Long-term trends in tree mortality rates in the Alberta foothills are driven by stand development

2012 ◽  
Vol 42 (9) ◽  
pp. 1687-1696 ◽  
Author(s):  
H.C. Thorpe ◽  
L.D. Daniels
Keyword(s):  
Mortality Risk ◽  
Forest Structure ◽  
Tree Mortality ◽  
Mortality Rates ◽  
Tree Level ◽  
Model Parameters ◽  
Stem Density ◽  
Stand Development ◽  
Individual Tree ◽  
Local Competition

Tree mortality is a critical driver of stand dynamics, influencing forest structure, composition, and capacity for ecosystem service provision. In recent years, tree mortality has been gaining attention as dramatic occurrences of forest die-off have been linked to climate change. Using permanent sample plot data, we examined tree mortality rates in mature forests in west-central Alberta from 1956 to 2007. We quantified mortality risk at an individual-tree level as a function of size, local competition, and calendar year, a proxy for increasing temperature, and used maximum likelihood methods to estimate species-specific model parameters. Tree size and local competition were both important predictors of mortality risk. However, once these factors were included in our model, no additional variation could be attributed to calendar year, indicating that the trend of increasing tree mortality over time found in our raw data is primarily a result of stand development processes. This finding is supported by the changes in forest structure and composition that we documented over the study period. Stands generally increased in basal area and stem density, and lodgepole pine ( Pinus contorta var. latifolia Engelm. ex S. Watson) declined in abundance relative to the more shade-tolerant black spruce ( Picea mariana (Mill.) B.S.P.) and white spruce ( Picea glauca (Moench) Voss). Our results indicate that warming-related changes did not affect background tree mortality rates in mature forests in the Alberta foothills over the study period. These results also provide critical information for future studies of forest dynamics in the region.

scholarly journals An Individual-Tree Mortality Model for Complex Stands of Southeastern British Columbia

2005 ◽  
Vol 20 (2) ◽  
pp. 101-109 ◽  
Author(s):  
Hailemariam Temesgen ◽  
Stephen J. Mitchell
Keyword(s):  
British Columbia ◽  
Tree Species ◽  
Tree Mortality ◽  
Model Development ◽  
Mortality Rates ◽  
Average Deviation ◽  
Individual Tree ◽  
Permanent Sample Plots ◽  
Diameter Increment ◽  
Mortality Model

Abstract An individual-tree mortality model was developed for major tree species in complex stands (multi-cohort, multiaged, and mixed species) of southeastern British Columbia (BC), Canada. Data for 29,773 trees were obtained from permanent sample plots established in BC. Average annual diameter increment and mortality rates ranged from 0.08 to 0.17 cm/year and from 0.3 to 2.6%, respectively. Approximately 70% of the trees were used for model development and 30% for model evaluation. After evaluating the model, all 29,773 trees were used to fit the final model. A generalized logistic model was used to relate mortality to tree size, competition, and relative position of trees in a stand. The evaluation test demonstrated that the model appears to be well behaved and robust for the tree species considered in this study. For the eight tree species, the average deviation between observed and predicted annual mortality rates varied from −0.5 to 0.7% in the test data. West. J. Appl. For. 20(2):101–109.

Tracking tree mortality across sites with repeat LiDAR data

2021 ◽  
Author(s):  
Toby Jackson ◽  
Matheus Nunes ◽  
Grégoire Vincent ◽  
David Coomes
Keyword(s):  
Forest Structure ◽  
Tree Mortality ◽  
Mortality Rates ◽  
Landscape Scale ◽  
Airborne Lidar ◽  
Lidar Data ◽  
Forest Types ◽  
Large Tree ◽  
Airborne Lidar Data ◽  
Field Plots

<p>Repeat airborne LiDAR data provides a unique opportunity to study tree mortality at the landscape scale. We use maps of canopy height derived from repeat LiDAR (two or more scans collected a few years apart) to detect changes in forest structure. Visually, the most obvious changes are caused by large treefall events, which are difficult to study using field plots due to their rarity. While repeat LiDAR data provides exciting new possibilities, validation is a challenge, since we cannot easily determine how many trees have died and we may miss trees which are dead but still standing. I will discuss our progress so far, studying large-tree mortality rates across multiple countries and forest types.</p>

scholarly journals Including tree spatial extension in the evaluation of neighbourhood competition effects in Bornean rain forest

2020 ◽  
Author(s):  
David M. Newbery ◽  
Peter Stoll
Keyword(s):  
Alternative Hypothesis ◽  
Species Abundance ◽  
Abundant Species ◽  
Root Competition ◽  
Light Limitation ◽  
Tree Level ◽  
Model Parameters ◽  
Individual Tree ◽  
Stem Size ◽  
Tree Survival

AbstractClassical tree neighbourhood models use size variables acting at point distances. In a new approach here, trees were spatially extended as a function of their crown sizes, represented impressionistically as points within crown areas. Extension was accompanied by plasticity in the form of crown removal or relocation under the overlap of taller trees. Root systems were supposedly extended in a similar manner. For the 38 most abundant species in the focal size class (10 - <100 cm stem girth) in two 4-ha plots at Danum (Sabah), for periods P1 (1986-1996) and P2 (1996-2007), stem growth rate and tree survival were individually regressed against stem size, and neighbourhood conspecific (CON) and heterospecific (HET) basal areas within incremented steps in radius. Model parameters were critically assessed, and statistical robustness in the modelling set by randomization testing. Classical and extended models differed importantly in their outcomes. Crown extension weakened the relationship of CON effect on growth versus plot species’ abundance, showing that models without plasticity over-estimated negative density dependence. A significant negative trend of difference in CON effects on growth (P2 − P1) versus CON or HET effect on survival in P1 was strongest with crown extension. Model outcomes did not then support an explanation of CON and HET effects being due to (asymmetric) competition for light alone. An alternative hypothesis is that changes in CON effects on small trees, largely incurred by a drought phase (relaxing light limitation) in P2, and following the more shaded (suppressing) conditions in P1, were likely due to species-specific (symmetric) root competition and mycorrhizal processes. The very high variation in neighbourhood composition and abundances led to a strong ‘neighbourhood stochasticity’, and hence to largely idiosyncratic species’ responses. A need to much better understand the roles of rooting structure and processes at the individual tree level was highlighted.

scholarly journals Forest Resistance to Extended Drought Enhanced by Prescribed Fire in Low Elevation Forests of the Sierra Nevada

Forests ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1248
Author(s):  
Phillip J. van Mantgem ◽  
Anthony C. Caprio ◽  
Nathan L. Stephenson ◽  
Adrian J. Das
Keyword(s):  
Sierra Nevada ◽  
National Parks ◽  
Prescribed Fire ◽  
Ponderosa Pine ◽  
Tree Mortality ◽  
Early Years ◽  
Current Evidence ◽  
Stem Density ◽  
Individual Tree ◽  
Sugar Pine

Prescribed fire reduces fire hazards by removing dead and live fuels (small trees and shrubs). Reductions in forest density following prescribed fire treatments (often in concert with mechanical treatments) may also lessen competition so that residual trees might be more likely to survive when confronted with additional stressors, such as drought. The current evidence for these effects is mixed and additional study is needed. Previous work found increased tree survivorship in low elevation forests with a recent history of fire during the early years of an intense drought (2012 to 2014) in national parks in the southern Sierra Nevada. We extend these observations through additional years of intense drought and continuing elevated tree mortality through 2017 at Sequoia and Kings Canyon National Parks. Relative to unburned sites, we found that burned sites had lower stem density and had lower proportions of recently dead trees (for stems ≤47.5 cm dbh) that presumably died during the drought. Differences in recent tree mortality among burned and unburned sites held for both fir (white fir and red fir) and pine (sugar pine and ponderosa pine) species. Unlike earlier results, models of individual tree mortality probability supported an interaction between plot burn status and tree size, suggesting the effect of prescribed fire was limited to small trees. We consider differences with other recent results and discuss potential management implications including trade-offs between large tree mortality following prescribed fire and increased drought resistance.

Evaluation of a tree classification system in relation to mortality risk in Québec northern hardwoods

2008 ◽  
Vol 84 (6) ◽  
pp. 886-899 ◽  
Author(s):  
François Guillemette ◽  
Steve Bédard ◽  
Mathieu Fortin
Keyword(s):  
Mortality Risk ◽  
Classification System ◽  
Sugar Maple ◽  
Tree Mortality ◽  
Tree Level ◽  
Betula Alleghaniensis ◽  
Yellow Birch ◽  
American Beech ◽  
Risk Class ◽  
Northern Hardwood

A tree classification system was developed in the 1980s as part of a guide for tree-marking in the rehabilitation of unevenaged northern hardwood stands in Québec. It differentiates trees that are at high and low risk of mortality, trees with sawlog potential and cull trees. The risk class was assessed based on the presence of major crown and bole defects. The main objective of the present study was to evaluate this system with respect to its capacity to predict the probability of tree mortality. The variables used to classify the trees were observed in 88 experimental plots (0.5 ha) established between 1983 and 1999. Tree-level mortality probabilities were modelled for sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh.) and yellow birch (Betula alleghaniensis Britt.) to test the significance of the classification variables. The presence of decay, fungus or canker, wounds, uprooting, the death of at least 30% of the crown or of the roots, and the product class had significant (p < 0.05) effects on mortality probabilities for at least one of the 3 species studied. In the main, the results supported the tree classification system. However, this system could be modified to differentiate not only trees with a high or low mortality risk, but also to identify some very high-risk trees. Key words: northern hardwood, mortality, defect, quality, classification, selection cutting, partial cut, sugar maple, American beech, yellow birch, uneven-aged, tree-marking

MODELING INDIVIDUAL TREE MORTALITY RATES USING MARGINAL AND RANDOM EFFECTS REGRESSION MODELS

2012 ◽  
Vol 26 (2) ◽  
pp. 131-153 ◽  
Author(s):  
ZHIHAI MA ◽  
CHANGHUI PENG ◽  
WEIZHONG LI ◽  
QIUAN ZHU ◽  
WEIFENG WANG ◽  
...  
Keyword(s):  
Random Effects ◽  
Regression Models ◽  
Tree Mortality ◽  
Mortality Rates ◽  
Individual Tree

The tree mortality regime in temperate old-growth coniferous forests: the role of physical damage

2010 ◽  
Vol 40 (11) ◽  
pp. 2091-2103 ◽  
Author(s):  
Andrew J. Larson ◽  
Jerry F. Franklin
Keyword(s):  
Tree Mortality ◽  
Stem Density ◽  
Natural Forests ◽  
Physical Processes ◽  
Physical Damage ◽  
Old Growth ◽  
Individual Tree ◽  
Decay Fungi ◽  
Stem Breakage

Aspects of the tree mortality regime were characterized for old-growth conifer forests in Mount Rainier National Park, Washington, USA, using individual tree (stems ≥5 cm diameter at breast height (dbh)) records from a network of permanent forest research plots. Average annual forest-wide mortality rates of trees ≥15 cm dbh never exceeded 1% on a stem-density or basal-area basis; mortality was slightly higher for stems <15 cm dbh. Physical agents of mortality (uprooting, stem breakage, and crushing by falling debris) accounted for approximately 40% and 45% of mortality events in trees <15 and ≥15 cm dbh, respectively. These physical processes were chronic sources of mortality: they were not associated with a single or few disturbance events. Preexisting decay fungi were associated with trees that died proximately due to stem breakage (41%) and uprooting (22%), consistent with a predisposing role of decay fungi in trees that die due to mechanical damage. Given the importance of physical processes in the tree mortality regime, we suggest that a richer mechanistic understanding of the causes and consequences of tree mortality in natural forests will be achieved with models that consider the physical, as well as the physiological, attributes of trees and forests.

scholarly journals Similar patterns of background mortality across Europe are mostly driven by drought in European beech and a combination of drought and competition in Scots pine

2019 ◽  
Author(s):  
Juliette Archambeau ◽  
Paloma Ruiz Benito ◽  
Sophia Ratcliffe ◽  
Thibaut Fréjaville ◽  
Alexandre Changenet ◽  
...  
Keyword(s):  
Scots Pine ◽  
Tree Mortality ◽  
Latitudinal Gradient ◽  
Basal Area ◽  
European Beech ◽  
Mortality Rates ◽  
Individual Tree ◽  
Southern Limit ◽  
Drought Intensity ◽  
Species Ranges

ABSTRACTAimBackground tree mortality is a complex demographic process that affects forest structure and long-term dynamics. We aimed to test how drought intensity interacts with interspecific and intraspecific competition (or facilitation) in shaping individual mortality patterns across tree species ranges.LocationEuropean latitudinal gradient (Spain to Finland).Time period1985 – 2014.Major taxa studiedScots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.).MethodsWe performed logistic regression models based on individual tree mortality recorded in five European National Forest Inventories. We computed the relative importance of climatic drought intensity, basal area of conspecific and heterospecific trees (proxy of indirect intra- and interspecific competition or facilitation) and the effects of their interactions on mortality along the latitudinal gradient of both species range.ResultsIncrease in drought intensity over the study period was associated with higher mortality rates in both species. Drought was the most important driver of beech mortality at almost all latitudes while Scots pine mortality was mainly driven by basal area. High conspecific basal area was associated with high mortality rates in both species while high heterospecific basal area was correlated with mortality rates that were high in Scots pine but low in beech.Main conclusionsBeech mortality was directly affected by drought while Scots pine mortality was indirectly affected by drought through interactions with basal area. Despite their different sensitivity to drought and basal area, the highest predicted mortality rates for both species were at the ecotone between Mediterranean and cool temperate biomes, which can be explained by the combined effect of drought and competition. In the context of global warming, which is expected to be particularly strong in the Mediterranean biome, our results suggest that populations at the southern limit of species ranges may experience increased mortality rates in the near future.BIOSKETCHThe authors’ research is focused on functional trait ecology and global change, with special attention to mortality and demography processes. The authors use modelling multidisciplinary approaches to understand complex processes in ecology on a large geographical scale.

scholarly journals Natürliche Baummortalität in Mitteleuropa: Mortalitätsraten und -muster im Vergleich

2018 ◽  
Vol 169 (3) ◽  
pp. 166-174 ◽  
Author(s):  
Lisa Hülsmann ◽  
Harald Bugmann ◽  
Peter Meyer ◽  
Peter Brang
Keyword(s):  
Mortality Risk ◽  
Tree Mortality ◽  
Small Diameter ◽  
Basal Area ◽  
Mortality Rates ◽  
Beech Forest ◽  
Successional Stage ◽  
Age Related ◽  
Mortality Probability ◽  
Species Specific

Natural tree mortality in Central Europe: a comparison of mortality rates and patterns Mortality is one of the key processes of forest dynamics. Yet, its investigation is challenging since trees can reach high ages, and tree death is the result of several interacting drivers. Long-term monitoring data from unmanaged forests are of great importance for studying mortality. Such data from strict forest reserves in Switzerland and Germany were used in this study to 1) derive mortality rates for 18 wooden species, and 2) build species-specific mortality models. Estimated mortality rates were highly variable among the reserves, and were particularly high in stands with many young trees and a high share of short-living pioneer species. For the calculation of accurate and comparable mortality rates, adjustments towards the same caliper threshold and mortality period are necessary. Models that predict the mortality probability of individual trees can be built based on stem diameter and basal area growth. Such models revealed that small and slow growing trees had the highest mortality risk. In addition, mortality patterns featured species-specific differences. Short-living species experienced high overall mortality probability. Shade-intolerant species showed a more pronounced mortality risk at small diameter and slow growth than shade-tolerant species. Competition as well as drought and frost were identified as the dominant drivers of tree mortality in the Swiss and German reserves. Pronounced age-related mortality due to senescence was not present, in contrast to a primeval beech forest in Ukraine. In the reserves, mortality rates and patterns should become more and more similar to those of primeval forests; however, it will require several decades or centuries of undisturbed forest development to reach identical successional stage.

scholarly journals Mid-term (2009-2019) demographic dynamics of young beech forest in Albongbunji Basin, Ulleungdo, South Korea

2020 ◽  
Vol 44 (1) ◽  
Author(s):  
Yong-Chan Cho ◽  
Hyung Seok Sim ◽  
Songhie Jung ◽  
Han-Gyeoul Kim ◽  
Jun-Soo Kim ◽  
...  
Keyword(s):  
South Korea ◽  
Tree Mortality ◽  
Mortality Rates ◽  
Stem Density ◽  
Demographic Dynamics ◽  
Horizontal Heterogeneity ◽  
The Mean ◽  
Fagus Engleriana ◽  
Density And Biomass ◽  
Over Time

Abstract Background The stem exclusion stage is a stage of forest development that is important for understanding the subsequent understory reinitiation stage and maturation stage during which horizontal heterogeneity is formed. Over the past 11 years (2009–2019), we observed a deciduous broad-leaved forest in the Albongbunji Basin in Ulleungdo, South Korea in its stem exclusion stage, where Fagus engleriana (Engler’s beech) is the dominant species, thereby analyzing the changes in the structure (density and size distributions), function (biomass and species richness), and demographics. Results The mean stem density data presented a bell-shaped curve with initially increasing, peaking, and subsequently decreasing trends in stem density over time, and the mean biomass data showed a sigmoidal pattern indicating that the rate of biomass accumulation slowed over time. Changes in the density and biomass of Fagus engleriana showed a similar trend to the changes in density and biomass at the community level, which is indicative of the strong influence of this species on the changing patterns of forest structure and function. Around 2015, a shift between recruitment and mortality rates was observed. Deterministic processes were the predominant cause of tree mortality in our study; however, soil deposition that began in 2017 in some of the quadrats resulted in an increase in the contribution of stochastic processes (15% in 2019) to tree mortality. The development of horizontal heterogeneity was observed in forest gaps. Conclusions Our observations showed a dramatic shift between the recruitment and mortality rates in the stem exclusion stage, and that disturbance increases the uncertainty in forest development increases. The minor changes in species composition are likely linked to regional species pool and the limited role of the life-history strategy of species such as shade tolerance and habitat affinity. Our midterm records of ecological succession exhibited detailed demographic dynamics and contributed to the improvement of an ecological perspective in the stem exclusion stage.

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