Fertilisation and vegetation management impacts on longer-term Pinus greggii productivity

Ndlovu N.N, Little K.M. and Titshall L.
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Robust management decision-making requires constant improvements to the understanding of the short- and longer-term impacts of re-establishment practices on tree performance. There is a lack of information regarding the impact of fertilisation and vegetation management on the longer-term (mature stand or rotation-end) yield of pines grown for pulpwood in South Africa. A trial was implemented in 1998 in the KwaZulu-Natal Midlands to determine whether different forms of fertilisation (No Fert, Maxiphos, Agriphos and NPK), different ring weeding diameters (0_m, 1_m, 2_m and 3_m) and interactions between these practices had a significant influence on longer-term (over 11.6 years) Pinus greggii productivity. Competitive vegetation biomass and cover abundance (2.6 years), foliar nutrients (2.6 years), crown diameter (2.6 years), and tree survival, growth and uniformity (from planting until 11.6 years) were recorded. Fertilisation did not have a notable influence on vegetation cover, nor did it have a significant influence on P. greggii survival and growth. However, fertilisation increased the vegetation biomass which indirectly influenced P. greggii uniformity at 11.6 years. During initial stand development (up to 3.1 years), vegetation management had a significant, positively linear (p < 0.001) influence on P. greggii productivity. This was no longer significant at 11.6 years, possibly due to the absence of woody competition. There was no significant interaction between the main factors of fertilisation and vegetation management. The results from this trial indicate that vegetation management during the re-establishment phase is important to achieve early site capture and canopy closure.