Deer Grazing Research Articles

特集「シカの採食圧による植生被害防除と回復」

特集「シカの採食圧による植生被害防除と回復」

特集「シカの採食圧による植生被害防除と回復」 ナラ枯れ被害跡地での更新に与えるシカ食害の影響

岐阜県西濃地域では，ナラ類の枯損による林冠ギャップ下であっても，植生の発達がみられない箇所が存在する。西濃地域は以前からニホンジカが生息し，生息密度も高いことから，シカの採食によって森林の更新が阻害されている可能性が考えられた。そこで，シカ柵を設置し，植生の変化を観察した。調査地は，岐阜県揖斐郡池田町のナラ枯れによって発生した林冠ギャップのうち4 カ所とした。シカ柵設置直後の各調査地の植被率合計は約6 ～23％ であった。柵外の方形区では，シカの嗜好性の低いシダ類以外の植被率の増加はほとんどみられなかった。柵内の方形区では植被率合計は増加し(52～138％)，特にキイチゴ類，ススキの増加が顕著であった。調査地4 では，表土流亡によって，実生の定着が妨げられている可能性が考えられた。高木性種は成長が比較的遅く，成長の早い低木生種などの下層に存在することが多いため，低木性種などが繁茂することにより，高木性種の侵入・生育が妨げられる可能性がある。これらのことから，この林分において，高木性種による速やかな更新を望む場合には，シカ柵を設置し，表土流亡の抑止や刈り出しなどの更新補助作業を実施する必要があると考えられた。

特集「シカの採食圧による植生被害防除と回復」 松くい虫被害を受けた島根半島弥山山地の天然林の再生と管理にニホンジカが与える影響

ニホンジカが生息している島根半島西部の弥山山地において，松くい虫被害跡地の再生方法や今後の森林管理方法を検討するため，16 ヶ所の植生を調査した。高・亜高木は常緑樹29 種，落葉樹42 種が確認された。このうち，出現本数や胸高断面積合計で高い値を示したのはアブラギリ，ヤブツバキ，シロダモ，アカマツであった。低木の総合優占度ではヤブツバキ，シロダモが高・亜高木と同様に高い値を示した。したがって，これらの樹種はシカが生息している状況でも本地域で生育が可能な樹種であると考えられる。一方，アブラギリ，アカマツは低い値であった。このことから，本地域の植生は，シカ防護柵など人為的にシカの排除を行わない限り，ヤブツバキやシロダモを主体とする多様性の低い常緑樹林に移行すると考えられた。

特集「シカの採食圧による植生被害防除と回復」

治山事業が対象とする山腹崩壊箇所や森林整備箇所でもシカ被害が問題となっている。そのため，シカ被害対策を講じることが多いが，その効果については明らかではない場合が多い。そこで，治山事業におけるシカ被害対策の現状を把握し課題を明らかにするために，各都道府県へアンケート調査を実施した。また，対策工の中で採用例が多い侵入防止柵の変状調査を行った。アンケート調査の結果，対策には侵入防止柵が多く使用されていることが分かった。また，治山事業対象地は急峻地や奥山であることが多く，維持管理を行うことが難しい等の課題が明らかとなった。このことから，治山事業に対応した侵入防止柵の開発や維持管理面の改善が必要であることが示唆された。また，侵入防止柵の変状調査を行った結果，治山事業特有の問題である落石や土砂の堆積が原因で変状が発生していることが分かった。そして，今回の調査で比較的軽微な変状の場合は補修部材・道具類を用いずに容易に補修を行うことができることを確認した。

特集「シカの採食圧による植生被害防除と回復」

シカの高密度化による植生への影響は，生態系機能や他の分類群への影響より早い段階から発生しやすいため，地域スケールで植物相を保全するには，影響が軽微な段階から予防的な対策を行うことが望ましい。保全に費やせる社会的資源が有限ななかで予防的な対策を行うには，地域の植物相を維持するうえで重要な場所を特定し，その優先順位を計画に盛り込む必要がある。本研究では秩父多摩甲斐国立公園において198 地点の植生調査資料をもとに，出現種を「シカ高密度地域での減少種／その他」「RDB 掲載種／非掲載種」の組み合わせから「減少種・RDB 掲載種(A) 」「減少種・RDB 非掲載種(B)」「その他・RDB 掲載種(C)」「その他・RDB 非掲載種(D) 」に区分し，各グループの総種数に対する占有率とシカの相対密度指標の関係を検討した。グループB はシカの相対密度指標の増大とともに減少したのに対し，グループD の種は増加した。また，グループC は相対密度指標の増大に対し一山型の応答を示した。群落型ごとの比較からグループA・B の占有率が高い亜高山帯～ 山地帯の草原や広葉高茎草本型のブナ林，シオジ林の保全危急性が最も高いと考えられた。

特集「シカの採食圧による植生被害防除と回復」 階段式防獣網「シカガエシ」の実証実験

ニホンジカの分布は依然として拡大傾向にあり，のり面緑化工事においても脅威となっている。獣害対策には多種の方法があるが，人為的活動を妨げず，植生の成立を阻害しない立体的構造物である階段式防獣網「シカガエシ」を地表に設置することで，ニホンジカによる食害を防除する方法を13 年間の設置実験により検証した。その結果，比較対照区においては，低木木本類は食害を受け成立本数は2 種0.6 本/mであったのに対し，階段式防獣網を設置した試験区では9 種2.0 本/m2 の低木木本植物による緑化の成立を確認できた。

Wild red deer [Cervus elaphus L.) grazing may seriously reduce forage production in mountain meadows

This study aimed at estimating the impact of red deer grazing on the productivity of meadows located in Pian Cansiglio, north-eastern Italian Pre-Alps. These meadows (185 ha; average elevation 1000 m asl are managed for hay/silage production (1–2 cuts per season) and are included in a protected area that hosts a high density of deer (around 30 heads/100 ha). In 2008 and 2010, dry matter (DM) production and loss due to deer grazing were estimated with exclusion cages (1 m2; 48 exclusion cages in 2008 and 52 in 2010). Night counts with spotlights were conducted to index deer use of meadows plots. DM production inside the cages was fairly good for the area (first-second cut: 4963-2297 kg DM/ha in 2008, and 4145-2475 kg DM/ha in 2010). DM production outside the cages was significantly lower (first-second cut in 2008: 4199-1378 kg DM/ha, and in 2010: 3376-2052 Kg DM/ha). Therefore, the magnitude of losses was of 15–20% at the first and 25–40% at the second cut. DM losses in the different meadow plots were positively correlated with index of deer use, which in some plots was as high as 7–8 heads/ha. Deer grazing reduced also crude protein (CP) content of forage (15.6±4.4% DM inside exclusion cages and 13.8±3.5% DM outside), with losses being greater where CP content was higher. This study demonstrates that high densities of grazing deer may seriously impact on forage production and quality.

シカの採食が一斉開花・枯死後のチュウゴクザサの実生更新に及ぼす影響

シカの採食が一斉開花・枯死後のチュウゴクザサの実生更新に及ぼす影響

Morphological adaptation of a palatable plant to long-term grazing can shift interactions with an unpalatable plant from facilitative to competitive

Unpalatable plants can protect palatable neighbor plants from grazing pressure, but morphological evolution of a palatable species might change its interactions with unpalatable plants. We predicted that when a palatable species has locally adapted to grazing by expressing a dwarf phenotype that reduces grazer accessibility, the dwarf plants experience relatively more competitive effects than facilitative effects from large, well-defended, unpalatable species. We used a transplant experiment, in which both dwarf and large ecotypes of a palatable annual species, Persicaria longiseta, were transplanted outside and inside the canopy of an unpalatable nettle, Urtica thunbergiana, in a long-term deer grazing habitat of Nara Park, Japan. The dwarf ecotype of Persicaria has adapted to the grazing environments of the park by exhibiting inherently short shoots and small leaves, whereas the large ecotype is found in habitats with no grazing history. A previous common-garden study suggested that the phenotypic differences were genetically based and that phenotypic plasticity contributed little to the morphological difference. The large-phenotype of Persicaria experienced significantly increased morphological size, survival, and reproductive output under the Urtica canopy compared to outside the canopy, whereas these traits of the dwarf phenotype were reduced under the Urtica canopy compared to outside. These results indicate that the net effects of Urtica on Persicaria were positive for the large ecotype and negative for the dwarf ecotype. Thus, the morphological adaptation of a palatable species to avoid grazing altered its interactions with a large, well-defended neighbor.

Testing the effects of deer grazing on two woodland rodents, bankvoles and woodmice

Over the past 200 years, deer numbers have risen world-wide. The associated increase in browsing pressure and trampling often resulted in significant vegetation changes and associated conservation problems in other taxa. In this study we investigated the effects of increased deer browsing (0.4–1.5 deer/ha) on a temperate woodland ecosystem by comparing small mammal communities and vegetation characteristics in 4 deer-free exclosures with adjacent woodland transects subjected to deer grazing. Jolly–Seber analyses of Capture-Mark-Recapture (CMR) results revealed that the significant reduction of bushes and shrubs in deer-grazed woodland was associated with significantly lower rodent densities than in deer-free exclosures at all times. However, whereas bankvoles ( Myodes glareolus) outnumbered woodmice ( Apodemus sylvaticus) in exclosures by 4:1, on average there were 1.6 times as many woodmice in the open woodland than bankvoles. Population structure did not differ between animals caught in exclosures vs. open woodland in terms of body weight, reproductive status, age structure nor sex ratio in either species. Our results highlight the need of bankvoles for denser understorey as protection from predators, compared with the woodmouse's greater agility and resulting ability to escape predators in open woodland as well as the ability to exploit arboreal habitats. The study emphasises the necessity for effective and informed deer management in order to conserve forest ecosystems.

Non-ryegrass pastures - the science and farmer practice

A review of recently published science demonstrates that relatively simple non-perennial ryegrass mixtures have performed well in environments as diverse as under deer grazing in Dunedin and the Manawatu, under sheep grazing in dryland mid-Canterbury, and under both irrigated and dryland dairy cow grazing in the Waikato and Northland. Animal productivity has been lifted by up to 30% in milk solids and 50% in deer liveweight gain in non-perennial ryegrass mixtures compared to perennial ryegrass-based pastures. In some cases, the ryegrass pasture has produced similar or more dry matter, yet animal performance has been greater on the non-perennial ryegrass pastures. In other cases, dry matter productivity from complex nonryegrass mixtures has been around 30% higher than from perennial ryegrass pastures. Interviews with farmers from South Canterbury to Northland have all reported positive experiences with non-ryegrass pastures and most have said they will not be planting perennial ryegrass-based pastures again.

Effects of cattle, sheep and deer grazing on soil physical quality and losses of phosphorus and suspended sediment losses in surface runoff

Livestock grazing and treading is strongly linked to a decrease in freshwater quality and promotes eutrophication. A two-year field trial was carried out to investigate the influence cattle, sheep and deer have on soil physical quality and the loss of phosphorus (P) and suspended sediment (SS) in surface runoff. Surface runoff plots (4m long by 1m wide) were installed within areas designated as stock or ungrazed (control). Surface runoff was collected and analysed for concentrations and loads of P fractions (dissolved reactive P-DRP, dissolved unreactive P-DUP, total dissolved P-TDP, particulate P-PP and total P-TP) and SS. Grazed at equivalent stocking density, soil physical samples (macroporosity, bulk density, and saturated hydraulic conductivity Ksat) were taken after each grazing event (n=11). Soil physical data indicated differences between cattle, sheep and deer with cattle having greater negative effects. However, these differences had no impact on P and SS losses between stock types in surface runoff. Significant relationships showed that an increase in macroporosity, Ksat, and time (days) since grazing decreased concentrations and loads of P and SS losses. A separate rainfall simulation study also revealed that an increase in simulated cattle treading intensity increased the volume of surface runoff and SS losses. Most surface runoff (> 90%) occurred in winter when soil moisture was at or above field capacity. A seasonal effect was observed and showed that although the greatest P loads occurred in winter, the greatest P concentrations occurred in summer months, under infiltration-excess conditions. These summer losses could pose a risk to receiving waterways because increased light and warmth may induce an algal response compared to winter. While there is limited scope to manage for infiltration-excess surface runoff losses from pasture, with most runoff occurring in winter, these findings reinforce the use of mitigation strategies such as restricted or nil grazing in winter when soil moisture has reached field capacity to minimise P and SS loss to surface water, regardless of stock type.

NICHE SEPARATION AND OVERLAP IN THE FOLIOSE LICHENS LOBARIA PULMONARIA (L.) HOFFM. AND L. VIRENS (WITH.) LAUNDON IN THE KILLARNEY OAK WOODS, IRELAND

An investigation of the lichens Lobaria pulmonaria and L. virens on the trunks of mature oak (Quercus spp) revealed differences in their ecological preferences. These species were found to occupy significantly different niches, with L. pulmonaria occurring in the more exposed sites. The niche widths were similar with respect to exposure and there was a high degree of overlap between the species, although they did not differ significantly in aspect preference. The chlorophyll content and biomass per unit area was similar for both species, but they showed strong morphological differences that could influence light capture. Fertility, measured as apothecium abundance, was greater in L. virens, but L. pulmonaria reproduced both asexually and asexually in this region. A recent decline in the abundance of Lobaria scrobiculata and the potential effects of deer grazing on the lichen flora are discussed.

Facilitative and competitive effects of a large species with defensive traits on a grazing-adapted, small species in a long-term deer grazing habitat

Plants can adapt to grazing environments by developing defensive traits, such as spines and toxins, or having a small phenotype, such as short and prostrate growth forms. This study examined facilitative and competitive interactions between species with different types of grazing adaptation. We predicted that large species with defensive traits sometimes protect grazing-adapted species without defensive traits from herbivores, but competitively suppress them overall. We conducted an experiment using fences and removals of an unpalatable plant in the long-term deer grazing habitat of Nara Park in Nara, Japan. We evaluated the seasonal variations in the facilitative and competitive effects of a defensive perennial, Urtica thunbergiana, on the growth, survival, reproduction, and final fitness of a small palatable annual species, Persicaria longiseta, during a growing season. The populations of the two species in the park have adapted to the grazed habitat by increasing the density of stinging hairs (Urtica) and developing inherently short shoots and small leaves (Persicaria). We found that Urtica individuals had facilitative effects on the growth of Persicaria individuals under grazing during a few periods of the growing season, but had neutral effects on survival and plant fitness throughout the season. In the fenced plots, Urtica had negative effects on the growth, survival, and reproduction of Persicaria. These results suggest that the relative importance of the facilitative and competitive effects of Urtica on Persicaria fluctuated due to seasonal variations in grazing pressure and vegetative productivity. Although well-defended plants often facilitate less-defended species, we conclude that the facilitative effects of Urtica on Persicaria are limited in a plant community with a long history of intensive grazing.

Ecological Responses of Osmunda regalis to Forest Canopy Cover and Grazing

Abstract The density and frond traits of the dimorphic fern Osmunda regalis were examined in 45 populations situated in central Italy, along a gradient of forest canopy cover and deer grazing. The survey involved 1704 ramets containing 6416 fronds, of which 5643 were sterile and 773 fertile. Within the ramets, the number of fertile fronds increased with the number of sterile fronds and with the mean height of ramets. Light seemed to promote fertility, as the number of fertile fronds decreased with increasing canopy cover. Fewer and smaller fronds were found in plots with high forest canopy cover. Our results showed that O. regalis performed best in conditions of full sunlight but can persist and recruit young sporophytes under closed canopy. As many marsh and lake environments have disappeared or been altered by human activity, more populations were located under high canopy cover in the forest than in open habitats. Deer grazing caused a significant decrease in fertile fronds, in total frond area and in ...

Investigating the interaction between ungulate grazing and resource effects on Vaccinium myrtillus populations with integral projection models

Dense ungulate populations in forest accompanied by high grazing intensities have the potential to affect plant population dynamics, and such herbivory effects on populations are hypothesised to differ along environmental gradients. We investigated red deer grazing and resource interaction effects on the performance and dynamics of the functionally important boreal shrub Vaccinium myrtillus using integral projection models (IPMs). We sampled data from 900 V. myrtillus ramets in 30 plots in two consecutive years across the boreo-nemoral pine forest on the island Svanøy, western Norway. The plots spanned two environmental gradients: a red deer grazing intensity gradient (assessed by Cervus elaphus faecal pellets), and a relative resource gradient (DCA-ordination of species composition). The use of IPMs enabled projections of population growth rate (lambda) using continuous plant size instead of forcing stage division upon the demographic data. We used the environmental gradients as continuous variables to explain the dynamics of V. myrtillus populations and found that both increasing grazing intensity and resource levels negatively affected lambda of the V. myrtillus populations. Interestingly, these factors interacted: the negative effects of grazing were strongest in the resource-rich vegetation, and higher resource levels reduced lambda more strongly than at low resource levels when grazing intensities became higher. Populations with lambda > 1 were projected if the grazing intensity was less than or equal to the mean grazing intensity on the island, and indicated that V. myrtillus is relatively tolerant of grazing. Variance decomposing showed that the decrease of lambda along the grazing gradient, both at low and high resource levels, was largely caused by reductions in plant growth. The use of IPMs together with important environmental gradients offered novel possibilities to study the synthesised effect of different factors on plant population dynamics. Here, we show that the population response of an abundant boreal shrub to ungulate grazing depends on resource level.

Assessing decline in physical structure of deciduous hardwood forest stands under sika deer grazing using shrub-layer vegetation cover

For 345 stands of deciduous hardwood forest in Hyogo Prefecture, Western Japan, we assessed the decline of shrub-layer vegetation due to sika deer in each stand by using the shrub-layer decline rank (SDR), determined by combining the shrub-layer vegetation cover and the presence of signs of grazing by sika deer in a stand. Since there was a geographical correlation between SDR and sighting per unit effort (SPUE), which is an index of the relative density of sika deer, it appeared that decline of shrub-layer vegetation in a stand can be accurately evaluated by SDR. There were correlations between SDR and several variables that indicate the status of components in forests (presence of saplings of tall trees, occurrence of bark stripping of tall trees, proportion of bark-stripped stems of Clethra barvinervis, decline of subtree-layer vegetation by bark stripping, cover of litter on the ground, and area of soil surface erosion). These results indicate that the status of these components changes with decline of shrub-layer vegetation by sika deer grazing. It is thought that such synchronizations are caused by sika deer grazing or a direct or indirect effect by decline of shrub-layer vegetation due to sika deer. Therefore, it is reasonable to assess decline in physical structure due to sika deer for stands of deciduous hardwood forests according to SDR.

Morphological and population responses to deer grazing for herbaceous species in Nara Park, western Japan

AbstractTo quantify the morphological and population responses of plants to grazing by deer, we conducted two deer‐exclusion experiments in Nara Park, western Japan. The first experiment assessed the morphological differences in 10 traits of two species with erect growth (Oxalis corymbosa and Cyperus brevifolius. var. leiolepis) and two species with prostrate growth (Oxalis corniculata and Hydrocotyle maritima) between shoots inside and outside of the exclosures at the end of a growing season (late autumn). The size and weight of the leaves, stems and reproductive organs of the four perennials were significantly smaller outside the exclosures. The degree of size reduction was highest for an erect species, O. corymbosa, compared with the other three species, and was similar between the two prostrate species. The second experiment, using 11 erect species and 15 prostrate species, demonstrated that erect species exhibited greater reduction in leaf length and cover in the grazing environments compared with prostrate species, suggesting that the erect species suffered more from grazing. In conclusion, many of the plant species reduced their size under grazing pressure during the growing season, but the nature of the changes depended on the growth form of each species. It remains unclear whether the morphological reduction was an adaptive response to grazing.

An Assessment of Agricultural Damage Caused by Red Deer (Cervus elaphus L.)and Fallow Deer (Dama dama L.) in Southwest England

The impact of deer grazing on agricultural grassland and cereal crops was assessed at two locations with medium to high deer densities in the Exmoor area of southwest England. Red deer impact on early spring grazing was measured at one site by comparing samples of herbage cut from inside and outside deer-proof exclosure cages, just prior to turn out of livestock, on 1 March 1989. Fallow deer impact on first-cut silage grass production was similarly measured using exclosure cages at a second site by cutting samples on 31 May 1990 and on 6 June 1995. In addition, impact of fallow deer on cereal crops was assessed at this site by measuring sample grain yields from areas of the crop used or unused by deer in 1995 (winter wheat), 1996 (winter barley) and 1997 (winter wheat). Significant dry matter yield losses were recorded for red deer impact on spring grazing in 1989 (14.5%) and for fallow deer impact on first-cut silage (15.9%) in 1995 but not in 1990. In 1995 a small but significant yield loss (7.1%) was recorded for winter wheat at the fallow deer site but no loss in cereal yield was recorded in 1996 or 1997. These assessments, carried out in response to complaints about deer damage, suggest that the impacts of deer in this area, where they occur at relatively high density, are only moderate. This highlights the need for careful assessment of cost-benefits when considering deer management strategies to reduce perceived agricultural damage.

Effects of sika deer on vegetation in Japan: A review

The Japanese sika deer Cervus nippon has expanded its range by nearly 70% during the last two decades. Browsing by sika deer affects vegetation in both agricultural and forested habitats. Effects of sika deer on vegetation are conspicuous on deer-inhabited islands: forest structure and composition are altered by deer grazing and browsing, and consequently regeneration is prevented. By felling of old trees, forest gaps are formed, but since sapling recruitment is prevented, shade intolerant plants invade. Unpalatable forbs like ragwort Senecio cannabifolius and ferns like bracken Pteridium aquilinum (Dennstaedtiaceae) become dominants in open habitats. At the places of highest deer density, the Zoysia japonica community, a low growing grass mat, develops. Sika deer function as a seed dispersal agent of this grass. Indirect effects of sika deer are not well studied, but some studies have shown reduction of understory bamboo cover, which in turn improves the survival of tree seedlings and declines of wood mice Apodemus spp. Japanese forests in lower mountainous areas were widely logged during the 1940s and 1950s. These areas were not well planted during the war and until 1950, but thereafter intensively planted to alter to conifer plantation as a nationwide campaign. For several decades after the war, rodents and hares grazed planted trees. According to growth of the planted trees to form canopy, which is unfavorable for rodents and hares, their damage declined. After the 1960s, old-growth forests in high mountainous areas were logged, and conifers were planted. Animals causing forestry damage were replaced by sika deer during the 1980s. Sika deer eat a wide variety of foods, and are gregarious, which causes heavy impacts on vegetation. Effects of sika deer are expanding to natural forests, alpine vegetation, and marshes. To reduce damages on forestry and natural vegetation, as many as 100,000 sika deer are culled every year. However, the hunter population is rapidly declining, and it is expected population control by culling will be insufficient. Although sika deer are an important component of Japanese forests, current population densities exceed the capacity of many ecosystems to tolerate herbivory.