Chemical Thinning and Mixed-Species Forestry in the US South with Dr. Adam Polinko | Episode 46

Forest management decisions are made under biological, financial, and market conditions that can change considerably during the life of a stand. In this episode of *Timber University*, Dr. Adam Polinko, formerly of Mississippi State University (now at Northern Arizona University), joins us to discuss two applied research projects examining how landowners and foresters can respond to those challenges: chemical thinning in overstocked pine stands and the long-term development of mixed cherrybark oak and sweetgum plantings. Dr. Polinko's research focuses broadly on silviculture and forest stand dynamics, including how forests respond to disturbances such as thinning, harvesting, and other management interventions. The first part of the conversation examines whether chemical thinning could help landowners manage dense pine stands that can no longer be commercially thinned because of weak pulpwood markets. Dr. Polinko explains how a modified "hack-and-squirt" treatment can be used to thin a stand from below by killing smaller trees in place, opening growing space for larger trees, and accelerating a process that would otherwise occur gradually through natural self-thinning. We discuss how chemical thinning differs from conventional row thinning and why it may be particularly useful on smaller properties where logging access, tract size, or limited markets make a commercial thinning difficult. Because the work can be completed by people on foot using relatively simple equipment, it could give some landowners a practical way to place an overstocked stand back on a more productive growth trajectory. The episode also explores the risks and trade-offs of killing trees in place. The research team is examining how treatment timing affects Ips engraver beetles, southern pine beetles, tree stress, and mortality. The study will also evaluate how standing dead trees, dry needles, fallen woody material, and changing fuel loads may influence wildfire behavior. At the same time, increased sunlight reaching the forest floor could stimulate vegetation that provides additional forage and habitat benefits for wildlife. The second half of the episode turns to a mixed-species study established in the early 1980s to examine the development of planted cherrybark oak and sweetgum. The study was designed to test observations from natural stands suggesting that sweetgum may initially grow as fast as, or faster than, cherrybark oak, while the oak eventually overtakes it. Recent measurements indicate that sweetgum remained highly competitive for approximately the first 25 years, after which its height growth began to level off, and the cherrybark oak pulled ahead. The result today is a stand containing large, high-quality cherrybark oak and much smaller sweetgum. Dr. Polinko explains that sweetgum may provide a valuable "training effect" for cherrybark oak. Competition between the species can help the oak maintain apical dominance, straighter stems, smaller branches, and better overall form than might develop in a widely spaced, single-species oak planting. The study also provides a rare opportunity to compare mixed stands directly with nearby pure sweetgum and mostly pure cherrybark oak stands on the same site. The conversation highlights why mixed-species forestry may offer more than biological benefits. Growing different species together can diversify future management options, reduce dependence on a single timber market, and give landowners greater flexibility when deciding which species to thin, retain, or manage as the final crop. Because forest rotations are long and markets can change much faster than stands can be replaced, this kind of biological and financial diversification may become increasingly valuable. This episode is a useful listen for forest landowners, consulting foresters, wildlife managers, forestry students, researchers, Extension professionals, and anyone interested in pine thinning, mixed-species management, stand dynamics, forest health, and the challenge of managing forests under changing market conditions. Questions for *Timber University* can be sent to [timberuniversity@gmail.com]()