The impact of broadleaved woodland on water resources in lowland UK: III. The results from Black Wood and Bridgets Farm compared with those from other woodland and grassland sites

Abstract

In the United Kingdom the planting of broadleaved woodland has led to concerns about the impact on water resources. Comparative studies, typically using soil water measurements, have been established to compare water use of broadleaved woodland and grassland. The diversity of outcomes from these studies makes it difficult to make any consistent prediction of the hydrological impact of afforestation. Most studies have shown greater drying of soils under broadleaved woodland than under grass. However, two studies in a beech wood growing on shallow soils above chalk at Black Wood, Micheldever, Hampshire showed little overall difference between broadleaved woodland and grass, either in soil water abstraction or in evaporation. Two factors are thought to contribute to the different results from Black Wood. It is known that evaporation can be considerably enhanced at the edges of woodlands or in small areas of woodlands. The studies at Black Wood were made well within a large area of fairly uniform woodland. Other studies in which a difference occurred in soil drying between broadleaved woodland and grass used measurements made in small areas of woodlands or at woodland edges. Another important difference between comparison of woodland at Black Wood and grassland growing nearby, also on shallow soils above Chalk, compared to other broadleaved woodland/grass comparisons, growing on other geologies, is the influence of the Chalk. Although vegetation such as grass (and woodland) does not populate the chalk profusely with roots, water can be removed from the Chalk by the roots which proliferate at the soil/chalk interface and which can generate upward water movement within the Chalk. Published work showed that only in a very dry summer did the evaporation from grass growing on shallow soils above chalk fall below potential. In broadleaved woodland/grass comparisons on non-chalky soils it is possible that moisture deficits in the soil below the grass may reach critical levels and reduce evaporation below that of the woodland with which it is being compared.

The impact of broadleaved woodland on water resources in lowland UK: II. Evaporation estimates from sensible heat flux measurements over beech woodland and grass on chalk sites in Hampshire

“…The Solent R2 sonic anemometer used in these studies is calibrated such that significant errors can arise if fluxes associated with wind deviating from the horizontal by more than 30º are encountered (Gash and Dolman, 2003;van der Molen et al, 2004). The error is likely to be larger in the measurement of fluxes over rough vegetation with high turbulence (i.e.…”

“…Some studies have demonstrated a substantially greater water use by woodland (Calder et al,1997(Calder et al, , 2000 whilst others have shown little difference (Harding et al, 1992;Roberts and Rosier 2005b).…”

Higher tree transpiration due to road-associated edge effects in a tropical moist lowland forest

“…These sharp boundaries alter the forest climate locally, with increased diurnal amplitude for temperature, humidity, radiation, wind speed close to the forest edge and advection energy (Ewers and Banks-Leite, 2013;Roberts and Rosier, 2005;Turton and Freiburger, 1997). This exposure and change in microclimate conditions results inevitably in an alteration of many tree physiological processes and forest structure in the short term, and forest species composition in the long term (Laurance et al, 2002;Ramos et al, 2013).…”

Spatio-temporal variation of throughfall in a hyrcanian plain forest stand in Northern Iran

“…Throughfall is the part of rainfall that reaches forest floor either through dripping from the tree canopies and after fulfilling initial interception storage or direct passing the canopy gaps (Chappell and Bidin, 2001;David et al, 2011;Díaz et al, 2007;Guswa and Spence, 2012;Huber and Iroumé, 2001;Rahmani et al, 2011;Roberts and Rosier, 2005;Wuyts et al, 2008;Zhang et al, 2006;Zimmermann and Zimmermann, 2014).…”