Local Basal Area Research Articles

Multi-taxon conservation in northern forest hot-spots: the role of forest characteristics and spatial scales

ContextBiodiversity is highly affected by industrial forestry, which leads to the loss and fragmentation of natural habitats. To date, most conservation studies have evaluated associations among a single species group, forest type, or spatial scale.ObjectiveThe objective was to evaluate the richness of multiple species groups across various forest types and characteristics at multiple scales.MethodsWe used the occurrence data for 277 species of conservation interest from 455 stands of high conservation value, including four species groups and four forest types.ResultsLocal, landscape, and regional forest characteristics influenced biodiversity in a non-uniform pattern among species groups and forest types. For example, an increased local spruce basal area in spruce forests was associated with higher vascular plant and bryophyte richness values, whereas macrofungi and lichen richness were positively correlated with deadwood availability, but negatively correlated with the spruce volume in the landscape. Furthermore, landscapes with twice as much mature forest as the average, had more than 50% higher richness values for vascular plants, macrofungi, and lichens.ConclusionAmong sessile species groups in northern forests, a uniform conservation strategy across forest types and scales is suboptimal. A multi-faceted strategy that acknowledges differences among species groups and forest types with tailored measures to promote richness is likely to be more successful. Nevertheless, the single most common measure associated with high richness across the species groups and forest types was mature forest in the landscape, which suggests that increasing old forests in the landscape is a beneficial conservation strategy.

The stochastic backward shifts model better corresponds to the fine-scale structural heterogeneity of old-growth Abies-Fagus-Picea forests than the ontogenic life cycle model

The ontogenic forest life cycle of regeneration, maturation, senescence and death is a common starting point for the conceptualization of developmental pathways in forest ecosystems. Nonetheless, the usefulness of this framework under natural stand dynamics in small tree collectives formed by individuals with overlapping and weakly synchronised life cycles is not evident. This research investigated empirical relationships between local structural attributes linked with biomass accumulation, mortality in the canopy zone, the occurrence of undercanopy trees and structural heterogeneity quantified in small spatial scales and compared them with anticipations derived from the theoretical ontogenic life cycle model. The material was collected in six old-growth, mixed-species and mixed-aged forests consisting of European beech (Fagus sylvatica L.), silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) H. Karst.) and situated in the central Dinaric Mts. (Bosnia and Herzegovina) and Western Carpathians (southern Poland). In each of the stands, a dense grid of circular plots with a radius of 7 and 15 m was established on an area of about 10 ha, and all live (d1.3 ≥ 7 cm) and dead trees (d1.3 ≥ 20 cm) growing within the plots were registered. The analyses indicated that the relationships between local basal areas of live and dead trees are very weak. Ambiguous relationships between the basal area of live and dead trees and the density of undercanopy trees, the high level of structural heterogeneity in small stand patches, and the tendency towards increasing structural heterogeneity with increasing biomass accumulation suggest that the life cycle model based on the sequence of ontogenic phases is a poor projection of the local developmental pathways in the studied ecosystem. The high level of structural heterogeneity found in small stand patches corroborated the alternative hypothesis that the mortality of canopy trees in most cases releases younger or suppressed individuals with delayed growth and only sporadically leads to the formation of a canopy opening reaching the forest floor. A general framework for an alternative model based on stochastic backward shifts was proposed. It emphasizes the diversity of possible developmental trajectories and assumes that the death of a canopy tree shifts local basal area and frequently also structural heterogeneity backwards on the developmental pathway. Depending on the pre-disturbance situation and the kind of disturbance factor, stochastic backward shifts may lead to different “states” in the space of structural attributes.

Assessing the influence of vegetation structure and phenological variability on pollen‐vegetation relationships using a 15‐year Neotropical pollen rain record

AbstractQuestionsPollen collected from aerial pollen traps are used to interpret compositional changes in the fossil pollen record. Relationships between pollen abundances and vegetation are commonly measured using the ratio between the abundance of a pollen type and its corresponding basal area in a plant community (R‐rel). Pollen–vegetation relationships have been extensively studied in temperate and boreal latitudes using surface sediment, moss polster and pollen trap samples, representing long‐term accumulations of pollen. In contrast, pollen–vegetation relationships are not well‐resolved in diverse tropical habitats because of a lack of modern long‐term pollen and vegetation datasets. In the present study, we address two primary questions: 1. How variable are tropical pollen–vegetation relationships measured using R‐rel over time? 2. To what extent are differences in pollen abundances among traps related to variability in basal area in the surrounding community?LocationBarro Colorado Island, Panama.MethodsVariability in an annually sampled, 15‐year pollen rain was compared with annual basal area data collected over the same timeframe using R‐rel.ResultsR‐rel values were highly variable on a year‐to‐year basis and more consistent over time‐averaged sampling windows ≥3 years. A strong positive relationship between pollen abundances and local basal area surrounding pollen traps was determined in eight taxa.ConclusionsThe pollen–vegetation relationships provide a summary of the pollen representation of Neotropical taxa common in paleoecological samples over an extended sampling duration that approaches the timespan represented in lake sediment samples (~20 years). The results highlight taxa in which differences in pollen abundances among traps were strongly correlated with changes in surrounding basal area.

Seedling emergence in uneven-aged Norway spruce stands in Finland

ABSTRACTThe emergence of Norway spruce seedlings on different types of germination sites in uneven-aged Norway spruce dominated stands four years after selection harvesting was studied. The data were collected from 20 stands in southern Finland. In each stand, ground cover was measured from a set of 64 one square metre subplots on a permanent experimental plot of 1600 m2. Correlation analysis, direct comparison of subplots with and without seedlings and mixed-effects models were used to estimate the influence of ground and tree cover on seedling occurrence. Grass cover, dwarf shrub cover, cover of certain moss species and close vicinity of trees decreased the occurrence probability and number of seedlings, while greater stand and local basal area around the subplots increased the seedling number. The cover of vegetation free surfaces, usually considered as good germination sites, was rather low. Variation in seedling emergence between plots was high. We concluded that spruce regeneration was slightly more abundant in stands with greater overall stand density and local density within a stand in postharvest conditions.

Local basal area affects needle litterfall, nutrient concentration, and nutrient release during decomposition in Pinus halepensis Mill. plantations in Spain

Stand density has a positive effect on C, K and Mg concentration in needle litterfall and a negative one on C, N, Ca, K, Mg, P, S, Zn, and Cu release from needle litter. Consequently, forest management practices such as thinning decrease nutrient concentration in needle litterfall and accelerate nutrient release from decomposing needles in Pinus halepensis plantations in Spain. Silvicultural practices usually include stand density reduction resulting in changes in litterfall and litter decomposition rates. Little is known about the effect on nutrient concentrations in litterfall and nutrient release during decomposition even when this is the main path of nutrient return to soils. The aims of the study are to evaluate the seasonal pattern of nutrient concentration in litterfall, to study how nutrients are released from needle litterfall during decomposition, and to assess whether local basal area of the stand affects nutrient concentration of litterfall and nutrient release during litter decomposition. Eight plots were established on each of four stands covering the widest range in local basal area. A littertrap and 15 litterbags were placed on each plot. Periodically, needle litterfall and litter contained in the litterbags were analyzed for C, N, Ca, K, Mg, P, S, Fe, Cu, Mn, and Zn. Local basal area had a positive effect on C, K, and Mg concentration in needle litterfall and a negative effect on the release of all the nutrients studied but Fe and Mn during the first 2 years of litter decomposition. Density management of stands has an impact on nutrient cycling, reducing nutrient concentration in needle litterfall, and accelerating nutrient release during decomposition.

Norway spruce cone crops in uneven-aged stands in southern Finland: A case study

Norway spruce cone crops in individual trees from two seed ripening years 2012 and 2014 were studied. Data were collected from five stands in southern Finland, managed by single-tree selection harvests since the 1980s. The upper third of living crown of each individual tree was photographed for digital cone counting with image analysis. The average number of cones per tree for trees bearing any cones was 92 in 2014 and 66 in 2012. Highest cone numbers found per individual tree were 526 in the year 2014 and 364 in the year 2012. Of all trees studied, 55.5% produced cones during both years, 9.6% produced cones once and 34.9% did not produce cones in 2012 or 2014. The number of cones per tree in 2014 was positively correlated with tree diameter at breast height and the presence of cones (at least twenty) in that particular individual two years earlier and negatively correlated with local basal area. The quality of the seed crop in 2014 as determined in two of the stands was poor. Based on X-ray analyses, 44% of seeds were empty, 29% were damaged by insects feeding on seeds (Plemeliella abietina or Megastigmus strobilobius) and only 25% were full and capable of germination. The results have implications for management practices in uneven-aged Norway spruce stands. It is suggested that at each harvest entry, some large, prolific trees should be retained in order to increase the total number of seeds produced in a stand to enhance regeneration and the recruitment of new seedlings.

Modeling and predicting solar radiation transmittance in mixed forests at a within-stand scale from tree species basal area

Light under tree canopy cover is essential for the study and understanding of plant diversity, regeneration, plant growth and many other forest ecosystem processes; however, quantifying light is difficult and requires specialized equipment. That is why proxies or models predicting light availability can help scientists to obtain estimates of transmittance and forest managers to better assess and adjust silvicultural practices at a reasonable cost. The main objective of our research was to develop a model to predict local solar radiation transmittance from species basal area in mono-specific and mixed stands of sessile oak (Quercus petraea) and Scots pine (Pinus sylvestris). Models based on the Beer-Lambert law were fitted and compared using 163 measures of solar radiation transmittance obtained from hemispherical photographs and light sensors. In mono-specific stands, local transmittance was predicted by local basal area considered on a radius equaling approximately tree height. In mixed stands, the same model broken down into its mono-specific components (local basal area of each species multiplied by their own extinction coefficients) predicted transmittance well. The extinction coefficients we obtained were very close to those previously established for these species and did not differ between mono-specific and mixed stands. Our model explained 77% of the variation in transmittance when random effects were included and 64% of the variance without taking into account these random effects. The predictive value of the model was good with high accuracy (mean signed deviation not significantly different from zero) and a fairly high precision (relative mean absolute error=20%). The fact that tree canopy transmittance in mixed stands can be predicted by extinction coefficients obtained from mono-specific stands indicates that modifications in crown structure and leaf distribution are only slight, or even non-existent, when the two species grow in a mixture.

Partial harvesting in boreal mixedwoods: A case for planned heterogeneity in industrial silvicultural prescriptions

In large areas of the boreal mixedwoods of eastern Canada, conventional forestry practices dominated by large-scale clearcutting have led to an increase in early-successional trembling aspen (Populus tremuloides Michx.) stands and a decrease in late-successional mixedwood stands. Partial harvesting provides an alternative practice that could promote a return to mixedwood composition with greater potential economic returns. Our objective was to identify the stand attributes that have an effect on trembling aspen regeneration following industrial harvest operations. Ninety plots were surveyed immediately before and five years after partial harvesting, to collect information on harvested trees (stumps), residual cover and pre- and post-harvesting regeneration. Using zero-inflated beta regression models, we found that the transition probabilities (projected relative abundance) of trembling aspen were positively influenced by an increase in removal percentage and by an increase in initial basal area of trembling aspen in the overstory. Abundant balsam fir advance growth had a strong negative influence on trembling aspen transition probabilities. This information could be incorporated into silvicultural prescription decision tools to suggest optimal local basal area removal targets that would limit the regeneration success of trembling aspen. Using these results, we propose a new approach that consists of deliberately introducing heterogeneity within partial cutting prescriptions in order to limit deciduous encroachment and to promote the recruitment of coniferous regeneration in eastern Canadian boreal mixedwoods.

Multiscale Controls on Natural Regeneration Dynamics after Partial Overstory Removal in Douglas-Fir Forests in Western Oregon, USA

We examined natural regeneration following operational-scale variable density retention treatments in 40 – 60-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests at seven sites for a decade following treatment. Treatments included residual overstory densities of 300, 200, and 100 trees/ha, with leave islands and gaps of three sizes (0.1, 0.2, and 0.4 ha) and an untreated control (600 trees/ha). Natural regeneration was influenced by factors from multiple spatial scales including broad-scale differences in overstory composition among sites, mesoscale variability in topographic position, and fine-scale variability in overstory and understory competition. High local basal area (BA) decreased the probability of seedling establishment, though some seedlings established even under high BA, particularly shade-tolerant western hemlock. In contrast, recruitment of saplings (> 1.37 m height) required lower residual overstory density (i.e., 100 trees/ha), especially for shade-intolerant Douglas-fir. Understory vegetation had little effect on saplings but was negatively related to seedling densities, particularly when overstory density was low. Variable density prescriptions can take advantage of the importance of fine-scale variability to promote regeneration of desired species mixtures, though other factors such as site overstory species composition and variation in topographic position will also influence regeneration dynamics. Including heavy overstory removal or gap creation could facilitate rapid recruitment of saplings, especially for shade-intolerant Douglas-fir.

Predicting Stem Windthrow Probability in a Northern Hardwood Forest Using a Wind Intensity Bio-Indicator Approach

Unlike fire or insect outbreaks, for which a suppression program can be implemented, it is impossible to prevent a windstorm event or stop it while it is occurring. Reducing stand susceptibility to windstorms requires a good understanding of the factors affecting this susceptibility. Distinct species- and size-related differences in stem windthrow susceptibility are difficult to obtain because it is impossible to distinguish their relative effects from those of wind intensity. Using a damage assessment database (60 20-metre radius plots) acquired after an exceptional wind storm in Western Quebec in 2007, we developed an approach in which proportions of windthrown sugar maple poles were used as bio-indicators of wind intensities affecting the plots. We distinguished between single and interactive effects of wind intensity, species, stem size, and local basal area on stem windthrow susceptibility. The best logistic regression model predicting stem windthrow included the wind intensity bio-indicator, species, basal area, and the species by diameter at breast height (DBH, 1.3 m) interaction. Stem windthrow probability generally increased with DBH and decreased with basal area. Species wind-firmness was ordered as: yellow birch > sugar maple = eastern hemlock = American beech > ironwood > basswood = other hardwoods = other softwoods. Our method remained an indirect method of measuring wind intensity and its real test would require a comparison with anemometer measurements during a windstorm. Despite its indirect nature, the method is both simple and ecologically sound. Hence, it opens the door to conducting similar windthrow studies in other ecosystems.

Dynamics of seedling establishment and survival in uneven-aged boreal forests

The aim of this study was to describe the dynamics of seedling establishment and development in spruce-dominated uneven-aged boreal forests. The study was based on empirical data from 15 stands with permanent plots, which had been intensively monitored for 10 years in southern Finland. All trees (height > 1.3 m) were measured every fifth year. Regeneration was measured on 64 permanent sample plots (4 m 2) in each stand. The establishment of first-year seedlings was analysed on a yearly basis. The survival and development of older Norway spruce ( Picea abies (L.) H. Karst.) seedlings were analysed based on observations made every five years. The establishment of spruce seedlings was closely correlated with the abundance of seed crops. Seedling cohorts originating from abundant seed crops were clearly detectable in the development of seedling height distributions over time. It took about 15 years for spruce seedlings to reach a height level of 15–30 cm. Local basal area had hardly any effect on the emergence or survival of small spruce seedlings, while the number of higher spruce seedlings decreased with increasing local basal area.

Precipitation water storage capacity in a temperate mixed oak–beech canopy

AbstractThe storage capacity of a temperate mixed oak–beech stand was investigated as a function of stand density and species composition. Measurements were performed in selected zones delimited by three neighbouring trees. Three independent approaches were compared: (i) a spraying laboratory experiment to estimate the water storage on foliage before and after dripping; (ii) a mechanistic model describing rainfall partitioning within the forest canopy and providing estimates of foliage storage capacities; and (iii) linear regression analyses to evaluate the canopy (foliage + branches) storage capacity using the relationship between throughfall and rainfall. Good agreement was generally observed between the laboratory experiment and the mechanistic model estimates, while estimations from the regression method tended to exceed those from the other approaches. Storage capacity estimates ranged from 0·22 mm to 0·80 mm for pure oak zones, from 0·24 mm to 1·12 mm for mixed zones and from 0·53 mm to 1·17 mm for pure beech zones. The increase of storage capacity with increasing proportion of beech in the canopy resulted from higher beech LAI compared with oak. Similarly, for mixed and pure beech canopies, storage capacity was higher for high density zones than for low density zones as a result of the increase in LAI with increasing local basal area; in contrast, for pure oak, the storage capacity was not related to basal area because of the lower shade‐tolerance of this species compared with beech. Copyright © 2008 John Wiley & Sons, Ltd.

Assessing the potential of native tree species for carbon sequestration forestry in Northeast China

Although the native forests of China are exceptionally diverse, only a small number of tree species have been widely utilized in forest plantations and reforestation efforts. We used dendrochronological sampling methods to assess the potential growth and carbon sequestration of native tree species in Jilin Province, Northeast China. Trees were sampled in and near the Changbaishan Biosphere Reserve, with samples encompassing old-growth, disturbed forest, and plantations. To approximate conditions for planted trees, sampling focused on trees with exposed crowns (dominant and co-dominant individuals). A log-linear relationship was found between diameter increment and tree diameter, with a linear decrease in increment with increasing local basal area; no significant differences in these patterns between plantations and natural stands were detected for two commonly planted species ( Pinus koraiensis and Larix olgensis). A growth model that incorporates observed feedbacks with individual tree size and local basal area (in conjunction with allometric models for tree biomass), was used to project stand-level biomass increment. Predicted growth trajectories were then linked to the carbon process model InTEC to provide estimates of carbon sequestration potential. Results indicate substantial differences among species, and suggest that certain native hardwoods (in particular Fraxinus mandshurica and Phellodendron amurense), have high potential for use in carbon forestry applications. Increased use of native hardwoods in carbon forestry in China is likely to have additional benefits in terms of economic diversification and enhanced provision of “ecosystem services”, including biodiversity protection.

Growth and population structure of timber species in Peruvian Amazon flood plains

This study provides specific ecological information on growth and population structure of important timber tree species of the Peruvian Amazon flood plains: Guatteria sp., Terminalia oblonga, Hura crepitans, Guarea macrophylla, Maquira coriacea, Virola elongata, Virola pavonis, and Minquartia guianensis. Furthermore, methods that can be applied to study population structure and growth of trees in natural forests are developed upon. The study is based on data collected over a period of 8 years from permanent sample plots covering a total of 18.6 ha in three flood plain forest types at the lower Río Ucayali. The population structure of the eight species varied considerably with maximum diameters at breast height ranging from 31 to 140 cm. For M. coriacea stem densities and basal areas were as high as 159 ha −1 and 3.4 m 2/ha, respectively, but for most other species, stem densities and basal areas were much lower. Seedling densities of the eight species ranged from 1 to 42,002 ha −1 with a mortality of 27–100% per year and for some species a significant relationship was found between mortality and duration of the flooding period. Diameter increments were analyzed using a simple diameter class approach as well as a more sophisticated single-tree growth model, for which a variety of competition indices were screened. Based on the statistical performance and practicability of the indices it appeared that the most successful measure of competition was the local basal area of trees with diameters exceeding that of the individual in question.

Spatial distribution of regeneration in West-Carpathian uneven-aged silver fir forests

The objective of our study was to examine whether distribution of regeneration in uneven-aged fir (Abies alba Mill.) forests is related to the spatial pattern of trees. In 12 sample plots of size 0.45–1.00 ha (in total 8.65 ha, with stand basal areas ranging from 27.6 m2 ha−1 to 39.5 m2 ha−1), all live and dead trees above 5 cm in d1.3 were mapped and their diameters measured. In eight plots, all live and dead fir saplings were mapped. In three plots, the number of live fir saplings and seedlings was registered on small systematically distributed circular plots. The values of an analytically developed index of stand influence were compared in patches occupied and unoccupied by live or dead fir regeneration. Contrary to preliminary assumptions, only in a few cases did saplings and trees 5–15 cm in d1.3 appear more often in gaps and looser stand patches. Rather, in many plots, the opposite tendency was observed. The seedling density showed a weak but positive correlation with the index of influence. If the spatial pattern of regeneration reflects the spatially varying mortality of juvenile trees, then no evidence was found that stand competition was the most important factor inducing this mortality. On the contrary, on the basis of the results obtained, we can presume that the survival rate of juvenile firs was higher in patches with a relatively higher local basal area. Thus, it was hypothesised that, first, dispersion of regeneration in uneven-aged fir forests is controlled by easy-to-change edaphic factors such as humus form and acidity of the upper soil horizons, and second, that these soil features are linked with the spatial pattern of trees.

Microclimate beneath pine plantation, semi-mature pine plantation and mixed broadleaved-pine forest

To study the dynamics of pine plantations, three stands were selected, which had matured from a pure pine plantation to a mixed broadleaved-pine forest. Microclimatic conditions inside the stands were monitored: air temperature, soil temperature, air relative humidity and global radiation. A reference station was installed in an open area nearby. Forest cover has a weak effect on temperatures: air and soil temperatures are warmer in the mixed broadleaved-pine stand and the coldest under the pine plantation. No difference in relative humidity ( h, %) or vapour pressure deficit ( D, Pa) was observed across the forest maturing stages, but a strong effect of forest cover in general was observed. Radiation was highly attenuated beneath the canopy and was the most heterogeneous variable between and within stands. These variations were significantly and negatively related to the local basal area or canopy cover; the exact shape of the relationship could not be assessed because of too few spatial data.

A Local Basal Area Adjustment for Crown Width Prediction

Abstract Nonlinear crown width regression equations were developed for 24 species common to the upper Lake States of Michigan, Minnesota, and Wisconsin. Of the species surveyed, 15 produced statistically significant (P < 0.05) local basal area effect coefficients showing a reduction in crown width with increasing stand density. No relation between shade tolerance and crown width was apparent, indicating the species-dependence of this parameter. Using adjusted R2 as a guide, nonlinear crown width models adapted for local basal area (NLCWadj) improved prediction for 20 of 24 species over a model lacking this component (NLCW). The ecological significance of the improvement shown for some species may be minor, but for others the difference was substantial (often 8%). North. J. Appl. For 18(1):22–28.

Dynamic steady state of patch‐mosaic tree size structure of a mixed dipterocarp forest regulated by local crowding

A patch age‐ and tree size‐structured simulator was applied to demonstrate the landscape dynamics of a lowland mixed dipterocarp forest, using census data over a 3 year interval from two 1 ha plots in northern West Kalimantan, Indonesia (Western Borneo). Tree growth rate and recruitment rate were estimated as functions of tree size and local crowding. The effect of local crowding was assumed to be one‐sided through light competition, where the basal area for all trees larger than a target tree inside the circle of 10 m radius around the target was employed as the index of crowding. Estimated parameters were similar between the two plots. Tree mortality was expressed by descending function of tree size with asymptotic mortality for large trees corresponding to the gap formation rate. One parameter specifying the survival of trees at gap formation, which was required for the landscape‐level simulation of a shifting‐gap mosaic, was left undetermined from plot census data. Through simulation, this parameter was estimated so as to best fit the observed among‐patch variation in terms of local basal area. The overall time course of simulation and tree size structure were not sensitive to this parameter, suggesting that one‐sided competition along the vertical forest profile is a stronger determinant of average forest structure than among‐patch horizontal heterogeneity in this forest. Simulated dynamic steady state successfully reproduced the observed forest architecture in the gap‐dynamic landscape. It took about 400 years for a vacant landscape to be replaced by a steady‐state architecture of forest. Sensitivity analysis suggests that steady‐state basal area and biomass are most sensitive to changing gap formation rate and intrinsic size growth rate.

Estimating Oak Leaf Area Index and Gypsy Moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), Defoliation Using Canopy Photographs

Oak leaf area index (LAI) was estimated using wide-angle photographs of the forest canopy taken from the ground at grid points throughout three sites on Cape Cod, Mass. Confidence intervals for these estimates and optimal sample sizes were calculated. Oak LAI estimates leveled off by early June when no defoliation was present. Within-plot two-dimensional spatial distribution of oak LAI was very similar to the spatial distribution of oak basal area. Consequently, there was a positive correlation between local oak leaf area and local basal area. Comparison of LAI estimates taken before and after gypsy moth, Lymantria dispar (L.), defoliation allowed the estimation of oak leaf area consumed. Leaf area loss was similar in areas of high and low host foliage densities. The correlation of leaf area lost with local density of early instars was greater than the correlation with the density of late instars.