Plotting the Future by Monitoring the Past

In 1971, Jerry Franklin stood, tape measure in hand, among large, old-growth Douglas-fir in reference plot one in the  H.J. Andrews Experimental Forest  near Blue River, Oregon. Then a forester with the  USDA Forest Service Pacific Northwest (PNW) Research Station , he began recording the first set of data from this stand of trees.

Fast forward to 2021—Franklin is retired but Dave Bell, a research forester with the station, stands in the same spot and collects measurements from the same trees. Their efforts, and those of all the researchers who measured plot one during the intervening decades, have contributed to an ever-growing forestry dataset that is being used to answer some of the most pressing questions about forests today.

In 1910, station scientists and their collaborators began establishing permanent sample plots across the region, generally in Douglas-fir forests, to study timber growth and yield. These plots were initially viewed as independent studies, but it became clear in the later part of the 20th century that treating them as a cohesive plot network would broaden understanding of forest dynamics. A plot network, as opposed to individually managed plots, could support consistent monitoring efforts at each location and produce a large-scale, long-term dataset that would enable scientists to answer more complex questions about how forest dynamics vary across space and time.

Reference plots one and two in H.J. Andrews Experimental Forest were the first official sites in what is now called the  Pacific Northwest Permanent Sample Plot (PNW-PSP) network . These two plots are also a central part of the  H.J. Andrews Long-Term Ecological Research program , which is a National Science Foundation-funded collaboration among multiple institutions including the PNW Research Station,  Oregon State University , and the  Willamette National Forest . Since its establishment in 1971, the network has grown. It now encompasses more than 140 research plots and 100,000 trees across Oregon and Washington.

Studying forest dynamics takes decades and even centuries. Changes in forest ecosystems typically occur over long periods, and it is not unusual for trees in the Pacific Northwest to live more than 500 years. A variety of modeling and statistical techniques can be used to generate information about variations in the forest ecosystem over space and time. However, only long-term observation of permanent sample plots can provide the necessary data to fully understand forest ecosystems, including the effects of climate change.

Answering certain questions about forest ecology requires data from years of consistent and sustained monitoring, measuring, and experimenting conducted in the same location. This type of long-term ecological research is incredibly valuable, but very challenging to sustain, requiring the efforts of countless researchers and multiple organizations.

Since its inception in 1971, the PNW-PSP network has grown to include more than 140 plots. Most were established from 1910 to 1948 and from 1970 to 1989. Long-term data from the network has formed the basis of a substantial body of research related to forest ecosystems, including forest succession, tree mortality, recovery after disturbance, carbon sequestration, timber yield, and response to climate change. Early research in the H.J. Andrews plots (1971–1981) specifically examined the structure and function of old-growth forests in western Oregon and Washington (Franklin et al. 1981) and furthered understanding of tree mortality (Harmon and Bell 2020) and forest succession processes (e.g., Harmon and Pabst 2015) that develop and maintain old-growth forests (Franklin et al. 1987, Harmon and Bell 2020).

Much of this work helped lay the foundation for the 1994  Northwest Forest Plan , which prioritized the conservation of old-growth forests and acted as a framework for adaptive forest management. Data from the network is regularly used to support the ongoing monitoring requirements of the Northwest Forest Plan.

Long-term monitoring also provides a critical baseline for understanding forest responses to climate change now and in the future. Because the PNW-PSP network includes sites with different disturbance histories, topography, and elevation, researchers can use the data to answer a variety of climate-related research questions. This long-term data is particularly useful for studying natural, unanticipated events, such as wildfires or droughts, that periodically impact these plots throughout their lifetime. With the increased use of remote sensing to study forests, these well-studied plots are also a valuable resource for developing and testing geospatial modeling and mapping methods to hone new technologies.

Over time, research using data from the PNW-PSP network has focused on a variety of themes and topic areas. Scroll through the timeline below to learn about some of the main research themes.

Research using data from the PNW-PSP network has increasingly shifted to examine forest response to disturbances, such as wildfire and landslides, as well as the effects of climate change. One specific area of focus is how local biological interactions among trees and other organisms may influence the way forests respond to climate change. The network is also being leveraged to develop and test new remote sensing and mapping technologies that will provide even more insight into the future of Pacific Northwest forests.

The PNW-PSP network includes some of the longest running ecological research sites in the world. As forests in the Pacific Northwest experience changes in climate, the data provided by the PNW-PSP network will continue to provide a valuable source of information to researchers globally. This information will improve our understanding of forest response to climate change and support effective management now and in the future.

Click through the slideshow below to meet some of the leading researchers involved with the Pacific Northwest Permanent Sample Plot network throughout its history.

In 1971, the first of PNW-PSP reference stands were established at the H.J. Andrews Experimental Forest ( Hawk et al. 1978 ), growing to a network of approximately 140 long-term tree measurement installations across Oregon and Washington ( Acker et al. 1998 ).

Early research with these reference stands (1971–1981) focused on characterizing the structure and function of old forests in western Oregon and Washington ( Franklin et al. 1981 ,  Harmon and Bell 2020 ). That work laid the foundation for the Northwest Forest Plan, which prioritized the conservation of old forests.

These plots also supported the development of ideas regarding the processes that help form and maintain old forests, such as tree mortality ( Franklin et al. 1987 ) and, tree growth ( Stephenson et al. 2014 ).

Long-term monitoring not only provides a basis for testing of forest ecology theory regarding forest succession (e.g.,  Harmon and Pabst 2015 ), but they are essential for documenting and understanding forest changes ( Franklin 1989 ), especially as it relates to emerging threats like climate change ( van Mantgem et al. 2009 ).

For example, a recent study highlighted the role that dwarf mistletoe–a parasitic plant–might play in amplifying western hemlock sensitivity to hot and dry climatic conditions ( Bell et al. 2020 ).

For an expanded list of publications please visit:  PNW-PSP publications by decade .