Treesearch

Nonlinear regression is increasingly used to develop allometric equations for forest biomass estimation (i.e., as opposed to the raditional approach of log-transformation followed by linear regression). Most statistical software packages, however, assume additive errors by default, violating a key assumption of allometric theory and possibly producing spurious models. Here, we show that such models may bias stand-level biomass estimates by up to 100 percent in young forests, and we present an alternative nonlinear fitting approach that conforms with allometric theory.

Successfully addressing the multitude of stresses influencing forest catchments, their native biota, and the vital ecological services they provide humanity will require adapting an integrated view that incorporates the full range of natural and anthropogenic disturbances acting on these landscapes and their embedded fluvial networks. The concepts of dendritic networks, disturbance domains, the stream continuum, and hydrologic connectivity can facilitate this integration. Managing catchments based on these combined concepts would better maintain all the components of watersheds and the...

Mechanical mastication converts shrub and small tree fuels into surface fuels, and this method is being widely used as a treatment to reduce fire hazard. The compactness of these fuelbeds is thought to moderate fire behaviour, but whether standard fuel models can accurately predict fire behaviour and effects is poorly understood. Prescribed burns were conducted in young ponderosa pine (Pinus ponderosa Laws.) forests at two sites in northern California where the midstorey layer dominated by shrubs had been masticated. Surface fuels were raked from the base of a subset of trees before...

Colonisation of Notholithocarpus densiflorus (Hook. and Arn.) Rehder tissues by Phytophthora ramorum Werres, De Cock & Man in't Veld is not well understood. The pathogen is able to colonise nearly all tissues of this host but it is unclear how a tree is ultimately killed. In this research, P. ramorum infected N. densiflorus bark tissues were examined using various microscopic techniques to better understand the role of bark infection in killing a tree. Host responses to infection were detected by histological methods in conjunction with examining P. ramorum colonisation. Results of this...

1. Spatial variation in species composition within and among communities may be caused by deterministic, niche-based species sorting in response to underlying environmental heterogeneity as well as by stochastic factors such as dispersal limitation and variable species pools. An important goal in ecology is to reconcile deterministic and stochastic perspectives of community assembly and to assess the contribution of each class of processes to community dynamics and structure.2. We present an 8-year field experiment of grassland secondary succession that documents plant community differentia...

Federal agencies have a responsibility to American Indian tribes and tribal communities for the management and protection of tribal trust resources for reservation and public lands within tribes’ ancestral lands and territories (Pevar 2002, Wilkinson and The American Indian Resources Institute 2004). The Indian Self Determination and Education Assistance Act (1975: Public Law 93-638) also provides mechanisms for establishing working relationships regarding the management of Federal programs (e.g., compact or cooperative agreements). The Federal Land Policy and Management Act (1976: Public...

Historical logging, fire suppression, and an invasive pathogen, Cronartium ribicola, the cause of white pine blister rust (WPBR), are assumed to have dramatically affected sugar pine (Pinus lambertiana) populations in the Lake Tahoe Basin. We examined population- and genetic-level consequences of these disturbances within 10 sugar pine populations by assessing current population structure and trends for 1129 individuals, genetic diversity for 250 individuals, and frequency of WPBR-resistance for 102 families. Logging had occurred in 9 of 10 sites and fire suppression was evident in all...

Motions of particles in fields characterized by real-valued potential functions, are considered. Three particular expressions for potential functions are studied. One, U, depends on the ith particle’s location, ri(t) at times ti. A second, V , depends on particle i’s vector distances from others, ri(t) − rj(t). This function introduces pairwise interactions. A third, W, depends on the Euclidian distances, || ri(t) − rj(t) || between particles at the same times, t. The functions are motivated by classical mechanics. Taking the gradient of the potential function, and adding a Brownian term...