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23 results for “stand development”
Looking beyond the mean: Drivers of variability in postfire stand development of conifers in Greater Yellowstone
High-severity, infrequent fires in forests shape landscape mosaics of stand age and structure for decades to centuries, and forest structure can vary substantially even among same-aged stands. This variability among stand structures can affect landscape-scale carbon and nitrogen cycling, wildlife habitat availability, and vulnerability to subsequent disturbances. We used an individual-based forest process model (iLand) to ask: Over 300 years of postfire stand development, how does variation in early regeneration densities versus abiotic conditions influence among-stand structural variability for four conifer species widespread in western North America? We parameterized iLand for lodgepole pine (Pinus contorta var. latifolia), Douglas-fir (Pseudotsuga menziesii var. glauca), Engelmann spruce (Picea engelmannii), and subalpine fir (Abies lasiocarpa) in Greater Yellowstone (USA). Simulations were initialized with field data on regeneration following stand-replacing fires, and stand development was simulated under historical climatic conditions without further disturbance. Stand structure was characterized by stand density and basal area. Stands became more similar in structure as time since fire increased. Basal area converged more rapidly among stands than tree density for Douglas-fir and lodgepole pine, but not for subalpine fir and Engelmann spruce. For all species, regeneration-driven variation in stand density persisted for at least 105 years postfire, and for lodgepole pine, early regeneration densities dictated among-stand variation for 203 years. Over time, stands shifted from competition-driven convergence to environment-driven divergence, in which variability among stands was maintained or increased. The relative importance of drivers of stand structural variability differed between density and basal area and among species due to differential species traits, growth rates, and sensitivity to intraspecific competition versus abiotic conditions. Understanding dy
Temporal nitrogen dynamics in intensively managed loblolly pine early stand development
<p>Forest production is strongly dependent on nutrient uptake; however, sustainable management of intensively managed plantations requires an improved understanding of this relationship when fertilization occurs frequently across short rotations. Here, we studied temporal nitrogen (N) concentration ([N]) and content (Nc) dynamics under different silvicultural practices (herbicide, fertilization, and planting density) throughout early loblolly pine (<i>Pinus taeda</i>) stand development (5 years). We describe relationships of [N] and Nc of different stand components (foliage, branches, stem, roots, and competing vegetation) with carbon and biomass. Our results demonstrate that [N] of perennial loblolly tissues do not respond to silvicultural practices and progressively decrease through development. While foliar [N] was most responsive to resource availability, it was not consistent across time. Controlling competing vegetation was crucial to promote the use of site resources by the crop tree and increased loblolly Nc by >500%. However, increased N uptake and expedited growth is dependent upon fertilization early in stand development. At age 5,<i> </i>herbicide<i> </i>plus <i>reduced </i>and <i>full </i>fertilization<i> </i>rates exhibited similar aboveground Nc, which was 32% higher than with <i>herbicide only</i>. Increasing planting density resulted in increased above- and belowground loblolly Nc; however, increases in Nc were not proportional with increases in planting density. Net primary productivity and N uptake were linearly related, but age/development strongly controlled N use efficiency. Our study helps to understand complex relationships between N, biomass, and silvicultural practices during early stand development and demonstrates that temporal evaluation of nutrient dynamics is crucial to better understand loblolly pine growth, carbon sequestration potential, and to inform sustainable silvicultural practices across short rotations.</p>
Developing crown width model for mixed forests using soil, climate, and stand factors
<ol> <li>The tree crown is a useful measure of tree vigor and is highly relevant to a tree's environmental adaptability. Crown allometry depends on environmental and stand conditions. Several studies have focused on the effects of climate change and competitive intensity on the crown, but the regulatory role of soil resources and diversity on crown allometry and carbon allocation has been neglected.</li> <li>Data from 20,994 trees in 232 mixed forests collected between 2011 and 2019 was located near four major mountain ranges in northeast China. The proposed crown width model includes the stand developmental stage, soil, climate, competition intensity, species mixture, species diversity, structural diversity, and their interactions.</li> <li>We observed that the cross-species allometric scaling exponent does not conform to the universal scaling law. Our results showed that crown width increased with increasing soil bulk density, quadratic mean diameter, and coefficient of diameter variation but decreased with increasing de Martonne aridity index, basal area, Simpson index, and species mixture. The interaction of quadratic mean diameter and soil bulk density had a significant negative effect on crown width. The influence of a particular factor within the interaction term on crown width was modulated by the gradients of other factors. Furthermore, soil bulk density contributed more to crown width modeling than the aridity index, and structural diversity had a greater effect on crown width than species diversity.</li> <li> <em>Synthesis</em>. Our results provide new insights into the environmental variability of crown allometry in mixed forests under global change, which is critical for improving regional and global estimates of forest biomass and carbon stocks.</li> </ol>
Data from: Shift from an extensive to an intensive root nutrient-acquisition mode with stand development of three Pinus species
<p>Plant roots employ diverse strategies to acquire soil nutrients, including direct nutrient uptake through absorptive fine roots and root hairs, scavenging nutrients by forming symbioses with mycorrhizal fungi, and mining nutrients by releasing root exudates. However, whether these three strategies are differently coordinated among phylogenetically closely-related tree species and how this coordination shifts with stand development remains largely unclear. To fill these knowledge gaps, we measured 13 root morphological, architectural, physiological and mycorrhizal traits tightly related to nutrient-acquisition of three <em>Pinus</em> species (<em>P. sylvestris</em> var. <em>mongolica</em>, <em>P. densiflora</em> and <em>P. tabuliformis</em>) at young (20-year-old) and mature (50-year-old) stages planted in nutrient-impoverished sandy soils, in Northeast China. We found that young trees had thinner absorptive fine roots and a higher specific root length than mature trees across three <em>Pinus</em> species, indicating that roots become morphologically less efficient in "do it yourself" scavenging nutrients during stand development. Moreover, young stands had greater root length density and root area index, and mature stands had faster root-exudation rates, suggesting that young stands rely more on expanding soil volumes to scavenge nutrients and mature stands depend more on root exudation to 'mine' nutrients. The three <em>Pinus</em> species exhibited different nutrient-acquisition strategies at the mature stage; <em>P. densiflora</em> had higher root length density and root area index, and the other two <em>Pinus</em> species had greater ectomycorrhizal colonization rates.</p> <p><em>Synthesis</em>. Our findings highlight that phylogenetically closely-related tree species may exhibit different nutrient-acquisition strategies, and suggest a shift from an extensive nutrient-acquisition mode depending more on absorptive fine roots to an intensive nutrient-acquisition mode relying more on root exudation during stand development.</p>
Temporal nitrogen dynamics in intensively managed loblolly pine early stand development
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Data from: Shift from an extensive to an intensive root nutrient-acquisition mode with stand development of three Pinus species
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Data from: Space-for-time substitution misleads projections of plant community and stand-structure development after disturbance in a slow-growing environment
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Developing crown width model for mixed forests using soil, climate, and stand factors
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Herbicide, fertilization, and planting density effects on intensively managed loblolly pine early stand development
<p><span><span>Production forestry in the southeast US has been partially transitioned to intensively managed short rotations (~10 years), in which multiple silvicultural interventions are performed during forest development. Understanding the responses to silvicultural practices and continued refinement of site-specific recommendations is critical to sustainably maximize forest production. We evaluated the effects of silvicultural practices (herbicide, fertilization, and planting density) on growth, stand homogeneity, and above- and belowground biomass accumulation and partitioning of loblolly pine (<i>Pinus taeda</i>) throughout early stand development (age 5 years) in the southeastern US. Five treatments with eight replications each were tested: no herbicide and no fertilization (<i>C</i>); herbicide only (<i>H</i>); herbicide and half-reduced fertilization rate (<i>R</i>); herbicide and full fertilization (<i>F</i>); and increased stand density (60+ %; 1346 <i>vs.</i> 2152 trees per hectare) with herbicide and full fertilization rate (<i>D</i>). Allometric equations generated from destructive harvests were applied to annual diameter measurements to estimate plot-level biomass and allocation. Herbicide was crucial to promote stand uniformity and increase yield (~600+ % stem biomass compared with <i>C</i> at age 5). Aboveground biomass was similar in <i>R</i> and <i>F</i> treatments, which was, on average, ~25% higher than in <i>H</i> at age 5. Increasing planting density along with multiple herbicide and fertilizer applications yielded higher biomass without compromising individual tree size (diameter and height). There was little effect of silviculture practices on allocation patterns. Our results parallel what was found for fertilization with herbicide from a number of loblolly stands under similar conditions and indicate a ~28% volume gain with fertilization during early stand development. Similarly, our results were consistent with other studies implementing similar differences in planting density and suggest a ~26% volume gain through early stand development with an initial 60% increase in planting density. Our study helps to understand complex relationships between production and silvicultural practices during early stand development and demonstrates that silvicultural prescriptions can be optimized to increase sustainability of production forestry.</span></span></p>
Data from: Effects of species diversity on fine root productivity increase with stand development and associated mechanisms in a boreal forest
There is a growing interest in understanding the relationship between diversity and below-ground productivity due to the critical contribution of below-ground systems to overall terrestrial productivity. Yet, the temporal (seasonal and developmental) changes in diversity effects on below-ground productivity and their underlying mechanisms remain unclear. We hypothesized that (i) diversity effects on fine root productivity increase with stand development, and (ii) increased diversity effects associated with stand development result from augmented horizontal soil space utilization, increased forest floor depth for rooting, enhanced effects in nutrient-poor soil layers and/or foraging towards high nutrient availability. We investigated the effects of tree species diversity on fine root productivity by sampling 18 stands dominated by single species and their mixtures in post-fire boreal forests of two stand ages (8 and 34 years following stand-replacing fire). Species evenness was significantly higher in species mixtures than in single-species-dominated stands at both age classes, while species richness did not differ across stand types and age classes. We found that the annual fine root production was higher in mixtures than the mean of single-species-dominated stands in both stand ages, with a significantly higher magnitude of effects in the 34-year-old than 8-year-old stands. Mixtures had higher horizontal soil volume filling than single-species-dominated stands with a more pronounced increase in the 34-year-old than 8-year-old stands. Compared with the 8-year-old stands, the 34-year-old stands had increased forest floor depth and greater overyielding with soil depth, and their fine root productivity was more responsive to the vertical variation in soil phosphorus concentrations among soil layers. Synthesis. Our results provide evidence for increasing positive diversity effects on fine root productivity with stand development in heterogeneous natural forests. Moreover, our results indicate that the increased positive diversity effects with stand development was the result of multiple mechanisms, including higher horizontal soil volume filling, a thicker forest floor layer for rooting, a higher magnitude of complementarity in nutrient-poor deep soil layers and stronger nutrient foraging towards soil layers with high nutrient concentrations in older than younger stands.
Data from: Climatic stress during stand development alters the sign and magnitude of age-related growth responses in a subtropical mountain pine
The modification of typical age-related growth by environmental changes is poorly understood, In part because there is a lack of consensus at individual tree level regarding age-dependent growth responses to climate warming as stands develop. To increase our current understanding about how multiple drivers of environmental change can modify growth responses as trees age we used tree ring data of a mountain subtropical pine species along an altitudinal gradient covering more than 2,200 m of altitude. We applied mixed-linear models to determine how absolute and relative age-dependent growth varies depending on stand development; and to quantify the relative importance of tree age and climate on individual tree growth responses. Tree age was the most important factor for tree growth in models parameterised using data from all forest developmental stages. Contrastingly, the relationship found between tree age and growth became non-significant in models parameterised using data corresponding to mature stages. These results suggest that although absolute tree growth can continuously increase along tree size when trees reach maturity age had no effect on growth. Tree growth was strongly reduced under increased annual temperature, leading to more constant age-related growth responses. Furthermore, young trees were the most sensitive to reductions in relative growth rates, but absolute growth was strongly reduced under increased temperature in old trees. Our results help to reconcile previous contrasting findings of age-related growth responses at the individual tree level, suggesting that the sign and magnitude of age-related growth responses vary with stand development. The different responses found to climate for absolute and relative growth rates suggest that young trees are particularly vulnerable under warming climate, but reduced absolute growth in old trees could alter the species' potential as a carbon sink in the future.
Changes in the direction of the diversity-productivity relationship over fifteen years of stand development in a planted temperate forest
<p>Experiments manipulating diversity in both forests and grasslands have often observed a positive diversity-productivity relationship (DPR) which tends to strengthen during plant community development. This pattern is generally attributed to an increase in niche complementarity or facilitation. Most analyses do not examine species dominance and density, which also change over time. Moreover, how neighbourhood scale interactions among tree species affect the DPR is not well understood.</p> <p>We analysed growth and mortality data from the Simplex experiment, a part of the BIOTREE tree diversity experiment. Simplex consists of 36 plots each planted with four common and commercially important tree species to create a gradient of tree species evenness at two tree densities (6667 and 3556 trees ha<sup>-1</sup>). We test whether: i) the effect of evenness on total aboveground biomass productivity increase with stand development (year), ii) the effect of evenness on productivity is stronger in dense plots; iii) intra-specific competition from neighbours negatively affect the growth of dominant species more strongly compared to co-dominant species, and whether this negative effect is stronger in denser plots.</p> <p>The direction of DPR was initially negative because the fast-growing long-lived pioneer Douglas fir (<em>Pseudotsuga menziesii</em> (Mirb.) Franco) dominated. However, with time, shade tolerant Norway spruce (<em>Picea abies </em>(L.) Karst.) and European beech (<em>Fagus sylvatica </em>L.) increased in abundance (by biomass), and the relationship between evenness and biomass increment changed from negative to positive in high-density plots. Neighbourhood analyses revealed that for Douglas fir and Norway spruce, conspecifics reduced individual growth rates across density levels and years.</p> <p>Synthesis: We observed a shift in the diversity-productivity relationship over 15 years in our experiment. Over time, increasing intraspecific competition limited the increment of the abundant Douglas fir in uneven plots, and a persistent increase in the abundance (by biomass) of shade tolerant Norway spruce and European beech in even plots led to a higher community biomass increment, which led to a positive DPR. Emergence of a positive DPR in temperate forest plantations requires significant time and is importantly promoted by diversity at the neighbourhood scale (intimate mixtures) as well as higher density planting.</p>
Data from: Effects of species diversity on fine root productivity increase with stand development and associated mechanisms in a boreal forest
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Changes in the direction of the diversity-productivity relationship over fifteen years of stand development in a planted temperate forest
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Data from: Climatic stress during stand development alters the sign and magnitude of age-related growth responses in a subtropical mountain pine
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Herbicide, fertilization, and planting density effects on intensively managed loblolly pine early stand development
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Data from: Spatial patterns and interspecific associations among trees at different stand development stages in the natural secondary forests on the Loess Plateau, China
Quercus wutaishansea populations on the Loess Plateau are currently becoming more dominant in natural secondary forests, whereas Pinus tabulaeformis is declining. In the present paper, the diameter class (instead of age) was used to classify the different growth stages as juvenile, subadult, or adult, and the univariate function g(r) was used to analyze the dynamic changes in spatial patterns and interspecific associations in three 1‐ha tree permanent plots on the Loess Plateau, NW China. Our results suggested that the niche breadth changed with the development stage. The diameter distribution curve was consistent with the inverted "J" type, indicating that natural regeneration was common in all three plots. There was a close relationship between the spatial pattern and scale, which showed significant aggregation at small distances, and became more random as distance increased, but in the Pinus + Quercus mixed forests, the whole species were aggregated at distances up to 50 m. The degree of spatial clumping decreased from juvenile to subadult and from subadult to adult. The spatial pattern also differed at different growth stages, likely due to strong intraspecific competition. Associations among different growth stages were positively correlated at small scales. Our study is important to the understanding of the development of the Q. wutaishansea forests; thus, the spatial dynamic change features should be received greater attention when planning forest management and developing restoration strategies on the Loess Plateau.
Fig. 2 in Centipede diversity in patches of different development phases in an unevenly-aged beech forest stand in Slovenia
Fig. 2. Average density estimates of some centipede species from different development phases in an unevenlyaged beech stand at Is˘ka (Slovenia), based on soil samples in 2000.
Fig. 1 in Centipede diversity in patches of different development phases in an unevenly-aged beech forest stand in Slovenia
Fig. 1. Dendrogram of similarities among centipede community samples from different forest development phases, sampled in three different periods in 2000 (distances calculated as (1-percentage similarity)).
Data from: Spatial patterns and interspecific associations among trees at different stand development stages in the natural secondary forests on the Loess Plateau, China
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