Variation in Tree Growth along Soil Formation and Microtopographic Gradients in Riparian Forests

For trees, fast growth rates and large size seem to be a fitness benefit because of increased competitiveness, attainment of reproductive size earlier, reduction of generation times, and increased short‐term survival chances. However, fast growth rates and large size entail reduced investment in defenses, lower wood density and mechanical strength, increased hydraulic resistance as well as problems with down‐regulation of growth during periods of stress, all of which may decrease tree longevity. In this study, we investigated the relationship between longevity and growth rates of trees and quantified effects of spatial environmental variation (elevation, slope steepness, aspect, soil depth) on tree longevity. Radial growth rates and longevities were determined from tree‐ring samples of 161 dead trees from three conifer species in subalpine forests of the Colorado Rocky Mountains ( Abies lasiocarpa , Picea engelmannii ) and the Swiss Alps ( Picea abies ). For all three species, we found an apparent tradeoff between growth rate to the age of 50 years and longevity (i.e. fast early growth is associated with decreased longevity). This association was particularly pronounced for larger P. engelmannii and P. abies , which attained canopy size, however, there were also significant effects for smaller P. engelmannii and P. abies . For the more shade‐tolerant A. lasiocarpa , tree size did not have any effect. Among the abiotic variables tested only northerly aspect significantly favored longevity of A. lasiocarpa and P. engelmannii . Trees growing on south‐facing aspects probably experience greater water deficits leading to premature tree death, and/or shorter life spans may reflect shorter fire intervals on these more xeric aspects. Empirical evidence from other studies has shown that global warming affects growth rates of trees over large spatial and temporal scales. For moist‐cool subalpine forests, we hypothesize that the higher growth rates associated with global warming may in turn result in reduced tree longevity and more rapid turnover rates.

基于动态监测样地(200 m × 40 m)的网格(10 m × 10 m)取样,以农作区为对照,用地统计学方法研究了喀斯特峰丛洼地人工林、次生林和原生林3类典型森林生态系统表层土壤(0-15 cm)有机质的空间变异,通过主成分分析和相关分析,探讨了其生态学过程和机制。结果表明:喀斯特峰丛洼地土壤有机质很高,沿着农作区-人工林-次生林-原生林的恢复梯度,土壤有机质显著提高,变异系数逐步增大;农作区和3类森林土壤表层有机质均具有良好的空间自相关性;农作区试验半变异函数<em>C₀/</em>(<em>C₀</em>+<em>C</em>)值为26.5%,呈中等程度的空间相关性;3类森林的<em>C₀/</em>(<em>C₀</em>+<em>C</em>)值为9.0%-22.6%,呈强烈的空间相关性;农作区和人工林土壤有机质呈单峰分布,次生林呈凹型分布,原生林呈凸型分布;不同森林的主导因子不同,农作区的主导因子为主要土壤养分,人工林为地形和物种多样性,次生林为森林结构和物种多样性,原生林为地形和物种多样性,且同一因子在不同森林与土壤表层有机质的正负作用关系和相关程度也不同。因此,农作区和3类森林应根据其土壤表层有机质的空间变异及主要影响因子制定相应的固碳措施。;The spatial variability of surface soil (0-15 cm) organic matter in plantation, secondary forest, and primary forest in depressions between hills in a karst region was examined using farmland as a control. The ecological processes and mechanisms behind this variability were also discussed. Eighty sample plots of 10 m × 10 m were established in 200 m × 40 m farmland, plantation, secondary fores, and primary forest plots in depressions between karst hills. Geostatistics was used to analyze the spatial pattern of surface soil organic matter in the plots and principal component analysis and correlation analysis were used to analyze the relationships with other factors. The soil organic matter content in the depressions between karst hills was high. Along the restoration gradient from farmland > plantation > secondary forest > primary forest, the surface soil organic matter content significantly increased and the coefficients of variation also increased. The vegetation in primary forest was well preserved and soil organic matter was up to 118 g/kg, 3.76 times that of farmland. The coefficients of variation of soil organic matter in the farmland and three forest types were 19.4%-48.5%. There was a fine spatial autocorrelation in the surface soil organic matter in the farmland and the three forest types. The farmland and plantation forest were strongly influenced by humans and therefore more balanced. This meant the correlogram range was large and the maximum correlogram coefficient Moran's I was 0.460 in the farmland and 0.780 in the plantation. The natural restoration time of the secondary forest was 22 years. Here there were more, but unevenly distributed, vegetation types meaning the correlogram range was smaller and Moran's I coefficients fluctuated considerably. In the primary forest, however, the disturbance was low and vegetation intact. This meant the correlation was mainly affected by the topography. The best fitting models for semi-variation of secondary forest soil organic matter function in Karst peak-cluster depressions are the exponential model and the Gaussian model. The resulting <em>R</em>² values of 0.926-0.971 demonstrate how well they reflected the soil organic matter spatial structure characteristics. The value of <em>C₀/</em>(<em>C₀</em>+<em>C</em>) of the surface soil organic matter in farmland was 26.5%, indicating a medium spatial correlation. The values of <em>C₀/</em>(<em>C₀</em>+<em>C</em>) in the three forest types ranged from 9.0% to 22.6%, suggesting strong spatial correlations. The spatial pattern of surface soil organic matter in farmland and plantation presented a unimodal distribution: in secondary forest it had a concave distribution and in primary forest it had a convex distribution. Soil nutrient content was the largest influencing factor on the variation in the farmland, topography and species diversity were the largest influencing factors in the plantation and primary forest, and forest structure and species diversity were the largest influencing factors in the secondary forest. Even when considering the same factor in the three forest types, the functions and correlations differed. Therefore, the corresponding strategies of fixing carbon should take the spatial variability of surface soil organic matter and its largest influencing factors in farmland and the three forest types into account.

Ensuring the sustainability of forest ecosystems requires understanding the mechanisms underlying tree growth and predicting their relative influence across taxa and environments. Functional ecology posits that variation in tree growth is related to individual differences in functional traits, which serve as proxies for resource acquisition and investment strategies. However, studies of trait–growth relationships have produced inconsistent results, likely due to unaccounted factors like interspecific interactions, ontogeny, differing leaf habit strategies, and variation in resource acquisition and allocation. We investigated the utility of key functional traits as predictors of tree height growth rates in common garden experiments in the absence of interspecific interactions. We posit that trait–growth relationships vary with age and between two groups relating to leaf habit: deciduous and evergreen species. Using data from 38 tree species planted in monoculture plots across seven sites of the International Diversity Experiment Network with Trees (IDENT) in North America and Europe, we compiled height growth rates over 9 years post‐germination. We modelled growth using a Bayesian hierarchical generalized linear model incorporating four above‐ground functional traits related to resource acquisition and investment: specific leaf area (SLA), wood density (WD), leaf dry matter content (LDMC) and seed mass (SM). Improvements in predictive power due to the variation of trait effects with age and leaf habit were evaluated via alternative hypothesis‐driven models, using the Expected Log Pointwise Predictive Density (ELPD) as a performance measure. Trait effects on growth varied with age and leaf habit, shifting between positive and negative effects, reflecting changes in resource acquisition and investment strategies. The relationships between traits and growth were strongest during the first three growing seasons for deciduous species and during the seventh to the ninth for evergreen species. Accounting for age and leaf habit substantially improved predictive power. Synthesis. Traits are not consistently associated with tree growth rates but instead reflect dynamic resource acquisition and investment strategies over time and between deciduous and evergreen species. Despite this variability, our findings confirm the utility of functional traits to predict tree growth rates, especially when trait effects are considered to vary with age and leaf habit.

Summary 1. Essential resources such as water, nutrients and light vary over space and time and plant growth rates are expected to vary accordingly. We examined the effects of climate, soil and logging disturbances on diameter growth rates at the tree and stand level, using 165 1‐ha permanent sample plots distributed across Bolivian tropical lowland forests. 2. We predicted that growth rates would be higher in humid than in dry forests, higher in nutrient‐rich than nutrient‐poor forests and higher in logged than non‐logged forests. 3. Across the 165 plots we found positive basal area increases at the stand level, which agree with the generally reported biomass increases in tropical forests. 4. Multiple regression analysis demonstrated that climate variables, in particular water availability, were the strongest drivers of tree growth. More rainfall, a shorter and less intense dry period and higher temperatures led to higher tree growth rates. 5. Tree growth increased modestly with soil fertility and basal area growth was greatest at intermediate soil fertility. Surprisingly, tree growth showed little or no relationship with total soil nitrogen or plant available soil phosphorus. 6. Growth rates increased in logged plots just after logging, but this effect disappeared after 6 years. 7. Synthesis. Climate is the strongest driver of spatial variation in tree growth, and climate change may therefore have large consequences for forest productivity and carbon sequestration. The negative impact of decreased rainfall and increased rainfall seasonality on tree growth might be partly offset by the positive impact of increased temperature in these forests.

&amp;lt;p&amp;gt;Forest demographic processes - growth, recruitment and mortality - are being altered by global change. The changing balance between growth and mortality strongly influences forest dynamics and the carbon balance. Elevated atmospheric carbon dioxide (eCO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) has been reported to enhance photosynthesis and tree growth rates by increasing both light-use efficiency (LUE) and water-use efficiency (WUE). Tree growth enhancement could be translated into an increase in biomass stocks or could be associated with a reduction in the longevity of trees, thus reducing the ability of forest ecosystems to act as carbon sinks over long timescales. These links between growth and mortality, and the implications for forest stand density and self-thinning relationships are still debated. Scarce empirical evidence exists for how changing drivers affect tree mortality due to existing data and modelling limitations. Understanding the causes of observed mortality trends and the mechanisms underlying these processes is critical for accurate projections of global terrestrial carbon storage and its feedbacks to anthropogenic climate change.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Here, we combine a mechanistic model with empirical forest data to better understand the causes of changes in tree mortality and the implications for past and future trends in forest tree density. Specifically, we test the Grow-Fast-Die-Young hypothesis to investigate if a leaf-level CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fertilization effect may lead to an increase in the biomass stock in forest stands. We use a novel vegetation demography model (LM3-PPA) which includes vegetation dynamics with biogeochemical processes allowing for explicit representation of individuals and a mechanistic treatment of tree mortality. The key links between leaf-level assimilation and stand dynamics depend on the carbon turnover time. In this sense, we investigate alternative mortality assumptions about the functional dependence of mortality on tree size, tree carbon balance or growth rate. These formulations represent typical approaches to simulate mortality in mechanistic forest models. Model simulations show that increasing photosynthetic LUE leads to higher biomass stocks, with contrasting behavior among mortality assumptions. Empirical data from Swiss forest inventories support the results from the model simulations showing a shift upwards in the self-thinning relationships, with denser stands and bigger trees. This data-supported mortality-modelling helps to identify links between forest responses and environmental changes at the leaf, tree and stand levels and yields new insight into the causes of currently observed terrestrial carbon sinks and future responses.&amp;lt;/p&amp;gt;

Functional traits regulate plant response to environmental changes, with consequences on population dynamics. However, how plant functional traits impact population dynamics, including growth, mortality, and recruitment, remains elusive in temperate forests across different successional stages. In this study, we compiled data on population dynamics and eight functional traits, encompassing hydraulic, wood, and leaf traits, from 35 species commonly found in a secondary poplar-birch forest and a broad-leaved Korean pine forest in Northeast China. We quantified the intrinsic relationships between plant population dynamics and assessed how plant functional traits influenced these dynamics. The results demonstrated a gradual increase in the correlation among population dynamics as forest succession progressed. In the secondary forest, tree growth rate and mortality rate were negatively correlated, while growth-death rate and growth-recruitment rate were not related. Conversely, in the broad-leaved Korean pine forest, there was a significant negative correlation between tree growth rate and mortality rate, as well as between growth rate and recruitment rate, while tree mortality rate positively correlated with recruitment rate. Additionally, functional traits effectively predicted population dynamics, but the predictive ability varied across successional stages. Functional traits, particularly xylem hydraulic traits (e.g., Huber value) and anatomical traits (e.g., mean xylem conduit diameter), were stronger predictors of tree growth, mortality, and recruitment rates at the late successional stage compared with the early stage. These findings indicated that population dynamics and functional traits exhibited strong regularity in the late successional stage of broad-leaved Korean pine forests.

Toposequence variability in tree growth associated with leaf traits for Larix gmelinii

Carbon isotope ratios in growth rings of a tropical tree species show that treefall gaps stimulate diameter growth mainly through changes in the availability of light and not water. The formation of treefall gaps in closed canopy forests usually entails considerable increases in light and nutrient availability for remaining trees, as well as altered plant water availability, and is considered to play a key role in tree demography. The effects of gaps on tree growth are highly variable and while usually stimulatory they may also include growth reductions. In most studies, the causes of changes in tree growth rates after gap formation remain unknown. We used changes in carbon isotope 13C discrimination (Δ13C) in annual growth rings to understand growth responses after gap formation of Peltogyne cf. heterophylla, in a moist forest of Northern Bolivia. We compared growth and Δ13C of the 7 years before and after gap formation. Forty-two trees of different sizes were studied, half of which grew close (<10 m) to single treefall gaps (gap trees), the other half more than 40 m away from gaps (controls). We found variable responses among gap trees in growth and Δ13C. Increased growth was mainly associated with decreased Δ13C, suggesting that the growth response was driven by increased light availability, possibly in combination with improved nutrient availability. Most trees showing zero or negative growth change after gap formation had increased Δ13C, suggesting that increased water stress did not play a role, but rather that light conditions had not changed much or nutrient availability was insufficient to support increased growth. Combining growth rates with Δ13C proved to be a valuable tool to identify the causes of temporal variation in tree growth.

To understand the relationship between the dynamics of tropical rain forests and the population processes of individual species, data are needed on the rates at which trees grow, die, and establish. Data on the family Moraceae have been extracted from long—term forestry studies in Sarawak, on the northwest coast of Borneo, an area at the center of species richness of Old World tropical forests. These data can also be combined with forest maps and logging studies to investigate the importance of competition and disturbance in controlling tree growth. Tree populations of Moraceae species had mean annual diameter increments of between 0.4 and 3 mm/yr. Growth rates increased two to six times in the 1st and 2nd yr following (selective) logging, but began to decline somewhat in the 3rd and 4th yr. Growth rate variation among trees in a population was considerable, with most trees showing little or no growth, and a few, high growth rates. Saplings of Artocarpus species increased in diameter at the same mean rate as adult trees. Annual mortality rates were low in primary forest, typically &lt;3%, and indicated stable populations. In logged forest, annual mortality of Artocarpus species was considerably higher, between 5 and 8% for trees and still higher for saplings. Adults and saplings of Ficus, a pioneer species, had much higher annual mortality rates than individuals of Artocarpus. Growth rates of Moraceae trees in primary forest were positively correlated with the growth of the nearest conspecific trees, the mean growth rates of the three nearest neighbors of any species, and the mean distance to the nearest neighbors, but were not correlated with the diameter of the tree itself and the mean diameter of the three nearest neighbors. Analysis of patches of three trees of any species in primary forest revealed that there were no detectable differences among patches in either tree size or growth rate. Tree growth rates of small patches in logged forest were negatively correlated with distance to the nearest forest opening. Even the significant relationships between tree growth rate and immediate neighborhood explained only a relatively small portion of the total variation in growth rate. The remaining variation may be due to variation in plant genotype and local environment.

Forests are the largest terrestrial biomass pool, with over half of this biomass stored in the highly productive tropical lowland forests. The future evolution of forest biomass depends critically on the response of tree longevity and growth rates to future climate. We present an analysis of the variation in tree longevity and growth rate using tree-ring data of 3,343 populations and 438 tree species and assess how climate controls growth and tree longevity across world biomes. Tropical trees grow, on average, two times faster compared to trees from temperate and boreal biomes and live significantly shorter, on average (186 ± 138 y compared to 322 ± 201 y outside the tropics). At the global scale, growth rates and longevity covary strongly with temperature. Within the warm tropical lowlands, where broadleaf species dominate the vegetation, we find consistent decreases in tree longevity with increasing aridity, as well as a pronounced reduction in longevity above mean annual temperatures of 25.4 °C. These independent effects of temperature and water availability on tree longevity in the tropics are consistent with theoretical predictions of increases in evaporative demands at the leaf level under a warmer and drier climate and could explain observed increases in tree mortality in tropical forests, including the Amazon, and shifts in forest composition in western Africa. Our results suggest that conditions supporting only lower tree longevity in the tropical lowlands are likely to expand under future drier and especially warmer climates.

The growth rate of a tree at any time relates to its size and the level of competition exerted by its neighbors for the resources it needs for growth. This work describes the development of a model to predict the maximum growth rate in stem basal area of Eucalyptus pilularis Smith trees in native and plantation forests of subtropical eastern Australia. It shows maximum growth rates increasing with size until the tree reaches a stem diameter at breast height of 27 cm. Thereafter, maximum growth rates decline progressively as the tree grows larger. Physiological reasons that might describe this growth pattern are discussed. The maxima are shown to be independent of tree age, stand stocking density or average tree size, and the productive capacity of the site on which the forest is growing.

To better understand the physiognomy and dynamics of tropical forest canopy trees, the mortality, recruitment, and growth rates of trees -30 cm DBH were quantified on a montane tropical rain forest hilislope over the 10-yr period 1982-1992. The results indicate that the smaller stature of canopy trees growing on or near ridge-crests of montane rain forests is a consequence of higher turnover rates, not slower growth rates. The annual canopy tree turnover rate of approximately 1.7 percent in the upslope section of the sample area was two times greater than in the downslope section. The DBH growth increments in the upslope and downslope sections also were significantly different (P < 0.05), but it was the upslope trees that grew at the faster rate (upslope = 3.1 mm yr-1; downslope = 2.4 mm yr -). The mean DBH growth increment of 2.7 mm yr-1 for the entire plot is relatively high compared to other montane tropical rain forests. Interspecific variation among the 23 tree species also was notable, with mean DBH increments ranging from 0.4 to 7.8 mm yr-1. Ceratopetalum virchowii and Elaeocarpus ferruginiflorus were the most dominant species in 1982: C. virchowii increased its dominance over the 10-year period with a higher rate of recruitment than mortality and a change in relative importance from 22.7 percent in 1982 to 28.4 percent in 1992; E. ferruginiflorus, in contrast, experienced the most significant change of all the species examined, with a decrease in relative importance from 14.1 percent in 1982 to 5.3 percent in 1992 as a result of its high mortality, its slow growth rates, and its failure to recruit any individuals into the -30 cm DBH size-class; the local demise of this species may be part of a shifting floristic mosaic associated with natural disturbance events or perhaps part of an irreversible trend. It is recommended that more attention be directed to the growth patterns of co-occurring species and the life histories of individual trees to obtain a clearer sense for the long-term dynamics of montane tropical rain forest canopy tree populations.

Tunnel excavation causes geological, hydrological, environmental and social changes. The effects of groundwater level changes caused by tunnelling on tree growth have been poorly understood. Dendrochronology was used to evaluate the impact of groundwater level drawdown on tree growth. Tree cores of Masson pines were collected from the areas affected by tunnel construction in the Zhongliang Mountains of Chongqing in south-western China to study the effects of tunnel excavation on the growth rate of trees by comparing with tree cores collected from unaffected areas. Excavation and early operation of the first tunnel in the Zhongliang Mountains from 1968 to 1984 caused a groundwater table drawdown in both karst aquifer and non-karst aquifer. The lowered groundwater table significantly reduced the growth rate of pine trees, and the low growth rate remained for 15 years. The effect was experienced up to at least 1 km from the tunnel axis. The decline in tree growth was higher in karst than in non-karst areas, though the effects on the trees of the karst areas were lagging. The high precipitation in 1998 contributed to groundwater recovery, after which the tree growth recovered moderately but not to the original level. Groundwater leakage of the recently excavated tunnels did not affect pine trees heavily, probably because the pines had adapted to the new hydrogeological conditions and new strategies in tunnel inflow management were adopted in the recently excavated tunnels. The use of tree growth rate as an indicator of groundwater table change in tunnelling areas offers a new option to study environmental impacts and the extent of tunnelling effects.

Summary Most experimental evidence on the relationship between biodiversity and ecosystem functioning comes from ecosystems with fast‐growing plants, such as grasslands. Although forests provide essential ecological services, they have been less well investigated. We used dendrochronology to compare the tree radial growth rates of four important timber species in replicated, spatially mapped stands that differed in tree composition and diversity within a central European managed forest. Growth rates differed among species but were largely unaffected by the density of neighbouring trees. Increasing stand diversity enhanced individual growth rates, after accounting for the effects of tree density and size. These increases were statistically indistinguishable among the four species. In contrast, the effects of stand and neighbourhood species composition on growth rates were non‐significant. Policy implications. Our study of long‐established central European forest stands revealed levels of tree diversity can be increased in managed forests, with the potential for modest increases in tree growth rates. These results suggest that in addition to the biodiversity and risk mitigation benefits associated with shifting practices away from monoculture management, increased carbon sequestration and yields in mature forests are likely to be realized. Our results suggest that it is possible to increase forest diversity with little or no costs to production and even with the potential for modest increases in tree growth rates.

Xylem anatomical and hydraulic traits vary within crown but not respond to water and nitrogen addition in Populus tomentosa