OBSERVATIONS OF TREE DAMAGE AFTER HURRICANE WILMA FROM BOTH HAND AND MECHANICALLY HARVESTED TREES

1. OBSERVATIONS OF TREE DAMAGE AFTER HURRICANE WILMA FROM BOTH HAND AND MECHANICALLY HARVESTED TREES Kelly Morgan, Mongi Zekri, Fritz Roka & Bob Rouse

2. Does mechanical harvesting make citrus trees more prone to hurricane damage? Assumptions Trunk shaker may cause more root damage Valencia more prone because last harvested prior to hurricane Long term shaking may lead to greater hurricane damage A survey was conducted to address growers question “ Does mechanical harvesting of citrus make trees more prone to hurricane damage”. The survey was conducted with a limited number of blocks as samples. Therefore, assumptions were made to answer the question while focusing on a limited number of variables. The assumptions were: 1) that the trunk shaker has the greatest potential to cause more damage that the canopy shaker, even though no reduction in tree health has been observed with mechanical harvesting. 2) Valencia trees may be more susceptible to hurricane damage since they were harvested nearest to the time of the hurricane and thus have less time to recover from any root damage caused by mechanical harvesting. And 3) trees harvested with trunk shakers for longer periods of time may be more susceptible to hurricane damage due to repeated root damage.A survey was conducted to address growers question “ Does mechanical harvesting of citrus make trees more prone to hurricane damage”. The survey was conducted with a limited number of blocks as samples. Therefore, assumptions were made to answer the question while focusing on a limited number of variables. The assumptions were: 1) that the trunk shaker has the greatest potential to cause more damage that the canopy shaker, even though no reduction in tree health has been observed with mechanical harvesting. 2) Valencia trees may be more susceptible to hurricane damage since they were harvested nearest to the time of the hurricane and thus have less time to recover from any root damage caused by mechanical harvesting. And 3) trees harvested with trunk shakers for longer periods of time may be more susceptible to hurricane damage due to repeated root damage.

3. Survey Harvesting History Only hand harvested Short term mechanical harvesting (= 2 yrs) Long term mechanical harvesting (= 4 yrs) Blocks Valencia only 2 groves 9 blocks 551 acres Damage levels Canopy loss greater than 25% (no trunk movement) Trunk leaning Tree blown over and reset (top buck-horned) To answer the growers question, blocks were identified and divided into three categories based on their harvesting history. The categories were 1) hand harvested only, 2) short term mechanical harvesting (<2 yrs), and 3) long term mechanical harvesting (>4yrs). Nine blocks of Valencia trees from two different groves totaling 551 acres were surveyed. Trees with three levels of tree damage were mapped within the blocks. These damage levels were 1) “pruned” canopy loss of > 25%, “leaning” trees left leaning and not set upright, and 3) “toppled” trees that had to be replanted and “buck-horned”. To answer the growers question, blocks were identified and divided into three categories based on their harvesting history. The categories were 1) hand harvested only, 2) short term mechanical harvesting (<2 yrs), and 3) long term mechanical harvesting (>4yrs). Nine blocks of Valencia trees from two different groves totaling 551 acres were surveyed. Trees with three levels of tree damage were mapped within the blocks. These damage levels were 1) “pruned” canopy loss of > 25%, “leaning” trees left leaning and not set upright, and 3) “toppled” trees that had to be replanted and “buck-horned”.

4. Pruned Tree The canopies of “Pruned” trees were severely impacted by the hurricane but not uprooted.The canopies of “Pruned” trees were severely impacted by the hurricane but not uprooted.

5. Leaning Tree “Leaning” trees not completely blown over by the hurricane was left with little attempt to cover exposed root systems.“Leaning” trees not completely blown over by the hurricane was left with little attempt to cover exposed root systems.

6. Toppled Tree “Toppled” trees were blown over with the majority of there root systems exposed to the air. The tree root systems were replanted and the canopies reduced to promote recovery. “Toppled” trees were blown over with the majority of there root systems exposed to the air. The tree root systems were replanted and the canopies reduced to promote recovery.

7. Results - Block Categorical data were analyzed for each block by harvesting method. Data were calculated as number of trees in each category per acre and as a percentage of total tree spaces in the block. No significant difference (P<0.05) was found for any damage category among harvesting methods. However, both long and short term mechanically harvested blocks tended to have higher numbers of toppled trees compared to the hand harvested blocks (data in Red). Categorical data were analyzed for each block by harvesting method. Data were calculated as number of trees in each category per acre and as a percentage of total tree spaces in the block. No significant difference (P<0.05) was found for any damage category among harvesting methods. However, both long and short term mechanically harvested blocks tended to have higher numbers of toppled trees compared to the hand harvested blocks (data in Red).

8. Hurricane Winds Hurricane strength winds were recorded for a period of approximately 4 hours at the Southwest Florida REC FAWN weather station peaking at > 90 mph.Hurricane strength winds were recorded for a period of approximately 4 hours at the Southwest Florida REC FAWN weather station peaking at > 90 mph.

9. Wind Direction Hurricane strength winds were initially out of the East and then turned out of the North while the winds were the highest. Hurricane strength winds were initially out of the East and then turned out of the North while the winds were the highest.

10. Edge Effect While taking the data it was noted that more trees in unprotected areas exposed to winds out of the North seemed to have higher numbers of toppled trees than in the rest of the block. While taking the data it was noted that more trees in unprotected areas exposed to winds out of the North seemed to have higher numbers of toppled trees than in the rest of the block.

11. Effects of Open Areas All blocks in the survey were mapped using GPS. Here, trees exposed to north winds over ponds, and to a limited extent ditches, suffered more damage than did trees in the remainder of the block. All blocks in the survey were mapped using GPS. Here, trees exposed to north winds over ponds, and to a limited extent ditches, suffered more damage than did trees in the remainder of the block.

12. Results – Exposed Areas Categorical data were analyzed by harvesting method for areas adjacent to open areas exposed to the north wind. Damage to both long term mechanical and hand harvested blocks were nearly 3 times as high per acre and double or more proportion of total tree space in areas open to the north wind. This was not true for the short term mechanically harvested block mean and there was no significant difference by harvest method. Categorical data were analyzed by harvesting method for areas adjacent to open areas exposed to the north wind. Damage to both long term mechanical and hand harvested blocks were nearly 3 times as high per acre and double or more proportion of total tree space in areas open to the north wind. This was not true for the short term mechanically harvested block mean and there was no significant difference by harvest method.

13. Conclusions Hurricane damage in mechanical harvested blocks was not significantly more severe than damage in hand harvested blocks. The exposed tree rows had about 3 times the amount of damage, but their damage was not significantly different from damage to trees in the rest of the block. No significant difference was found among harvesting methods for the blocks surveyed in this study. However, damage for all methods were greater for trees exposed to hurricane winds from the North.No significant difference was found among harvesting methods for the blocks surveyed in this study. However, damage for all methods were greater for trees exposed to hurricane winds from the North.