Treesearch

The walnut twig beetle, Pityophthorus juglandisBlackman (Coleoptera: Scolytidae), vectors a phytopathogenic fungus, Geosmithia morbidaKolařík et al. (Hypocreales), which causes thousand cankers disease (TCD) in walnut (Juglanssp.) and wingnut (Pterocaryasp., both Juglandaceae) trees. We investigated an early point in disease inception in two walnut species – Juglans californicaS. Wats. and Juglans major(Torr. ex Sitsgr.) Heller – native to riparian forests of the western USA by comparing P. juglandisflight and landing responses to small‐diameter branch sections. Twenty unbaited branch...

Climate change is expected to alter precipitation patterns worldwide, which can have direct effects on streamflow dynamics. In many tropical regions, climate‐driven changes in rainfall are predicted to decrease streamflow and increase flash flooding, but the implications of these changes for stream ecosystem function are poorly understood. We used a rainfall gradient on Hawaii Island that mimics projected changes in rainfall and streamflow in order to estimate how climate change affects nutrient recycling. We measured per‐capita excretion (nitrogen, phosphorus) and egestion rates of three...

Natural regeneration cannot be effectively evaluated by tree density because of spatial heterogeneity typically observed. A proper interpretation of natural regeneration will consider some evaluation of area stocked. However, stocking estimates for natural regeneration are plot-size-dependent. Stocking at the 1-milacre scale is not generally comparable to that on a 4-milacre scale unless a generalized relation with stand density can be established. A generalized relation was first suggested to hold in a paper by Lynch and Schumacher (1941), but this has not been confirmed in subsequent...

Many animals make contingent decisions, such as when and where to feed, as trade-offs between growth and risk when these vary not only with activity and location but also 1) in cycles such as the daily light cycle and 2) with feedbacks due to competition. Theory can assume an individual decides whether and where to feed, at any point in the light cycle and under any new conditions, by predicting future conditions and maximizing an approximate measure of future fitness. We develop four such theories for stream trout and evaluate them by their ability to reproduce, in an individual-based...

A multiyear study of forest-to-alpine ecotones across extensive krummholz zones in whitebark pine (WBP; Pinus albicaulis), Sierra Nevada, California, resolved mean treeline growing season temperature (GST) of 9.3°C, 2.6°C warmer than global thresholds previously described, and mean growing season length of 143 days. Temperatures declined with increasing elevation; GST at the upper krummholz line (8.9°C), however, was 2.2°C warmer than the mean global treeline threshold, suggesting that by thermal criteria these environments should support tree growth. Possible explanations for the warm...

Sometimes the exceptions prove the rule, and lianas show some of the most exceptional stem anatomical variation in plants. New research describes the evolution and development of liana stem anatomical variants, and reveals new rules of woody growth.

A ‘resilient’ forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine‐scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long‐lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that...

Past research on plant-soil feedbacks (PSF), largely undertaken in highly controlled greenhouse conditions, has established that plant species differentially alter abiotic and biotic soil conditions that in turn affect growth of other conspecific and heterospecific individuals in that soil. Yet, whether feedbacks under controlled greenhouse conditions reflect feedbacks in natural environments where plants are exposed to a range of abiotic and biotic pressures is still unresolved. To address how environmental context affects PSF, we conducted a meta-analysis of previously published studies...

We developed a technique for reconstructing annual gravel yields and generated a 55‐year record of gravel transport for the North Fork catchment of the Caspar Creek Experimental Watersheds in Northern California. The technique relies on field data collection including annual surveys of weir pond volumes and suspended sediment measurements, as well as an accounting for settling of suspended sediment and organic matter in the pond. We compared these annual yields to gravel yields predicted by the Wilcock two‐fraction bed load transport model, which we calibrated from measured values at...

Pyrolysis and combustion of a solid fuel representing a vertically oriented leaf of manzanita (Arctostaphylos glandulosa) were computationally investigated. Various fuel moisture content (FMC) values corresponding to four manzanita leaf treatments studied experimentally by others, were considered. The fuel was exposed to an upward stream of hot gases in a computational configuration resembling the experimental setup where leaves were burned. Time evolution of the normalized mass of the leaves was used to validate the simulations against the experimental data. Examining the time history of...