Eric J. Larsen

Trophic cascades among wolves, elk and aspen on Yellowstone National Park's northern range

Quaking aspen (Populus tremuloides) biomass has declined in Yellowstone National Park (YNP) in the past century. We installed permanent belt transects (plots) for long-term monitoring of aspen stands both within and outside of established wolf pack territories on YNP’s northern range to determine if reintroduced wolves are influencing elk browsing patterns and aspen regeneration through a trophic cascades interaction. Wolves may have an indirect effect on aspen regeneration by altering elk movements, browsing patterns, and foraging behavior (predation risk effects). Elk pellet groups, aspen sucker heights, and the percentage of browsed suckers were the variables used to measure differences in aspen stands in high and low wolf-use areas of the northern range. The aspen stands in the high wolf-use areas had significantly lower counts of elk pellet groups in the mesic upland steppe and the combined mesic upland steppe and riparian/wet meadow habitat types. Based on our pellet group results, it appears that elk foraging behaviors may have been altered by the increased risk of predation due to the reintroduction of the wolf. In the riparian/ wet meadow habitat type, mean aspen sucker heights were significantly higher in the high wolf-use areas than in the low wolf-use areas. The percentage of browsed suckers in high and low wolf-use areas showed no significant differences in any of the habitat types. Considering the high browsing pressure in YNP aspen stands, it is uncertain whether the taller aspen suckers measured in the high wolf-use areas will eventually join the aspen overstory. These permanent plots represent a valuable baseline data set to assess any current and future aspen regeneration responses to the reintroduction of wolves in YNP. # 2001 Elsevier Science Ltd. All rights reserved.

Historic aspen recruitment, elk, and wolves in northern Yellowstone National Park, USA

We conducted an analysis of aspen (Populus tremuloides) overstory recruitment on the northern range of Yellowstone National Park (YNP) using information provided in a monograph published by Warren (Warren, E.R., 1926. A study of beaver in the Yaney region of Yellowstone National Park, Roosevelt-Wildl. Ann. 1, 1‐191), increment cores collected from riparian aspen stands in 1998, and an extensive random sample of aspen increment cores collected over YNP’s entire northern range in 1997 and 1998. We summarized aspen size classes reported by Warren and estimated overstory origination dates of the stands he described using a linear regression based on our riparian aspen diameter/age relationship. Applying our regression results to Warren’s diameter measurements, we predicted that the stands measured by Warren contained aspen that originated between approximately 1751 and 1920. The random set of aspen increment cores were used to analyze the age distribution of the current aspen overstory on YNP’s northern range. These increment core data showed that approximately 10% of the current overstory aspen originated before 1871, 85% between 1871 and 1920, and 5% after 1921. Based upon our analysis of the Warren data and our aspen increment cores, we conclude that successful aspen overstory recruitment occurred on the northern range of YNP from the middle to late 1700’s until the 1920’s, after which it essentially ceased. Rocky Mountain Elk (Cervus elaphus) browsing has been identified as significantly impacting aspen overstory recruitment on YNP’s northern range. We hypothesized why elk browsing has a diAerent influence on aspen now than it did historically. We discussed several potential social and ecological factors and hypothesize that a main factor is YNP’s loss of significant predator/prey relationships in the early 1900’s, especially the influence of gray wolves (Canis lupus). We found that aspen overstory recruitment ceased during the same years that wolves, a significant source of elk predation, were removed from YNP. Wolves may positively influence aspen overstory recruitment through a trophic cascades eAect by reducing elk populations, modifying elk movement, and changing elk browsing patterns on aspen. # 2000 Elsevier Science Ltd. All rights reserved.

Aspen age structure in the northern Yellowstone ecosystem: USA

Abstract Age-structure analysis of aspen (Populus tremuloides) was conducted on Rocky Mountain elk (Cervus elaphus) winter range in the northern Yellowstone area by collecting increment cores from aspen trees in Yellowstone National Park, the Gallatin National Forest, and the Sunlight/Crandall area of the Shoshone National Forest. Our goal was to compare aspen age structure for elk winter range in the park with age structures developed for elk winter range in the national forests. We collected increment cores from aspen in three diameter size classes and three aspen habitat types (xeric, mesic, and scree). A special effort was made to collect increment cores from the relatively rare scree habitat type, since scree forms a “natural exclosure” where browsing pressure on aspen is reduced. The age structure of aspen in Yellowstone was significantly different from the age structures of aspen in either of the national forest areas (P

Recovering aspen follow changing elk dynamics in Yellowstone: evidence of a trophic cascade?

To investigate the extent and causes of recent quaking aspen (Populus tremuloides) recruitment in northern Yellowstone National Park, we measured browsing intensity and height of young aspen in 87 randomly selected aspen stands in 2012, and compared our results to similar data collected in 1997-1998. We also examined the relationship between aspen recovery and the distribution of Rocky Mountain elk (Cervus elaphus) and bison (Bison bison) on the Yellowstone northern ungulate winter range, using ungulate fecal pile densities and annual elk count data. In 1998, 90% of young aspen were browsed and none were taller-than 200 cm, the height at which aspen begin to escape from elk browsing. In 2012, only 37% in the east and 63% in the west portions of the winter range were browsed, and 65% of stands in the east had young aspen taller than 200 cm. Heights of young aspen were inversely related to browsing intensity, with the least browsing and greatest heights in the eastern portion of the range, corresponding with recent changes in elk density and distribution. In contrast with historical elk distribution (1930s-1990s), the greatest densities of elk recently (2006-2012) have been north of the park boundary (approximately 5 elk/km2), and in the western part of the range (2-4 elk/km2), with relatively few elk in the eastern portion of the range (<2 elk/km2), even in mild winters. This redistribution of elk and decrease in density inside the park, and overall reduction in elk numbers, explain why many aspen stands have begun to recover. Increased predation pressure following the reintroduction of gray wolves (Canis lupius) in 1995-1996 played a role in these changing elk population dynamics, interacting with other influences including increased predation by bears (Ursus spp.), competition with an expanding bison population, and shifting patterns of human land use and hunting outside the park. The resulting new aspen recruitment is evidence of a landscape-scale trophic cascade in which a resurgent large carnivore community, combined with other ecological changes, has benefited aspen through effects on ungulate prey.

Notes on New Zealand mammals 8. Predation on nesting southern royal albatrosses Diomedea epomophora by a New Zealand sea lion Phocarctos hookeri

Abstract This note documents unusual predation of southern royal albatrosses Diomedea epomophora on land by an individual New Zealand sea lion Phocarctos hookeri. During a survey of albatross nests on Campbell Island in the New Zealand sub‐antarctic in January 2005, 128 corpses of adult albatrosses were found at or near nests within a 230 ha area. Flattened vegetation and flipper prints near the nests suggested sea lion predation, and subsequently a male sea lion was found near a line of freshly killed birds. The predation rate was estimated to be at least seven birds per day over a number of weeks; similar skeletal remains from the previous year were observed in a neighbouring area. The impact of one threatened species on another can be a dilemma for conservation managers. In this case, apparently only one male sea lion was involved and, because of the ongoing impact to the albatross population, permission was obtained to cull that individual on 17 January 2005. No further incidents were observed over the following three seasons (2006–08).

Urban forest assessment in Bangkok, Thailand

ABSTRACT The objective of this study was to conduct an urban forest assessment for Bangkok and pilot the appropriateness of adapting the i-Tree Eco International software in Thailand. Urban forest structure, function, and value were estimated from 184 stratified random sample plots. A total 48 tree species were encountered and the three most common that contributed 34.1% of total tree population were Polyalthia longifolia Sonn. (15.7%), Mangifera indica L. (13.0%), and Pithecellobium dulce (Roxb.) Benth. (5.4%). The majority of trees (approximately 70%) were <23 cm in diameter. An estimated 2.5 (0.4 SEM) million trees with a canopy cover of 8.6% (1.3 SEM) exist in the Bangkok study area. These trees store an approximate total of 309,700 (73,726 SEM) metric tons of carbon and sequester 16,271 (2965 SEM) metric tons of CO2 annually. Additional research is needed to develop functional relationships for urban trees in Thailand to overcome a current limitation for using i-Tree Eco in Thailand to estimate structural and functional value of urban forests. Study results also provide land-use planners information on the current urban forest resource and the potential for future urban greening.