Woody Basal Area Research Articles

The Effects of Legacy Sediment Removal and Floodplain Reconnection on Riparian Plant Communities

Stream restoration includes a number of different approaches intended to reduce sediment and nutrient export. Legacy sediment removal (LSR) and floodplain reconnection (FR) involve removing anthropogenically derived sediment accumulated in valley bottoms to reconnect incised streams to their floodplains. These projects also present an opportunity to create high-quality riparian and wetland plant communities and provide information about the early stages of wetland vegetation development and succession. We surveyed vegetation immediately after restoration at three sites and at three additional sites 1–3 years post-restoration to determine how LSR/FR affects riparian plant communities. Restoration increased the prevalence of hydrophytic herbaceous species at all sites, suggesting these projects successfully reconnected the stream to the floodplain. Pronounced decreases in woody basal area and stem density likely also influenced an increase in native and graminoid species after restoration. Only 16% of the indicator species identified for restored reaches were planted as part of the restoration, suggesting the local seed bank and other seed sources may be important for vegetation recovery and preservation of regional beta diversity. Although vegetation quality increased after restoration in reaches with initially low-quality herbaceous vegetation, vegetation quality did not improve or decreased after restoration in reaches with higher-quality vegetation before restoration. The practice of LSR/FR has the potential to improve the quality of some riparian vegetation communities, but the preservation of high-quality forested areas, even if they are atop legacy sediment terraces, should be considered, particularly if reductions in nutrient export do not offset losses in tree canopy.

Grasses continue to trump trees at soil carbon sequestration following herbivore exclusion in a semiarid African savanna

Although studies have shown that mammalian herbivores often limit aboveground carbon storage in savannas, their effects on belowground soil carbon storage remain unclear. Using three sets of long-term, large herbivore exclosures with paired controls, we asked how almost two decades of herbivore removal from a semiarid savanna in Laikipia, Kenya affected aboveground (woody and grass) and belowground soil carbon sequestration, and determined the major source (C3 vs. C4 ) of belowground carbon sequestered in soils with and without herbivores present. Large herbivore exclusion, which included a diverse community of grazers, browsers, and mixed-feeding ungulates, resulted in significant increases in grass cover (~22%), woody basal area (~8m2 /ha), and woody canopy cover (31%), translating to a ~8.5t/ha increase in aboveground carbon over two decades. Herbivore exclusion also led to a 54% increase (20.5t/ha) in total soil carbon to 30-cm depth, with ~71% of this derived from C4 grasses (vs. ~76% with herbivores present) despite substantial increases in woody cover. We attribute this continued high contribution of C4 grasses to soil C sequestration to the reduced offtake of grass biomass with herbivore exclusion together with the facilitative influence of open sparse woody canopies (e.g., Acacia spp.) on grass cover and productivity in this semiarid system.

Quantifying the impact of an extreme climate event on species diversity in fragmented temperate forests: the effect of theOctober 1987 storm onBritish broadleaved woodlands

SummaryWe report the impact of an extreme weather event, theOctober 1987 severe storm, on fragmented woodlands in southernBritain. We analysed ecological changes between 1971 and 2002 in 143 200‐m2plots in 10 woodland sites exposed to the storm with an ecologically equivalent sample of 150 plots in 16 non‐exposed sites. Comparing both years, understorey plant species‐richness, species composition, soilpHand woody basal area of the tree and shrub canopy were measured.We tested the hypothesis that the storm had deflected sites from the wider national trajectory of an increase in woody basal area and reduced understorey species‐richness associated with ageing canopies and declining woodland management. We also expected storm disturbance to amplify the background trend of increasing soil pH, aUK‐wide response to reduced atmospheric sulphur deposition. Path analysis was used to quantify indirect effects of storm exposure on understorey species richness via changes in woody basal area and soil pH.By 2002, storm exposure was estimated to have increased mean species richness per 200 m2by 32%. Woody basal area changes were highly variable and did not significantly differ with storm exposure.Increasing soil pHwas associated with a 7% increase in richness. There was no evidence that soil pHincreased more as a function of storm exposure. Changes in species richness and basal area were negatively correlated: a 3.4% decrease in richness occurred for every 0.1‐m2increase in woody basal area per plot.Despite all sites substantially exceeding the empirical critical load for nitrogen deposition, there was no evidence that in the 15 years since the storm, disturbance had triggered a eutrophication effect associated with dominance of gaps by nitrophilous species.Synthesis. Although the impacts of the 1987 storm were spatially variable in terms of impacts on woody basal area, the storm had a positive effect on understorey species richness. There was no evidence that disturbance had increased dominance of gaps by invasive species. This could change if recovery from acidification results in a soil pHregime associated with greater macronutrient availability.

Nitrogen and Carbon Biogeochemistry in Forest Sites along an Indirect Urban–Rural Gradient in Southeastern Michigan

To evaluate the impacts of urbanization on soil and vegetation in protected forest areas, 12 forest sites in Southeastern Michigan USA were studied in an indirect urban–rural gradient. Field study plots were established in forest edge zones of each protected area. Significant findings were that in these edge zones of protected areas: (a) soil nitrogen tended to be greater where surrounding housing density was greater; (b) overstory woody biomass and basal area were greater where surrounding housing density was greater; and (c) the study region overall exhibited low soil carbon content (mean 2.71%) and relatively high soil nitrogen content (mean 0.20%), yielding a surprisingly low surface soil C/N ratio (mean 13.4). Overall, 24 woody plant genera were encountered, with the three genera Acer, Carya and Quercus accounting for 83.7% of total biomass and 74.1% of total basal area. No significant relationships were observed between housing density and soil C/N ratio or between housing density and foliar N. Results indicate that a halo of urban-ecological impacts exists in the landscape of Southeastern Michigan, similar to previously studied linear urban–rural gradients in other regions.

Plant functional types and traits as biodiversity indicators for tropical forests: two biogeographically separated case studies including birds, mammals and termites

Multi-taxon surveys were conducted in species-rich, lowland palaeotropical and neotropical forested landscapes in Sumatra, Indonesia and Mato Grosso, Brazil. Gradient-directed transects (gradsects) were sampled across a range of forested land use mosaics, using a uniform protocol to simultaneously record vegetation (vascular plant species, plant functional types (PFTs) and vegetation structure), vertebrates (birds, mammals) and invertebrates (termites), in addition to measuring site and soil properties, including carbon stocks. At both sites similar correlations were detected between major components of structure (mean canopy height, woody basal area and litter depth) and the diversities of plant species and PFTs. A plant species to PFT ratio [spp.:PFTs] was the best overall predictor of animal diversity, especially termite species richness in Sumatra. To a notable extent vegetation structure also correlated with animal diversity. These surrogates demonstrate generic links between habitat structural elements, carbon stocks and biodiversity. They may also offer practical low-cost indicators for rapid assessment in tropical forest landscapes.

Liana Abundance, Diversity, and Distribution on Barro Colorado Island, Panama

Lianas are a key component of tropical forests; however, most surveys are too small to accurately quantify liana community composition, diversity, abundance, and spatial distribution – critical components for measuring the contribution of lianas to forest processes. In 2007, we tagged, mapped, measured the diameter, and identified all lianas ≥1 cm rooted in a 50-ha plot on Barro Colorado Island, Panama (BCI). We calculated liana density, basal area, and species richness for both independently rooted lianas and all rooted liana stems (genets plus clones). We compared spatial aggregation patterns of liana and tree species, and among liana species that varied in the amount of clonal reproduction. We also tested whether liana and tree densities have increased on BCI compared to surveys conducted 30-years earlier. This study represents the most comprehensive spatially contiguous sampling of lianas ever conducted and, over the 50 ha area, we found 67,447 rooted liana stems comprising 162 species. Rooted lianas composed nearly 25% of the woody stems (trees and lianas), 35% of woody species richness, and 3% of woody basal area. Lianas were spatially aggregated within the 50-ha plot and the liana species with the highest proportion of clonal stems more spatially aggregated than the least clonal species, possibly indicating clonal stem recruitment following canopy disturbance. Over the past 30 years, liana density increased by 75% for stems ≥1 cm diameter and nearly 140% for stems ≥5 cm diameter, while tree density on BCI decreased 11.5%; a finding consistent with other neotropical forests. Our data confirm that lianas contribute substantially to tropical forest stem density and diversity, they have highly clumped distributions that appear to be driven by clonal stem recruitment into treefall gaps, and they are increasing relative to trees, thus indicating that lianas will play a greater role in the future dynamics of BCI and other neotropical forests.

Bush clump succession in grassland in the Kei Road region of the Eastern Cape, South Africa

Bush encroachment is a vegetation dynamic of global interest. This study describes the pattern of succession of bush clumps in the Eastern Cape, South Africa, using a space-for-time substitution. Clumps formed following establishment of mainly Acacia karroo in grassland through nucleation via animal dispersal. A total of 49 tree or shrub species were recorded in 40 clumps. With increasing clump size, there was a corresponding increase in woody basal area, species richness and diversity, but not evenness. Correspondence analysis showed that the pattern of compositional variation was closely related to clump size; differences resulting from clump establishment disappeared as clumps developed. Population size structure of 20 (of 21) species was dominated by small individuals, indicating that regeneration has increased over time. Coddia rudis was prolific on a clump periphery; Scutia myrtina and A. karroo were dominant within clumps. Seven shrub and nine tree species were encountered more frequently within a clump than on its periphery. All species other than A. karroo had fruits suited to dispersal by birds or mammals. The overall pattern of bush clump succession shows close parallels with that initiated by invasion of Prosopis glandulosa into grassland in Texas, USA.

Effects of Land-Use Change on Under Storey Species Composition and Distribution in a Tropical Rainforest

The forest land’s conversion into tree crops plantations plays a major role in the loss of biodiversity. Therefore, understanding the impacts of land-use change on species diversity is very critical for ecosystem functioning and stability. This study was carried out to evaluate the effect of land-use changes on under storey species diversity in the Theobroma cacao and Citrus sinensis plantations. Two, 25 m × 25 m plots were sampled in each plantation and a nearby undisturbed secondary rainforest for comparison. The diameters (dbh-1.3 m) of all trees at breast height >10 cm were measured in each plot. Five line transect were systematically laid and a quadrat of 50 cm × 50 cm placed at every 1 m point to identify the under storey species (herbaceous, shrubs, tree saplings and climbers) present in each plot. Percentage canopy, species diversity using Shannon-Wiener, Simpson’s index and Evenness were determined, while species similarity was determined using the Jaccard’s similarity index. Results indicate that woody basal area and stem density in Theobroma cacao were significantly (P<0.05) higher than the Citrus sinensis plantation. A total number of 25, 27, and 14 under storey species distributed in 16, 19 and 11 families were found in Theobroma cacao , Citrus sinensis plantations and secondary forest respectively. Panicum maximum and Axonopus compressus were the dominant grasses in the Theobroma cacao and Citrus sinensis plantations respectively. The percentage canopy cover was significantly (P<0.05) higher in the secondary forest than the plantations. The land use modification has significantly increased the under storey species composition.

Structural analysis of woody species in Mediterranean old fields

The study analyses the changes in vegetation structure and composition within a sere of secondary succession at Pantelleria Island (Sicilian Channel, Italy). It aims to show that not only phytosociological data but also structural parameters, like woody species’ height and spatial distribution indices are useful to describe and interpret renaturation processes. Woody species structure was recorded on abandoned terraces, both on north-facing and on south-facing slopes. Relevés were made in fallows representing five different stages of succession. The pace of succession, measured through the analysis of woody species cover, basal area, height distribution and spatial indices, resulted quite rapid: already after 50 years of abandonment terraces are covered by dense maquis communities. Our study also revealed that different plant species or groups prevail during colonisation dynamics, mostly depending on exposition, a factor which strongly influences also the speed of colonisation by woody species. In this case study, human activity seems to be unnecessary to accelerate the process of renaturation, except in some unfavourable contexts. Species turnover rate, biodiversity value, and structural evolution along progressive succession must be taken into account in nature management and conservation policies of terraced landscapes, which are nowadays one of the most endangered landscape types throughout the Mediterranean area.

Trends in savanna structure and composition along an aridity gradient in the Kalahari

Abstract. The Kalahari sand sheet occupies 2.5 million ha in southern Africa. It is an area with relatively similar deep aeolian soils, and a strong south to north gradient in rainfall, from 200 to 1000 mm mean annual precipitation (MAP) in the region studied. This provides an excellent basis for gradient studies at the subcontinental scale. This paper briefly reviews the literature on the vegetation of the Kalahari and describes the vegetation structure and composition at 11 new sites. There is a clear gradient in woody plant biomass (as indexed by basal area) from south to north. Above the minimum level of 200 mm MAP, the woody basal area increases at a rate of ca. 2.5 m2.ha‐1 per 100 mm MAP. Mean maximum tree height also increases along the gradient, reaching 20 m at ca. 800 mm MAP. The number of species to contribute &gt; 95% of the woody basal area increases from one at 200 mm to 16 at 1000 mm MAP. Members of the Mimosaceae (mainly Acacia) dominate the tree layer up to 400 mm MAP. They are replaced by either the Combretaceae (Combretum or Terminalia) or Colophospermum mopane of the Caesalpinaceae between 400 and 600 mm MAP, and by other representatives of the Caesalpinaceae above 600 mm MAP. The vegetation is largely deciduous up to 1000 mm MAP, except for species that apparently have access to groundwater, which may be locally dominant above about 600 mm MAP.

Trends in savanna structure and composition along an aridity gradient in the Kalahari

Abstract The Kalahari sand sheet occupies 2.5 million ha in southern Africa. It is an area with relatively similar deep aeolian soils, and a strong south to north gradient in rainfall, from 200 to 1000 mm mean annual precipitation (MAP) in the region studied. This provides an excellent basis for gradient studies at the subcontinental scale. This paper briefly reviews the literature on the vegetation of the Kalahari and describes the vegetation structure and composition at 11 new sites. There is a clear gradient in woody plant biomass (as indexed by basal area) from south to north. Above the minimum level of 200 mm MAP, the woody basal area increases at a rate of ca. 2.5 m2.ha−1 per 100 mm MAP. Mean maximum tree height also increases along the gradient, reaching 20 m at ca. 800 mm MAP. The number of species to contribute > 95% of the woody basal area increases from one at 200 mm to 16 at 1000 mm MAP. Members of the Mimosaceae (mainly Acacia) dominate the tree layer up to 400 mm MAP. They are replaced by ei...

Vegetative Response to 37 Years of Seasonal Burning on a Louisiana Longleaf Pine Site

Abstract From 1962 through 1998, 20 prescribed burns were applied in a natural stand of longleaf pine (Pinus palustris Mill.) to determine the effects of various fire regimes on the forest plant community. The original longleaf seedlings regenerated from the 1955 seed crop and were growing in a grass-dominated cover when the study began. By 1999, prescribed burning in March and May resulted in a significantly greater stocking of longleaf pine (203 trees/ac) than on the unburned and July burned treatments (72 trees/ac) (α = 0.05). Fire arrested the growth of natural loblolly pine (P. taeda L.) and hardwoods, but loblolly pines and hardwoods of at least 4 in. dbh added 70 ft2/ac of basal area on the unburned plots. Thus, total woody basal area was significantly greater on the unburned (117 ft2/ac) and May burned (132 ft2/ac) treatments than on the July burned treatment (66 ft2/ac); basal area was intermediate on the March burned treatment (97 ft2/ac). Pine volume was 4,315, 2,870, 2,652, and 1,970 ft3 inside-bark/ac on the May burned, March burned, unburned, and July burned treatments, respectively, but these differences were not statistically significant (P = 0.06). There was only 11 lb/ac of herbaceous plants on the unburned plots. Herbaceous plants averaged 993 lb/ac on the three burned treatments, with pinehill bluestem (Schizachyrium scoparium var. divergens [Hack] Gould) being the most common herbaceous plant. We believe the chief influence of burning in this natural longleaf pine forest was not on pine yield but how fires influenced overall stand structure and species composition. South. J. Appl. For. 25(3):122–130.

Relationships between loblolly pine yield and woody plant diversity in Virginia Piedmont plantations

This study was established to determine the effects of competition control on loblolly pine (Pinus taeda L.) yield and woody plant diversity in Virginia Piedmont plantations 12-14 years of age. In a factorial experiment, loblolly pine and competing woody vegetation were analyzed at eight levels of competition control: total, two-thirds, one-third, or no woody stem control in combination with either total or no herbaceous vegetation control. Pine yield increased linearly with increasing levels of woody control intensity. As woody control increased, noncrop woody plant basal area and woody plant diversity (Shannon index (H')) in the canopy decreased. Woody plant species richness in the canopy was reduced by herbaceous control and by total woody control. Percent woody cover, H', and species richness in the understory were not affected at any level of competition control. Regression analysis was used to examine relationships between loblolly pine yield, noncrop woody dominance and canopy plant diversity (H'). Pine yield was negatively correlated (R2 = 0.74) with the percentage of noncrop woody basal area (PNCW BA) in the canopy, while canopy diversity was proportional to PNCW BA (R2 = 0.97). Canopy diversity was inversely related to pine yield (R2 = 0.77), with a high trade-off in diversity at low yield levels, but with decreasing sensitivity as pine yield increased.

The burning of fuelwood in South Africa: When is it sustainable?

Fuelwood harvesting is considered sustainable when consumption is equal to or less than production. An empirical model was developed to estimate potential fuelwood production from savannas. The model is based on the observation that in semiarid savannas, biomass production is linearly dependent on rainfall. Woody basal area is linked to mean annual precipitation, and aboveground woody biomass is proportional to basal area. Production averages 4% of standing woody biomass and is corrected to exclude stems that are too small for harvesting. The model assumes that the entire area consists of seminatural savanna. Corrections for the land lost as a result of land transformation and degradation would have to be included. Data on land loss can most effectively be obtained from satellite imagery, with appropriate ground calibration. The model is based on limited data sets but in most instances has been validated against independently collected data. The model yields a reasonable prediction at a national and regional level, but estimates for limited areas or specific points on the ground may differ substantially from the predicted values. Model results indicate a potential for sustainable fuelwood production at the national level, but specific regions are using fuelwood at nonsustainable levels.

Response of a monsoon forest‐savanna boundary to fire protection, Weipa, northern Australia

AbstractA numerical floristic analysis of samples across a monsoon forest‐savanna boundary, from an area that had been actively protected from fire for 15 years, at Weipa, northern Australia, revealed three communities: (i) a monsoon forest with a low closed canopy composed mainly of tree species with extra‐Australian tropical affinities and a sparse ground layer; (ii) an ecotone with a distinct closed microphyll shrub layer beneath the open canopy of savanna trees; and (iii) a savanna dominated by Eucalyptus tetrodonta. The development of the ecotone has occurred since fire protection and is of limited extent within the fire protected block. The monsoon forest occurred on soils with significantly higher concentrations of bauxitic pisoliths than the other two communities. Soils under the monsoon forest had significantly higher concentrations of total K, S, C, N, exchangeable K and Ca, and higher pH and electrical conductivity than for soils of either of the other communities. A positive relationship between woody basal area and concentrations of surface soil total P, N, C, exchangeable Ca, CEC and gravel was detected across a 20 m transect from the ecotone community into the savanna. The invasion of monsoon forest seedlings was greatest in the ecotone, with few occurring in the savanna. It appears that the expansion of the monsoon forest requires the development of a layer of shrubs. The mechanism of this facilitation is unclear, although the possible role of nutrient enrichment by the shrubs requires further investigation.

Discriminant analysis some east Tennessee forest herb niches

Niche differences in four species of Galium were quantified by using discriminant function analysis (DFA) of site characteristics including biotic variables. Data were analyzed separately for a mesic hardwood site and cedar barrens. Significant differences in niche centroids were also determined for 17 co-occurring herbs in the mesic hardwood site using similar variables. Variables used in the analysis included site characteristics such as aspect and percent slope, biotic variables such as total woody basal area and litter composition, and soil characteristics (for the seventeen species) including pH and texture. Biotic variables were included as indicators of environmental variables and possible allelopathic influence. In the Galium data, variables highly correlated with discriminant axes included canopy density, litter type, and overstory type. In the co-occurring species data, litter composition, slope position, soil pH and texture, and steepness of slope were most correlated with discriminant axes. Discriminant axes derived from the Galium cedar barren data set proved a poor predictor of species occurrence in the mesic hardwood site. The utility of DFA in plant niche analysis is discussed.