Integration of trees with forage and livestock production (silvopastoralism) could increase productivity of forest and range resources in western North America. Pre-commercial thinning (PCT) and fertilization are two silvicultural practices that could enhance silvopasture. We tested two hypotheses (H): that yield and quality of forage would be enhanced by (H 1 ) heavy thinning (PCT) to ≤1000 stems·ha −1 and by (H 2 ) repeated fertilization in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands. Study areas were located near Summerland and Kelowna in south-central British Columbia, Canada. Each study area had six treatments: three pairs of stands thinned to densities of ϳ500 (low), ϳ1000 (medium), and ϳ2000 (high) stems·ha −1 with one stand of each pair fertilized five times at 2 year intervals. Forage yield was enhanced by PCT, but only within fertilized stands. Forage quality was generally not affected by PCT, except for crude protein of herbs that was poorer in heavily thinned stands. Fertilization tended to enhance forage yield and quality in the heavily thinned stands. Significantly improved quality of pinegrass (Calamagrostis rubescens Buckley) indicated that repeated fertilization, coupled with heavy thinning, may extend the period when high-quality forage is available, thereby allowing for increased stocking densities of cattle (Bos taurus L.) and perhaps extending the grazing season into the fall.Résumé : L'intégration d'arbres à la production de fourrage et de bétail (sylvopastoralisme) pourrait augmenter la productivité des ressources forestières et des pâturages dans l'ouest de l'Amérique du Nord. L'éclaircie précommerciale (EPC) et la fertilisation sont deux pratiques sylvicoles pouvant accroître le sylvopâturage. Nous avons testé les hypothèses (H) que la production et la qualité du fourrage seraient améliorées par une éclaircie forte (EPC) laissant moins de 1000 tiges·ha −1 (H 1 ) et par des fertilisations répétées dans des peuplements de pin tordu latifolié (Pinus contorta var. latifolia Engelm.) (H 2 ). Les aires d'étude étaient situées près de Summerland et de Kelowna, dans le centre-sud de la Colombie-Britannique, au Canada. Chaque aire d'étude comprenait six traitements : trois paires de peuplements éclaircis à des densités approximatives de 500 (faible), 1000 (modérée) et 2000 (forte) tiges·ha −1 dont un peuplement de chaque paire a été fertilisé cinq fois à intervalles de deux ans. La production de fourrage a été améliorée par l'EPC, mais seulement dans les peuplements fertilisés. La qualité du fourrage n'a généralement pas été influencée par l'EPC, sauf pour les protéines brutes des herbacées dont la quantité était moins élevée dans les peuplements fortement éclaircis. La fertilisation tendait à augmenter la production et la qualité du fourrage dans les peuplements fortement éclaircis. L'augmentation significative de la qualité du calamagrostis rougissant (Calamogrostis rubescens Buckley) indique que la fertilisation répétée, jumelée à une éclaircie forte, peut allo...

The effects of cattle ( Bos taurus L.) grazing on upland plant communities in forested rangelands are poorly understood. Cattle interactions with plant communities were studied in intensively managed (precommercially thinned (PCT) and repeatedly fertilized) silvopasture systems in young lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forests. We investigated the response of plant community abundance and diversity to cattle grazing and how these responses were affected by PCT and repeated fertilization. The study was conducted inside and outside cattle exclosures over 10 years in two regional replicates in south-central British Columbia, Canada. PCT and repeated fertilization increased both the amount and quality of forage. Effects of cattle grazing on plant community abundance and diversity were variable and significantly influenced by the nutrient status of the site. In fertilized stands, cattle grazing increased species richness and diversity, particularly for the herb layer, although these treatment effects often took several years to be expressed. In unfertilized stands, cattle grazing did not significantly reduce herb or shrub volumes; however, species richness and, to a lesser extent, diversity of the shrub layer declined. In a landscape context, management strategies for silvopasture should promote heterogeneity for conservation of plant diversity through a variety of grazing pressures, as well as forest enhancement treatments such as PCT and repeated fertilization.