Growth and water relations of Eucalyptus marginata (jarrah) stands in response to thinning and fertilization

Abstract

We studied the effects of five thinning treatments (T1 = 5.5, T2 = 11, T3 = 16.5, T4 = 22.5 and T5 = 28.5 m(2) ha(-1) basal area under bark) x two fertilizer treatments (F0 = unfertilized and F1 = fertilized with 400 kg ha(-1) N plus 229 kg ha(-1) P) on growth and water relations of pole-sized Eucalyptus marginata J. Donn ex Sm. trees growing in southwestern Australia. Thinning reduced leaf area index (LAI) from 2.1 in the T4 and T5 treatments to 0.8 in the T1F0 treatment. Fertilizer had no effect on LAI in the T2, T4 or T5 treatments, but increased LAI by 45 and 20% in the T1 and T3 treatments, respectively. Thinning plus fertilizing increased diameter growth most in the fastest growing trees, from 0.4 cm year(-1) for trees in the T5F0 and T5F1 treatments to 0.7 and 1.2 cm year(-1) for trees in the T1F0 and T1F1 treatments, respectively. In both fertilizer treatments, stand basal area and volume growth increased with increasing stand density up to 15 m(2) ha(-1), and thereafter declined with increasing stand density, such that the growth rate of trees in the T5 treatment was only half of that at a stand density of 15 m(2) ha(-1). In response to fertilizer, growth rates of the slowest and fastest-growing trees increased from 0.35 and 3.5 m(2) ha(-1) year(-1) (F0) to 0.56 and 5.4 m(3) ha(-1) year(-1) (F1), respectively. Stand growth efficiency (growth per unit LAI) increased in response to thinning, and fertilizer increased stand growth efficiency at all stand densities. Throughout the dry season, T5 trees had lower predawn shoot water potentials (Psi(pd)) (minimum of -1.5 MPa) than T1 or T2 trees (minimum of -0.7 MPa). Fertilizer decreased Psi(pd) in T5 trees (by -0.9 and -1.5 MPa, respectively, in F0 and F1), but not in T1 or T2 trees. Stand growth rate was closely related to cumulative midday water stress (CMWS) over the dry season, and volume growth rate declined sharply from 6 m(3) ha(-1) year(-1) at a CMWS of 130 MPa days, to zero at a CMWS of 220 MPa days. Application of fertilizer to thinned stands increased LAI, stand growth efficiency and stand growth. In unthinned stands, fertilizer increased stand growth efficiency and stand growth; however, it also increased tree water stress, which limited the fertilizer-induced increases in LAI and growth. We attribute the increase in tree and stand growth in response to application of fertilizer to increased photosynthetic rates, increased allocation to stem wood, and in thinned stands also to higher LAIs.

The water adaptability of Jatropha curcas is modulated by soil nitrogen availability

“…Water and nutrients (particularly nitrogen (N)), as the essential resources to plants, are two of the most important factors controlling tree growth [1,2] and productivity [3], and there are interactions between them. Matching N supply to plant water availability is essential for a successful crop yield [4,5].…”

Successional changes in feeding activity by threatened cockatoos in revegetated mine sites

“…Second, young trees in revegetated areas are unlikely to provide the large fruit crops that older trees in unmined forest can. Additionally, high tree stem densities -typically much higher in revegetation than in unmined forest -can limit tree growth rates (Stoneman et al 1997;Grigg and Grant 2009) and may also constrain flowering and fruit crops (Arista 1996;Williams et al 2006). Glossy black cockatoos (Calyptorhynchus lathami) preferentially feed in trees with large fruit crops, probably because it is more energy efficient (Chapman and Paton 2005); so, the same may hold true for our study species in the jarrah forest.…”

High-intensity thinning treatments in mature Pinus halepensis plantations experiencing prolonged drought

“…Measurements began right after thinning conducted every 45 days during 2 years following thinning. Sample collection and treatment was applied following (Stone et al 1999). It began two hours prior to dawn and ended before dawn.…”

“…First, temporal variation in individual tree parameters, e.g., tree leaf area (LA tree ), BAI tree as well as tree mortality rate, was all associated with inter-year fluctuations in rainfall amount (Dorman et al 2013;Tesemma et al 2014). Secondly, better tree performance and reduced mortality rate following thinning were associated with changes in predawn shoot water potential (Stoneman et al 1997;Stone et al 1999). According to previous work looking at hydraulic adjustments of Pinus halepensis, the variation in shoot water potential observed in our work among thinning treatments, i.e., -1.7, -1.85, and -2.0 MPa in the intense, moderate, and control treatment, respectively, corresponds to twofold variation in stomatal conductance (g s ), i.e., *0.2, 0.15, and 0.1 mol m -2 s -1 , respectively (Klein et al 2011(Klein et al , 2013.…”

“…As thinning operations are costly and the financial return expected from these forests is very limited, the idea was to test one-time high-intensity thinning treatments with the aim of achieving a long-term facilitating effect on residual trees while allowing more growing space for natural regeneration and gradual development of a more complex and resilient forest ecosystem (Osem et al 2009. Forest thinning was previously shown as an effective silvicultural tool for promoting tree performance in general (González-Ochoa et al 2004;Ruano et al 2013;Olivar et al 2013) and alleviating drought stress in particular (Stoneman et al 1997;Zausen et al 2005;Rais et al 2014;Gebhardt et al 2014). However, the usefulness of applying high-intensity thinning in mature excessively dense stands has been very little studied (del Campo et al 2014).…”