Recovery dynamics of wetland vegetation along a hydrological gradient in an agriculturally used inland valley in Uganda

Inadequate knowledge exists on the distribution of soil moisture and shallow groundwater in intensively cultivated inland valley wetlands in tropical environments, which are required for determining the hydrological regime. This study investigated the spatial and temporal variability of soil moisture along 4 hydrological positions segmented as riparian zone, valley bottom, fringe, and valley slope in an agriculturally used inland valley wetland in Central Uganda. The determined hydrological regimes of the defined hydrological positions are based on soil moisture deficit calculated from the depth to the groundwater table. For that, the accuracy and reliability of satellite‐derived surface models, SRTM‐30m and TanDEM‐X‐12m, for mapping microscale topography and hydrological regimes are evaluated against a 5‐m digital elevation model (DEM) derived from field measurements. Soil moisture and depth to groundwater table were measured using frequency domain reflectometry sensors and piezometers installed along the hydrological positions, respectively. Results showed that spatial and temporal variability in soil moisture increased significantly (p < .05) towards the riparian zone; however, no significant difference was observed between the valley bottom and riparian zone. The distribution of soil hydrological regimes, saturated, near‐saturated, and nonsaturated regimes does not correlate with the hydrological positions. This is due to high spatial and temporal variability in depth to groundwater and soil moisture content across the valley. Precipitation strongly controlled the temporal variability, whereas microscale topography, soil properties, distance from the stream, anthropogenic factors, and land use controlled the spatial variability in the inland valley. TanDEM‐X DEM reasonably mapped the microscale topography and thus soil hydrological regimes relative to the Shuttle Radar Topography Mission DEM. The findings of the study contribute to improved understanding of the distribution of hydrological regimes in an inland valley wetland, which is required for a better agricultural water management planning.

Biomass estimation within an Australian eucalypt forest: Meso-scale spatial arrangement and the influence of sampling intensity

In the coming century, forecast climate changes caused by increasing greenhouse gases may produce dramatic shifts in tree species distributions and the rates at which individual tree species sequester carbon or release carbon back to the atmosphere. The species composition and carbon storage capacity of northern Wisconsin (USA) forests are expected to change significantly as a result. Projected temperature changes are relatively large (up to a 5.8°C increase in mean annual temperature) and these forests encompass a broad ecotone that may be particularly sensitive to climate change. Our objective was to estimate the combined effects of climate change, common disturbances, and species migrations on regional forests using spatially interactive simulations. Multiple scenarios were simulated for 200 years to estimate aboveground live biomass and tree species composition. We used a spatially interactive forest landscape model (LANDIS‐II) that includes individual tree species, biomass accumulation and decomposition, windthrow, harvesting, and seed dispersal. We used data from two global circulation models, the Hadley Climate Centre (version 2) and the Canadian Climate Center (version 1) to generate transient growth and decomposition parameters for 23 species. The two climate change scenarios were compared with a control scenario of continuing current climate conditions. The results demonstrate how important spatially interactive processes will affect the aboveground live biomass and species composition of northern Wisconsin forests. Forest composition, including species richness, is strongly affected by harvesting, windthrow, and climate change, although five northern species (Abies balsamea,Betula papyrifera,Picea glauca,Pinus banksiana,P. resinosa) are lost in both climate scenarios regardless of disturbance scenario. Changes in aboveground live biomass over time are nonlinear and vary among ecoregions. Aboveground live biomass will be significantly reduced because of species dispersal and migration limitations. The expected shift towards southern oaks and hickory is delayed because of seed dispersal limitations.

The bulk density and nutrient distribution in soil profiles as affected by various land use systems were studied. Mean bulk densities of the various soil profiles, 0-20, 20-40, and 4060 cm in the selected five land use systems along the upland / lowland topo-sequences were, 1.26, 1.73, and 1.44 Mg m-3 for the primary forest (PF) plot in the upland area, 1.13, 1.51, and 1.50 Mg m-3 for the cacao farm (CP) plot, 1.16, 1.63, and 1.26 Mg m-3 for the mixed cropping (MC) plot, 1.39, 1.61, and 1.50 Mg m-a for the fallow (Fallow) plot, all three land use systems being in the upland / fringe areas, and 1.46, 1.72, and 1.60 Mg m-3 for the lowland traditional rice farming (TR) plot, respectively. The very high bulk density of the second layer, especially in the PF plot, may be related to the hardening of the iron / quartz stone layer due to prolonged dry conditions, which may affect plant growth and hydrological cycles in the benchmark inland valley watersheds. The TC contents of the topsoil samples were 43, 32, 24, 26, 18, and 15 g kgm-1 for the PF, CP, Fallow, MC, TR, and sawah (Sawah) plots, respectively. The C / N ratios of the topsoil samples were 10, 10, 9.8, 9.1, 8.8, and 8.8 for the CP, Fallow, MC, Sawah, TR, and PF plots, respectively, displaying a higher natural fertility, especially for the N supply in the PF plot in the upland area. The available phosphorus levels were low even for the topsoil samples, 1.8 to 3.4 mg kg-1 for the upland soils while the lowland TR and Sawah plots recorded values of 4.4 and 4.9 mg kg-1, respectively. The contents of exchangeable K, 0.1-0.4 cmole kg-1, of the topsoil samples were in the range of those of normal inland valley soils in West Africa. In contrast to the content of available P, although the MC plot showed a depletion, the PF, Fallow, and CP plots showed a replenishment of available K through biological nutrient cycling. The levels of exchangeable Ca and Mg as well as eCEC, were also relatively high compared to those of mean inland valley soils in West Africa. The major component of eCEC was Ex. Ca. The levels of Ex. Ca in the topsoil samples were 11.1, 9.1, 7.8, 4.7, 5.1, and 3.9 cmolc kg-1 for the PF, CP, Fallow, MC, TR, and Sawah plots, respectively. The distinctive feature of Ex. Mg was its large distribution in the upper soil profiles in the CP plot, indicating that in the cacao farms, Ex. Mg was enriched, probably due to the high level of Mg in the leaf litter. The lowland soils, normally, should have been enriched in exchangeable bases such as Ca, K, and Mg, leading to a higher eCEC value and higher general fertility through the process of geological fertilization, Le., nutrient flows from upland to lowland areas, as in the case of lowland sawah in monsoon Asia. At the benchmark sites, however, the effects of the geological fertilization process were not evident. This is one of the most important characteristics of West African inland valley watersheds.

Riparian buffers mitigate effects of pine plantation logging on New Zealand streams1. Riparian vegetation structure, stream geomorphology and periphyton

Riparian buffers mitigate effects of pine plantation logging on New Zealand streams: 1. Riparian vegetation structure, stream geomorphology and periphyton

The riparian vegetation along water courses and the health of the river’s basin, regarding the aquatic and terrestrial ecosystems associated with them, are widely discussed in literature. However, the maintenance of the services and the conservation role that riparian forests provide to flora and fauna may be affected by the regional matrix that surrounds the water course and by the length and composition of the riparian vegetation associated with them. This study aimed to evaluate the relationships among the grass cover and arboreal species diversity in three watercourses surrounded by a pasture dominated with the alien grass Uroclhoa decumbens (Stapf) R.D. Webster (former Brachiaria decumbens). Two hypotheses were tested: (i) watercourses with larger riparian forest width present higher richness and abundance of native and zoochoric tree species and those associated to late succession stages, and (ii) watercourses with larger riparian forest width present a lower grass cover on their interior. The study was conducted under domain of Semideciduous Seasonal Forest, belonging to the Atlantic Forest biome, municipality of Londrina, Paraná State, south Brazil. The regional climate is Köppen’s Cfa humid subtropical. The soil is classified as a mosaic of eutroferric red nitosols and lithosols. The studied sites mostly comprise pasture with U. decumbens alien grass and small patches of woody vegetation amidst an open pasture dominated by species attributed to the first’s stages of secondary succession. The studied site is immersed in Cambé’s River watershed and contain three watercourses, Cristal River, tributary to São Lourenço River, that, in turn, is tributary to Cambé River. All watercourses are classified as small rivers (Brazilian Forestry Code, federal law: n. 12.651/2012), with length inferior to 10 m between both riversides. The riparian vegetation shares similar characteristics and structure, encompassing woody vegetation with pioneer trees species and high canopy openness. All riparian forests are immersed in pastures with U. decumbens grass. Transects of 200 meters long, measuring one meter wide from the line on both sides of the transect, and one square plot (25 m2) were allocated on the interior of each riparian forest. Transects were evaluated as arboreal species richness and the length of the riparian forest strip. In each plot, the arboreal vegetation was inventoried as species richness, abundance and density, and the U. decumbens cover was measured. The riparian forest width was arranged in two classes, forests with width ≤ 5 m or ≥ 10 m. The studied forests were compared as richness, abundance, density, and grass cover. The correlations among the riparian vegetation with the forest width and grass coverage (%) were evaluated. Species richness, abundance and density did not differ among the watercourses. However, species abundance and density presented positive correlations with the riparian forest width, indicating that the larger is the riparian vegetation, the higher is the species density. Grass cover presents a strong negative correlation with the riparian forest width, indicating that narrow strips of woody vegetation present higher grass cover. A high positive correlation was observed with riparian strip width and native trees, suggesting that native woody species establishment is limited by the riparian strip width and that those rustic trees species are more capable to colonize these environments. Also, the correlation found with species that present abiotic syndromes and pioneer species indicates that trees that can colonize open areas are more suitable to establish on narrow strips of vegetation amidst a pasture. The relationships observed with zoochoric trees suggests that the fauna that visits these forests are tolerant to open areas and visit these areas independently of their vegetation width. The larger riparian forests present lower grass cover and these can be related to shadow micro-sites that reduce the luminosity which can affect the permanence potential of the dominance of U. decumbens. In this way, the data suggests that few plants can establish in these pasture landscape, and those more rustic trees which are able to establish under open areas, high grass cover and canopy openness, and that re-sprout after a fire, became more dominant. For these watercourses, with narrow riparian vegetation strips surrounded by an U. decumbens pasture, the high grass cover can restrict and plant diversity, acting on the course and velocity of secondary succession in these areas.

Situated on the southeastern coast at 34°S 151°E, Sydney was established in 1788 as Australia's first permanent European settlement. Clearing of natural vegetation and environmental degradation associated with the country's largest population concentration over the past 200 years have severely affected the nearby Hawkesbury-Nepean River. A strategy for rehabilitation of the riparian vegetation to conserve and enhance the natural conditions remaining along the river, with particular emphasis on habitat and natural biodiversity, has been developed. The study area encompassed the most modified part of the river, where it passes alternately through 80 km of sandstone terrain, where the natural vegetation of waterside scrub backed by open-forest remains largely unchanged, and 135 km of floodplain terrain, where most of the indigenous tall open-forest has been cleared and associated wetlands have been greatly modified. Indigenous riparian zone vegetation was recognized as critical to the maintenance of river health, providing a reservoir of biodiversity as a major value, upon which other values, including enhancement of water quality, bank stablility and erosion control, depend. As 47 per cent of study area riverbank was found to have less than 25 per cent tree cover, the strategy recommended that all remnant native vegetation and remnant native trees along the river be protected and that a substantial long-term aim should be the establishment of a 50-metre wide strip of native riparian forest vegetation on each bank along the full length of the river, to be linked ultimately with other areas of natural vegetation on the floodplain. To provide practical resources for revegetation, the strategy assembled a botanical database, including maps showing present tree cover and the past extent of floodplain vegetation types, descriptions and locations of sites where significant native riparian vegetation remains, ecological information on approximately 300 locally indigenous riparian and wetland plant species, guidelines on selection of appropriate species, replanting methods and determination of priorities at both site and landscape scale.

Carbon (C), nitrogen (N), and phosphorus (P) are essential nutrients that promote plant growth and development and maintain the stability of ecosystem structure and function. Analyzing the C, N, and P characteristics of plant leaves aids in understanding the plant's nutrient status and nutrient limitation. Seasonal water-level fluctuations in riparian zones lead to various ecological problems, such as reduced biodiversity and decreased ecosystem stability. Therefore, comprehending the stoichiometric characteristics of riparian zone plants and their nutrient response to plant traits is important for a deeper insight into riparian zone forest ecosystems. This study analyzed the C, N, and P contents of the leaves of 44 woody plants in the riparian zone of the Dahuofang Reservoir to investigate the stoichiometric characteristics of C, N, and P of trees in the region. The results showed that the average C content of the leaves in woody plants was 446.9 g kg-1; the average N content was 28.42 g kg-1; and the average P content was 2.26 g kg-1. Compared to global and regional scales, woody plants in the riparian zone of the Dahuofang Reservoir exhibited higher N and P contents but lower N:P ratios. Compared to other riparian zones, woody plant leaves in the riparian zone of Dahuofang Reservoir had relatively high N content and N:P ratios. Variations in plant stoichiometric characteristics across different life forms were minimal, with only tree leaf P content significantly lower than its in shrubs. There was no significant correlation between leaf C, N, and P in woody plants, while specific leaf area showed a negative correlation with leaf C content. Trees in the riparian zone have high leaf N and P content and are primarily N-limited during the growing season. This study reveals the stoichiometric characteristics of leaves of woody plants in the riparian zone, which can contribute to an in-depth understanding of leaf stoichiometric patterns and the factors influencing them among plant life types in the riparian zone.

O presente trabalho teve como objetivo conhecer a composição florística e estágio sucessional das espécies arbóreas que compõem as margens da mata ciliar do Ribeirão da Içara (23º09’51.74’’S e 51º39’21.60’’W), no município de Astorga, na região norte do Estado do Paraná. O clima da região é classificado como Cfa, e altitude média de 532 m. A área de estudo apresenta 0,5 ha, pertence ao domínio de Floresta Estacional Semidecidual, consiste em um trecho de mata ciliar formado por uma vegetação nativa com agrupamentos densos de árvores, cipós (trepadeiras), pouca vegetação rasteira e reflorestamento. A ocupação do solo do entorno é a pecuária e a produção de culturas de cana-de-açúcar e laranja. As coletas de material botânico foram realizadas através de expedições mensais com duração de três dias no período de dezembro de 2010 a março de 2011. Foram amostrados os indivíduos arbóreos em estágio reprodutivo, os quais foram incorporados ao acervo do HUEM. Algumas espécies foram coletadas apenas suas partes vegetativas. O material coletado foi identificado com auxílio de bibliografia específica e por comparação com o material do acervo do HUEM, seguindo o sistema APG III. As espécies foram classificadas quanto ao estágio sucessional através de consulta a bibliografias específicas e observações de campo, sendo que as exóticas e as indeterminadas não foram consideradas para esta análise. Foram registradas 84 espécies reunidas em 77 gêneros e 28 famílias, das quais seis foram identificadas apenas em nível de gênero, quatro ao nível de família e uma de família indeterminada. Fabaceae apresentou o maior número de espécies (23), seguida de Myrtaceae com seis, Malvaceae e Meliaceae com cinco, Anacardiaceae, Bignoniaceae, Euphorbiaceae e Sapindaceae com quatro, Rutaceae com três. Nestas famílias estão contidos 69,05% do número de espécies. O gênero com maior número de espécies foi o Machaerium (três). Quanto ao estágio sucessional, 35,93% das espécies pertencem à classe sucessional pioneira, 32,81% secundária inicial, 20,31% secundária tardia e 10,44% clímax. Este resultado, com predomínio de espécies pioneiras e secundárias, mostra que existe uma substituição gradual das espécies, o que possivelmente pode estar relacionado com a retirada de espécies de importância comercial. Flower Survey of Tree Species of Riparian Vegetation in Astorga, Brazil The floristic composition and successional stage of tree species in riparian vegetation of the Ribeirão da Içara (23º09’51.74’’S and 51º39’21.60’’W) in the municipality of Astorga in the northern region of the state of Paraná, Brazil, are analyzed. Climate is Cfa and average altitude is 532 m. The 0.5 ha area under analysis belongs to the Semideciduous Seasonal Forest and consists of a stretch of riparian vegetation formed by native vegetation with dense tree groups, creepers, ground vegetation and reforestation. Surrounding ground is occupied by livestock and the production of sugar cane and orange trees. Botanic material was collected by 3-day monthly expeditions between December 2010 and March 2011. Tree specimens in the reproduction stage were sampled and voucher specimens were incorporated to the collection of the State University of Maringá. Only the vegetal parts of some species were collected and the material was identified by specific bibliography and compared with specimens at the university, following the APG III system. Species were classified with regard to their successional stage by specific bibliography and field observations, although exotic and indeterminate plants were not taken into account in current analysis. Eighty-four species, with 77 genera and 28 families, were registered. Six were identified at genus level, four at family level and one family was undetermined. The Fabaceae had the highest number of species (23), followed by Myrtaceae (6), Malvaceae and Meliaceae (5), Anacardiaceae, Bignoniaceae, Euphorbiaceae and Sapindaceae (4), Rutaceae (3). Further, 69.05% of species belong to these families. Machaerium (3) was the genus with the highest number of species. With regard to the successional stage, 35.93% were species of the pioneer succession class; 32.81% initial secondary class; 20.31% late secondary class and 0.44% climax class. Results, featuring predominantly pioneer and secondary species, show a gradual replacement of species, perhaps related to the removal of commercially relevant species. KEYWORDS: Água do Içara Stream; Successional Stage; Native Vegetation.

Wildfire frequency and intensity are increasing in many parts of the world, often with substantial repercussions for stream ecosystems. The severity, scale, and patterns of wildfire burning can differ between riparian and upland zones due to differences in environmental conditions and vegetation. However, little research has focused on differences in burn patterns in riparian versus upland zones and their implications for stream characteristics. We studied fire patterns and postfire vegetation trajectories in riparian versus upland areas across 26 stream sites in coastal southern California over 12 years, as well as the relationships of burn patterns to stream variables after fire. Upland environments burned more severely and more extensively than did riparian woodlands, and this difference was magnified for perennially flowing streams, along which riparian woodlands burned less severely than those along intermittent streams. Burned vegetation returned to prefire canopy cover and greenness in both riparian and upland areas in about 8 years with regrowth delayed by a prolonged drought. Additionally, we observed differences in spatial burn patterns and vegetation regrowth in upland versus riparian zones, with greater local patchiness in upland settings, likely due to differences between upland and riparian areas in the spatial patterns of hydrologic, topographic, and vegetative drivers of fire and vegetation reestablishment. We then assessed relationships between spatial fire patterns and geomorphological, physical, hydrochemical, and biological conditions at creek sites. We observed relationships that were generally attributable to either the local destruction of riparian woodland along the streams or to changes in the basin-scale movement of water, nutrients, and sediment following fire and postfire floods. Basin-scale burn patterns were associated with increases in sediment deposition, reduction in pool and riffle habitat extents, and changes in particulate organic matter during the first and second years after fires; impacts subsided about a year after the first substantial postfire flows. In contrast, loss of riparian canopy cover was associated with increases in light level, temperature, algal cover and biomass, density of algivorous invertebrates and amphibians, and water conductivity, as well as decreases in particulate organic matter and invertebrate shredders. In contrast to impacts from basin-scale burn patterns, impacts from the local loss of riparian canopy cover persisted for longer periods of time, paralleling riparian woodland reestablishment and growth.

Full-waveform LiDAR (FWF) offers a promising advantage over other technologies to represent the vertical canopy structure of secondary successions in the Amazon region, as the waveform encapsulates the properties of all elements intercepting the emitted beam. In this study, we investigated modifications in the vertical structure of the Amazonian secondary successions across the vegetation gradient from early to advanced stages of vegetation regrowth. The analysis was performed over two distinct climatic regions (Drier and Wetter), designated using the Maximum Cumulative Water Deficit (MCWD). The study area was covered by 309 sample plots distributed along 25 LiDAR transects. The plots were grouped into three successional stages (early—SS1; intermediate—SS2; advanced—SS3). Mature Forest (MF) was used as a reference of comparison. A total of 14 FWF LiDAR metrics from four categories of analysis (Height, Peaks, Understory and Gaussian Decomposition) were extracted using the Waveform LiDAR for Forestry eXtraction (WoLFeX) software (v1.1.1). In addition to examining the variation in these metrics across different successional stages, we calculated their Relative Recovery (RR) with vegetation regrowth, and evaluated their ability to discriminate successional stages using Random Forest (RF). The results showed significant differences in FWF metrics across the successional stages, and within and between sample plots and regions. The Drier region generally exhibited more pronounced differences between successional stages and lower FWF metric values compared to the Wetter region, mainly in the category of height, peaks, and Gaussian decomposition. Furthermore, the Drier region displayed a lower relative recovery of metrics in the early years of succession, compared to the areas of MF, eventually reaching rates akin to those of the Wetter region as succession progressed. Canopy height metrics such as Waveform distance (WD), and Gaussian Decomposition metrics such as Bottom of canopy (BC), Bottom of canopy distance (BCD) and Canopy distance (CD), related to the height of the lower forest stratum, were the most important attributes in discriminating successional stages in both analyzed regions. However, the Drier region exhibited superior discrimination between successional stages, achieving a weighted F1-score of 0.80 compared to 0.73 in the Wetter region. When comparing the metrics from SS in different stages to MF, our findings underscore that secondary forests achieve substantial relative recovery of FWF metrics within the initial 10 years after land abandonment. Regions with potentially slower relative recovery (e.g., Drier regions) may require longer-term planning to ensure success in providing full potential ecosystem services in the Amazon.

QuestionsPlant community resilience largely depends on the secondary succession induced by species re‐colonization from seed banks. Soil seed bank resilience is, however, poorly understood, especially in regularly disturbed habitats like riparian zones. Two questions were asked: (1) what are the changes in species diversity experienced by riparian soil seed banks along successional trajectories, and (2) to what extent do riparian soil seed banks promote vegetation resilience during secondary succession?LocationSoutheast Quebec, Canada.MethodsSoils were collected along five rivers in field edges and riverbanks of post‐agricultural riparian zones with three contrasting successional stages (unplanted, planted with trees 15–17 yr prior to sampling, natural riparian forests), and their seed bank composition determined with the seedling emergence method. Species richness in seed banks was assessed along successional trajectories for distinct ecological groups, using LMM. The compositions of soil seed banks and standing vegetation (from botanical surveys) were compared based on NMDS and indicator species analysis.ResultsSeed bank species richness decreased along successional trajectories. Tree‐planted riparian zones were generally closer to unplanted riparian zones than to natural riparian forests, the latter being more species‐rich for natives, trees, shrubs and zoochores, and species‐poor for exotics, forbs and stress‐tolerators. Likewise, seed bank species composition of unplanted and tree‐planted riparian zones was similar but differed from that of natural riparian forests. Conversely, standing vegetation of tree‐planted riparian zones was intermediate between early and late successional stages, at least at field edges. For the three successional stages, seed bank composition clearly differed from standing vegetation.ConclusionsThe high resilience of riparian plant communities appeared poorly related to the dynamics of their soil seed banks. This species shift between seed banks and standing vegetation during secondary succession is likely due to periodic flooding, leading to the regular turnover of seeds. The resilience of riparian communities might thus be more influenced by spatial dispersal along rivers and across landscapes than by in situ temporal dispersal in soils.

Summary Pervasive increases in biomass and stem density of tropical forests have been recorded in recent decades, potentially having significant implications for carbon storage, biodiversity and ecosystem function. This trend is widely considered to be the result of multidecadal and global scale growth stimulation arising from increases in atmospheric CO2 and temperatures. However, contrasting patterns have been recorded across the tropics, and the role of disturbance in driving biomass and stem dynamics has been highlighted as an alternative explanation. Australian tropical forests have rarely been assessed in pan‐tropical analyses of long‐term dynamics. We have measured recruitment, mortality and growth in 20 permanent plots in tropical forest across north‐eastern Australia since 1971. We assess changes in plot level above‐ground live biomass (AGB) and stem density, and compare our results with those documented over a similar time frame in the neo‐tropics. No significant increase in AGB was found over the 40‐year time period. Above‐ground biomass tended to increase over the first two decades of the monitoring period and decrease in the final two with gain terms (growth and recruitment) lower than loss terms (mortality) by the final decade (2000s). Stem density significantly decreased over the monitoring period with recruitment consistently lower than mortality. There was large variation in individual plots in their pattern of AGB and stem density changes over time which was consistent with the response of each plot to known disturbance events, including cyclones, pathogen outbreaks and drought. Our results are in contrast to those described for neo‐tropical plots which appear to show a widespread pattern of increasing growth and stem density. Synthesis. The trend towards increasing biomass and stem density of tropical forests described for the neo‐tropics does not necessarily reflect patterns in areas of the tropics where large‐scale natural disturbances are relatively frequent. Australian tropical rain forests are either not increasing in productivity in response to global change, or cyclones and other regional and local mechanisms of change mask any evidence of larger‐scale patterns.

Drought diminishes aboveground biomass accumulation rate during secondary succession in a tropical forest on Hainan Island, China