Mean Tree Basal Area Research Articles

Unveiling urbanization effects on trees outside forests along the urban-rural gradient in megacity Bengaluru

Rapid urbanization has caused significant changes along the urban-rural gradient, leading to a variety of landscapes that are mainly shaped by human activities. This dynamic interplay also influences the distribution and characteristics of trees outside forests (TOF). Understanding the pattern of these trees will support informed decision-making in urban planning, in conservation strategies, and altogether in sustainable land management practices in the urban context. In this study, we employed a deep learning-based object detection model and high resolution satellite imagery to identify 1.3 million trees with bounding boxes within a 250 ​km2 research transect spanning the urban-rural gradient of Bengaluru, a megacity in Southern India. Additionally, we developed an allometric equation to estimate diameter at breast height (DBH) from the tree crown diameter (CD) derived from the detected bounding boxes. Our study focused on analyzing variations in tree density and tree size along this gradient. The findings revealed distinct patterns: the urban domain displayed larger tree crown diameters (mean: 8.87 ​m) and DBH (mean: 43.78 ​cm) but having relatively low tree density (32 trees per hectare). Furthermore, with increasing distance from the city center, tree density increased, while the mean tree crown diameter and mean tree basal area decreased, showing clear differences of tree density and size between the urban and rural domains in Bengaluru. This study offers an efficient methodology that helps generating instructive insights into the dynamics of TOF along the urban-rural gradient. This may inform urban planning and management strategies for enhancing green infrastructure and biodiversity conservation in rapidly urbanizing cities like Bengaluru.

Comparison on Vegetation Composition and Structure in Fire Prone Forest of Ilunde and Fire Suppressed Forest of Kitwe in Tanzania

Fire is among the factors influencing survival and development of plants in ecosystems. This study was conducted in frequently burnt and fire suppressed miombo woodlands of Ilunde and Kitwe, respectively. Tree stem density, basal area and composition of plants were determined. The methods used involved recording the numbers of tree stems, diameter at breast height and classifying vegetation to species level. In Kitwe forest, mean stem density of 582.7 ± 52.90 stems ha– was higher than 356.8 ± 38.98 stems ha– which was recorded in Ilunde forest (t = 15.98, df = 29, p < 0.05). Similarly, a higher mean tree basal area of 16.14 ± 1.32 m2 ha– was recorded in Kitwe forest, while 8.54 ± 0.94 m2 ha– being recorded in Ilunde forest (t = 3.34, df = 14, p < 0.05). Czekanowski’s similarity coefficients for trees, shrubs and saplings, and herbs and grasses were 0.46, 0.34 and 0.22, respectively. Fire adapted species were recorded in Ilunde forest. Fire prone miombo woodland had lower tree stem density, basal area and dominated by fire adapted species. Similarity coefficient between the two forests was also low. Prescribed burning is recommended in miombo woodlands for sustainable species composition and tree structure.
 Keywords: vegetation; composition, structure, fire prone, miombo.

Reduced tree density and basal area in Andean forests are associated with bamboo dominance

Forest structure and composition play an essential role in determining the carbon storage capacity of tropical forests. Andean forests, with great potential for carbon accumulation, include large expanses of high-density woody bamboo communities. Woody bamboos can potentially alter forest structure, composition and dynamics and thus can affect carbon storage capacity; however, they are commonly excluded from forest monitoring and modelling. With the aim of documenting patterns of bamboo abundance and disentangling its association with forest structure, we carried out a bamboo census in seven 1-ha long-term forest monitoring plots situated across a large elevation gradient (1000–3600 m a.s.l.) in the Peruvian Andes. We determined that bamboo is a dominant plant group in the study area. In every plot, bamboos were the most common genera in terms of number of stems, and in two of the plots bamboo species were among those with the greatest basal area. We used a combination of Generalized linear mixed models (GLMM) and structural equation modelling (SEM) to hypothesize a causal framework and determine the direction and size of the effects of bamboo abundance (basal area) on number of individual trees, total tree basal area, mean tree basal area, mean tree growth rate and tree mortality rate. We found an overall negative association between bamboo abundance and total tree basal area driven mainly by reduced tree density (directly and indirectly mediated by an increase in tree mortality). However, the decrease in tree density and the increase in tree mortality are also associated with a small increase in tree diameter (mean tree basal area). Overall, the negative association between bamboo abundance and tree basal area suggests a lower biomass accumulation and thus a lower carbon storage capacity of trees in Andean forests where bamboo is dominant. Our results, which show the importance of bamboo in determining forest function, highlight the need for including bamboo in monitoring efforts and modeling studies.

Asymmetric competition, ontogenetic growth and size inequality drive the difference in productivity between two-strata and one-stratum forest stands

Size inequality has been considered a key feature of plant population structure with impacts on ecosystem functions. In forest ecosystems, studies examining the relationship between tree size inequality and stand productivity have produced mixed outcomes. These studies found positive, neutral or negative relationships and discussed how this could be influenced by competition for light between trees (e.g. light interception efficiency), but far less attention has been paid to the role played by tree ontogenetic growth. In this article, we present a simple mathematical model that predicts the basal area growth of a two-strata stand as a function of tree basal areas and asymmetric competition. Comparing the growth of this stand to the growth of a spatially homogeneous one-stratum stand and a spatially heterogeneous one-stratum stand, we show that higher growth of the two-strata stand is achieved for concave shape, increasing functions of ontogenetic growth and for low intensities of absolute size-asymmetric competition. We also demonstrate that the difference in growth between the two-strata stand and the one-stratum stands depends on tree size inequality, mean tree basal area and total basal area in the two-strata stand. We finally found that the relationships between tree size inequality and productivity can vary from positive to negative and even non-monotonous. However, we highlight that negative relationships may be more frequent. As a conclusion, our results indicate that ontogenetic growth can have a major impact on the form and the magnitude of the size inequality–productivity relationship.

Decoupling of nutrient cycles in a Eucalyptus woodland under elevated CO2

Abstract Elevated atmospheric [CO2] (eCO2) is currently altering nutrient cycling and availability in ecosystems worldwide. If the availabilities and turnover rates of macro‐ and micronutrients are differentially affected, then nutrient cycles may become out of sync (i.e., decoupled). We evaluated the impacts of 3 years of eCO2 (550 µmol CO2/mol) on the availability, stability and coupling of eleven essential macro and micronutrients in a mature, P‐limited Eucalyptus woodland from Eastern Australia (EucFACE). Despite increases in N and P availability in the first 18 months of study, nutrient availabilities and their stoichiometric ratios were unaffected by eCO2 across the study period (26–57 months of experimental duration). In contrast, the stability of nutrient availability increased under eCO2, which was concomitant with a reduction in the degree of biogeochemical coupling. Synthesis. We demonstrate that macro‐ and micro‐nutrient cycles can quickly become out of sync (i.e., decoupled) under eCO2 in a low‐nutrient Australian eucalypt woodland, despite the lack of consistent effects on nutrient availability; such decoupling of nutrient cycles may have unpredicted consequences in terms of ecosystem functioning under the widely assumed positive relationship between biogeochemical coupling and ecosystem functioning.

Advancement of tree species across ecotonal borders into non-forested ecosystems

Woody species are increasing in density, causing transition to more densely wooded vegetation states, and encroaching across ecotonal borders into non-forested ecosystems. We examined USDA Forest Service Forest Inventory and Analysis data to identify tree species that have expanded longitudinally in range, particularly into the central United States. We analyzed compositional differences within ecological regions (i.e., subsections) in eastern and western ranges of species using repeated measures ANOVA. We considered differences in outer ranges to indicate range expansion or contraction. We also estimated the shift in forest area and basal area relative to the center of the US and compared change in deciduous forest land cover. Out of 80 candidate species, 22 species expanded to the west, seven species expanded to the east, and five species expanded in both directions. During the survey interval, eastern tree species advanced into the predominantly non-forested ecosystems of central United States. Eastern cottonwood, eastern hophornbeam, eastern redbud, honeylocust, Osage–orange, pecan, red mulberry, and Shumard oak represent some of the species that are advancing eastern forest boundaries across forest-grassland ecotones into the central United States. Forest land has shifted towards the center of the continent, as has the center of mean tree basal area, and a simple comparison of deciduous cover change also displayed forest advancement into the central United States from eastern forests. The expanding species may spread along riparian migration corridors that provide protection from drought. Humans use the advancing tree species for windbreaks, fencerows, and ornamental landscaping, while wildlife spread fruit seeds, which results in unintentional assisted migration, or translocation, to drier sites across the region.

Fine root dynamics of trees and understorey vegetation in a chronosequence of Betula platyphylla stands

Despite the recognized importance of fine roots in influencing forest carbon and nutrient cycling, knowledge of how fine root biomass, production and turnover rates change with stand age is still limited. In this study, we applied both sequential soil coring and ingrowth cores techniques to assess the influence of stand age on fine root biomass, live/dead ratio, production and turnover rates of trees and understorey vegetation in 20-, 36-, 57- and 82-year-old Betula platyphylla stands in northeastern China. A total of 1440 sequential cores and 288 ingrowth cores were collected from three soil depths (0–10, 10–20, and 20–30cm) during 2009–2010. Fine root biomass of trees increased from 20- to 36-year-old stands, and decreased thereafter in 57- and 82-year-old stands, while the distribution of understorey fine roots differed from that of tree fine roots. Fine root biomass of the understorey vegetation accounted for 49%, 12%, 31% and 60% of total fine root biomass in 20-, 36-, 57- and 82-year-old stands, respectively. Total biomass of fine roots (trees and understorey vegetation) increased with stand age. The live/dead ratio decreased with stand age, indicating that the older the stands, the greater the proportion of fine root necromass. Furthermore, our results showed that the mean tree basal area could explain 67% of the variation in tree fine root biomass and 53% of that in the total fine root biomass at the tree level. These tree-level analyses may be of great value in predicting fine root biomass values in B.platyphylla stands at the stand and/or tree level. Fine root production and turnover rates based on both sequential soil coring and ingrowth cores techniques exhibited similar age-related patterns, strengthening the results that fine root production and turnover rates increased with stand age in the B.platyphylla chronosequence we studied.

Influence of Forest Fragmentation on the Winter Abundance of Mammals in Mt. Chirisan National Park, South Korea

Abstract: We examined the influence of both local habitat and landscape variables on mammal species abundance in a forest fragmented by road construction and in continuous forest in 8 study sites in Mt. Chirisan National Park, South Korea, from 2001 to 2004. We recorded tracks of 8 species of mammals, Siberian weasels (Mustela sibirica), yellow‐throated martens (Martes flavigula), Bengal cats (Felis bengalensis), wild boars (Sus scrofa), water deer (Hydropotes inermis), roe deer (Capreolus capreolus), Korean hares (Lepus coreanus), and red squirrels (Sciurus vulgaris), on the snow on 8 2‐km transects in our study areas. There were significant differences in density of snags, mean tree basal area, and in shrub coverage between the fragmented and unfragmented forest areas. We found significant differences in abundance index of tracks between the fragmented and unfragmented areas for 5 mammal species; the others had even distributions. Of the 8 mammal species analyzed, 5 species related to landscape and local vegetation variables in a stepwise approach with repeated measures. Landscape variables are significant predictors of abundance for many mammal species. Forest managers should consider multiple measures of forest fragmentation sensitivity when making forest management decisions.

Tree species diversity and ecosystem function: Can tropical multi-species plantations generate greater productivity?

Results from the humid tropics of Australia demonstrate that diverse plantations can achieve greater productivity than monocultures. We found that increases in both the observed species number and the effective species richness were significantly related to increased levels of productivity as measured by stand basal area or mean individual tree basal area. Four of five plantation species were more productive in mixtures with other species than in monocultures, offering on average, a 55% increase in mean tree basal area. A general linear model suggests that species richness had a significant effect on mean individual tree basal area when environmental variables were included in the model. As monoculture plantations are currently the preferred reforestation method throughout the tropics these results suggest that significant productivity and ecological gains could be made if multi-species plantations are more broadly pursued.

Fourteen-year growth response of young lodgepole pine to repeated fertilization

Four rates of N (0, 50, 100, and 150 kg·ha–1) with and without a fertilizer mix containing P, K, S, Ca, Mg, and micronutrients were applied to a stand of 8-year-old lodgepole pine (Pinus contorta var. latifolia Engelm.) in four applications during 7 years. Fourteen years after the first fertilization, mean tree basal area and volume were significantly increased in the treatments containing the two highest rates of N plus the fertilizer mix. Mean tree basal area was 38% greater and mean tree volume was 42% greater in the highest N (525 kg·ha–1) plus mix treatment than in the control treatment. Stand basal area increased 48% over the control in the highest N plus mix treatment. Mean tree basal area and volume were 27 and 25% greater than the control under the intermediate N rate (350 kg·ha–1) with mix, respectively. Height growth was not significantly increased by fertilization. Both higher rates of N (four applications of >100 kg·ha–1) and the fertilizer mix were required for significant growth responses to occur. Addition of N alone or mix alone had a negative effect on mean tree basal area and volume. Addition of higher N rates without the mix decreased foliar total S and SO4-S concentration and increased the N/S ratio. Addition of the higher rates of N without the mix aggravated slight K deficiencies. The responses to the higher N rates in combination with the fertilizer mix are mainly attributable to S.

Comparison of altitudinal sequences of vegetation on granite and metasedimentary rocks in the Preservation Ecological District, southern Fiordland, New Zealand

Abstract Vegetation and soils were sampled along paired altitudinal sequences on granite and adjoining metasedimentary rocks from sea level to treeline at approximately 900 m elevation at Dusky Sound, Fiordland. Soils derived from granite are less fertile, and are inferred to provide less rooting volume than those on metasediment. Nothofagus menziesii alone dominates the continuous tall forest on metasediment; in the forest on granite, four or more species form the canopy. On granite, treeline is depressed by 150 m, and shrubland and grassland alternate on mineral soil and peat respectively, at altitudes supporting N. menziesii forest 11 – 15 m tall on metasediment. Total species richness and density of woody stems are greater on granite, but mean tree basal area is consistently less than that on metasediment. The dominance/diversity models tested indicate that community structure changes with altitude in different ways on the two substrates, a pattern that is difficult to explain until we know more about the influence of the environment on dominance/diversity relations.

A Stand Table Projection Approach to Yield Prediction in Plantations

SYNOPSIS A procedure is presented whereby an initial stand table is projected to a future age. Application of the procedure requires the availability of a survival prediction, as well as a total basal area projection equation. Relative tree size is defined as the ratio of tree basal area to the mean tree basal area, and the stand table projection procedure is based on an hypothesis concerning the expected change in relative tree size over time. The projected stand table will have an implied basal area that is consistent with the observed or predicted future total basal area. Long-term remeasurement data from a slash pine (Pinus elliottii Engelm.) spacing and thining study in Zululand are used to examine the validity of the hypothesis over a range of planting densities and site quality. Application of the proposed procedure is demonstrated with a survival function and basal area projection equation derived from the same data base.

Expected decrease in diameter growth of even-aged red spruce

Weibull functions provide close least square fits to tables for stand basal area and density versus age in even-aged, second-growth red spruce as reported by W. H. Meyer (USDA Tech. Bull. No. 142. 1929). The annual mean radial and basal area increments of the trees can be calculated from the two Weibull functions. For a stand following Meyer's tables and reaching breast height in 1915, mean tree basal area increment increases steadily to a maximum in the early 1960's and then declines; mean radial increment is constant from 1925 to 1955 and then declines rapidly. This behavior matches very closely the results from 3001 red spruce increment cores in New England and New York, which suggests that forest aging is an important cause of decreasing red spruce diameter growth.