatia. In total, 48 plots were sampled (ages between 3 and 91 years) and, on average, 28.3 trees (between 17 and 43 trees) were measured [diameter at breast height (dbh), total height, two crown diameters, increment core] on each plot. Management scenarios with rotations of 50, 60, 70 and 80 years were developed under three different management regimes: conservative (CAS), high individual tree growth (HTGS) and high stand growth (HSGS). Indicators of competition (current annual increment in dbh, basal area and crown area) were used for scheduling thinning and the intensity of interventions for the intensive scenarios. Depending on the management options and rotation, final stand densities varied between 105 and 210 trees ha−1, mean dbh between 30.4 and 46.1 cm, and total heights between 25.9 and 29.5 m. The mean annual increment in total volume varied between 7.1 and 11.0 m3 ha−1 per year under different rotations and management options, yielding in total accumulated volume of 529–666 m3 ha−1. The CAS yielded the lowest and the HSGS the highest total volume, and HTGS yielded the highest mean dbh.

Subsidy or stress? Tree structure and growth in wetland forests along a hydrological gradient in Southern Europe

In forested wetlands, hydrology exerts complex and sometimes compensatory influences on tree growth. This is particularly true in semi-arid ecosystems, where water can be both a limiting resource and a stressor. To better understand these relationships, we studied hydrologic and edaphic controls on the density, growth, tree architecture and overall productivity of forested wetlands dominated by the tree species Alnus glutinosa and Salix atrocinerea in Southern Europe. We sampled 49 plots set within 21 stands in the Atlantic coastal zone of the Iberian Peninsula, and quantified woody composition, size structure (diameter and height), and radial growth using dendrochronology. Plots were grouped into three saturation classes to compare tree growth characteristics (tree density, degree of sprouting, live basal area and productivity) across levels of saturation. We used Principal Component Analysis (PCA) to create integrated explanatory factors of hydrology, soil nutrient status and soil texture for use in linear mixed models to predict stand characteristics. Increased site saturation favoured a shift in species dominance from Alnus to Salix and resulted in a higher degree of multi-stemmed tree architecture (‘shrubbiness’), particularly for Alnus. Radial growth was negatively correlated with long-term soil saturation; however, annual productivity on a per-tree basis varied by species. Alnus growth and tree density were negatively correlated with waterlogging and fine-textured soils, possibly due to anaerobiosis in the rooting zone. In contrast, Salix growth was more influenced by nutrient limitation. Overall site productivity as measured by annual basal area increment decreased with prolonged saturation. In summary, soil saturation appears to act as a chronic stressor for tree species in this ecosystem. However, these species persist and maintain a dominant canopy position in the most permanently flooded patches through increased sprouting, albeit at a reduced rate of overall biomass accumulation relative to well-drained sites. The diversity in functional responses among wetland forest species has important implications for the conservation and management of these ecosystems. The sustainable management of these ecosystems is directly tied to their vulnerability to changing hydrological conditions. Non-equilibrium modifications to the hydrologic regime from land use and climate change, which are particularly severe in semi-arid regions, may further decrease productivity, integrity and resilience in these stress-adapted communities.

Modelling the production and species richness of wild mushrooms in pine forests of the Central Pyrenees in northeastern Spain

Multiple-use forestry requires comprehensive planning to maximize the utilization and sustainability of many forest resources whose growth and productivity are interconnected. Forest fungi represent an economically important nonwood forest resource that provides food, medicine, and recreation worldwide. A vast majority of edible and marketed forest mushrooms belong to fungi that grow symbiotically with forest trees. To respond to the need for planning tools for multiple-use forestry, we developed empirical models for predicting the production of wild mushrooms in pine forests in the South-Central Pyrenees using forest stand and site characteristics as predictors. Mushroom production and species richness data from 45 plots were used. A mixed modelling technique was used to account for between-plot and between-year variation in the mushroom production data. The most significant stand structure variable for predicting mushroom yield was stand basal area. The stand basal area associated with maximum mushroom productivity (15–20 m2·ha–1) coincides with the peak of annual basal area increment in these pine forests. Other important predictors were slope, elevation, aspect, and autumn rainfall. The models are aimed at supporting forest management decisions and forecasting mushroom yields in forest planning.

Patterns of tree growth in a single tree selection silver fir–European beech forest

The basal area and height growth of trees and saplings in silver fir–European beech single stem selection forest were studied with regard to their social status and crown parameters of size, coverage, shading and vitality. On 24 permanent research plots (20 m × 20 m each) all trees [diameter at breast height (dbh) ≥10 cm] and saplings (≥1.3 m tall and dbh <10 cm) were surveyed. Repeated measurements of dbh (N = 1,608) and height (N = 1,135) 10 years apart enabled the calculation of annual basal area increment (BAI) of trees and saplings, and annual height (HI) increment of saplings. To obtain the growth characteristics for individual trees and saplings, their social status and crown parameters were assessed by rank. In the multivariate general linear model for BAI, social status, crown size and crown coverage of individuals as the predictors, and dbh2 as the covariate, explained 70% of total variability. Similarly, social status, crown size, crown coverage and crown shading had a significant impact on the HI of saplings, explaining 70% of total variability. Among the observed variables, social status determined according to the individual's position in vertical stand structure was, in addition to dbh, the most important predictor for both BAI and HI. Significant differences were observed between the BAI and HI models for the main tree species (European beech and silver fir), indicating their different growth characteristics. The applied method could be used as a supplement to the more widely used approaches for studying basal area and height growth of individual trees in selection forest stands.

Tree Basal Growth Response to Flooding in a Bottomland Hardwood Forest in Central Ohio1

Abstract: Tree basal growth in response to flooding regime was evaluated at a 5.2‐ha bottomland forest along the Olentangy River in central Ohio. Tree‐ring analysis was used to develop a 14‐year basal area increment (BAI) (cm2/year) series for 42 canopy trees (representing 10 species) throughout the bottomland. Mean annual BAI was evaluated relative to the frequency and duration of bankfull (&gt;70 m3/s) and high‐flood (&gt;154 m3/s) river discharge for a given water year (October 1‐September 30) and growing season (April 1‐September 30). A significant polynomial relationship was detected between the number of days of high‐flood river discharge over a combined two‐year period (Year i + Year i − 1) and mean annual BAI. No significant relationships were detected when only the concurrent‐year or previous‐year flood regimes were considered or when growing season was considered. A similar relationship was detected when duration of high‐flood discharge days and BAI were both evaluated in two‐year increments (Year i + Year i − 1). Mean annual BAI was most influenced by boxelder (Acer negundo) which was the dominant species and exhibited strong agreement with the overall BAI series. In each case, the resulting parabolic curve of tree basal growth in response to flooding suggests an optimal number of flooding days, a response to perturbation consistent with the subsidy‐stress model. Dendrochronology may be a useful tool for managers looking to restore environmental flows to regulated rivers.

Watersheds in layers: Landform influences on tree growth and understory species richness

AbstractQuestions:1. Does tree growth differ among bedrock‐controlled and depositional (floodplains and alluvial fans) riparian landforms? 2. Will the elemental composition of tree cores reveal long‐term differences in nutrient availability among bedrock‐controlled and depositional landforms? 3. Is under‐story vascular plant species richness higher on depositional landforms than bedrock‐controlled landforms, and highest yet on floodplains?Location:Lower Indian Creek watershed, a tributary of Turnagain Arm of Cook Inlet, Alaska, USA.Methods:Sampling of riparian forests was stratified by land‐form type. Forest structure, tree growth characteristics, and the elemental composition of tree cores were assessed within point‐centered‐quarter plots (n= 30). Plots were oriented along transects bisecting the valley floor, along which 50 m × 2 m plots (n= 35) were also sampled for understory species composition and richness.Results:Bedrock‐controlled and depositional landforms supported mature trees that did not differ in age, yet structural differences were significant. Forests on depositional landforms were less dense, radial tree growth (cm.a‐1) and annual basal area increments were significantly higher, and tree cores revealed lower C: N ratios than trees growing on bedrock‐controlled landforms. Species richness of vascular plants was higher on depositional landforms at the landform and plot (100 m2) scale. Floodplains supported higher species richness than fans at the landscape scale yet differences at the plot scale were insignificant.Conclusions:Stratification of sampling by landform showed that structural differences between landforms may strongly influence the ecology of riparian plants, and that studies conducted without regard to landform structure may overlook fundamental influences on the ecology of riparian forests.

Long-term calcium addition increases growth release, wound closure, and health of sugar maple (Acer saccharum)trees at the Hubbard Brook Experimental Forest

We surveyed and wounded forest-grown sugar maple ( Acer saccharum Marsh.) trees in a long-term, replicated Ca manipulation study at the Hubbard Brook Experimental Forest in New Hampshire, USA. Plots received applications of Ca (to boost Ca availability above depleted ambient levels) or Al (to compete with Ca uptake and further reduce Ca availability). We found significantly greater total foliar and membrane-associated Ca in foliage of trees in plots fertilized with Ca when compared with trees from Al-addition and control plots (P = 0.005). Coinciding with foliar Ca differences, trees exhibited a significant difference in crown vigor and in percent branch dieback among treatments (P &lt; 0.05), with a trend towards improved canopy health as Ca levels increased. Annual basal area increment growth for the years following treatment initiation (1998–2004) was significantly greater in trees subjected to Ca addition compared with trees in control and Al treatments. Treatment-related improvements in growth were particularly evident after overstory release following a 1998 ice storm. The amount of wound closure was also greatest for trees in Ca-addition plots relative to Al-addition and control plots (P = 0.041). These findings support evidence that ambient Ca depletion is an important limiting factor regarding sugar maple health and highlight the influence of Ca on wound closure and growth following release from competition.

Dynamics of sapling population in savanna woodlands of Burkina Faso subjected to grazing, early fire and selective tree cutting for a decade

Fire, grazing, browsing and tree cutting are major anthropogenic determinants of vegetation patterns in African savannas. In Burkina Faso forest management policies prohibit grazing while recommending annual early fire and selective tree cutting of 50% of the merchantable standing volume on a 20-year rotation period. These management prescriptions are not based on long-term experimental evidence, particularly the responses of saplings to these management regimes are not well known. A factorial experiment with two levels was designed to examine the effects of moderate level of grazing, early fire and selective tree cutting on the dynamics of sapling populations on two sites, Laba and Tiogo, in the savanna woodland of Burkina Faso and assessed for 10 years from 1992 to 2002. Species richness, sapling population density, structure and growth were analysed. The results provide evidence that fire, grazing and selective cutting acted independently to influence the population dynamics of saplings. Annual early fire significantly reduced species richness ( p = 0.037 in Laba and p = 0.016 in Tiogo), population density ( p < 0.001 in Laba and p = 0.003 in Tiogo) and current annual increment (CAI) in basal area ( p < 0.001 in Laba and p = 0.016 in Tiogo). Grazing and fire affected sapling morphology but the response was site specific. Selective removal of trees did not affect any of the parameters studied, except the CAI in dominant height at the Tiogo site which was significantly ( p = 0.028) reduced by the cutting treatment. Early fire also significantly reduced the CAI in dominant height at Laba. The height class distribution revealed that more than 93% of the saplings recorded were less than 400 cm tall, and fire significantly reduced the rate of change in density of saplings in the 200–400 cm height class. It can be concluded that annual early fire was the factor that most affected sapling recruitment. The sapling response to these management regimes was species specific.