seeds of the corsican pine, a key ressource for the corsican nuthatch
TRANSCRIPT
Seeds pine are an abundant and energetic source of food for generalist seedpredators and specialist seed predators.But, in Pinus, cone and seed production have interannual and spatial variations,also seeds and cones characteristics are variables.
The forest’s granivorous develop specific adaptations to their habitat and food. But,these adaptations create a dependency that may be restricting, in case ofdisturbances affecting the productivity of trees (logging, fire,…)
The Corsican nuthatch is sedentary and remains in an area of only a few hectaresthroughout the years, at altitudes above 900 m. Nuthatch develop specificadaptations to their habitat and food, specifically important in winter when laricioseeds are the essential of the diet of nuthactches
Quantify the relationship between the Corsican nuthatch and
Corsican pine seed :
1. the energy needs of the bird
2. energy intake of the seeds
3. availability / accessibility of the resource
Description of Corsican pine seed and cone production :
1. Quantitative aspects of cone crop,
2. Cone and seed caracteristics
3. Spatio-temporal variation of cone crop
4. Dendrometric and fire severity variables influence cone crop
Cones and seeds characteristics
1. Cone harvested before seed dispersal
2. Cones were placed at a temperature of 35°C for twelve hours to trigger the opening and release the seeds
3. Measuresi. Diameter at breast height (DBH)ii. Full and empty seed numberiii. Seed weight
Cone production
1. Monitoring during 3 years : 2004-2005-2006
2. Study area : 8 pinewoods, elevations 150-1400 m.
3. Visual counting
4. 3 diameter classes : 20-49, 50-79, ≥80 cm
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%U
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4
2
3
6
1
5
7
8 1 – Tartagine
2 – Aitone-Lindinosa
3 – Vizzavona
4 – Vallée d’Asco
5 – Basse vallée du Golo
6 – Restonica
7 – Basse vallée du Tavignano
8 – Petrapiana – Poggio di Nazza
- light green : pinewood at lowaltitude (altitude below 1000 m)
- dark green : homogeneous standsof altitude (altitude above 1000 m)
To assess the availability of seeds for nuthatches, we quantify four parameters :
Field metabolic rates of Corsican nuthatches: it represents the total daily energy requirement for an animal in the wild.
Equation relating FMR for birds to body weight :FMR (kJ/day) = 10,4×(weight)0,68
Metabolizable energy: it depends on characteristics of both the food and the organism eating it.ME = GE × AE
where:ME = Metabolizable energy (e.g., in kj/g)GE = Gross energy (e.g., in kcal/g) is the total energy content of a foodAE = Assimilation efficiency by animal : AE = 0.75 for the passerineseating seeds
Energy value of Corsican pine seeds, measured with a bomb calorimeter
Cone production/ha
Variation in cone productionSeeds and cones characterists
Variation in number and weight of seed per coneFood needs of the nuthatch
Estimation pinewood area required to maintain a pair of Nuthatch
Cone production is highly variable :
1. The number of cones produced by trees varies according to the year
2. Production varies according to location of trees :
i. production varies from one forest to another for the same years
ii. production varies within forest
iii. production varies between the altitudes
3. Cone production depends strongly on the diameter of pins
Effect of geographical area according to
year, on the cone production
0
20
40
60
80
100
120
140
160
180
NS1 NS2 NS3 NS4
Co
ne
nu
mb
er
pe
r tr
ee
Forest
2004
2005
2006
NS1 Vallée d’AscoNS2 Forêt de Petrapiana-Poggio di NazzaNS3 Forêt d’Aitone-LindinosaNS4 Forêt de Vizzavona
0
100
200
300
400
500
600
300 600 900 1200 1500
Co
ne
nu
mb
er
pe
r tr
ee
Elevation (m)
Année 2006
D=40cm
D=60cm
D=80cm
Effect of altitude and diameter of the tree on
the cone production in 2005 and 2006
0
100
200
300
400
500
600
300 600 900 1200 1500
Co
ne
nu
mb
er
pe
r tr
ee
Elevation (m)
Année 2005
D=40cm
D=60cm
D=80cm
We have also seen that :
1. Pines with larger diameters are more productive.
2. In the pine forests of altitude(alt.>1000 m.), there are many small producersand few large producers. But large producers produce a large number ofcones constituting the majority of production. They may even be the onlyproducers.
3. Change in proportion of non-producing trees at altitudes above 1000meters : between 13 and 64% depending on the year.
The years of low cone production correspond to the years of low frequencyof producing trees when production is low, it is concentrated on a fewtrees.
And, the proportion of non-producers trees is higher in high altitudeduring the years of low production. However, during the good years, theproportion of non-producers trees was the same regardless of altitude.
YearNumber of
cones measured
Variables Mean min - max
2004 263
Length cone (mm) 53,3 31,7 - 82,1
n seed empty 22 0-57
n seed full 20 1-83
n seed 42 1-97
% seed empty 54 0-98
weight of seeds /cone
299,26 7,7-1542,4
2005348
Length cone (mm) 54,4 30,5-81,6
n seed empty 15 0-49
n seed full 29 0-69
n seed 44 7-79
% seed empty 36 0-100
weight of seeds /cone
418,81 0-1361
46 number of scales 43 26-58
Without being able to identify
the precise reasons, we observed
that could coexist :
1. full seeds
2. empty seeds
3. scales without seeds
developed where only the
wing was present
Sample 1:Asco forestElevation > 1000 mFebruary 2003495 cones from 36 trees
1. The individual weight seed (WGP) varied between the cones and the trees.
2. The individual weight seed (WGP) was influenced by :• DBH,• the number of empty seeds per cone• the total number of seeds per cone
12,0
13,0
14,0
15,0
16,0
17,0
18,0
19,0
20,0
20 40 60 80 100
WG
P
D
NTG=12
NTG=32
NTG=52
NTG=7212,0
13,0
14,0
15,0
16,0
17,0
18,0
19,0
20,0
20 40 60 80 100
WG
P
D
NTG=12
NTG=32
NTG=52
NTG=72
12,0
13,0
14,0
15,0
16,0
17,0
18,0
19,0
20,0
20 40 60 80 100
WG
P
D
NTG=32
NTG=52
NTG=72
12,0
13,0
14,0
15,0
16,0
17,0
18,0
19,0
20,0
20 40 60 80 100
WG
P
D
NTG=32
NTG=52
NTG=72
Effect of diameter (D) on the seed weight (WGP) according to number of empty seeds per cone (NGV) and total number of seeds per cone (NTG)
NGV=0 NGV=11
NGV=22 NGV=32
…but the effect of the diameter depends on the total number of seeds and thenumber of empty seeds :
The weight of seeds per cone (=food quantity per cone) varied between the forestsand the years.
The weight of seeds per cone (=food quantity per cone) was influenced by :• the total number of seeds per cone a positive effect• the number of empty seeds per cone a negative effect• the length of the cone a positive effect• the year 2005 good year• the size of the cone a positive effect
Sample 2 : ForestElevation
(m)
2004 2005
Number
of trees
Number of cones
harvested
Number
of trees
Number of cones
harvested
Vizzavona 1150 9 74 10 83
Petrapiana 1150-1500 9 68 12 89
Asco
1300 6 59 10 97
800 4 34 0 0
440 3 28 10 80
Our knowledge suggest that, at least during the 3 months of winter, the nuthatcheats almost exclusively some seeds. It means that a pair needs at least 50.000 seeds (more than 2 500 cones) peryear, that is to say more than 250 seeds/bird/day.
These quantities are to be compared to the one observed on forest Tits (passerinewith a body weight and a trophic ecology comparable to the nuthatch). Indeed, theseed availability for nuthatches is clearly limited by competition with othergranivores in Corsican pine forest, the main competitor is Coal tit (Parus ater).
Parus ater
Field Metabolic rate = 46.3 Kj/day,but seeds only a third of the diet seeds provide only 15.4 Kj/day
Need food = 80 seeds/day/ind.7 198 seeds/year/ind215 954 seeds/year/10ha
Density =15-21 pairs/10ha
Corsican Nuthatches with densities of only 1 pair/10 ha, collect only
587 seeds/day/10ha
Sitta whiteheadi
Field Metabolic rate = 56.7 Kj/day
Need food = 294 seeds/day/ind.26 446 seeds/year/ind52 892 seeds/year/10ha
Density = 1 pair/10ha .
Coal tits collect more than 2 400 seeds/day/10ha
10 ha 1 pair of nuthatch and 15 pairs of tit needs at least 13 443 cones/year
10 ha (nuthatch
density = 1 pair/10ha),
1300 cones are
required to maintain 1
pair of Nuthatch, and
15 pairs of Coal tit
Area of the stand to feed the Corsican nuthatches and
Coal tits, depending on the production of cones
Area of the stand to feed the Corsican nuthatches and Coal tits,
depending on the production of cones
TerritorySitta
Altitude (m)
Number of cones per ha
Minimale area (ha)
2005 2006 2005 2006X8 1067 34 272 25 377 0,4 0,5
ZA7 1086 22 616 15 116 0,6 0,9V10 1110 29 052 17 131 0,5 0,8T14 1200 31 343 11 640 0,4 1,2ZD9 1240 21 950 6 494 0,6 2,1O23 1285 8 345 1 870 1,6 7,2V16 1310 21 772 4 146 0,6 3,2W15 1310 24 219 4 490 0,6 3,0P21 1315 16 481 3 066 0,8 4,4R22 1330 28 475 4 727 0,5 2,8N24 1337 22 534 3 495 0,6 3,8S20 1400 37 267 3 886 0,4 3,5H25 1465 7 988 487 1,7 27,6
year 2005 : NC = 3,42 + 0,02(D) + 0,002(ALT) - 0,0001(ALT²/100)year 2006 : NC = 3,37 + 0,15(D) + 0,006(ALT) - 0,0005(ALT²/100)
0,0
2,0
4,0
6,0
8,0
10,0
10
67
10
86
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10
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00
12
40
12
85
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10
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10
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15
13
30
13
37
14
00
14
65
Min
ima
le a
rea
(h
a)
Altitude of the territory (m)