The Roles of Competition and Facilitation in Producing Zonation Along an Experimental Flooding Gradient: A Tale of Two Tails with Ten Freshwater Marsh Plants

Plant zonation is conspicuous in wetlands. The cause is frequently assumed to be the direct physiological effects of physical factors (termed ‘stress’), however many experiments show that competition and facilitation also cause zonation patterns. We conducted a field experiment with freshwater marsh emergent plants to test the causes of zonation along a single stress gradient: flooding duration. We constructed an experimental wetland with ten flooding levels to ensure that the environmental conditions represented the full range of potential flooding levels, from never flooded to continually flooded. We planted ten common marsh plants with varied ecology along the flooding duration gradient. We grew them alone and in mixture for three years and measured changes in the minimum and maximum limits, the mode and the range of distribution, and interaction importance. The mode of distribution did not shift, whether species were grown alone or with neighbours. We found strong effects of competition under low flooding stress. We found no effects from facilitation under high flooding stress. Flooding duration alone controlled the lower limits of plants. The effects of competition were intense enough to eliminate half of the species within three growing seasons. Our experiment showed that competition and physical stresses, but not facilitation, controls the zonation of emergent macrophytes along a flooding duration gradient, at least in freshwater wetlands. Models guiding wetland restoration need to include competition as well as flood duration as causal factors, but not facilitation.

Pengaruh Durasi Penggenangan terhadap Pertumbuhan Vegetatif dan Waktu Berbunga Cabai Merah Keriting Capsicum annum (L.) Varietas Jacko

Cabai merah keriting (C. annum L.) merupakan salah satu komoditas holtikultura yang mempunyai nilai ekonomis tinggi. Musim penghujan di Indonesia menyebabkan lahan pertanian tergenang sehingga mempengaruhi pertumbuhan dan hasil panen cabai. Tujuan penelitian ini untuk mengkaji pengaruh durasi penggenangan terhadap pertumbuhan vegetatif dan waktu berbunga cabai merah keriting (C. annum L.) varietas Jacko. Perlakuan terdiri dari kontrol, penggenangan durasi 1 hari, 3 hari, dan 10 hari. Masing-masing perlakuan menggunakan 5 ulangan. Desain penelitian menggunakan RAL satu faktor yaitu durasi penggenangan. Analisis data setelah perlakuan penggenangan menggunakan uji T taraf signifikansi 5% dan analisis data setelah periode pemulihan 30 hari menggunakan one-way ANOVA yang dilanjutkan ke uji LSD taraf signifikansi 5%. Hasil penelitian menunjukkan terjadi penurunan panjang akar, jumlah daun, ukuran daun, perubahan warna daun, tinggi tanaman, bobot segar akar, dan bobot segar tajuk tanaman setelah perlakuan penggenangan. Diakhir periode pemulihan terjadi peningkatan pertumbuhan vegetatif pada semua perlakuan. Peningkatan durasi penggenangan menurunkan pertumbuhan vegetatif tanaman dan menunda waktu pembentukan tunas bunga. Pertumbuhan akar dan jumlah daun selama periode pemulihan merupakan faktor penting dalam adaptasi tanaman terhadap penggenangan. Capsicum annum L. is a horticultural commodity that has high economic value. The rainy season in Indonesia caused agricultural land to be flooded, which affected chili pepper's growth and yield. The purpose of this study was to examine the effect of flooding duration on vegetative growth and flowering time of C. annum L. var. Jacko. The treatments consisted of control, flooding duration of 1 day, three days, and ten days. Each treatment used five replications. The research design used one-factor RAL, namely the duration of flooding. Data analysis after flooding treatment used the T-test with a significance level of 5%, and data analysis after the recovery period used one-way ANOVA followed by the LSD test with a significance level of 5%. The results showed a decrease in root length, leaf number, leaf size, leaf color change, plant height, root fresh weight, and shoot fresh weight after flooding treatment. At the end of the recovery period, there was an increase in vegetative growth in all treatments. Increasing the duration of flooding reduces the vegetative growth of plants and delays the time of flower bud formation. Root growth and number of leaves during the recovery period are important factors in plant adaptation to flooding.

Colonization of Trees by Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae) Is Influenced by Duration of Flood Stress

The ambrosia beetles Xylosandrus germanus (Blandford) and Xylosandrus crassiusculus (Motschulsky) bore into flood-stressed trees to establish colonies, but the influence of flooding duration on colonization is unknown. This relationship was examined by flooding trees for various time periods and evaluating colonization. In one experiment, X. germanus bored into 20 dogwood (Cornus florida L.) trees during a 3-d flood treatment. Ten trees dissected that season had no offspring present in tunnels; the remaining trees appeared healthy and bloomed the following spring. In another experiment, dogwood trees were flooded for 3 or 7 d and then dissected to assess colonization. The incidence of superficial (short unbranched) and healed (callus tissue in entrance) tunnels was greater in the 3-d trees, while the incidence of tunnels with X. germanus or offspring was greater in the 7-d trees. Four experiments (three in Ohio and one in Virginia) had flood treatments of 0 (nonflooded), 3, 5, 7, and 10 d. Numbers of tunnel entrances, tunnels with X. germanus, and incidence of tunnels with offspring or live foundresses tended to increase as flood duration increased on apple (Malus × domestica Borkh.), dogwood, and redbud (Cercis canadensis L.) in Ohio and redbud in Virginia. Nonflooded trees in Ohio had no boring activity, but ambrosia beetles bored into three nonflooded trees in Virginia. Indicators of unsuccessful colonization, such as superficial tunnels and healing, decreased as flood duration increased. These results suggest tree crops may recover from boring by ambrosia beetles following short-duration flood events, and not necessarily require culling.

Hydroperiod and Salinity Interactions Control Mangrove Root Dynamics in a Karstic Oceanic Island in the Caribbean Sea (San Andres, Colombia)

Mangroves sustain high soil accretion and carbon sequestration rates, yet it is still unknown if they can keep pace with increasing sea level rise (SLR) across a wider range of coastal geomorphic settings. Because accretion rates are controlled by mineral sediment inputs and organic matter accumulation, it is paramount to assess the relative contribution of root productivity to soil formation. Here, we evaluated root biomass, production, and turnover in three mangrove ecotypes to evaluate the role of soil nutrient limitation, stressors, and hydroperiod in controlling root dynamics in San Andres Island (SAI), a karstic oceanic island in the Caribbean Sea. Root production was modulated by soil stress conditions and not by nutrient availability as it has been reported for other karstic environments. The lowest root biomass allocation, and both production and turnover of fine roots were measured under low flooding duration, and low salinity (<20 PSU) and sulfide concentrations (0.84 ± 0.4 mM). Yet, when soil stress conditions increased during high flooding duration (6207 h y–1) and low oxygen conditions (Eh), root tissues reached the highest biomass and production values, including a relative fast turnover of fine roots (<2 mm; 0.75 y–1). Our results follow the predictions of the plant root longevity cost-benefit hypothesis where plants maintain roots only until the efficiency of resource acquisition is maximized by water and nutrient acquisition. Because of the importance of groundwater in controlling porewater salinity and mangrove root productivity in karstic oceanic islands such as SAI, water use and coastal development should be regulated in the short term to avoid the loss of mangrove area and concomitant ecosystem services.

Economic assessment of flood damage

Flooding is a natural hazard. In this regard, the topic of floodprone area management is being actively explored. The study of this issue is a combination of two aspects - environmental and economic. The economic assessment of the consequences of flooding is a single cost model based on an economic criterion. Characteristics such as flooding depth, flooding duration and flooding rate have the greatest influence on the severity of subsequent damage. Standard damage tables are usually based on some damage versus flooding depth. Assuming that the conceptual basis for estimating damages is the same, the expected damages from flooding might be expected to vary between two countries if the flood characteristics are different and the damageability of properties varies between the two countries. The main factors identified by the authors in the course of the study, influencing the amount of damage from flooding, are: flood resistance group; existing physical wear and tear; flooding level. The damage is considered as a percentage of the decrease in the real value of the object. To improve the accuracy of determining flood damage, a multivariate regression analysis tool with the interdependence of influencing factors was selected. It should be noted that the most significant factor is the level (depth) of flooding. The factor of the flood resistance group, which depends on the capital group of the object, seems to be less significant. The least significant factor is the degree of physical deterioration of the object.

The Response of Lateral Flow to Peak River Discharge in a Macrotidal Estuary

The Ou River, a medium-sized river in southeastern China, is selected to study the lateral flow response to rapidly varied river discharge, i.e., peak river discharge (PRD). A three-dimensional model based on the Finite-Volume Community Ocean Model is validated by in situ measurements from 15 June to 16 July 2005. PRD, which considers the extra buoyancy and longitudinal momentum in a short time, rebuilds the stratification and lateral flow. PRD, compared with low-discharge, generally makes stratification stronger and lateral flow weaker. PRD mainly rebuilds lateral flow by changing lateral advection, lateral Coriolis, and lateral-barotropic pressure gradient terms. After PRD, the salinity recovery time is longer than that of the flow because the impact on buoyancy lasts longer than that on longitudinal flow. Longitudinal flow is mostly affected by the momentum transferred during PRD; therefore, the recovery time is close to the flooding duration. However, the lateral flow is affected by the buoyancy, and its recovery time is generally longer than the flooding duration. The lateral flow recovery time depends on transect width, flow velocity and the variation caused by PRD. PRD occurs widely in global small-/medium-sized river estuaries, and the result of this work can be extended to other estuaries.