Harvesting Fresh Trees on the Farm Jeff Owen Area Extension Forestry Specialist NC State University
Harvesting Fresh Trees on the Farm
Jeff Owen Area Extension Forestry Specialist
NC State University
Harvesting Fresh Trees on the Farm
• Freshness definitions • Practices to maintain freshness
– Harvest timing – Managing harvest – Storage choices
Many ways to Define Freshness • Frequently, freshness is defined by a point
when your responsibility for a tree ends – Fresh when the tree leaves the farm – Fresh displayed on a retail lot – Fresh when the customer buys it – Or, ideally… Fresh when the customer takes it
down after Christmas
Attribute-Based Definitions • A tree that holds its needles • A tree with high moisture content • A tree with limber twigs & branches • A tree that does not catch fire • These definitions sometimes conflict!
A Tree that Holds its Needles • Adequate moisture
– Moderate T: Good – High T: Poor
• Dry – Moderate T: Poor – High T: Good – Fails to meet
other definitions of freshness
A tree that loses its needles • Process of needle abscission
– Occurs in living, not dead foliage • A natural process for old interior needles to drop
– Controlled by genetics • Measurable differences among families
– Influenced by cold acclimation & dormancy – In a cut tree, it may be aggravated by high
temperatures, moisture stress, high salts, & low calcium
• Dormancy develops over time • Biochemical chain reaction triggered by:
– Short days – Cool night time temperatures – Water stress
• These conditions stimulate cellular changes during photosynthesis: – Storage of sugars that lower the freezing point – Concentration of lipids & proteins in cells
Dormancy Drives Harvest Date
Freshness Issues on the Farm ? • Needle loss? • String burn? • Sunscald? • Trunk cracks? • Or simply not preserving freshness as
well as you could? – Loss of stored sugars burned in respiration – Loss of moisture content
“Freshness” is a Perishable Quality
• Fresh cut tree • Harvested on hot, sunny day • Delays in field handling • Flatbed trailer transport to yard • Grocery store in Miami, FL • 1- quart tree stand dries out • Displayed next to a heat vent
• 100% fresh • 90% fresh • 70% fresh • 60% fresh • 50% fresh • 20% fresh • 10% fresh
What about measuring “freshness” • Moisture Content
– Oven dry weights (fresh – dry / dry * 100 = %)
– Pressure chamber • Measures the pressure
needed to drive water out of a twig
– Wood moisture meter • Stick pins & read
• Frequency of problems • Problem rating scales
– Direct
– Indirect, but correlated
– Indirect, subjective (% of trees) (average)
Harvest Timing Studies • I conducted annual timing studies for 5 yrs • Branches harvested from the same 30
trees early and late October and early and middle November
• Similar – but not identical – patterns observed across all 5 years
My Needle Loss Rating Scale
0 = 0 1 < 1% 2 = 1-3% 3 = 3-5% 4 = 6-10% 5 = 11 -20% 6 = 21-50% 7 = 51 +
Needle Loss Rating - Simplified • 0-1 = no gaps, scant mess • 2-3 = no gaps, some mess • 4-5 = visible gaps, lots of mess
• 6-7 = more on the floor than on the tree
Needle Retention
across 4 Harvest Dates
Needle Retention by Severity Class After Six Weeks
Needle Retention by Severity Class January 16, 2014 Evaluation
14 wks 12 wks 12 wks 10 wks 8 wks
NC Harvest Timing Studies • Better performance when branches are
stored in water (but not compacted) • Better performance after dormancy occurs
– Several cold nights (4-7) below 4 C – Shorter days, longer nights
• Dormancy requires photosynthesis – Cannot be induced in a warehouse
Can we Forecast Dormancy? • I have needle retention and other data by
date, but have not taken the next step to model it against temperature.
• Will a chilling hour model work as well as a growing degree day model? – Fraser only seems to need a week of cold nights – Cold acclimation ebbs and flows with temps
• In the spring, Balsam breaks bud earlier than Fraser. Probably different in the fall too.
Managing Temperature at Harvest • Field heat: Tree temperature at harvest
reflects recent ambient conditions • Added exposure: temperature can increase
from exposure during harvest – Loose trees – Baled trees – Piled or stacked trees – Critical during warm weather, but not as important
when conditions are cool • Check with a composting thermometer
Managing Tree Temperature During Harvest
• Establish tighter harvest goals to reduce the risk of trees drying out
• Time trees lay after cutting
• Time trees lay after baling
• Time trees lay in the yard prior to storage
• Extent of shade cover in the yard
Temperature Accumulation • Field heat: Tree temperature at harvest
reflecting recent ambient conditions • Exposure to sun during harvest
– Loose trees – Baled trees – Piled or stacked trees
• Heat of Respiration: Heat released in a chemical reaction which produces energy from stored carbohydrates
Heat of Respiration • 4X the heat released at
21C vs. 4 C • 2X the heat on 1st day
after harvest compared to 2nd day
• Possible explanation for heat associated with fresh tree storage
(Blankenship & Hinesley, 1990)
Heat of Respiration • In a healthy tree, it occurs at night when a
tree is not able to conduct photosynthesis. • In a cut tree, it occurs because the tree is
wounded, baled, and/or foliage is blocked from sunlight.
• It occurs within the first few days after harvest where ever trees are stored.
• It is the reason trees benefit from “curing” before storage.
Heat of Respiration Problems • Scalded spots in trees in pallets, piles, and
stacks of loose trees • At pressure points among compressed trees
2015 Heat of Respiration Study • 6 Pallets of trees provided by Kathy Shore
Nursery & Cubby Steinhart – 33 6-8 ft. trees per pallet
• Palletized at 5 different intervals after harvest • Harvested on October 21
– (High of 23 C) – Earlier than any NC grower
• Evaluated on November 3 – Right as growers started
experiencing their own problems
Treatments
Day 0 – Cooler Day 0 – Outside Day 1 – Outside Day 2 – Outside Day 4 – Outside Day 7 – Outside
November 3 Evaluation • Pockets of foliage warm to the touch • Hot spots with bronze scalded patches or bands • Bright green foliage – melted waxy cuticle • Additional coin-sized brown spots
Frequency of Scalded Trees
Treatment No Dmg Very Light Light Moderate Severe
Day 0-cooler 18 13 1
Day 0-outside 17 7 4 2
Day 1-outside 6 6 7 5 9
Day 2-outside 3 5 2 4 16
Day 4-outside 14 7 10 2
Day 7-outside 20 8 5
Ambient Temperatures in Sparta October 21 to November 3
Day “0,” Stored in Cooler
Day “0,” Stored Outside
Heat of Respiration • Similar “bumps” in curves for days
1, 2, & 4
• Not all data loggers were in “hot spots”
Day “7,” Outside
Heat of Respiration • Pattern of heating above
ambient temperature when trees are palletized in first 1- 4 days after harvest
• Followed by a drop back to ambient temperature
• Hottest areas in pallets were associated with the scald symptoms
Day “7,” Outside
A Different Mechanism ? • Heat of microbial respiration
– Temperatures were still ascending when opened. – Heavy rain occurred at the time of palletization. – Internal needle drop was late in 2015. Dead
needles were trapped in trees harvested early • Delayed rising temperatures observed in
other pallets in this study to a lesser degree • Similar heating observed during farm storage
in 2014 retail pallet study
Managing Heat of Respiration • Heat of respiration will occur – what you
do will increase or decrease its impact • Potential management strategies:
– Field curing of unbaled cut trees – Vertical storage of trees (chimney effect) – More air circulation around piles of trees – Fewer trees per pallet – Grow pallet-trees, not garden-center-trees – Forced air cooling
Forced Air Cooling of Pallets • A possible treatment for heat
of respiration. • Concept: To use portable
fan(s) to pull “field” heat from trees during 1st night on yard.
• Technology borrowed from fruit & vegetable postharvest research.
• Tested on 2 farms in 2016
Managing Potential Microbial Heat • Palletize dry trees • Palletize clean, shaken trees • Put fewer trees in each pallet • Keep pallets of trees cool • Only store pallets of trees for short periods
Growers can control the number of trees per pallet
• Manage / reduce compaction in pallets – Even a 3-tree reduction / pallet could make
a difference (lose 78 trees in 26 pallets) – Compared to bulging pallets, square
pallets allow 2 additional pallets / trailer (+ 60 trees)
– Real sacrifice in efficiency is only 18 trees and the cost of filling two extra pallets
2012 Bough Storage Study • Factors to control:
– Temperature – Humidity – Light
• NC Storage Practices – Full sun – Chilled warehouse – Unheated warehouse – White pine stands – Humidified & chilled
warehouse • Storage study check
– Branches in a bucket
Farm Storage after 3 Weeks
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
Moisture Content
Farm Storage: Moisture Content %
Full Sun
Chilled Warehouse
Dry Barn
White Pine Stand
Humidified Warehouse
Water Bucket
Farm Storage after 3 Weeks
Bough Study Conclusions • Storage makes a difference compared to
none • Type of storage makes more of a
difference during stressful weather • Water & needle retention are complicated • Water & flammability are closely linked
Optimum Storage
• Cold, dark, & … – Humid in a drought – Dry in a flood
Critical Elements for Storage
• Yes, cool, dark, & humid… • But also:
– Good traffic flow in and out – A reliable road surface – Good water drainage – Maybe a snow removal plan? – Lights & fencing for security
Other Postharvest Concerns • Baling clamp damage to tree trunks?
– Wood takes up water, not the bark • Baling compression – 1, 2, or 3 strings?
– Trees can be baled too tightly – Tight baling increases risk of string burn
• Trunk cracks – shifted to my other presentation
A Team Effort
• NCCTA grant • NCDA Specialty
Crops Block Grant
• Extension agents helped to plan & conduct the research
• Upper Mt. Research Station provided trees & labor
• Growers provided trees & labor
Questions?