Projecting climate change effects on forest net primary productivity in subtropical Louisiana, USA

This study projected responses of forest net primary productivity (NPP) to three climate change scenarios at a resolution of 5 km x 5 km across the state of Louisiana, USA. In addition, we assessed uncertainties associated with the NPP projection at the grid and state levels. Climate data of the scenarios were derived from Community Climate System Model outputs. Changes in annual NPP between 2000 and 2050 were projected with the forest ecosystem model PnET-II. Results showed that forest productivity would increase under climate change scenarios A1B and A2, but with scenario B1, it would peak during 2011-2020 and then decline. The projected average NPP under B1 over the years from 2000 to 2050 was significantly different from those under A1B and A2. Forest NPP appeared to be primarily a function of temperature, not precipitation. Uncertainties of the NPP projection were due to large spatial resolution of the climate variables. Overall, this study suggested that in order to project effects of climate change on forest ecosystem at regional level, modeling uncertainties could be reduced by increasing the spatial resolution of the climate projections.

Using Simple Marginal Analysis and Density Management Diagrams for Prescribing Density Management

This article presents a procedure to produce management regimes that not only maximize land value but also reflect stand development with simple marginal analyses of the accumulation and control of growing stock. An upper limit of growing stock is determined by translating management objectives into a future desired structure, and with this value as a guide for thinning age, marginal analysis is used to determine the planting density and the residual basal area after thinning. The procedure is demonstrated for a hypothetical loblolly pine plantation growing on land with a site index of 65 ft at 25 yr. The effects of various interest rates for a fixed rotation length and various rotation lengths for a fixed interest rate on initial planting density and residual growing stock after low thinning are analyzed. Optimal planting density decreased with increasing interest rate and rotation length. Thinning ages increased as initial planting density decreased, which caused optimal residual growing stock to increase with increasing interest rate and rotation age. According to this study, maximum land value is achieved when the growing stock limits are set to approximately the lower limit of full-site occupancy and the threshold of self-thinning. In terms of relative density, the ideal limits in growing stock for maximizing land value identified in this study are 35 and 55% of maximum SDI. South. J. Appl. For. 26(2):85–92.

A Density-Management Diagram for Slash Pine Plantations in the Lower Coastal Plain

Data from 92 regional, midrotation-fertilizer trials were used to develop a density-management diagram for site-prepared slash pine (Pinus elliottii var. elliottii) plantations. The density-management diagram shows the interrelationships of five important stand variables (i.e., quadraticmean diameter (Dq), trees/ac, site height, standing volume/ac, and relative current annual increment) in a graphical form. The diagram can aid foresters in designing and comparing alternative density-management regimes for slash pine. In doing so, foresters can evaluate individualtree and stand level performances in relation to growing stock levels and make field approximations of growth and yield for various density-management regimes. Results indicated that fertilization and soil type had minimal effects on the diagram's isolines. This suggests broad applicabilityof the diagram for fertilized or unfertilized plantations found in the lower Coastal Plain. The use of the diagram is illustrated with three alternative density-management regimes, and a method is presented for estimating midrotation fertilization responses. South. J. Appl. For. 16(4):178-185

Seasonal response of slash pine (Pinus elliottii var. elliottii Engelm.) photosynthesis to long-term exposure to ozone and acidic precipitation

Four half-sib families of slash pine (Pinus elliottii var. elliottii) were planted in open-top chambers and exposed to ozone and simulated acidic precipitation (3: 7 molar ratio of nitric and sulphuric acids). The 4 ozone treatments were (1) charcoal-filtered air, (2) unfiltered ambient air, (3) twice ambient and (4) three times ambient ozone, with treatments applied 12 h per day, 11 months per year for 28 months. Seedlings were irrigated weekly with one of three rain acidities: pH 33, 4.3 or 5.3 at a total rainfall equivalent of 133 cm per year. Photosynthetic rates were measured approximately every 10 weeks, on the most recently emerged branches each year. In 1988 the 3rd flush was measured, and in 1989 and 1990 the 1st flush of each year was measured. Elevated ozone concentrations generally reduced photosynthetic rates, especially during the summer months, but there was no evidence of either a threshold dose or a simple linear relationship between photosynthesis and ozone exposure. There was a seasonal drop in photosynthetic rates from March to September each year. An ontogenetic decrease in photosynthesis was also evident as trees matured. Stomatal conductance also decreased as the needles aged. Seedlings irrigated with pH 3.3 solution typically exhibited the highest photosynthetic rates, presumably due to a fertilizer effect.