2 Environmental Forestry Research, Weyerhaeuser Company, Tacoma, Washington 98422 USA Abstract. Although most temperate forests are actively managed for timber production, few data exist regarding the long-term effects of forest management on understory plant communities. We investigated the responses of understory communities to a factorial com- bination of silvicultural-thinning and nutrient-addition treatments maintained for 12-16 yr in a set of 21-27 yr old Douglas-fir (Pseudotsuga menziesii) plantations. The four thinning levels span those used operationally (final stem densities of 494-1680 trees/ha); the two fertilization levels included a control and N addition in the form of urea at ;60 kg N·ha 21 ·yr 21 , about twice the dosage used operationally. Understory vegetation cover showed significant effects of thinning, with the highest thinning level resulting in the highest observed cover values. However, in some cases low levels of thinning resulted in a reduction in understory cover compared to unthinned con- trols. Understory vegetation declined dramatically in response to urea fertilization, with up to a 10-fold drop in herb-layer cover in unthinned stands. Species richness showed a simpler response to treatments, increasing in response to thinning, but decreasing in response to fertilization. Examination of species-area relationships indicated that effects of thinning and fertilization on species richness were similar across the range of spatial scales examined. Tree canopy cover, assessed by means of hemispherical photograph analysis, increased with fertilization, and estimated understory light levels decreased with fertilization, but neither showed a significant response to thinning at the time of measurement (12-16 yr after tree removal). Thus, treatment effects on understory cover and species richness were not a simple function of canopy cover or estimated light availability. Rather, there was a weak positive relationship between estimated understory light flux and vascular plant cover and diversity in nonfertilized plots, and no such relationship in fertilized plots. The lack of correspondence between treatment effects on canopy cover and understory vegetation may be due to time lags in understory response to changes in canopy cover or to treatment effects not mediated by light availability, such as physical disturbance during thinning operations and toxicity responses following application of urea fertilizer. Species-specific responses to treatments were in part predictable as a function of plant life-form and edaphic association: species affinity for high soil moisture was the best predictor of fertilization responses, while life-form was the best predictor of thinning responses, with ferns and graminoids showing the largest positive responses to thinning. The successional status and stature of understory plant species were not significantly related to treatment responses. In sum, our results indicate that silvicultural thinning and fertilization can have large effects on understory plant diversity and community composition. However, such effects were not a simple function of understory light levels, and conventional ''functional types'' were of only limited value in predicting species-specific responses to silvicultural treatments.

https://faculty.washington.edu/chalpern/Thomasetal1999.pdf

Plant diversity in managed forests: understory responses to thinning and fertilization

The influence of disturbance and habitat on the presence of non-native plant species along transport corridors.

Variations in vertical and horizontal forest structure are often difficult to quantify as field-based methods are labour intensive and passive optical remote sensing techniques are limited in their capacity to distinguish structural changes occurring below the top of the canopy. In this study the capacity of small footprint (0.19 cm), discrete return, densely spaced (0.7 hits/m−2), multiple return, Light Detection and Ranging (LiDAR) technology, to measure foliage height and to estimate several stand and canopy structure attributes is investigated. The study focused on six Douglas-fir [Pseudotsuga menziesii spp. menziesii (Mirb.) Franco] and western hemlock [Tsuga heterophylla (Raf.) Sarg.] stands located on the east coast of Vancouver Island, British Columbia, Canada, with each stand representing a different structural stage of stand development for forests within this biogeoclimatic zone. Tree height, crown dimensions, cover, and vertical foliage distributions were measured in 20 m × 20 m plots and correlated to the LiDAR data. Foliage profiles were then fitted, using the Weibull probability density function, to the field measured crown dimensions, vertical foliage density distributions and the LiDAR data at each plot. A modified canopy volume approach, based on methods developed for full waveform LiDAR observations, was developed and used to examine the vertical and horizontal variation in stand structure. Results indicate that measured stand attributes such as mean stand height, and basal area were significantly correlated with LiDAR estimates (r
 2 = 0.85, P < 0.001, SE = 1.8 m and r
 2 = 0.65, P < 0.05, SE = 14.8 m2 ha−1, respectively). Significant relationships were also found between the LiDAR data and the field estimated vertical foliage profiles indicating that models of vertical foliage distribution may be robust and transferable between both field and LiDAR datasets. This study demonstrates that small footprint, discrete return, LiDAR observations can provide quantitative information on stand and tree height, as well as information on foliage profiles, which can be successfully modelled, providing detailed descriptions of canopy structure.

/pdf/estimating-canopy-structure-of-douglas-fir-forest-stands-4086u9eqzw.pdf

Estimating canopy structure of Douglas-fir forest stands from discrete-return LiDAR

Heavy metal adsorption properties of a submerged aquatic plant (Ceratophyllum demersum).

https://sites.ualberta.ca/~scottn/documents/NielsenEtAl2004a.pdf

Grizzly bears and forestry I: Selection of clearcuts by grizzly bears in west-central Alberta, Canada

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