Production of Perennial Vegetation in an Oasis-desert Transition Zone in NW China - Allometric Estimation, and Assessment of Flooding and Use Effects

Abstract

River oases at the southern fringe of the Taklamakan desert in NW China are surrounded by belts of spontaneous vegetation that protect the oases from sand drift. As an important source of forage, fuel and construction wood, this foreland vegetation is also a component part of the agricultural system of the oases but has been, and still is, destroyed through overuse. Within a broader study that aimed to provide a basis for a sustainable management of this foreland vegetation, biomass and production were studied in four vegetation types dominated either by Alhagi sparsifolia, Calligonum caput-medusae, Populus euphratica, or Tamarix ramosissima that were thought to occur under different regimes of natural flooding in the foreland of Qira (Cele) oasis, Xinjiang, NW China. Shoot biomass components were closely correlated to basal area (Calligonum, Populus, Tamarix) or shrub volume and projection area (Alhagi), enabling non-destructive estimation of stand biomass from shoot diameters or shrub dimensions with sufficient precision using allometric regression equations. Relationships between shoot basal area and biomass of the woody species (Calligonum, Populus and Tamarix) agreed with predictions by a theoretical model of plant vascular systems, suggesting that they are determined by hydraulic and mechanical requirements for shoot architecture. Average aboveground biomass densities of typical stands in late summer were 2.97 Mg/ha in Alhagi, 3.6 Mg/ha in a row plantation and 10.9 Mg/ha in homogenous stands of Calligonum, 22-29 Mg/ha in 22 year-old Populus forests and 1.9-3.1 Mg/ha in Tamarix-dominated vegetation. Annual aboveground production including wood and assimilation organs ranged from 2.11 to 11.3 Mg/ha in plantations of Calligonum, 3.17 to 6.12 Mg/ha in Populus, and 1.55 to 1.74 Mg/ha (based on total ground area) or 3.10 to 7.15 Mg/ha (in homogenous stands) in Tamarix. Production of Alhagi is equal to peak biomass. A thinning treatment simulating use by the local population enhanced productivity of Calligonum, Populus and Tamarix. A complete harvest of Alhagi in late August decreased production in the following year. An artificial flood irrigation treatment did not sufficiently increase soil water content except in the uppermost layer and had no clear beneficial effect on growth of the four species and even a negative effect on Alhagi, which was due to increased competition from annual species. As biomass and production with or without artificial irrigation were much higher than values expected for rain-fed desert vegetation at a mean annual precipitation of 35 mm, it is concluded that the existence of all vegetation types studied is probably based on permanent access to groundwater and that natural floods or precipitation do not contribute to their Plant Ecology (2005) 181:23-43 Ó Springer 2005

Root suckering patterns in Populus euphratica (Euphrates poplar, Salicaceae)

“…As typical for the genus, the trees are dioecious, possessing very short-lived seeds that germinate only on wet ground or if floating in water (personal observation, Schnittler). Due to the hyperarid environment with an annual precipitation below 50 mm, seedlings can establish only on riverbanks or oxbow ponds and must have continuous access to ground water to survive (Gries et al 2005). In the area, such sites are created only by flooding events, where seedlings often arrange in rows marking former flood lines after the retreat of the summer flood (Thevs 2007).…”

Myxomycete diversity in the Tarim basin and eastern Tian-Shan, Xinjiang Prov., China

“…Night temperatures are below zero from mid-October to the end of March; we thus conclude that these few suitable days with dew and moderate night temperatures are the only time window for the active life of myxomycetes. There is one other possible source of water for myxomycetes living on poplar wood and bark: especially in spring, the trees build up high water pressure (Gries et al 2005), and xylem water leaks frequently out of the trees at points where dead lower branches penetrate the later grown wood. Although the xylem soap is salty (Wang et al 1996), often forming significant salt crusts around the leaks by evaporation, it may be a possible water source for myxamoebae.…”

The benefit of synthetically generated RapidEye and Landsat 8 data fusion time series for riparian forest disturbance monitoring

“…reduced water availability, occur (Li et al, 2013a). As a consequence, there are fluctuations in the above-ground net primary productivity, which have been accurately measured by means of litter mass (Niu et al, 2015), diameter (Westermann et al, 2008;Li et al, 2006;Qisen et al, 2010;Yu et al, 2012) or basal area (Gries et al, 2003), and volume increments (Ni et al, 2001;Gries et al, 2005). However, these field methods may not be suitable for long term and large scale forest monitoring due to low sample coverage and infrequent survey opportunities.…”