Fall 2024 9 One of the six areas (each about one-tenth acre) bordering progeny population 3 treated to secure natural regeneration of roundleaf birch. The adult trees providing the seeds are shown in the background. (PHOTO BY BUTCH SHAW, NOVEMBER 2023) mechanical removal of competing vegetation, and targeted application of pesticides to control pests. At the end of the 1987 growing season, survival averaged 81 percent among the 20 populations and ranged from 21–99 percent. The 21 percent was an outlier and occurred in a former pasture area, a last-minute substitute for one of the forested areas, demonstrating that birch seedlings do poorly under such highly exposed, not-forested conditions. In 2023, survival averaged 56 percent and ranged from 2–89 percent. Most of the mortality was due to natural causes, including ice damage, deer-antler rubbing, and competition for space. All of the populations, except for the former pasture area, have birches forming closed canopies, with trees on the best sites (i.e., bottomlands and lower slopes bordering small streams) having diameters exceeding 11 in. and heights in excess of 80 ft. (See the photo on page 8). There were no appreciable differences between round-leaf birch and sweet birch in growth rates or mortality. Virtually all of the mortality recorded since 2021 occurred in trees that were relegated to the understory for various reasons, harking back to what occurred in the original population. The establishment of the additional/progeny populations resulted in the USFWS downlisting round-leaf birch from “endangered” to “threatened” in 1994. In keeping with the Recovery Plan and in order to have the species delisted, the next step was to secure natural regeneration in these populations, which had not occurred as of 2021 despite the trees in these populations having produced billions of seeds over several decades. This was not surprising given what we know about the regeneration of birches (demonstrated in the original population in the 1980s), that regeneration will not occur beneath woody vegetation and with a litter layer on the forest floor associated with this vegetation. Moreover, the exposed forest floor must provide cool, moist conditions over several weeks in the spring—conditions provided by moderate temperatures and well-drained mineral soil, decayed logs, or crevices between rocks—given the tiny seeds with little food reserves and a tiny emerging primary root highly susceptible to desiccation. The emerged seedlings in turn require partial shading, typical of small gaps in the forest or burned over areas. Thus, in 2023 we systematically went about deciding on which populations should be treated to secure this regeneration based on site conditions and the production of male (pollen-bearing) and female (fruit and seed-bearing) reproductive structures. Highest preference would be given to high-quality sites that produced an abundance of both pollen and seeds to maximize the genetic diversity of the resulting seedlings and their survival. Five populations were identified as meeting these criteria, but limited funding only allowed one to be treated. Several areas bordering the selected population were cleared of woody vegetation, and the litter layer was removed using mechanized equipment in mid-November prior to dispersal of the tiny wind-blown seeds in December through February (see the photo above). The intent was to mimic natural disturbances, such as fire, in creating the conditions for optimum seed germination and seedling establishment. The number of birch seeds produced by the population in that year was estimated at 5.6 million. In early September 2024 near the end of the first growing season, we sampled the treated areas for birch regeneration, along with other trees species and substrate conditions. The result was an average of 2.1 birch seedlings per square meter, with 15 percent being positively identified as round-leaf birches and the remainder being largely sweet birch with a few perhaps being yellow birch from wild trees bordering the progeny population. However, with interbreeding and genetic-trait dominance of sweet birch, 15 percent is a conservative estimate as some of the trees appearing to be sweet birch undoubtedly contain round-leaf birch genes. Interestingly, this percentage closely approximates the percentage of adult round-leaved trees in the progeny population and more than twice that in the original population. In total, we found 54 round-leaf birch seedlings, which when extrapolated to the area treated as a whole, is 864 seedlings (of 5,968 total birch seedlings). The area treated is capable of supporting 270 trees at reproductive maturity, a number that seems reachable given normal rates of mortality over time. We will resample the treated areas near the end of the 2025 growing season and take measures to maximize seedling survival, as implemented in the population following its establishment in 1984. One limiting factor was the USFS regulation that no treatments could be implemented within 15 ft. of a streambank in order
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