Long‐term effects of defoliation: incomplete recovery of a New Zealand alpine tussock grass, Chionochloa pallens, after 20 years

Abstract

Summary1. Chionochloa pallens, a New Zealand low alpine tussock grass, is an important food plant of the takahe Porphyrio hochstetteri, a rare endemic¯ightless rail. Introduced red deer Cervus elaphus compete with the takahe for this resource. 2. The experiment reported here measured the long-term rate of recovery of the grass after simulated severe deer grazing by means of a single clipping in 1977. Biomass, tillering and levels of six mineral nutrients (N, P, K, Ca, Mg, Na) were measured in tussocks 20 years after the clipping was carried out. Growth was compared between treatments (control vs. defoliated) and with a previous sampling in 1986. 3. Even after two decades, recovery was incomplete. Tiller dry weights and size (length and basal diameter) and tussock dry weight per unit area remained signi®-cantly depressed in the clipped plots (by about 30%) compared with the control plots. 4. Other features, such as biomass allocation to plant parts and mineral concentrations in tissues, no longer showed many signi®cant dierences between the treated and control plots, indicating continued convergence towards the controls. 5. However, at the present rate of recovery it is estimated that the eects of a single severe defoliation on biomass (per tiller and per unit area) will persist for nearly three decades. 6. As C. pallens is known to be a relatively fast-growing species of Chionochloa, recovery of other native snow tussock grasses in these alpine habitats damaged by deer grazing is likely to take even longer.

Effects of Root-trimming and Cutting-heights on Growth Performance of Potted Native Warm-season Grasses

“…The treatment differences in forage biomass were actually consistent with reported negative effects of severe defoliation on plant growth (Ferraro & Oesterheld, 2002 warm-season grasses by over 60% (Mullahey, 1990;Forwood & Magai, 1992). This is so because proportions of photosynthetic tissue retained on defoliated plants usually influence how quickly they repair their damaged tissues (Oesterheld & McNaughton, 1991;Lee et al, 2000;Ferraro & Oesterheld, 2002). With severe defoliation, plants lack sufficient residual leaves to supply enough carbon for maintenance and regrowth.…”

Yield Response of Native Warm-Season Forage Grasses to Harvest Intervals and Durations in Mixed Stands

“…It also implies that plants in Y108 plots exploited relatively smaller soil volumes for nutrients and water. Similar yield reductions due to prior defoliation regimes have also been reported [18,22]. Above ground biomass differences between previously harvested areas and those being harvested for the first time may also vary [29] due to other factors like species composition, weather, and soil fertility [30].…”

“…First year of production (Y109) yields averaged 3596 kg ha , respectively, (Figure 2a). Usually, effects of defoliation on stand performance, regardless of the harvest interval, do impact the succeeding post-season growth [22]. Regrowth of defoliated grasses usually has smaller tiller size and less tiller dry weight than undefoliated ones [17,22,26].…”

“…Because of differences in species morphological adaptations, plant growth responses to defoliation vary [20] and are reportedly influenced by their retained proportions of photosynthetic tissues [17,21,22]. Recovery also depends on the time interval between successive defoliations [17], precipitation, and duration of repeat defoliations [18,23].…”

Review on the Geographic and Elevational Distribution of the Mountain Long-Eared Bat Plecotus Macrobullaris, Completed by Utilising a Specific Mist-Netting Technique

“…Nevertheless, in the communities of the highest alpine zone, grazing pressure is usually not very high and the plant communities are adapted to grazing by ibex and chamois (Körner 1999). Some alpine species are tolerant to high levels of herbivory (Diemer 1996, Lee et al 2000. In addition, the impacts of herbivores on mountain grasslands are more a consequence of the spatial distribution of fertilization and trampling than an effect of defoliation (Erschbamer et al 2003).…”