Crown Growth Rates Research Articles

Assessing the Relationship between Ecological Water Demand of Haloxlon ammodendron and Its Wind Erosion Prevention Effect

Desert vegetation in the outer transition zone of an arid oasis serves as a protective barrier against wind and sand, safeguarding the oasis ecosystem. However, intensive agricultural water usage within the oasis has led to water depletion, posing a threat to the survival and growth of desert vegetation, as well as the associated increase in wind and sand phenomena. To ensure the sustainable distribution of water resources and maintain the stability of the oasis peripheral ecosystem, this study aimed to investigate the relationship between the ecological water demand of desert vegetation and its effectiveness in preventing wind erosion. Through a combination of field sample tests, field pit tests, and data analysis, this research focused on Haloxlon ammodendron, the most prevalent species on the oasis periphery, to explore the intricate relationship between its ecological water demand and resistance to wind erosion. The results showed that medium-vegetation-coverage soils exhibited a higher soil moisture content (7.02%) compared to high-vegetation-coverage soils (1.57%) and low-vegetation-coverage soils (3.41%). As the soil water content decreased, the growth rate of H. ammodendron’s plant height, new branches, and crown width decelerated. The ecological water requirement of H. ammodendron during its growth period was 70.95 mm under medium-vegetation-coverage conditions, exhibiting a significant increase of 14.6% and 12.3% compared to high- and low-vegetation-coverage conditions, respectively. Meanwhile, H. ammodendron exhibits remarkable wind erosion prevention effects in moderate coverage conditions, resulting in a significant reduction in surface sand collection and sand transport by 53.15% and 51.29%, respectively, compared to low vegetation coverage; however, no significant difference was observed when compared to high vegetation coverage. The SEM model results revealed that soil water content had an indirect effect on sand transport (R2 = 0.90) and sand collection (R2 = 0.96) through three pathways of action, namely: volatile water content–crown growth rate–wind speed–sediment discharge; volatile water content–plant height growth rate–vegetation coverage–wind speed–sediment discharge; and volatile water content–plant height growth rate–vegetation coverage–sediment accumulation. This study provides valuable insights for the scientific formulation and implementation of strategies aimed at protecting desert vegetation.

Estimating the age and population structure of encroaching shrubs in arid/semiarid grasslands using high spatial resolution remote sensing imagery

Many arid and semiarid grasslands around the world are suffering from shrub encroachment to a great extent. However, the process of shrub encroachment is still poorly understood. Particularly, there has been limited historical datasets and inadequate field samples about the encroachment species. Shrub age can serve as an important indicator of the shrub encroachment history; and the population structure based on the shrub age distribution can reflect the population dynamics of an encroachment species. Using a high spatial resolution (HSR) remote sensing data, this paper estimates the age and population structure of a typical shrub, the Caragana genus (hereafter shrubs) in the temperate arid and semiarid grasslands of Inner Mongolia, China. The primary methods include: (1) building a shrub age estimation model considering different shrub crown growth rates affected by different precipitation regimes in the Inner Mongolian grassland; (2) identifying shrub individuals from multiple HSR remote sensing images and estimating the age of shrub individuals using the developed shrub age estimation model; (3) establishing a shrub age histogram, fitting the population structure, and calculating the survival rate and regeneration count using a negative exponential function. The results indicate that this shrub age estimation model performs better than a simple statistical regression using only the shrub crown area. Further, employing the negative exponential function for research on shrub encroachment provides supporting evidence of its effective role in capturing the population structure. Result also identifies that the survival rate increases with precipitation.

Effects of pit plantings on tree growth in semi-arid environments

ABSTRACTThis study developed a pit planting technique in which only planting spots were dug to reduce earthwork costs and to enhance tree growth. This technique, in which pits of different depths were dug, was actually applied to a semi-arid experiment site to analyze its effects on soil moisture and tree growth. The soil moisture content in the pit planting 30 cm in depth (30 cm pit planting) and 50 cm in depth (50 cm pit planting) was 6.5 ± 0.1% and 6.7 ± 0.1%, respectively, which was at least 1.3 times higher (P < 0.01) than that of the control plot (surface planting). The crown growth rate of Populus sibirica trees for 2 years following the planting was 733.5 ± 43.3% in the 30 cm pit planting and 889.4 ± 58.5% in the 50 cm pit planting which, at their maximum, were 1.7 times higher than in the control plot. The stem diameter growth and the new shoot length were maximally 1.5 times better in the pit planting than in the control plot. The pit planting technique developed will be widely useful to promote the rooting and growth of trees in planting areas with problems of strong winds and dryness.

Early subtropical forest growth is driven by community mean trait values and functional diversity rather than the abiotic environment.

While functional diversity (FD) has been shown to be positively related to a number of ecosystem functions including biomass production, it may have a much less pronounced effect than that of environmental factors or species-specific properties. Leaf and wood traits can be considered particularly relevant to tree growth, as they reflect a trade-off between resources invested into growth and persistence. Our study focussed on the degree to which early forest growth was driven by FD, the environment (11 variables characterizing abiotic habitat conditions), and community-weighted mean (CWM) values of species traits in the context of a large-scale tree diversity experiment (BEF-China). Growth rates of trees with respect to crown diameter were aggregated across 231 plots (hosting between one and 23 tree species) and related to environmental variables, FD, and CWM, the latter two of which were based on 41 plant functional traits. The effects of each of the three predictor groups were analyzed separately by mixed model optimization and jointly by variance partitioning. Numerous single traits predicted plot-level tree growth, both in the models based on CWMs and FD, but none of the environmental variables was able to predict tree growth. In the best models, environment and FD explained only 4 and 31% of variation in crown growth rates, respectively, while CWM trait values explained 42%. In total, the best models accounted for 51% of crown growth. The marginal role of the selected environmental variables was unexpected, given the high topographic heterogeneity and large size of the experiment, as was the significant impact of FD, demonstrating that positive diversity effects already occur during the early stages in tree plantations.

The effects of belowground resources on aboveground allometric growth in Bornean tree species

Tree height and crown allometries reflect adaptations for resource acquisition and structural stability, as well as plastic responses to a heterogeneous environment. While both light and soil resources limit growth and influence competitive responses in tropical forests, the effects of belowground resources on allometries are less understood, especially within the understory. To characterize outcomes of tree competition along an edaphic resource gradient, we quantified variation in height and crown allometries of six Bornean tree species from contrasting regeneration niches (light-demanding vs. shade-tolerant) on two soil habitats (clay-fine loam and sandy loam) within a 52-ha forest dynamics plot. Using empirically-fit allometric parameters and diameter growth rates from plot census data, we modeled tree height and crown area growth over the projected life span of each species. Based on resource competition theory, we hypothesized that tree species specializing on and populations of generalist species growing on the relatively moister, more fertile clay-fine loam soil habitat would have faster height and crown growth rates, compared to those on the sandy loam habitat, regardless of regeneration niche. Among soil specialists and within generalists of both genera, trees growing on clay-fine loam had taller stems and larger crowns at a given age and faster height and crown area growth rates at most sizes than trees on sandy loam. Differences in height and crown growth were driven by the faster diameter growth rates of trees on clay-fine loam, not by differences in height- and crown-diameter allometries, as trees on sandy loam were significantly taller at a given diameter, and differences in crown allometry were not consistent across soil habitats. Characterizing the height and crown growth responses of trees along resource gradients provides insight into the mechanisms that maintain diversity in tropical forests. Our results point to the importance of adaptive and plastic responses to both above and belowground resource availability in determining the allometric growth of trees and suggest that this diversity of responses may contribute tree species coexistence through competition-based trade-off mechanisms and variation in growth among individuals. Additionally, as the importance estimating natural carbon sequestration increases with the escalating effects of anthropogenic climate change, differences in tree growth and architecture across soil habitats also have implications for the approximation of forest carbon storage on heterogeneous tropical soils.

Growth differences in the saber-tooth of three felid species

Abstract Analysis of the saber-tooth morphology within the Felidae indicates that canines of various saber-toothed species grow differently. Stable oxygen isotopes analyzed from tooth enamel reveal that the scimitar-toothed Homotherium serum, which possessed short, broad sabers, had tooth crown growth rates similar to modern lions. This contrasts with the longer and thinner, dirk-toothed saber species in the genus Smilodon, S. gracilis and S. fatalis, which had much faster growth rates. With a more rapid growth rate, Smilodon reduced the total duration of crown growth to a period of time similar to that observed in modern lions, even though its tooth crown was twice as large. While comparable in overall morphology, developmental differences may reflect ecological differences among taxa bearing saber-toothed canines.

Different cost of reproduction for the males and females of the rare dioecious shrub Corema conradii (Empetraceae)

Males and females of dioecious plant species often differ in their reproductive investment. Such differences frequently result in differential demographic costs represented by lower growth, survival, and/or frequency of reproduction, and/or by more variable reproductive effort through time for females. We present the results of a study on Corema conradii, a rare dioecious shrub of the coastal dune heathlands of northeastern North America. We estimated the reproductive investment of both males and females, determined their age structure, and compared their spatial patterns in a population at Îles-de-la-Madeleine, Quebec. We also determined the sex ratio of the four populations known to occur on the islands. Males invested more in reproduction at flowering, but when fruit production was considered, female reproductive investment was higher in terms of biomass, Mg, and Ca, but not in terms of N, P, and K. The age frequency distribution of males and females did not differ significantly from one another. The population dispersion pattern was contagious, with patches of similar-age individuals. There was no spatial segregation between males and females, although the sex ratio varied somewhat spatially. Females did not start reproducing at a later age than males and did not appear to have a shorter longevity. However, the crown and radial growth rates of females were lower than those of males. When estimated by the crown intercept method, the sex ratio of all four populations was male biased. However, because males had a higher crown growth rate, genet sex ratio was in fact balanced. Higher investment in reproduction was associated with a lower growth rate, which represents a differential cost of reproduction according to sex in this species.

Twenty-one years of crown area change in the Jasper Ridge Biological Preserve based on georeferenced multitemporal aerial photographs

A time series of large-scale aerial photographs of a 25 ha section of the Jasper Ridge Biological Preserve (JRBP) in California was analysed for the quantification of long-term changes in the orthogonally projected crown areas of a sample of mature canopy trees growing in closed woodland and open grassland habitats. Crown area changes were computed on the basis of pairwise image comparisons for the years 1974, 1980, 1988, 1989, 1990, 1991, 1993 and 1995. Single frame image correction methods were assessed by comparing a high-resolution physical-system based method of photogrammetric orthorectification with a low-resolution method of georeferencing that involved the use of ground control points (GCPs) for the derivation of best-fit statistical transformations. The same crown digitization procedure was used for both methods, and a statistically significant difference was not found between the high-resolution and low-resolution measured crown areas. Crown area changes were not correlated with differences in sun position at the time of aerial photo acquisition nor with differences in the off-nadir distances of each crown in the images being compared. The upper limit of digitizing error was 3.5% based on the mean coefficient of variation plus one standard deviation computed from repeat digitization measures of each crown. Crown area changes exceeding 3.5%in the pairwise image comparisons were attributed to actual crown growth or crown reduction. Expressed as a percentage of the original crown area, the mean annual rate of change for each pairwise sample period was 4.9% yr-1. In absolute terms, the mean annual rate of crown area change over the 21-year period 1974-1995 was 1.4m2 yr-1. The long-term mean annual crown growth rate of the clustered woodland trees (1.3m2yr-1) was not significantly different from the isolated grassland trees (1.5m2 yr-1). The mean annual rates of change for the periods 1974-1980, 1980-1989 and 1991-1993 were similar to the long-term average. Unusually low mean growth rates characterized the drought years of 1989-1990 and 1990-1991, while the relatively wet period of 1993-1995 exhibited the most dramatic increase in crown area at a mean rate of 3.0m2yr-1.

Redefining the ecological niche of a tropical rain forest canopy tree species using airborne imagery: long-term crown dynamics of Toona ciliata

Past controlled growth experiments indicate that the seedling and sapling responses of the tropical rainforest canopy tree species Toona ciliata are most consistent with a light-demanding, early successional pioneer. This ecological niche assignment was tested in the mature stage of its life cycle after it achieves a position in the upper canopy. Mortality, survivorship and crown growth rates over the 18-y period 1976–1994 were measured using co-registered repeat airborne stereophotographic coverage of a representative forest stand in northeast Queensland, Australia, where T. ciliata had the fourth highest relative importance in a population of 46 co-occurring canopy tree species. The airborne re-inventory was conducted in a 3.6-ha sample area and limited to only canopy trees. The results were compared with a ground-based inventory of both canopy and subcanopy trees ≥10 cm dbh in a 0.5-ha permanent plot. Over the period 1976–1994, there was no mortality and no evidence of decline among T. ciliata conspecifics having crown areas &gt;60 m2 and trunk diameters &gt;30 cm. In the 3.6-ha airborne sample area, more than 85% of T. ciliata survivors experienced positive crown growth, in contrast to only 57% of the other co-occurring canopy trees. Toona ciliata's crown growth rates were highest in the 60–80-m2 crown size class. Upon reaching an upper canopy position, T. ciliata not only persisted as a dominant canopy tree species, but it also achieved some of the largest crown areas (&gt;100 m2). Toona ciliata mortality in the ground-based plot involved mainly subcanopy trees of 10 – 30 cm dbh that had not yet assumed a canopy position and were not detectable in the aerial stereopairs. Both the crown and dbh growth rates of T. ciliata indicate enhanced vigour in the later stage of its life cycle. Its long-term survivorship and growth patterns are indicative of a persistent canopy tree species that fits the niche of a long-lived, shade-intolerant pioneer. These results demonstrate the usefulness of a long-term airborne database on the life-histories of canopy tree crowns for more clearly defining their ecological niches.

Allozyme Heterosis in Radiata Pine is Poorly Explained by Overdominance

Heterosis, the superior vegetative or reproductive vigor associated with heterozygosity, has been observed for allozymes in a wide variety of plant and animal taxa. Its causes, however, are widely debated. To gain insight into the causes of heterosis, we examined the relationship of allozyme heterozygosity and growth rate in a sample from a natural population of radiata pine. Some 244 clones derived from 30 natural stands were grown for 14 yr in an experimental plantation. Height, diameter, and crown growth rates were determined for six to nine ramets per clone; clonal genotypes were scored at 27 polymorphic allozyme loci. Levels of heterozygosity well below average were associated with depressed growth rates. The strength of heterosis within stands was positively associated with the estimated level of natural inbreeding and negatively associated with mean observed heterozygosity. Heterosis varied sporadically among loci and was unrelated to their levels of polymorphism, thus failing to support the hypothesis that the major polymorphisms are maintained by overdominant selection. Rates of growth also declined at high levels of heterozygosity, suggesting that the less frequent allozymes and/or tightly linked loci, which occur predominantly in heterozygous condition, tended to have deleterious effects.

A GRAVIMETRIC STUDY OF CROWN GROWTH RATE OF THE HUMAN DECIDUOUS DENTITION.

A GRAVIMETRIC STUDY OF CROWN GROWTH RATE OF THE HUMAN DECIDUOUS DENTITION.