Phytodiversity and Phytosociology of Riparian Trees Along the Elevation Gradient In The Pamba River, Southern Western Ghats, India

BackgroundThe riparian vegetation along the tropical rivers become threatened due to anthropogenic interference. The tree species diversity and distribution along longitudinal and transversal dimensions is variable and has a pivotal role in the river ecology. The data on the riparian tree species diversity and distribution is inevitable for the nature-based restoration efforts. To test the variability along with the river profile, we investigated the tree species diversity and phytosociology in the tropical river Pamba, Southern Western Ghats. Variation of elevation (701–1923m asl Highrange; 71–700m asl Highland; 8–70m asl Midland and <7.0m asl Lowland) as an indicator of topographic species diversity, we laid a total of 54 × 3 quadrats and data were analyzed with Excel and PC-Ord. ResultsShannon-Wiener's diversity is uniform (1.43689–1.84841) and showed homogeneity (Multiple site similarity index = 0.825396825). Humboldtia vahliana, Neolamarckia cadamba, Vateria indica and Syzygium hemisphericum were showed the highest Importance Value Index. DBH size class (15–>331cm) demonstrated a reverse ‘J’ shaped curve. The tree density and total basal area demonstrated an increasing trend from Lowland to Highrange. Validation of Quadrat data with TWINSPAN and Braun-Blanquet table analysis indicated Ochreinauclea missionis-Ficus hispida-Neolamarckia cadamba in Lowland, Mallotus philippensis-Macaranga peltata-Ficus hispida in Midland, Madhuca neriifolia-Hydnocarpus alpina-Humboldtia vahliana in Highland and Symplocos cochinchinensis var. laurina-Syzygium hemisphericum-Cullenia exarillata in Highrange as dominant stand types. Reciprocal Averaging and Hierarchical Clustering revealed unequivocal classification of quadrats following species composition and elevation. Clumped dispersion was noticed in the Midland and Highland. High regeneration of Madhuca neriifolia, Hopea ponga and Humboldtia vahliana were observed along the elevation gradient.ConclusionsThe present research illustrated that the species diversity of riparian forest in the Pamba river is high and comparable with similar tropical rivers. The phytodiversity, phytosociology and regeneration data are significant for developing a conservation strategy of the anthropogenically fragmented Pamba river. Based on the stand type and regeneration data, Madhuca neriifolia, Hopea ponga, Humboldtia vahliana and Ochreinauclea missionis were suitable for buffer design and restoration along with the Pamba river profile.

Equids engineer desert water availability

Megafauna play important roles in the biosphere, yet little is known about how they shape dryland ecosystems. We report on an overlooked form of ecosystem engineering by donkeys and horses. In the deserts of North America, digging of ≤2-meter wells to groundwater by feral equids increased the density of water features, reduced distances between waters, and, at times, provided the only water present. Vertebrate richness and activity were higher at equid wells than at adjacent dry sites, and, by mimicking flood disturbance, equid wells became nurseries for riparian trees. Our results suggest that equids, even those that are introduced or feral, are able to buffer water availability, which may increase resilience to ongoing human-caused aridification.

Comparison of Nesting Features and Breeding Success of Turtle Dove Streptopelia turtur between Orchards and Riparian Habitats

The European turtle dove Streptopelia turtur breeds in both farmlands and woodlands, and it is important to explore the difference in breeding ecology of this threatened game in these two ecosystem types. This study, carried out during four years (2015–2018), compares nesting features of this species and its breeding success between apple orchards and riparian vegetation in Midelt Province, Morocco. The main result revealed that the nest placement, including nesting-tree height and nest height, is similar between orchards and riparian trees. However, the nest dimensions (big and small diameters) were larger in orchards. Correlations were variable among nest placement parameters and dimensions. On the contrary, in four breeding seasons, where 566 nests were monitored (467 in orchards and 99 in riparian sites), the average breeding success was different (57% of chicks in apple farms and 53% in riparian vegetation). Moreover, in apple orchards, clutches’ failure is due to both predation (18.89% of eggs and 10.54% of chicks) and temperature lowering (5.03% of unhatched eggs and 5.49% of dead chicks), while in riparian vegetation, the loss is due to nest desertion (21.33% of clutches) and mostly predation (33.16% of clutches).

Column experiments show that cycling of both nitrogen and phosphorus is altered by dissolved organic carbon in river sediments

&lt;p&gt;Since agriculture and wider development have altered simultaneously runoff, pollution and natural structures in catchments (e.g. wetlands, floodplains, soil drainage, riparian trees) aquatic ecosystems deviate from background concentrations of N and P, but also organic C (OC). Hence mechanistic studies coupling OC, N and P are needed and whilst data coupling OC:N is becoming more available and interpreted this is not yet the case for aquatic OC:P.&amp;#160; Column flow experiments (excluding light) allow preliminary controlled study of microbial biogeochemical processes in benthic sediments exposed to factorial nutrients (here +C, +NP, +CNP using simple dissolved substrates glucose, nitrate, and phosphate).&lt;/p&gt;&lt;p&gt;Based on the stoichiometric theory, we tested the hypothesis that bioavailable DOC will stimulate the heterotrophic uptake of soluble reactive P (SRP) and dissolved inorganic nitrogen in stream sediments. Glucose-C additions increased nutrient uptake, but also NP additions enhanced consumption of native and added OC. The effects of C addition were stronger on N than P uptake, presumably because labile C stimulated both assimilation and denitrification, while adsorption (unaffected by the presence or not of OC) formed a part of P uptake. Internal biogeochemical cycling lessened net nutrient uptake due to N and P recycling into dissolved organically-complexed forms (DOP and DON).&lt;/p&gt;&lt;p&gt;Simple column experiments point to mechanisms whereby availability of organic carbon can stimulate N and P sequestration in the bed of nutrient-polluted streams. This should promote further studies coupling OC with N and, especially P, towards better knowledge and ability to incorporate coupled macronutrient cycles into nutrient models and, potentially, ecosystem management.&lt;/p&gt;

Near stream groundwater table fluctuations impact transpiration rates of riparian plants: a field study with stomatal conductance and dendrometry measurements

&lt;p&gt;Vegetation establishment, growth, and succession in riparian ecosystems are linked to river and groundwater dynamics. This is especially true in Alpine gravel-bed rivers with wide floodplains and a strong river-aquifer exchange. Here we provide data evidence of riparian plant response to short-term groundwater table fluctuations in a braided gravel-bed river (Maggia). We used indirect physiological variables for photosynthesis and transpiration &amp;#8211; stomatal conductance g&lt;sub&gt;s&lt;/sub&gt; and daily variation in stem diameter &amp;#916;D&lt;sub&gt;d&lt;/sub&gt; &amp;#8211; which we measured at six mature riparian trees of the Salicaceae family, one Populus nigra and one Alnus incana specimen at two sites during two growing seasons. The site where g&lt;sub&gt;s&lt;/sub&gt; measurements were conducted showed a greater depth to groundwater with higher variability compared to the site were dendrometers were placed.&lt;/p&gt;&lt;p&gt;We analysed the data by means of two different random forest regression algorithms for the two study sites. One with the transpiration-induced daily tree diameter drop during the growing season 2017 as the dependent variable, and one with the raw g&lt;sub&gt;s&lt;/sub&gt; measurement sequence, obtained on 10 days throughout the growing season 2019, as the dependent variable. In both algorithms the independent variables consisted of meteorological measures (locally measured and at valley scale) and of groundwater and river stages near the individual plants. We also separated the g&lt;sub&gt;s&lt;/sub&gt; measurements into low and high groundwater stage conditions observed during the g&lt;sub&gt;s&lt;/sub&gt; field campaign and applied traditional regression analysis of g&lt;sub&gt;s &lt;/sub&gt;on vapor pressure deficit VPD and global radiation r&lt;sub&gt;g&lt;/sub&gt; for the 2 groundwater stage conditions separately.&lt;/p&gt;&lt;p&gt;The data analyses demonstrate that:&lt;/p&gt;&lt;p&gt;(a) short-term variation of the groundwater table affects riparian vegetation: at the site with deeper groundwater, the water table depth was the best predictor of g&lt;sub&gt;s&lt;/sub&gt; variability, while at the site with shallower groundwater, temperature and vapor pressure deficit were the best predictors of &amp;#916;D&lt;sub&gt;d&lt;/sub&gt;&amp;#160; variability;&lt;/p&gt;&lt;p&gt;(b) instantaneous stomatal conductance is related to vapor pressure deficit (VPD), but conditioned by groundwater levels, with higher stomatal conductance for the same radiative input and VPD when the water table was higher.&lt;/p&gt;&lt;p&gt;(c) local micro-climate measured at tree locations had a stronger predictive power for g&lt;sub&gt;s&lt;/sub&gt; than valley scale climate, suggesting local climate may be an important control on vegetated stands on gravel bars.&lt;/p&gt;&lt;p&gt;Even though the considered plants are located in close proximity to the river and could be considered to be unaffected by water stress, our analysis provides evidence of riparian trees undertaking physiological adjustments to transpiration in response to groundwater stage, depending on their riparian floodplain settings. In the heavily regulated Maggia river this has implications on the minimum flow release by dams, as prolonged periods of low water stage in the river will lead to a decrease in groundwater stage, and subsequently in reduced growth of phreatophytic riparian plants on the floodplain. We argue such plant-scale measurements should be helpful for the optimisation of flow release levels in regulated riparian systems.&lt;/p&gt;

Riverscape-scale airborne TIR assessment of weirs and riparian cover effects on lowland river temperature

&lt;p&gt;&lt;span&gt;The development of Airborne Infrared Thermal sensing (TIR) is an example of how technological advancement&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; and the field that they focus on have fostered one another. The pace at which global change is occurring has fed the demand for better understanding of the thermal behaviour of rivers. In turn, the improvement of remote sensing and data processing techniques has provided researchers and managers with new tools to apprehend such aspects at ever larger scales. Still, recent studies have mostly focussed on rivers showing little human alteration, with a particular interest on groundwater&amp;#8211;surface water interactions. Lowland streams are scarcely considered when it comes to the study of temperature despite their widespread occurrence, their relatively high degree of disturbance and the risks that they face in the light of temperature rising following climate change. Some of these streams already display critically high maximum summer temperatures and their state is likely to worsen in the future, putting all compartments of biota at risk.&lt;br&gt;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The aims of this project were twofold. We first tested the applicability of airborne TIR to study lowland, slow-flowing stream reaches draining agricultural catchments, some of which being particularly narrow and sinuous. We then sought to understand the role of different environmental factors, observed in such context, on driving river temperature during the warmest days of the year. A number of anthropogenic actions such as clear-cutting of riparian trees, stream rectification and the construction of weirs are likely to influence the longitudinal temperature profile of such streams. By choosing rivers with no or limited groundwater inputs, we were able to quantify the relative role of each of the three tested factors and identify stream sections showing critically high maximum temperature over the summer.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;A final step was proposed to upscale these results in order to identify sections of streams showing high risks of reaching critically high summer temperature at a regional network scale. To do so, we used a combination of high resolution land-cover data, digital elevation models and other existing databases (e.g. national inventory of weirs). Identification of the risks in relation with the relative contribution of the different factors is key to process-based river management. This type of output is valuable to river basin managers and decision makers as it can be used to implement targeted restoration initiatives or remediation actions in areas where these have higher chances of being effective.&lt;/span&gt;&lt;/p&gt;