Peter L. Lorio

Growth-differentiation balance: A basis for understanding southern pine beetle-tree interactions

Interrelationships between the southern pine beetle (SPB), Dendroctonus frontalis Zimm.) and its host pines are explained in terms of the growth-differentiation balance concept. A general hypothesis is proposed based on growth-differentiation balance in southern pines (radial growth of stems versus synthesis and yield of oleoresin) and seasonal activity of the SPB based on knowledge from experimentation and observations reported in the literature. The spring appears to be particularly favorable for successful SPB attack because of the strong demand for available photosynthates by growth processes at that time, whereas, in the summer, strong resin flow increases the potential resistance of trees to attack. Growth-differentiation balance provides a basis for understanding SPB-tree interactions, a rationale for commonly experienced problems in identifying consistent precursors to SPB outbreaks, and a philosophical basis for future research. The concept has potential application to other bark beetle-host conifer relationships.

Seasonal cambial growth and development of loblolly pine: Xylem formation, inner bark chemistry, resin ducts, and resin flow

Abstract Cambial activity of loblolly pine in central Louisiana under mild soilwater deficit lasted for 252 days, one-third of which was used in the formation of early-wood. Although more cells formed in the late-wood, the radial increments for both were statistically similar (1750 μm). Vertical resin duct formation started 12 weeks after cambial reactivation with the first duct in each tree, except two, forming at the early-wood. Resin flow, an important factor in pine resistance to bark beetle attack, was moderately correlated with vertical duct density, growth variables, and all measured environmental variables with total soilwater storage, cumulative water deficit, and maximum air temperature combined accounting for 73% of the variation. Levels of starch continuously declined from May to December, while total sugar fluctuated with no seasonal pattern. Amino nitrogen and total nitrogen changed seasonally with peak concentrations coinciding with cell initiation and active growth, leaf fall, and winter cold temperatures. Seasonal change in resin flow was associated with changes in physiology related to ontogeny as well as environment. Knowledge of such relationships improves the basis for future study of pine/bark beetle interactions.

Environment and ontogeny modify loblolly pine response to induced acute water deficits and bark beetle attack

Abstract We evaluated the impact of tree resistance on within-tree population dynamics of southern pine beetle, Dendroctonus frontalis Zimm. (Coleoptera: Scolytidae) in loblolly pine, Pinus taeda L., as affected by prevailing water regimes, acute water deficits imposed by applying dry-ice (solid CO2) collars to tree boles, and by the seasonal ontogeny of pines. We conducted the study in the spring of 1986, when bole cambial growth had not yet shifted from earlywood to latewood formation, and in the summer of 1987, when latewood formation was well advanced. In each year there were five treated and five control trees. In 1986, under relatively well-watered conditions, results did not support the hypothesis that induced acute water deficit will enhance success of southern pine beetle attack and brood production. All trees were readily attacked and overcome with no apparent beneficial effects of the dry-ice treatment on within-tree population dynamics. In 1987, under drier conditions, results supported the hypothesis. Treated trees again were readily colonized, but three of the five control trees resisted attack to the extent that all attacks eventually failed. In 1986, all study trees maintained relatively high water potentials for more than 3 weeks following beetle attack. However, resin yields from bark wounds decreased rapidly. In contrast, water potentials of controls decreased gradually in 1987 and resin yields increased as controls resisted beetle attacks. Water potential of treated trees dropped rapidly 2 weeks after initial beetle attack, and resin yields decreased rapidly, as they did in 1986. Consideration of environmental conditions and ontogenetic stage of host trees is extremely important in attempts to assess the effects of manipulative treatments on tree susceptibility to beetle attacks. Further, they illustrate the dynamic nature of tree resistance to beetle attack in the absence of abnormal stresses. Simultaneous study of environmental conditions, as well as physiological changes associated with ontogeny of trees, can effectively support research on interactions between bark beetles and host trees.

Microsite Effects on Oleoresin Exudation Pressure of Large Loblolly Pines

Daily average oleoresin exudation pressure (OEP) of 40—year—old loblolly pines was not significantly reduced until severe soil and atmospheric moisture stress occurred from mid—September to mid—October. Under these conditions OEP was reduced more in trees on flat, usually wet sites than in trees on low (0.3—0.6 m) mounds. This response is attributed to a deficient fine root system on flat sites. See full-text article at JSTOR

Loblolly Pine Rooting Varies with Microrelief on Wet Sites

Loblolly pine root systems on flat or slightly concave sites had significantly less surface area and dry weight in fine roots (<5 mm) in the top 15 cm of soil than comparable neighbors on low mounds. Surface area of mycorrhizal tips was usually lower on the intermound areas over a 2—year sampling period. Root mapping in soil pits and root washing revealed differences between mound and intermound areas in terms of root numbers, distribution, and condition that indicated the eventual development of deficient root systems and intermittent severe moisture stress on flat sites. These conditions probably contribute to premature tree decline and tree susceptibility to bark beetle attack on such areas. See full-text article at JSTOR

Environmental effects on pine tree carbon budgets and resistance to bark beetles

Pine trees are a dominant component of primary production in natural and man- aged ecosystems throughout the southeastern United States. Because of the economic importance of pines in the Southeast, the southern pine beetle (Dendroctonus frontalis Zirnmerman, Coleoptera: Scolytidae) can cause losses in excess of

PREDICTIONS OF SOUTHERN PINE BEETLE POPULATIONS USING A FOREST ECOSYSTEM MODEL

236 million per year by attacking and killing pine trees (Price et al., 1992), and is arguably the greatest source of natural disturbance in ecosystems of the southeast. Interactions between pine trees and bark beetles have become a focus of global change research because it has long been hypothesized that bark beetle outbreaks are linked to climatic patterns (Beal 1927; Beal, 1933; Berryman and Ferrel, 1988; Christiansen and Bakke, 1988; Craighead, 1925; Gregoire, 1988; Kalkstein, 1976; King, 1972; Kroll and Reeves, 1978; Michaels, 1984; Raffa, 1988; St. George, 1930; Wyman, 1924). This implies that climate change will probably alter the frequency and intensity of forest disturbance from pest outbreaks. However, the mechanisms by which climatic patterns impact bark beetle population dynamics have remained obscure (Martinat, 1987; Mattson, 1980; Reeve et al., 1995). The development of accurate, physiologically explicit models is an essential first step in assessing the ecological risks associated with global change (Ayres, 1993). The research reported in this chapter was designed to test and refine a model of environmental effects on tree carbon budgets that provides a promising tool for understanding and predicting the effects of global change on interactions between pine trees and the southern pine beetle (SPB) (Figure 32.1).

Southern Pine Beetles Attack Felled Green Timber

Dendroctonus frontalis Zirnm. (southern pine beetle (SPB)) has caused over

Environmental effects on constitutive and inducible resin defences of Pinus taeda

900 million in damage to pines in the southern United States between 1960 and 1990 (Price et al., 1992). The damage of SPB to loblolly (Pinus taeda L.), shortleaf (Pinus echinata Mill.), and pitch (Pinus rigida Mill.) pine has long been established (Hopkins, 1899), however, extensive mapping of SPB infestations has only existed since 1960 (Price and Doggett, 1982). Early detection of SPB outbreak areas is essential to controlling population increases (Swain and Remion, 1981), but the range of SPB is large, SPB have six to eight generations per year, and there is inconsistency in the monitoring methods used to measure SPB populations across its range. Therefore, various models have been developed that attempt to predict SPB outbreak severity across the region (Hansen et al., 1973; Kalkstein, 1974; Michaels, 1984).

Why Do Populations of Southern Pine Beetles (Coleoptera: Scolytidae) Fluctuate?

Although Hopkins (1909) briefly mentioned that the southern pine beetle (SPB) (Dendroctonus frontalis Zimmermann) will breed in felled pines (Pinus spp.), this behavior has been thought to be uncommon (Gara and others 1965). MacAndrews (unpublished MS thesis 1926)’ first reported SPB completing a generation in felled logs of shortleaf pine (Pinus echinata Miller) in an “epidemic”situation. In summer and fall he noticed that the logs were attacked simultaneously by SPB and Ips calligraphus (Germar) within 2 days after felling and that the bottoms of logs were colonized more heavily by SPB than the tops. Highest emergence:attack ratio (E/A) (10.4) was in the butt logs where bark was thickest. The average number of beetles was 21 .4/cm2 (198/ft2). In standing timber, the VA was lower (about 8.0), but numbers of emerging SPB were higher (32.41 cm2 or 300/ft2).