Spatial Pattern Of Trees Research Articles

Tree growth and competition in an old‐growthPicea abiesforest of borealSweden: influence of tree spatial patterning

AbstractQuestionWhat factors best characterize tree competitive environments in this structurally diverse old‐growth forest, and do these factors vary spatially within and among stands?LocationOld‐growthPicea abiesforest of borealSweden.MethodsUsing long‐term, mapped permanent plot data augmented with dendrochronological analyses, we evaluated the effect of neighbourhood competition on focal tree growth by means of standard competition indices, each modified to include various metrics of trees size, neighbour mortality weighting (for neighbours that died during the inventory period), and within‐neighbourhood tree clustering. Candidate models were evaluated using mixed‐model linear regression analyses, with mean basal area increment as the response variable. We then analysed stand‐level spatial patterns of competition indices and growth rates (viakriging) to determine if the relationship between these patterns could further elucidate factors influencing tree growth.ResultsInter‐tree competition clearly affected growth rates, with crown volume being the size metric most strongly influencing the neighbourhood competitive environment. Including neighbour tree mortality weightings in models only slightly improved descriptions of competitive interactions. Although the within‐neighbourhood clustering index did not improve model predictions, competition intensity was influenced by the underlying stand‐level tree spatial arrangement: stand‐level clustering locally intensified competition and reduced tree growth, whereas in the absence of such clustering, inter‐tree competition played a lesser role in constraining tree growth.ConclusionsOur findings demonstrate that competition continues to influence forest processes and structures in an old‐growth system that has not experienced major disturbances for at least two centuries. The finding that the underlying tree spatial pattern influenced the competitive environment suggests caution in interpreting traditional tree competition studies, in which tree spatial patterning is typically not taken into account. Our findings highlight the importance of forest structure – particularly the spatial arrangement of trees – in regulating inter‐tree competition and growth in structurally diverse forests, and they provide insight into the causes and consequences of heterogeneity in this old‐growth system.

Quantifying spatial patterns of tree groups and gaps in mixed-conifer forests: Reference conditions and long-term changes following fire suppression and logging

Fire suppression and past logging have dramatically altered forest conditions in many areas, but changes to within-stand tree spatial patterns over time are not as well understood. The few studies available suggest that variability in tree spatial patterns is an important structural feature of forests with intact frequent fire regimes that should be incorporated in restoration prescriptions. We used a rare dataset consisting of mapped locations for all trees ⩾10cm in three 4-ha plots in 1929 before logging and in 2007/2008, 78 and 79years after logging, to assess changes in three spatial components of forest structure: individual trees, tree clusters and gaps. Comparing 1929 old growth to modern conditions, area in gaps decreased from 20% to zero, the percentage of stems that were single trees from 6% to 2% and in small or medium clumps (2–9 trees) from 28% to 9%, while trees in large clumps (⩾10trees) increased from 66% to 89%. Concurrent with these changes, canopy cover increased from 45% to 62%, and the average number of trees in a clump increased from 11 to 26, resulting in much more homogenous conditions across the stand. These changes also altered tree size and species associations within different structural groups (i.e., single tree, small, medium and large clumps). In an effort to account for the alteration of the fire regime that had already taken place in 1929 (the last fire recorded in tree rings was in 1889) we also analyzed spatial patterns of 1929 conditions removing all trees <25cm. In this analysis, 35% of the plot area was in gaps and canopy cover averaged 36%. Tree clusters had an average of 5.2 trees per clump, with 13% of trees being singles, 30% in small clumps, 24% in medium clumps and 33% in large clumps. Our results provide metrics that quantify spatial patterns and composition of individual trees, tree clumps, and gaps under the historical fire regime that may be useful to forest managers. Our study demonstrates that the contemporary forest is more homogeneous than it was historically, and variability that likely provided diverse microclimate and habitat conditions and fostered resilience to a variety of stressors and disturbances such as fire, insects and drought has been lost. Future management may benefit from restoring these structural components.

Predicting the spatial pattern of trees by airborne laser scanning

The spatial pattern of trees can be defined as a property of their location in relation to each other. In this study, the spatial pattern was summarized into three categories, regular, random, and clustered, using Ripley's L-function. The study was carried out at 79 sample plots located in a managed forest in Finland. The goal was to study how well the spatial pattern of trees can be predicted by airborne laser scanning (ALS) data. ALS-derived predictions were based upon individual tree detection (ITD), semi-individual tree detection (semi-ITD), and plot-level metrics calculated from the canopy height model, AREA. The kappa value for ITD was almost zero, which indicates no agreement. The semi-ITD and AREA methods performed better, although kappa values were only 0.34 and 0.24, respectively. It appears difficult to detect a particularly clustered spatial pattern.

Spatial pattern of trees in tropical lowland rain forest in Bawangling of Hainan Island, China

Aims Understanding processes underlying spatial distribution of tree species is fundamental to the study of spe-cies coexistence and diversity.Our objective was to determine the spatial structure and identify the processes that may generate spatial patterns of trees in a tropical lowland rain forest community on Hainan Island of South China.Methods Based on four models of point pattern analysis (homogenous Poisson process,inhomogenous Poisson process,homogenous Thomas process and inhomogenous Thomas process),we evaluated the potential contribu-tion of habitat heterogeneity and dispersal limitation to the formation of spatial patterns of tree species in two 1-hm2 stem-mapped forest dynamic plots.The relative importance of each process was assessed at six different spatial scales ( 2 m,2-5 m,5-10 m,10-15 m,15-20 m and 20-25 m).Important findings All stems combined revealed a strong aggregation at short distance (≤2 m),and the degree of aggregation decreased with increasing distance.Among the four models simulating tree distribution and pat-terning,the homogeneous Thomas process was the best-fit model.This result suggested that spatial patterns of tree species in tropical lowland rain forest might be formed by dispersal limitation.The homogeneous Poisson process that models the effect of spatial complete randomness was the second-best model.The inhomogeneous Thomas process and inhomogeneous Poisson process were equally important to forming spatial patterns of trees;they simulated the joint effects of habitat associations and dispersal limitation and modeled heterogeneity,respec-tively.The proportion of best-fit models differed across different scales.The dispersal limitation was a most im-portant mechanism in spatial patterning of tree species at most scales,while complete randomness process was second in importance.The joint effects of habitat associations and dispersal limitation mainly influenced tree dis-tribution at small scales (0-5 m).However,habitat heterogeneity only affected the distribution at larger scales (15-25 m).

Spatially explicit structure of natural stands dominated by black spruce

Black spruce [Picea mariana (Mill.) BSP] regeneration emerges in clusters near the pre-existing boles within a few years after the passage of fire. This paper tested the hypothesis that black spruce forests still maintain the spatial structure deriving from postfire stand initiation. Trees and saplings were monitored during 2000-2007 and the horizontal and vertical structure of the stands were investigated on four permanent plots in the boreal forest of Quebec, Canada. Plots showed 1300-2150 trees ha-1, and were composed of trees with homogeneous sizes and a very small proportion of saplings. These characteristics identify single cohorts generated by complete, or almost-complete, stand replacement by fire. Ripley's L(r) functions showed that the spatial pattern of trees and saplings ranged from random to aggregated, thus demonstrating that the clustering distribution of the individuals in black spruce forests can be maintained even after 80-120 years from stand initiation. These findings could results from incomplete self-thinning or from an environment with heterogeneous distribution of resources. The practices of ecosystem management recently developed in Eastern Canada should take into account both the horizontal and vertical structure to better modulate the competition among individuals during partial harvesting.

Spatial Distribution and Exploitation of Trees Gouged by Common Marmosets (Callithrix jacchus)

Resource distribution shapes many aspects of primate behavioral ecology. Though the spatial patterning of fruits, leaves, and insects has been explored among primate foods, comparatively less is known about exudate distributions. Tree exudates are a renewable resource, provide long-term evidence of exploitation, and may be selectively exploited to manipulate spatial distribution. We assessed the spatial patterning of trees gouged by common marmosets (Callithrix jacchus) to determine if they exhibit a uniform, random, or clumped distribution. We also asked whether marmosets selectively gouge trees in home range centers, which may afford them exclusive access to exudates. We explored whether spatial or physical characteristics of trees predict how intensely gouged trees were exploited. The mean nearest neighbor distance of gouged trees was significantly closer than expected for a random distribution and Ripley’s K-function showed that gouged trees were clumped across all spatial scales in our study area. Clumping may enable marmosets to reduce day and home ranges and facilitate repeated gouging of trees. Gouged trees were not closer to marmosets’ home range centers than peripheries, nor were centrally located trees more intensely gouged. Increased gouging intensity was associated with larger tree circumferences, although this effect was primarily driven by interspecific differences in circumference. Although marmosets may benefit from exploiting clumped exudates, they do not concentrate gouging in areas where they are more likely to gain exclusive access. Species-specific tree characteristics such as exudate quality and/or bark properties may play a larger role in determining gouging patterns than intergroup feeding competition.

Spatiotemporal differences in tree spatial patterns between alluvial hardwood and mountain fir–beech forests: do characteristic patterns exist?

AbstractQuestionsWhat are the differences between the tree spatial patterns (TSP) of various recruit and mortality waves in alluvial hardwood forests and mountain fir–beech forests? Are there any statistically significant differences between the mean TSP of these forest types? Are these differences stable over time?LocationAlluvial floodplain forests at the confluence of the Morava and Dyje rivers, and mountain fir–beech forests in the Outer Western Carpathians, Czech Republic.MethodsIn both forest types, seven 2‐ha rectangular plots were analysed. The pair correlation function g(r) was used to describe tree density variability of trees with DBH ≥ 10 cm. The analyses were carried out for data sets from the 1970s, 1990s and 2000s. A bootstrap method was used to test for significant differences between the mean values of g(r) from alluvial forests and from fir–beech forests.ResultsRecruits in mountain fir–beech forests revealed consistent clustering to at least 5 m. In alluvial hardwood forests, recruits also showed random distribution as well as occasional regular distribution at distances over 20 m. Bootstrap significance tests revealed significant differences between the mean values of g(r) for alluvial forests and fir–beech forests. Alluvial floodplain forests showed statistically significant stronger clustering up to a distance of 4 m in all study periods. At distances over 20 m, mountain fir–beech forests demonstrated stronger clustering. In the 1970s, this was statistically significant only at a distance of 32 m, but in the 2000s, it was at intervals of 22–30 and 34–38 m.ConclusionsThe methods of data analysis in this study enabled us to find significant features of TSP at finer resolution than the common resulting trichotomy of univariate analysis: clustering, randomness and regularity. We believe that, on the basis of detailed spatial analyses, it is possible to create a TSP model that reflects the typical features of particular forest types.

Análise espacial de um fragmento florestal baseada no mosaico de dirichlet

A configuração espacial das árvores afeta grande número de processos fisiológicos e ecológicos em uma floresta, incluindo competição, distribuição, tamanho, crescimento e mortalidade da espécie. Métodos baseados na função K de Ripley têm sido usados com frequência para caracterizar a configuração espacial de uma floresta. Neste artigo foram propostos alguns métodos, que são baseados nas áreas do mosaico de Dirichlet (função D), para descrever a distribuição espacial de árvores. Devido à importância da Xylopia brasiliensis (pindaíba) na estrutura e dinâmica de floresta Semidecidual Montana, este trabalho avaliou as funções K e D para descrever a distribuição espacial da espécie. Os resultados indicaram que os estimadores das funções K e D, combinados com simulações Monte Carlo, levaram à rejeição da hipótese de completa aleatoriedade espacial (p &lt; 0,10) da Xylopia brasiliensis em favor da presença de agrupamento espacial da espécie dentro do fragmento florestal.

Seeing the forest for the heterogeneous trees: stand-scale resource distributions emerge from tree-scale structure

Forest ecosystem processes depend on local interactions that are modified by the spatial pattern of trees and resources. Effects of resource supplies on processes such as regeneration are increasingly well understood, yet we have few tools to compare resource heterogeneity among forests that differ in structural complexity. We used a neighborhood approach to examine understory light and nutrient availability in a well-replicated and large-scale variable-retention harvesting experiment in a red pine forest in Minnesota, USA. The experiment included an unharvested control and three harvesting treatments with similar tree abundance but different patterns of retention (evenly dispersed as well as aggregated retention achieved by cutting 0.1- or 0.3-ha gaps). We measured light and soil nutrients across all treatments and mapped trees around each sample point to develop an index of neighborhood effects (NI). Field data and simulation modeling were used to test hypotheses that the mean and heterogeneity of resource availability would increase with patchiness because of greater variation in competitive environments. Our treatments dramatically altered the types and abundances of competitive neighborhoods (NI) in each stand and resulted in significantly nonlinear relationships of light, nitrogen and phosphorus availability to NI. Hence, the distribution of neighborhoods in each treatment had a significant impact on resource availability and heterogeneity. In dense control stands, neighborhood variation had little impact on resource availability, whereas in more open stands (retention treatments), it had large effects on light and modest effects on soil nutrients. Our results demonstrate that tree spatial pattern can affect resource availability and heterogeneity in explainable and predictable ways, and that neighborhood models provide a useful tool for scaling heterogeneity from the individual tree to the stand. These insights are needed to anticipate the outcomes of silvicultural manipulations and should become more holistically integrated into both basic ecological and management science.

Seeing the forest for the heterogeneous trees: stand‐scale resource distributions emerge from tree‐scale structure

Forest ecosystem processes depend on local interactions that are modified by the spatial pattern of trees and resources. Effects of resource supplies on processes such as regeneration are increasingly well understood, yet we have few tools to compare resource heterogeneity among forests that differ in structural complexity. We used a neighborhood approach to examine understory light and nutrient availability in a well-replicated and large-scale variable-retention harvesting experiment in a red pine forest in Minnesota, USA. The experiment included an unharvested control and three harvesting treatments with similar tree abundance but different patterns of retention (evenly dispersed as well as aggregated retention achieved by cutting 0.1- or 0.3-ha gaps). We measured light and soil nutrients across all treatments and mapped trees around each sample point to develop an index of neighborhood effects (NI). Field data and simulation modeling were used to test hypotheses that the mean and heterogeneity of resource availability would increase with patchiness because of greater variation in competitive environments. Our treatments dramatically altered the types and abundances of competitive neighborhoods (NI) in each stand and resulted in significantly nonlinear relationships of light, nitrogen and phosphorus availability to NI. Hence, the distribution of neighborhoods in each treatment had a significant impact on resource availability and heterogeneity. In dense control stands, neighborhood variation had little impact on resource availability, whereas in more open stands (retention treatments), it had large effects on light and modest effects on soil nutrients. Our results demonstrate that tree spatial pattern can affect resource availability and heterogeneity in explainable and predictable ways, and that neighborhood models provide a useful tool for scaling heterogeneity from the individual tree to the stand. These insights are needed to anticipate the outcomes of silvicultural manipulations and should become more holistically integrated into both basic ecological and management science.

Mining simulation data by rule induction to determine critical source areas of stream water pollution by herbicides

Modelling in environmental sciences is becoming increasingly complex because ever-increasing numbers of processes are combined, thus making model-based decision aids both more relevant but more difficult to develop. Our approach focused on water quality and aimed to identify spatial tree patterns that represent surface flow and pollutant pathways from plot to plot involved in water pollution by herbicides. First, a simulation model predicted herbicide transfer rate, the proportion of applied herbicide that reaches water courses, based on the spatial and temporal distribution of weed-control activities. These predictions were used as a set of learning examples for symbolic learning techniques to induce rules based on qualitative and quantitative attributes and explain two classes of transfer rate. In this study we compared two automatic symbolic learning techniques applied to a set of simulations: (1) a relational-inductive method using the inductive logic programming (ILP) approach to induce spatial tree patterns; and (2) an attribute-value method to induce aggregated attributes of the trees. Twenty-eight and thirty-three rules were learnt by the ILP and attribute-value approaches which explained 81% and 88% of the examples, respectively. The ILP approach provided relevant indicators of plot-to-plot connectivity. The integrated attribute-value approach is simpler and quicker, but the ILP patterns are more useful for stakeholders.

Exploring horizontal area-based metrics to discriminate the spatial pattern of trees and need for first thinning using airborne laser scanning

Summary The objectives of this study were (1) to identify point cloud metrics and horizontal texture and landscape metrics from airborne laser scanning (ALS) data, which can be used to determine the spatial pattern of trees and, further, the need for first thinning and (2) to study if the clustered spatial pattern of trees and the need for first thinning can be separated from other spatial patterns and need for thinning classes. The field data consisted of 28 microstands, which had reached the first thinning height but had not yet been thinned. Linear discriminant analysis was used to classify microstands by means of the metrics calculated from the ALS data. A classification based on the spatial pattern of trees discriminated stands with the overall accuracy (OA) being 0.89 and kappa-value (k) 0.77. Similarly, a classification based on the need for first thinning was also successful (OA = 0.96 and k = 0.93). Horizontal landscape metrics were found to be good predictors of the spatial patterns of trees, whereas the landscape and point cloud metrics were found good predictors of the need for first thinning.

Spatial patterns in different forest development stages of an intact old-growth Oriental beech forest in the Caspian region of Iran

Spatial patterns of trees are important structural characteristics that can provide insights into forest dynamics and may be related to the development stages of forests. The spatial patterns of three development stages (i.e., initial, optimal, and decay) of an intact old-growth beech (Fagus orientalis Lipsky) forest in the Caspian region of Iran were quantified within one-hectare permanent plots. All trees with a diameter at breast height of more than 7.5 cm were measured, stem-mapped, and then assigned to one of four diameter size classes (small, medium, large, and extra-large timbers). Spatial patterns of all trees and spatial associations among tree size classes were analyzed using Ripley’s K-function, and the spatial dependence of tree diameters was analyzed using variograms. Results showed that trees in the small size class exhibited an aggregated distribution in every development stage, which matched the overall spatial pattern of all trees in each stage. However, the degree of aggregation of all trees as well as association patterns among the size classes differed among the three development stages. Further, the average spatial dependence of tree diameters was 24, 14, and 19 m in the initial, optimal, and decay stages, respectively. Differences in spatial patterns among the development stages in this beech old-growth forest are consistent with the gap-dynamics paradigm and likely reflect different canopy disturbance events coupled with associated regeneration, release, and competition processes (e.g., shade-tolerance characteristics, seed dispersal limitation, and intraspecific competition).

The criterion for space-age organization of stand

A statistical criterion for randomness of spatial tree patterns in stands with account of trees age is proposed. Interpretation of the criterion statistic and numerical experiments on collected spatial data are presented.

Fine spatial pattern of an epiphytic lichen species is affected by habitat conditions in two forest types in the Iberian Mediterranean region

Persistence and abundance of species is determined by habitat availability and the ability to disperse and colonize habitats at contrasting spatial scales. Favourable habitat fragments are also heterogeneous in quality, providing differing opportunities for establishment and affecting the population dynamics of a species. Based on these principles, we suggest that the presence and abundance of epiphytes may reflect their dispersal ability, which is primarily determined by the spatial structure of host trees, but also by host quality. To our knowledge there has been no explicit test of the importance of host tree spatial pattern for epiphytes in Mediterranean forests. We hypothesized that performance and host occupancy in a favourable habitat depend on the spatial pattern of host trees, because this pattern affects the dispersal ability of each epiphyte and it also determines the availability of suitable sites for establishment. We tested this hypothesis using new point pattern analysis tools and generalized linear mixed models to investigate the spatial distribution and performance of the epiphytic lichen Lobaria pulmonaria, which inhabits two types of host trees (beeches and Iberian oaks). We tested the effects on L. pulmonaria distribution of tree size, spatial configuration, and host tree identity. We built a model including tree size, stand structure, and several neighbourhood predictors to understand the effect of host tree on L. pulmonaria. We also investigated the relative importance of spatial patterning on the presence and abundance of the species, independently of the host tree configuration. L. pulmonaria distribution was highly dependent on habitat quality for successful establishment, i.e., tree species identity, tree diameter, and several forest stand structure surrogates. For beech trees, tree diameter was the main factor influencing presence and cover of the lichen, although larger lichen-colonized trees were located close to focal trees, i.e., young trees. However, oak diameter was not an important factor, suggesting that bark roughness at all diameters favoured lichen establishment. Our results indicate that L. pulmonaria dispersal is not spatially restricted, but it is dependent on habitat quality. Furthermore, new spatial analysis tools suggested that L. pulmonaria cover exhibits a distinct pattern, although the spatial pattern of tree position and size was random.

Plot size for modelling the spatial structure of Sudanian woodland trees

Introduction Over the past decades, savannah woodland management in the Sudanian region of Africa has focused on rotation and enrichment. To best manage these resources, it is critical to first understand the ecological processes influencing the behaviour of plants in their habitats. Previous work on the spatial patterns of trees has failed to account for the effects of plot size.

Spatial and volume patterns of an unmanaged submontane mixed forest in Central Europe: 160 years of spontaneous dynamics

The long-term development of stand characteristics and tree spatial patterns (TSP), their mutual relation, and linkage to site and tree species were studied in the Boubín primeval forest (protected since 1858). Surveys were carried out in 1851, 1961/1964, 1972, 1984/1989, 1996 and 2010 on one to six research plots sized 0.58–1.00 ha. To see how results from these surveys could be generalized, results were also compared with whole-area data sets (46 ha) from 1972 to 2010. The proportion of Abies alba continually decreased, from 20% in 1851 to 2–3% in 2010. This decrease started no later than at the beginning of the 20th century. In contrast, the proportion of Fagus sylvatica slightly increased. The sum of dead and living wood volume was stable during the 159 year period, with deviations of only up to 5%. From 1961/64 to 2010, the number of living trees continually decreased, but the mean-tree volume and volume of dead wood increased. The distribution of dead wood always differed from the distribution of living trees. A random TSP was always most common, which seems to be typical for this type of forest. This was true even when A. alba was gradually forced out from the stand structure. Nevertheless, the pronounced decrease of A. alba found during the 1961/64 survey compared with 1851 was reflected in a tendency towards clustering, as gaps from A. alba dieback gradually closed. In these gaps, competitive pressure was lower, resulting in more clustered distributions. Regular distribution was recorded only rarely. F. sylvatica maintained a random or clustered TSP over long periods, depending on site conditions. On water-affected plots, it had a consistently higher tendency towards clustering. The only step change in TSP occurred due to Hurricane Emma in 2008. Otherwise, the most marked TSP changes over time were found for Picea abies, in which there was a gradual trend from clustered to random, connected with a decreasing number of individuals. The main reason for the decline of A. alba and the decreased number of living trees from 1961/64–2010 was the on-going effect of a high stock of red deer at the turn of the 19th and 20th centuries. The decreasing trend in the number of living trees showed no marked change, even 60 years after the game pressure was strongly reduced. However, the vertical structure became increasingly homogenized due to the long-term absence of severe abiotic and/or biotic disturbances.

Tree spatial pattern within the forest–tundra ecotone: a comparison of sites across CanadaThis article is a contribution to the series Tree recruitment, growth, and distribution at the circumpolar forest–tundra transition.

Although many studies have focused on factors influencing treeline advance with climate change, less consideration has been given to potential changes in tree spatial pattern across the forest–tundra ecotone. We investigated trends in spatial pattern across the forest–tundra ecotone and geographical variation in the Yukon, Manitoba, and Labrador, Canada. Tree cover was measured in contiguous quadrats along transects up to 100 m long located in Forest, Ecotone, and Tundra sections across the forest–tundra transition. Spatial patterns were analyzed using new local variance to estimate patch size and wavelet analysis to determine the scale and amount of aggregation. Compared with the Forest, tree cover in the Ecotone was less aggregated at most sites, with fewer smaller patches of trees. We found evidence that shorter trees may be clumped at some sites, perhaps due to shelter from the wind, and we found little support for regular spacing that would indicate competition. With climate change, trees in the Ecotone will likely become more aggregated as patches enlarge and new patches establish. However, results were site-specific, varying with aspect and the presence of krummholz (stunted trees); therefore, strategies for adaptation of communities to climate change in Canada’s subarctic forest would need to reflect these differences.

Tree recruitment, growth, and distribution at the circumpolar forest–tundra transition: introduction

Causes and consequences of changes in the circumpolar forest–tundra transition have received recent interest due to the increasing awareness of human-caused global climate change. The International Polar Year core project PPS Arctic focused these topics through exploring processes, changes, and spatiotemporal variability of biotic and abiotic drivers of change in the forest–tundra transition. The papers in this special feature present constraints and drivers of tree recruitment and tree encroachment of tundra areas, climate – tree growth relations in the ecotone, and changes in tree spatial pattern across the forest–tundra ecotone.

The contribution of competition to tree mortality in old-growth coniferous forests

Competition is a well-documented contributor to tree mortality in temperate forests, with numerous studies documenting a relationship between tree death and the competitive environment. Models frequently rely on competition as the only non-random mechanism affecting tree mortality. However, for mature forests, competition may cease to be the primary driver of mortality. We use a large, long-term dataset to study the importance of competition in determining tree mortality in old-growth forests on the western slope of the Sierra Nevada of California, U.S.A. We make use of the comparative spatial configuration of dead and live trees, changes in tree spatial pattern through time, and field assessments of contributors to an individual tree's death to quantify competitive effects. Competition was apparently a significant contributor to tree mortality in these forests. Trees that died tended to be in more competitive environments than trees that survived, and suppression frequently appeared as a factor contributing to mortality. On the other hand, based on spatial pattern analyses, only three of 14 plots demonstrated compelling evidence that competition was dominating mortality. Most of the rest of the plots fell within the expectation for random mortality, and three fit neither the random nor the competition model. These results suggest that while competition is often playing a significant role in tree mortality processes in these forests it only infrequently governs those processes. In addition, the field assessments indicated a substantial presence of biotic mortality agents in trees that died. While competition is almost certainly important, demographics in these forests cannot accurately be characterized without a better grasp of other mortality processes. In particular, we likely need a better understanding of biotic agents and their interactions with one another and with competition.