Biomass equations for Brazilian semiarid caatinga plants Equações para estimar a biomassa de plantas da caatinga do semi-árido brasileiro

Allometric equations to estimate total aboveground alive biomass (B) or crown projection area (C) of ten caatinga species based on plant height (H) and/or stem diameter at ground level (DGL) or at breast height (DBH) were developed. Thirty plants of each species, covering the common range of stem diameters (3 to 50 cm), were measured (C, H, DGL, DBH), cut at the base, separated into parts, weighted and subsampled to determine dry biomass. Wood density (p) of the stem and the largest branches was determined. B, C, H and p ranged from 1 to 500 kg, 0.2 to 112 m², 1.3 to 11.8 m, and 0.45 to 1.03 g cm-3. Biomass of all 10 species, separately or together (excluding one cactus species), could be estimated with high coefficients of determination (R²) using the power equation (B = aDGLb) and DGL, DBH, H or combinations of diameter, height and density. Improvement by multiplying H and/or p to DGL or DBH was small. The mixed-species equation based only on DBH (valid up to 30 cm) had a = 0.173 and b = 2.295, similar to averages of these parameters found in the literature but slightly lower than most of those for humid tropical vegetation. Crown area was significantly related to diameter, height and biomass.<br>Equações alométricas foram desenvolvidas para estimar a biomassa aérea viva (B) e a área de projeção da copa (C) de dez espécies da caatinga, com base na altura da planta (H) e/ou do diâmetro do caule ao nível do solo (DNS) ou à altura do peito (DAP). Trinta plantas de cada espécie, cobrindo a faixa usual de diâmetros (3 a 50 cm), foram medidas (C, H, DNS, DAP), cortadas na base, separadas em partes, pesadas e subamostradas para determinação da biomassa seca. A densidade (p) da madeira dos caules e galhos maiores foi determinada. B, C, H e p variaram de 1 a 500 kg, 0,2 a 112 m², 1,3 a 11,8 m e 0,45 a 1,03 g cm-3. A biomassa das 10 espécies, separadamente ou em conjunto (exceto pela espécie de Cactaceae), foi estimada com alto coeficiente de determinação (R²), usando a equação de potência (B = aDNSb) e DNS, DAP ou combinações de diâmetro, altura e densidade. A melhora com a multiplicação de DNS ou DAP por H e/ou p foi pequena. A equação de DAP (válida até 30 cm) para o conjunto das nove espécies teve a = 0,173 e b = 2,295, semelhantes aos valores das médias das equações encontradas na literatura, mas um pouco abaixo dos referidos para vegetação tropical úmida. A projeção das copas foi significativamente relacionada com diâmetros do caule, alturas e biomassas

Shallow Flows Over a Permeable Medium: The Hydrodynamics of Submerged Aquatic Canopies

Aquatic flow over a submerged vegetation canopy is a ubiquitous example of flow adjacent to a permeable medium. Aquatic canopy flows, however, have two important distinguishing features. Firstly, submerged vegetation typically grows in shallow regions. Consequently, the roughness sublayer, the region where the drag length scale of the canopy is dynamically important, can often encompass the entire flow depth. In such shallow flows, vortices generated by the inflectional velocity profile are the dominant mixing mechanism. Vertical transport across the canopy–water interface occurs over a narrow frequency range centered around f v (the frequency of vortex passage), with the vortices responsible for more than three-quarters of the interfacial flux. Secondly, submerged canopies are typically flexible, coupling the motion of the fluid and canopy. Importantly, flexible canopies can exhibit a coherent waving (the monami) in response to vortex passage. This waving reduces canopy drag, allowing greater in-canopy velocities and turbulent stresses. As a result, the waving of an experimental canopy reduces the canopy residence time by a factor of four. Finally, the length required for the set-up and full development of mixing-layer-type canopy flow is investigated. This distance, which scales upon the drag length scale, can be of the same order as the length of the canopy. In several flows adjacent to permeable media (such as urban canopies and reef systems), patchiness of the medium is common such that the fully developed condition may not be representative of the flow as a whole