Greater carrying capacity has been reported for a variety of tree species planted in favorable, exotic environments outside their native range but mechanisms supporting greater growth potential are unclear and relevant to understanding potential climate change effects on tree growth. A longer growing season and milder climate, changes in leaf area and higher photosynthetic rates are factors that may influence tree growth in exotic environments. We revisited a loblolly pine density study that was planted in 1961 on the island of Maui. To our knowledge, the study is the only replicated, long-term study of loblolly pine in an exotic location. Up to age 34 years, trees produced double the maximum basal area and volume observed in loblolly pine’s native range. The objectives of this research were to re-define biological growth potential of loblolly pine at age 47 years and identify potential factors that may influence carrying capacity and growth potential such as climate, leaf physiology, needle and shoot morphology, woody root allocation and soil and foliar nutrients. We measured growth, leaf light use efficiency and maximum photosynthesis, nutrition and shoot morphology during two intensive sampling campaigns conducted in July 2008 and January 2009.
Results/Conclusions
Basal area and volume were extremely high even at age 47 years and averaged 93 m2 ha-1 and 1076 m3 ha-1, respectively. Maximum density remained high at 1700 trees ha-1 in the two closest spacings. Leaf light-saturated net photosynthesis, stomatal conductance and quantum yield were similar among spacings and similar to values reported for mainland stands. Foliar nutrient concentrations and in particular calcium, specific leaf area, and flush number were high in the Hawaii study compared to mainland trees. Allocation to woody root biomass relative to stem plus woody root biomass was 13% and lower than allocation reported for loblolly pine in its native range. A more favorable climate conducive to sustained year round leaf carbon gain and low leaf dark respiration rates, fertile soils and less allocation to belowground mass may be related to greater carrying capacity in Hawaii stands.