Treesearch

Aim Landscape and climatic change are promoting range shifts, potentially leading to competition and hybridization between formerly isolated species. However, density-dependent interactions can impede the timely identification of associated conservation problems. The barred owl's expansion into the spotted owl's range provides a natural experiment to test for density dependence in niche overlap and hybridization in the early versus late stages of a biological invasion, thus illuminating an important biogeographical process. Location Pacific Northwest, USA to the northern Sierra Nevada,...

Pyrodiversity or variation in spatio-temporal fire patterns is increasingly recognized as an important determinant of ecological pattern and process, yet no consensus surrounds how best to quantify the phenomenon and its drivers remain largely untested. We present a generalizable functional diversity approach for measuring pyrodiversity, which incorporates multiple fire regime traits and can be applied across scales. Further, we tested the socioecological drivers of pyrodiversity among forests of the western United States. Largely mediated by burn activity, pyrodiversity was positively...

Sierra Nevada mixed-conifer forests have undergone significant changes in structure and composition and are increasingly vulnerable to altered disturbance regimes and climate-related extreme events. Fuel reduction treatments, including thinning and follow-up surface fuel treatments, can reduce this vulnerability by creating forest structural and woody fuel conditions that not only allow forest stands to mitigate wildfire, but also alleviate individual tree stress. However, direct observations that quantify these longer-term effects are lacking. This study compares observed changes in...

As a result of climatic warming, tree species ranges are generally expected to move upslope in elevation. Although this upward range migration is likely determined principally by temperature, other factors such as habitat and soil moisture availability contribute to a species’ ability to establish in new areas. Throughout the montane ecosystems of the western US, effective drying is predicted, resulting from increasing temperatures and potentially reduced precipitation. The tree species that can better establish in these future high-elevation forests will likely expand their ranges while...

A complex landscape lies on an alpine plateau in the high Sierra Nevada, California, and comprises spatially organized physical and ecological features that interact to create a unique ecosystem. At the upslope end a tree-limited ribbon forest of whitebark pines grows on the crest of a short, steep slope, which is the only deformation on the otherwise flat plateau. A long-persistent snowbank forms on the slope in the lee of the ribbon forest; meltwater provides moisture to support a productive wet meadow just below. Below the meadow is a narrow, linear “rampart” comprising large sorted...

1. The complex effects of global environmental changes on ecosystems result from the interaction of multiple stressors, their direct impacts on species and their indirect impacts on species interactions. Air pollution (and resulting depletion of soil base cations) and biotic invasion (e.g. beech bark disease [BBD] complex) are two stressors that are affecting the foundational tree species of northern hardwood forests, sugar maple and American beech, in northeastern North America. 2. At the Hubbard Brook Experimental Forest in New Hampshire, a watershed-scale calcium (Ca) addition in 1999...

Non-native invasive plants often outcompete native species under high resource availability. Restoration techniques that lower resources may, therefore, create favorable conditions for resource conservative native species over resource exploitative invasive species. Research on this topic has focused on temperate grass and forb-dominated ecosystems and has rarely been tested for woody species or tropical vegetation. We evaluated growth, resource-use efficiency (RUE), ecophysiology, and competition (i.e. a relative interaction index based on biomass) of four woody native and two dominant...

Reducing soil nutrient availability has been proposed as a strategy to favor native vs. non-native invasive plant species and represents a potential alternative to traditional manual removal or chemical control methods. We implemented a field experiment in invaded dry and wet montane Hawaiian ecosystems to test responses of soil and dominant plant species to three soil nutrient treatments (Control = no nutrient manipulation; Carbon = C substrate added to reduce nutrients; Fertilizer = fertilizer added to increase nutrients) and two non-native plant treatments (Weeds removed; Weeds present)...

Bedrock weathering regulates nutrient mobilization, water storage, and soil production. Relative to the mobile soil layer, little is known about the relationship between topography and bedrock weathering. Here, we identify a common pattern of weathering and water storage across a sequence of three ridges and valleys in the sedimentary Great Valley Sequence in Northern California that share a tectonic and climate history. Deep drilling, downhole logging, and characterization of chemistry and porosity reveal two weathering fronts. The shallower front is ∼7 m deep at the ridge of all three...

Mycorrhizae alter global patterns of CO2fertilization, carbon storage, and elemental cycling, yet knowledge of their global distributions is currently limited by the availability of forest inventory data. Here, we show that maps of tree-mycorrhizal associations (hereafter “mycorrhizal maps”) can be improved by the novel technology of imaging spectroscopy because mycorrhizal signatures propagate up from plant roots to impact forest canopy chemistry. We analyzed measurements from 143 airborne imaging spectroscopy surveys over 112,975 individual trees collected across 13 years. Results show...