The State of Pine Research
by Laura Nelson
What Microplots Reveal About Forest Management
If you were walking the trails of the Cloquet Forestry Center in early October, you might have seen a team of people sprawled on the ground, carefully measuring seedlings planted in small clusters. It is not the typical sight that comes to mind of foresters, often pictured staring up at trees. The small clusters, called microplots, are being used to study stand productivity of two species not often paired for research, red pine and white spruce. Forest Resources’ Associate Professor Matt Russell and Cloquet Forestry Center Forest Manager Kyle Gill developed a project to examine how co-management of these species may lead to increased wood fiber production and carbon sequestration. “I came up with the idea of replicating the early-successional and late-successional pairing that forest managers are doing in aspen-dominated forested lands. I thought pairing conifers would be an interesting comparison to pairing a hardwood with a softwood that others might find useful for discussion and informing their own practices,” said Kyle.
A method to shorten the cycle of forest experiments and reduce data collection costs is to implement miniature scale or microplot experiments. Kyle, Matt and their research team planted both red pine, white spruce, and mixed red pine and white spruce microplots as well as five-acre macroplots of mixed red pine and white spruce. Planting at a known micro-scale will allow them to scale up height and diameter growth and timing of thinnings to the larger operational plots. “What I hope to learn from the micro plots and translate into the operational scale is mostly the proposed timing of thinnings,” said Kyle. “My hope is that the 1:16 spatial scale might be relevant to the time scale, though I’m not at all sure if this will be the case. If it is, one growing season in the microplots would translate to 16 years at the operational scale,” he said. While it is uncertain if spatial scales directly translate to time scales, Kyle notes that “having discussions about the interactions of spatial scale, time scale, live crown ratios, and active management practices will help us to be better informed, even if the lesson is that these variables are less correlated than we hoped for.”
Ponderosa Pine: A New Species for a New Climate?
Pinus ponderosa is a two or three-needle pine, native to the western United States. It looks similar to Minnesota’s state tree, the red pine (Pinus resinosa), with reddish bark and needles in groups of two or occasionally three. Not only does it look similar, ponderosa pine is said to occupy a similar ecological niche as red pine. This means that both species have similar characteristics in how they reproduce, survive, and in how they provide food and habitat for wildlife. Ponderosa pine is not native to Minnesota, but researchers and forest managers are wondering how this species might fare in Minnesota. Because of its relatively high drought tolerance, ponderosa pine is being examined as a species for planting in anticipation of warmer and drier climates.
Several faculty members and graduate students in the Department of Forest Resources are involved in the Adaptive Silviculture for Climate Change (ASCC) program, a collaborative effort at the Chippewa National Forest among scientists and land managers to study long-term ecosystem responses to adaptive forest management. Adaptive forest management seeks to make the uncertainty of climate change more certain by testing out different forest management strategies. When it comes to ponderosa pine, the team at ASCC is exploring the idea of adaptive plantings of ponderosa pine as an alternative, not a replacement, to red pine. Red pine is the most abundant cover type of Minnesota’s pine forested area, providing the majority of softwood sawtimber harvested annually.
Ponderosa pine is also a valued timber product which supports the utilization of ponderosa as an economic alternative to red pine. Before researchers can determine if ponderosa pine should be planted in Minnesota, they need to predict how much it would grow in its non-native range. Foresters use mathematical models to forecast how much wood volume will be produced over time, called growth, and how much volume will be available to be harvested at a given time, called yield. These “growth and yield” models are well-established for key timber-producing tree species within their native range. Predicting the volume of a tree depends on the species and where it is growing because different types of trees have different growth patterns, and growth is dependent on regional characteristics such as annual precipitation and soil composition. There are few models that predict growth and yield of a tree species outside of its native range.
That brought Forest Resources researchers to the question, what is the growth and yield of ponderosa pine, a non-native species, in Minnesota? A key consideration in their research was which mathematical model to use in forecasting ponderosa pine growth. Since red pine is ecologically similar to ponderosa pine, they wondered about predicting growth and yield using red pine models based in Minnesota over ponderosa pine models based in western regions.
Researchers measured indicators of ponderosa growth at three long-term provenance, or genetic, trial sites in Minnesota. Growth can be measured in many ways, and researchers were able to take advantage of two common methods, repeated measurements of tree height and diameter as well as tree cores. In summer 2018, they collected measurements at two sites in the prairie parklands (Lamberton and Morris) and one in the Laurentian mixed forest region (Grand Rapids). They found that ponderosa pine did better overall in the prairie parklands than in the Laurentian mixed forest. In other words, ponderosa pine did better in farm country than forest country!
Researchers compared their growth and yield measurements of ponderosas at the three sites with the mathematical models. They found that the models for western region’s ponderosa pine growth aligned more closely with tree measurements than models of red pine in Minnesota. The results imply that if forest managers plant non-native species in new regions, using models developed from their native region may be a useful starting point for determining growth and yield.
The findings also indicate that ponderosa pine can survive and thrive in warmer regions with lower precipitation in Minnesota. Although Minnesota is projected to see more rainfall in the future, much of it could be lost as runoff in more frequent large-scale rain events. There is projected to be longer periods of time between rain events, making ponderosa pine a species that forest managers could consider because of its adaptability to drought.