Andrew S. Nelson

Acetophenone superior to verbenone for reducing attraction of western pine beetle Dendroctonus brevicomis to its aggregation pheromone

1 The western pine beetle Dendroctonus brevicomis LeConte (Coleoptera: Scolytidae) is one of the most damaging insect pests of ponderosa pines Pinus ponderosa Douglas ex P. & C. Lawson in Western U.S.A. We compared the effect of verbenone, a well known bark beetle anti‐aggregation pheromone, with that of acetophenone on the attraction of D. brevicomis to its aggregation pheromone in a ponderosa pine forest in northern California. We tested the D. brevicomis aggregation pheromone alone and with three different release ratios of the aggregation pheromone (attractant) to verbenone or acetophenone (1 : 1, 1 : 2 and 1 : 5).

Spatial variation in specific leaf area and horizontal distribution of leaf area in juvenile western larch (Larix occidentalis Nutt.)

Key messageModels were developed to predict spatial distribution of specific leaf area (SLA) and horizontal distribution of leaf area for western larch. Cardinal branch direction significantly influenced both SLA and horizontal leaf area distributions.AbstractLeaf area, specific leaf area (SLA), and their spatial distribution in the crown are important indicators of biological response to changes in growing conditions including light and water availability. Western larch (Larix occidentalis Nutt.) is a deciduous coniferous pioneer species in the U.S. Inland Northwest known for its rapid growth, high-quality wood, and ecological importance. Analysis with nonlinear models revealed that SLA and horizontal leaf area distributions differ between cardinal quadrants of juvenile western larch crowns. SLA was significantly higher in the more illuminated, southern side of the crown, and leaf area peaked closer to the stem in the southwest quadrant. Similar to other conifers, horizontal distributions of foliage in western larch also shifted further outward towards the branch tips with increasing depth in the crown. Models developed for horizontal distribution of leaf area and spatial distribution of specific leaf area for western larch may be extended by future researchers to predict its response to environmental variables or management practices.

Forest regeneration in changing environments

Successfully regenerating young forests following harvesting or natural disturbances is the first principle of sustainable forest management. Whether regeneration practices are successful or not can have substantial long-term effects on future stand dynamics, management options, and whether overall goals are achieved. Continuously adapting forest regeneration practices to changing societal needs, human and natural disturbances, policies, markets, technologies and climate, presents recurring challenges and opportunities to successfully managing forests around the globe. Therefore, testing new methods for regenerating forests is vital for meeting current and future forest management goals and ensuring the overall sustainability of forests. Advancing the science and practice of forest regeneration and early stand management requires a regular exchange of information about new concepts, scientific methodologies, and technologies among forest researchers and managers. From July 11–13, 2017 an international conference entitled Forest Regeneration in Changing Environments was held at Oregon State University in Corvallis, OR, USA. The goal of the conference was to bring forest researchers and practitioners together to share the latest research findings related to forest regeneration and early stand dynamics in changing environments around the globe. Nearly 90 registered participants from more than 25 countries made over 70 scientific presentations. A proceedings from the conference (Wagner et al. 2017) with abstracts from all presentations was provided at the meeting and is available at: https ://www.iufro .org/downl oad/file/27365 /1434/10104 -20115 -corva llis1 7-abstr acts_pdf/. The conference was jointly sponsored and organized by Oregon State University’s College of Forestry, Purdue University’s Department of Forestry and Natural Resources, and the University of Idaho’s Department of Forest, Rangeland and Fire Sciences.

Partial harvesting effects on seedling growth and physiology of three hardwood species in mature pine (Pinus spp., Pinaceae)-hardwood mixtures1

Abstract. Nonindustrial private forest (NIPF) landowners own a substantial amount of acreage within the southern USA. The NIPF landowners are usually less financially motivated and implement relatively less-intensive management options, such as partial harvesting, to pursue a variety of multiuse objectives. Understanding how developmental processes are influenced by partial harvesting is vital to constructing viable silvicultural prescriptions. Liquidambar styraciflua L., Quercus alba L., and Ostrya virginia (Mill.) K. Koch seedling (10–105 cm tall) growth and physiology were investigated in relation to different gap sizes and within-gap positions in a mixed Pinus L.–hardwood forest. The levels of photosynthetically active radiation that penetrated the overstory conditions allowed shade-intolerant Liquidambar styraciflua to produce greater (mean ± SE) monthly height and groundline diameter growth (12 ± 0.94 cm and 0.2 ± 0.02 cm, respectively) than Ostrya virginia (8 ± 0.87 cm and 0.1 ± 0.02 cm, respectively) and Quercus alba (4 ± 0.51 cm and 0.1 ± 0.01 cm, respectively), which was facilitated, in part, by significantly higher photosynthetic rates (P < 0.01). Solely manipulating the overstory conditions within mature, Pinus-hardwood mixtures may not be adequate for Quercus regeneration in those mixtures and is conducive to Liquidambar styraciflua obtaining a more-dominant canopy position in the future.

Natural conifer regeneration patterns in temperate forests across the Inland Northwest, USA

Key messageNatural regeneration patterns of conifer species were studied. Seedling regeneration follows patterns responding to stand structure and site condition factors along shade and drought tolerance gradients. Our findings can assist in adaptive forest management for maintaining sustainable regeneration and plant biodiversity.ContextSeedling regeneration can vary with stand factors of overstory trees and understory non-tree vegetation and site conditions.AimsNatural seedling regeneration patterns of coniferous species were investigated using Forest Inventory and Analysis (FIA) data of 10 common species across the Inland Northwest, USA.MethodsZero-inflated negative binomial models were developed to understand the responses of natural regeneration to stand factors and site conditions.ResultsSeedling occurrence varies along shade and drought tolerance gradients responding to stand structure and site conditions. Two moderate shade-tolerant species of different drought tolerance contributed as a transition. Strong response patterns were revealed for seedling density, in which seedling density was improved with the presence of conspecific trees while limited by competition, especially from the understory vegetation layer.ConclusionOverstory structure and understory vegetation could improve or hinder natural regeneration of coniferous tree species given different shade tolerance and site conditions. Our findings can be effectively implemented in adaptive forest management for maintaining sustainable regeneration of specific conifers in broad temperate mixed forests.

Density reduction in loblolly pine ( Pinus taeda L.) stands to increase tree C assimilation: an approach with the dual δ 13 C and δ 18 O isotope signatures in needles

Key messageIn the context of increasing droughts related to climate change, our results showed that heavy thinning and/or very low initial planting density can increase CO2assimilation rate in needles, and may be used as a short-term management strategy for loblolly pine plantation across sites prone to drought.ContextThe dry summer of 2013 provided us an opportunity to understand the CO2 assimilation rate and stomatal conductance after density manipulation treatments using the dual isotope (δ13C and δ18O) signatures in needles of planted loblolly pine (Pinus taeda L.) trees in the southeastern USA.AimsTo our knowledge, this is the first study using the dual isotope approach to examine the physiological response of loblolly pine trees, one of the most widely planted tree species in the world, to stand density manipulation treatments (i.e., thinning intensity and planting density).MethodsIn 2001–2003, trees were planted with five different planting densities, 494, 1111, 1729, 2346, and 2964 trees ha−1 at three sites. In 2009–2011, two thinning treatments (none and moderate thinning) were applied in the 1111 trees ha−1 plots, whereas three treatments (none, light and heavy thinning) were applied in the 1729 trees ha−1 plots. Response variables (specific leaf area (SLA), foliar N, δ13C and δ18O) were measured in February 2014.ResultsSLA was lower, while δ18O was higher in the 494 trees ha−1 plots than the 2964 trees ha−1 plots without thinning. In plots planted to 1729 trees ha−1 SLA was lower, while δ13C and δ18O were higher following heavy thinning than in the unthinned control. These responses plus increased crown length, DBH, and height following heavy thinning may reflect an increased tree-level CO2 assimilation rate.ConclusionOur results showed that heavy thinning and/or very low initial planting density can be used as a short-term management strategy for loblolly pine plantation across sites prone to drought.