Initial Effects of Brush Cutting and Shoot Removal on Willow Browse Quality

Abstract

We examined the initial effects of brush cutting (removal of all aboveground biomass), as well as clipping (removal of current annual shoots) and ungulate browsing (collectively referred to as shoot removal) on the morphology and nutrient quality of Scouler's willow (Salix scouleriana J. Barratt ex Hook.) for ungulates on sites 2 and 4 years after brush cutting. We specifically assessed changes in the biomass, tannin content, digestible energy, and digestible protein of shoots from brush-cut willows relative to shoots of uncut willows to determine how browse plants respond to this form of vegetation management. In winter, the resprouted current annual shoots of willows that had been brush cut were larger in mass and lower in digestible protein than shoots of uncut willows for at least 4 years after brush cutting. Shoots of brush-cut willows were also lower in tannin and digestible energy than the shoots of uncut plants for two winters after brush cutting. In the second winter after brush cutting, shoot biomass decreased and tannin content increased with increasing shoot removal during the previous winter. In the fourth winter after brush cutting, shoot mass increased and digestible energy decreased in shoots with greater shoot removal. Nutrient quality was otherwise unaffected by the amount of shoot removal during the previous winter. Because of the occasional importance of site effects in this study, we recommend that long-term studies maximize the number of sampled sites. Because brush cutting alters the quality of regenerating browse and can affect how ungulates utilize such browse for several years after brush cutting, we further recommend that forest vegetation managers consider potential impacts of brush cutting on ungulate winter range. Resumen Examinamos los efectos iniciales del corte de arbustos (remoción de toda la biomasa aérea), corte (remoción del crecimiento del añ o en curso), y el ramoneo por ungulados (referidos colectivamente como remoción de ramas) sobre la morfología y calidad de nutrientes del Scouler's willow (Salix scouleriana J. Barratt ex Hook.) para los ungulados en sitios con 2 y 4 añ os posteriores al corte de arbustos. Específicamente evaluamos los cambios de la biomasa, contenido de taninos, energía y proteína digestibles de las ramas de ''Scouler's willow'' con corte de arbustos en relación a ramas de ''Scouler's willow'' sin corte de arbustos (sin corte) para determinar como las plantas responden a esta forma de manejo de la vegetación. En invierno, las ramas rebrotadas en el añ o en curso de plantas de ''Scouler's willow'' que habían recibido corte de arbusto fueron superiores en biomasa y más bajas en proteína digestible que las ramas sin corte, al menos cuatro añ os despue´s del corte de arbustos. Durante los dos inviernos posteriores al corte de arbustos, las ramas de ''Scouler's willow'' con corte de arbusto tambie´n presentaron contenidos más bajos de taninos y energía digestible que las ramas de plantas sin corte. En el segundo invierno despue´s del corte, la biomasa de las...

Moose–tree interactions: rebrowsing is common across tree species

“…Although some other studies have shown a decrease in shoots size in response to winter browsing [7, 33], most previous studies have shown increases in shoot size [9, 10, 23, 26, 32, 34], or needle size in pine [24], which we did not measure. The discrepancy may have arisen because we studied multiple species in natural forest stands with low productivity and recurring browsing, whilst most other studies focused on only one species in one season, and, in some cases, were simulated browsing experiments.…”

“…However, the observed preference for trees with high accumulated browsing could be caused by increased nutrient concentration or reduced concentration of plant secondary compounds. Previous studies have found that the carbon demands of regrowth reduces production of secondary defense compounds in previously browsed trees [7, 16, 28, 34], while increased nutrient concentration can occur because of the reduced number of meristems [18, 19]. Moose selection of winter browse is known to be negatively related to the concentration of specific phenolics in Salix phylicifolia , and concentrations were lower in previously browsed shoots [63].…”

“…Plant responses to herbivory are context dependent, varying with plant species [5], competition [6], season [7–9], time since previous browsing [10] and frequency and intensity of browsing [5, 11], as well as the plant part browsed [8] and habitat productivity [5, 10]. Avoidance strategies include having thorns and small leaves, and responding to herbivory by increasing these traits to reduce intake rate and bite size, thus deterring herbivory on the same plant [12].…”

“…Browsing may affect the concentration of nutrients and secondary compounds in shoots. Increases in structural carbohydrates may be required to support the growth of large compensatory shoots but reduces their digestibility [7]. In contrast, regrowth from browsed shoots in willow ( Salix phylicifolia ) was less toxic and more digestible than growth from unbrowsed shoots [34].…”

Biomass Harvest from Natural Willow Rings around Prairie Wetlands

“…Differences between biomass regrowth for the Bio-Baler and hand-prune treatments were statistically significant for S. discolor but not S. eriocpehala or S. petiolaris. Other studies have shown that brush cutting willow resulted in production of large stems and vigorous vegetative regeneration [21]. The production of large stems is a growth strategy employed by several Salix species [20] especially where competition for canopy occupancy is intense [22], which is typical of the moist, nutrient-rich areas on the periphery of wetlands.…”