The Experience in the Western Forest in the United States

For my six-month short-term scholarship, I scheduled a three-month field season with James A. Lutz and planned to use the remaining three months to compile my experiences and knowledge into a scientific paper. Dr. Lutz has dedicated 17 years of research to western forest dynamics plots. He has long-term mortality and recruitment data collected annually, which forms the largest dataset of its kind in the world. No one else has such continuous data, and these data are now crucial for understanding species changes and mortality under climate change. Therefore, it is a great opportunity to gain experience and learn how Dr. Lutz’s team conducts research in western forests in the United States.


Figure 1. Wind River Forest Dynamics Plot

Wind River Forest Dynamics Plot
The Wind River Forest Dynamics Plot (WFDP) is a forest dominated by Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). The largest tree has a diameter at breast height (DBH) of up to 200 cm, and the tallest tree can reach 65 m. This forest is 500 years old. Due to a fire 500 years ago, the age of the Douglas-fir can be calculated to be up to 500 years, but no older. Subsequently, the pioneer species, Douglas-fir, was gradually replaced by hemlock and other conifers. The oldest recorded hemlock can reach 200-300 years. The forest structure can be roughly divided into three layers: the first layer is a coniferdominated canopy (40-50 m), the second layer consists of broadleaf trees (15-30 m), and the third layer includes conifer saplings and trees growing close to the ground. On the first day of the survey, I struggled to adapt to this tall forest. Unlike the Nanjenshan area, where bamboo and vine plants cause disturbances, walking here felt somewhat dizzying. Surrounded by 70 cm trees, each standing 40-60 m tall, the scale was overwhelming. Although the forest is primarily composed of hemlock and fir, there are, of course, more than two plant species. Among the firs are Pacific silver fir (Abies amabilis), grand fir (Abies grandis), and noble fir (Abies procera), while there is only one species of hemlock, the western hemlock, distributed in this area. Another familiar tree is the western redcedar (Thuja plicata), whose bark is similar to the elongated, flaking bark of Taiwan's Chamaecyparis. The plot is also home to massive Douglas-firs and the water-loving Pacific yew (Taxus brevifolia).

Figure 2. Measuring and checking the live status of Taxus brevifolia seedlings.

As for angiosperms, some can be frustrating to survey, such as vine maple (Acer circinatum) and blueberry (Vaccinium parvifolium). Initially, I found the presence of maple leaves in the plot quite romantic. However, this species of maple loves sunlight and water; wherever there is a canopy gap or water, they immediately extend their small branches. Even if they are knocked to the ground by fallen deadwood, they will still take root deeply and reach for sunlight. Especially near a small stream in the plot, where both gaps and streams exist, I once spent three hours in the rain searching for each tag. They may not be tall, but I have stood in a gap, looking out at a beautiful coniferous forest, only to find that right underfoot, in a place less than a meter high, there are 10-30 small trees that need to be recorded for their survival.

So, what is our work in the forest? Primarily, it is just to survey tree survival, which is quite simple. However, if a tree dies, we must examine the cause of death (which could be due to fungi, beetle infestation, being crushed by other trees, or animal damage). If a tree with a DBH greater than 10 cm falls to the ground, it is necessary to map and measure it. Jim's team has been conducting research since 2010, with over a decade of data collected annually. The temporal precision and scale of this data are unparalleled globally; most of the ForestGEO data only started in 2016.

Thus, touching each tag and confirming survival status is a crucial part of this work. Recording the factors leading to death, which truly reflects the natural state of mortality, is our goal. After three weeks of work in WFDP, we moved to Yosemite to continue our second site of the summer.

Figure 3. Detecting the mortality factor to Tsuga heterophylla by a hatchet in Wind River Forest Dynamics Plot.

Yosemite Forest Dynamics Plot
Our survey team is conducting a growth measurement survey of every Quercus kelloggii seedling in the Yosemite Forest Dynamics Plot. We're camping at Hodgedon Meadow Campground in Yosemite—a campsite with toilets but no showers—while conducting the survey for two weeks.

The Yosemite Forest Dynamics Plot (YFDP) is a 25.6-ha (320 m × 800 m) plot dominated by sugar pine (Pinus lambertiana) and white fir (Abies concolor), located at an elevation of 1774-1911 m. Climbing from the north to the south of the plot each day involves an elevation gain of 200 m, with additional ups and downs throughout the terrain (not to mention the steep slope leading into the plot). The trees, including snags, can reach heights of 40-50 m, and the DBH of the canopy trees can reach 100-200 cm. The plot was established in 2009-2010, and every tree with a DBH greater than 1 cm has its diameter, species, and location recorded. In 2013, a fire occurred, which fortuitously provided the plot with vegetation dynamics data from both before and after the fire. The post-fire mortality status, along with risk factors and biomass, has already been published.

Figure 4. Yosemite Forest Dynamics Plot.

However, beyond the regeneration and growth of seedlings, other interesting questions remain, such as the impact of soil nutrients and moisture on species distribution. I have observed that most calocedrus (Calocedrus decurrens) prefers to be distributed in areas with valleys, while the shade-tolerant species sugar pine and white fir are found throughout the plot. On the other hand, ponderosa (Pinus ponderosa), a non-shade-tolerant species, is not only scarce in the plot but also shows very limited regeneration in the understory.

As of now, we do not know why this is the case.

Interestingly, compared to the Wind River plot, both plots share similar pioneer large tree species as well as similar shade-tolerant species, and each has specific understory species that survive in a twisted, resilient state. Although the species differ, the roles within the ecosystem are similar, as if they exist in different spaces without knowing each other, yet they occupy similar ecological niches and undergo comparable ecological processes that maintain the stability and balance of their respective ecosystems.

Figure 5. Measurement of Quercus kelloggii in Yosemite Forest Dynamics Plot.

Utah Forest Dynamics Plot
The Utah Forest Dynamics Plot (UFDP) is a 15.32-ha forest dynamics plot located in Cedar Breaks National Monument, Utah, at an elevation of 3039-3109 m. In this forest dynamics plot, in addition to conducting mortality risk and snag surveys, we also need to carry out the third re-census of the plot. This means that in addition to confirming the survival of every woody plant, we also need to measure the diameter at breast height (DBH), which adds to the workload and makes the survey progress even slower.

Unlike the previous two plots (WFDP and YFDP) with trees that reach 50-60 m in height, the trees here, due to their location on the edge of a cliff, are heavily influenced by the wind, resulting in an average height of about 20 m. The tree density is relatively high, and the branch height of the conifers is significantly lower—about 0-1 m. Additionally, these trees, in order to resist beetles and fire, start reproducing at a very low height to quickly increase their population. You can often see a dense ring of small trees within a 2 m radius around a large tree as the trees strive to resist the wind. As a result, when it’s time to start measuring trees, we must navigate through these small trees, constantly maneuvering the measuring tape around various branches. Moving too quickly can lead to injuries, such as a finger being pierced by a branch, which, if you’re unlucky, might end up under your fingernail, inflicting excruciating pain. The dead branches are even more painful.

Figure 6. Utah Forest Dynamics Plot.

Although the tree density is high, the beautiful scenery is not deceiving. When you’re tired from measuring trees, you can look out over the entire canyon. The Cedar Breaks canyon consists of upper volcanic rock and lower sedimentary rock, which, after being uplifted by geological forces, has brought rocks that should have remained at an elevation of 1800 m up to over 3000 m. After being eroded by summer rains and winter snow, the canyon has slowly transformed into a landscape of large and small castles.

Figure 7. Measuring all trees' diameter at breast height in Utah Forest Dynamics Plot.

This plot extends from the edge of the canyon towards a flatter area to the north. The shape of the plot is not a rectangle but rather a triangle cut in half along the diagonal. We usually refer to the edge of the canyon as the cliff. Surveying the cliff typically requires experienced or highly balanced surveyors. For safety, we use radios to say, "Chen-Chia is on the cliff, having a good view here ." A single misstep could be fatal, so every action must prioritize safety. Apart from the cliff, the steep slopes in the plot can also be mentally exhausting. Although these slopes are not as life-threatening as the cliff, measuring a 70 cm tree on a 30-40 degree slope alone can really make you want to cry.

Are there really trees growing in those dangerous places? Yes, there is a strong relationship between species and habitat. The primary reason for this is the canyon. Wind, rain, and snow not only create diverse rock formations on the ground but also lead to varied plant distribution in the canyon. The summer monsoon blows into the canyon from Cedar City to the west, and as the air is uplifted by the terrain, it quickly condenses into water, leading to strong winds and afternoon thunderstorms in the summer (though this year has been unusual). Winter blizzards blow up from the canyon, mixing wind, snow, and sand, testing the plants' resilience. This results in different species distributions across various terrains.

Figure 8. Aspen (Populus tremuloides) forest in Utah Forest Dynamics Plot.

The dominant species in the plot is subalpine fir (Abies bifolia), which can be found in almost every terrain. In flatter areas, there are large expanses of aspen (Populus tremuloides), while limber pine (Pinus flexilis), which prefers slopes and can grow very large, is difficult to measure. Two other spruce species, engelmann spruce (Picea engelmannii) and blue spruce (Picea pungens), have very low branch heights and sharp needles, making measurement particularly challenging. These two species grow in different elevational habitats. The pesky small shrub juniper (Juniperus scopulorum) often pricks you as you pass by, and finding the measurement point and tag within a dense cluster of Juniper can be very frustrating. In the flat area between the cliff and the steep slope, there is a large population of bristlecone pine (Pinus longaeva). This species is very long-lived; the oldest bristlecone pine in the plot is about 1500 years old, and a fallen one is estimated to be 2200 years old. The longevity of these trees in this flat area above the cliff is not only due to the species’ characteristics but also because this area is less prone to fire. The fire cycle in Cedar Breaks is about once every 200 years, and these trees have survived these fires because their location is well-shielded and the environment is moist enough, making them less susceptible to burning and allowing them to live much longer.

We have recorded the growth history of these trees over the past millennium, documenting their growth year by year.

While I was deeply moved and my mind was constantly racing, by the time we were wrapping up the survey, I was eager to finish. Although descending into the plot each day was done with joy, the return journey involved constant uphill climbing at an elevation of 3000 m. On our four-day-on, three-day-off schedule, by the fourth day, I was utterly exhausted. After a whole day of climbing the exhausting plot and measuring trees that felt like torture, the swarms of flies that plagued us in the first two weeks made me long for Nanjenshan. However, this survey made me realize that I’ve been doing aerobic exercise at 3000 m every day for a month, adding a new record to my life: "Achieved continuous daily life and work at an elevation of 3000 m.”

Figure 9. Bristlecone pine (Pinus longaeva) in Utah Forest Dynamics Plot.

Overall, after the three-month field season, the forest and the fieldwork inspired me to do more data analysis to better understand the “DYNAMICS” in the forest and how these species survive over time. I believe these experiences not only broadened my perspective but also contributed more knowledge to long-term science. This is especially relevant in the context of climate change and forest carbon dynamics, which are long-term processes and critical issues in the world today. In the remaining time of my stay, I hope to translate these insights into a scientific manuscript to contribute some knowledge to the world.

Figure 10. Picture with Wind River Forest Dynamics Plot.