Tree Canopy Closure Research Articles

Conservation value of timber quality versus associated non-timber quality stands for understory diversity in Nothofagus forests

Conservation strategies of forested landscapes must consider biodiversity of the included site types, i.e. timber-quality forests and associated non-timber-quality stands. The objectives were to characterize forest overstory structure in timber-quality versus associated non-timber-quality stands; and to compare their understory communities. Six forest types were sampled in Nothofagus forests of Tierra del Fuego (Argentina): two timber-quality N. pumilio forests, and four associated non-timber-quality stands (edge, N. antarctica, wetlands and streamside forests). Overstory structure and understory vegetation (species richness, frequencies, cover and biomass) were characterized during spring and summer seasons. Analysis of variance and multivariates were carried out. Overstory structure differed across the site types, with higher tree size, canopy closure and tree volume in timber-quality stands. Fifty-one understory plant species were observed, but understory variables varied with site types, especially wetlands (highest native and exotic richness, cover and biomass, and 25% of exclusive species). Site types were grouped in three: N. antarctica stands, streamside stands and the other N. pumilio forests according to multivariate analysis. Forty three percent of plants were distributed in all site types, and all timber-quality forest understory species were present in some associated non-timber-quality stands. Timber-quality N. pumilio forests have a marginal value for understory conservation compared to associated non-timber-quality stands, because these last include all the plants observed in timber-quality forests and also possess many exclusive species. Therefore, protection of associated non-timber-quality stands during forest management planning could increase understory conservation at landscape level, and these could be better reserves of understory diversity than retentions of timber-quality stands.

Canopy Closure, Competition, and the Endangered Dusky Gopher Frog

Abstract: A major challenge facing wildlife biologists is understanding why some species go extinct while others persist in the same habitat. To address this question, we investigated whether tree canopy closure over ponds affects growth and survival of rare and common tadpoles within ponds and mediates competitive interactions among species. We conducted 2 experiments to test whether canopy closure and competition may have contributed to the decline of the endangered dusky gopher frog (Rana sevosa), but allowed the persistence of the southern leopard frog (R. sphenocephala). We explored the response of both species to canopy closure in single‐species and mixed‐ (1:1) species treatments of identical total tadpole density. An experiment using aquatic enclosures in temporary ponds showed that canopy closure reduced tadpole growth approximately 20% for both species. Survival of dusky gopher frog tadpoles was higher in mixed‐species enclosures than in single‐species enclosures. In a complementary experiment using artificial ponds, dusky gopher frogs had lower survival to metamorphosis, reduced size at metamorphosis, and produced a lower total biomass of metamorphosed juveniles in shaded ponds. Southern leopard frogs exhibited reduced body size at metamorphosis only when shaded. These studies suggest that pond canopy closure, not larval competition, may be contributing to the decline of the dusky gopher frog. The different responses to canopy closure suggest a potential mechanism for the loss of dusky gopher frogs and the persistence of southern leopard frogs. Removal of trees from historically open‐canopy ponds may help facilitate the recovery of dusky gopher frogs and benefit similar species.

Nitrogen utilization by Hylocomium splendens in a boreal forest fertilization experiment

Summary 1Nitrogen uptake in the terricolous bryophyte Hylocomium splendens (Hedw.) B.S.G. was studied in a boreal forest long-term N-treatment experiment including control plots, N-addition plots (50 kg N ha−1 year−1 for 8 years) and recovery plots (50 kg N ha−1 year−1 for 5 years and thereafter no N addition for 3 years). 2A main objective was to explore whether the N treatments changed bryophyte uptake of different inorganic and organic N forms. In addition, we estimated the contribution of N from throughfall precipitation to the bryophyte N supply. 3The results demonstrated that bryophyte N uptake was similar in all the long-term N-treatment plots. Hylocomium splendens took up more 15N labelled than or glycine when these N forms were applied in situ by the spraying of solutions with N concentrations similar to those in precipitation. 4Analysis of the precipitation collected beneath the closed tree canopy from late May to early October revealed that it contributed 2·0 kg N ha−1 during the period studied, distributed between (78%), amino acid N (17%) and (5%). 5The study highlights that, in addition to analyses of and (normally included in standard environmental monitoring of precipitation), analysis of amino acid N must be performed to account fully for the precipitation N input to bryophytes in boreal forest ecosystems.

Seasonal pattern of leaf production and its effects on assimilation in giant summer-green herbs in deciduous forests in northern Japan

Understory vegetation of northern deciduous forests in far eastern Asia is characterized by giant summer-green herbs. We examined the patterns of height growth, leaf accumulation, photosynthetic characteristics, daily net assimilation, and dry matter allocation within aboveground parts of six giant summer-green herbs with reference to light conditions in deciduous forests. Plant height, leaf number, and total leaf area per plant increased with progressing tree-canopy closure in five species ( Cacalia hastata L. subsp. orientalis Kitam., Cirsium kamtschaticum Ledeb., Filipendula kamtschatica (Pall.) Maxim. f. kamtschatica, Senecio cannabifolius Less., and Urtica platyphylla Wedd.) that had continuous leaf production throughout the growing season, whereas one species ( Veratrum album L. subsp. oxysepalum Hulten) with early leaf production, completed leaf production mostly before the beginning of tree-canopy closure. Maximum photosynthetic and dark respiration rates decreased seasonally in all species. Species with continuous leaf emergence accumulated leaves acclimatized to shade conditions, which offset the decreasing photosynthesis of individual leaves with progressing tree-canopy closure, resulting in stable carbon gain even under decreasing light availability. In contrast, V. album assimilated vigorously during the short period of high irradiance before tree-canopy closure, and decreased its assimilation rate continuously thereafter.

Succession of understory vegetation in managed and seminatural Scots pine forests in eastern Finland and Russian Karelia

The aim of this study was to compare the understory vegetation in chronosequences representing seminatural and managed Scots pine (Pinus sylvestris L.) forests on dryish heaths of the Vaccinium type. The data represent the middle boreal vegetation zone and were collected in eastern Finland and the Dvina area of Karelia, on both sides of the border between Finland and the Russian Federation. Species diversity and the coverage of the various life-form groups (ground lichens, mosses, liverworts, grasses, herbs, dwarf shrubs, and tree seedlings) were used to analyse the properties of the ground vegetation over the succession from open forest land to closed forest communities. The clearest differences in diversity between the seminatural forests mainly influenced by fire and managed forests occurred in the early stages of succession. Forest management appeared to increase the species richness at the beginning of succession. The seminatural stands were rich in Cladonia lichens and dwarf shrubs up until tree canopy closure; however, the abundance of mosses was lower in the seminatural stands. Forest management favoured an abundance of grasses, notably Deschampsia flexuosa, which was common after clear-cutting. The use of prescribed burning in silviculture could result in more natural vegetation succession dynamics in managed stands.

Fruit maturation, not deteriorating light conditions, is the primary cue of senescence in a spring ephemeral annual plant—Floerkea proserpinacoides (Limnanthaceae)

In monocarpic plants, reproduction is closely associated with senescence, which is itself often correlated to specific environmental signals. Floerkea proserpinacoides (Limnanthaceae) is a spring ephemeral annual of the deciduous forests of eastern North America. The phenology of its growth and reproduction is considered to be a specific adaptation to the short period during which there is a high availability of resources (mostly light). Indeed, flowering starts 2-3 wk following seedling emergence soon after snowmelt and continues until tree canopy closure. However, fruit maturation is postponed for several weeks and is followed by the plant's death. The objective of this study is to determine if senescence in F. proserpinacoides is primarily cued by fruit maturation or deteriorating light conditions associated with tree canopy closure. Plants for which reproductive investment was manipulated by removing their carpels were grown either in full light or in the shade. Carpel-removal plants reached a higher biomass than control plants (46.0- 57.5% higher), especially in full light. However, longevity was greater in carpel-removal plants, particularly in the shade (25.3-37.8% greater). These results thus suggest that fruit maturation, not deteriorating light conditions associated with canopy closure, is the primary cue of plant senescence in F. proserpinacoides.

THE CONTRIBUTION OF RED WOOD ANTS TO SOIL C AND N POOLS AND CO2EMISSIONS IN SUBALPINE FORESTS

Little information is available regarding red wood ant (RWA; Formica rufa group) impacts on soil carbon (C) and nitrogen (N) cycling in forest ecosystems. We found that RWA mound density (number per ha) was linked to forest tree species composition, slope aspect, and canopy closure. The size of RWA mounds was positively correlated with successional age of the stands. C and N concentrations of mound material were significantly higher than in the forest floor, while C:N ratios were not. RWA mound C and N pools were found to be significantly lower (≤990 kg C/ha and ≤21 kg N/ha) than in the forest floor. RWA mounds were “hot spots” for CO2 emissions ranging from 12.4 (mid July) to 3.5 (early September) times higher than the adjacent forest floor. Overall, they contributed 0.7– 2.5% to total forest soil CO2 emissions. Consequently, the contribution of RWA to total forest soil C and N pools and forest CO2 emission is minor and likely not important when calculating or modeling C and N pools or C fluxes. Yet, RWA...

Lizard Distributions and Reproductive Success in a Ponderosa Pine Forest

We assessed relative abundance, demographic, and reproductive success data for two lizard species in a Northern Arizona ponderosa pine forest, a fire-dependent system unnaturally modified by fire suppression over the past century. During May to October 1997-1999, we employed up to 70 pitfall arrays to sample lizards over 6990 array-days. At each array, we described macro-vegetative cover, stand, and microhabitat characteristics. Sceloporus graciosus responded to habitat variation at all three spatial scales. Adult S. graciosus were widely distributed among cover and stand types. However, reproductive success and hatchling abundance were highest in the most open cover (meadow) and stand (savannah) types, and lowest in pure ponderosa cover and dense ponderosa stands. Adult females replaced themselves annually only in meadows, savannahs, and forest with a deciduous component. Eumeces skiltonianus adults and juveniles were least abundant in meadows, but females replaced themselves each year in meadow and ponderosa-pinyon- juniper vegetative cover and in savannahs. Hatchlings were least abundant in intermediate- and high-density ponderosa stands, whereas juveniles of both species were most abundant in areas containing a deciduous tree component. Both species were present in plots having lower percent duff groundcover than at plots containing no lizards. Increased tree densities, canopy closure, and litter accumulation influenced distributions of both lizards. Furthermore, abundance and reproduction in these lizards were generally optimized in habitat with features most similar to that present prior to fire suppression activities and in areas containing a deciduous tree component.

Simulating the effects of lidar scanning angle for estimation of mean tree height and canopy closure

A three-dimensional simulation model was used for modeling the scanning angle effect when measuring tree height and canopy closure in boreal forest with a laser scanner. The height distribution of the laser returns and the proportion of laser returns from the canopy were simulated using ray-tracing applied to a computer modeled forest. The proportion of canopy returns is commonly used as a measure of canopy closure, and height percentiles are commonly used to estimate mean tree height. Laser scanner data and field measurements of tree position, tree height, crown diameter, and crown base height were used for validating the simulation model. The correlation coefficient between simulated and real laser height percentiles was 0.96 and the simulation model systematically overestimated the laser height percentiles by 2.25 m. Simulations show that laser height percentiles and proportion of canopy returns changed more with an increased scanning angle for long crown species like spruce, compared with short crown species like pine. The change of height percentiles due to scanning angle was greater in forests with low stem numbers than with high stem numbers. The proportion of canopy returns was more affected by scanning angle than were the laser height percentiles.

Increases in tree growth and nutrient supply still apparent 10 to 13 years following fertilization and vegetation control of salal-dominated cedar–hemlock stands on Vancouver Island

Cedar–hemlock forests on Vancouver Island are primarily nitrogen limited and characterized by an under story dominated by the ericaceous shrub salal (Gaultheria shallon Pursh.). In 1984, an experiment was established on regenerating cedar–hemlock forests to determine the effects of nitrogen and phosphorus (N + P) fertilization and vegetation control on conifer growth. It was hypothesized that these treatments would not only stimulate tree growth, but also improve nutrient supply, stand productivity, and site quality. To test this hypothesis, tree height growth, canopy closure, salal biomass, foliar and forest floor N and P concentrations, and seedling growth on forest floor were measured 10–13 years after treatment. Both salal control and fertilization increased tree growth and canopy cover, and reduced salal biomass. However, only fertilized plots showed changes in site quality measurable 10–13 years following N + P application. Hemlock foliar P concentrations, forest floor total N and P levels, and hemlock height increments were higher in these plots. Forest floors from the fertilized plots also supported greater growth of conifer seedlings. These results suggest that sustained changes to site quality may be achieved with N + P fertilization of cedar–hemlock forests.

Seed germination ecology of Polymnia canadensis (Asteraceae), a monocarpic species of the North American temperate deciduous forest.

The seed germination of Polymnia canadensis was studied in relation to its wide variation in life history and its ecology as a mostly facultative biennial, a life cycle type that is rare in stable forest habitats in eastern North America. The seed dormancy and germination characteristics of P. canadensis were like some other herbaceous woodland species of diverse life cycle types. That is, its seeds have physiological dormancy, and they (1) germinated to higher percentages after cold stratification, (2) germinated better in light than in darkness and (3) formed a persistent soil seed bank. Since its seed dormancy and germination characteristics are not uncommon and are not particularly associated with any one life cycle type in woodlands, those properties do not contribute to the rarity of its life cycle type in deciduous forests. These properties are also found in many facultative biennials of open, disturbed habitats and in other Asteraceae of various life cycle types. In addition, the germination phenology of P. canadensis differed between mesic and dry field sites in central Kentucky. At the dry sites, most of the yearly germination occurred in fall, while at the mesic sites most germination occurred in the spring due to being inhibited during fall. A reciprocal seed transplant experiment conducted in two different years demonstrated that the cause of this difference was environmental and that there was no source x site interaction; i.e., no difference between sources in phenotypic plasticity for germination phenology. Absence of genetic effects was also shown by no consistent pattern in the few differences between seed sources in seed incubation laboratory experiments and in a germination phenology experiment in glasshouse flats. Exposure of seeds to a high ratio of far-red/red light prior to or during incubation did not inhibit germination. Neither did changes in leaf litter thickness qualitatively alter germination phenology in field quadrats or in glasshouse flats. Thus, germination in fall at mesic sites was inhibited by other unknown factor(s), perhaps interacting with the effects of closed tree canopy and/or thick leaf litter.

Influence of soil and organic residue management on biomass and biodiversity of understory vegetation in a Eucalyptus globulus Labill. plantation

The objective of this study was to assess the effect of different options of soil preparation and management of harvesting debris on biodiversity and biomass of understory vegetation in plantations of Eucalyptus globulus of Central Portugal. The experiment consisted of six treatments in a replanted area and four treatments in a coppice area with five replicates, following a randomised block design. Surveys of vegetation were performed for 6 years. The proportion of soil cover by plant species was estimated and the Shannon–Wiener diversity and equitability indexes determined for each treatment and year. After the 2nd year, the understory vegetation was randomly sampled for above-ground biomass determination. Within the planted area, the removal of slash without soil preparation induced the highest number of species during the experimental period. A similar trend was observed in the coppice area, but less regularly. Significant differences in the proportion of soil cover only occurred within the planted area in the first year, when slash removal without soil preparation induced the highest understory cover. Species diversity was not clearly affected by treatments: significant differences only occurred occasionally and were apparently related to differences in the number of species. Therefore, differences in the equitability index between treatments never were significant. Removal of slash without soil disturbance and broadcast of slash over the soil usually shared the highest biodiversity. Differences between treatments in the amount of understory biomass were never statistically significant during the experimental period. Tendency for a negative influence of soil mobilisation on the amount of understory biomass was observed within the planted area, as well as a similar effect of the treatments consisting of broadcast of slash over the soil surface in the coppice area. In parallel to tree development and canopy closure biomass of that vegetation along the study period was reduced, especially in the planted area.

Light occlusion at forest edges: an analysis of tree architectural characteristics

We examined the phenomenon of tree canopy closure by lateral branch expansion at the edges of temperate forest fragments bordering fields, in southwestern Ontario, Canada. We evaluated the relationship between tree crown characteristics and the degree of light reduction (a measure of canopy closure) among six tree species of differing shade tolerance ( Fagus grandifolia Ehrh., Acer saccharum Marsh., Quercus rubra L., Prunus serotina Ehrh., Juglans nigra L. and Populus grandidentata Michx.). Tree species differed in their capacity to occlude light: the most effective were the most shade tolerant species, F. grandifolia and A. saccharum, while the most shade intolerant trees, J. nigra and P. grandidentata, had the highest percentage of light transmission. The most shade tolerant species presented most of their branches and foliage towards the field and resulted in the most voluminous crowns with the largest values in branch density, branch clumping, canopy depth and canopy width. The best model to predict light occlusion was obtained when we considered the effect of each species as a factor, and foliage biomass facing the field as covariates; this explained 80% of the total variation in light transmission. The ability of shade tolerant trees to enlarge their crowns in response to an increase in light availability allows them to occlude light better. To maximize the protection of microclimates in forest fragments, shade tolerant trees should be encouraged at forest edge communities by favoring recruitment or by selective thinning of the least shade tolerant species.

Vegetation development on reclaimed lands in the Coal Valley Mine of western Alberta, Canada

Revegetated lands within the Coal Valley Mine were sampled for species composition, woody plant frequencies, and tree heights. The vegetation on 68 sampled sites was dominated by a mixture of Festuca rubra L. and Trifolium repens L. Four distinctive plant communities were present. A Lodgepole pine/Willow/Lindley's aster community represented the most advanced stage of forest development, having a multilayered structure and composed primarily of indigenous species, although only 19 years old. Deciduous shrubs and trees (<50 cm tall) occurred on 43% of the sites (mean 364 plants/ha). Salicaceae were the primary species. Total plant cover averaged >85% in all community types with plant litter covering >75% of the ground surface. There were 123 plant species found growing on the mine with 77% indigenous species, although they represented <5% of the total vegetation cover. The height of planted Pinus contorta Loudon and Picea glauca (Moench) Voss were modelled over a 24-year period. Both species had reduced height growth and significant attrition for several years after planting. On average, however, surviving trees had 8- and 14-year heights similar to local provincial reforestation standards. It is hypothesized that tree canopy closure is a key factor in facilitating the naturalization of forest understory vegetation on reclaimed lands.Key words: succession, plant community development, afforestation, perturbation.

The vegetative spread of Pteridium aquilinum in a hemiboreal forest – invasion or revegetation?

The purpose of this study was to determine whether Pteridium aquilinum (L. Kuhn) invades new ground or remain static under a closed forest canopy. It was also to study whether the species invades into new areas or revegetate previous occupied ground after clear-cutting in the hemiboreal zone. Two separate experiments were conducted over a six-year period: (1) The change in P. aquilinum frond density and cover under a closed tree canopy was studied on permanent plots; (2) P. aquilinum spread after clear-cutting was studied in terms of expanding fronts into new ground. The density of fronds did not change beneath the closed tree canopy during the study period. Expansion of the front of adjacent established P. aquilinum into one of two clear-cut sites was extremely rapid indicating an already present rhizome system, while expansion into the other site without rhizomes present was very slow. The results indicate that P. aquilinum does not increase its frond density or colonize new ground in the closed forest or invade new ground on clear-cut areas in the studied forest stands, but instead revegetates clear-cut areas in which it has previously been more abundant. However, forestry practices such as clear-cutting in areas in which P. aquilinum is sparsely distributed in the field layer in the closed forest prior to clear-cutting results in an increasing density of P. aquilinum which is sufficient to restrain forest regeneration.

Using Presence‐Absence Data to Build and Test Spatial Habitat Models for the Fisher in the Klamath Region, U.S.A.

Abstract: Forest carnivores such as the fisher ( Martes pennanti) have frequently been the target of conservation concern because of their association in some regions with older forests and sensitivity to landscape‐level habitat alteration. Although the fisher has been extirpated from most of its former range in the western United States, it is still found in northwestern California. Fisher distribution, however, is still poorly known in most of this region where surveys have not been conducted. To predict fisher distribution across the region, we created a multiple logistic regression model using data from 682 previously surveyed locations and a vegetation layer created from satellite imagery. A moving‐window function in a geographic information system was used to derive landscape‐level indices of canopy closure, tree size class, and percent conifer. The model was validated with new data from 468 survey locations. The correct classification rate of 78.6% with the new data was similar to that achieved with the original data set (80.4%). Whereas several fine‐scale habitat attributes were significantly correlated with fisher presence, the multivariate model containing only landscape‐ and regional‐scale variables performed as well as one incorporating fine‐scale data, suggesting that habitat selection by fishers may be dominated by factors operating at the home‐range scale and above. Fisher distribution was strongly associated with landscapes with high levels of tree canopy closure. Regional gradients such as annual precipitation were also significant. At the plot level, the diameter of hardwoods was greater at sites with fisher detections. A comparison of regional fisher distribution with land‐management categories suggests that increased emphasis on the protection of biologically productive, low‐ to mid‐elevation forests is important to ensuring the long‐term viability of fisher populations.

Canopy phenology of some mopane and miombo woodlands in eastern Zambia

SummaryMeasurements of tree canopy closure and field‐layer reflectance were made in a series of plots in protected areas of eastern Zambia as part of a multiyear study of savanna woodlands. The plots were located in the Luangwa Valley and adjacent plateaux, which contained a range of vegetation types found in southern Africa. The vegetation consisted of four broad types: 1.plateau miombo woodland; 2.valley miombo woodland; 3.scrub miombo woodland; and 4.scrub and woodland mopane. Hemispherical photographs of the tree layer provided measurements of tree canopy phenology in the different vegetation plots. The most seasonal woodland type was mopane, where tree canopy closure ranged from about 15% at the end of the dry season to just over 60% during the peak of the rains. Plateau miombo exhibited the lowest range of seasonality in the tree layer, ranging from about 40% to 60% closure over one complete seasonal cycle. Phenology of the field layer, expressed as the normalized difference vegetation index (NDVI), closely followed that of the tree layer, although the field layer senesced earlier than trees, especially in plots with relatively low tree canopy closure. The relationship between tree‐canopy closure and field‐layer NDVI was positive and statistically significant for all sites of the study area, which suggests that woody biomass and herbaceous biomass are related positively in these savanna woodland ecosystems.

Seasonal and successional understory vascular plant diversity in second-growth hardwood clearcuts of western Maryland, USA

Understory vegetation of 17 clearcuts (1–26 years old) and three mature secondary forested sites in Garrett County, MD, USA was sampled three times (June, August, and October) during a single growing season to investigate vascular plant species diversity during forest regeneration. Vegetation was sampled in 0.1 ha quadrats and nested subplots to determine species richness and derive species-area relations which served as a measure of diversity. Subplots of 1-m 2 were established to yield percent cover estimates of understory vegetation. These data were used to calculate Shannon–Wiener diversity values and mean species richness m −2. Twelve of the study sites were established on opposite aspects (northwest and southeast) to investigate potential differences in plant diversity on sites of varying soil moisture. Diversity and species richness remained constant from June to August but decreased in October. However, percent cover of understory vegetation was greatest in August, and June vegetation was more abundant than in October. Therefore, data collected from June to August were comparable regarding diversity and richness but not abundance. Overall, there were no significant trends in diversity with stand age; clearcutting did not have a dramatic influence on plant diversity in this chronosequence. However, diversity may have been slightly higher on recently clearcut sites, lower on older clearcut sites, and higher again on control sites. Dominance by Allegheny blackberry ( Rubus allegheniesis) may have had a greater influence on diversity than tree canopy closure on recent clearcuts. Percent cover of understory vegetation was negatively correlated with stand age. No differences in diversity or richness were found between sites with northwest and southeast aspects.

Litter production and nutrient return in New Zealand eucalypt short-rotation forests: implications for land management

Litter fall plays a major role in the cycling of energy and nutrients in woodland ecosystems. The amount of litter produced and nutrients returned in two population-density trials of Eucalyptus brookerana and E. saligna short rotation forests were monitored over a one-year period in Palmerston North, New Zealand. The results showed that the higher the plant density, the greater the weight of the litter fall and with higher levels of nutrients. The differences were less evident after tree canopy closure. The highest annual litter fall recorded was >10 Mg ha −1 oven dry, of which leaves contributed over 90%. Total nitrogen and phosphorus return was up to 140 and 8.2 kg ha −1, respectively. About 70% to 80% of the total annual litter fall occurred during summer time. To minimise depletion of nutrients from the site, trees should be harvested in autumn or winter to ensure a sustainable production system. However, to remove as many nutrients as possible in an effluent land treatment system where nutrient removal is the main objective, trees should be harvested in summer before the peak time of nutrient return.

Assessing components of a competition index to predict growth in an even-aged Pinus nigra stand

The relationship between tree growth and competition may depend on some subjective choices that are commonly left to the researcher. Among these are the neighborhood radius, the number of years of growth that are integrated, and tree age. We have evaluated the importance of these factors when relating growth and competition in a forest stand with contrasted densities of the dominant tree species (Pinus nigra) and understory shrub species (Adenocarpus decorticans). Previous to this evaluation we performed a randomization test to assess the relationship between tree growth and neighbors. By using Daniels index of competition we found that the use of a fixed neighborhood radius underestimated the importance of tree competition. The coefficient of determination (r2) of the relationship between tree growth and Daniels index increased asymptotically with the number of years considered. Five years of growth gave high r2 independently of the density of trees and shrubs. The intensity of competition was weakly affected by the characteristics of the plot (tree and shrub densities), and did not change with time. In contrast, the potential growth at equal competition – as represented by constant “a” in the allometric model – changed with time suggesting a gradual decrease in potential tree growth in the plots with higher tree density, and a gradual increase in those plots with high density of shrubs. These results may reflect tree canopy closure and the senescence of Adenocarpus decorticans. A method is suggested to select optimum neighborhood radius and growing period for the calculation of competition indices. By applying this method we were able to explain as much as 79–84% of the variability in tree growth of this stand.