Standing Crop Values Research Articles

Effectiveness of alien brown troutSalmo truttaL. removal activities for the native trout conservation in Mediterranean streams

In Italian freshwaters the introgressive hybridization with the alien Atlantic trout represents the principal threat to the native endangered Mediterranean trout. The aim of the research was to test the effectiveness of alien trout removal activities carried out by electrofishing in four streams in Central Italy. The four sites were chosen on the basis of the severe genetic introgression level of the trout populations. The removal activities were carried out from December 2014 to July 2017, for a total of 10 eradication campaigns in each site. During each field activity, five environmental parameters (flow rate, conductivity, average depth, average width, accessibility) were collected, since they could influence both the effectiveness of the electrofishing and the biological characteristics of the fish populations. A total of over 22,000 alien trout accounting for a biomass of over 700 kg were removed from the removal sites. For each site, a progressive drastic decrease over time in density and standing crop values was observed. Removal rates ranged from 94.22% to 100.00% for density, and from 96.57% to 100.00% for standing crop. The correlation analysis showed an inverse significant relationship between catchability and populations abundance, confirming that low density populations are more suitable to removal efforts. The progressive removal of specimens improved the catchability over time, indicating that even the largest populations could be eradicated, providing the necessary number of steps in a fishing season. The improved body condition and the greater growth rates observed during the eradication period, in low abundance conditions, seemed to confirm the key role that intraspecific competition and density-dependent phenomena play in the Apennine trout population dynamics. The results obtained in the present research provided evidence that electrofishing removal could be an effective management tool for the Mediterranean trout conservation, especially in watercourses of modest dimensions in terms of flow rates, width and depth.

Строение древостоев среднетаежных сосняков лишайниковых на европейском северо-востоке России

В статье представлены результаты, характеризующие строение древостоев среднетаежных сосняков лишайниковых на европейском северо-востоке России. Проведен статистический анализрядов распределения деревьев сосны по диаметру и высоте ствола. Установлено, что коэффициентвариации высоты в древостоях сосняков изменяется от 9 до 34 %, а асимметрия близка к нулевомузначению, что свидетельствует о почти нормальном распределении деревьев. Коэффициент вариации диаметра колеблется от 27 до 67 %, что говорит о растянутости распределения особей сосны в насаждениях по этому показателю. Показан вклад деревьев разных ступеней толщины в накопление запасов древесины древостоем. В средневозрастных и приспевающих насаждениях 41–55 % от числа деревьев и 32–41 % от объема древесины приходится на ступень толщины, соответствующую среднему диаметру дерева в древостое, и на две соседние ступени толщины. В спелых и перестойных сосняках эти величины составили 6–48 и 4–46 % соответственно, что отражает наличие нескольких поколений в древостоях на этих стадиях развития. Выявлена статистически достоверная взаимосвязь (положительная и отрицательная) между средним диаметром дерева и числом крупно- и тонкомерных деревьев, тогда как корреляции между средним диаметром дерева и запасом древесины в крупномерных и деревьях средних ступеней толщины не обнаружено. Выведено обобщенное регрессионное уравнение взаимосвязи высоты дерева от его диаметра, которое можно использовать для определения высоты деревьев среднетаежных сосняков лишайниковых на европейском северо-востоке России.

Characterizing and evaluating successional pathways of fen degradation and restoration

The definition of restoration targets and the evaluation of restoration success require a comprehensive, ecosystem-based analysis of all successional pathways, which proceed along gradients of land use intensification and continue after implementation of restoration measures. In the presented study, such analysis was applied to fen ecosystems. Study areas were river valleys and eutrophic lakes in The Netherlands and in Schleswig-Holstein, the northernmost state of Germany. At these sites high fen degradation has taken place and restoration strategies such as “recovery of peat-forming systems” and “development of species-rich fen grasslands” have recently been pursued. Based on an indirect successional analysis, we derived characteristic shifts of abiotic (hydrodynamics, soil parameter) and biotic (species composition, phytomass production) ecosystem traits relative to increasing land use intensity. Species richness and nature conservation value (NCV) initially increased and afterwards decreased during the process of land use intensification. This floristic change was accompanied by an initial decrease and subsequent increase in system productivity. Indicators for P-availability showed the same trend and there was evidence that nutrient limitation changed initially from N- (tall sedge reeds) to P- or P/N (co)-limitation (small sedge reeds) and afterwards again to N-limitation (wet and mesic grasslands). The successional analysis documented the abiotic requirements of vegetation types and their characteristic species, and thus, allowed for the use of these ecosystem traits as indicators to evaluate the success of specific restoration targets. For example, the decrease of Scheuchzerio-Caricetea species could be related more directly to reduced light availability than to an increase of the groundwater tables. Furthermore, we calculated threshold values of these traits for the occurrence of target species. For instance, a sustainable establishment of light-demanding mesotrophic species can only be expected if the standing crop value is less than 400gm−2. In a further step, we estimated the restoration success in selected study areas by applying the findings of the successional analysis. Results showed that rewetting measures have to be carried out with caution if both restoration strategies are aspired in one specific area. Moreover, restoration success of both strategies is limited in initially highly degraded areas. Sources for target species are often missing and abiotic conditions such as nutrient levels and flooding periods are often inappropriate. Consequently, expectations for restoration success should be adapted to the realistic development potential of the individual system and a cost–benefit analysis has to be carried out to avoid unnecessary management costs.

Ludwigia grandiflora and L. peploides Onagraceae – Water primroses

<i>Ludwigia grandiflora</i> and <i>L. peploides</i> Onagraceae – Water primroses

Macroalgal standing crop estimate &amp;ndash; fast method using ultralight aircraft

A simple and low-cost method for monitoring macroalgal standing crops in shallow water consists of flying over and photographing the areas in an ultralight aircraft to determine the surface area of macroalgal mats. In the proposed method, photos are analysed by AUTOCAD software and mat density is then estimated in the field. Using mat density and bottom surface covered by mats, a rough estimate of the Standing Crop (SC) can be computed. Total of all estimated SCs in a given period is the Total Macroalgal Standing Crop (TMSC). The method was developed to support macroalgal harvesting operations in Orbetello lagoon. SC and TMSC values were needed to decide places and times of macroalgal harvesting and to estimate the boat work required. Applied to ecological studies, this method called Fast Valuation Method (FVM) and is compared with a more time-consuming Accurate Valuation Method (AVM), which calls for extensive sampling and statistical processing. The t-test did not show significant differences between the results provided by the two methods. The results were more similar in winter, when macroalgal growth is slow and wind concentrates the mats. The results may diverge in summer when floating macroalgae are more evenly distributed, with FVM tending to underestimate TMSC. FVM is in any case of potential interest for monitoring studies.

Relationship between light availability and species richness during fen grassland succession

The complex relation between standing crop and species richness in herbaceous plant communities is still one of the most intensively discussed topics in vegetation ecology. In this study, we focus on the extent to which light availability is able to explain this relationship in fen grasslands. We analyse changes of light availability (measured as relative irradiance, RI), standing crop and species richness during fen grassland succession. Our study include communities representing differences in drainage intensity and nutrient status (‘land use intensification sere’) and successional stages developing after abandonment (‘abandonment seres’). Both in the land use intensification sere and in the abandonment seres, we recorded an increase in standing crop reaching highest values of approx. 800 g m‐2. RI, species richness and number of small‐growing species declined in the successional seres. RI was highest in stands of low‐productive communities, where light compensation points (5% RI) were already attained at soil surface and light saturation points (30% RI) at soil surface or at 15 cm height. Horizontal heterogeneity of RI at soil surface and at 30 cm height decreased in the abandonment seres, but not at 30 cm height in the land use intensification sere. Furthermore, we detected a signiñcant negative relation between standing crop and RI. Species richness declined with increasing standing crop and thus consequently also with decreasing RI. This result points out that light competition might be of importance for this pattern. The number of small‐growing species decreased exponentially with an increase in standing crop (and decrease in RI). It can be assumed that low light availability negatively affects small‐growing species at standing crop values higher than 400–500 g m2. As the maintenance of small‐growing species and the improvement of habitat conditions for their establishment are important aims of nature conservation in fen grasslands, management strategies should be orientated at maintaining standing crops that are not higher than these values.

Aquaculture risk management and marine mammal interactions in the Pacific Northwest

This paper reviews current aquatic farm production in the USA and estimates an annual financial exposure of US$350 million in the marine and coastal environments made up of sales, standing crop value and capital investment. In addition, nationwide aquatic farming creates almost 200,000 jobs and, with secondary and downstream activities combined, contributes about US$5600 million to the GNP. The paper then reviews the increasing risk that elements of the coastal aquaculture industry in the Pacific Northwest face from interactions with populations of marine mammals. These are particularly California sea lions and seals, which have greatly increased in the last 20 years from California to British Columbia. Specifically: (i) shellfish from traditional beds have been contaminated by fecal coliforms from seals and made unfit for human consumption, and have been experiencing increasing losses to river otters and sea otters; (ii) culture-based salmon fisheries, including endangered salmon stocks, have been exposed to heavy predation by sea lions and seals, resulting in both direct losses and reduced market value of wounded survivors; (iii) net-pen farms have been exposed to the same heavy losses from predatory sea lions and seals attacking fish in the pens, together with added financial burdens for anti-predator nets, increased maintenance and labor; and (iv) workers in aquaculture and fisheries, and other waterborne industries, have been observing less fear of humans by sea lions and seals, and more direct damage to servicing facilities. The four issues are discussed both technically and economically, and a number of solutions proposed for managing and controlling these increasing risks.

Spatial dynamics of coccolithophore communities during an upwelling event in the Southern Benguela system

The spatial dynamics of coccolithophore communities were investigated in the top 100 m of a longitudinal transect off Hondeklip Bay, Southern Benguela region, during a period of active upwelling in late June 1993. This transect crossed five hydrological domains that were identified from the vertical sections of temperature and salinity, namely the upwelling zone, the upwelling front, the intermediate domain, the offshore divergence, and the oceanic region. Total coccolithophore standing crops ranged from less than 10 × 10 3 cells 1 −1 to a maximum of 278 × 103 cells 1-1. Highest values were recorded in the top 25 m in the upwelling zone and at the offshore edge of the upwelling front. Fifty different taxa were identified with Emiliania huxleyi and Syracosphaera epigrosa being the dominant forms in the standing stock. The offshore divergence and upwelling front effectively isolated assemblages with distinct species compositions and diversity trends. The most successful assemblage in terms of both species diversity and standing crop was found in the intermediate domain where oceanic and upwelled water mix. Equally important was the control of the water-masses motion on the vertical distribution of coccolithophore communities. Shallow-dwelling communities thrived in the inshore upwelling and offshore divergence areas, whereas deep-dwelling communities were found in the intermediate domain, where surface waters downwell. No clear relationship was found between the concentrations in major nutrients, and the species diversity and total standing crop values. S. epigrosa was the only recorded species whose absolute abundance showed a positive relationship with the nitrate and phosphate surface-water concentrations.

STANDING CROP OF THE COASTAL MACROLICHEN MASTODIA TESSELATA, AND ITS RELATIONSHIP TO NUTRIENT CONCENTRATIONS, ON PETERMANN ISLAND, ANTARCTICA

The standing crop of the epilithic foliose lichen Mastodia tesselataand some other species, the nutrient status (chloride, phosphate, nitrate and ammonium) of the substratum, slope and moisture availability were studied in 29 sample plots on Petermann Island (65°10′S, 66°30′W), Antarctica. The observed standing crop values for Mastodiaranged from 49 to 614 g m −2, with an average of 310 g m −2(17 sample plots), and were 542 g m −2for Rinodina petermannii(one sample plot) and 314 g m −2for the alga Prasiola crispain two meltwater pools. A regression equation with log-transformed ammonium and phosphate concentrations as predictors explained 75% of the observed variance in Mastodiastanding crop. No significant influence of chloride or nitrate concentration on the Mastodiastanding crop was detected, indicating that Mastodiais a salt-tolerant lichen species, but is not an obligate halophyte. The maximal standing crop of Mastodiaon Petermann Island proved to be lower than maximal values found for fruticose macrolichen vegetation in maritime and continental Antarctic. The Mastodiastanding crop on Petermann Island was similar to the standing crop of this species on subantarctic Marion Island.

HIGH‐RESOLUTION AIRBORNE REMOTE SENSING OF BLOOM‐FORMING PHYTOPLANKTON1

ABSTRACTRemote sensing of highly turbid finfish aquaculture impoundments using the Calibrated Airborne Multispectral Scanner (CAMS) mounted on a Lear jet flown at 900 m was conducted in central Mississippi on 16 May 1990. Concurrent in situ data consisted of phytoplankton pigment concentrations and standing crop, water color, turbidity, and surface‐water temperature. Surface and near‐surface assemblages of cyanophytes and chlorophytes varied dramatically among impoundments; total chlorophyll concentrations and standing crop values ranged from 8 to 483 mg·m−3 and 8.0 × 102 to 2.2 × 106 cells‐mL−1, respectively. Regression models fit to CAMS data provided reliable estimates for and produced accurate digital cartographs of total chlorophyll and carotenoid concentrations, phytoplankton standing crop, and turbidity. Although a model to effectively estimate in situ c‐phycocyanin concentrations was not identified, the lack of a suitable model may have resulted from variability of pigment extraction during quantification rather than failure of remotely sensed imagery to detect c‐phycocyanin. Models derived from imagery of impoundments directly beneath the aircraft sufficiently described in situ parameters in imagery of adjacent series of impoundments not directly below the aircraft. High‐resolution airborne remote sensing provides a means for monitoring local phytoplankton dynamics in temporal and spatial scales analogous to biotic and abiotic processes affecting such dynamics and necessary for applications to ecological research and fisheries or aquacultural management.

Mowing and Fertilization Effect on Productivity and Spectral Reflectance in Bromus Inermis Plots

Experiments were conducted to examine the potential role of grazing on ecosystem-level parameters as part of the NASA-sponsored First Isabela (International Satellite Land Surface Climatology Programmed) Field Experiment (FIFE) conducted at Konza Prairie Research Natural Area in 1987. Here we report results of one experiment conducted in a field consisting primarily of Bromus inermis, a cool season C3 grass. The experiment involved four simulated grazing components (unmowed control, 20-, 10-, and 5-cm mowing heights) and fertilization (untreated control and ammonium nitrate application). The plots were mowed to ground level and raked in April, following which they were mowed seven times during the growing season from May to October. Biomass production, N production, and spectral reflectance data were collected with a hand-held radiometer throughout the growing season, with standing crop estimates taken at two periods (7 August [day 219] and 27 October [day 300]) to correlate with the remote sensing information base. Standing crop values of mowed plots were as much as 67-70% lower than controls, but they produced significantly larger amounts of both biomass and total N. Maximum seasonlong production values in the mowed plots were °43% above controls, with major differences developing as a result of fertilization. Fertilized plots produced 67% more foliage than unfertilized plots. Our data show over-compensatory growth as a result of the simulated grazing treatments. Indexes (NDVI [normalized difference vegetation index] and greenness) derived from the reflectance data were poorly correlated with biomass. The correlation of NDVI with N content of the canopy foliage was somewhat stronger, particularly if stratified by mowing class. NDVI was a better predictor of vegetation status than the greenness indexes, but in plots stimulating heavily grazed areas where leafy vegetation was sparse and soil became more visible from above the canopy its utility decreased significantly.

Competition, survivorship and growth in macrophyte communities

SUMMARY. 1. Transplant experiments tested the proposition that the intensity of competition within macrophyte communities varies with standing crop in a freshwater marsh in Ontario, Canada.2. Transplants of three species (Carex lasiocarpa, Juncus brachycephalus, Scripus validus) were grown at sixty‐six locations chosen to represent a range of standing crop values. At each location, transplants were grown in plots with all neighbours removed and in adjacent plots with all neighbours present.3. The effect of neighbours on transplant growth did not vary with standing crop, soil, or water depth, with the exception of one species which was most suppressed by neighbours in shallow water. In contrast, the effect of neighbours on the survivorship of transplants was greatest on organic soils supporting high values of standing crop in shallow water, and least on mineral soils supporting low values of standing crop in deeper water.4. The results indicated that establishment and survivorship of vegetative propagules was most likely to be affected by neighbours in shallow water, but that the growth of established plants was not influenced by neighbours anywhere. Growth results corroborate earlier findings that competition has little effect on aquatic macrophytes.

Species richness – standing crop relationships along four lakeshore gradients: constraints on the general model

The applicability of a model describing the relationship between species richness and standing crop and litter was tested in each of four lakeshore habitats within Wilsons Lake, Nova Scotia. The shapes of the curves describing the species richness – standing crop relationships in the four habitats were significantly different. Standing crop and litter values were positively correlated with measured indices of soil fertility (loss on ignition and silt and clay content) and negatively correlated with disturbance as determined by the location of the shrub zone and overwinter damage to wooden pegs. Sites with high standing crop had a lower proportion of biomass composed of evergreen and isoetid species than the proportion in sites where standing crop was low. The among habitat variation observed in this study, and the variation in published values of standing crop values yielding maximum species richness, limit the accuracy of predictions from this model. Steps for refinement are suggested.

Radon profiles in the Indonesian archipelago

A series of near-bottom excess radon profiles was measured in the Indonesian archipelago during the Snellius-II Expedition. The results show considerable variations in structure, 222Rn concentrations and integrated excess 222Rn inventory in the water column. Near-bottom vertical eddy diffusion coefficients vary from 46.4 to 63.6 cm 2·s −1 in the basins; they are in general much higher on slopes and sills. The standing crop (the integrated amount of excess 222Rn) ranges from 0.9 to 49.6 dpm·cm −2. 226Radium supported 222Rn concentrations range from 9 to 3888·10 −2 dpm·kg −1 Compared to mid-ocean basins the vertical mixing processes of near-bottom water masses in the Indonesian archipelago is fast, especially in the water layer from 50 to 200 m above the bottom, with diffusion coefficients in the order of 10 times higher than in the Pacific Ocean. With the exception of two stations standing crop values were comparable with those found in the Pacific Ocean but higher than those from the Atlantic Ocean. 210Pb analyses show high sedimentation rates, up to 75 cm·10 −3·a −1. This does not agree with related standing crops. One explanation can be that erosion plays an important role on the sills and slopes.

Radon fluxes measured with the MANOP bottom lander

At five Pacific Ocean sites, radon fluxes were determined from water samples collected by the MANOP Lander, from measurements of 222Rn and 226Ra concentrations in Lander-collected box core sediments, and from measurements of excess radon in the water column. At MANOP sites H and M, fluxes (all in atoms m −2 s −1) determined with Lander water samples (2200 and 1540 ± 480) agree within the measurement uncertainty with water column standing crop measurements (2220 ± 450, 2040 ± 470). At MANOP site C, the diffusive flux calculated from measurements of 226Ra in box core sediments (550 ± 20), the integrated deficiency of 222Rn in the sediments (720 ± 90), and the water column standing crop (500 ± 160) are in agreement, but all are about twice as large as the single Lander water measurement of the radon flux (330). At MANOP site S radon fluxes from measurements of Lander water (3000 ± 260) are in agreement with the predicted diffusive flux from site S sediments (2880), and both fluxes are close to the lower end of the range of water column standing crop measurements (3000–5170). In San Clemente Basin, California, the Lander water flux measurements at four different sites vary by a factor of 3 due to variability in the sediment radium distribution, but the average (1030 ± 190) is close to the water column standing crop value (780 ± 230). Because there is excellent agreement between the fluxes measured with Lander water samples and the predicted diffusive fluxes in most cases, diffusion must be the primary process controlling benthic exchange of radon at the sites studied. The agreement between the Lander water flux estimates and the water column standing crop estimates indicates that the MANOP Lander functions as an accurate benthic flux chamber in water depths ranging from 1900 to 4900 m. In San Clemente Basin, surficial sediments are enriched in manganese and radium, due to manganese cycling near the sediment-water interface. Molecular diffusion of radon from this radium-rich surficial layer is sufficient to obscure any effect of macrofaunal irrigation on the standing crop of radon in this basin.

Plant Growth and Productivity along Complex Gradients in a Pacific Northwest Brackish Intertidal Marsh

Environmental characteristics were measured and recorded in the Skagit Marsh, a brackish intertidal marsh on Puget Sound, Washington. Four transects were placed perpendicular to a known gradient of increasing salinity which began with fresh water at the bank of one of the outlets of the Skagit River and reached a surface water salinity of 22‰ at a point alongshore 5 km north of the outlet. The environmental characteristics which were measured varied along gradients (soil texture, organic carbon in fines, soil column temperature, free soil water salinity) or had a patchy distribution (soil redox potential, soil macro-organic matter). Growth and production vary across the marsh. The maximum aboveground standing crop (1,742 g m−2 dry weight) was measured at a site with 0–4‰ free soil water salinity, dominated by the sedgeCarex lyngbyei. In more saline areas (8–12‰), the bulrushScirpus americanus was dominant and standing crop values dropped to a third of the maximum. Species performance varied in a complex manner as did the environment.C. lyngbyei had diminished growth and decreased standing crop in areas where salinity was higher.S. americanus was equally productive in low elevation, high salinity sites and in high elevation, low salinity sites. An increase in shoot density for dominant species occurred in saline areas as individual shoot weights and leaf areas decreased. Because species responded differently, environmental variation was magnified in the population and community responses of the marsh vegetation.

Distribution and Standing Crop of Living and Dead Roots in Three Wetland Carex Species

BERNARD, J. M. AND K. FIALA (Dept. Biol., Ithaca College, Ithaca, NY 14850 and Inst. Bot., Czechoslovak Acad. Sci. Brno, Czech.). Distribution and standing crop of living and dead roots in three wetland Carex species. Bull. Torrey Bot. Club 113:1-5. 1986.-Living and dead root standing crop of Carex rostrata Stokes, C. trichocarpa Muhl., and C. lasiocarpa Ehrh. was estimated and its distribution in the soil profile determined. The percentage of living roots in total root standing crop was relatively low, 1 1.9-18.8%, while belowground standing crop values were high; 2237 g/m2 in Carex trichocarpa, 4464 g/m2 in C. rostrata, and 4948 g/m2 in C. lasiocarpa. Living roots contributed less than 600 g/m2 in the three species. Carex rostrata had almost 70% of living roots from 0-10 cm, C. trichocarpa 63.9% from 5-15 cm, and C. lasiocarpa 92% in the 0-5 cm layer of the soil profile.

Recent Foraminifera from the North Sea (Forties and Ekofisk areas) and the continental shelf west of Scotland

Abstract. The regions studied are all of mid continental shelf depth (70–145 m) and have bottom waters of normal marine salinity. The North Sea has lower bottom water temperatures than those to the west of Scotland. However, the major difference between the two regions is one of tidal and/or wave energy: the northern North Sea is a low energy environment of muddy sand deposition whereas the sampled part of the continental shelf west and north of Scotland is a moderate to high energy environment of medium to coarse biogenic carbonate sedimentation.The physical differences between the two main areas are reflected in the living and dead foraminiferal assemblages. The northern North Sea is a region of free-living species whereas the continental shelf west of Scotland has immobile and mobile attached species living on firm substrates. The northern North Sea is very fertile and has high standing crop values.The dead assemblages are small in size and very abundant. To the west of Scotland the sea is less fertile, standing crop values are low, the dead assemblages are moderate to large in size and reasonably abundant due to the slow rate of dilution by sediment.

Oxygen and carbon isotopic composition of living planktonic foraminifera from the northeast Pacific Ocean

Stable isotopic analyses were performed on the tests of five species of living planktonic foraminifera which are important in paleoclimatic studies of high-latitude Late Cenozoic sequences. All but two of the samples used are from horizontal plankton tows of known depths between 0–500 m in the northeastern Pacific Ocean (50°N, 145°W). In situ hydrographic, seawater stable isotopic, and quantitative species-distribution data are used in the interpretation of the results. All of the species show depletions in both 18O and 13C in their calcite tests relative to calcite precipitated in isotopic equilibrium with ambient seawater. Estimates of the departures from isotopic equilibrium range from −0.35‰ in Globigerinita glutinata to −2.24‰ in Neogloboquadrina pachyderma (sinistral) with respect to δ 18O, and from −0.5‰ in Orbulina universa to −4.34‰ <n Globigerina bulloides with respect to δ 13C. The δ 18O data suggest that primary test growth for individual species is not restricted to the depth interval where highest total standing crop values occur. Oxygen and carbon isotopic depth rankings for G. bulloides, N. pachyderma and G. glutinata reflect the relative magnitude of the vital effect in these species and not necessarily different depth habitats. The vital effect for δ 18O in these species remains approximately constant with changing temperature/water depth, while the vital effect for δ 13C strongly decreases with increasing depth. Temperature also does not appear to directly affect the coiling ratios of G. bulloides, but a significant negative correlation exists between the percentage of sinistrally coiled G. glutinata and water temperature.

The phenology and growth of water hyacinth ( Eichhornia crassipes (Mart.) Solms) in a eutrophic north-central Florida lake

A population of water hyacinth in north-central Florida was monitored at weekly intervals to determine annual changes in maximum leaf length, lamina and petiole area, lamina area index, number of leaves per plant, plant density, leaf density, biomass distribution, root/shoot ratio and standing crop. Three distinct phases were apparent in the annual re-development of the population. The first was characterized by a reapportioning of the biomass distribution following winter freeze damage to the emergent shoot. The second phase began in early spring and was characterized by increased branching and ramet production, high leaf densities, and high foliar height diversity. The third phase began in late spring and was characterized by increases in leaf size, a stable number of leaves per rosette, a loss of the smaller plants resulting in a lower absolute density, and maximal standing crop values. The lamina area index began to increase during the first phase and continued through the third phase. All three phases are interpreted as mechanisms enabling an increase in the leaf area index (increases in leaves per plant, leaf density and leaf size, respectively) which closely paralleled solar radiation intensities. The maximum rate of biomass accumulation was estimated to be ca. 20 g m −2 day −1, and the maximum relative growth rate was ca. 1.50% day −1. Peak efficiency of tissue storage relative to solar input was estimated to be ca. 1.4%. The period of maximum growth occurred in April before the attainment of the peak standing crop (ca. 2.3–2.5 kg m −2). Growth appeared to be a function of an interaction between the lamina area ratio (lamina area index: standing crop) and solar radiation. Plant density was inversely related to plant size and appeared to be a function of the degree of intraspecific competition for light and space. Peak densities as high as 180 plants m −2 occurred in April but this was reduced to stable values of 70–80 during the summer. Root, stem and leaf ratios were very constant during the frost-free period of the year. Following the attainment of the ceiling yield in June a gradual decline began during which standing crop values appeared to track climatic conditions in a ‘steady-state’ situation. As the standing crop declined, so did the average height of the canopy and the population responded through an increase in plant density. We suggest that the response of water hyacinth to various environmental conditions through changes in plant proportions, leaf size and form, sexual or vegetative reproduction, etc. is the result of its adaptation to tropical riverine systems in which the plant is likely to encounter frequent expansions or contractions of the available habitat with alternating wet and dry seasons. These adaptations permit the plant to persist upstream following flooding, rapidly recolonize areas after being washed out, and to establish new populations if swept downstream. This ability to rapidly re-establish populations following extreme perturbations makes permanent control of this weed difficult in its adventive range.